Immunohistochemical demonstration of choline acetyltransferase of a peripheral type (pChAT) in the enteric nervous system of rats

Enteric Nervous System: Identification of a Novel Neuronal Sensory Network in the Duodenal Epithelium

The communication between the intestinal epithelium and the enteric nervous system has been considered indirect. Mechanical or chemical stimuli activate enteroendocrine cells inducing hormone secretion, which act on sub-epithelial nerve ends, activating the enteric nervous system. However, we identified an epithelial cell that expresses NKAIN4, a neuronal protein associated with the β-subunit of Na+/K+-ATPase. This cell overexpresses Na+/K+-ATPase and ouabain-insensitive Na+-ATPase, enzymes involved in active sodium transport. NKAIN4-positive cells also express neuronal markers as NeuN, acetylcholine-esterase, acetylcholine-transferase, α3- and α7-subunits of ACh receptors, glutamic-decarboxylase, and serotonin-receptor-7, suggesting they are neurons. NKAIN4-positive cells show a polarized shape with an oval body, an apical process finished in a knob-like terminal in contact with the lumen, a basal cilia body at the base of the apical extension, and basal axon-like soma projections connecting sub-epithelial nerve terminals, lymphoid nodules, glial cells, and enterochromaffin cells, forming a network that reaches the epithelial surface. We also showed, using retrograde labeling and immunofluorescence, that these cells receive afferent signals from the enteric nervous system. Finally, we demonstrated that acetylcholine activates NKAIN4-positive cells inducing Ca2+ mobilization and probably serotonin secretion in enterochromaffin cells. NKAIN4-positive cells are neurons that would form a part of a duodenal sensory network for physiological or noxious luminal stimuli.

Topographical distribution and morphology of SP-IR axons in the antrum, pylorus, and duodenum of mice

Substance-P (SP) is a commonly used marker of nociceptive afferent axons, and it plays an important role in a variety of physiological functions including the regulation of motility, gut secretion, and vascular flow. Previously, we found that SP-immunoreactive (SP-IR) axons densely innervated the pyloric antrum of the flat-mount of the mouse whole stomach muscular layer. However, the regional distribution and morphology of SP-IR axons in the submucosa and mucosa were not well documented. In this study, the mouse antrum-pylorus-duodenum (APD) were transversely and longitudinally sectioned. A Zeiss M2 imager was used to scan the serial sections of each APD (each section montage consisted of 50-100 all-in-focus maximal projection images). To determine the detailed structures of SP-IR axons and terminals, we used the confocal microscope to scan the regions of interest. We found that 1) SP-IR axons innervated the muscular, submucosal, and mucosal layers. 2) In the muscular layer, SP-IR varicose axons densely innervated the muscles and formed varicose terminals which encircled myenteric neurons. 3) In the submucosa, SP-IR axons innervated blood vessels and submucosal ganglia and formed a network in Brunner's glands. 4) In the mucosa, SP-IR axons innervated the muscularis mucosae. Some SP-IR axons entered the lamina propria. 5) The muscular layer of the antrum and duodenum showed a higher SP-IR axon density than the pyloric sphincter. 6) SP-IR axons were from extrinsic and intrinsic origins. This work provided a comprehensive view of the distribution and morphology of SP-IR axons in the APD at single cell/axon/varicosity scale. This data will be used to create a 3D scaffold of the SP-IR axon innervation of the APD.

Intrinsic cholinergic innervation in the human sigmoid colon revealed using CLARITY, three-dimensional (3D) imaging, and a novel anti-human peripheral choline acetyltransferase (hpChAT) antiserum

BACKGROUND

We previously reported the specificity of a novel anti-human peripheral choline acetyltransferase (hpChAT) antiserum for immunostaining of cholinergic neuronal cell bodies and fibers in the human colon. In this study, we investigate 3D architecture of intrinsic cholinergic innervation in the human sigmoid colon and the relationship with nitrergic neurons in the enteric plexus.

METHODS

We developed a modified CLARITY tissue technique applicable for clearing human sigmoid colon specimens and immunostaining with hpChAT antiserum and co-labeling with neuronal nitric oxide synthase (nNOS) antibody. The Z-stack confocal images were processed for 3D reconstruction/segmentation/digital tracing and computational quantitation by Imaris 9.2 and 9.5.

KEY RESULTS

In the mucosa, a local micro-neuronal network formed of hpChAT-ir fibers and a few neuronal cell bodies were digitally assembled. Three layers of submucosal plexuses were displayed in 3D structure that were interconnected by hpChAT-ir fiber bundles and hpChAT-ir neurons were rarely co-labeled by nNOS. In the myenteric plexus, 30.1% of hpChAT-ir somas including Dogiel type I and II were co-labeled by nNOS and 3 classes of hpChAT-ir nerve fiber strands were visualized in 3D images and videos. The density and intensity values of hpChAT-ir fibers in 3D structure were significantly higher in the circular than in the longitudinal layer.

CONCLUSIONS AND INFERENCES

The intrinsic cholinergic innervation in the human sigmoid colon was demonstrated layer by layer for the first time in 3D microstructures. This may open a new venue to assess the structure-function relationships and pathological alterations in colonic diseases.

Cholinergic nervous system and glaucoma: From basic science to clinical applications

The cholinergic system has a crucial role to play in visual function. Although cholinergic drugs have been a focus of attention as glaucoma medications for reducing eye pressure, little is known about the potential modality for neuronal survival and/or enhancement in visual impairments. Citicoline, a naturally occurring compound and FDA approved dietary supplement, is a nootropic agent that is recently demonstrated to be effective in ameliorating ischemic stroke, traumatic brain injury, Parkinson's disease, Alzheimer's disease, cerebrovascular diseases, memory disorders and attention-deficit/hyperactivity disorder in both humans and animal models. The mechanisms of its action appear to be multifarious including (i) preservation of cardiolipin, sphingomyelin, and arachidonic acid contents of phosphatidylcholine and phosphatidylethanolamine, (ii) restoration of phosphatidylcholine, (iii) stimulation of glutathione synthesis, (iv) lowering glutamate concentrations and preventing glutamate excitotoxicity, (v) rescuing mitochondrial function thereby preventing oxidative damage and onset of neuronal apoptosis, (vi) synthesis of myelin leading to improvement in neuronal membrane integrity, (vii) improving acetylcholine synthesis and thereby reducing the effects of mental stress and (viii) preventing endothelial dysfunction. Such effects have vouched for citicoline as a neuroprotective, neurorestorative and neuroregenerative agent. Retinal ganglion cells are neurons with long myelinated axons which provide a strong rationale for citicoline use in visual pathway disorders. Since glaucoma is a form of neurodegeneration involving retinal ganglion cells, citicoline may help ameliorate glaucomatous damages in multiple facets. Additionally, trans-synaptic degeneration has been identified in humans and experimental models of glaucoma suggesting the cholinergic system as a new brain target for glaucoma management and therapy.

A Novel Antiserum Against a Predicted Human Peripheral Choline Acetyltransferase (hpChAT) for Labeling Neuronal Structures in Human Colon

Choline acetyltransferase (ChAT), the enzyme synthesizing acetylcholine (ACh), has an exon-skipping splice variant which is expressed preferentially in the peripheral nervous system (PNS) and thus termed peripheral ChAT (pChAT). A rabbit antiserum previously produced against rat pChAT (rpChAT) has been used for immunohistochemistry (IHC) to study peripheral cholinergic structures in various animals. The present study was undertaken to develop a specific antiserum against a predicted human pChAT (hpChAT) protein. A novel mouse antiserum has been successfully raised against a unique 14-amino acid sequence of hpChAT protein. Our Western blot using this antiserum (termed here anti-hpChAT serum) on human colon extracts revealed only a single band of 47 kDa, matching the deduced size of hpChAT protein. By IHC, the antiserum gave intense staining in many neuronal cells and fibers of human colon but not brain, and such a pattern of staining seemed identical with that reported in colon of various animals using anti-rpChAT serum. In the antibody-absorption test, hpChAT-immunoreactive staining in human colon was completely blocked by using the antiserum pre-absorbed with the antigen peptide. Double immunofluorescence in human colon moreover indicated that structures stained with anti-hpChAT were also stained with anti-rpChAT, and vice versa. hpChAT antiserum allowed the identification of cell types, as Dogiel type cells in intramural plexuses, and fiber innervation of colon muscles and mucosae. The present results demonstrate the specificity and reliability of the hpChAT antiserum as a novel tool for immunohistochemical studies in human colon, opening venues to map cholinergic innervation in other human PNS tissues.

