The effects of age on the overall population and on sub-populations of myenteric neurons in the rat small intestine

News from the old: Aging features in the intracardiac, musculoskeletal, and enteric nervous systems

Aging strongly affects the peripheral nervous system (PNS), triggering alterations that vary depending on the innervated tissue. The most frequent alteration in peripheral nerve aging is reduced nerve fiber and glial density which can lead to abnormal nerve functionality. Interestingly, the activation of a destructive phenotype takes place in macrophages across the PNS while a reduced number of neuronal bodies is a unique feature of some enteric ganglia. Single cell/nucleus RNA-sequencing has unveiled a striking complexity of cell populations in the peripheral nerves, and these refined cell type annotations could facilitate a better understanding of PNS aging. While the effects of senescence on individual PNS cell types requires further characterization, the use of senolytics appears to improve general PNS function in models of aging. Here, we review the current understanding of age-related changes of the intracardiac, musculoskeletal, and enteric nervous system sub-sections of the PNS, highlighting their commonalities and differences.

Mechanisms of enteric neuropathy in diverse contexts of gastrointestinal dysfunction

The enteric nervous system (ENS) commands moment-to-moment gut functions through integrative neurocircuitry housed in the gut wall. The functional continuity of ENS networks is disrupted in enteric neuropathies and contributes to major disturbances in normal gut activities including abnormal gut motility, secretions, pain, immune dysregulation, and disrupted signaling along the gut-brain axis. The conditions under which enteric neuropathy occurs are diverse and the mechanistic underpinnings are incompletely understood. The purpose of this brief review is to summarize the current understanding of the cell types involved, the conditions in which neuropathy occurs, and the mechanisms implicated in enteric neuropathy such as oxidative stress, toll like receptor signaling, purines, and pre-programmed cell death.

Biomechanical correlates of sequential drinking behavior in aging

BACKGROUND

The timed water swallow test (TWST) is a test of sequential swallowing where a measured volume is ingested as quickly as comfortably possible. We undertook a study of the biomechanics underpinning the TWST in healthy young and older participants.

METHODS

Thirty healthy volunteers underwent high-resolution impedance manometry (MMS; Unisensor, 2.7 mm diameter, 32 pressure sensors, 16 impedance segments). Participants were asked to drink 150 mL, 0.9% normal saline solution rapidly. Swallowing biomechanics and bolus flow characteristics were assessed using pressure-flow analysis and compared using t test and Fisher's exact test with significance as P < .05.

KEY RESULTS

Older participants (n = 18; 76 ± 11 years) took longer to complete the TWST (21.2 ± 2.5 vs 9.2 ± 1.0 seconds; P < .001) and displayed reduced volume per swallow (16.6 ± 1.3 vs 27.8 ± 2.9 mL; P < .001) compared to younger participants (n = 12; 29 ± 5 years). Two distinctive pharyngeal swallowing patterns were observed: (a) a single rapid sequence of swallows with or without a clearing swallow (Pattern I) or (b) multiple, shorter sequences interrupted and/or interspersed with single swallows or breaks (Pattern II). Some older participants showed biomechanical evidence of upper esophageal sphincter restriction (n = 7) or impaired deglutitive inhibition (n = 7), associated with the more prolonged Pattern II (TWST duration 30.1 ± 1.5 vs Pattern I 11.9 ± 1.5 seconds; P < .001).

CONCLUSIONS AND INFERENCES

Healthy older participants had an increased duration of TWST, suggesting a need to adapt normative values for this population. Rapid sequential swallowing was associated with evidence of UES restriction and impaired deglutitive inhibition in some older participants.

DOES THE RHEUMATOID ARTHRITIS AFFECT THE ENTERIC NERVOUS SYSTEM?

BACKGROUND

Few studies regarding arthritic diseases have been performed to verify the presence of the neurodegeneration. Given the increased oxidative stress and extra-articular effects of the rheumatoid arthritis, the gastrointestinal studies should be further investigated aiming a better understanding of the systemic effects the disease on enteric nervous system.

OBJECTIVE

To determine whether the rheumatoid arthritis affects the nitrergic density and somatic area of the nNOS- immunoreactive (IR) myenteric neurons, as well as the morphometric areas of CGRP and VIP-IR varicosities of the ileum of arthritic rats.

METHODS

Twenty 58-day-old male Holtzmann rats were distributed in two groups: control and arthritic. The arthritic group received a single injection of the Freund's Complete Adjuvant in order to induce arthritis model. The whole-mount preparations of ileum were processed for immunohistochemistry to VIP, CGRP and nNOS. Quantification was used for the nitrergic neurons and morphometric analyses were performed for the three markers.

RESULTS

The arthritic disease induced a reduction 6% in ileal area compared to control group. No significant differences were observed in nitrergic density comparing both groups. However, arthritic group yielded a reduction of the nitrergic neuronal somatic area and VIP-IR varicosity areas. However, an increase of varicosity CGRP-IR areas was also observed.

CONCLUSION

Despite arthritis resulted in no alterations in the number of nitrergic neurons, the retraction of ileal area and reduction of nitrergic somatic and VIP-IR varicosity areas may suggest a negative impact the disease on the ENS.

Chemically induced inflammation and nerve damage affect the distribution of vasoactive intestinal polypeptide-like immunoreactive (VIP-LI) nervous structures in the descending colon of the domestic pig

BACKGROUND

The enteric nervous system (ENS), situated in the wall of the gastrointestinal tract, regulates the majority of intestinal activities in physiological conditions and during pathological processes. Enteric neurons are diversified in terms of active substance expression. One of the most important neuropeptides within the ENS is vasoactive intestinal polypeptide (VIP). It seems to be one among the important inhibitory peptides in addition to neuropeptide Y (NPY), nitric oxide (NO), and adenosine triphosphate (ATP) of the intestinal motility and secretion, however, many issues connected with distribution and roles of VIP in the large intestine, especially during pathological states, still remain unknown.

