Distribution of growth-associated protein, B-50 (GAP-43) in the mammalian enteric nervous system

Noradrenergic and Cholinergic Reinnervation of Islet Grafts in Diabetic Rats

Grafted islets become denervated due to the islet transplantation procedure. The aim of the present study was 1) to examine whether islet grafts in the liver, the spleen, and under the kidney capsule in rats become reinnervated following the transplantation and experimental procedures used in our laboratory, 2) whether there is any difference in reinnervation at these different sites, and 3) how these results relate to previous physiological experiments. Isogeneic isolated islets were transplanted into diabetic Albino Oxford rats, resulting in normoglycaemia. After at least 5 wk, graft-receiving organs were removed and several antibodies were employed to detect insulin, neuron-specific proteins, and cholinergic and noradrenergic nerve fibers. Islets in all three receiving organs contained viable insulin-positive B-cells. Neuron-specific enolase (NSE) as well as the growth-associated protein B-50 was observed at all sites. The cholinergic marker choline acetyltransferase (ChAT) was localized in islets grafts at all sites, but with the lowest density in the spleen. Staining for the noradrenergic markers tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH) was observed in islet grafts at all sites with the lowest density in grafts under the kidney capsule. All these neurochemical substances were most frequently observed in fibers associated with blood vessels, which may be the route along which nerves grow into the graft. It can be concluded that 1) islet grafts in the liver, in the spleen and under the kidney capsule become reinnervated; 2) the innervation pattern of the islet grafts differs only slightly from that in the control pancreatic islets; and 3) in combination with our previously physiological data, we can conclude that these nerve fibers are, at least partly, functionally active.

Enteric Neuronal Damage, Intramuscular Denervation and Smooth Muscle Phenotype Changes as Mechanisms of Chagasic Megacolon: Evidence from a Long-Term Murine Model of Trypanosoma cruzi Infection

We developed a novel murine model of long-term infection with Trypanosoma cruzi with the aim to elucidate the pathogenesis of megacolon and the associated adaptive and neuromuscular intestinal disorders. Our intent was to produce a chronic stage of the disease since the early treatment should avoid 100% mortality of untreated animals at acute phase. Treatment allowed animals to be kept infected and alive in order to develop the chronic phase of infection with low parasitism as in human disease. A group of Swiss mice was infected with the Y strain of T. cruzi. At the 11th day after infection, a sub-group was euthanized (acute-phase group) and another sub-group was treated with benznidazole and euthanized 15 months after infection (chronic-phase group). Whole colon samples were harvested and used for studying the histopathology of the intestinal smooth muscle and the plasticity of the enteric nerves. In the acute phase, all animals presented inflammatory lesions associated with intense and diffuse parasitism of the muscular and submucosa layers, which were enlarged when compared with the controls. The occurrence of intense degenerative inflammatory changes and increased reticular fibers suggests inflammatory-induced necrosis of muscle cells. In the chronic phase, parasitism was insignificant; however, the architecture of Aüerbach plexuses was focally affected in the inflamed areas, and a significant decrease in the number of neurons and in the density of intramuscular nerve bundles was detected. Other changes observed included increased thickness of the colon wall, diffuse muscle cell hypertrophy, and increased collagen deposition, indicating early fibrosis in the damaged areas. Mast cell count significantly increased in the muscular layers. We propose a model for studying the long-term (15 months) pathogenesis of Chagasic megacolon in mice that mimics the human disease, which persists for several years and has not been fully elucidated. We hypothesize that the long-term inflammatory process mediates neuronal damage and intramuscular and intramural denervation, leading to phenotypic changes in smooth muscle cells associated with fibrosis. These long-term structural changes may represent the basic mechanism for the formation of the Chagasic megacolon.

The gut microbiome restores intrinsic and extrinsic nerve function in germ-free mice accompanied by changes in calbindin

BACKGROUND

The microbiome is essential for normal myenteric intrinsic primary afferent neuron (IPAN) excitability. These neurons control gut motility and modulate gut-brain signaling by exciting extrinsic afferent fibers innervating the enteric nervous system via an IPAN to extrinsic fiber sensory synapse. We investigated effects of germ-free (GF) status and conventionalization on extrinsic sensory fiber discharge in the mesenteric nerve bundle and IPAN electrophysiology, and compared these findings with those from specific pathogen-free (SPF) mice. As we have previously shown that the IPAN calcium-dependent slow afterhyperpolarization (sAHP) is enhanced in GF mice, we also examined the expression of the calcium-binding protein calbindin in these neurons in these different animal groups.

METHODS

IPAN sAHP and mesenteric nerve multiunit discharge were recorded using ex vivo jejunal gut segments from SPF, GF, or conventionalized (CONV) mice. IPANs were excited by adding 5 μM TRAM-34 to the serosal superfusate. We probed for calbindin expression using immunohistochemical techniques.

KEY RESULTS

SPF mice had a 21% increase in mesenteric nerve multiunit firing rate and CONV mice a 41% increase when IPANs were excited by TRAM-34. For GF mice, this increase was barely detectable (2%). TRAM-34 changed sAHP area under the curve by -77 for SPF, +3 for GF, or -54% for CONV animals. Calbindin-immunopositive neurons per myenteric ganglion were 36% in SPF, 24% in GF, and 52% in CONV animals.

CONCLUSIONS & INFERENCES

The intact microbiome is essential for normal intrinsic and extrinsic nerve function and gut-brain signaling.

Depressed neuronal growth associated protein (GAP)-43 expression in the small intestines of mice experimentally infected with Neodiplostomum seoulense

Neodiplostomum seoulense (Digenea: Neodiplostomidae) is an intestinal trematode that can cause severe mucosal pathology in the small intestines of mice and even mortality of the infected mice within 28 days after infection. We observed neuronal growth associated protein-43 (GAP-43) expression in the myenteric plexus of the small intestinal wall of N. seoulense-infected mice until day 35 post-infection (PI). BALB/c mice were infected with 200 or 500 N. seoulense metacercariae isolated from naturally infected snakes and were killed every 7 days for immunohistochemical demonstration of GAP-43 in the small intestines. N. seoulense-infected mice showed remarkable dilatation of intestinal loops compared with control mice through days 7-28 PI. Conversely, GAP-43 expression in the mucosal myenteric plexus was markedly (P<0.05) reduced in the small intestines of N. seoulense-infected mice during days 7-28 PI and was slightly normalized at day 35 PI. From this study, it is evident that neuronal damage occurs in the intestinal mucosa of N. seoulense-infected mice. However, the correlation between intestinal pathology, including the loop dilatation, and depressed GAP-43 expression remains to be elucidated.

Current insights in to the pathophysiology of Irritable Bowel Syndrome

Irritable Bowel Syndrome (IBS) represents a functional disorder of gastrointestinal tract without the presence of an anatomic defect, in which abdominal pain is relieved with defecation and is associated with altered bowel habits.

IBS includes a wide range of symptoms while its pathophysiology is very complicated. Recent studies indicate that the most important mechanisms include visceral sensitivity, abnormal gut motility and autonomous nervous system dysfunction. The interactions between these three mechanisms make bowel's function susceptible to many exogenous and endogenous factors like gastrointestinal flora, feeding and psychosocial factors. Recent data indicate that according to the above mechanisms, the influence of genetic factors and polymorphisms of human DNA in the development of IBS is equally important.

Subthalamic nucleotomy alleviates parkinsonism in the 1 -methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP)-exposed primate

Research into the neural mechanisms underlying the symptoms of parkinsonism utilizing the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-exposed primate model have shown that the subthalamic nucleus (STN) occupies a central role. As a logical development of this theory, we have studied the effects of thermocoagulative lesions of the STN in the primate model. Such lesions can cause remarkable symptom reversal in the experimental primate model.