Acetylcholine signaling system in progression of lung cancers

The neurotransmitter acetylcholine (ACh) acts as an autocrine growth factor for human lung cancer. Several lines of evidence show that lung cancer cells express all of the proteins required for the uptake of choline (choline transporter 1, choline transporter-like proteins) synthesis of ACh (choline acetyltransferase, carnitine acetyltransferase), transport of ACh (vesicular acetylcholine transport, OCTs, OCTNs) and degradation of ACh (acetylcholinesterase, butyrylcholinesterase). The released ACh binds back to nicotinic (nAChRs) and muscarinic receptors on lung cancer cells to accelerate their proliferation, migration and invasion. Out of all components of the cholinergic pathway, the nAChR-signaling has been studied the most intensely. The reason for this trend is due to genome-wide data studies showing that nicotinic receptor subtypes are involved in lung cancer risk, the relationship between cigarette smoke and lung cancer risk as well as the rising popularity of electronic cigarettes considered by many as a "safe" alternative to smoking. There are a small number of articles which review the contribution of the other cholinergic proteins in the pathophysiology of lung cancer. The primary objective of this review article is to discuss the function of the acetylcholine-signaling proteins in the progression of lung cancer. The investigation of the role of cholinergic network in lung cancer will pave the way to novel molecular targets and drugs in this lethal malignancy.

S. Typhimurium challenge in juvenile pigs modulates the expression and localization of enteric cholinergic proteins and correlates with mucosal injury and inflammation

The cholinergic system plays a central role in regulating critical gastrointestinal functions, including motility, secretion, barrier and immune function. In rodent models of acute, non-infectious gastrointestinal injury, the cholinergic system functions to inhibit inflammation; however, during inflammation local expression and regulation of the cholinergic system is not well known, particularly during infectious enteritis. The objective of this study was to determine the intrinsic expression of the enteric cholinergic system in pig ileum following an acute challenge with Salmonella enterica serovar Typhimurium DT104 (S. Typhimurium). At 2 d post-challenge, a three-fold reduction in ileal acetylcholine (ACh) levels was observed in challenged animals, compared with controls. Ileal acetylcholinesterase (AChE) activity was decreased (by four-fold) while choline acetyltransferase (ChAT) expression was increased in both the ileum and mesenteric lymph nodes. Elevated ChAT found to localize preferentially to mucosa overlying lymphoid follicles of the Peyers patch in challenged pigs, with more intense labeling for ChAT in S. Typhimurium challenged pigs compared to controls. Ileal mRNA gene expression of muscarinic receptor 1 and 3 was also increased in challenged pigs, while muscarinic receptor 2 and the nicotinic receptor alpha 7 subunit gene expression were unaffected. A positive correlation was observed between ChAT protein expression in the ileum, rectal temperature, and histopathological severity in challenged animals. These data show that inflammation from S. Typhimurium challenge alters enteric cholinergic expression by down-regulating acetylcholine concentration and acetylcholine degrading enzymes while increasing acetylcholine synthesis proteins and receptors. Given the known anti-inflammatory role of the cholinergic system, the divergent expression of cholinergic genes may represent an attempt to limit tissue damage by preserving cholinergic signaling in the face of low ligand availability.

Abdominal surgery induced gastric ileus and activation of M1-like macrophages in the gastric myenteric plexus: prevention by central vagal activation in rats

Inflammation plays a role in abdominal surgery (AS)-induced intestinal ileus that is alleviated by electrical vagal stimulation. Intracisternal injection of RX-77368, the stable thyrotropin-releasing hormone agonist, activates dorsal motor nucleus neurons and gastric vagal efferent discharges. We investigated the gastric inflammation induced by AS and the modulation by intracisternal RX-77368 in rats. RX-77368 (50 ng/rat) or saline was injected followed, 1 h later, by laparotomy and small intestinal/cecal manipulation. The sham group had anesthesia alone. After 6 h, gastric emptying (GE) and the inflammation in gastric corpus were determined. AS inhibited GE by 72% vs. control and doubled the number of M1-like macrophage immunoreactive for major histocompatibility complex class II (MHCII; M1 marker) but not for cluster of differentiation 206 (CD206; M2 marker) (MHCII⁺/CD206^-) while there was no change in M2-like macrophages (MHCII^-/CD206⁺). AS increased mRNA levels of interleukin-1β (IL-1β) and tumor necrosis factor α (TNF-α) by 1.7- and 1.5-fold, respectively, in the gastric submucosa plus muscle layers and the infiltration of neutrophils labeled by myeloperoxidase by 9.5-fold in the muscularis externa. RX-77368 inhibited AS-related gastric changes while not altering these parameters in the sham group. There was a significant negative correlation between GE and IL-1β (r = -0.46), TNF-α (r = -0.44), M1 macrophage (r = -0.82), and neutrophils (r = -0.91). The M2-like macrophages and IL-10 expression were unchanged by AS with intracisternal saline or RX-77368. These data indicate that AS activates gastric M1 macrophages and increases proinflammatory cytokines expression, which are prevented by central vagal activation and may contribute to the correlated dampening of postoperative gastric ileus.NEW & NOTEWORTHY MHCII⁺/CD206^- (M1) and MHCII^-/CD206⁺ (M2) constitute two distinct populations of macrophages that are in close apposition to the cholinergic neurons in the rat gastric myenteric plexus (MP). Abdominal surgery (6 h) activates M1 macrophage leading to inflammation in the gastric MP correlated with the delayed gastric emptying, which was abolished by central vagal stimulation via intracisternal injection of RX-77368. Vagal stimulation linked with the cephalic phase may have potential beneficial effects to curtail postoperative gastric ileus.

Alterations in the small intestinal wall and motor function after repeated cisplatin in rat

BACKGROUND

Gastrointestinal adverse effects occurring during cancer chemotherapy are well known and feared; those persisting once treatment has finished are relatively unknown. We characterized the alterations occurring in the rat small intestine, after repeated treatment with cisplatin.

METHODS

Male Wistar rats received saline or cisplatin (2 mg kg^-1  week^-1 , for 5 weeks, ip). Gastric motor function was studied non-invasively throughout treatment (W1-W5) and 1 week after treatment finalization (W6). During W6, upper gastrointestinal motility was also invasively studied and small intestinal samples were collected for histopathological and molecular studies. Structural alterations in the small intestinal wall, mucosa, submucosa, muscle layers, and lymphocytic nodules were histologically studied. Periodic acid-Schiff staining and immunohistochemistry for Ki-67, chromogranin A, and neuronal-specific enolase were used to detect secretory, proliferating, endocrine and neural cells, respectively. The expression of different markers in the tunica muscularis was analyzed by RT/qPCR.

KEY RESULTS

Repeated cisplatin induced motility alterations during and after treatment. After treatment (W6), the small intestinal wall showed histopathological alterations in most parameters measured, including a reduction in the thickness of circular and longitudinal muscle layers. Expression of c-KIT (for interstitial cells of Cajal), nNOS (for inhibitory motor neurons), pChAT, and cChAT (for excitatory motor neurons) increased significantly (although both ChATs to a lesser extent).

CONCLUSIONS & INFERENCES

Repeated cisplatin induces relatively long-lasting gut dysmotility in rat associated with important histopathological and molecular alterations in the small intestinal wall. In cancer survivors, the possible chemotherapy-induced histopathological, molecular, and functional intestinal sequelae should be evaluated.

Reduction of epithelial secretion in male rat distal colonic mucosa by bile acid receptor TGR5 agonist, INT-777: role of submucosal neurons

BACKGROUND

Recent evidence from rat neuron-free mucosa study suggests that the membrane bile acid receptor TGR5 decreases colonic secretion under basal and stimulated conditions. As submucosal neurons are key players in secretory processes and highly express TGR5, we investigated their role in TGR5 agonist-induced inhibition of secretion and the pathways recruited.

METHODS

TGR5 expression and localization were assessed in rat proximal (pC) and distal (dC) colon by qPCR and immunohistochemistry with double labeling for cholinergic neurons in whole-mount preparations. The influence of a selective (INT-777) or weak (ursodeoxycholic acid, UDCA) TGR5 agonist on colonic secretion was assessed in Ussing chambers, in dC preparation removing seromuscular ± submucosal tissues, in the presence of different inhibitors of secretion pathways.

KEY RESULTS

TGR5 mRNA is expressed in full thickness dC and pC and immunoreactivity is located in colonocytes and pChAT-positive neurons. Addition of INT-777, and less potently UDCA, decreased colonic secretion in seromuscular stripped dC by -58.17± 2.6%. INT-777 effect on basal secretion was reduced in neuron-free and TTX-treated mucosal-submucosal preparations. Atropine, hexamethonium, indomethacin, and L-NAME all reduced significantly INT-777's inhibitory effect while the 5-HT₄ antagonist, RS-39604, and lidocaine abolished it. INT-777 inhibited stimulated colonic secretion induced by nicotine, but not cisapride, carbachol or PGE2.

CONCLUSIONS & INFERENCES

TGR5 activation inhibits basal and stimulated distal colonic secretion in rats by acting directly on epithelial cells and also inhibiting submucosal neurons. This could represent a counter-regulatory mechanism, at the submucosal level, of the known prosecretory effect of bile acids in the colon.