METHODS

Changes in the VIP-like immunoreactivity of the enteric nervous structures under experimental pathological states, including chemically induced inflammation and nerve damage was examined using the double immunofluorescence technique with commercial antibodies.

KEY RESULTS

Generally, both pathological factors studied caused an increase in the number of VIP-like immunoreactive (VIP-LI) neurons and nerve fibers, but the intensity of fluctuations depended on both the acting factor and the part of the ENS studied.

CONCLUSIONS AND INFERENCES

The obtained results suggest that VIP participates in pathological processes concerning the digestive tract, and its exact functions probably depend on the type of damaging factor acting on the intestine.

Balanced Caloric Restriction Minimizes Changes Caused by Aging on the Colonic Myenteric Plexus

Aging can promote significant morphofunctional changes in the gastrointestinal tract (GIT). Regulation of GIT motility is mainly controlled by the myenteric neurons of the enteric nervous system. Actions that aim at decreasing the aging effects in the GIT include those related to diet, with caloric restriction (CR). The CR is achieved by controlling the amount of food or by manipulating the components of the diet. Therefore, the objective of this study was to evaluate different levels of CR on the plasticity of nicotinamide adenine dinucleotide phosphate- (NADPH-) reactive myenteric neurons in the colon of Wistar rats during the aging process using ultrastructural (transmission electron microscopy) and morphoquantitative analysis. Wistar male rats (Rattus norvegicus) were distributed into 4 groups (n = 10/group): C, 6-month-old animals; SR, 18-month-old animals fed a normal diet; CRI, 18-month-old animals fed a 12% CR diet; CRII, 18-month-old animals fed a 31% CR diet. At 6 months of age, animals were transferred to the laboratory animal facility, where they remained until 18 months of age. Animals of the CRI and CRII groups were submitted to CR for 6 months. In the ultrastructural analysis, a disorganization of the periganglionar matrix with the aging was observed, and this characteristic was not observed in the animals that received hypocaloric diet. It was observed that the restriction of 12.5% and 31% of calories in the diet minimized the increase in density and cell profile of the reactive NADPH neurons, increased with age. This type of diet may be adapted against gastrointestinal disturbances that commonly affect aging individuals.

The Impact of T-2 Toxin on Vasoactive Intestinal Polypeptide-Like Immunoreactive (VIP-LI) Nerve Structures in the Wall of the Porcine Stomach and Duodenum

T-2 toxin is a secondary metabolite of some Fusarium species. It is well-known that this substance can harmfully impact living organisms. Among others, thanks to the ability of crossing the blood–brain barrier, T-2 toxin can affect the central nervous system. Mycotoxins mostly get into the organism through the digestive tract; therefore, first of all they have to break the intestinal barrier, wherein the important component is the enteric nervous system (ENS). However, knowledge about the impact of T-2 toxin on the ENS is rather scant. As a result of the influence of various physiological and pathological agents, ENS can undergo adaptive and reparative processes which manifest as changes in the immunoreactivity of perikaryons for neuronal active substances. So, the aim of the present investigation was to study how low doses of T-2 toxin affect vasoactive intestinal polypeptide-like immunoreactive (VIP-LI) nervous structures in the ENS of the porcine stomach and duodenum. Obtained results have shown that T-2 toxin causes an percentage increase of VIP-LI nerve cells and nerve fibers in every enteric plexus in both fragments of gastrointestinal tract studied. This shows that even low doses of T-2 toxin can have an influence on living organisms.

Heparin-binding EGF-like growth factor promotes neuronal nitric oxide synthase expression and protects the enteric nervous system after necrotizing enterocolitis

BackgroundNeonatal necrotizing enterocolitis (NEC) is associated with alterations of the enteric nervous system (ENS), with loss of neuronal nitric oxide synthase (nNOS)-expressing neurons in the intestine. The aim of this study was to investigate the roles of heparin-binding EGF-like growth factor (HB-EGF) in neural stem cell (NSC) differentiation, nNOS expression, and effects on ENS integrity during experimental NEC.MethodsThe effects of HB-EGF on NSC differentiation and nNOS production were determined using cultured enteric NSCs. Myenteric neuronal subpopulations were examined in HB-EGF knockout mice. Rat pups were exposed to experimental NEC, and the effects of HB-EGF treatment on nNOS production and intestinal neuronal apoptosis were determined.ResultsHB-EGF promotes NSC differentiation, with increased nNOS production in differentiated neurons and glial cells. Moreover, loss of nNOS-expressing neurons in the myenteric plexus and impaired neurite outgrowth were associated with absence of the HB-EGF gene. In addition, administration of HB-EGF preserves nNOS expression in the myenteric plexus and reduces enteric neuronal apoptosis during experimental NEC.ConclusionHB-EGF promotes the differentiation of enteric NSCs into neurons in a nitric oxide (NO)-dependent manner, and protects the ENS from NEC-induced injury, providing new insights into potential therapeutic strategies for the treatment of NEC in the future.

