Reactive oxygen species, dietary restriction and neurotrophic factors in age-related loss of myenteric neurons

The effects of dietary restriction on oxidative stress in rodents

Oxidative stress is observed during aging and in numerous age-related diseases. Dietary restriction (DR) is a regimen that protects against disease and extends life span in multiple species. However, it is unknown how DR mediates its protective effects. One prominent and consistent effect of DR in a number of systems is the ability to reduce oxidative stress and damage. The purpose of this review is to comprehensively examine the hypothesis that dietary restriction reduces oxidative stress in rodents by decreasing reactive oxygen species (ROS) production and increasing antioxidant enzyme activity, leading to an overall reduction of oxidative damage to macromolecules. The literature reveals that the effects of DR on oxidative stress are complex and likely influenced by a variety of factors, including sex, species, tissue examined, types of ROS and antioxidant enzymes examined, and duration of DR. Here we present a comprehensive review of the existing literature on the effect of DR on mitochondrial ROS generation, antioxidant enzymes, and oxidative damage. In a majority of studies, dietary restriction had little effect on mitochondrial ROS production or antioxidant activity. On the other hand, DR decreased oxidative damage in the majority of cases. Although the effects of DR on endogenous antioxidants are mixed, we find that glutathione levels are the most likely antioxidant to be increased by dietary restriction, which supports the emerging redox-stress hypothesis of aging.

Sympathetic axonopathies and hyperinnervation in the small intestine smooth muscle of aged Fischer 344 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.

Alpha-synuclein expression patterns in the colonic submucosal plexus of the aging Fischer 344 rat: implications for biopsies in aging and neurodegenerative disorders?

BACKGROUND

This experiment assessed normative expression patterns of alpha-synuclein (SYNC), including ganglionic remodeling and development of SYNC pathologies, in the submucosal plexus (SMP) of the colon during healthy aging. The observations address age-associated changes in bowel function and are relevant to evaluations of SMP-containing colonic biopsies for SYNC or synucleinopathies associated with aging and peripheral neurodegenerative diseases.

METHODS

Colonic submucosal whole mounts from groups of virgin male Fischer 344 rats (n ≥ 8 per group) at 4, 8, 16, and 24 months of age were processed immunohistochemically for SYNC and the pan-neuronal marker HuC/D. In addition, macrophages immunoreactive for MHCII were examined. Stereological protocols were used to generate unbiased estimates of neuron density, neurons per ganglion, neurons per ganglionic area, and neuron size.

KEY RESULTS

The protein SYNC was expressed in a subpopulation of SMP neurons, in both nucleus and cytoplasm. The general age-associated pattern across different cell counts was an increase in the number of SYNC+ neurons between 4 and 8 months of age, with progressively decreasing numbers of both SYNC+ and SYNC- neurons over the remaining lifespan. The soma size of SYNC+ neurons increased progressively with age. Aggregated SYNC occurred in the aging SMP, and macrophages with alternatively activated profiles were located adjacent to pathological SYNC deposits, consistent with ongoing phagocytosis.

CONCLUSIONS & INFERENCES

Changes in SYNC expression with age, including a baseline of accumulating synucleinopathies in the healthy aging SMP, need to be considered when interpreting either functional disturbances or biopsies of the aging colon.

Counting neurons is not as easy as 'one-two, three'

An accurate determination of the number of neurons in a segment of bowel is fundamental to establish population norms and identify neurodegenerative conditions, including age-related loss of myenteric ganglion cells. Although the latter phenomenon has been observed by several laboratories in various mammals, in this issue of Neurogastroenterology and Motility, Gamage et al. present evidence that colonic myenteric ganglion cells are maintained in aged mice. These discordant findings prompt a thoughtful consideration, the range of variables affecting the accuracy of neuronal counts and the survival of neuronal populations in aging animals.

Myenteric neuron numbers are maintained in aging mouse distal colon

BACKGROUND Age-associated myenteric neuronal loss has been described in several species. In some studies,cholinergic neurons have been reported to be selectively vulnerable, whereas nitrergic neurons are spared. Aging of the mouse enteric nervous system(ENS) and the subtypes of mouse myenteric neurons that may be lost have been little studied. We therefore investigated changes in the numbers of total neurons and two neuronal subpopulations in the mouse distal colon during aging. METHODS Wholemount preparations from 3–4-, 12–13-, 18–19-, and 24–25-month-old C57BL/6 mice were double immunolabeled with HuC/D antibody to identify the total neuronal population and antisera to either calbindin or neuronal nitric oxide synthase (nNOS) to identify myenteric neuronal subpopulations. Samples were analyzed by confocal microscopy. New procedures were employed to ensure unbiased counting and to correct for changes in gut dimensions with age and stretch during sample preparation. The density of nerve fibers in the tertiary plexus was also studied. KEY RESULTS No significant change in numbers of total neurons or of either subpopulation with age was measured, but because of gut growth, the density of myenteric neurons decreased between 3–4 and 12–13 months. The density of nNOS-immunoreactive nerve fibers in the tertiary plexus increased significantly with age, up to 18–19 months. Numerous swollen processes of CB and nNOS-immunoreactive neurons were observed in 18–19- and 24–25-month-old animals. Conclusions &Inferences These results indicate that aging does not result in a loss of myenteric neurons in mouse distal colon at the ages studied, although neurodegenerative changes, which may impact on neuronal function, do occur.

Changes in the innervation of the mouse internal anal sphincter during aging

BACKGROUND

The innervation of the mouse internal anal sphincter (IAS) has been little studied, and how it changes during aging has not previously been investigated. The aim of this study was therefore to characterize the distribution and density of subtypes of nerve fibers in the IAS and underlying mucosa in 3-, 12- to 13-, 18- and 24- to 25-month-old male C57BL/6 mice.

