Constipation and other digestive disorders are common in older adults. The autonomic nervous system plays a critical role in regulating digestive motility in the intestinal tract. However, studies on age-related changes in autonomic function and receptor expression in the intestinal tract are limited. In this study, we examined the expression of neurotransmitter receptors in the autonomic nervous system and the effects of acetylcholine and β-agonists on intestinal contraction and relaxation in the jejunum of aged rats. Jejunal sections collected from male and female Wistar/ST rats aged 4, 11, and 18 months were analyzed. Immunohistochemical staining and enzyme-linked immunosorbent assay were used to measure the expression of muscarinic acetylcholine receptors (CHRM2 and CHRM3) and β-adrenergic receptors (β2-ADR and β3-ADR). The effects of acetylcholine, isoproterenol, and mirabegron were assessed in the isolated jejunum for each age group. There was no significant difference in CHRM2 receptor expression among the age groups; however, CHRM3 receptor expression decreased with age. Additionally, the sensitivity to acetylcholine-induced contractile responses decreased with age. Although β2-ADR receptor expression did not differ among the age groups, β3-ADR receptor expression increased with age. Despite this, the relaxation response to isoproterenol and mirabegron decreased with age. Our study revealed an age-related decrease in CHRM3 expression and the contractile response to acetylcholine in the small intestine of rats. Although β-ADR expression, particularly β3-ADR, increased with age, the relaxation response to β-adrenergic agonists gradually decreased.

The sympathetic nervous system inhibits gut motility, secretion, and blood flow in the gut microvasculature and can modulate gastrointestinal inflammation. Sympathetic neurons signal via catecholamines, neuropeptides, and gas mediators. In the current review, we summarize the current understanding of the mature sympathetic innervation of the gastrointestinal tract with a focus mainly on the prevertebral sympathetic ganglia as the main output to the gut. We also highlight recent work regarding the developmental processes of sympathetic innervation. The anatomy, neurochemistry, and connections of the sympathetic prevertebral ganglia with different parts of the gut are considered in adult organisms during prenatal and postnatal development and aging. The processes and mechanisms that control the development of sympathetic neurons, including their migratory pathways, neuronal differentiation, and aging, are reviewed.

Gastrointestinal (GI) dysmotility is common in patients with cancer. There are a few studies about the myenteric plexus in the presence of anatomically remote tumors.

Forty-eight male Wistar rats were divided into a control (CT) or Walker-256 (TW) group. Tumor cells were subcutaneously injected and saline was injected in the CT group. After 14 days, the small and large intestines were removed for histochemical analysis. The macroscopic morphology of the intestines and the fecal excretion were also observed.

The upper GI transit and weight of fecal pellets were reduced and the walls of the large intestine in tumor-bearing rats showed multiple constrictions. In the capsules' constitution of the myenteric plexus of the TW group, there were type III collagen fibers in addition to type I fibers, and the thin septa inside the capsule were absent. The large intestine in the TW group exhibited smaller neurons and the number of nitrergic-positive neurons was also reduced in the myenteric plexus, compared to the CT group. In the TW group, the neuronal numbers and the staining intensity of acetylcholinesterase (AChE) were reduced in the large intestine. Staining was not different in the small intestine.

This study showed that the Walker-256 tumor induced alterations in the morphology of nitrergic and cholinergic neurons in the myenteric plexus and decreased the upper GI transit with the presence of multiple constrictions in the colon. Therefore, these alterations can interfere on neurotransmission and can be related to the intestinal motility alterations observed in tumor-bearing rats.

It is well documented that the intrinsic enteric nervous system of the gastrointestinal (GI) tract sustains neuronal losses and reorganizes as it ages. In contrast, age-related remodeling of the extrinsic sympathetic projections to the wall of the gut is poorly characterized. The present experiment, therefore, surveyed the sympathetic projections to the aged small intestine for axonopathies. Furthermore, the experiment evaluated the specific prediction that catecholaminergic inputs undergo hyperplastic changes. Jejunal tissue was collected from 3-, 8-, 16-, and 24-month-old male Fischer 344 rats, prepared as whole mounts consisting of the muscularis, and processed immunohistochemically for tyrosine hydroxylase, the enzymatic marker for norepinephrine, and either the protein CD163 or the protein MHCII, both phenotypical markers for macrophages. Four distinctive sympathetic axonopathy profiles occurred in the small intestine of the aged rat: (1) swollen and dystrophic terminals, (2) tangled axons, (3) discrete hyperinnervated loci in the smooth muscle wall, including at the bases of Peyer's patches, and (4) ectopic hyperplastic or hyperinnervating axons in the serosa/subserosal layers. In many cases, the axonopathies occurred at localized and limited foci, involving only a few axon terminals, in a pattern consistent with incidences of focal ischemic, vascular, or traumatic insult. The present observations underscore the complexity of the processes of aging on the neural circuitry of the gut, with age-related GI functional impairments likely reflecting a constellation of adjustments that range from selective neuronal losses, through accumulation of cellular debris, to hyperplasias and hyperinnervation of sympathetic inputs.