Experimental Cancer Cachexia Changes Neuron Numbers and Peptide Levels in the Intestine: Partial Protective Effects after Dietary Supplementation with L-Glutamine

Gastrointestinal dysmotility frequently occurs in cancer cachexia and may result from damage to enteric innervation caused by oxidative stress, especially due to glutathione depletion. We assessed the effect of dietary supplementation with 20 g/kg l-glutamine (a glutathione precursor) on the intrinsic innervation of the enteric nervous system in healthy and Walker 256 tumor-bearing Wistar rats during the development of experimental cachexia (14 days), in comparison with non-supplemented rats, by using immunohistochemical methods and Western blotting. The total neural population and cholinergic subpopulation densities in the myenteric plexus, as well as the total population and VIPergic subpopulation in the submucosal plexus of the jejunum and ileum, were reduced in cachectic rats, resulting in adaptive morphometric alterations and an increase in vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) expression, suggesting a neuroplastic response. l-glutamine supplementation prevented decrease in myenteric neuronal density in the ileum, morphometric alterations in the neurons and nerve fibers (in both the plexuses of the jejunum and ileum), and the overexpression of VIP and CGRP. Cancer cachexia severely affected the intrinsic innervation of the jejunum and ileum to various degrees and this injury seems to be associated with adaptive neural plasticity. l-glutamine supplementation presented partial protective effects on the enteric innervation against cancer cachexia, possibly by attenuating oxidative stress.

Aqueous Extract of Agaricus blazei Murrill Prevents Age-Related Changes in the Myenteric Plexus of the Jejunum in Rats

This study evaluated the effects of the supplementation with aqueous extract of Agaricus blazei Murrill (ABM) on biometric and blood parameters and quantitative morphology of the myenteric plexus and jejunal wall in aging Wistar rats. The animals were euthanized at 7 (C7), 12 (C12 and CA12), and 23 months of age (C23 and CA23). The CA12 and CA23 groups received a daily dose of ABM extract (26 mg/animal) via gavage, beginning at 7 months of age. A reduction in food intake was observed with aging, with increases in the Lee index, retroperitoneal fat, intestinal length, and levels of total cholesterol and total proteins. Aging led to a reduction of the total wall thickness, mucosa tunic, villus height, crypt depth, and number of goblet cells. In the myenteric plexus, aging quantitatively decreased the population of HuC/D(+) neuronal and S100(+) glial cells, with maintenance of the nNOS(+) nitrergic subpopulation and increase in the cell body area of these populations. Supplementation with the ABM extract preserved the myenteric plexus in old animals, in which no differences were detected in the density and cell body profile of neurons and glial cells in the CA12 and CA23 groups, compared with C7 group. The supplementation with the aqueous extract of ABM efficiently maintained myenteric plexus homeostasis, which positively influenced the physiology and prevented the death of the neurons and glial cells.

Benefits of caloric restriction in the myenteric neuronal plasticity in aging rats

Aging is a biologic process characterized by progressive damage of structures and functions of organic systems. In gastrointestinal tract, it can involve enteric nervous system, which plays an important role in digestion and absorption of nutrients, causing hastening of intestinal transit thus reducing its absorptive function. Caloric restriction has been used in several studies with the intention of delaying deleterious effects of aging. This study aimed to evaluate the effects of caloric restriction on myenteric neurons of ileum by aging in rats. 30 Wistar rats were grouped as follows: GI (animals aged 6 months fed with normal diet), GII (animals aged 18 months fed with normal diet) and GIII (animals aged 18 months subject to 31% of caloric restriction). The rats of the GI group were euthanized at 6 months of age and after experimental period of 12 months animals of the group GII and GIII were euthanized, the ileum of all groups were collected, measured and processed by NADPH-dp and Acetylcholinesterase. Quantitative analysis of neurons revealed that aging promotes the increasing of myenteric neurons NADPH-dp and reduces Acetylcholinesterase neuronal population. However, in the cellular profile area, were not observed significant differences between the groups. The caloric restriction has been efficient and can be used preventively because it minimizes quantitative changes associated with aging on ileum myenteric plexuses.

Aging of the mammalian gastrointestinal tract: a complex organ system

Gastrointestinal disorders are a major cause of morbidity in the elderly population. The gastrointestinal tract is the most complex organ system; its diverse cells perform a range of functions essential to life, not only secretion, digestion, absorption and excretion, but also, very importantly, defence. The gastrointestinal tract acts not only as a barrier to harmful materials and pathogens but also contains the vast number of beneficial bacterial populations that make up the microbiota. Communication between the cells of the gastrointestinal tract and the central nervous and endocrine systems modifies behaviour; the organisms of the microbiota also contribute to this brain-gut-enteric microbiota axis. Age-related physiological changes in the gut are not only common, but also variable, and likely to be influenced by external factors as well as intrinsic aging of the cells involved. The cellular and molecular changes exhibited by the aging gut cells also vary. Aging intestinal smooth muscle cells exhibit a number of changes in the signalling pathways that regulate contraction. There is some evidence for age-associated degeneration of neurons and glia of the enteric nervous system, although enteric neuronal losses are likely not to be nearly as extensive as previously believed. Aging enteric neurons have been shown to exhibit a senescence-associated phenotype. Epithelial stem cells exhibit increased mitochondrial mutation in aging that affects their progeny in the mucosal epithelium. Changes to the microbiota and intestinal immune system during aging are likely to contribute to wider aging of the organism and are increasingly important areas of analysis. How changes of the different cell types of the gut during aging affect the numerous cellular interactions that are essential for normal gut functions will be important areas for future aging research.

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.

Neurochemistry of myenteric plexus neurons of bank vole (Myodes glareolus) ileum

The neurochemistry of enteric neurons differs among species of small laboratory rodents (guinea-pig, mouse, rat). In this study we characterized the phenotype of ileal myenteric plexus (MP) neuronal cells and fibers of the bank vole (Myodes glareolus), a common rodent living in Europe and in Northern Asia which is also employed in prion experimental transmission studies. Six neuronal markers were tested: choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), calbindin (CALB), calcitonin gene-related peptide (CGRP) and substance P (SP), along with HuC/D as a pan-neuronal marker. Neurons expressing ChAT- and nNOS-immunoreactivity (IR) were 36 ± 12% and 24 ± 5%, respectively. Those expressing CGRP-, SP- and CALB-IR were 3 ± 3%, 21 ± 5% and 6 ± 2%, respectively. Therefore, bank vole MPs differ consistently from murine MPs in neurons expressing CGRP-, SP- and CALB-IR. These data may contribute to define the prion susceptibility of neuron cell populations residing within ileal MPs from bank voles, along with their morpho-functional alterations following oral experimental prion challenge.