METHODS

Nerve fibers were immunolabeled with antibodies against protein gene product 9.5 (PGP9.5), neuronal nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP), and calretinin (CR). Immunoreactivity in nerve fibers in the circular muscle and mucosa was quantified using Image J software.

KEY RESULTS

In young adult (3 month) mice, nNOS-immunoreactive (IR) nerve fibers were densely distributed in the circular muscle, but relatively few in the mucosa; VIP-IR nerve fibers were abundant in the circular muscle and common in the mucosa; SP-IR nerve fibers were common in circular muscle and mucosa; CGRP- and CR-IR nerve fibers were dense in mucosa and sparse in circular muscle. The density of PGP9.5 immunoreactivity (IRY) was not significantly reduced with age, but a significant reduction in nNOS-IRY and SP-IRY with age was found in the IAS circular muscle. Neuronal nitric oxide synthase-, VIP-, and SP-IRY in the anal mucosa were significantly reduced with age. CGRP-IRY in both circular muscle and mucosa was increased in 18-month-old animals.

CONCLUSIONS & INFERENCES

The density of immunoreactivity of markers for some types of IAS nerve fibers decreases during aging, which may contribute to age-related ano-rectal dysfunction.

Cellular changes in the enteric nervous system during ageing

The intrinsic neurons of the gut, enteric neurons, have an essential role in gastrointestinal functions. The enteric nervous system is plastic and continues to undergo changes throughout life, as the gut grows and responds to dietary and other environmental changes. Detailed analysis of changes in the ENS during ageing suggests that enteric neurons are more vulnerable to age-related degeneration and cell death than neurons in other parts of the nervous system, although there is considerable variation in the extent and time course of age-related enteric neuronal loss reported in different studies. Specific neuronal subpopulations, particularly cholinergic myenteric neurons, may be more vulnerable than others to age-associated loss or damage. Enteric degeneration and other age-related neuronal changes may contribute to gastrointestinal dysfunction that is common in the elderly population. Evidence suggests that caloric restriction protects against age-associated loss of enteric neurons, but recent advances in the understanding of the effects of the microbiota and the complex interactions between enteric ganglion cells, mucosal immune system and intestinal epithelium indicate that other factors may well influence ageing of enteric neurons. Much remains to be understood about the mechanisms of neuronal loss and damage in the gut, although there is evidence that reactive oxygen species, neurotrophic factor dysregulation and/or activation of a senescence associated phenotype may be involved. To date, there is no evidence for ongoing neurogenesis that might replace dying neurons in the ageing gut, although small local sites of neurogenesis would be difficult to detect. Finally, despite the considerable evidence for enteric neurodegeneration during ageing, and evidence for some physiological changes in animal models, the ageing gut appears to maintain its function remarkably well in animals that exhibit major neuronal loss, indicating that the ENS has considerable functional reserve.

Administering ascorbic acid to rats undergoing ageing processes: effects on myosin-V immunoreactive myenteric neurons

During the ageing process the enteric nervous system undergoes morphofunctional changes, such as enteric neurodegeneration. Neuronal death can be attributed to increase radicals free, and ascorbic acid (AA), known antioxidant, could minimize damage cause by oxidative stress. The objective of this study is to analyse the behaviour of morphoquantative myenteric neurons in the duodenum of adult Wistar rats with aged 90 (C90), 345 (E345) and 428 (E428) days, as well as animals of the same age who received ascorbic acid supplementation for 120 days (EA345 and EA428). Whole-mount preparations of muscle layer from the duodenum of the animals were immunostained by the method myosin V. 80 microscopic fields were quantified (14.8 mm2/animal) and measured 100 neuronal cell bodies per animal. During the aging process, there was a reduction in neuronal density in all animals groups, indicating that the effects of age were not attenuated with AA supplementation. The increase in the neuronal area of the cell bodies in 428-day-old animals proved the influence of age on this parameter. There was no observed a neuroprotective effect of AA (1 mL/g body weight) on the neuronal population myenteric myosin V immunoreactive.

Dietary restriction interferes with oxidative status and intrinsic intestinal innervation in aging rats

OBJECTIVES

To evaluate the effects of dietary restriction on oxidative status, the HuC/D-neuronal nitric oxide synthase (nNOS) myenteric neuron population, HuC/D-S100 glial cells, and the morphometry of the small intestine in rats at various ages.

METHODS

Fifteen Wistar rats were divided into 7-and 12-mo-old control groups and a 12-mo-old experimental group subjected to dietary restrictions (50% of normal ration) for 5 mo. At 7 and 12 mo of age, the animals were anesthetized, and blood was collected to assess the biochemical components and oxidative status. Ileum samples were subjected to double-marker (HuC/D-nNOS and HuC/D-S100) immunostaining and histologic processing to morphometrically analyze intestinal wall elements and determine the metaphase index and rate of caliciform cells. The data were subjected to analysis of variance and the Tukey post hoc test with a 5% significance level.

RESULTS

Age affected the oxidative status by increasing lipid peroxidation, with no effect on blood components, intrinsic innervation, and intestinal wall elements. The animals subjected to dietary restriction showed improved levels of total cholesterol, triacylglycerols, and oxidative status, with no changes in the nNOS neuron population. However, the dietary restriction dramatically decreased the glial and HuC/D myenteric populations, led to atrophy of the neuronal cell body, induced glial hypertrophy, and decreased the thickness of the intestinal wall.

CONCLUSION

The high oxidative status of the aging animals was reversed by dietary restriction, which also lowered cholesterol and triacylglycerol levels. The present dietary restriction elicited morpho-quantitative changes in the myenteric plexus and histology of the ileum, with likely effects on intestinal functions.

