Partial, selective survival of nitrergic neurons in chagasic megacolon

One frequent chronic syndrome of Chagas’ disease is megacolon, an irreversible dilation of a colonic segment. Extensive enteric neuron loss in the affected segment is regarded as key factor for deficient motility. Here, we assessed the quantitative balance between cholinergic and nitrergic neurons representing the main limbs of excitatory and inhibitory colonic motor innervation, respectively. From surgically removed megacolonic segments of four patients, each three myenteric wholemounts (from non-dilated oral, megacolonic and non-dilated anal parts) was immunohistochemically triple-stained for choline acetyltransferase, neuronal nitric oxide synthase (NOS) and the panneuronal human neuronal protein Hu C/D. Degenerative changes were most pronounced in the megacolonic and anal regions, e.g. bulked, honeycomb-like ganglia with few neurons which were partly enlarged or atrophic or vacuolated. Neuron counts from each 15 ganglia of 12 megacolonic wholemounts were compared with those of 12 age- and region-matched controls. Extensive neuron loss, mainly in megacolonic and anal wholemounts, was obvious. In all three regions derived from megacolonic samples, the proportion of NOS-positive neurons (control: 55%) was significantly increased: in non-dilated oral parts to 61% (p = 0.003), in megacolonic regions to 72% (p < 0.001) and in non-dilated anal regions to 78% (p < 0.001). We suggest the chronic dilation of megacolonic specimens to be due to the preponderance of the nitrergic, inhibitory input to the intestinal muscle. However, the observed neuronal imbalance was not restricted to the dilated regions: the non-dilated anal parts may be innervated by ascending, cholinergic axons emerging from less affected, more anally located regions.

Autonomic control of the eye and the iris

The vertebrate eye receives innervation from ciliary and pterygopalatine parasympathetic and cervical sympathetic ganglia as well as sensory trigeminal axons. The sympathetic and parasympathetic pathways represent the classical "core" of neural regulation of ocular homeostasis. Sensory trigeminal neurons are also involved in autonomic regulation by both providing the afferent limb of various reflexes and exerting their peptide-mediated local effector function. This arrangement is remarkably conserved throughout vertebrate classes although significant modifications are observed in anamniotes, in particular their irises. In higher primates and birds, intrinsic choroidal neurons emerged as a significant additional innervation component. They most likely mediate local vascular regulation and other local homeostatic tasks in foveate eyes. This review across the vertebrate classes outfolds the complex neuronal regulatory underpinnings across vertebrates that ensure proper visual function.

Quantitative estimation and chemical coding of spiny type I neurons in human intestines

Previous studies have shown that most human myenteric neurons co-staining for vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS) and neurofilaments (NF) display the morphology of spiny type I neurons displaying a descending projection pattern. Here, we estimated the proportions of spiny neurons in human intestines, the amount of congruence of VIP/nNOS-immunoreactive with spiny neurons and whether galanin (GAL) is co-localized with VIP. Three sets of colchicine-pretreated and fixed whole mounts of 21 patients or body donors (median age 65 years; 10 female, 11 male) were stained for VIP, nNOS and NF, for VIP, nNOS and the human neuronal protein Hu C/D (HU) as well as for VIP, nNOS and GAL. The majority of VIP/nNOS-co-reactive neurons were spiny neurons (79/80% in small/large intestine, respectively) and the majority of spiny neurons co-stained for VIP and nNOS (82/69%). Neurons co-immunoreactive for VIP/nNOS/HU amounted to 7 and 4%, respectively. GAL/VIP-co-immunoreactivity was demonstrated in 69 and 27% of spiny neurons, respectively. We conclude that the number of neurons displaying co-reactivity for VIP and nNOS is a quantitative indicator of spiny neurons in both small and large intestine and that the proportion of spiny neurons is about 7% in small and 4% in large intestines. Since nerve fibres co-staining for NF/VIP/nNOS were found mainly in the circular muscle layer but not the surrounding perikarya of spiny neurons, we suggest that they may represent inhibitory motor neurons rather than descending interneurons.