Identification and Molecular Characterization of Two Acetylcholinesterases from the Salmon Louse, Lepeophtheirus salmonis

Acetylcholinesterase (AChE) is an important enzyme in cholinergic synapses. Most arthropods have two genes (ace1 and ace2), but only one encodes the predominant synaptic AChE, the main target for organophosphates. Resistance towards organophosphates is widespread in the marine arthropod Lepeophtheirus salmonis. To understand this trait, it is essential to characterize the gene(s) coding for AChE(s). The full length cDNA sequences encoding two AChEs in L. salmonis were molecularly characterized in this study. The two ace genes were highly similar (83.5% similarity at protein level). Alignment to the L. salmonis genome revealed that both genes were located close to each other (separated by just 26.4 kbp on the L. salmonis genome), resulting from a recent gene duplication. Both proteins had all the typical features of functional AChE and clustered together with AChE-type 1 proteins in other species, an observation that has not been described in other arthropods. We therefore concluded the presence of two versions of ace1 gene in L. salmonis, named ace1a and ace1b. Ace1a was predominantly expressed in different developmental stages compared to ace1b and was possibly active in the cephalothorax, indicating that ace1a is more likely to play the major role in cholinergic synaptic transmission. The study is essential to understand the role of AChEs in resistance against organophosphates in L. salmonis.

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.

Excitatory and inhibitory enteric innervation of horse lower esophageal sphincter

The lower esophageal sphincter (LES) is a specialized, thickened muscle region with a high resting tone mediated by myogenic and neurogenic mechanisms. During swallowing or belching, the LES undergoes strong inhibitory innervation. In the horse, the LES seems to be organized as a "one-way" structure, enabling only the oral-anal progression of food. We characterized the esophageal and gastric pericardial inhibitory and excitatory intramural neurons immunoreactive (IR) for the enzymes neuronal nitric oxide synthase (nNOS) and choline acetyltransferase. Large percentages of myenteric plexus (MP) and submucosal (SMP) plexus nNOS-IR neurons were observed in the esophagus (72 ± 9 and 69 ± 8 %, respectively) and stomach (57 ± 17 and 45 ± 3 %, respectively). In the esophagus, cholinergic MP and SMP neurons were 29 ± 14 and 65 ± 24 vs. 36 ± 8 and 38 ± 20 % in the stomach, respectively. The high percentage of nitrergic inhibitory motor neurons observed in the caudal esophagus reinforces the role of the enteric nervous system in the horse LES relaxation. These findings might allow an evaluation of whether selective groups of enteric neurons are involved in horse neurological disorders such as megaesophagus, equine dysautonomia, and white lethal foal syndrome.

Expression and localization of pChAT as a novel method to study cholinergic innervation of rat adrenal gland

Cholinergic innervation of the rat adrenal gland has been analyzed previously using cholinergic markers including acetylcholinesterase (AChE), choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT). In the present study, we demonstrate putative cholinergic neurons in the rat adrenal gland using an antibody to pChAT, which is the product of a splice variant of ChAT mRNA that is preferentially localized in peripheral cholinergic nerves. Most of the ganglionic neurons as well as small single sporadic neurons in the adrenal gland were stained intensely for pChAT. The density of pChAT-immunoreactive (IR) fibers was distinct in the adrenal cortex and medulla. AChE-, cChAT- and VAChT-immunoreactivities were also observed in some cells and fibers of the adrenal medulla, while the cortex had few positive nerve fibers. These results indicate that ganglionic neurons of the adrenal medulla and nerve fibers heterogeneously express cholinergic markers, especially pChAT. Furthermore, the innervation of the adrenal gland, cortex and medulla, by some cholinergic fibers provides additional morphological evidence for a significant role of cholinergic mechanisms in adrenal gland functions.

Appearance of cholinergic myenteric neurons during enteric nervous system development: comparison of different ChAT fluorescent mouse reporter lines

BACKGROUND

Cholinergic neurons have been identified with the acetylcholine synthetic enzyme choline acetyltransferase (ChAT). However, ChAT is difficult to localize in newly differentiated peripheral neurons making the study of cholinergic neuronal development problematic. Consequently, researchers have used mouse reporter lines to indicate the presence of ChAT.

METHODS

Our objective was to determine which ChAT reporter line was the most sensitive indicator of ChAT expression. We utilized two different fluorescent ChAT reporter lines (ChAT-GFP and ChAT-Cre;R26R:floxSTOP:tdTomato) together with immunolocalization of ChAT protein (ChAT-IR) to characterize the spatial and temporal expression of ChAT in myenteric neurons throughout enteric nervous system (ENS) development.

KEY RESULTS

ChAT-IR cells were first seen in the intestine at E10.5, even within the migration wavefront of neural precursors. Myenteric neurons within the distal small intestine (dSI) and proximal colon were first labeled by ChAT-IR, then ChAT-GFP, and finally ChAT-Cre tdTomato. The percentage of ChAT-IR neurons is equivalent to adult levels in the dSI by E13.5 and proximal colon by P0. After these stages, the percentages remained relatively constant throughout development despite dramatic changes in neuronal density.

CONCLUSIONS & INFERENCES

These observations indicate that neurotransmitter expression occurs early and there is only a brief gap between neurogenesis and neurotransmitter expression. Our finding that the proportion of ChAT myenteric neurons reached adult levels during embryonic development suggests that the fate of cholinergic neurons is tightly regulated and that their differentiation might influence further neuronal development. ChAT-GFP is a more accurate indicator of early ENS cholinergic neuronal differentiation than the ChAT-Cre;R26R:floxSTOP:tdTomato reporter mouse.

Distinct localization of peripheral and central types of choline acetyltransferase in the rat cochlea

We previously discovered a splice variant of choline acetyltransferase (ChAT) mRNA, and designated the variant protein pChAT because of its preferential expression in peripheral neuronal structures. In this study, we examined the immunohistochemical localization of pChAT in rat cochlea and compared the distribution pattern to those of common ChAT (cChAT) and acetylcholinesterase. Some neuronal cell bodies and fibers in the spiral ganglia showed immunoreactivity for pChAT, predominantly the small spiral ganglion cells, indicating outer hair cell type II neurons. In contrast, cChAT- and acetylcholinesterase-positive structures were localized to fibers and not apparent in ganglion cells. After ablation of the cochlear nuclei, many pChAT-positive cochlear nerve fibers became clearly visible, whereas fibers immunopositive for cChAT and acetylcholine esterase disappeared. These results suggested that pChAT and cChAT are localized in different systems of the rat cochlea; pChAT in the afferent and cChAT in the efferent structures.

Immunoreactivity for Choline Acetyltransferase of Peripheral-Type (pChAT) in the Trigeminal Ganglion Neurons of the Non-Human Primate Macaca fascicularis

Transcripts of the choline acetyltransferase (ChAT) gene reveal a number of different splice variants including ChAT of a peripheral type (pChAT). Immunohistochemical staining of the brain using an antibody against pChAT clearly revealed peripheral cholinergic neurons, but failed to detect cholinergic neurons in the central nervous system. In rodents, pChAT-immunoreactivity has been detected in cholinergic parasympathetic postganglionic and enteric ganglion neurons. In addition, pChAT has been observed in non-cholinergic neurons such as peripheral sensory neurons in the trigeminal and dorsal root ganglia. The common type of ChAT (cChAT) has been investigated in many parts of the brain and the spinal cord of non-human primates, but little information is available about the localization of pChAT in primate species. Here, we report the detection of pChAT immunoreactivity in trigeminal ganglion (TG) neurons and its co-localization with Substance P (SP) and/or calcitonin gene-related peptide (CGRP) in the cynomolgus monkey, Macaca fascicularis. Neurons positive for pChAT were observed in a rather uniform pattern in approximately half of the trigeminal neurons throughout the TG. Most pChAT-positive neurons had small or medium-sized cell bodies. Double-immunofluorescence staining showed that 85.1% of SP-positive cells and 74.0% of CGRP-positive cells exhibited pChAT immunoreactivity. Most pChAT-positive cells were part of a larger population of neurons that co-expressed SP and/or CGRP.

Lack of cholinergic innervation in gastric mucosa does not affect gastrin secretion or basal acid output in neurturin receptor GFRα2 deficient mice

Efferent signals from the vagus nerve are thought to mediate both basal and meal-induced gastric acid secretion, and provide trophic support of the mucosa. However, the underlying mechanisms are incompletely understood. Neurturin, signalling via glial cell line-derived neurotrophic factor (GDNF)-family receptor α2 (GFRα2), is essential for parasympathetic innervation of many target tissues but its role in gastric innervation is unknown. Here we show that most nerve fibres in wild-type mouse gastric mucosa, including all positive for gastrin-releasing peptide, are cholinergic. GFRα2-deficient (KO) mice lacked virtually all cholinergic nerve fibres and associated glial cells in the gastric (oxyntic and pyloric) mucosa but not in the smooth muscle, consistent with the selective expression of neurturin mRNA in the gastric mucosa. 2-Deoxyglucose and hexamethonium failed to affect acid secretion in the GFRα2-KO mice indicating the lack of functional innervation in gastric mucosa. Interestingly, basal and maximal histamine-induced acid secretion did not differ between wild-type and GFRα2-KO mice. Moreover, circulating gastrin levels in both fasted and fed animals, thickness of gastric mucosa, and density of parietal and different endocrine cells were similar. Carbachol-stimulated acid secretion was higher in GFRα2-KO mice, while atropine reduced basal secretion similarly in both genotypes. We conclude that cholinergic innervation of gastric mucosa depends on neurturin-GFRα2 signalling but is dispensable for gastrin secretion and for basal and maximal acid output. Basal acid secretion in the KO mice appears to be, at least partly, facilitated by constitutive activity of muscarinic receptors.