Distribution and function of monoacylglycerol lipase in the gastrointestinal tract

The endogenous cannabinoid system plays an important role in the regulation of gastrointestinal function in health and disease. Endocannabinoid levels are regulated by catabolic enzymes. Here, we describe the presence and localization of monoacylglycerol lipase (MGL), the major enzyme responsible for the degradation of 2-arachidonoylglycerol. We used molecular, biochemical, immunohistochemical, and functional assays to characterize the distribution and activity of MGL. MGL mRNA was present in rat ileum throughout the wall of the gut. MGL protein was distributed in the muscle and mucosal layers of the ileum and in the duodenum, proximal colon, and distal colon. We observed MGL expression in nerve cell bodies and nerve fibers of the enteric nervous system. There was extensive colocalization of MGL with PGP 9.5 and calretinin-immunoreactive neurons, but not with nitric oxide synthase. MGL was also present in the epithelium and was highly expressed in the small intestine. Enzyme activity levels were highest in the duodenum and decreased along the gut with lowest levels in the distal colon. We observed both soluble and membrane-associated enzyme activities. The MGL inhibitor URB602 significantly inhibited whole gut transit in mice, an action that was abolished in cannabinoid 1 receptor-deficient mice. In conclusion, MGL is localized in the enteric nervous system where endocannabinoids regulate intestinal motility. MGL is highly expressed in the epithelium, where this enzyme may have digestive or other functions yet to be determined.

Cannabinoid CB2 receptors in the enteric nervous system modulate gastrointestinal contractility in lipopolysaccharide-treated rats

Enhanced intestinal transit due to lipopolysaccharide (LPS) is reversed by cannabinoid (CB)2 receptor agonists in vivo, but the site and mechanism of action are unknown. We have tested the hypothesis that CB2 receptors are expressed in the enteric nervous system and are activated in pathophysiological conditions. Tissues from either saline- or LPS-treated (2 h; 65 microg/kg ip) rats were processed for RT-PCR, Western blotting, and immunohistochemistry or were mounted in organ baths where electrical field stimulation was applied in the presence or absence of CB receptor agonists. Whereas the CB2 receptor agonist JWH133 did not affect the electrically evoked twitch response of the ileum under basal conditions, in the LPS-treated tissues JWH133 was able to reduce the enhanced contractile response in a concentration-dependent manner. Rat ileum expressed CB2 receptor mRNA and protein under physiological conditions, and this expression was not affected by LPS treatment. In the myenteric plexus, CB2 receptors were expressed on the majority of neurons, although not on those expressing nitric oxide synthase. LPS did not alter the distribution of CB2 receptor expression in the myenteric plexus. In vivo LPS treatment significantly increased Fos expression in both enteric glia and neurons. This enhanced expression was significantly attenuated by JWH133, whose action was reversed by the CB2 receptor antagonist AM630. Taking these facts together, we conclude that activation of CB2 receptors in the enteric nervous system of the gastrointestinal tract dampens endotoxin-induced enhanced intestinal contractility.

Role of enteric glia in intestinal physiology: effects of the gliotoxin fluorocitrate on motor and secretory function

The role of enteric glia in gastrointestinal physiology remains largely unexplored. We examined the actions of the gliotoxin fluorocitrate (FC) on intestinal motility, secretion, and inflammation after assessing its efficacy and specificity in vitro. FC (100 microM) caused a significant decrease in the phosphorylation of the glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diaz-4-yl)amino]-2-deoxyglucose in enteric glial cultures and a reduction in glial uptake of the fluorescent dipeptide Ala-Lys-7-amino-4-methylcoumarin-3-acetic acid in both the ileum and colon. Dipeptide uptake by resident murine macrophages or guinea pig myenteric neurons was unaffected by FC. Incubation of isolated guinea pig ileal segments with FC caused a specific and significant increase in glial expression of the phosphorylated form of ERK-1/2. Disruption of enteric glial function with FC in mice reduced small intestinal motility in vitro, including a significant decrease in basal tone and the amplitude of contractility in response to electrical field stimulation. Mice treated with 10 or 20 micromol/kg FC twice daily for 7 days demonstrated a concentration-dependent decrease in small intestinal transit. In contrast, no changes in colonic transit or ion transport in vitro were observed. There were no changes in glial or neuronal morphology, any signs of inflammation in the FC-treated mice, or any change in the number of myenteric nitric oxide synthase-expressing neurons. We conclude that FC treatment causes enteric glial dysfunction, without causing intestinal inflammation. Our data suggest that enteric glia are involved in the modulation of enteric neural circuits underlying the regulation of intestinal motility.

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.

Effects of gastrointestinal inflammation on enteroendocrine cells and enteric neural reflex circuits

Inflammation of the gastrointestinal (GI) tract has pronounced effects on GI function. Many of the functions of the GI tract are subject to neural regulation by the enteric nervous system (ENS) and its extrinsic connections. Therefore, it is possible that inflammatory effects on the ENS contribute to altered function during GI inflammation. The reflex circuitry of the ENS is comprised of sensory transducers in the mucosa (enteroendocrine cells), afferent neurons, interneurons and motor neurons. This review focuses on recent data that describe inflammation-induced changes to the ENS and mucosal enteroendocrine cells. Studies of tissues from patients with inflammatory bowel disease (IBD) and from animal models of IBD have demonstrated marked changes in mucosal enteroendocrine cell signaling. These changes, which have been studied most intensely in 5-HT-containing enterochromaffin cells, involve changes in the number of cells, their signaling molecule content or their means of signal termination. Morphological evidence of enteric neuropathy during inflammation has been obtained from human samples and animal models of IBD. The neuropathy can reduce the number of enteric neurons in the inflamed region and is often accompanied by a change in the neurochemical coding of enteric neurons, both in the inflamed region and at distant sites. Electrophysiological recordings have been made from enteric neurons in inflamed regions of the colon of animal models of IBD. These studies have consistently found that inflammation increases excitability of intrinsic primary afferent neurons and alters synaptic transmission to interneurons and motor neurons. These data set the stage for a comprehensive examination of the role of altered neuronal and enteroendocrine cell signaling in symptom generation during GI inflammation.

Vagal influences over mast cells

The established microanatomical association of rat intestinal mucosal mast cells (IMMC) and mucosal nerves raises the possibility that there is crosstalk between mast cells and extrinsic nerves that connect to the CNS. The idea of mast cell-CNS interactions is supported by the demonstration that rat mast cell protease II (RMCPII), found predominantly in IMMC, can be conditionally released by pairing an audio-visual cue with antigen challenge. That the vagus nerve is involved in the IMMC-nerve axis was further demonstrated in a series of our studies showing that: (a) vagal afferents penetrate the small intestinal mucosa and contact IMMC; (b) vagotomy causes a reduction in IMMC density, suggesting a trophic relationship (typical of nerve-target interactions); and (c) stimulation of the cervical vagus causes an increase in histamine and serotonin in IMMC. To further investigate the IMMC-nerve axis in a model of post-inflammatory bowel disorders, infection with Nippostrongylus brasiliensis (Nb) was used to demonstrate an increase in mast cell numbers in the intestinal mucosa and mucosal nerve remodelling with hyperinnervation. Administration of Nb antigen resulted in dramatic increases in mesenteric afferent nerve firing in Nb infected rats, that was absent in sham animals. Moreover, challenge of post-Nb rats with 2-methyl-5HT caused increased mesenteric afferent firing, indicating that vagal afferent innervation remains intact in the post-infection state. These data suggest a functional connection between mast cells and extrinsic afferent nerves. Nb infection provides a useful model of altered communication between IMMCs, peripheral nerves and the CNS, as may occur in post-inflammatory disease states. Since a close anatomical relationship has also previously been demonstrated between nerves and IMMC in humans, further understanding the mast cell-nerve axis may be of critical importance in the development of treatments for various human disease states, including functional bowel disorders.

Plasticity of the enteric nervous system during intestinal inflammation

Inflammation of the bowel causes structural and functional changes to the enteric nervous system (ENS). While morphological alterations to the ENS are evident in some inflammatory conditions, it appears that relatively subtle modifications to the neurophysiology of enteric microcircuits may play a role in gastrointestinal (GI) dysfunction. These include changes to the excitability and synaptic properties of enteric neurones. The response of the ENS to inflammation varies according to the site and type of inflammation, with the functional consequences depending on the nature of the inflammatory stimulus. It has become clear that inflammation at one site can produce changes that occur at remotes sites in the GI tract. Immunohistochemical data from patients with inflammatory bowel disease (IBD) and animal models indicate that inflammation alters the neurochemical content of some functional classes of enteric neurones. A growing body of evidence supports an active role for enteric glia in neuronal and neuroimmune communication in the GI tract, particularly during inflammation. In conclusion, plasticity of the ENS is a feature of intestinal inflammation. Elucidation of the mechanisms whereby inflammation alters enteric neural control of GI functions may lead to novel treatments for IBD.