Postmitotic neurons develop a p21-dependent senescence-like phenotype driven by a DNA damage response

In senescent cells, a DNA damage response drives not only irreversible loss of replicative capacity but also production and secretion of reactive oxygen species (ROS) and bioactive peptides including pro-inflammatory cytokines. This makes senescent cells a potential cause of tissue functional decline in aging. To our knowledge, we show here for the first time evidence suggesting that DNA damage induces a senescence-like state in mature postmitotic neurons in vivo. About 40–80% of Purkinje neurons and 20–40% of cortical, hippocampal and peripheral neurons in the myenteric plexus from old C57Bl/6 mice showed severe DNA damage, activated p38MAPkinase, high ROS production and oxidative damage, interleukin IL-6 production, heterochromatinization and senescence-associated β-galactosidase activity. Frequencies of these senescence-like neurons increased with age. Short-term caloric restriction tended to decrease frequencies of positive cells. The phenotype was aggravated in brains of late-generation TERC−/− mice with dysfunctional telomeres. It was fully rescued by loss of p21(CDKN1A) function in late-generation TERC−/−CDKN1A−/− mice, indicating p21 as the necessary signal transducer between DNA damage response and senescence-like phenotype in neurons, as in senescing fibroblasts and other proliferation-competent cells. We conclude that a senescence-like phenotype is possibly not restricted to proliferation-competent cells. Rather, dysfunctional telomeres and/or accumulated DNA damage can induce a DNA damage response leading to a phenotype in postmitotic neurons that resembles cell senescence in multiple features. Senescence-like neurons might be a source of oxidative and inflammatory stress and a contributor to brain aging.

Ageing of enteric neurons: oxidative stress, neurotrophic factors and antioxidant enzymes

BACKGROUND

Ageing is associated with gastrointestinal dysfunction, which can have a major impact on quality of life of the elderly. A number of changes in the innervation of the gut during ageing have been reported, including neuronal loss and degenerative changes. Evidence indicates that reactive oxygen species (ROS) are elevated in ageing enteric neurons, but that neurotrophic factors may reduce generation of neuronal ROS. Two such factors, glial cell line derived neurotrophic factor (GDNF) and neurotrophin-3 (NT-3) have also been found to protect enteric neurons against oxidative stress induced cell death of enteric ganglion cells in vitro. We have investigated the possible roles of neurotrophic factors further, by examining their expression in the gut during ageing, and by analysing their effects on antioxidant enzyme production in cultures of enteric ganglion cells.

RESULTS

Analysis of the expression of GDNF and its receptors c-Ret and GFR α - 1 in rat gut by RT-PCR showed that expression continues throughout life and into ageing, in both ad libitum(AL) and calorically-restricted (CR) animals. Levels of expression of GDNF and GFR α - 1 were elevated in 24 month AL animals compared to 24 month CR animals, and to 24 CR and 6 month control animals respectively. The related factor Neurturin and its receptor GFR α - 2 were also expressed throughout life, the levels of the GFR - α-2(b) isoform were reduced in 24 m AL animals. Immunolabelling showed that c-Ret and GFR α - 1 proteins were expressed by myenteric neurons in ageing animals. GDNF, but not NT-3, was found to increase expression of Cu/Zn superoxide dismutase and catalase by cultured enteric ganglion cells.

CONCLUSIONS

The neurotrophic factors GDNF and neurturin and their receptors continue to be expressed in the ageing gut. Changes in the levels of expression of GDNF , GFR α-1 and GFR α-2(b) isoform occurred in 24 m AL animals. GDNF, but not NT-3, increased the levels of antioxidant enzymes in cultured enteric ganglion cells, indicating a possible mechanism for the reported protective effect of GDNF against menadione-induced neuronal apoptosis in the ageing gut. Together these data suggest that GDNF family members may play a protective role in the gut throughout life, and support the suggestion that dysregulation of neurotrophic factor support could contribute to neuronal ageing in the gut.

Effects of aging on cholinergic neuromuscular transmission in isolated small intestine of ad libitum fed and calorically-restricted rats

BACKGROUND

Age-associated losses of enteric neurons have been described. In rat ileum, myenteric neurons lost during aging have been reported to be predominantly cholinergic, and caloric restriction (CR) has been shown to protect against these losses. Cholinergic myenteric neurons include excitatory motor neurons, so the aim of this work was to determine whether neuronal loss in ad libitum (AL)-fed animals is reflected in dysfunctional cholinergic neuromuscular transmission, and if CR reduces any such dysfunction.

METHODS

Effects of electrical field stimulation (EFS) and applied acetylcholine (ACh) were examined in the longitudinal muscle of isolated ileal segments from 6-month-old rats and from 13- and 24-month-old rats fed either AL or CR diets.

KEY RESULTS

Contractile responses to EFS were abolished by atropine and potentiated by the acetylcholinesterase inhibitor, eserine. Frequency-response relationships were not significantly different amongst the three age-groups. Sensitivity to applied ACh, however, was three-fold lower in the oldest animals (P < 0.05). Eserine potentiated responses to ACh; there were no statistically significant differences amongst the sensitivities to ACh in its presence. No significant differences between AL- and CR-fed animals were measured, although variability was less in CR-fed than in AL-fed groups.

CONCLUSIONS & INFERENCES

The cholinergic system supplying the rat ileum longitudinal muscle did not appear to be impaired in old age. Decreased sensitivity to applied ACh in old tissues may have been due to increased acetylcholinesterase activity. Caloric restriction had no significant effect on responses to EFS or applied ACh. The implications of these results are discussed.

Differing effects of NT-3 and GDNF on dissociated enteric ganglion cells exposed to hydrogen peroxide in vitro

Oxidative stress is widely recognized to contribute to neuronal death during various pathological conditions and ageing. In the enteric nervous system (ENS), reactive oxygen species have been implicated in the mechanism of age-associated neuronal loss. The neurotrophic factors, neurotrophin 3 (NT-3) and glial cell line-derived neurotrophic factor (GDNF), are important in the development of enteric neurons and continue to be expressed in the gut throughout life. It has therefore been suggested that they may have a neuroprotective role in the ENS. We investigated the potential of NT-3 and GDNF to prevent the death of enteric ganglion cells in dissociated cell culture after exposure to hydrogen peroxide (H(2)O(2)). H(2)O(2) treatment resulted in a dose-dependent death of enteric neurons and glial cells, as demonstrated by MTS assay, bis-benzimide and propidium iodide staining and immunolabelling. Cultures treated with NT-3 prior to exposure showed reduced cell death compared to untreated control or GDNF-treated cultures. GDNF treatment did not affect neuronal survival in H(2)O(2)-treated cultures. These results suggest that NT-3 is able to enhance the survival of enteric ganglion cells exposed to oxidative stress.