Expression of neuropeptides and anoctamin 1 in the embryonic and adult zebrafish intestine, revealing neuronal subpopulations and ICC-like cells

This immunohistochemical study in zebrafish aims to extend the neurochemical characterization of enteric neuronal subpopulations and to validate a marker for identification of interstitial cells of Cajal (ICC). The expression of neuropeptides and anoctamin 1 (Ano1), a selective ICC marker in mammals, was analyzed in both embryonic and adult intestine. Neuropeptides were present from 3 days postfertilization (dpf). At 3 dpf, galanin-positive nerve fibers were found in the proximal intestine, while calcitonin gene-related peptide (CGRP)- and substance P-expressing fibers appeared in the distal intestine. At 5 dpf, immunoreactive fibers were present along the entire intestinal length, indicating a well-developed peptidergic innervation at the onset of feeding. In the adult intestine, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), galanin, CGRP and substance P were detected in nerve fibers. Colchicine pretreatment enhanced only VIP and PACAP immunoreactivity. VIP and PACAP were coexpressed in enteric neurons. Colocalization stainings revealed three neuronal subpopulations expressing VIP and PACAP: a nitrergic noncholinergic subpopulation, a serotonergic subpopulation and a subpopulation expressing no other markers. Ano1-immunostaining revealed a 3-dimensional network in the adult intestine containing multipolar cells at the myenteric plexus and bipolar cells interspersed between circular smooth muscle cells. Ano1 immunoreactivity first appeared at 3 dpf, indicative of the onset of proliferation of ICC-like cells. It is shown that the Ano1 antiserum is a selective marker of ICC-like cells in the zebrafish intestine. Finally, it is hypothesized that ICC-like cells mediate the spontaneous regular activity of the embryonic intestine.

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.

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.

Characterization of the myenteric neuronal population and subpopulation of the duodenum of adult wistar rat fed with hypoproteic chow

The effects of severe protein malnutrition (4%) on myenteric neurons of Wistar rat duodenum, in relation to a standard 22%-protein diet for rodents, were assessed in this study. Segments of the duodenum from 10 rats from each nutritional group were submitted to the elaboration of whole mounts - 5 stained with Giemsa to determine the total population of myenteric neurons and the others stained by a histochemical method to detect nervous cells through the NADPH-diaphorase enzyme activity for studying the subpopulation of nitrergic neurons. The area of 100 neurons per animal, totalizing 2,000 neurons, were randomly measured by using the Image Pro-Plus®software. Malnourished rats presented 34.38% lower body weight and 10.60% duodenum length reduction when compared to the control group. Quantitative analysis demonstrated no significant differences between control and malnourished group by using Giemsa; however, as the organ reduction was not followed by an increase inversely proportional to the density of neurons, the condition imposed suggests the loss of neurons from the total population. Nevertheless, through NADPH-d histochemistry, there was a neuronal density increase for the malnourished group. There was no significant difference between the groups for both techniques with respect to the morphometric analysis of the body cell.

Chromatographic analysis of age-related changes in mucosal serotonin transmission in the murine distal ileum

BACKGROUND

In the upper bowel, alterations in motility and absorption of key nutrients have been observed as part of the normal ageing process. Serotonin (5-HT) is a key signalling molecule in the gastrointestinal tract and is known to influence motility, however little is known of how the ageing process alters 5-HT signalling processes in the bowel.

RESULTS

An isocratic chromatographic method was able to detect all 5-HT precursors and metabolites. Using extracellular and intracellular sampling approaches, we were able to monitor all key parameters associated with the transmission process. There was no alteration in the levels of tryptophan and 5-HTP between 3 and 18 month old animals. There was a significant increase in the ratio of 5-HT:5-HTP and an increase in intracellular 5-HT between 3 and 18 month old animals suggesting an increase in 5-HT synthesis. There was also a significant increase in extracellular 5-HT with age, suggesting increased 5-HT release. There was an age-related decrease in the ratio of intracellular 5-HIAA:extracellular 5-HT, whilst the amount of 5-HIAA did not change with age. In the presence of an increase in extracellular 5-HT, the lack of an age-related change in 5-HIAA is suggestive of a decrease in re-uptake via the serotonin transporter (SERT).

CONCLUSIONS

We have used intracellular and extracellular sampling to provide more insight into alterations in the neurotransmission process of 5-HT during normal ageing. We observed elevated 5-HT synthesis and release and a possible decrease in the activity of SERT. Taken together these changes lead to increased 5-HT availability and may alter motility function and could lead to the changes in adsorption observed in the elderly.

Analysis of myosin-V immunoreactive myenteric neurons from arthritic rats

CONTEXT

The inflammatory response itself and the consequent oxidative stress are able to promote neurodegeneration. So, it is possible that enteric nervous system is affected by inflammatory diseases threatening quality of life of patients. However, gastrointestinal symptoms of arthritis are usually attributed to anti-inflammatory drugs rather than neural damage.

OBJECTIVE

To confirm if the general population of myenteric neurons from the ileum and jejunum of rats is affected by arthritis.

METHODS

Twenty Holtzmann rats, 58-day-old male, were used and divided in four groups: control group (C30), arthritic group (Art30), older control group (C60) and older arthritic group (Art60). At 58 days old, the animals in groups Art30 and Art60 received an injection of the complete Freund's adjuvant in order to induce arthritis. The whole-mount preparations of ileum and jejunum were processed for myosin-V immunohistochemistry. Quantitative and morphometric analyses were performed.