Origin of symptoms in diverticular disease

BACKGROUND

A significant number of patients with colonic diverticula experience unexplained, recurrent, short-lived but often debilitating abdominal pain and alteration in bowel habit. Such patients account for many medical consultations every year but, as our understanding of the cause of their symptoms remains imperfect, treatment options are limited. This article reviews the possible mechanisms that may be responsible for the symptoms of diverticular disease.

METHODS

Medline and Science Citation Index searches were performed to locate English language articles relating to colonic diverticula and symptoms published between January 1966 and July 2002. Manual cross-referencing was also performed and some historical articles were included.

RESULTS AND CONCLUSION

Several theories now exist about the mechanisms underlying the symptoms of diverticular disease. Initial studies suggested that they may be due to alterations in the intracolonic pressure, extrapolating earlier thoughts on the likely pathogenesis of diverticula. It seems more likely, however, that several inter-related processes, such as muscular dysfunction, visceral hypersensitivity and inflammation, are involved in symptom generation.

Regeneration of periodontal Ruffini endings in adults and neonates

We reviewed the regeneration of periodontal Ruffini endings, primary mechanoreceptors in the periodontal ligament, following injury to the inferior alveolar nerve (IAN) in adult and neonatal rats. Morphologically, mature Ruffini endings are characterized by an extensive arborization of axonal terminals and association with specialized Schwann cells, called lamellar or terminal Schwann cells. Following injury to IAN in the adult, the periodontal Ruffini endings of the rat lower incisor ligament regenerate more rapidly than Ruffini endings in other tissues. During regeneration, terminal Schwann cells migrate into regions where they are never found under normal conditions. The development of periodontal Ruffini endings of the rat incisor is closely associated with the eruption of the teeth; the morphology and distribution of the terminal Schwann cells became almost identical to those in adults during postnatal days 15-18 (PN 15-18d) when the first molars appear in the oral cavity, while the axonal elements showed extensive ramification around PN 28d when the functional occlusion commences. When the IAN was injured in neonates, the regeneration of periodontal Ruffini endings was delayed compared with the adults. The migration of terminal Schwann cells is also observed following IAN injury, after which the distribution of terminal Schwann cells became almost identical to that of the adults, i.e., PN 14d. Since the interaction between axon and Schwann cell is important during regeneration and development, further studies are required to elucidate its molecular mechanism during the regeneration as well as the development of the periodontal Ruffini endings.

Expression of neuropeptides and growth-associated protein 43 (GAP-43) in cutaneous and mucosal nerve structures of the adult rat lower lip after mental nerve section

The reinnervation of the adult rat lower lip has been investigated after unilateral section of the mental nerve. Rats were sacrificed at 4, 7, 9, 14, 30, and 90 days after the operation. A further group of animals with section of the mental nerve and block of the alveolar nerve regeneration, was sacrificed at 14 days. Specimens were processed for immunocytochemistry with antibodies against PGP 9.5, GAP-43 or neuropeptides (CGRP, SP and VIP). Four days after nerve section, axonal degeneration seems evident in the mental nerve branches and inside skin and mucosa. GAP-43 immunoreactivity is intense in the mental nerve 7 days after nerve section and it reaches its maximal expression and distribution in peripheral nerve fibres at 14 days. At 30 days, the decline in its expression is associated with the increase of PGP9.5-, SP-, and CGRP immunopositivity. VIP is observed only in perivascular fibres at all times observed. Present results suggest that, after sensory denervation of the rat lip, nerve fibres in skin and mucosa remain at lower density than normal. The different time courses in the expression of neuropeptides and GAP-43 suggest a possible early involvement of GAP-43 in peripheral nerve regeneration.

On the Distribution of GAP-43 and its Relation to Serotonin in Adult Monkey and Cat Spinal Cord and Lower Brainstem

By use of a monoclonal antibody, the distribution of growth-associated protein (GAP)-43-like immunoreactivity (LI) has been studied in the spinal cord of adult grey monkeys (Macaca fascicularis) and adult cats by use of immunofluorescence and peroxidase - antiperoxidase techniques. The brainstem was also studied with in situ hybridization histochemistry. In both monkeys and cats, a dense innervation of GAP-43-immunoreactive (IR) fibres was seen in close apposition to large cell bodies and their processes in the motor nucleus of the ventral horn. Double-labelling experiments revealed a high degree of coexistence between GAP-43- and 5-hydroxytryptamine (5-HT, serotonin)-LI in the monkey motor nucleus, while in the cat no such colocalization could be verified. At the electron microscopic level, GAP-43 labelling was seen as a coating of vesicles and axolemma inside the terminals. In both monkey and cat, cell bodies expressing mRNA encoding GAP-43 were demonstrated in the medullary midline raphe nuclei. A similar location was also encountered for mRNA for aromatic l-amino acid decarboxylase, an enzyme found in both catecholamine- and serotonin-containing neurons. The present results suggest that GAP-43 is present in the 5-HT bulbospinal pathway of the monkey. In the cat, GAP-43 mRNA-expressing cell bodies were demonstrated in areas where descending 5-HT neurons are located, but no convincing colocalization of 5-HT- and GAP-43-LI was found at spinal cord levels, despite the existence of extensive fibre networks containing either of the two compounds. Possible explanations for this species discrepancy are discussed. The function of GAP-43 in nerve terminals impinging on the motoneurons is unknown. However, it may play a role in transmitter release and/or plasticity, since such roles have been proposed for this protein in other systems.

Growth-associated protein-43 immunohistochemical and ultrastructural changes in jaw muscle spindles of the rat following loss of occlusion

The effects of complete loss of occlusion on the structural and functional status of these muscle spindles were investigated by immunohistochemistry either for protein gene product 9.5 (PGP 9.5) or growth-associated protein-43 (GAP-43) by light and electron microscopy. All the upper molars of 4-week-old Wistar rats were extracted and the erupted portions of the upper and lower incisors of the same animals were cut-off at the level of the interdental papilla every other day. In a control group, immunoreactivity for GAP-43 was positive in the developing annulospiral endings of 2-week-old rats, but was not detected in any of the muscle spindles after 3 weeks of age. At 4 weeks of age, the PGP 9.5 immunostained spindles had well-differentiated annulospiral endings. Ultrastructurally, these afferent endings showed lenticular or circular profiles in cross-sections, and were differentially indented into the intrafusal-fibres. The inner surfaces of the terminals formed rather smooth myoneural junctions, while the outer surfaces were covered only by basal lamina continuous with that of the underlying intrafusal muscle fibres. After the experimental elimination of occlusal contact, GAP-43 immunoreactivity reappeared in some nerve endings of muscle spindles by 3 days, and persisted for at least 28 days. During this period, the afferent-terminals exhibited various fine structural abnormalities such as irregular outlines and invaginated neuromuscular interfaces. Some sensory-terminal (ST) profiles were completely engulfed by intrafusal-fibres. However, GAP-43 expression and ultrastructural alterations became undetectable within a week of the end of incisal cutting and the recovery of incisal-contact. These data indicate that remodelling of nerve terminals in muscle spindles, as assessed by GAP-43 expression and ultrastructural changes, occurs soon after a loss of occlusion, and ceases if incisal-contact is restored. It is concluded that possible changes in jaw muscle function, as well as a sudden loss of proprioceptive sensory input from the periodontal mechanoreceptors of molars and incisors, induce the structural reorganisation of nerve terminations in jaw muscle spindles that is associated with the appearance and disappearance of GAP-43 immunoreactivity.

Enteric glial cells. An upstream target for induction of necrotizing enterocolitis and Crohn's disease?

As a direct consequence of the sophisticated arrangement of its intrinsic neurons, the gastrointestinal tract is unique among peripheral organs, in its ability to mediate its own reflexes. Neurons of the enteric nervous system are intimately associated with enteric glial cells. These supporting cells do not resemble Schwann cells, the glial cell found in all other parts of the peripheral nervous system, but share many similarities with astrocytes of the central nervous system. Ablation of enteric glial cells in adult transgenic mice has demonstrated that these cells are essential to maintain the integrity of the small intestine. Acute loss of enteric glial cells induces massive pathological changes with similarities to necrotizing enterocolitis (NEC) and early Crohn's disease. These human conditions share some mechanistic similarities. Identification of enteric glial cell dysfunction/loss as sufficient to induce necrotic/inflammatory bowel disease may be important to understand the pathogenesis of both NEC and Crohn's disease.