With age, alpha-synuclein (α-SYNC) misfolds and forms insoluble deposits of protein in the myenteric plexus, leading presumably to dystrophy and degeneration in the circuitry controlling gastrointestinal (GI) function. The present experiment examined aggregates of α-SYNC in the aging small intestine and investigated how macrophages in the wall of the GI tract respond to these aberrant deposits. Groups of adult and aged Fisher 344 rats were studied. Whole mounts of duodenal, jejunal, and ileal smooth muscle wall, including the myenteric plexus, were prepared. Double labeling immunohistochemistry was used to stain α-SYNC protein and the phenotypic macrophage antigens CD163 and MHCII. Alpha-synuclein accumulated in dense aggregates in axons of both postganglionic and preganglionic neurons throughout the small intestine. Staining patterns suggested that deposits of protein occur initially in axonal terminals and then spread retrogradely toward the somata. Macrophages that were adjacent to dystrophic terminal processes were swollen and contained vacuoles filled with insoluble α-SYNC, and these macrophages commonly had the phenotype of alternatively activated phagocytes. The present results suggest that macrophages play an active phagocytotic role in removing α-SYNC aggregates that accumulate with age in the neural circuitry of the gut. Our observations further indicate that this housekeeping response does not clear the protein sufficiently to eliminate all synucleinopathies or their precursor aggregates from the healthy aging GI tract. Thus, accumulating deposits of insoluble α-SYNC in the wall of the GI tract may contribute, especially when compounded by disease or inflammation, to the age-associated neuropathies in the gut that compromise GI function.

Dystrophic axons and terminals are common in the myenteric plexus and smooth muscle of the gastrointestinal (GI) tract of aged rats. In young adult rats, alpha-synuclein in its normal state is abundant throughout the myenteric plexus, making this protein-which is prone to fibrillization-a candidate marker for axonopathies in the aged rat. To determine if aggregation of alpha-synuclein is involved in the formation of age-related enteric neuropathies, we sampled the stomach, small intestine and large intestine of adult, middle-aged, and aged virgin male Fischer 344 rats stained for alpha-synuclein in both its normal and pathological states. Alpha-synuclein-positive dystrophic axons and terminals were present throughout the GI tract of middle-aged and aged rats, with immunohistochemical double labeling demonstrating co-localization within nitric oxide synthase-, calretinin-, calbindin-, or tyrosine hydroxylase-positive markedly swollen neurites. However, other dystrophic neurites positive for each of these four markers were not co-reactive for alpha-synuclein. Similarly, a subpopulation of alpha-synuclein inclusions contained deposits immunostained with an anti-tau phospho-specific Ser(262) antibody, but not all of these hyperphosphorylated tau-positive aggregates were co-localized with alpha-synuclein. The presence of heteroplastic and potentially degenerating neural elements and protein aggregates both positive and negative for alpha-synuclein suggests a complex chronological relationship between the onset of degenerative changes and the accumulation of misfolded proteins. Additionally, proteins other than alpha-synuclein appear to be involved in age-related axonopathies. Finally, this study establishes the utility of the aging Fischer 344 rat for the study of synucleopathies and tauopathies in the GI tract.

The gastrointestinal (GI) tract is innervated by intrinsic enteric neurons and by extrinsic projections, including sympathetic and parasympathetic efferents as well as visceral afferents, all of which are compromised by age to different degrees. In the present review, we summarize and illustrate key structural changes in the aging innervation of the gut, and suggest a provisional list of the general patterns of aging of the GI innervation. For example, age-related neuronal losses occur in both the myenteric plexus and submucosal plexus of the intestines. These losses start in adulthood, increase over the rest of the life span, and are specific to cholinergic neurons. Parallel losses of enteric glia also occur. The extent of neuronal and glial loss varies along an oral-to-anal gradient, with the more distal GI tract being more severely affected. Additionally, with aging, dystrophic axonal swellings and markedly dilated varicosities progressively accumulate in the sympathetic, vagal, dorsal root, and enteric nitrergic innervation of the gut. These dramatic and consistent patterns of neuropathy that characterize the aging autonomic nervous system of the GI tract are candidate mechanisms for some of the age-related declines in function evidenced in the elderly.