Effect of caloric restriction on myenteric neuroplasticity in the rat duodenum during aging

The objective of this study was to evaluate the effects of caloric restriction (CR) on myenteric neurons in the duodenum of Wistar rats during aging. Thirty rats were divided into three groups: the C group (six-month-old animals that were fed a normal diet from weaning until six months of age), the SR group (18-month-old animals that were fed a normal diet from weaning until 18 months of age) and the CR group (18-month-old animals that were fed a 30% CR diet after six months of age). After 12 months, the animals were euthanized. Whole-mount preparations of the duodenums were either stained with Giemsa or underwent NADPH-diaphorase histochemistry to determine the general myenteric neuron population and the nitrergic neuron subpopulation (NADPH-d+), respectively. The NADPH-d-negative (NADPH-d-) neuron population was estimated based on the difference between the Giemsa-stained and NADPH-d+ neurons. The neurons were counted, and the cell body areas were measured. Aging was associated with neuronal loss in the SR group, which was minimized by caloric restriction in the CR group. The density (mm(2)) of the Giemsa-stained neurons was higher in the SR group (79.09 ± 6.25) than in the CR (92.37 ± 11.6) and C (111.68 ± 15.26) groups. The density of the NADPH-d+ neurons was higher in the SR group (44.90 ± 5.88) than in the C (35.75 ± 1.6) and RC (39.14 ± 7.02) groups. The density of NADPH-d- neurons was higher in the CR (49.73 ± 12.08) and C (75.64 ± 17.05) groups than in the SR group (33.82 ± 4.5). In the C group, 32% and 68% of the Giemsa-stained myenteric neurons were NADPH-d+ or NADPH-d-, respectively. With aging (SR group), the percentage of nitrergic neurons (56.77%) increased, whereas the percentage of NADPH-d- neurons (43.22%) decreased. In the CR group, the change in the percentage of nitrergic (42.37%) and NADPH-d- (57.62%) neurons was lower. As NADPH-d- neurons will be mostly cholinergic neurons, CR appears to reduce the loss of cholinergic neurons during aging. The cell body dimensions (μm(2)) were not altered by aging or CR. Thus, CR had a protective effect on myenteric neurons during aging.

Extraction of Lepidium apetalum seed oil using supercritical carbon dioxide and anti-oxidant activity of the extracted oil

The supercritical fluid extraction (SFE) of Lepidium apetalum seed oil and its anti-oxidant activity were studied. The SFE process was optimized using response surface methodology (RSM) with a central composite design (CCD). Independent variables, namely operating pressure, temperature, time and flow rate were evaluated. The maximumextraction of Lepidium apetalum seed oil by SFE-CO₂ (about 36.3%) was obtained when SFE-CO₂ extraction was carried out under the optimal conditions of 30.0 MPa of pressure, 70 °C of temperature, 120 min of extraction time and 25.95 L/h of flow rate. GC-MS analysis showed the presence of four fatty acids in Lepidium apetalum seed oil, with a high content (91.0%) of unsaturated fatty acid. The anti-oxidant activity of the oil was assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay and 2,2′-azino- bis(3-ethylbenzthiazoline-6-sulphonic acid) diammonium salt (ABTS) test. Lepidium apetalum seed oil possessed a notable concentration-dependent antioxidant activity, with IC₅₀ values of 1.00 and 3.75 mg/mL, respectively.

Reduced oxygen stress promotes propagation of murine postnatal enteric neural progenitors in vitro

BACKGROUND

Neural stem and progenitor cells of the Enteric Nervous System (ENS) are regarded as a novel cell source for applications in regenerative medicine. However, improvements to the current ENS cell culture protocols will be necessary to generate clinically useful cell numbers under defined culture conditions. Beneficial effects of physiologically low oxygen concentrations and/or the addition of anti-oxidants on propagation of various types of stem cells have previously been demonstrated. In this study, we tested the effects of such culture conditions on ENS stem and progenitor cell behavior.

METHODS

Enteric neural progenitor cells were isolated from postnatal day 3 mouse intestine and propagated either as monolayers or neurosphere-like bodies. The influence of hypoxic culture conditions and/or anti-oxidants on enteric cell propagation were studied systematically using proliferation, differentiation and apoptosis assays, whereas effects on gene expression were determined by qRT-PCR, western blot, and immunocytochemistry.

KEY RESULTS

Both hypoxic culture conditions and anti-oxidants supported a significantly improved enteric cell propagation and the generation of differentiated neural cell types. Enteric neural progenitors were shown to be specifically vulnerable to persistent oxidative stress.

CONCLUSIONS & INFERENCES

Our findings are consistent with previous reports of improved maintenance of brain stem cells cultured under reduced oxygen stress conditions and may therefore be applied to future cell culture protocols in ENS stem cell research.

Anti-epileptic drugs delay age-related loss of spiral ganglion neurons via T-type calcium channel

Loss of spiral ganglion neurons is a major cause of age-related hearing loss (presbycusis). Despite being the third most prevalent condition afflicting elderly persons, there are no known medications to prevent presbycusis. Because calcium signaling has long been implicated in age-related neuronal death, we investigated T-type calcium channels. This family is comprised of three members (Ca(v)3.1, Ca(v)3.2, and Ca(v)3.3), based on their respective main pore-forming alpha subunits: α1G, α1H, and α1I. In the present study, we report a significant delay of age-related loss of cochlear function and preservation of spiral ganglion neurons in α1H null and heterozygous mice, clearly demonstrating an important role for Ca(v)3.2 in age-related neuronal loss. Furthermore, we show that anticonvulsant drugs from a family of T-type calcium channel blockers can significantly preserve spiral ganglion neurons during aging. To our knowledge, this is the first report of drugs capable of diminishing age-related loss of spiral ganglion neurons.