Quantitative comparison of growth-associated protein-43 and substance P in ulcerative colitis

The aim of this study was to compare immunoreactivities for substance P with other enteric neuropeptides and GAP-43, a general marker for enteric nerves, in normal human colon and in different stages of ulcerative colitis. Tissue samples from normal colon and regions of ulcerative colitis colon were obtained at surgery and immunostained for substance P, vasoactive intestinal polypeptide (VIP), somatostatin, calcitonin gene-related peptide (CGRP), enkephalin, galanin, GAP-43, and neuron-specific enolase (NSE). Visual examination and semiquantitative analysis revealed a clear increase in the immunoreactivity for substance P in ulcerative colitis, whereas no differences were observed in the distribution of the other peptides. Therefore, quantitative analysis was performed only for substance P immunoreactivity in the lamina propria, circular muscle layer, and myenteric ganglia. In the lamina propria, the score of total intensity of substance P immunoreactivity was 0.55 +/- 0.15 (mean +/- SEM) in normal colon, 1.30 +/- 0.35 (p = 0.087) in least affected colon, and 2.22 +/- 0.28 (p < 0.001) in moderately affected colon, whereas no significant differences were observed in immunoreactivities for GAP-43. Similar results were obtained for the mean substance P- or GAP-43-immunoreactive area. In the circular muscle layer, the number, density, total intensity, and perimeter of substance P- and GAP-43-immunoreactive fibers were essentially similar in normal colon, and in mild or moderately affected colon. We conclude that ulcerative colitis does not change the density of gut innervation as a whole. However, the density of substance P-containing nerves is specifically increased, probably due to increased peptide synthesis leading to better visibility of the fibers.

Consequences of intestinal inflammation on the enteric nervous system: neuronal activation induced by inflammatory mediators

The ENS is responsible for the regulation and control of all gastrointestinal functions. Because of this critical role, and probably as a consequence of its remarkable plasticity, the ENS is often relatively well preserved in conditions where the architecture of the intestine is seriously disrupted, such as in IBD. There are structural and functional changes in the enteric innervation in animal models of experimental intestinal inflammation and in IBD. These include both up and down regulation of transmitter expression and the induction of new genes in enteric neurons. Using Fos expression as a surrogate marker of neuronal activation it is now well established that enteric neurons (and also enteric glia) respond to inflammation. Whether this "activation" is limited to a short-term functional response, such as increased neuronal excitability, or reflects a long-term change in some aspect of the neuronal phenotype (or both) has yet to be firmly established, but it appears that enteric neurons are highly plastic in their response to inflammation.

Morphological and cytochemical characteristics of periodontal Ruffini ending under normal and regeneration processes

Current knowledge on the Ruffini endings, primary mechanoreceptors in the periodontal ligament is reviewed with special reference to their cytochemical features and regeneration process. Morphologically, they are characterized by extensive ramifications of expanded axonal terminals and an association with specialized Schwann cells, called lamellar or terminal Schwann cells, which are categorized, based on their histochemical properties, as non-myelin-forming Schwann cells. Following nerve injury, the periodontal Ruffini endings of the rat incisor ligament can regenerate more rapidly than Ruffini endings in other tissues. During regeneration, terminal Schwann cells associated with the periodontal Ruffini endings migrate into regions where they are never found under normal conditions. Also during regeneration, alterations in the expression level of various bioactive substances occur in both axonal and Schwann cell elements in the periodontal Ruffini endings. Neuropeptide Y, which is not detected in intact periodontal Ruffini endings, is transiently expressed in their regenerating axons. Growth-associated protein-43 (GAP-43) is expressed transiently in both axonal and Schwann cell elements during regeneration, while this protein is localized in the Schwann sheath of periodontal Ruffini endings under normal conditions. The expression of calbindin D28k and calretinin, both belonging to the buffering type of calcium-binding proteins, was delayed in periodontal Ruffini endings, compared to their morphological regeneration. As the importance of axon-Schwann cell interactions has been proposed, further investigations are needed to elucidate their molecular mechanism particularly the contribution of growth factors during the regeneration as well as development of the periodontal Ruffini endings.

Plasticity in the enteric nervous system

Enteric ganglia can maintain integrated functions, such as the peristaltic reflex, in the absence of input from the central nervous system, which has a modulatory role. Several clinical and experimental observations suggest that homeostatic control of gut function in a changing environment may be achieved through adaptive changes occurring in the enteric ganglia. A distinctive feature of enteric ganglia, which may be crucial during the development of adaptive responses, is the vicinity of the final effector cells, which are an important source of mediators regulating cell growth. The aim of this review is to focus on the possible mechanisms underlying neuronal plasticity in the enteric nervous system and to consider approaches to the study of plasticity in this model. These include investigations of neuronal connectivity during development, adaptive mechanisms that maintain function after suppression of a specific neural input, and the possible occurrence of activity-dependent modifications of synaptic efficacy, which are thought to be important in storage of information in the brain. One of the applied aspects of the study of plasticity in the enteric nervous system is that knowledge of the underlying mechanisms may eventually enable us to develop strategies to correct neuronal alterations described in several diseases.

Quantitative comparison of growth-associated protein GAP-43, neuron-specific enolase, and protein gene product 9.5 as neuronal markers in mature human intestine

This study was performed to compare GAP-43, PGP 9.5, synaptophysin, and NSE as neuronal markers in the human intestine. GAP-43-immunoreactive nerve fibers were abundant in all layers of the ileum and colon. GAP-43 partially co-localized partially with every neuropeptide (VIP, substance P, galanin, enkephalin) studied. All neuropeptide-immunoreactive fibers also showed GAP-43 reactivity. By blind visual estimation, the numbers of GAP-43-immunoreactive fibers in the lamina propria were greater than those of PGP 9.5, synaptophysin, or NSE. In the muscle layer, visual estimation indicated that the density of GAP-43-immunoreactive fiber profiles was slightly greater than that of the others. The number and intensity of GAP-43-, PGP 9.5-, and NSE-immunoreactive fibers were estimated in sections of normal human colon and ileum using computerized morphometry. In the colon, the numbers of GAP-43-immunoreactive nerve profiles per unit area and their size and intensity were significantly greater than the values for PGP and NSE. A similar trend was observed in the ileum. Neuronal somata lacked or showed only weak GAP-43 immunoreactivity, variable PGP 9.5 immunoreactivity, no synaptophysin immunoreactivity, and moderate to strong NSE immunoreactivity. We conclude that GAP-43 is the superior marker of nerve fibers in the human intestine, whereas NSE is the marker of choice for neuronal somata. (J Histochem Cytochem 47:1405-1415, 1999)

Immediate-early gene expression in the inferior mesenteric ganglion and colonic myenteric plexus of the guinea pig

Activation of neurons in the inferior mesenteric ganglion (IMG) was assessed using c-fos, JunB, and c-Jun expression in the guinea pig IMG and colonic myenteric plexus during mechanosensory stimulation and acute colitis in normal and capsaicin-treated animals. Intracolonic saline or 2% acetic acid was administered, and mechanosensory stimulation was performed by passage of a small (0.5 cm) balloon either 4 or 24 hr later. Lower doses of capsaicin or vehicle were used to activate primary afferent fibers during balloon passage. c-Jun did not respond to any of the stimuli in the study. c-fos and JunB were absent from the IMG and myenteric plexus of untreated and saline-treated animals. Acetic acid induced acute colitis by 4 hr, which persisted for 24 hr, but c-fos was found only in enteric glia in the myenteric plexus and was absent from the IMG. Balloon passage induced c-fos and JunB in only a small subset of IMG neurons and no myenteric neurons. However, balloon passage induced c-fos and JunB in IMG neurons (notably those containing somatostatin) and the myenteric plexus of acetic acid-treated animals. After capsaicin treatment, c-fos and JunB induction by balloon passage was inhibited in the IMG, but there was enhanced c-fos expression in the myenteric plexus. c-fos and JunB induction by balloon stimulation was also mimicked by acute activation of capsaicin-sensitive nerves. These data suggest that colitis enhances reflex activity of the IMG by a mechanism that involves activation of both primary afferent fibers and the myenteric plexus.