Neurotrophin-4 dependency of intraepithelial vagal sensory nerve terminals that selectively contact pulmonary NEBs in mice

Important physiological functions of neurotrophins (NTs) in airways and lungs are the early development, differentiation and maintenance of peripheral sensory neurons. The main pulmonary sensory innervation is of vagal origin, with several nerve fibre populations that selectively contact complex morphologically well-characterized receptor end-organs, called neuroepithelial bodies (NEBs). NEBs in mouse lungs are innervated by at least two separate myelinated vagal sensory nerve fibre populations, of which the neurochemical coding is suggestive of a mechanosensory function. Since neurotrophin-4 (NT-4) has been especially described to be important for the maintenance of mechanosensory nerve terminals, the present study aimed at investigating the NT-4 dependency of the two myelinated vagal sensory nerve fibre populations innervating mouse pulmonary NEBs. Multiple immunostaining in 21-day-old and adult mouse lungs revealed the expression of the NT-4 receptor TrkB on the two different myelinated vagal sensory nerve fibre populations, i.e., the vesicular glutamate transporter/calbindin-positive and the P2X2/3-positive fibres, which selectively contact pulmonary NEBs. Examination of the effect of the lack of NT-4 on these NEB-related nerve fibre populations, by comparing adult NT-4-/- and wild-type mice, revealed that in NT-4-/- mice the percentage of NEBs contacted by P2X2/3+ is reduced by 75%, while the VGLUT+/CB+ population seemed to be unaffected. This study demonstrated that although mouse pulmonary NEBs are contacted by two distinct TrkB expressing populations of vagal myelinated afferents, only one is distinctly reduced in NT-4 deficient mice, suggesting the involvement of NTs. In view of the growing evidence for the involvement of NTs in neuronal plasticity associated with airway diseases, pulmonary NEBs innervated by NT-sensitive vagal afferents may play a significant role.

Low proliferation and differentiation capacities of adult hippocampal stem cells correlate with memory dysfunction in humans

The hippocampal dentate gyrus maintains its capacity to generate new neurons throughout life. In animal models, hippocampal neurogenesis is increased by cognitive tasks, and experimental ablation of neurogenesis disrupts specific modalities of learning and memory. In humans, the impact of neurogenesis on cognition remains unclear. Here, we assessed the neurogenic potential in the human hippocampal dentate gyrus by isolating adult human neural stem cells from 23 surgical en bloc hippocampus resections. After proliferation of the progenitor cell pool in vitro we identified two distinct patterns. Adult human neural stem cells with a high proliferation capacity were obtained in 11 patients. Most of the cells in the high proliferation capacity cultures were capable of neuronal differentiation (53 ± 13% of in vitro cell population). A low proliferation capacity was observed in 12 specimens, and only few cells differentiated into neurons (4 ± 2%). This was reflected by reduced numbers of proliferating cells in vivo as well as granule cells immunoreactive for doublecortin, brain-derived neurotrophic factor and cyclin-dependent kinase 5 in the low proliferation capacity group. High and low proliferation capacity groups differed dramatically in declarative memory tasks. Patients with high proliferation capacity stem cells had a normal memory performance prior to epilepsy surgery, while patients with low proliferation capacity stem cells showed severe learning and memory impairment. Histopathological examination revealed a highly significant correlation between granule cell loss in the dentate gyrus and the same patient's regenerative capacity in vitro (r = 0.813; P < 0.001; linear regression: R²(adjusted) = 0.635), as well as the same patient's ability to store and recall new memories (r = 0.966; P = 0.001; linear regression: R²(adjusted) = 0.9). Our results suggest that encoding new memories is related to the regenerative capacity of the hippocampus in the human brain.

Effect of an herbal preparation, STW 5, in an acute model of reflux oesophagitis in rats

A multitarget herbal preparation, STW 5, has been used clinically in different gastro-intestinal disorders including functional dyspepsia and irritable bowel syndrome. Previous studies have shown that it possesses properties that may render it useful in gastro-oesophageal reflux disease (GERD). We performed this study to test this compound in an acute model of reflux oesophagitis in rats. Oesophagitis was induced surgically by ligating the pyloric end and fore-stomach. Lower oesophageal pH was measured 3 h later in conscious animals. Five hours after surgery, animals were sacrificed and the oesophagi were examined macroscopically and histologically. Selected markers of inflammation were measured in oesophageal homogenates. STW 5 was given orally for 5 days before induction of oesophagitis. Pantoprazole was used as a reference standard. Ligated animals showed a high incidence of ulcerative lesions associated with a marked increase in myeloperoxidase, thiobarbituric acid-reactive substances, tumor necrosis factor-alpha, and interleukin-1beta. STW 5 did not affect oesophageal pH, but dose-dependently reduced the severity of the oesophageal lesions and normalized the deranged level of the inflammation markers. The beneficial effects were confirmed histopathologically. STW 5 proved to be effective in protecting against inflammatory lesions in this model of oesophagitis, thus warranting further investigation of its potential therapeutic usefulness in GERD.