Generalized neuromuscular hypoplasia, reduced smooth muscle myosin and altered gut motility in the klotho model of premature aging

BACKGROUND

  Gastrointestinal symptoms, particularly constipation, increase with aging, but their underlying mechanisms are poorly understood due to lack of experimental models. Previously we established the progeric klotho mouse as a model of aging-associated anorexia and gastric dysmotility. We also detected reduced fecal output in these animals; therefore, the aim of this study was to investigate in vivo function and cellular make-up of the small intestinal and colonic neuromuscular apparatus.

METHODS

Klotho expression was studied by RT-PCR and immunohistochemistry. Motility was assessed by dye transit and bead expulsion. Smooth muscle and neuron-specific gene expression was studied by Western immunoblotting. Interstitial cells of Cajal (ICC) and precursors were analyzed by flow cytometry, confocal microscopy, and three-dimensional reconstruction. HuC/D(+) myenteric neurons were enumerated by fluorescent microscopy.

KEY RESULTS

Klotho protein was detected in neurons, smooth muscle cells, and some ICC classes. Small intestinal transit was slower but whole-gut transit of klotho mice was accelerated due to faster colonic transit and shorter intestinal lengths, apparent only after weaning. Fecal water content remained normal despite reduced output. Smooth muscle myosin expression was reduced. ICC, ICC precursors, as well as nitrergic and cholinergic neurons maintained their normal proportions in the shorter intestines.

CONCLUSIONS & INFERENCES

Progeric klotho mice express less contractile proteins and develop generalized intestinal neuromuscular hypoplasia mainly arising from stunted postweaning growth. As reduced fecal output in these mice occurs in the presence of accelerated colonic and whole-gut transit, it likely reflects reduced food intake rather than intestinal dysmotility.

Gender- and age-related differences in muscular and nerve-mediated responses in human colon

BACKGROUND

Gender- and age-related differences in muscular and nerve-mediated responses in human colon are poorly characterized. We studied carbachol-induced motor responses and electrically evoked contractions in sigmoid circular muscle from adult and elderly patients of different gender.

METHODS

Sigmoid colon segments were obtained from 24 men and 16 women undergoing left hemicolectomy for colon cancer. Isometric tension was measured on muscle strips exposed to increasing carbachol concentrations. The effects of atropine, guanethidine, L-nitro arginine methyl ester (L-NAME), and tetrodotoxin on electrically evoked contractions were also studied.

RESULTS

Female patients showed higher maximal response to carbachol than male patients, elderly females being the most sensitive to carbachol among all patient groups. Electrically evoked contractions were linearly related to stimulation frequency and abolished by tetrodotoxin. Electrically evoked contractions were significantly more pronounced in elderly male patients; they were reduced by atropine and guanethidine and increased by L-nitro arginine methyl ester in the presence of atropine and guanethidine (P < 0.05). The effect of L-NAME was most marked in elderly male patients and least pronounced in elderly females.

CONCLUSIONS

The response to carbachol and the role of nitrergic pathways differ according to age and gender; this may depend on muscarinic receptor upregulation or humoral factors affecting nitric oxide release, respectively.

Age-related synaptic loss of the medial olivocochlear efferent innervation

Age-related functional decline of the nervous system is consistently observed, though cellular and molecular events responsible for this decline remain largely unknown. One of the most prevalent age-related functional declines is age-related hearing loss (presbycusis), a major cause of which is the loss of outer hair cells (OHCs) and spiral ganglion neurons. Previous studies have also identified an age-related functional decline in the medial olivocochlear (MOC) efferent system prior to age-related loss of OHCs. The present study evaluated the hypothesis that this functional decline of the MOC efferent system is due to age-related synaptic loss of the efferent innervation of the OHCs. To this end, we used a recently-identified transgenic mouse line in which the expression of yellow fluorescent protein (YFP), under the control of neuron-specific elements from the thy1 gene, permits the visualization of the synaptic connections between MOC efferent fibers and OHCs. In this model, there was a dramatic synaptic loss between the MOC efferent fibers and the OHCs in older mice. However, age-related loss of efferent synapses was independent of OHC status. These data demonstrate for the first time that age-related loss of efferent synapses may contribute to the functional decline of the MOC efferent system and that this synaptic loss is not necessary for age-related loss of OHCs.

Neuroinflammation in inflammatory bowel disease

Inflammatory bowel disease is a chronic intestinal inflammatory condition, the pathology of which is incompletely understood. Gut inflammation causes significant changes in neurally controlled gut functions including cramping, abdominal pain, fecal urgency, and explosive diarrhea. These symptoms are caused, at least in part, by prolonged hyperexcitability of enteric neurons that can occur following the resolution of colitis. Mast, enterochromaffin and other immune cells are increased in the colonic mucosa in inflammatory bowel disease and signal the presence of inflammation to the enteric nervous system. Inflammatory mediators include 5-hydroxytryptamine and cytokines, as well as reactive oxygen species and the production of oxidative stress. This review will discuss the effects of inflammation on enteric neural activity and potential therapeutic strategies that target neuroinflammation in the enteric nervous system.