Axons containing the growth associated protein GAP-43 specifically target rat corticotrophs following adrenalectomy

An extensive network of nerve fibers immunoreactive for the neuronal growth associated protein GAP-43 (GAP-43-IR) is present within the anterior pituitary (AP) of the rat, and the density of these fibers has been reported to increase 4 days after adrenalectomy (ADX). In the present study, we employed confocal dual-label immunofluorescence microscopy to determine whether GAP-43-IR fibers are specifically associated with corticotrophs at various intervals after ADX. A dramatic increase in the density of GAP-43-IR was apparent 4 days after ADX, and this increase was sustained at 7 and 14 days post-ADX. The percentage of corticotrophs in apparent contact with GAP-43-IR axons was 87% at 4 days after ADX and 92% at 14 days. In addition, fewer than 15% of GAP-43-IR terminals were associated with cells other than corticotrophs in either group. This highly specific targeting of corticotrophs during a period in which these cells are undergoing both hypertrophy and hyperplasia indicates that axonal sprouting is occurring in response to ADX. While the less intense GAP-43-IR in the AP of intact rats precluded precise quantitative analysis, the majority of corticotrophs also appeared to be selectively innervated in these animals. The observations that GAP-43-IR axons selectively contact corticotrophs, and that both the specificity and thoroughness of innervation are maintained by targeted growth of GAP-43-IR axons following ADX, strongly suggest that these fibers are of functional significance.

Distribution of calcitonin gene-related peptide, somatostatin, substance P and vasoactive intestinal polypeptide in experimental colitis in rats

Immunohistochemistry was used to examine the distribution of calcitonin gene-related peptide (CGRP), substance P, somatostatin and vasoactive intestinal polypeptide (VIP) in experimental colitis induced with trinitrobenzene sulphonic acid (TNBS) in rats. CGRP immunoreactivity was observed throughout the colonic wall. A significant reduction of CGRP-immunoreactive (IR) nerve fibres was observed in the mucosa after the induction of colitis. After TNBS treatment substance P immunoreactivity was reduced throughout the colon; however, after 7 days there was a marked re-innervation of the circular muscle. Somatostatin immunoreactivity was distributed sparsely within the colonic wall, and was comparatively less affected by colitis. VIP immunoreactivity was abundantly distributed in the colonic wall and underwent an immediate reduction in the mucosa after TNBS treatment. After 2 days, there was a consistent and progressive increase in the number and density of VIP-IR nerve fibres in the inflamed colon, particularly the circular muscle. This change was associated with a proliferation of nerve fibres within the muscle layers. It was concluded that the early decrease in these neuropeptides was consistent with release from peripheral nerve terminals or the loss of nerves during the initial stages of colonic inflammation, which may be an essential condition for the development of colitis in this model. The observation that the intensity and density of substance P and VIP-IR nerve fibres increased in the circular muscle 7 days after the induction of colitis suggests their possible involvement in tissue repair.

Fulminant jejuno-ileitis following ablation of enteric glia in adult transgenic mice

To investigate the roles of astroglial cells, we targeted their ablation genetically. Transgenic mice were generated expressing herpes simplex virus thymidine kinase from the mouse glial fibrillary acidic protein (GFAP) promoter. In adult transgenic mice, 2 weeks of subcutaneous treatment with the antiviral agent ganciclovir preferentially ablated transgene-expressing, GFAP-positive glia from the jejunum and ileum, causing a fulminating and fatal jejuno-ileitis. This pathology was independent of bacterial overgrowth and was characterized by increased myeloperoxidase activity, moderate degeneration of myenteric neurons, and intraluminal hemorrhage. These findings demonstrate that enteric glia play an essential role in maintaining the integrity of the bowel and suggest that their loss or dysfunction may contribute to the cellular mechanisms of inflammatory bowel disease.

Growth-associated protein-43 (GAP-43) in the regenerating periodontal Ruffini endings of the rat incisor following injury to the inferior alveolar nerve

Alterations in the levels of growth-associated protein 43 (GAP-43)-like immunoreactivity (-LI) were examined in the lingual periodontal ligament of the rat incisor following two types of injury (resection and crush) to the inferior alveolar nerve (IAN). In normal animals, GAP-43-like immunoreactive (IR) structures were observed as tree-like ramifications in the alveolar half of the lingual periodontal ligament of incisors. Under immunoelectron microscopy, GAP-43-LI appeared in the Schwann sheaths associated with periodontal Ruffini endings; neither cell bodies of the terminal Schwann cells nor axonal profiles showed GAP-43-LI. During regeneration of the periodontal Ruffini endings following resection of the IAN, GAP-43-LI appeared in the cytoplasm of the terminal Schwann cell bodies and axoplasm of the terminals. The distribution of GAP-43-LI in the Ruffini endings returned to almost normal levels on days 28 and 56 following the injury. The changes in the distribution of GAP-43-LI following the crush injury were similar to those following resection; however, expression of GAP-43-LI was slightly higher for the entire experimental period compared with the resection. The transient expression of GAP-43 in the terminal Schwann cells and axonal profiles of the periodontal Ruffini endings following nerve injury suggests that GAP-43 is closely associated with axon-Schwann cells interactions during regeneration.

Increase of growth-associated protein-43 immunoreactivity following cyclophosphamide-induced cystitis in rats

We examined the effect of inflammation on immunoreactivity of growth-associated protein (GAP-43) in the rat urinary bladder in which acute cystitis was induced with cyclophosphamide (CPA). Following CPA injection, the number of GAP-43 labeled nerves was significantly increased in the muscle layer. Immunoreactivity of PGP9.5, which was used as an axonal marker, was not augmented following CPA injection. Double fluorescence immunohistochemistry revealed that substance P immunoreactivity was present in most GAP-43 immunoreactive fibers (90.2%) in the inflamed bladder. Electron microscopic examination showed that GAP-43 immunoreactivity was localized on axons. Some GAP-43 positive axons showed degeneration. Possible significance of the increase of GAP-43 immunoreactive afferent nerve fibers in the muscle layer of acutely inflamed bladder was discussed.

B-50, the growth associated protein-43: modulation of cell morphology and communication in the nervous system

The growth-associated protein B-50 (GAP-43) is a presynaptic protein. Its expression is largely restricted to the nervous system. B-50 is frequently used as a marker for sprouting, because it is located in growth cones, maximally expressed during nervous system development and re-induced in injured and regenerating neural tissues. The B-50 gene is highly conserved during evolution. The B-50 gene contains two promoters and three exons which specify functional domains of the protein. The first exon encoding the 1-10 sequence, harbors the palmitoylation site for attachment to the axolemma and the minimal domain for interaction with G0 protein. The second exon contains the "GAP module", including the calmodulin binding and the protein kinase C phosphorylation domain which is shared by the family of IQ proteins. Downstream sequences of the second and non-coding sequences in the third exon encode species variability. The third exon also contains a conserved domain for phosphorylation by casein kinase II. Functional interference experiments using antisense oligonucleotides or antibodies, have shown inhibition of neurite outgrowth and neurotransmitter release. Overexpression of B-50 in cells or transgenic mice results in excessive sprouting. The various interactions, specified by the structural domains, are thought to underlie the role of B-50 in synaptic plasticity, participating in membrane extension during neuritogenesis, in neurotransmitter release and long-term potentiation. Apparently, B-50 null-mutant mice do not display gross phenotypic changes of the nervous system, although the B-50 deletion affects neuronal pathfinding and reduces postnatal survival. The experimental evidence suggests that neuronal morphology and communication are critically modulated by, but not absolutely dependent on, (enhanced) B-50 presence.

Prostaglandin E2 activation of VIP secretomotor neurons in the guinea pig ileum

The effect of prostaglandin E2 (PGE2) on the activity-related expression of the proto-oncogene c-fos in specific populations of enteric neurons was investigated. Segments of guinea-pig ileum were incubated in vitro in the presence or absence of PGE2, and whole mounts of the myenteric and submucosal plexus were prepared for immunocytochemical localization of Fos, VIP and NPY. Control tissues exhibited a low number of Fos-immunoreactive (Fos-IR) neurons (7 +/- 2% of total). Incubation of the tissues with 10-1000 nM PGE2 for 30 min caused a concentration-dependent increase in Fos-IR submucosal neurons (maximum at 100 nM; 39 +/- 6%), which was not inhibited by TTX. PGE2 did not evoke an increase in Fos-IR myenteric neurons. In double labeling experiments, Fos colocalized exclusively with VIP in the submucosal plexus, and not with NPY. Exposure of stripped segments of guinea pig ileum in Ussing chambers to 100 nM PGE2 evoked an increase in short circuit current (20 +/- 7 microA/cm2), of which the initial rapid phase could be abolished by TTX, and not by atropine and hexamethonium. It is concluded that PGE2 can activate VIP non-cholinergic secretomotor neurons.