Loss of myenteric neurons with age is well documented, however little is known about age-related changes of the sympathetic innervation of the myenteric plexus and gastrointestinal smooth muscle. The goal of the present study, therefore, was to evaluate the influence of age on the sympathetic innervation of the myenteric plexus throughout the gastrointestinal tract. Ad libitum fed virgin male Fischer 344 rats at 3, 15-16, 24, and 27-28 months of age were sampled. Whole mounts of the stomach, small intestine, and large intestine were processed with an antibody to tyrosine hydroxylase (TH). Additionally, some specimens labeled for TH were stained for NADPH-diaphorase to selectively label the nitrergic subpopulation of neurons in the myenteric plexus. Age-related changes in the TH-positive axons occurred as early as 15-16 months and became more pronounced by 27-28 months. Changes included markedly swollen axons and terminals and a decrease in the intensity of TH staining in some of the surviving processes. Similarly, swollen NADPH-diaphorase-positive axons were found in the myenteric ganglia and secondary plexus between ganglia in the whole mounts of rats 15-28 months of age, but swollen nitrergic axons and dystrophic TH-positive axons were never present in the same ganglion or connective. Therefore, in the aged rat, deterioration of the sympathetic innervation of the myenteric plexus could be one possible mechanism for the age-related decline in gastrointestinal motor function evidenced in the elderly.

The intrinsic neurones of the enteric nervous system (ENS) play a fundamental role in the regulation of gastrointestinal functions. Although much remains to be learnt about the changes that take place in intestinal nerves during ageing, evidence suggests that selective neurodegeneration may occur in the ageing ENS. Age-associated changes in intestinal innervation may contribute to the gastrointestinal disorders that increase in incidence in the elderly, such as dysphagia, gastrointestinal reflux and constipation. A number of other factors, such as immobility, co-morbidity, and side effects of therapeutic medication for other disorders however, are also likely to contribute to the aetiology of these conditions. An important finding in rodents is that the neuronal losses that take place in the ENS during ageing may be prevented by calorie restriction; an indication that diet may influence gastrointestinal ageing. Thus, it is of importance to understand not only how the ENS changes during 'normal' ageing, but also how external factors contribute to these changes. Here, current knowledge of how intestinal innervation is affected during normal ageing and how these changes may impact upon gastrointestinal physiology are reviewed.

Several studies have suggested an age-related reduction in the number of myenteric neurons in the lower gastrointestinal (GI) tract linked to changes in GI neuromuscular functions. The present study, combining protein gene product 9.5 immunostaining and NADPH-diaphorase histochemistry, aimed at quantifying the proportion of nitrergic neurons compared to the overall number of enteric neurons in the esophagus of young (3-4.5 months) and aged (18-20 months) Sprague-Dawley and Wistar rats. In both strains, the neuron numbers per ganglion in the cervical region were almost twice as high as in the other esophageal regions. Irrespective of age or strain, the esophagus harbored a very high proportion of intrinsic nitrergic neurons (greater than approximately 65%). Both strains showed with aging an overall neuronal loss of approximately 27%. While a significant increase (young: 64-71%; aged: 82-89%) was observed in all esophageal regions in the Wistar strain, the proportion of nitrergic neurons remained stable with aging in the Sprague-Dawley strain (range: 72-82%). In conclusion, the age-related reduction in the overall number of myenteric, nitrergic, and non-nitrergic neurons observed in the rat esophagus, appears to be highly region- and strain-dependent. Therefore, a protective mechanism against neuronal cell loss, selectively present in specific (nitrergic) enteric subpopulations, as suggested in earlier reports, cannot be put forward as a general phenomenon throughout the entire GI tract.

Elderly people frequently have symptoms of fullness and appetite loss due to impaired gastric motor activity. These symptoms may cause malnutrition, immunosuppression and other complications.

The effects of aging and daily activity on gastric motility in the elderly were investigated by electrogastrography and the (13)C-acetate breath test.

We enrolled seven active elderly subjects (active elderly group), seven elderly subjects staying at a geriatric facility who had reduced mental and physical capacities (inactive elderly group) and seven healthy young volunteers (young group). Electrogastrography was recorded before and after ingestion of a (13)C-acetate-mixed liquid meal. Expired air was sampled every 10 min after the meal to measure the (13)CO(2) concentration.

The ratio of the incidence of the 3-cpm wave (gastric intrinsic frequency) during the postprandial period compared to the fasting state was reduced in both elderly groups compared to young subjects, and the reduction was greater in the inactive elderly than in the active elderly group. The ratio of the amplitude of the peak frequency during the postprandial period to that in the fasting state (power ratio) was also lower in the elderly groups. The time of peak (13)CO(2) expiration was delayed in the active elderly and more so in the inactive elderly group.

Postprandial peristalsis and gastric contractile force are reduced in the elderly, and gastric emptying is delayed indicating a reduction in gastric motor activity.