RESULTS

Groups Art30 and Art60 presented, respectively, a reduction of 2% and 6% in intestinal area when compared to their control groups. No significant differences were observed in general neuronal density among the four groups (P>0.05). Group C60 presented a reduction of 14.4% and 10.9% in mean neuronal cell body area when compared to group C30 (P<0.05), for the ileum and jejunum, respectively. The other groups had a similar mean neuronal cell body area (P>0.05).

CONCLUSION

Arthritis does not promote quantitative or morphological damages in general myenteric population. However, studies in progress have revealed some significant alterations in myenteric neurons subpopulations (nitrergic and VIP-ergic neurons).

Morphological changes in the enteric nervous system of aging and APP23 transgenic mice

Gastrointestinal motility disorders often pose a debilitating problem, especially in elderly patients. In addition, they are frequently occurring co-morbidities in dementia. Whereas a failing enteric nervous system has already been shown to be involved in gastrointestinal motility disorders and in Parkinson's disease, a relationship with the neurodegenerative process of Alzheimer's disease was not yet shown. Therefore, we sought to document quantitative changes in the distribution of βIII-tubulin (general neuronal marker), Substance P, neuronal nitric oxide synthase (NOS), glial fibrillary acidic protein (GFAP) and S-100 immunoreactivity in addition to a qualitative assessment of the presence of amyloid in the small and large intestines of 6, 12 and 18-month-old wild type and transgenic Thy-1-APP23 mice. Amyloid deposits were seen in the vasculature, the mucosal and muscle layer of both heterozygous and wild type mice. Amyloidβ₁₋₄₂ could not be detected, pointing to a different amyloid composition than that found in senile plaques in the mice's brains. The finding of an increased density of βIII-tubulin-, Substance P- and NOS-IR-nerve fibres in heterozygous mice could not undoubtedly be related to amyloid deposition or to an activation of glial cells. Therefore, the alterations at the level of the enteric nervous system and the deposition of amyloid seem not primarily involved in the pathogenesis of Alzheimer's disease. At most they are secondary related to the neurodegenerative process. Additionally, our data could not show extensive neuronal or glial cell loss associated with aging, in contrast to other reports. Instead an increase in S100-IR was observed in senescent mice.

Enteric nervous system in the small intestine: pathophysiology and clinical implications

The digestive system is endowed with its own, local nervous system, referred to as the enteric nervous system (ENS). Given the varied functions of small intestine, its ENS has developed individualized characteristics relating to motility, secretion, digestion, and inflammation. The ENS regulates the major enteric processes such as immune response, detecting nutrients, motility, microvascular circulation, intestinal barrier function, and epithelial secretion of fluids, ions, and bioactive peptides. Remarkable progress has been made in understanding the signaling pathways in this complex system and how they work. In this article, we focus on recent advances that have led to new insights into small intestinal ENS function and the development of new therapies.

Decrease in nerve fibre density in human sigmoid colon circular muscle occurs with growth but not aging

BACKGROUND

Studies in animals suggest that enteric neurons decrease in density or number with increasing age. Neurons containing nitric oxide (NO), vasoactive intestinal peptide (VIP) and Substance P (SP) have been implicated. In human large intestine, NO-utilizing neurons decrease during childhood or early adulthood but it is not known if the innervation of the muscle changes. This study examined the density of nerve fibres containing these transmitters in sigmoid colon circular muscle from children and adults.

METHODS

Fluorescence immunohistochemistry using antibodies to neuronal NO synthase (nNOS), VIP and SP was performed on sigmoid colon from 18 adults with colorectal cancer, two children with familial adenomatous polyposis, and normal colon from nine children with Hirschsprung's disease. The percentage area of immunoreactive (IR) nerve fibres containing each transmitter in circular muscle was quantified in confocal images.

KEY RESULTS

In the adult sigmoid colon circular muscle, the percentage area of nerve fibres containing nNOS>VIP>SP (6 : 2 : 1). Paediatric groups had significantly higher percentage area of nerve fibres containing nNOS, VIP or SP-IR than adults, with the decrease in nerve fibre density occurring from birth to 30 years. Circular muscle thickness increased between 12 and 30 years. Total nerve fibre area remained constant, while the muscle increased in thickness.

CONCLUSIONS & INFERENCES

In human sigmoid colon circular muscle, there are reductions in nNOS-, VIP- and SP-IR nerve fibre density with growth from newborn to late adolescence but little further change with aging. The reduction in nerve density is due to an increase in circular muscle thickness rather than a loss of nerve fibres.

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.

5-HT4 receptor-mediated neuroprotection and neurogenesis in the enteric nervous system of adult mice

Although the mature enteric nervous system (ENS) has been shown to retain stem cells, enteric neurogenesis has not previously been demonstrated in adults. The relative number of enteric neurons in wild-type (WT) mice and those lacking 5-HT(4) receptors [knock-out (KO)] was found to be similar at birth; however, the abundance of ENS neurons increased during the first 4 months after birth in WT but not KO littermates. Enteric neurons subsequently decreased in both WT and KO but at 12 months were significantly more numerous in WT. We tested the hypothesis that stimulation of the 5-HT(4) receptor promotes enteric neuron survival and/or neurogenesis. In vitro, 5-HT(4) agonists increased enteric neuronal development/survival, decreased apoptosis, and activated CREB (cAMP response element-binding protein). In vivo, in WT but not KO mice, 5-HT(4) agonists induced bromodeoxyuridine incorporation into cells that expressed markers of neurons (HuC/D, doublecortin), neural precursors (Sox10, nestin, Phox2b), or stem cells (Musashi-1). This is the first demonstration of adult enteric neurogenesis; our results suggest that 5-HT(4) receptors are required postnatally for ENS growth and maintenance.