Peripheral choline acetyltransferase in rat skin demonstrated by immunohistochemistry

Conventional choline acetyltransferase immunohistochemistry has been used widely for visualizing central cholinergic neurons and fibers but not often for labeling peripheral structures, probably because of their poor staining. The recent identification of the peripheral type of choline acetyltransferase (pChAT) has enabled the clear immunohistochemical detection of many known peripheral cholinergic elements. Here, we report the presence of pChAT-immunoreactive nerve fibers in rat skin. Intensely stained nerve fibers were distributed in association with eccrine sweat glands, blood vessels, hair follicles and portions just beneath the epidermis. These results suggest that pChAT-positive nerves participate in the sympathetic cholinergic innervation of eccrine sweat glands. Moreover, pChAT also appears to play a role in cutaneous sensory nerve endings. These findings are supported by the presence of many pChAT-positive neuronal cells in the sympathetic ganglion and dorsal root ganglion. Thus, pChAT immunohistochemistry should provide a novel and unique tool for studying cholinergic nerves in the skin.

Do cholinergic nerves innervating rat mesenteric arteries regulate vascular tone?

Vascular blood vessels have various types of cholinergic acetylcholine receptors (AChR), but the source of ACh has not been confirmed. Perivascular adrenergic nerves and nonadrenergic calcitonin gene-related peptide (CGRP)-containing (CGRPergic) nerves innervate rat mesenteric arteries and regulate vascular tone. However, function of cholinergic innervation remains unknown. The present study investigated cholinergic innervation by examining effects of cholinesterase inhibitor (neostigmine), a muscarinic AChR antagonist (atropine), and a nicotinic AChR antagonist (hexamethonium) on adrenergic nerve-mediated vasoconstriction and CGRPergic nerve-mediated vasodilation in rat mesenteric vascular beds without endothelium. In preparations treated with capsaicin (CGRP depletor) or in the presence of N(ω)-nitro-l-arginine methyl ester (nonselective nitric oxide synthase inhibitor), perivascular nerve stimulation (PNS; 2-12 Hz) evoked a frequency-dependent vasoconstriction. In the same preparations, exogenous norepinephrine induced a concentration-dependent vasoconstriction. Atropine, hexamethonium, and neostigmine had no effect on vasoconstrictor responses to PNS and norepinephrine injections. In denuded preparations, these cholinergic agents did not affect the PNS (12 Hz)-evoked release of norepinephrine in perfusate. In preconstricted preparations without endothelium in the presence of guanethidine (adrenergic neuron blocker), PNS (1-4 Hz) induced a frequency-dependent vasodilation, which was not affected by atropine, hexamethonium, and neostigmine. In denuded preparations treated with capsaicin and guanethidine, PNS did not induce vascular responses, and atropine, neostigmine, and physostigmine had no effect on PNS. Immunohistochemistry study showed choline acetyltransferase-immunopositive fibers, which were resistant to capsaicin and 6-hydroxydopamine (adrenergic toxin). These results suggest that rat mesenteric arteries have cholinergic innervation, which is different from adrenergic and capsaicin-sensitive nerves and not associated with vascular tone regulation.

Effects of ischemia and reperfusion on P2X2 receptor expressing neurons of the rat ileum enteric nervous system

PURPOSE

We investigated the effects of ischemia/reperfusion in the intestine (I/R-i) on purine receptor P2X2-immunoreactive (IR) neurons of the rat ileum.

METHODS

The superior mesenteric artery was occluded for 45 min with an atraumatic vascular clamp and animals were sacrificed 4 h later. Neurons of the myenteric and submucosal plexuses were evaluated for immunoreactivity against the P2X2 receptor, nitric oxide synthase (NOS), choline acetyl transferase (ChAT), calbindin, and calretinin.

RESULTS

Following I/R-i, we observed a decrease in P2X2 receptor immunoreactivity in the cytoplasm and surface membranes of neurons of the myenteric and submucosal plexuses. These studies also revealed an absence of calbindin-positive neurons in the I/R-i group. In addition, the colocalization of the P2X2 receptor with NOS, ChAT, and calretinin immunoreactivity in the myenteric plexus was decreased following I/R-i. Likewise, the colocalization between P2X2 and calretinin in neurons of the submucosal plexus was also reduced. In the I/R-i group, there was a 55.8% decrease in the density of neurons immunoreactive (IR) for the P2X2 receptor, a 26.4% reduction in NOS-IR neuron, a 25% reduction in ChAT-IR neuron, and a 47% reduction in calretinin-IR neuron. The density of P2X2 receptor and calretinin-IR neurons also decreased in the submucosal plexus of the I/R-i group. In the myenteric plexus, P2X2-IR, NOS-IR, ChAT-IR and calretinin-IR neurons were reduced in size by 50%, 49.7%, 42%, and 33%, respectively, in the I/R-i group; in the submucosal plexus, P2X2-IR and calretinin-IR neurons were reduced in size by 56% and 72.6%, respectively.

CONCLUSIONS

These data demonstrate that ischemia/reperfusion of the intestine affects the expression of the P2X2 receptor in neurons of the myenteric and submucosal plexus, as well as density and size of neurons in this population. Our findings indicate that I/R-i induces changes in P2X2-IR enteric neurons that could result in alterations in intestinal motility.

Peripheral type of choline acetyltransferase: biological and evolutionary implications for novel mechanisms in cholinergic system

The peripheral type of choline acetyltransferase (pChAT) is an isoform of the well-studied common type of choline acetyltransferase (cChAT), the synthesizing enzyme of acetylcholine. Since pChAT arises by exons skipping, its amino acid sequence is similar to that of cChAT, except the lack of a continuous peptide sequence encoded by all the four exons from 6 to 9. While cChAT expression has been observed in both the central and peripheral nervous systems, pChAT is preferentially expressed in the peripheral nervous system. pChAT appears to be a reliable marker for the visualization of peripheral cholinergic neurons and their processes, whereas other conventional markers including cChAT have not been used successfully for it. In mammals like rodents, pChAT immunoreactivity has been observed in most, if not all, physiologically identified peripheral cholinergic structures such as all parasympathetic postganglionic neurons and most neurons of the enteric nervous system. In addition, pChAT has been found in many peripheral neurons that are derived from the neural crest. These include sensory neurons of the trigeminal ganglion and the dorsal root ganglion, and sympathetic postganglionic neurons. Recent studies moreover indicate that pChAT, as well as cChAT, appears ubiquitously expressed among various species not only of vertebrate mammals but also of invertebrate mollusks. This finding implies that the alternative splicing mechanism to generate pChAT and cChAT has been preserved during evolution, probably for some functional benefits.

Effects of protein deprivation and re-feeding on P2X2 receptors in enteric neurons

AIM: To investigate the effects of malnutrition and re-feeding on the P2X₂ receptor, nitric oxide synthase (NOS), calretinin, calbindin and choline acetyltransferase (ChAT) in neurons of the rat ileum.

METHODS: We analyzed the co-localization, numbers and sizes of P2X₂-expressing neurons in relation to NOS-immunoreactive (IR), calbindin-IR, ChAT-IR, and calretinin-IR neurons of the myenteric and submucosal plexus. The experimental groups consisted of: (1) rats maintained on normal feed throughout pregnancy until 42 d post-parturition (N); (2) rats deprived of protein throughout pregnancy and 42 d post-parturition (D); and (3) rats undernourished for 21 d post-parturition and then given a protein diet from days 22 to 42 (DR). The myenteric and submucosal plexuses were evaluated by double labeling by immunohistochemical methods for P2X₂ receptor, NOS, ChAT, calbindin and calretinin.

RESULTS: We found similar P2X₂ receptor immunoreactivity in the cytoplasm and surface membranes of myenteric and submucosal neurons from the N, D and DR groups. Double labeling of the myenteric plexus demonstrated that approximately 100% of NOS-IR, calbindin-IR, calretinin-IR and ChAT-IR neurons in all groups also expressed the P2X₂ receptor. In the submucosal plexus, the calretinin-IR, ChAT-IR and calbindin-IR neurons were nearly all immunoreactive for the P2X₂ receptor. In the myenteric plexus, there was a 19% increase in numbers per cm² for P2X₂ receptor-IR neurons, 64% for NOS-IR, 84% for calretinin-IR and 26% for ChAT-IR neurons in the D group. The spatial density of calbindin-IR neurons, however, did not differ among the three groups. The submucosal neuronal density increased for calbindin-IR, calretinin-IR and ChAT-IR neurons. The average size of neurons in the myenteric plexus neurons in the D group was less than that in the controls and, in the re-fed rats; there was a 34% reduction in size only for the calretinin-IR neurons.

CONCLUSION: This work demonstrates that expression of the P2X₂ receptor is present in inhibitory, intrinsic primary afferent, cholinergic secretomotor and vasomotor neurons. Undernutrition affected P2X₂ receptor expression in the submucosal plexus, and neuronal and size. These changes were rescued in the re-fed rats.