Age-related neuronal loss in the cochlea is not delayed by synaptic modulation

Age-related synaptic change is associated with the functional decline of the nervous system. It is unknown whether this synaptic change is the cause or the consequence of neuronal cell loss. We have addressed this question by examining mice genetically engineered to over- or underexpress neuregulin-1 (NRG1), a direct modulator of synaptic transmission. Transgenic mice overexpressing NRG1 in spiral ganglion neurons (SGNs) showed improvements in hearing thresholds, whereas NRG1 -/+ mice show a complementary worsening of thresholds. However, no significant change in age-related loss of SGNs in either NRG1 -/+ mice or mice overexpressing NRG1 was observed, while a negative association between NRG1 expression level and survival of inner hair cells during aging was observed. Subsequent studies provided evidence that modulating NRG1 levels changes synaptic transmission between SGNs and hair cells. One of the most dramatic examples of this was the reversal of lower hearing thresholds by "turning-off" NRG1 overexpression. These data demonstrate for the first time that synaptic modulation is unable to prevent age-related neuronal loss in the cochlea.

Age-related loss of spiral ganglion neurons

Spiral ganglion neurons (SGNs) are the relay station for auditory information between hair cells and central nervous system. Age-related decline of auditory function due to SGN loss can not be ameliorated by hearing aids or cochlear implants. Recent findings clearly indicate that survival of SGNs during aging depends on genetic and environmental interactions, which can be demonstrated at the systemic, tissue, cellular, and molecular levels. At the systemic level, both insulin/insulin-like growth factor-1 and lipophilic/steroid hormone pathways influence SGN survival during aging. At the level of organ of the Corti, it is difficult to determine whether age-related SGN loss is primary or secondary degeneration. However, a late stage of SGN degeneration may be independent of age-related loss of hair cells. At the cellular and molecular level, several pathways, particularly free radical and calcium signaling pathways, can influence age-related SGN loss, and further studies should determine how these pathways contribute to SGN loss, such as whether they directly or indirectly act on SGNs. With the advancement of recent genetic and pharmacologic tools, we should not only understand how SGNs die during aging, but also find ways to delay this loss.

Age-related changes in vagal afferents innervating the gastrointestinal tract

Recent progress in understanding visceral afferents, some of it reviewed in the present issue, serves to underscore how little is known about the aging of the visceral afferents in the gastrointestinal (GI) tract. In spite of the clinical importance of the issue-with age, GI function often becomes severely compromised-only a few initial observations on age-related structural changes of visceral afferents are available. Primary afferent cell bodies in both the nodose ganglia and dorsal root ganglia lose Nissl material and accumulate lipofucsin, inclusions, aggregates, and tangles. Additionally, in changes that we focus on in the present review, vagal visceral afferent terminals in both the muscle wall and the mucosa of the GI tract exhibit age-related structural changes. In aged animals, both of the vagal terminal types examined, namely intraganglionic laminar endings and villus afferents, exhibit dystrophic or regressive morphological changes. These neuropathies are associated with age-related changes in the structural integrity of the target organs of the affected afferents, suggesting that local changes in trophic environment may give rise to the aging of GI innervation. Given the clinical relevance of GI tract aging, a more complete understanding both of how aging alters the innervation of the gut and of how such changes might be mitigated should be made research priorities.

Enteric neuroglial apoptosis in inflammatory bowel diseases

BACKGROUND

Enteric nervous system abnormalities have been described in patients with inflammatory bowel diseases. However, the mechanisms responsible for these abnormalities remain to date largely unknown.

AIMS

We investigated the potential role of apoptotic phenomena in enteric neurons and enteroglial cells in patients with inflammatory bowel diseases.

PATIENTS AND METHODS

Full-thickness surgical specimens of 19 patients undergoing surgery for medically refractory disease (9 from the ileum of patients with Crohn's disease, 10 from the colon of patients with ulcerative colitis) were assessed for the presence of enteric neurons and enteroglial cells and for their apoptosis by two immunohistochemical methods, one also able to distinguish apoptosis from necrosis. The results were compared with those obtained in control specimens.

RESULTS

Concerning Crohn's disease, the ileal segments displayed a significant increase of apoptotic enteric neurons and enteroglial cells in both the submucous and the myenteric plexus compared to controls. In patients with ulcerative colitis, compared to controls, apoptotic phenomena were significantly reduced in enteric neurons, whereas they were increased in the enteroglial cell population (submucous and myenteric plexus).

CONCLUSIONS

In patients with inflammatory bowel disease apoptotic phenomena involve both enteric neurons and enteroglial cells, and may play a role in the abnormalities of the enteric nervous system. The importance of these findings in the pathophysiology of these conditions remains to be determined.

Potential of cell therapy to treat pediatric motility disorders

Gut motility disorders represent a significant challenge in clinical management with current palliative approaches failing to overcome disease and treatment-related morbidity. The recent progress with stem cells to restore missing or defective elements of the gut neuromusculature offers new hope for potential cure. Focusing on enteric neuropathies such as Hirschsprung's disease, the review discusses the progress that has been made in the sourcing of putative stem cells and the studies into their biology and therapeutic potential. It also explores the practical challenges that must be overcome before stem cell-based therapies can be applied in the clinical arena. Although many obstacles remain, the speed of advancement of the enteric stem cell field suggests that such therapies are on the horizon.

Fall in density, but not number of myenteric neurons and circular muscle nerve fibres in guinea-pig colon with ageing

In guinea-pig ileum, ageing has been associated with a decrease in enteric neurons. This study examined guinea-pig colon and measured changes in gut dimensions, neuron size, density and ganglionic area. Changes in motor nerve fibres in the circular muscle were also measured. Myenteric neurons in whole-mount preparations of mid-colon from 2-week, 6-month, and 2-year-old guinea-pigs were labelled immunohistochemically with the neuronal marker human neuronal protein HuC/HuD, and numbers of neurons mm(-2), neuronal size, ganglionic area mm(-2), gut length, circumference and muscle thickness were measured. Corrected numbers of neurons mm(-2) and ganglionic area mm(-2) accounting for growth of the colon were calculated. Additionally, nerve fibres in circular muscle cross-sections were labelled with antibodies against nitric oxide synthase (NOS) and substance P (SP) and the density of nerve fibres in circular muscle was measured. The numbers of neurons mm(-2) decreased by 56% (from 2 weeks to 2 years) with no change in neuron size. Total neuron numbers decreased by 19% (P = 0.14) when adjusted for changes in length and circumference with age. The percentage area of NOS- and SP-immunoreactive (IR) nerve fibres in the circular muscle decreased (P < 0.001), but the total area of NOS and SP-IR nerve fibres increased (P < 0.01) due to an age-related increase in muscle thickness. The density of myenteric neurons in guinea-pig mid-colon halved from 2 weeks to 2 years, but when the increase in colon dimensions was considered, the number of neurons decreased by only 19%. The percentage area of motor nerve fibres in the circular muscle decreased with no change in total volume of nerve fibres.