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.

Effects of insulin treatment on HuC/HuD, NADH diaphorase, and nNOS-positive myoenteric neurons of the duodenum of adult rats with acute diabetes

We carried out this investigation with the purpose of verifying whether insulin treatment prevents changes in the density of myoenteric neurons of the duodenum of Wistar rats with streptozotocin short-term diabetes. The animals from the diabetic group (D) lost more weight than the controls (group C), while the insulin treatment (group T) prevented weight loss in three animals and increased visceral fat in all of the animals of this group. Insulin treatment did not prevent the early loss of HuC/HuD myoenteric neurons. The density of nNOS-positive neurons did not change significantly in groups D and T. The density of NADHd-positive neurons in these groups was greater than in group C, indicating that short-term diabetes increases the activity of respiratory chain enzymes.

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.

Quantitative assessment of glial cells in the human and guinea pig enteric nervous system with an anti-Sox8/9/10 antibody

Quantitative changes of enteric glia (EGC) have been implicated in gastrointestinal disorders. To facilitate future studies of EGC in human pathology, we aimed to characterize thoroughly glial markers in the human enteric nervous system (ENS) and to compare EGC in man and guinea pig. Whole-mount preparations of the enteric nerve plexuses from human and guinea pig ileum and colon were labeled with antibodies against S100b, glial fibrillary acidic protein (GFAP), and p75NGFR and the transcription factors Sox8/9/10 and neuronally counterstained. Abundant immunoreactivity (IR) for S100b, GFAP, p75NGFR, and Sox8/9/10 was detected in EGC of all studied regions. Although the cytoplasmatic staining pattern of most markers did not permit glial quantification, the nuclear localization of Sox8/9/10-IR allowed to identify and count all EGC individually. In both man and guinea pig, myenteric ganglia were larger and contained more EGC and neurons than submucous ganglia. Furthermore, there were more EGC in the human than in the guinea pig myenteric plexus (MP), glial density was consistently higher in the human ENS, and the glia index (glia:neuron ratio) ranged from 1.3 to 1.9 and from 5.9 to 7.0 in the human submucous plexus (SMP) and MP, respectively, whereas, in guinea pig, the glia index was 0.8-1.0 in the SMP and 1.7 in the MP. The glia index was the most robust quantitative descriptor within one species. This is a comprehensive set of quantitative EGC measures in man and guinea pig that provides a basis for pathological assessment of glial proliferation and/or degeneration in the diseased gut.

Exercise reduces inhibitory neuroactivity and protects myenteric neurons from age-related neurodegeneration

The practice of regular exercise is indicated to prevent some motility disturbances in the gastrointestinal tract, such as constipation, during aging. The motility alterations are intimately linked with its innervations. The goal of this study is to determine whether a program of exercise (running on the treadmill), during 6 months, has effects in the myenteric neurons (NADH- and NADPH-diaphorase stained neurons) in the colon of rats during aging. Male Wistar rats 6 months (adult) and 12 months (middle-aged) old were divided into 3 different groups: AS (adult sedentary), MS (middle-aged sedentary) and MT (middle-aged submitted to physical activity). The aging did not cause a decline significant (p>0.05) of the number of NADH-diaphorase stained neurons in sedentary rats (AS vs. MS group). In contrast, a decline of 31% was observed to NADPH-diaphorase stained neurons. Thus, animals that underwent physical activity (AS vs. MT group) rescued neurons from degeneration caused by aging (total number, density and profile of neurons did not change with age--NADH-diaphorase method). On the other hand, physical activity augmented the decline of NADPH-diaphorase positive neurons (total number, density and profile of neurons decreased). Collectively, the results show that exercise inhibits age-related decline of myenteric neurons however, exercise augments the decline of neurons with inhibitory activity (nitric oxide) in the colon of the rats.

Quantitative analysis of the neurons from the myenteric plexus in the ileum of rats submitted to severe protein deficiency

The effects of protein malnutrition on the quantitative aspects of the myenteric plexus in the ileum of adult Rattus norvegicus were assessed. Thirty 90-day-old rats were divided into two groups: Control Group (CG, n=15) and Experimental Group (EG, n=15). The CG received 26% protein chow and the EG received 4% protein chow for 90 days. At the end of the experiment, the animals from the CG weighed 369.63±26.33, and the ones from the EG 215.34±56.31. The ileum was submitted to Giemsa, NADH- and NADPH-diaphorase technique in order to evidence nervous cells in the whole-mount preparations. Animals from the EG presented a 41.75% body weight loss in relation to the CG as well as 17.6% length reduction for the ileum-jejunum. Moreover, the organ was 41% lighter for the EG. Giemsa-stained neurons were 17.02% more concentrated in the EG (p>0.05). NADH-diaphorase-stained neurons were 26.6% more concentrated in the EG (p<0.05), while the NADPH-diaphorase were 26.28% more concentrated in this group (p<0.05).

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.