Immunohistochemical characteristics of submucosal Dogiel type II neurons in rat colon

Secretory and motility reflexes are evoked by physiological stimuli in the isolated rat distal colon, which is therefore expected to contain intrinsic primary afferent (sensory) neurons. Dogiel type II neurons (putative intrinsic primary afferent neurons) exhibit several long processes emerging from large oval or round cell bodies. This study has examined the immunohistochemical characteristics of type II neurons in the submucosal plexus of rat distal colons by using whole-mount preparations. Neuronal cell bodies positive for both substance P (SP) and calretinin have been observed in colchicine-treated rats. Neurofilament 200 immunostaining has confirmed the type II morphology of SP-positive neurons. Moreover, all submucosal type II neurons identified by neurofilament 200 immunoreactivity are positive for calretinin. Calcitonin gene-related peptide (CGRP)-positive neurons in the submucosal plexus are distinct from type II neurons because they are negative for calretinin and have smaller cell bodies than the SP-positive submucosal type II neurons. Most (73%) of the submucosal neurons including type II neurons exhibit immunoreactivity for the neurokinin-1 receptor (NK1R), a receptor for SP, on the surface of cell bodies. Immunoreactivity for the EP3 receptor (EP3R), a receptor for prostaglandin E2, has been detected in 51% of submucosal neurons including type II neurons. Thus, submucosal type II neurons in the rat distal colon are immunopositive for SP/calretinin but immunonegative for CGRP. SP released from submucosal type II neurons probably acts via NK1Rs on type II and non-type II submucosal neurons to mediate intrinsic reflexes. EP3R-positive submucosal type II neurons may be potential targets of prostaglandin E2.

Axotomy alters alternative splicing of choline acetyltransferase in the rat dorsal motor nucleus of the vagus nerve

Choline acetyltransferase of the peripheral type (pChAT) is a splice variant that lacks exons 6-9 of the common-type ChAT (cChAT); the role of pChAT remains unknown. We investigated the expression of pChAT and cChAT after axotomy to try to elucidate its function. In the dorsal motor nucleus of the vagus nerve (DMNV), nucleus ambiguus (NA), and hypoglossal nucleus (HN) of control rats, we observed neural expression of cChAT but no pChAT-positive neurons. Following nerve transection, we clearly detected pChAT-labeled neurons in the DMNV and weakly labeled neurons in the NA, but pChAT was not seen in the HN. In the DMNV, the mean number of cChAT-positive neurons decreased rapidly to 40.5% of control at 3 days post transection, and to 5.0% of control after 7 days. The number of cChAT-positive neurons then gradually increased and reached a plateau of about 25% of control value at 28 days post transection. pChAT-positive neurons did not appear until 7 days after transection. On the same day, pChAT mRNA was detected in the DMNV neurons by reverse transcription-polymerase chain reaction (RT-PCR) by using laser capture microdissection. The number of pChAT-positive neurons gradually decreased, and only 10% of the cholinergic neurons retained pChAT expression 56 days post transection. Double-immunofluorescence analysis showed that some of the DMNV neurons expressed both cChAT and pChAT upon recovery from axotomy. These results suggest that the expression of pChAT is associated with the regenerative or degenerative processes of motoneurons especially for general visceral efferents.

Expression of nicotinic acetylcholine receptors and subunit messenger RNAs in the enteric nervous system of the neonatal rat

In the enteric nervous system (ENS) excitatory nicotinic cholinergic transmission is mediated by neuronal nicotinic acetylcholine receptors (nAChR) and is critical for the regulation of gastric motility. nAChRs are ligand-gated pentameric ion channels found in the CNS and peripheral nervous system. The expression of heteromeric nAChR and receptor subunit mRNAs was investigated in the neonatal rat ENS using receptor autoradiography with the radiolabeled ligand (125)I-epibatidine, and in situ hybridization with subtype specific probes for ligand binding alpha (alpha2, alpha3, alpha4, alpha5, alpha6) and structural beta (beta2, beta3, beta4) subunits. The results showed strong nicotine sensitive binding of (125)I-epibatidine around the stomach, and small and large intestines. The binding was partially displaced by A85380, a nicotinic ligand which differentiates between different heteromeric nAChR subtypes, suggesting a mixed receptor population. Radioactive in situ hybridization detected expression of alpha3, alpha5, alpha7, beta2 and beta4 mRNA in the myenteric plexus of the stomach, and small and large intestines. In the submucosal plexus of the small and large intestines expression of alpha3, alpha5 and beta4 was found in some ganglia. There was no signal for alpha4, alpha6 and beta3 in the ENS but positive hybridization signal for alpha2 transcripts was seen in some areas of the small intestines. However, the signal was not associated with any ganglion cells. The results confirm the presence of heteromeric nAChRs in the ENS similar to those found in the peripheral nervous system, with the majority being composed of alpha3(alpha5)beta4, and a few alpha3beta2 nAChRs. In addition, homomeric alpha7 nAChRs could be present.

Immunohistochemical characterization and quantitative analysis of neurons in the myenteric plexus of the equine intestine

The present study was performed on whole-mount preparations to investigate the chemical neuroanatomy of the equine myenteric plexus throughout its distribution in the intestinal wall. The objective was to quantify neurons of the myenteric plexus, especially the predominant cholinergic and nitrergic subpopulations. Furthermore, we investigated the distribution of vasoactive intestinal polypeptide and the calcium-binding protein calretinin. Samples from different defined areas of the small intestine and the flexura pelvina were taken from 15 adult horses. After fixation and preparation of the tissue, immunofluorescence labeling was performed on free floating whole-mounts. Additionally, samples used for neuropeptide staining were incubated with colchicine to reveal the neuropeptide distribution within the neuronal soma. The evaluation was routinely accomplished using confocal laser-scanning microscopy. For quantitative and qualitative analysis, the pan-neuronal marker anti-HuC/D was applied in combination with the detection of the marker enzymes for cholinergic neurons and nitrergic nerve cells. Quantitative data revealed that the cholinergic subpopulation is larger than the nitrergic one in several different locations of the small intestine. On the contrary, the nitrergic neurons outnumber the cholinergic neurons in the flexura pelvina of the large colon. Furthermore, ganglia are more numerous in the small intestine compared with the large colon, but ganglion sizes are bigger in the large colon. However, comparison of the entire population of neurons in the different locations of the gut showed no difference. The present study adds further data on the chemoarchitecture of the myenteric plexus which might facilitate the understanding of several gastrointestinal disorders in the horse.

Distribution of a splice variant of choline acetyltransferase in the trigeminal ganglion and brainstem of the rat: comparison with calcitonin gene-related peptide and substance P

Rat trigeminal ganglion neurons have been shown to contain a splice variant of choline acetyltransferase (pChAT). Here we report the distribution pattern of pChAT-containing afferents from the trigeminal ganglion to the brainstem, compared with that of calcitonin gene-related peptide (CGRP) and substance P (SP), by use of the immunohistochemical techniques in the rat. Most of CGRP(+) SP(+) ganglion cells contain pChAT, whereas half of the pChAT(+) ganglion cells possess neither CGRP nor SP. In the brainstem, pChAT(+) nerve fibers are found exclusively in the trigeminal and solitary systems, although the distribution pattern differs from that of CGRP(+) or SP(+) fibers. First, the ventral portion of the principal sensory nucleus contains many pChAT(+) fibers, with few CGRP(+) or SP(+) fibers. Because this portion receives projections of nociceptive corneal afferents, a subpopulation of pChAT(+) CGRP(-) SP(-) primary afferents is most probably nonpeptidergic nociceptors innervating the cornea. Second, the superficial laminae of the medullary dorsal horn, the main target of nociceptive afferents, contain dense CGRP(+) and SP(+) fibers but sparse pChAT(+) fibers. Because pChAT occurs in most CGRP(+) SP(+) ganglion cells, such sparseness of pChAT(+) fibers implies poor transportation of pChAT to axon branchlets. Another important finding is that pChAT(+) axons are smooth and nonvaricose, whereas CGRP(+) or SP(+) fibers possess numerous varicosities. Our confocal microscopy suggests colocalization of these three markers in the same single axons in some brainstem regions. The difference in morphological appearance, nonvaricose or varicose, appears to reflect the difference in intraaxonal distribution between pChAT and CGRP or SP.

Culture of porcine fetal pancreatic neurons

OBJECTIVES

Pancreatic neurons have not been cultured commonly. Cultured neurons can be continuously observed, and their external environment is easy to be controlled. We report here a simple method for separating and cultivating neuronal cells from pancreas.

METHODS

Pancreata of fetal swine were digested with collagenase. Clusters were collected with a sieve and digested with trypsin. Digested clusters were collected and cultured in Dulbecco modified Eagle medium containing serum and basic fibroblast growth factor. Cultured cells were investigated morphologically.

RESULTS

Cultured cells formed spiderweblike colonies. These cells were distinguished into Schwann cells and 2 types of neurons. The neurons were positive on immunocytochemical staining with antigrowth-associated protein-43 and cytochemical staining for cholinesterase. One type of neuron was located in the central cluster and had very long processes extending radially. The other type of neuron was sparsely scattered, had long processes, and was connected to other neurons. The neurotransmitter of these neurons was concluded to be acetylcholine.

CONCLUSIONS

Using our method, neuronal cells were readily cultured from pancreatic tissue. These cells will be useful in elucidating the physiology and pharmacology of pancreatic neurons.