Systematic studies of the autonomic nervous system of human subjects and development of well-defined animal models have begun to substantially improve our understanding of the pathogenesis of autonomic dysfunction in aging and may eventually provide strategies for intervention. Neuropathological studies of the sympathetic ganglia of aged human subjects and rodent models have demonstrated that neuroaxonal dystrophy involving intraganglionic terminal axons and synapses is a robust, unequivocal and consistent neuropathological finding in the aged sympathetic nervous system of man and animals. Quantitative studies have demonstrated that markedly swollen argyrophilic dystrophic axon terminals develop in the prevertebral superior mesenteric (SMG) and coeliac, but to a much lesser degree in the superior cervical ganglia (SCG) as a function of age, sex (males more than females) and diabetes. Dystrophic axons were immunoreactive for neuropeptide Y, tyrosine hydroxylase, dopamine-beta-hydroxylase, trkA and p75NTR, an immunophenotype consistent with their origin from postganglionic sympathetic neurons, and contained large numbers of highly phosphorylated neurofilaments or tubulovesicular elements. The sympathetic ganglia of aged rodents also showed the hallmark changes of neuroaxonal dystrophy as a function of age and location (many more in the SMG than in the SCG). Plasticity-related synaptic remodeling could represent a highly vulnerable target of the aging process. The fidelity of animal models to the neuropathology of aged humans suggests that similar pathogenetic mechanisms may be involved in both and that therapeutic advances in animal studies may have human application.

To explore the effects of aging on the vagal innervation of the gastrointestinal (GI) tract, male Fischer 344 rats at 3 and 24 months of age were injected in the left nodose ganglion with 3 microl of either 4% wheat germ agglutinin-horseradish peroxidase (to label sensory endings) or 1% cholera toxin subunit B-horseradish peroxidase (to label motor endings). The stomach and duodenum were prepared as wholemounts and processed with tetramethyl benzidine. In addition, to study age-related changes in the myenteric plexus, the stomachs, small intestines, and large intestines from 3-, 12-, 21-, 24- and 27-month-old rats were prepared as wholemounts and processed with Cuprolinic Blue (to stain the neurons). Vagal afferent endings, motor terminal profiles, and myenteric neurons were counted and mapped with a sampling grid. In the stomach, both the vagal and myenteric innervation were stable between the ages of 3 and 24 months; however, a decrease in the number of myenteric neurons in the forestomach was noted at 27 months. In the small and large intestines, myenteric cell loss occurred by 12 months of age, progressed with age, and appeared to be governed by several general principles: (1) the rate of cell loss was organ-specific, with a gradient of increasing severity from proximal to distal in the gut; (2) within organs of the GI tract, the rate of cell loss differed between regions; and (3) for given regions, cell losses progressed linearly with increasing age. The findings suggest that a positive relationship exists between the density of vagal extrinsic innervation and myenteric neuron survival; however, whether this results from the vagal innervation and/or other factor(s) protecting or rescuing myenteric neurons from age-related attrition remains to be determined.

The incidence of constipation increases with age. This has been linked to age-related changes in the structure and function of myenteric neurons regulating intestinal motility; however, the role of submucous neurons is unknown. The aim of this study was to determine the effect of maturation on cholinergic receptor-induced ion secretion in guinea pig colon. Changes in the short-circuit current (Isc) and tissue conductance were monitored in muscle-stripped colonic segments from young (3-4-month-old) and mature (12-15-month-old) male guinea pigs. Thirty-one percent of colonic segments from young guinea pigs exhibited ongoing neural activity, which was absent in mature animals. Baseline Isc was significantly higher only in young guinea pig tissues with ongoing activity. Tissue conductance was similar in all tissues. Electrical field stimulation caused a biphasic increase in the Isc. At 15 V/10 Hz, only Peak 1 was attenuated, whereas both peaks were reduced in mature guinea pigs at 10 V/5Hz. 1,1, dimethyl-4-phenyl-piperazinium(DMPP)-induced ion secretion was blunted in mature guinea pigs. Atropine reduced the 1,1, dimethyl-4-phenyl-piperazinium response only in young guinea pigs. Carbachol-induced ion secretion was similar in tissues from both age groups. In conclusion, nicotinic receptor-induced secretion mediated by both cholinergic and noncholinergic secretomotor neurons was blunted; however, epithelial muscarinic receptor activity was unaltered during maturation.