A role for the enteric nervous system in the response to helminth infections

The enteric nervous system (ENS) in the gut contains a particularly high concentration of nerve cells, and effectively functions as an independent 'minibrain'. Interactions between nerve, endocrine, immune and other cell types allow the sophisticated regulation of normal gut physiology. They can also bring about a co-ordinated response to parasitic infection, possibly leading to expulsion of the parasite. In this review, Derek McKay and Ian Fairweather will consider, in brief, data pertaining to changes in the ENS following intestinal helminth infections and speculate on the role that these alterations may have in the expulsion of the parasite burden and the putative ability of the parasite to modulate these events.

Immunohistochemically-defined subtypes of neurons in the inferior mesenteric ganglion of the guinea-pig

The distribution of somatostatin (SOM), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), tyrosine hydroxylase (a marker of noradrenergic neurons, NA) and nitric oxide synthase-immunoreactivity (NOS-IR) was examined in the inferior mesenteric ganglion of guinea pigs with double- and triple-labelling immunohistochemistry. About 75% of neurons identified were NA/SOM, almost 20% were NA/NPY and the remainder consisted of small groups of NA/- (1-5%), NA/NPY/SOM (2-5%) and VIP (1-2%) neurons. VIP neurons contained NPY-IR, usually contained SOM-IR and were surrounded by dense pericellular baskets of SP fibres. NOS-IR was found in a small proportion of neurons colocalized with VIP but both NOS- and VIP-IR were also found alone in some neurons. Some NOS reactive varicose fibres throughout the ganglia also contained VIP-IR but much of the NOS- and VIP-IR appeared to be localized in discrete varicosities. SOM-IR was also detectable in TH fibres within myenteric ganglia of the distal colon. We conclude that the subtypes of neurons in the inferior mesenteric ganglion share some properties with other sympathetic and abdominal ganglia but they exist in distinct proportions and may make dissimilar projections along the length of the gut.

Noradrenergic and cholinergic reinnervation of islet grafts in diabetic rats

Grafted islets become denervated due to the islet transplantation procedure. The aim of the present study was 1) to examine whether islet grafts in the liver, the spleen, and under the kidney capsule in rats become reinnervated following the transplantation and experimental procedures used in our laboratory, 2) whether there is any difference in reinnervation at these different sites, and 3) how these results relate to previous physiological experiments. Isogeneic isolated islets were transplanted into diabetic Albino Oxford rats, resulting in normoglycaemia. After at least 5 wk, graft-receiving organs were removed and several antibodies were employed to detect insulin, neuron-specific proteins, and cholinergic and noradrenergic nerve fibers. Islets in all three receiving organs contained viable insulin-positive B-cells. Neuron-specific enolase (NSE) as well as the growth-associated protein B-50 was observed at all sites. The cholinergic marker choline acetyltransferase (ChAT) was localized in islets grafts at all sites, but with the lowest density in the spleen. Staining for the noradrenergic markers tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) was observed in islet grafts at all sites with the lowest density in grafts under the kidney capsule. All these neurochemical substances were most frequently observed in fibers associated with blood vessels, which may be the route along which nerves grow into the graft. It can be concluded that 1) islet grafts in the liver, in the spleen and under the kidney capsule become reinnervated; 2) the innervation pattern of the islet grafts differs only slightly from that in the control pancreatic islets; and 3) in combination with our previously physiological data, we can conclude that these nerve fibers are, at least partly, functionally active.

The increase in B-50/GAP-43 in regenerating rat sciatic nerve occurs predominantly in unmyelinated axon shafts: a quantitative ultrastructural study

The growth-associated protein B-50/GAP-43 is thought to play a crucial role in axonal growth. We investigated, by quantitative immunoelectron microscopy, whether there are differences in the subcellular distribution of B-50 in unmyelinated and myelinated axons of intact and regenerating sciatic nerves. Adult rats received an unilateral sciatic nerve crush and were euthanized 8 days later. Nerve pieces proximal from the crush site were embedded, and B-50 was visualized by specific B-50 antibodies and immunogold detection in ultrathin sections. The density of B-50 at the plasma membrane of unmyelinated axon shafts was significantly increased in the ipsilateral regenerating nerve in comparison to that of the contralateral intact nerve. In contrast, there was no significant difference in the B-50 density at the axolemma of myelinated regenerating and intact axon shafts. In the contralateral intact nerve, more B-50 was associated with the axolemma of unmyelinated axons than with the plasma membrane of myelinated axons. The density of axoplasmic B-50 was similar in intact unmyelinated and myelinated axon shafts, but was higher in regenerating nerve than in intact nerve. This suggests that enhanced axonal transport of B-50 occurs during axon outgrowth. Our study demonstrates a differential subcellular distribution of B-50 in unmyelinated and myelinated axon shafts in both the intact and regenerating sciatic nerve, indicating a differential inducible capacity for remodeling of the axon shafts.

Ultrastructural examination of B-50(GAP-43) immunoreactivity in rat jejunal villi

The lamina propria of rat jejunum is densely innervated with nerve fibres extending to the tips of the villi. A large number of these nerve fibres were previously shown to be B-50-immunoreactive at the light microscope level, whereas neurofilament immunoreactivity was found to be sparse in the mucosa. In this study we used immunoelectron microscopy to determine what proportion of nerve fibres in the lamina propria express B-50. Jejuna from male Lewis rats were immunolabelled for B-50 and neurofilament proteins. For electron microscopy, postembedding immunogold-silver techniques and LR White embedded tissues were used. Light microscopical immunostaining was performed by the streptavidin-biotin-peroxidase technique on deparaffinized tissue sections. We found that all ultrastructurally identifiable nerve profiles in jejunum were B-50 immunoreactive. Immunoelectron microscopy for neurofilament proteins failed to label fibres in the villi, whereas myelinated nerves in tongue sections processed in parallel (positive controls) were strongly neurofilament-protein-immunoreactive. The dominant B-50-positive and neurofilament-protein-negative phenotype supports the hypothesis of ongoing modelling or plasticity of intestinal mucosal nerves.

Growth-associated protein-43 and protein gene-product 9.5 innervation in human pancreas: changes in chronic pancreatitis

Growth-associated protein-43, an established marker of neuronal plasticity during development and in injury, was used to characterize innervation in the normal human pancreas and changes in chronic alcohol-induced pancreatitis by using light microscopic immunocytochemistry and computer-assisted image analysis. Immunostaining for the pan-neuronal marker protein gene-product 9.5 served as a reference for the characterization of total innervation in both groups. In normal human pancreas, strong protein gene-product 9.5 immunostaining revealed all nerve fibres in nerve trunks, all neuronal cell bodies and the entire parenchymal innervation. In contrast, growth-associated protein-43 immunoreactivity was restricted to a few nerve fibres in interlobular nerve trunks and to fine varicose nerve fibres supplying the parenchyma, blood vessels, pancreatic ducts and intrinsic ganglia. In cell bodies of intrinsic neurons, growth-associated protein-43 immunoreactivity was absent or extremely faint. In chronic pancreatitis, the protein gene-product 9.5 innervation exhibited region-specific changes. In areas with reduced parenchyma, the protein gene-product 9.5 innervation was sparse. In fibrotic regions, which are characteristic for advanced stages of chronic pancreatitis, enlarged nerve trunks showing neuroma-like formations were heavily stained for protein gene-product 9.5. In fibrotic tissue, protein gene-product 9.5-containing nerve fibres were extremely rare. The growth-associated protein-43 innervation in chronic pancreatitis was characterized by a dramatic increase, which was most pronounced in the enlarged nerve trunks. Such nerve trunks were frequently surrounded by infiltrates of immune cells, which in some cases formed follicle-like structures. Digital image analysis of adjacent sections and double fluorescence immunocytochemistry revealed that growth-associated protein-43 immunoreactivity was present in the vast majority of protein gene-product 9.5-immunoreactive nerve fibres. In contrast to the normal pancreas, a major subpopulation of intrinsic neurons immunostained for growth-associated protein-43. The expression of growth-associated protein-43 in the terminal fields of pancreatic nerve suggests that the innervation of the normal human pancreas undergoes continual and toposelective remodelling. The increase in the density of growth-associated protein-43 immunoreactive nerve fibres in enlarged nerve trunks paralleled by augmented expression of growth-associated protein-43 in intrinsic neurons and reduced parenchymal growth-associated protein-43-immunoreactive innervation underline the dramatic plasticity of pancreatic innervation in chronic pancreatitis.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of constitutive nuclear oncoproteins to count neurons in the enteric nervous system of the guinea pig