Peripheral corticotropin releasing factor (CRF) and a novel CRF1 receptor agonist, stressin1-A activate CRF1 receptor expressing cholinergic and nitrergic myenteric neurons selectively in the colon of conscious rats

Intraperitoneal (i.p.) corticotropin releasing factor (CRF) induced a CRF(1) receptor-dependent stimulation of myenteric neurons and motility in the rat proximal colon. We characterize the colonic enteric nervous system response to CRF in conscious rats. Laser capture microdissection combined with reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry in longitudinal muscle myenteric plexus whole-mount colonic preparations revealed CRF(1) receptor expression in myenteric neurons. CRF (i.p., 10 microg kg(-1)) induced Fos immunoreactivity (IR) (cells per ganglion) selectively in myenteric plexus of proximal (18.3 +/- 2.4 vs vehicle: 0.0 +/- 0.0) and distal colon (16.8 +/- 1.2 vs vehicle: 0.0 +/- 0.0), but not in that of gastric corpus, antrum, duodenum, jejunum and ileum. The selective CRF(1) agonist, stressin(1)-A (i.p., 10 microg kg(-1)) also induced Fos IR in myenteric but not in submucosal plexus of the proximal and distal colon. Fos IR induced by CRF was located in 55 +/- 1.9% and 53 +/- 5.1% of CRF(1) receptor-IR myenteric neurons and in 44 +/- 2.8% and 40 +/- 3.9% of cholinergic neurons with Dogiel type I morphology, and in 20 +/- 1.6% and 80 +/- 3.3% of nitrergic neurons in proximal and distal colon respectively. CRF and stressin(1)-A elicit defecation and diarrhoea. These data support that one mechanism through which peripherally injected CRF ligands stimulate colonic function involves a direct action on colonic cholinergic and nitrergic myenteric neurons expressing CRF(1) receptor.

Acetylcholine synthesis by choline acetyltransferase of a peripheral type as demonstrated in adult rat dorsal root ganglion

pChAT is a splice variant of a peripheral type encoded alternatively by the gene for choline acetyltransferase of the common type (cChAT), the enzyme responsible for acetylcholine synthesis. Immunohistochemistry using pChAT antiserum has successfully visualized many known peripheral cholinergic cells, whereas most cChAT antibodies failed to do so. As, however, accumulating evidence indicates that pChAT expression also occurs in various non-cholinergic neurons, we examined possible acetylcholine production by pChAT in rat dorsal root ganglion as a model. The present study indicated that the ganglion neurons possessed pChAT, but never cChAT, mRNA and protein. Our detailed analysis further showed that, despite low enzyme activities of both choline acetyltransferase and acetylcholinesterase, the level of acetylcholine in the ganglion was as high as to that in various brain regions receiving cholinergic innervation. By using immunoprecipitation methods, we here provide evidence that pChAT definitely has enzyme activity enough to supply physiological concentrations of acetylcholine in the ganglion. We propose that pChAT contributes both to acetylcholine neurotransmission in physiologically identified cholinergic cells and to functions yet unknown in non-cholinergic neurons. Thus pChAT provides a new window on the role of neuronal acetylcholine.

The distribution and chemical coding of intramural neurons supplying the porcine stomach - the study on normal pigs and on animals suffering from swine dysentery

The present study was designed to investigate the expression of biologically active substances by intramural neurons supplying the stomach in normal (control) pigs and in pigs suffering from dysentery. Eight juvenile female pigs were used. Both dysenteric (n = 4; inoculated with Brachyspira hyodysenteriae) and control (n = 4) animals were deeply anaesthetized, transcardially perfused with buffered paraformalehyde, and tissue samples comprising all layers of the wall of the ventricular fundus were collected. The cryostat sections were processed for double-labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene-product 9.5) and their chemical coding using antibodies against vesicular acetylcholine (ACh) transporter (VAChT), nitric oxide synthase (NOS), galanin (GAL), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), Leu(5)-enkephalin (LENK), substance P (SP) and calcitonin gene-related peptide (CGRP). In both inner and outer submucosal plexuses of the control pigs, the majority of neurons were SP (55% and 58%, respectively)- or VAChT (54%)-positive. Many neurons stained also for CGRP (43 and 45%) or GAL (20% and 18%) and solitary perikarya were NOS-, SOM- or VIP-positive. The myenteric plexus neurons stained for NOS (20%), VAChT (15%), GAL (10%), VIP (7%), SP (6%) or CGRP (solitary neurons), but they were SOM-negative. No intramural neurons immunoreactive to LENK were found. The most remarkable difference in the chemical coding of enteric neurons between the control and dysenteric pigs was a very increased number of GAL- and VAChT-positive nerve cells (up to 61% and 85%, respectively) in submucosal plexuses of the infected animals. The present results suggest that GAL and ACh have a specific role in local neural circuits of the inflamed porcine stomach in the course of swine dysentery.

Neonatal maternal separation of rat pups results in abnormal cholinergic regulation of epithelial permeability

Neonatal maternal separation (MS) predisposes adult rats to develop stress-induced mucosal barrier dysfunction/visceral hypersensitivity and rat pups to develop colonic epithelial dysfunction. Our aim was to examine if enhanced epithelial permeability in such pups resulted from abnormal regulation by enteric nerves. Pups were separated from the dam for 3 h/day (days 4-20); nonseparated (NS) pups served as controls. On day 20, colonic tissues were removed and mounted in Ussing chambers. Horseradish peroxidase (HRP) flux was used to measure macromolecular permeability. HRP flux was increased in MS versus NS pups. The enhanced flux was inhibited by the cholinergic muscarinic antagonist atropine and the nicotinic antagonist hexamethonium. The cholinergic component was greater in tissues from MS versus NS pups, suggesting that increased cholinergic activity was responsible for the MS elevated permeability. Western blots and immunohistochemistry of colonic tissues demonstrated increased expression of choline acetyltransferase (ChAT) in MS pups, indicating greater synthesis of acetylcholine. Since a previous study indicated that corticotrophin-releasing factor (CRF) mediates barrier dysfunction in MS pups, we examined if the two pathways were linked. In MS tissues, nonselective CRF receptor antagonism inhibited the enhanced flux, and the addition of atropine did not produce further inhibition. Using selective receptor antagonists, we identified that CRF receptor 2 was involved in mediating this effect. These findings suggest that CRF, via CRF receptor 2, acts on cholinergic nerves to induce epithelial barrier dysfunction. Our study provides evidence that MS stimulates synthesis of acetylcholine, which, together with released CRF, creates a condition conducive to the development of epithelial barrier defects.

Water avoidance stress activates colonic myenteric neurons in female rats

Stress stimulates colonic motor function and plays a role in functional bowel disorders, prevalently in women. We examined, in conscious female rats, the influence of water avoidance stress for 60 min on colonic myenteric neuron activity using immunohistochemical detection of Fos as a marker of neuronal activity. In control rats, Fos immunoreactive nuclei were rare in proximal and distal colon and no defecation was observed. Water avoidance stimulated fecal pellet output, which was associated with Fos expression in myenteric ganglia of proximal and distal colon including in a population of peripheral choline acetyltransferase-immunoreactive neurons. Atropine blocked fecal pellet output but not Fos expression in myenteric ganglia. These results indicate that psychological stress stimulates the activity of colonic cholinergic myenteric neurons.

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.

Primary sensory neurons containing choline acetyltransferase of the peripheral type in the rat trigeminal ganglion and their relation to neuropeptides-, calbindin- and nitric oxide synthase-containing cells

We have previously demonstrated that a variant form of choline acetyltransferase (pChAT) is expressed in rat trigeminal neurons. To assess the significance of pChAT in sensory functions, we characterized immunohistochemically pChAT-positive trigeminal neurons in the rat. pChAT-immunoreactivity was observed in a rather uniform pattern in about half of all trigeminal neurons throughout the trigeminal ganglion. The majority of pChAT-positive neurons had small to medium-sized cell bodies. Double immunofluorescent study showed that more than 90% of substance P (SP)-positive trigeminal cells and about 80% of calcitonin gene-related peptide (CGRP)-positive cells exhibited pChAT-immunoreactivity. pChAT-positive cells formed a larger population of neurons than SP-positive or CGRP-positive cells, but they were a different population from calbindin-D(28k)-positive neurons. In addition, pChAT-immunoreactivity was present in a subset of neurons positive for neuronal nitric oxide synthase. The present results suggest that pChAT plays roles not only in nociception, but also in other sensory functions such as mechanoreception mediating tactile sensation.

Quantification of subclasses of human colonic myenteric neurons by immunoreactivity to Hu, choline acetyltransferase and nitric oxide synthase

An accurate method to count human enteric neurons is essential to develop a comprehensive account of the classes of nerve cells responsible for gut function and dysfunction. The majority of cells in the enteric nervous system utilize acetyl choline, or nitric oxide, or a combination of these, as neurotransmitters. Antisera raised against the RNA-binding protein Hu, were used to identify nerve cell bodies in whole mounts of the myenteric plexus of human colon, and then were utilized to analyse cells immunoreactive for combinations of choline acetyltransferase and nitric oxide synthase. Antisera to Hu provided a reliable means to count apparently all enteric nerve cell bodies, revealing 10% more cell bodies than labelling with neuron specific enolase, and no labelling of glial cells as revealed by S100. ChAT+/NOS- neurons accounted for 48% (+/-3%) of myenteric neurons and ChAT-/NOS+ neurons accounted for 43% (+/-2.5%). ChAT+/NOS+ neurons comprised 4% (+/-0.5) of the total number of neurons, and a novel class of small ChAT-/NOS- neurons, making up 5% (+/-0.9%) of all cells, was described for the first time.