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Normal aging is associated with different changes in the cardiovascular system that lead to an increase in pathological processes, such as hypertension, coronary artery disease, heart failure, and postural hypotension with enhancement of both morbidity and mortality. The vascular alterations consist of changes in the function and structure of the arteries, and increasing vascular stiffness, mainly when atherosclerosis is present, whose incidence is increased with age. The arteries accumulate lipids, collagen, and minerals. Cerebral perfusion may be reduced in the elderly, mainly regional cerebral blood flow, which leads to a deterioration of mental and physical functions. The degree of deterioration is increased when aging is associated with hypertension. Aging alters endothelial cells, which play an important role in vascular tone regulation. Such a process tends to reduce endothelium-dependent relaxations, and clearly reduces the vasodilation elicited by beta-adrenoceptor agonists. The contractions induced by different agents, such as 5-hydroxytryptamine, histamine, high potassium and angiotensin are barely affected with aging, whereas those elicited by noradrenaline or endothelin are usually reduced. However, plasma noradrenaline levels are increased with age, mainly due to a reduction in the sensitivity of presynaptic alpha 2-adrenoceptors and also of noradrenaline uptake. Sodium pump activity, that controls cellular ionic homeostasis, may be altered depending on animal species. Finally, vascular Ca2+ regulation appears to be altered and the extracellular Ca2+ dependence of contractile responses elicited by agonists is increased, which justifies the enhanced sensitivity to Ca2+ antagonists in senescence.

Dysfunction of the sympathetic autonomic nervous system is an increasingly recognized, although poorly understood, complication of increasing age in experimental animals and man. In this study of young adult (4-6 months old) and aged (12-24 months old) mice we have examined the ultrastructural appearance of perikarya, dendritic processes, preterminal axons, and synapses in selected sympathetic ganglia as well as the three-dimensional structure of the dendritic arborizations of principal sympathetic neurons using intracellular injections of Lucifer Yellow. Ultrastructural examination demonstrated numerous markedly enlarged presynaptic terminal axons and synapses which distorted the contours of perikarya and dendrites of neurons within the prevertebral celiac/superior mesenteric and paravertebral superior cervical and stellate sympathetic ganglia of aged mice. Dilated preterminal axons had the distinctive ultrastructural appearance of neuroaxonal dystrophy, a pathologic process described in a wide variety of clinical and experimental entities. Dystrophic axons were identical in ultrastructural appearance in young and old animals, differing only in frequency. A distinctive type of ultrastructural alteration, characterized by markedly distended neurites containing numerous vacuoles, was confined to the superior cervical ganglia and also increased in frequency with aging. Although many intraganglionic vacuolated processes disappeared with surgical interruption of the cervical sympathetic trunk, which contains the preganglionic axons innervating the superior cervical ganglia, others persisted. In addition, the presence in some processes of admixed ribosomes, lipofuscin, or continuity with the cell body indicated that numerous neuritic alterations within aged sympathetic ganglia were likely of dendritic origin. Intracellular injections of Lucifer Yellow into principal sympathetic neurons demonstrated that the dendritic arborizations of the celiac/superior mesenteric ganglia neurons of young adult mice were significantly more complex and extensive than those of the superior cervical ganglia. Sympathetic neurons of aged superior cervical ganglia, but not superior mesenteric ganglia, appeared significantly smaller with regard to total dendritic length, extent, and branching when compared to those of young animals. In the aged superior cervical ganglia, short, stunted dendritic processes also exhibited large, focal, often multiple, swellings, a phenomenon infrequently observed in the superior cervical ganglia of young animals. The celiac/superior mesenteric ganglia of aged or young adult mouse failed to exhibit comparable dendritic swellings.

The effect of age on the distribution of NADPH-diaphorase-containing neurones was investigated in the myenteric plexus of ileum and proximal colon of embryonic day-19 rats, as well as in rats at postnatal day 4, 6 months and 26 months. The mean percentage of NADPH-diaphorase-stained neurones per ganglion was established using protein gene product 9.5(protein found in most if not all neurones)-immunostained neurones as 100%. The results revealed that there was a significant relative increase in NADPH-diaphorase-positive neurones with increasing age in the myenteric plexus of proximal colon with nearly all protein gene product 9.5-immunoreactive neurones staining for NADPH-diaphorase in 26-month-old rats. This was in marked contrast with the ileum, where no significant relative increase in NADPH-diaphorase-positive neurones was seen in aged rats. The implications of these findings in relation to programmed cell survival and cell death are discussed.

NADPH-diaphorase staining was performed on wholemount preparations of the muscularis externa (which includes the myenteric plexus) of the rat small intestine taken from animals of 4, 24 and 30 months of age. A population of NADPH-diaphorase-stained neuron cell bodies was observed predominantly in the ganglia of the plexus. There were also many stained axons throughout the plexus and in the muscularis at all ages. The distribution of stained neurons around the circumference of the intestine was the same at all ages, being greater on the mesenteric than on the anti-mesenteric aspect. The numbers of NADPH-diaphorase-positive neurons in the myenteric plexus were counted by a systematic random sampling method. At 4 months there were 3716 +/- 219 stained neurons per cm2. There was no difference in the neuron numbers between the 24- and 30-month animals but they were decreased in number by 15.01% in comparison to the 4-month rats when growth in the length of the intestine was taken into account. This reduction in neuron numbers is markedly less than that previously recorded for the total numbers of myenteric neurons in the aged rat small intestine suggesting that the NADPH-diaphorase neurons are relatively spared in old age. The density of NADPH-diaphorase-positive varicose axons in the myenteric plexus and in the muscularis appeared to be slightly greater in the aged animals. These results provide evidence that the majority of the population of the myenteric NADPH-diaphorase-stained neurons, which may play a part in relaxation of the gut, survive in old age.