Immunohistochemical double labelling of the enteric nervous system of the guinea pig ileum was performed with a monoclonal antibody (anti-MYC 033) directed against a peptide sequence of the human c-Myc protein together with antibodies directed against either the neuron-specific antigens neuron-specific enolase or PGP 9.5 or the glia-specific marker S-100 to demonstrate that anti-MYC 033 labelled the nuclei of all enteric neurons but not glia. This strategy was also employed to demonstrate that another anti-c-Myc monoclonal antibody, anti-MYC 070, labelled the nuclei of all neurons and glia, as well as perhaps all other cells in these preparations. A polyclonal antiserum raised against a peptide sequence of the human c-Fos protein (anti-FOS 4) was shown to label the identical nuclei as anti-MYC 033. The ganglionic density of nuclei labelled by anti-FOS 4 was found to be similar to previous measures of the ganglionic density of neurons. Double labelling with anti-MYC 033 and an antiserum directed against vasoactive intestinal polypeptide was performed to reexamine the ganglionic density of neurons that express this neuropeptide. Our results suggest that the ganglionic density of these neurons might be less than previously determined.

Innervation and mast cells of the rat exorbital lacrimal gland: the effects of age

The distribution of nerves and mast cells was studied in the lacrimal glands of 3-5-, 14- and 24-month-old rats, using light microscopic histochemical and immunohistochemical techniques. In 14-month and, to a greater extent, in 24-month-old rats there were signs of chronic inflammation and patchy destruction of acinar, ductal and vascular tissue. The glands of the three different age groups contained acetylcholinesterase (AChE), vasoactive intestinal polypeptide (VIP)-, neuropeptide Y (NPY)-, calcitonin gene-related peptide (CGRP)-, tyrosine hydroxylase-, substance P- and the phosphoprotein B-50-immunoreactive nerves. B-50-immunoreactive nerves were distributed around acini, blood vessels and ducts, in a similar manner to VIP and AChE. Substance P- and CGRP-immunoreactive nerves were sparsely distributed in interlobular connective tissue and around ducts and blood vessels. Tyrosine hydroxylase- and NPY-containing nerves were found around blood vessels. The 3-5- and 14-month-old rats had a similar pattern of innervation, however, by 24 months there was a reduction in the number and intensity of immunoreactive nerves. The loss of nerves was particularly associated with damage to the gland. Mast cells were also found in the lacrimal, mostly associated with neurovascular tissue. These could be histochemically labelled with alcian blue/safranin or toluidine blue and were immunohistochemically labelled with histamine and serotonin. Substance P-, CGRP-, VIP- and NPY-immunoreactive nerves were found apposed to mast cells. A large increase in mast cells was observed in 24-month compared to 3-5-month-old rats and these were found throughout the acinar tissue. These results show that a decrease in innervation and also chronic inflammation, with mast cell infiltration, occurs in aged rats. These findings may be contributing factors to reduced tear output in aging.

c-Myc antigens in the mammalian enteric nervous system

We have investigated the presence of c-Myc-like antigens in the enteric nervous system of the guinea-pig, rat, dog, sheep, monkey and human. c-Myc-like immunoreactivity was demonstrated by immunohistochemistry in the enteric nervous system of all animals tested, with one or more monoclonal antibodies raised against peptide sequences found in the human c-Myc protein. While in most cases the labelling was nuclear, cytoplasmic labelling was also observed. In the guinea-pig enteric nervous system, c-Myc-like immunoreactivity detected by two different antibodies remained detectable for up to 4 h in the presence of cycloheximide. The size and density of labelled nuclei in the ileal submucous plexus were consistent with exclusive neuronal labelling by one antibody and neuronal plus glial labelling by the other. Double-labelling with antiserum directed against vasoactive intestinal peptide revealed a subset of c-Myc-immunoreactive neurons that also contain this neuropeptide. Anti-c-Myc antibodies specifically immunoprecipitated proteins from guinea-pig myenteric plexus-longitudinal muscle preparations whose sizes were consistent with previous observations for c-Myc antigens and whose distribution was consistent with synthesis in the myenteric plexus. We conclude that c-Myc proteins are expressed in mammalian enteric neurons and that they have characteristics similar to those of c-Myc proteins in other nonproliferative cells.

Substance P-, calcitonin gene-related peptide, growth-associated protein-43, and neurotrophin receptor-like immunoreactivity associated with unmyelinated axons in feline ventral roots and pia mater

The spinal pia mater receives a rich innervation of small sensory axons via the ventral roots. Other sensory axons enter the ventral roots but end blindly or turn abruptly in hairpin loop-like formations and continue in a distal direction. In the present study, the content of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, growth-associated protein (GAP-43)-, and low-affinity neurotrophin receptor protein (p75NGFr)-like immunoreactivity (-LI) associated with these different types of sensory axons was assessed with light and electron microscopic immunohistochemical techniques. In addition, the binding of antibodies against synthetic peptides representing unique sequences of residues in the products of the trk and trkB protooncogenes was analyzed. These genes encode membrane spanning proteins, which have been shown to constitute specific high affinity binding sites for several members of the nerve growth factor family of neurotrophic factors. The results of the present study imply that the ventral root afferents comprise several different types of sensory axons, which all contain SP-, CGRP-, GAP-43-, and p75NGFr-like immunoreactivities. In addition, at least some of the presumed sensory fiber bundles in ventral roots and the pia mater were immunoreactive for the trkB gene product. Moreover, leptomeningeal cells and nonneuronal cells of the ventral roots were shown to bind antibodies to both the trk and trkB gene products. The ventral root afferents seem to share their immunohistochemical pattern with pain-transducing axons at some other locations, such as the tooth pulp. The contents of SP- and CGRP-LI in sensory axons that reach the central nervous system (CNS) through the ventral root indicate that ventral root afferents may be involved in sensory mechanisms, such as the ventral root pain reaction, as well as in the control of the pial blood vessels. The demonstration of GAP-43 and neurotrophin receptor-immunoreactivities associated with unmyelinated fibers in ventral roots and the pia mater is discussed in relation to previous reports on postnatal plasticity in these axonal populations.

Distribution of GAP-43 in relation to CGRP and synaptic vesicle markers in rat skeletal muscles during development

GAP 43 in nerve terminal structures of rat skeletal muscles, was investigated during postnatal development using immunofluorescence and confocal laser scanning microscopy. Comparison with synaptophysin, synapsin, SV2, CGRP, SP and NF was done in double immunoincubation studies. GAP 43-like immunoreactivity (LI) was demonstrated in preterminal axons and motor endplates in all age groups (from E18 to adult), although the intensity of immunofluorescence was considerably higher in the younger rats. The outgrowing nerve sprouts in E18 muscles were strongly GAP 43-positive. The intensity decreased with increasing age, but even in adult animals GAP 43-LI was present in some p38- or SV2-positive endplates. GAP 43-LI was also present in muscle spindles and preterminal nerve branches, and likewise decreased with age. Perivascular nerve terminals (around arteries mainly) were, however, strong in GAP 43-LI during both development and adulthood. GAP 43-LI was strong, and present in both small and large granules. SP-LI was observed in a few thin, presumably sensory, axons around vessels, which also contained a few GAP 43-positive large granules. Most of the strongly GAP 43-positive terminals around vessels were probably autonomic postganglionic terminals. The results suggest that GAP 43, in addition to development and regeneration, may play a significant role also in normal adult rats, especially in perivascular nerve terminals, possibly connected with a high potential for plasticity in this kind of nerve terminals.