5-Hydroxytryptophan activates colonic myenteric neurons and propulsive motor function through 5-HT4 receptors in conscious mice

Serotonin [5-hydroxytryptamine (5-HT)] acts as a modulator of colonic motility and secretion. We characterized the action of the 5-HT precursor 5-hydroxytryptophan (5-HTP) on colonic myenteric neurons and propulsive motor activity in conscious mice. Fos immunoreactivity (IR), used as a marker of neuronal activation, was monitored in longitudinal muscle/myenteric plexus whole mount preparations of the distal colon 90 min after an intraperitoneal injection of 5-HTP. Double staining of Fos IR with peripheral choline acetyltransferase (pChAT) IR or NADPH-diaphorase activity was performed. The injection of 5-HTP (0.5, 1, 5, or 10 mg/kg ip) increased fecal pellet output and fluid content in a dose-related manner, with a peak response observed within the first 15 min postinjection. 5-HTP (0.5-10 mg/kg) dose dependently increased Fos expression in myenteric neurons, with a maximal response of 9.9 +/- 1.0 cells/ganglion [P < 0.05 vs. vehicle-treated mice (2.3 +/- 0.6 cells/ganglion)]. There was a positive correlation between Fos expression and fecal output. Of Fos-positive ganglionic cells, 40 +/- 4% were also pChAT positive and 21 +/- 5% were NADPH-diaphorase positive in response to 5-HTP, respectively. 5-HTP-induced defecation and Fos expression were completely prevented by pretreatment with the selective 5-HT4 antagonist RS-39604. These results show that 5-HTP injected peripherally increases Fos expression in different populations of cholinergic and nitrergic myenteric neurons in the distal colon and stimulates propulsive colonic motor function through 5-HT4 receptors in conscious mice. These findings suggest an important role of activation of colonic myenteric neurons in the 5-HT4 receptor-mediated colonic propulsive motor response.

Demonstration of Choline Acetyltransferase of a Peripheral Type in the Rat Heart

Cholinergic innervation of the heart has been analyzed using cholinergic markers including acetylcholinesterase, choline acetyltransferase (ChAT), and vesicular acetylcholine transporter (VAChT). In the present study we demonstrate putative cholinergic nerves in the rat heart using an antibody to ChAT of a peripheral type (pChAT), which is the product of a splice variant of ChAT mRNA and preferentially localized to peripheral cholinergic nerves. Expression of mRNAs for pChAT and the conventional form of ChAT (cChAT) were verified in the rat atrium by RT-PCR. Localization of both protein products in the atrium was confirmed by Western blotting. Virtually all neurons and small intensely fluorescent cells in the intrinsic cardiac ganglia were stained immunohistochemically for pChAT. The density of pChAT-positive fibers was very high in the conducting system, high in both atria, the right atrium in particular, and low in the ventricular walls. pChAT and VAChT immunoreactivities were closely associated in some fibers and fiber bundles in the ventricular walls. These results indicate that intrinsic cardiac neurons homogeneously express both pChAT and cChAT. Furthermore, innervation of the ventricular walls by pChAT- and VAChT-positive fibers provides morphological evidence for a significant role of cholinergic mechanisms in ventricular functions.

High affinity choline transporter immunoreactivity in rat ileum myenteric nerves

Recently, an antibody against the choline transporter (CHT), an essential molecule involved in ACh uptake, was used to label cholinergic nerves in the central nervous system; however, the enteric nervous system (ENS) was not examined. The present study localised CHT immunoreactivity (CHT-IR) within the rat ileum ENS and determined whether it colocalised with immunoreactivity for markers of cholinergic, tachykinergic and nitrergic circuitry. Segments of rat ileum were fixed, prepared for sectioning or whole-mounts and incubated with anti-CHT antisera followed by a fluorescent secondary antibody. Samples were double-labelled with antibodies to nitric oxide synthase, substance P (SP), common choline acetyltransferase (cChAT) and vesicular acetylcholine transporter (VAChT). CHT-IR was present in varicosities of nerve fibres in the myenteric plexus and muscle layers of rat ileum. In the myenteric ganglia, CHT-IR was found in nerve fibres and the cytoplasm of some nerve cell bodies. In the myenteric ganglia, no CHT/cChAT-immunoreactive neurons were present. A small number of CHT/SP-immunoreactive neurons and CHT/SP-immunoreactive nerve fibres clustered around unlabelled neurons. CHT-IR colocalised with VAChT-IR in the myenteric plexus but only half of the CHT-immunoreactive myenteric nerve fibres were VAChT-immunoreactive and half of VAChT-immunoreactive fibres were CHT-immunoreactive. In the circular muscle, 75% of CHT-immunoreactive fibres were VAChT-immunoreactive. Thus, the anti-CHT antiserum labels neurons and nerve fibres in the rat ENS. It does not label cholinergic cChAT-immunoreactive neurons, although it does immunostain cholinergic VAChT-immunoreactive nerve fibres and a population of nerves that are not VAChT-immunoreactive.

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

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

Localization of Fibroblast Growth Factor-1 in Cholinergic Neurons Innervating the Rat Larynx

Cholinergic neurons in the dorsal motor nucleus of the vagus (DMNV) are particularly vulnerable to laryngeal nerve damage, possibly because they lack fibroblast growth factor-1 (FGF1). To test this hypothesis, we investigated the localization of FGF1 in cholinergic neurons innervating the rat larynx by immunohistochemistry using central-type antibodies to choline acetyltransferase (cChAT) and peripheral type (pChAT) antibodies, as well as tracer experiments. In the DMNV, only 9% of cChAT-positive neurons contained FGF1, and 71% of FGF1-positive neurons colocalized with cChAT. In the nucleus ambiguus, 100% of cChAT-positive neurons were FGF1 positive. In the intralaryngeal ganglia, all ganglionic neurons contained both pChAT and FGF1. In the nodose ganglia, 66% of pChAT-positive neurons were also positive for FGF1, and 90% of FGF1-positive ganglionic cells displayed pChAT immunoreactivity. Neuronal tracing using cholera toxin B subunit (CTb) demonstrated that cholinergic neurons sending their axons from the DMNV and nucleus ambiguus to the superior laryngeal nerve were FGF1 negative and FGF1 positive, respectively. In the nodose ganglia, some FGF1-positive cells were labeled with CTb. The results indicate that for innervation of the rat larynx, FGF1 is localized to motor neurons, postganglionic parasympathetic neurons, and sensory neurons, but expression is very low in preganglionic parasympathetic cholinergic neurons.

Role of brainstem TRH/TRH-R1 receptors in the vagal gastric cholinergic response to various stimuli including sham-feeding

Pavlov's pioneering work established that sham-feeding induced by sight or smell of food or feeding in dogs with permanent esophagostomy stimulates gastric acid secretion through vagal pathways. Brain circuitries and transmitters involved in the central vagal regulation of gastric function have recently been unraveled. Neurons in the dorsal vagal complex including the dorsal motor nucleus of the vagus (DMN) express thyrotropin-releasing hormone (TRH) receptor and are innervated by TRH fibers originating from TRH synthesizing neurons in the raphe pallidus, raphe obscurus and the parapyramidal regions. TRH injected into the DMN or cisterna magna increases the firing of DMN neurons and gastric vagal efferent discharge, activates cholinergic neurons in gastric submucosal and myenteric plexuses, and induces a vagal-dependent, atropine-sensitive stimulation of gastric secretory (acid, pepsin) and motor functions. TRH antibody or TRH-R1 receptor oligodeoxynucleotide antisense pretreatment in the cisterna magna or DMN abolished vagal-dependent gastric secretory and motor responses to sham-feeding, 2-deoxy-D-glucose, cold exposure and chemical activation of cell bodies in medullary raphe nuclei. TRH excitatory action in the DMN is potentiated by co-released prepro-TRH-(160-169) flanking peptide, Ps4 and 5-HT, and inhibited by a number of peptides involved in the stress/immune response and inhibition of food-intake. These neuroanatomical, electrophysiological and neuropharmacological data are consistent with a physiological role of brainstem TRH in the central vagal stimulation of gastric myenteric cholinergic neurons in response to several vagal dependent stimuli including sham-feeding.