Age-differences in the sensitivity of peripheral sympathetic neurons to chronic ethanol exposure and ethanol withdrawal were studied in male Wistar rats aged 4 months, 12 months, or 24 to 25 months. The superior cervical ganglia (SCG) of the young (4 months) and the 2-year-old rats responded to a 12-day or 4-week ethanol exposure with significantly increased catecholamine turnover, while the ganglia of the middle-aged rats (12 months) showed only a minor increase in the intensity of catecholamine fluorescence and tyrosine hydroxylase immunoreactivity. Extensive neuronal vacuolation was found in the 4 months ethanol-exposed SCG, probably as a reaction of a subpopulation of neurons to increased stimulation. Ethanol-induced neuronal loss was most prominent in the SCG of the oldest age group. Contrary to the marked changes in SCG functional and morphometric parameters, the pelvic sympathetic neurons in the hypogastric ganglion showed no significant changes after ethanol exposure. The pattern of ethanol-induced morphological alterations found in the present study did not provide unambiquous support for either the "accelerated aging" or the "increased vulnerability" concept regarding ethanol-aging interactions in the nervous system.

The sympathetic innervation of the urinary tract of young adult (4 months) and aged (24+ months) rats has been examined by glyoxylic acid-induced fluorescence for the detection of noradrenaline and by immunofluorescence using antisera against tyrosine hydroxylase (TH) and neuropeptide Y (NPY). Immunostaining for calcitonin gene-related peptide (CGRP), known to be present in pelvic sensory nerves, was also performed. Semi-quantitative estimations of nerve densities were made of noradrenergic and peptidergic fibres innervating the smooth musculature of the ureter, bladder and urethra, and of the urinary tract vasculature. In the aged rats the overall patterns of innervation remained unchanged. However, with the exception of the vesical vasculature, the density of noradrenergic innervation decreased as did the intensity of histofluorescence. A similar pattern of results was observed by TH and NPY immunofluorescence. The results present evidence for a diminution in the sympathetic control of the urinary tract in aged rats. The pattern and density of CGRP-immunoreactive nerves was unchanged in the aged animals suggesting that pelvic visceral sensory innervation is more resistant to the effects of advancing age.

There are few generalisations that can be made regarding the changes that occur in autonomic nerves during ageing. Old age has different effects, including loss of neurones, loss of axon branches and alterations in neurotransmitters and other intracellular features. However, these age-related events are associated with particular and often small groups of neurones and are frequently species specific. Changes occur at different periods during development and maturity without any obvious age-stage at which neurodegenerative changes come to predominate. Some of the observations regarding neuronal changes in old age can be interpreted as the result of altered interactions between neurones and their peripheral target tissues. Recent studies in my laboratory support this contention. The neurotrophic theory has been used to explain such interactions during early development and it seems possible that, for example, alterations in the access of neurones to target-derived growth factors may underlie some of the changes that have been observed in old age. Plasticity in the mature autonomic nervous system may also be governed by similar relationships between nerves and their target tissues.

We have previously found in rat superior cervical ganglion that there is a fall in neuron numbers and in cellular neuropeptide Y (NPY) immunoreactivity over the first year of life. In this study, we have used computerized image analysis to quantitate changes in neuron size, numbers and immunoreactivity for neuron-specific enolase (NSE), tyrosine hydroxylase (TH) and NPY in this ganglion between 1 and 85 weeks of age. Neuronal cytoplasmic area increased between 1 and 11 weeks and then remained stable until after 67 weeks, when there was a further increase in size of both NPY-positive and NPY-negative cells. Numbers of NPY-positive cells, but not those of NPY-negative cells, fell between 11 and 30 weeks. Both populations were stable after this time. Neuronal levels of NSE and TH remained constant, but levels of NPY fell between 58 and 67 weeks. These results indicate that changes in adult neuronal size, numbers and neurochemistry are independent phenomena. The increase in cell size and the fall in NPY after 58 weeks correspond to the time of withdrawal of some preganglionic inputs and may be responses to this event. By contrast, the decrease in NPY-positive cell numbers occurs some months before this time.