Peptide-immunoreactive neurons and nerve fibres in lumbosacral sympathetic ganglia: selective elimination of a pathway-specific expression of immunoreactivities following sciatic nerve resection in kittens

The distributions of peptide-immunoreactive nerve fibres and cell bodies in lumbosacral paravertebral sympathetic ganglia of young cats were analysed with antibodies to calcitonin gene-related peptide, enkephalin, neurotensin, somatostatin, substance P, galanin, neuropeptide Y and vasoactive intestinal polypeptide. Fairly dense networks of nerve fibres showing enkephalin-, neurotensin-, somatostatin- or substance P-like immunoreactivity were observed in the ganglia. Double-staining experiments revealed that enkephalin- and somatostatin-immunoreactive nerve fibres preferentially surrounded calcitonin gene-related peptide- and/or vasoactive intestinal polypeptide-immunoreactive cell bodies. Neurotensin- and substance P-immunoreactive nerve fibres were mainly associated with neurons showing neuropeptide Y and/or galanin-like immunoreactivity. Occasional nerves containing calcitonin gene-related peptide-, galanin-, neuropeptide Y- or vasoactive intestinal polypeptide-like immunoreactivity were observed. These fibres did not seem to have any direct regional distribution within the ganglia. In kittens surviving for three months after early postnatal sciatic nerve resection, no calcitonin gene-related peptide-immunoreactive cell bodies could be detected in ganglia ipsilateral to the operation. In contrast, vasoactive intestinal polypeptide-like immunoreactivity, which partly co-exists with calcitonin gene-related peptide, was observed to the same extent as in control ganglia. Furthermore, almost all of the somatostatin-immunoreactive varicose nerve fibres had disappeared, whereas a fairly dense network of calcitonin gene-related peptide-immunoreactive nerve fibres could be observed. This change was paralleled by an increased content of nerve fibres that were immunoreactive to antibodies against the growth-associated protein GAP-43 (also known as B-50). The present findings suggest that experimental perturbations where postganglionic neurons are separated from their target areas by axotomy, not only induce differential changes in neurotransmitter expression in the principal ganglion cells, but also in preganglionic sympathetic neurons projecting to the ganglia. One possible explanation for the occurrence of an axotomy-induced network of calcitonin gene-related peptide-immunoreactive nerve fibres, is that extrinsic sensory nerve fibres grow into the ganglia after the sciatic nerve lesion. Thus, these findings seem to suggest one additional possibility with regard to the question of a possible interaction between sympathetic and sensory neurons after peripheral nerve injury.

Expression of GAP-43 in normal and regenerating nerves in the frog

A polyclonal antiserum to chicken, growth-associated protein-43 (GAP-43), raised in rabbit, was shown to recognize a molecule with similar properties to GAP-43 in frogs. Using this antiserum, GAP-43 immunoreactivity was shown to be present throughout the brain and white matter of the spinal cord of larval frogs, but became restricted to specific regions in the adult frog central nervous system. In the peripheral nervous system, GAP-43 was present in normal tadpole and adult axons. After cutting the adult sciatic nerve, GAP-43 slowly disappeared from axons in the distal stump, but appeared in Schwann cells and other (uncharacterized) cells. The constitutive expression of GAP-43 in the adult frog sciatic nerve may be related to the phenomenon of remodelling of motor end-plates, which is known to occur throughout life in frogs.

Nerve remodelling during intestinal inflammation

The intestinal mucosa contains a dense nerve network and many inflammatory cells, and these may interact through the exchange of regulatory molecules. Evidence suggests that intestinal mucosal mast cells are innervated, and it is known that the density of this cell type changes significantly in nematode-infected rats. Recent data indicates that rat jejunal mucosal nerves remodel after Nippostrongylus brasiliensis infection, with degenerative and regenerative phases during the acute and recovery stages of inflammation. Seven weeks postinfection there is a net increase in the density and number per villus of mucosal nerves. These changes suggest that mucosal nerves exhibit structural plasticity in inflamed tissues, which must impact on interactions between the enteric nervous system and other mucosal elements in disease.

Cellular distribution of the new growth factor pleiotrophin (HB-GAM) mRNA in developing and adult rat tissues

Pleiotrophin (PTN), also known as HB-GAM, belongs to an emerging cytokine family unrelated to other growth factors. We report here the first comprehensive study using in situ hybridization on the cellular distribution of this new heparin-binding growth factor mRNA in rat tissues. PTN mRNA was developmentally expressed in many--but not all--neuroectodermal and mesodermal lineages, whilst no PTN mRNA was detected in endoderm, ectoderm and trophoblast. PTN mRNA was found in the nervous system throughout development, with a post-natal peak of expression. In the adult nervous system, significant expression persisted in hippocampal CA1 pyramidal neurons and in cortical neurons, but also in different non-neuronal cells types in various locations (olfactory nerve, cerebellar astrocytes, pituicytes, Schwann cells surrounding the neurons in sensory ganglia). PTN mRNA was also found during development in the mesenchyme of lung, gut, kidney and reproductive tract, in bone and cartilage progenitors, in dental pulp, in myoblasts, and in several other sites. Expression was differently regulated in each location, but usually faded around birth. In the adult, PTN mRNA was still present in the meninges, the iris, the Leydig cells of the testis and in the uterus. PTN mRNA was also strongly expressed in the basal layers of the tongue epithelium, which is the only epithelium and ectodermal derivative to express PTN mRNA, and this only after birth. PTN is known to be a growth factor for perinatal brain neurons and a mitogen for fibroblasts in vitro. Recently, trophic effects on epithelial cells and a role as a tumour growth factor have been reported. The mechanisms of regulation and the functions of PTN are however still uncertain. Its expression pattern during development suggests important roles in growth and differentiation. Moreover, the presence of PTN mRNA in several adult tissues and the up-regulation of PTN mRNA expression in the gravid uterus indicate that PTN also has physiological functions during adulthood.

Peptides in the gastrointestinal tract in human immunodeficiency virus infection. The GI/HIV Study Group of the University of Calgary

The presence of immunoreactivity to the neuronal phosphoprotein B-50 and the peptides bombesin, calcitonin gene-related peptide, galanin, neurotensin, neuropeptide Y, somatostatin, substance P, and vasoactive intestinal polypeptide was examined in biopsy specimens from the duodenum and rectum of human immunodeficiency virus (HIV)-seropositive and HIV-seronegative male homosexual patients. The distribution of B-50 and the peptides was correlated with HIV serology, number of CD4+ lymphocytes, and the presence of HIV in biopsy culture. There was a very low incidence of enteric pathogens in both groups of patients. It was found that HIV-seropositive patients had a greater incidence of abnormal patterns of immunoreactivity (reduced intensity and/or density of innervation) in enteric nerves and enteroendocrine cells than HIV-seronegative patients. A reduction of substance P immunoreactivity was significantly correlated with reduced CD4+ lymphocyte count and HIV status; a similar trend was also seen for somatostatin and vasoactive intestinal polypeptide. Using B-50 as a marker, it was found that both groups of patients had altered patterns of immunoreactivity in rectal nerves. The findings of this study suggest that some of the clinical symptoms associated with HIV infection may be caused by a specific HIV enteropathy that influences enteric nerve and/or enteroendocrine cell function by altering the density of peptide immunoreactivity.

GAP-43 immunoreactivity is widespread in the autonomic neurons and sensory neurons of the rat

GAP-43 is a membrane-bound phosphoprotein generally associated with axon growth during development and regeneration. Using immunohistochemical and immunoblotting techniques this study shows that GAP-43 is expressed extensively in the unperturbed adult autonomic nervous system. Strong immunoreactivity was seen in the developing and mature enteric subdivision of the autonomic nervous system and in nerves of the iris and various blood vessels. The presence of GAP-43 immunoreactivity in varicose nerve fibres, and a comparison of the labelling pattern of GAP-43 with the nerve associated marker PGP 9.5 suggests that GAP-43 is present in most or all autonomic nerve fibres in these organs. Immunoblotting of gut samples on 10% polyacrylamide gels revealed a single band of approximately 45,000 mol. wt that co-migrated with pure central nervous system GAP-43. Surgical sympathectomy experiments resulting in almost complete elimination of sympathetic fibres did not markedly affect the pattern of GAP-43 immunoreactivity in the iris, indicating that GAP-43 is expressed not only in sympathetic nerves but also in parasympathetic and sensory fibres. These findings show that GAP-43 is expressed extensively in autonomic nerves of the adult rat, at levels comparable to those seen during development. High levels of GAP-43 are not therefore restricted to development and regeneration in this part of the nervous system.