Expression and effects of metabotropic CRF1 and CRF2 receptors in rat small intestine

Corticotropin-releasing factor (CRF)-like peptides mediate their effects via two receptor subtypes, CRF1 and CRF2; these receptors have functional implication in the motility of the stomach and colon in rats. We evaluated expression and functions of CRF1 and CRF2 receptors in the rat small intestine (i.e., duodenum and ileum). CRF(1-2)-like immunoreactivity (CRF(1-2)-LI) was localized in fibers and neurons of the myenteric and submucosal ganglia. CRF(1-2)-LI was found in nerve fibers of the longitudinal and circular muscle layers, in the mucosa, and in mucosal cells. Quantitative RT-PCR showed a stronger expression of CRF2 than CRF1 in the ileum, whereas CRF1 expression was higher than CRF2 expression in the duodenum. Functional studies showed that CRF-like peptides increased duodenal phasic contractions and reduced ileal contractions. CRF1 antagonists (CP-154,526 and SSR125543Q) blocked CRF-like peptide-induced activation of duodenal motility but did not block CRF-like peptide-induced inhibition of ileal motility. In contrast, a CRF2 inhibitor (astressin2-B) blocked the effects of CRF-like peptides on ileal muscle contractions but did not influence CRF-like peptide-induced activation of duodenal motility. These results demonstrate the presence of CRF(1-2) in the intestine and demonstrate that, in vitro, CRF-like peptides stimulate the contractile activity of the duodenum through CRF1 receptor while inhibiting phasic contractions of the ileum through CRF2 receptor. These results strongly suggest that CRF-like peptides play a major role in the regulatory mechanisms that underlie the neural control of small intestinal motility through CRF receptors.

Rat choline acetyltransferase of the peripheral type differs from that of the common type in intracellular translocation

Choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine, has been implicated to involve multiple isoforms of ChAT mRNA in several animals. Since these isoforms are mostly non-coding splice variants, only a homologous ChAT protein of about 68 kDa has been shown to be produced in vivo. Recent evidence indicates the existence of a protein coding splice variant of ChAT mRNA, which lacks exons 6-9 of the rat ChAT gene. The encoded protein was designated ChAT of a peripheral type (pChAT), because of its preferential expression in the peripheral nervous system as confirmed by Western blot and immunohistochemistry. However, functional significance of pChAT is unknown. To obtain a clue to this question, we examined a possible difference in intracellular trafficking between pChAT and the well-known ChAT of the common type (cChAT) using green fluorescent protein (GFP) in living human embryonic kidney cells. Confocal laser scanning microscopy revealed that pChAT-GFP was detectable in the cytoplasm but not in the nucleus, whereas cChAT-GFP was found in both cytoplasm and nucleus. Following treatment with leptomycin B, a nuclear export pathway inhibitor, pChAT-GFP became detectable in both cytoplasm and nucleus, indicating that pChAT can be translocated to the nucleus. In contrast, the leptomycin B treatment did not seem to affect the content of intranuclear cChAT-GFP. After incubation with protein kinase C inhibitors, enhanced accumulation of pChAT-GFP but not cChAT-GFP occurred in the nucleus. These results clearly indicate that pChAT varies from cChAT in intracellular transportation, probably reflecting the difference in physiological roles between pChAT and cChAT.

Central vagal stimulation activates enteric cholinergic neurons in the stomach and VIP neurons in the duodenum in conscious rats

The influence of central vagal stimulation induced by 2h cold exposure or intracisternal injection of thyrotropin-releasing hormone (TRH) analog, RX-77368, on gastro-duodenal enteric cholinergic neuronal activity was assessed in conscious rats with Fos and peripheral choline acetyltransferase (pChAT) immunoreactivity (IR). pChAT-IR was detected in 68%, 70% and 73% of corpus, antrum and duodenum submucosal neurons, respectively, and in 65% of gastric and 46% of duodenal myenteric neurons. Cold and RX-77368 induced Fos-IR in over 90% of gastric submucosal and myenteric neurons, while in duodenum only 25-27% of submucosal and 50-51% myenteric duodenal neurons were Fos positive. In the stomach, cold induced Fos-IR in 93% of submucosal and 97% of myenteric pChAT-IR neurons, while in the duodenum only 7% submucosal and 5% myenteric pChAT-IR neurons were Fos positive. In the duodenum, cold induced Fos in 91% of submucosal and 99% of myenteric VIP-IR neurons. RX-77368 induces similar percentages of Fos/pChAT-IR and Fos/VIP-IR neurons. These results indicate that increased central vagal outflow activates cholinergic neurons in the stomach while in the duodenum, VIP neurons are preferentially stimulated.

Co-expression pattern of neuronal nitric oxide synthase and two variants of choline acetyltransferase in myenteric neurons of porcine ileum

Cholinergic enteric neurons were demonstrated immunohistochemically so far by using antibodies staining the common choline acetyltransferase (cChAT) in neurons of the central nervous system. The results of staining in the enteric nervous system of various species were, however, not satisfactory. We describe here findings obtained with a newly raised antibody against a peripheral variant of choline acetyltransferase (pChAT) in myenteric neurons of the pig small intestine. Triple labelling for pChAT/cChAT/neuronal nitric oxide synthase (nNOS) revealed 19.7% of 1664 neurons (within 40 ganglia) to be immunoreactive exclusively for pChAT whereas 29.6% were positive for cChAT alone and 18.8% were reactive only for nNOS. Colocalization of pChAT and cChAT was found in 22.4%, of pChAT and nNOS in 8.1% and of cChAT and nNOS in 1.4%. All three markers were simultaneously found in only 1 of 1664 neurons. To investigate the presence and possible colocalization of the above markers within morphologically defined neuron types, triple labelling of cChAT or nNOS with pChAT and a neurofilament (NF) antibody pool was applied and the coexpression patterns of pChAT and cChAT as well as of pChAT and nNOS in 120 neurons of each type were recorded. All type I, II, IV and V neurons displayed immunoreactivity either for one or both cholinergic markers. These neuron types were considered to be cholinergic. All type VI neurons, a descending neuron population, were negative for cChAT but positive for nNOS. However, 95% were immunoreactive for both pChAT and nNOS. The physiological significance of the possible co-existence of acetylcholine and nitric oxide within type VI neurons remains to be clarified. It is concluded that the pChAT and cChAT antibodies used here recognize partly different populations of enteric neurons in the pig. Thus, for total immunohistochemical characterization of cholinergic enteric neurons both forms of choline acetyltransferase have to be considered.

Autonomic microganglion cells: a source of acetylcholine in the rat carotid body

Hypoxic chemosensitivity of peripheral arterial chemoreceptors and the ventilatory response to O2 deprivation increases with postnatal development. Multiple putative neurotransmitters, which are synthesized in the carotid body (CB), are thought to mediate signals generated by hypoxia. Acetylcholine (ACh) is believed to be a major excitatory neurotransmitter participating in hypoxic chemosensitivity. However, it is not known whether ACh originates from type I cells in the CB. In these studies, we tested the hypothesis that choline acetyltransferase (ChAT) and vesicular ACh transporter (VAChT) mRNAs are expressed in the CB and that mRNA levels would increase with postnatal maturation or exposure to hypoxia. Semiquantitative in situ hybridization histochemistry and immunohistochemistry were used to localize cholinergic markers within neurons and cells of the rat CB, the nodose-petrosal-jugular ganglion complex, and the superior cervical ganglion up to postnatal day 28. We show that the pattern of distribution, in tissue sections, is similar for both ACh markers; however, the level of VAChT mRNA is uniformly greater than that of ChAT. VAChT mRNA and immunoreactivity are detected abundantly in the nodose-petrosal-jugular ganglion complex in a number of microganglion cells embedded in nerve fibers innervating the CB for all postnatal groups, whereas ChAT mRNA is detected in only a few of these cells. Contrary to our hypothesis, postnatal maturation caused a reduction in ACh trait expression, whereas hypoxic exposure did not induce the upregulation of VAChT and ChAT mRNA levels in the CB, microganglion, or within the ganglion complex. The present findings indicate that the source of ACh in the CB is likely within autonomic microganglion cells and cholinergic nerve terminals.

Innervation of rat iris by trigeminal and ciliary neurons expressing pChAT, a novel splice variant of choline acetyltransferase

We have recently discovered a splice variant of choline acetyltransferase (ChAT) mRNA and designated the variant protein pChAT because of its preferential expression in peripheral neuronal structures. In this study, the presence of pChAT in rat iris was examined by immunohistochemistry and Western blot using a pChAT antiserum, in combination with RT-PCR analysis and ChAT enzyme assay. For comparison, the conventional ChAT (cChAT) was studied in parallel. By pChAT immunohistochemistry, intense labeling was found to occur in nerve fibers of the iris and in neurons of the ciliary and trigeminal ganglia. Denervation studies, analyzed by semiquantitative morphometry, indicated that these iridial pChAT fibers originated about half from the ciliary ganglion and the other half from the trigeminal ganglion. The presence of pChAT protein in the iris and trigeminal ganglion was confirmed by Western blot. The expression of pChAT mRNA in the ciliary and trigeminal ganglia was proved by RT-PCR. Although cChAT protein and mRNA were detected in the ciliary ganglion, neither was detectable in the trigeminal ganglion. The contributions of the ciliary and trigeminal ganglia to the iridial ChAT enzyme activity were verified by the present ChAT assay. Here, we provide evidence that iridial pChAT nerves are composed of postganglionic parasympathetic efferents from the ciliary ganglion and, more interestingly, somatic sensory afferents of the trigeminal ophthalmic nerve.