Effect of chronic, extrinsic denervation on functional NANC innervation with vasoactive intestinal polypeptide and substance P in longitudinal muscle of rat jejunum

Intestinal denervation contributes to enteric motor dysfunction after intestinal transplantation [small bowel transplantation (SBT)]. Our aim was to determine long-term effects of extrinsic denervation on functional non-adrenergic, non-cholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P. Contractile activity of jejunal longitudinal muscle from six age-matched, naïve control rats (NC) and eight rats 1 year after syngeneic SBT were studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently in both groups, greater in NC than in SBT. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor l-N(G)-nitro arginine prevented inhibition by exogenous VIP and electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than in SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and increased the EFS-induced inhibitory response. Immunohistofluorescence showed staining for tyrosine hydroxylase in the jejunoileum 1 year after SBT suggesting sympathetic reinnervation. In rat jejunal longitudinal muscle after chronic denervation, response to exogenous VIP and substance P is decreased, while endogenous release of both neurotransmitters is preserved. These alterations in excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

Alterations of the number and the profile of myenteric neurons of Wistar rats promoted by age

The objective of this study was to analyze the morpho quantitative behaviour of duodenum myenteric neurons of Wistar rats (Rattus norvegicus), aged 21, 60, 90, 210, 345 and 428 days, using wholemount preparations of the muscular tunica obtained by dissecting the intestinal tunica for neuronal revealing, through the Giemsa non-histochemical and Myosin-V immunohistochemical techniques. The neurons were quantified in 80 microscopic fields (14.832 mm(2)) for each animal and neuronal cell body morphometry was carried out on 100 neurons/rat. Duodenal samples were submitted to histological routine processing, stained by hematoxylin-eosin method in order to perform morphometric analysis of the muscular tunica. An increase in the length of the small intestine was observed up to the age of 60 days, which was maintained up to 210 days, with a reduction in this parameter from 345 days. Muscular tunica thickness was maintained independently of the animal age. During the course of the study, there was a reduction in the mean neuron population in both techniques used. However, in all of the ages evaluated, the use of the Myosin-V technique lead to a reduced mean number of neurons compared to the Giemsa method. The cellular profile morphometry revealed, with both techniques, the predominance of smaller neurons in young animals, and bigger neurons in animals from higher age groups. It was concluded that advanced age is a determinant factor in the number reduction of myenteric neurons, with maintenance of the intrinsic intestinal innervation by the remaining neurons and that the use of the Giemsa non-histochemical technique showed itself more adequate to determine the total neuronal population.

Long-term effects of extrinsic denervation on VIP and substance P innervation in circular muscle of rat jejunum

Intestinal denervation contributes to enteric motor dysfunction after small bowel transplantation (SBT). Our aim was to determine long-term effects of extrinsic denervation on function of nonadrenergic, noncholinergic innervation with substance P and vasoactive intestinal polypeptide (VIP). Contractile activity of jejunal circular muscle strips from six age-matched, naive control rats (NC) and eight rats 1 year after syngeneic SBT was studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently to a comparable degree in both groups. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor L-NG-nitro-arginine did not affect VIP-induced inhibition but increased contractile activity during electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and decreased the excitatory EFS response. Immunohistofluorescence showed tyrosine hydroxylase staining after SBT indicating sympathetic reinnervation. In jejunal circular muscle after chronic denervation, response to exogenous substance P, but not VIP, is decreased, whereas endogenous release of both neurotransmitters is preserved. Alterations in balance of excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

Evaluation of the effect of Ginkgo biloba extract (EGb 761) on the myenteric plexus of the small intestine of Wistar rats

BACKGROUND

The aging process causes a reduction in the myenteric neuronal population, related to oxidative stress, resulting in malfunctioning of the digestive tract. The purpose of this study was to evaluate the action of Ginkgo biloba extract (EGb 761), an important antioxidant drug, on the myenteric plexus of the jejunum and ileum of rats after treatment for 120 days.

METHODS

Fragments of the jejunum and ileum were collected from three groups of rats: a 90-day-old group (group Y), a 210-day-old group (group A), and a 210-day-old group treated daily with the extract EGb 761 (50 mg/kg body weight) (group TA). The analysis was carried out by using the myosin-V immunohistochemical technique. Neuronal densities were estimated, and a study of the neuronal profile area of 500 neurons from each group was carried out.

RESULTS

In the jejunum, there was a significant neuronal population reduction of 17% only in group A compared with group Y. In the ileum, there was a significant neuronal reduction of 36% in group A compared with group Y, and a significant reduction in group TA of 20%. The difference in the reduction between groups A and TA in the ileum was also significant. In the jejunum, only group A showed a significant increase in neuronal profile area, but in the ileum, there was a significant increase in both groups A and TA.

CONCLUSIONS

A daily dose of 50 mg/kg body weight of Ginkgo biloba extract has a significant neuroprotector effect on the myenteric plexus of the ileum during the aging process in rats.

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.

Apoptotic phenomena are not a major cause of enteric neuronal loss in constipated patients with dementia

Chronic constipation is a frequent symptom in patients with dementia, especially in those institutionalized. However, few data are available on the neuropathological aspects of the colon in such patients. We investigated the enteric neuropathology of the colon in two patients with longstanding dementia and intractable constipation, requiring surgery to alleviate symptoms. The results were compared to those obtained in 10 controls. No abnormalities were found at conventional histological examination, except for the presence of melanosis coli. Immunohistochemical evaluation revealed no important difference between patients and controls, except for a decreased number of enteric neurons in patients. However, this neuronal decrease was not associated to apoptotic phenomena, as observed in patients with severe idiopathic constipation. We concluded that in severely constipated patients with dementia the neuropathological abnormalities might be reconducted to a physiological neuronal decrease as a result of aging, and that the pathophysiological aspects of constipation in these subjects differ from those found in idiopathic constipation.