Age-related changes in functional NANC innervation with VIP and substance P in the jejunum of Lewis rats

Age-related changes in non-adrenergic, non-cholinergic (NANC) neurotransmission might contribute to differences in gastrointestinal motility. Our aim was to determine age-related changes in functional innervation with vasoactive intestinal polypeptide (VIP) and substance P (Sub P) in rat jejunum. We hypothesized that maturation causes changes in neurotransmission with these two neuropeptides. Longitudinal and circular jejunal muscle strips from young (3 months) and middle-aged (15 months) rats (total: 24 rats) were studied; the response to exogenous VIP and Sub P and the effect of their endogenous release from the enteric nervous system during electrical field stimulation (EFS) were evaluated. In longitudinal muscle, response to exogenous VIP and endogenously released VIP during EFS were increased in middle-aged rats, while the effect of endogenously released Sub P was decreased. In the circular muscle, the response to endogenously released VIP was increased in middle-aged rats, while the effects of exogenous VIP and endogenously released Sub P were unchanged. Response to exogenous Sub P was unaffected by maturation in both muscle layers. Spontaneous contractile activity was increased in the longitudinal and circular muscle of the older rats. In the jejunum of middle-aged rats, participation of VIP in functional NANC innervation was increased, while functional innervation with Sub P was decreased. These changes in the balance of inhibitory and excitatory neurotransmission occur during the year of maturation in rats and demonstrate an age-dependant plasticity of neuromuscular bowel function.

Alpha-synuclein immunopositive aggregates in the myenteric plexus of the aging Fischer 344 rat

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.

Effect of age on the enteric nervous system of the human colon

The effect of age on the anatomy and function of the human colon is incompletely understood. The prevalence of disorders in adults such as constipation increase with age but it is unclear if this is due to confounding factors or age-related structural defects. The aim of this study was to determine number and subtypes of enteric neurons and neuronal volumes in the human colon of different ages. Normal colon (descending and sigmoid) from 16 patients (nine male) was studied; ages 33-99. Antibodies to HuC/D, choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), and protein gene product 9.5 were used. Effect of age was determined by testing for linear trends using regression analysis. In the myenteric plexus, number of Hu-positive neurons declined with age (slope = -1.3 neurons/mm/10 years, P = 0.03). The number of ChAT-positive neurons also declined with age (slope = -1.1 neurons/mm/10 years of age, P = 0.02). The number of nNOS-positive neurons did not decline with age. As a result, the ratio of nNOS to Hu increased (slope = 0.03 per 10 years of age, P = 0.01). In the submucosal plexus, the number of neurons did not decline with age (slope = -0.3 neurons/mm/10 years, P = 0.09). Volume of nerve fibres in the circular muscle and volume of neuronal structures in the myenteric plexus did not change with age. In conclusion, the number of neurons in the human colon declines with age with sparing of nNOS-positive neurons. This change was not accompanied by changes in total volume of neuronal structures suggesting compensatory changes in the remaining neurons.

Ginkgo biloba (EGb 761) extract: effects on the myenteric plexus of the large intestine in Wistar rats

The objective of this study was to evaluate the effect of the purified extract of the Ginkgo biloba (EGb 761) plant on the myenteric plexus in the proximal and distal colon of Wistar rats for a period of 120 days. The experimental rats were divided into two age groups: a young group, sacrificed at age 90 days, and an adult group, sacrificed at age 210 days. We observed a significant reduction in the number of neurons in the myenteric plexus of the adult group compared to the young group in both of the segments studied (P < 0.01). The adult group treated with Ginkgo biloba showed a significant increase in neuronal profile area in both the segments studied (P < 0.001). It can be concluded from these results that treatment with the purified Ginkgo biloba (EGb 761) plant extract at a dose of 50 mg/kg body weight has neurotrophic effect on the myenteric plexus in the proximal and distal colon of rats after 120 days of treatment.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

The neuroprotective properties of calorie restriction, the ketogenic diet, and ketone bodies

Both calorie restriction and the ketogenic diet possess broad therapeutic potential in various clinical settings and in various animal models of neurological disease. Following calorie restriction or consumption of a ketogenic diet, there is notable improvement in mitochondrial function, a decrease in the expression of apoptotic and inflammatory mediators and an increase in the activity of neurotrophic factors. However, despite these intriguing observations, it is not yet clear which of these mechanisms account for the observed neuroprotective effects. Furthermore, limited compliance and concern for adverse effects hamper efforts at broader clinical application. Recent research aimed at identifying compounds that can reproduce, at least partially, the neuroprotective effects of the diets with less demanding changes to food intake suggests that ketone bodies might represent an appropriate candidate. Ketone bodies protect neurons against multiple types of neuronal injury and are associated with mitochondrial effects similar to those described during calorie restriction or ketogenic diet treatment. The present review summarizes the neuroprotective effects of calorie restriction, of the ketogenic diet and of ketone bodies, and compares their putative mechanisms of action.