Intestinal disorders suggesting impaired gastrointestinal motility due to aging have been reported, but the influence of advanced age on the patterns of motility in the human small intestine is unknown. The present prospective study describes these patterns of motility in 15 healthy old subjects with a median of 84 years (range, 81-91 years). Nineteen healthy young adults served as controls. Ambulatory manometry was performed at home, with two sensors located in the proximal small intestine. Postprandial motility was induced by a standardized meal at 1800 h, and fasting motility was recorded during the subsequent night. Migrating motor complex (MMC) data were analysed by means of an expanded variance component model. Recurrent MMCs were identified during fasting in all individuals, with similar periodicity in old and young adults (p = 0.4). The propagation velocity of phase III of MMC was slower in the old subjects (6.5 +/- 0.8 cm/min versus 10.8 +/- 1.2 cm/min; p less than 0.01). Duration of postprandial motility was preserved, as were the amplitude and frequency of contractions during phase III and the postprandial state. Propagated clustered contractions were more frequently present in old subjects both after a meal (67% versus 11%; p less than 0.01) and during fasting (p less than 0.01); otherwise the patterns of motility are maintained in the human small intestine throughout the process of aging.

Elements of the cervical part of the sympathetic nervous system have been examined quantitatively in four and twenty-four month Wistar rats. The number of unmyelinated axons in the cervical trunk had significantly (P less than 0.002) increased in the old animals and the number of myelinated axons comprised less than 4% of the total number at both ages. The number of neurons in the superior cervical ganglion and the density of noradrenergic innervation of two of its target organs, the iris and the submandibular gland, were insignificantly different at the two ages. These results are consistent with other evidence which suggests that the cervical sympathetic system is maintained throughout the adult lifespan in rats.

Immunoreactivity for substance P (SP-LI) and vasoactive intestinal polypeptide (VIP-LI) in the stomach, duodenum, jejunum and ileum of young (3-month-old), adult (12-month-old) and old (28-month-old) male Wistar rats were determined by radioimmunoassay. SP-LI and VIP-LI did not show changes in the stomach or in the small intestine portions investigated in adult in comparison with young rats. In old rats SP-LI levels were unchanged in the stomach and in the duodenum, reduced in the jejunum and increased in the ileum. VIP-LI concentrations were unchanged in the stomach, and remarkably reduced in the duodenum, jejunum and ileum of old rats. Since the two neuropeptides investigated are localized primarily within different intrinsic gastrointestinal neurons, the present findings suggest that the various populations of gastrointestinal neurons are affected in a different manner during aging.

The ability of carbachol and isoprenaline to contract and relax respectively the longitudinal layer of ileal smooth muscle has been compared in rats aged six and twenty-four months. The concentration response curve to carbachol did not vary with the age of the animal. In contrast, the ability of isoprenaline to relax longitudinal smooth muscle precontracted with carbachol was significantly (p less than 0.02) reduced in the twenty-four month age group. This reduced response was due to a decrease in the maximal relaxation induced by isoprenaline rather than by a shift to the right of its dose-response curve. These results are discussed in the context of previous histochemical and microscopical studies which have shown a marked reduction in the density of the sympathetic innervation of the rat small intestine in old age.

This study evaluates sudomotor function in the hindpaw of young and aged mice. Sweating was stimulated by pilocarpine injection and by electrical stimulation of the sciatic, tibial, peroneal, sural and saphenous nerves. The number of responsive sweat glands of the paw was determined by the silicon mold technique. The results obtained provide evidence that the number of functioning sweat glands of the hindpaw tended to decrease in aged mice. The peripheral sudomotor territories and the complement of sweat glands for individual nerves declined slightly with age. Moreover, the number of sweat glands responsive to cholinergic stimulation was decreased when compared with the number responsive to electrical stimulation of the sciatic nerve in aged mice. These and previous observations suggest that the number of sudomotor axons in the peripheral nerve, as well as their capabilities for compensatory reinnervation of sweat glands by regeneration and by sprouting, is reduced with aging.

Mechanisms of autonomic neuroeffector transmission are summarised, including evidence for a multiplicity of transmitters, co-transmission, neuromodulation and 'chemical coding' of individual autonomic neurons, where the combination of transmitters they contain is known, as well as their projections and central connections. Changes in expression of autonomic nerves and co-transmitters that occur during development and aging, following trauma, surgery, after chronic exposure to drugs, and in a number of disease situations are described. It is suggested that in neuropathological analysis, compensatory increases in innervation should be considered as well as loss or damage to nerves. Studies of the molecular mechanisms involved in the control of co-transmitter and receptor expression are now needed.