Age-related changes in urinary bladder intramural neurons

A quantitative morphometric evaluation of the intramural plexus of the urinary bladder of adult and aged guinea-pigs was performed by histological analysis, scanning electron microscopy, and hystochemical methods, such as NADH-diaphorase and acetylcholinesterase (AChE). The round or oval shaped intramural neurons were revealed among the bundles of the smooth detrusor muscle in clusters containing a variable number of cells in the groups. In both adult control and aged animals, the ganglia were enveloped by a ganglionar capsule of connective tissue mainly composed of type I collagen fibers. The number of neurons NADH-diaphorase positives estimated in the intramural plexus was 1433+/-187.71 and 1107+/-120.67 in the adult control and aged groups, respectively. The perikaryon areas of the NADH-diaphorase neurons reactives ranged from 216.40 to 1809.30 microm(2) in adult control group and from 198.20 to 2096.25 microm(2) in aged group. The nuclear area showed an increase in aged animals. The number of AChE-positive neurons estimated in the intramural plexus was 3294.67+/-415 microm(2) in the adult control group and 1960.33+/-526 microm(2) in the aged group, showing a significant decrease in the latter group. This age-related morphological change in intramural neurons may contribute to changes in urinary bladder activities in the elderly.

The serotonin signaling system: from basic understanding to drug development for functional GI disorders

Serotonin is an important gastrointestinal signaling molecule. It is a paracrine messenger utilized by enterochromaffin (EC) cells, which function as sensory transducers. Serotonin activates intrinsic and extrinsic primary afferent neurons to, respectively, initiate peristaltic and secretory reflexes and to transmit information to the central nervous system. Serotonin is also a neurotransmitter utilized by a system of long descending myenteric interneurons. Serotonin is synthesized through the actions of 2 different tryptophan hydroxylases, TpH1 and TpH2, which are found, respectively, in EC cells and neurons. Serotonin is inactivated by the serotonin reuptake transporter (SERT)-mediated uptake into enterocytes or neurons. The presence of many serotonin receptor subtypes enables selective drugs to be designed to therapeutically modulate gastrointestinal motility, secretion, and sensation. Current examples include tegaserod, a 5-HT(4) partial agonist, which has been approved for treatment of irritable bowel syndrome (IBS) with constipation in women and for chronic constipation in men and women. The 5-HT(3) antagonists, granisetron and ondansetron, are useful in combating the nausea associated with cancer chemotherapy, and alosetron is employed in the treatment of IBS with diarrhea. Serotonergic signaling abnormalities have also been putatively implicated in the pathogenesis of functional bowel diseases. Other compounds, for which efficacy has not been rigorously established, but which may have value, include tricyclic antidepressants and serotonin selective reuptake inhibitors to combat IBS, and 5-HT(1) agonists, which enhance gastric accommodation, to treat functional dyspepsia. The initial success encountered with serotonergic agents holds promise for newer and more potent insights and therapies of brain-gut disorders.

Effects of the neonatal treatment with monosodium glutamate on myenteric neurons and the intestine wall in the ileum of rats

BACKGROUND

The neonatal administration of a 4 mg/g dose of monosodium glutamate (MSG) to rodents leads to neuronal death in the hypothalamus arcuate nucleus, which leads in turn to obesity in the adult animal. However, few studies have investigated the effects on the enteric nervous system. This study evaluated the effects of the neonatal administration of MSG on the frequency and morphometry of the myenteric as well as the ileum wall morphometry of adult Wistar male rats.

METHODS

Whole-mount preparations of ileum samples were stained by the Giemsa or NADH-diaphorase histochemical methods. For histological processing, hematoxylin and eosin staining was used.

RESULTS

The treatment with MSG led to obesity, as shown by the higher values for Lee's index and the weights of periepididimal and retroperitoneal adipose tissues. The Giemsa staining revealed a significantly larger neuronal density in the MSG group, which is explained by smaller physical growth and a reduction in the weight of the small intestine. The mean neuronal profile did not change between groups. The NADH-diaphorase-positive neuronal subpopulation kept its neuronal density but its average cellular profile was reduced in the MSG group. A morphometric analysis of the intestinal wall, muscular layer, villi, and intestinal crypts showed that their characteristics did not change.

CONCLUSIONS

The treatment with MSG did not cause alteration of the total myenteric population of the ileum, but it influenced the NADH-diaphorase-positive subpopulation. From the maintenance of the morphometric parameters of the ileum intestinal wall, we inferred that intestinal function was preserved in obese animals.

Distribution of adrenergic receptors in the enteric nervous system of the guinea pig, mouse, and rat

Adrenergic receptors in the enteric nervous system (ENS) are important in control of the gastrointestinal tract. Here we describe the distribution of adrenergic receptors in the ENS of the ileum and colon of the guinea pig, rat, and mouse by using single- and double-labelling immunohistochemistry. In the myenteric plexus (MP) of the rat and mouse, alpha2a-adrenergic receptors (alpha2a-AR) were widely distributed on neurons and enteric glial cells. alpha2a-AR mainly colocalized with calretinin in the MP, whereas submucosal alpha2a-AR neurons colocalized with vasoactive intestinal polypeptide (VIP), neuropeptide Y, and calretinin in both species. In the guinea pig ileum, we observed widespread alpha2a-AR immunoreactivity on nerve fibers in the MP and on VIP neurons in the submucosal plexus (SMP). We observed extensive beta1-adrenergic receptor (beta1-AR) expression on neurons and nerve fibers in both the MP and the SMP of all species. Similarly, the beta2-adrenergic receptor (beta2-AR) was expressed on neurons and nerve fibers in the SMP of all species, as well as in the MP of the mouse. In the MP, beta1- and beta2-AR immunoreactivity was localized to several neuronal populations, including calretinin and nitrergic neurons. In the SMP of the guinea pig, beta1- and beta2-AR mainly colocalized with VIP, whereas, in the rat and mouse, beta1- and beta2-AR were distributed among the VIP and calretinin populations. Adrenergic receptors were widely localized on specific neuronal populations in all species studied. The role of glial alpha2a-AR is unknown. These results suggest that sympathetic innervation of the ENS is directed toward both enteric neurons and enteric glia.