Enteric neurodegeneration in ageing

The objective of this article is to review the clinical presentation and neurobiology of degeneration of the enteric nervous system with emphasis on human data where available. Constipation, incontinence and evacuation disorders are frequently encountered in the ageing population. Healthy lower gastrointestinal function is essential for successful ageing as it is critical to maintaining independence and autonomy to pursue further activity. One clinical expression of enteric neurodegeneration is constipation. However, the aetiology may be multifactorial as disturbances of epithelial, muscle or neural function may all result from neurodegeneration. There is evidence of loss of excitatory (e.g. cholinergic) enteric neurons and interstitial cells of Cajal, whereas inhibitory (including nitrergic) neurons appear unaffected. Understanding neurodegeneration in the enteric nervous system is key to developing treatments to reverse it. Neurotrophins have been shown to accelerate colonic transit and relieve constipation in the medium term; they are also implicated in maintenance programmes in adult enteric neurons through a role in antioxidant defence. However, their effects in ageing colon require further study. There is evidence that 5-HT(2) and 5-HT(4) mechanisms are involved in development, maintenance and survival of enteric neurons. Further research is needed to understand and potentially reverse enteric neurodegeneration.

Enteric neurodegeneration in ageing

The objective of this article is to review the clinical presentation and neurobiology of degeneration of the enteric nervous system with emphasis on human data where available. Constipation, incontinence and evacuation disorders are frequently encountered in the ageing population. Healthy lower gastrointestinal function is essential for successful ageing as it is critical to maintaining independence and autonomy to pursue further activity. One clinical expression of enteric neurodegeneration is constipation. However, the aetiology may be multifactorial as disturbances of epithelial, muscle or neural function may all result from neurodegeneration. There is evidence of loss of excitatory (e.g. cholinergic) enteric neurons and interstitial cells of Cajal, whereas inhibitory (including nitrergic) neurons appear unaffected. Understanding neurodegeneration in the enteric nervous system is key to developing treatments to reverse it. Neurotrophins have been shown to accelerate colonic transit and relieve constipation in the medium term; they are also implicated in maintenance programmes in adult enteric neurons through a role in antioxidant defence. However, their effects in ageing colon require further study. There is evidence that 5-HT(2) and 5-HT(4) mechanisms are involved in development, maintenance and survival of enteric neurons. Further research is needed to understand and potentially reverse enteric neurodegeneration.

Neurotrophic factors in autonomic nervous system plasticity and dysfunction

During development, neurotrophic factors are known to play important roles in regulating the survival of neurons in the autonomic nervous system (ANS) and the formation of their synaptic connectivity with their peripheral targets in the cardiovascular, digestive, and other organ systems. Emerging findings suggest that neurotrophic factors may also affect the functionality of the ANS during adult life and may, in part, mediate the effects of environmental factors such as exercise and dietary energy intake on ANS neurons and target cells. In this article, we describe the evidence that ANS neurons express receptors for multiple neurotrophic factors, and data suggesting that activation of those receptors can modify plasticity in the ANS. Neurotrophic factors that may regulate ANS function include brain-derived neurotrophic factor, nerve growth factor, insulin-like growth factors, and ciliary neurotrophic factor. The possibility that perturbed neurotrophic factor signaling is involved in the pathogenesis of ANS dysfunction in some neurological disorders is considered, together with implications for neurotrophic factor-based therapeutic interventions.

Future horizons in the treatment of enteric neuropathies

Enteric neuropathies comprise a vast and disparate array of congenital and acquired disorders of the enteric nervous system (ENS), reflecting both the complexity of its neuronal composition and the many interactions that modulate its function. Although present therapeutic strategies, largely limited to surgery and the provision of artificial nutrition, have transformed the early survival and life of sufferers, levels of morbidity and mortality remain unacceptably high. This highlights the need to develop new treatments for enteric neuropathies. In the last decade, the tremendous advances in molecular biology and genetics have significantly enhanced our understanding of ENS development and function. Coupled with equivalent progress in the fields of pharmacology and stem-cell biology, this has led to the identification of novel tools and targets for therapy, which either aim to optimise the function of the intrinsic ENS or replace/replenish components of an inadequate or dysfunctional ENS. This article reviews current work on a number of these interventions with a particular focus on the use of ENS stem cells as potential therapeutic tools for enteric neuropathies.

Innervation of the gastrointestinal tract: patterns of aging

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.

Intravenous mononuclear marrow cells reverse neuropathic pain from experimental mononeuropathy

BACKGROUND

Stem cells mediate neuroprotection in a variety of nervous system injury models. In this study, we evaluated a potential role for stem cells in pain therapies. Marrow mononuclear cells containing mixed stem cell populations were used because of wide experience with these cells in experimental and clinical transplantation.

METHODS

After sciatic nerve chronic constriction injury (CCI), adult male Sprague Dawley rats were treated with freshly isolated marrow mononuclear cells (10(7) cells in 0.5 mL IV) from the same strain, or with carrier. The major end points of analysis were thermal and mechanical hypersensitivity using paw withdrawal latency (PWL) to a calibrated heat source and paw withdrawal response to von Frey filaments, evaluated by a blinded investigator.

RESULTS

Marrow transplantation did not prevent pain, and 5 days after CCI all animals were equivalently lesioned. However, 10 days after CCI, rats that received marrow transplants demonstrated paw withdrawal response and PWL patterns indicating recovery from pain, whereas untreated rats continued to have significant pain behavior patterns. For example, PWL values for marrow-treated animals were similar to baseline pre-CCI values (P = 0.54) but significantly shorter latency to withdrawal indicative of continuing pain was seen in untreated rats compared with pre-CCI values (P < 0.001).

CONCLUSIONS

These studies suggest that stem or progenitor cell-mediated therapies may be useful for the treatment of pain after nerve injury, and deserve further study to elucidate the mechanisms of analgesia.

Effects of age on sympathetic innervation of the myenteric plexus and gastrointestinal smooth muscle of Fischer 344 rats

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.