The correlation between catecholamine histofluorescence, tyrosine hydroxylase (TH) immunoreactivity and accumulation of age pigment was studied in the superior cervical ganglia (SCGL) of young (3 months) and old (28 months) rats. In the young animals there was a positive correlation between TH-immunoreactivity and catecholamine stores in most of the neurons. A pigment accumulation covering the profile area was found in approximately 10 per cent of the neurons in the young rats. In these neurons strong TH-immunoreactivity was associated with weak catecholamine histofluorescence. In the ganglia of the old animals there were considerable differences between individual cells in TH-activities, catecholamine stores and amounts of age pigment. In addition, there was a marked uncoupling between TH-activity and catecholamine fluorescence in a number of neurons, i.e. there were neurons with strong TH-immunoreactivity but weak catecholamine histo- fluorescence and vice versa. The functional implications of this uncoupling are discussed in the article.

Morphometric measurements have been made by light and electron microscopy on sections of perfused sympathetic ganglia from rats of 6-24 months of age with special reference to the microvascular bed. Capillaries, postcapillary venules and small venules comprised the majority of the vessels studied but small arterioles were, in addition, included in the light microscopical part of the study. Light microscopical measurements using image analysis showed that there was a decrease in the density of the microvascular bed (number of vascular profiles/area) and in the total vascular luminal area with age in both ganglia. The ratio of neurons to microvessels remained constant in the superior cervical ganglion (SCG) but decreased with age in the coeliac-superior mesenteric ganglion (CSMG). However, the distribution of microvessels in relation to individual neurons remained unchanged throughout life in both ganglia. Ultrastructural studies revealed fenestrations in 12% of SCG microvessel profiles and in 38% of CSMG microvessels at 6 months, but the percentage of fenestrated profiles in the CSMG had declined by 24 months. There were no significant differences in the number of fenestrations per fenestrated profile. The basal lamina surrounding the microvessels increased significantly (almost doubling) in thickness with age. The range and distribution of microvessel wall thicknesses, expressed as harmonic mean wall thickness, were comparable in both ganglia at both ages and increased linearly according to the amount of pericyte covering present. No consistently significant relationships could be discerned between the microvessel wall thickness and luminal diameter or between the wall thickness and the area available to a given volume of blood for exchange of metabolites (luminal perimeter/luminal area). We conclude that the ganglionic capillary bed is similar in both ganglia and, in old age, accommodates structural changes that occur in the ganglion by maintaining its structure and relationship to individual neurons.

The neurons of the myenteric plexus of the entire small intestine were stained in young adult (3-4 mo old) and aging guinea pigs (26-30 mo old). Total length and circumference of the intestine were measured in the same experiments. The small intestine of the aging guinea pigs was longer, and (in the conditions of distention used) had a total serosal surface approximately 70% greater than in young adult animals. The spatial density of myenteric neurons per unit of serosal surface fell dramatically in aging animals, and the total number of myenteric neurons in the small intestine ranged between 1.1 and 1.6 million, i.e., it was only 40%-60% of the value obtained in young adult guinea pigs (2.75 million). The light microscope appearance of the neurons of the two groups of animals was markedly different and the suggestion is put forward that in aging guinea pigs the substantial reduction in neuron number is accompanied by structural changes and reorganization of the neurons that are left.

1. The arrangement of the sympathetic innervation of the myenteric plexus varies between mammalian species. 2. In larger mammals the density of sympathetic innervation of the myenteric plexus is significantly less than in small (less then 1 kg) species. 3. The number of varicosities on the terminal parts of sympathetic neurons innervating the gut is significantly less in larger mammals.

Neurons in the myenteric plexus of Auerbach of the jejunum, ileum, colon and rectum in 6- and 24-month-old rats have been visualised by an enzyme histochemical method in laminar preparations of the muscularis externa. Neuron somata numbers and sizes were recorded in the preparations. Significant reductions, of at least 40%, in the numbers of neurons in the ganglia of the myenteric plexus of the 24-month animals were recorded in all regions of the intestine, especially in the colon where the neuron number decreased by over 60%. These figures do not take into account changes that might have occurred in the overall length of the intestine during adult life. Measurements of neuron sizes suggest that the neuronal fall-out with age affects all categories of neuron equally and implies that all the intrinsic neuronal systems of the gut could be equally affected in old age.

Morphometric measurements have been made on rat sympathetic neurons at ages between 6 and 24 months. In neurons of the coeliac-superior mesenteric ganglion there is a marked decrease in the neuronal packing density between 12 and 18 months which is accompanied by increases in the size of the neurons and their nuclei. In the superior cervical ganglion, no changes in packing density are seen until 18 months after which a decrease occurs, accompanied by slight increases in the neuronal parameters. These post-maturation changes occurring throughout adult life reveal a continued dynamism of sympathetic neurons into old age as well as revealing further differences between populations of sympathetic neurons.