BK channels control cerebellar Purkinje and Golgi cell rhythmicity in vivo

Calcium signaling plays a central role in normal CNS functioning and dysfunction. As cerebellar Purkinje cells express the major regulatory elements of calcium control and represent the sole integrative output of the cerebellar cortex, changes in neural activity- and calcium-mediated membrane properties of these cells are expected to provide important insights into both intrinsic and network physiology of the cerebellum. We studied the electrophysiological behavior of Purkinje cells in genetically engineered alert mice that do not express BK calcium-activated potassium channels and in wild-type mice with pharmacological BK inactivation. We confirmed BK expression in Purkinje cells and also demonstrated it in Golgi cells. We demonstrated that either genetic or pharmacological BK inactivation leads to ataxia and to the emergence of a beta oscillatory field potential in the cerebellar cortex. This oscillation is correlated with enhanced rhythmicity and synchronicity of both Purkinje and Golgi cells. We hypothesize that the temporal coding modification of the spike firing of both Purkinje and Golgi cells leads to the pharmacologically or genetically induced ataxia.

Do distinct populations of dorsal root ganglion neurons account for the sensory peptidergic innervation of the kidney?

Peptidergic afferent renal nerves (PARN) have been linked to kidney damage in hypertension and nephritis. Neither the receptors nor the signals controlling local release of neurokinines [calcitonin gene-related peptide (CGRP) and substance P (SP)] and signal transmission to the brain are well-understood. We tested the hypothesis that PARN, compared with nonrenal afferents (Non-RN), are more sensitive to acidic stimulation via transient receptor potential vanilloid type 1 (TRPV1) channels and exhibit a distinctive firing pattern. PARN were distinguished from Non-RN by fluorescent labeling (DiI) and studied by in vitro patch-clamp techniques in dorsal root ganglion neurons (DRG; T11-L2). Acid-induced currents or firing due to current injection or acidic superfusion were studied in 252 neurons, harvested from 12 Sprague-Dawley rats. PARN showed higher acid-induced currents than Non-RN (transient: 15.9 ± 5.1 vs. 0.4 ± 0.2* pA/pF at pH 6; sustained: 20.0 ± 4.5 vs. 6.2 ± 1.2* pA/pF at pH 5; * P < 0.05). The TRPV1 antagonist capsazepine inhibited sustained, amiloride-transient currents. Forty-eight percent of PARN were classified as tonic neurons (TN = sustained firing during current injection), and 52% were phasic (PN = transient firing). Non-RN were rarely tonic (15%), but more frequently phasic (85%), than PARN ( P < 0.001). TN were more frequently acid-sensitive than PN (50–70 vs. 2–20%, P < 0.01). Furthermore, renal PN were more frequently acid-sensitive than nonrenal PN (20 vs. 2%, P < 0.01). Confocal microscopy revealed innervation of renal vessels, tubules, and glomeruli by CGRP- and partly SP-positive fibers coexpressing TRPV1. Our data show that PARN are represented by a very distinct population of small-to-medium sized DRG neurons exhibiting more frequently tonic firing and TRPV1-mediated acid sensitivity. These very distinct DRG neurons might play a pivotal role in renal physiology and disease.

The influence of concentric and eccentric loading on the finger pulley system

In this study we investigated the influence of the loading condition (concentric vs. eccentric loading) on the pulley system of the finger. For this purpose 39 cadaver finger (14 hands, 10 donors) were fixed into an isokinetic loading device. The forces in the flexor tendons and at the fingertip were recorded. In the concentric loading condition A2 and A4 ruptures as well as alternative events such as fracture of a phalanx or avulsion of the flexor tendons were almost equally distributed, whereas the A2 pulley rupture was the most common event (59%) in the eccentric loading condition and alternative events were rare (23.5%). The forces in the deep flexor tendon, the fingertip and in the pulleys were significantly lower in the eccentric loading condition. As the ruptures occurred at lower loads in the eccentric than in the concentric loading condition it can be concluded that friction may be an advantage for climbers, supporting the holding force of their flexor muscles but may also increase the susceptibility to injury.

The influence of concentric and eccentric loading on the finger pulley system

In this study we investigated the influence of the loading condition (concentric vs. eccentric loading) on the pulley system of the finger. For this purpose 39 cadaver finger (14 hands, 10 donors) were fixed into an isokinetic loading device. The forces in the flexor tendons and at the fingertip were recorded. In the concentric loading condition A2 and A4 ruptures as well as alternative events such as fracture of a phalanx or avulsion of the flexor tendons were almost equally distributed, whereas the A2 pulley rupture was the most common event (59%) in the eccentric loading condition and alternative events were rare (23.5%). The forces in the deep flexor tendon, the fingertip and in the pulleys were significantly lower in the eccentric loading condition. As the ruptures occurred at lower loads in the eccentric than in the concentric loading condition it can be concluded that friction may be an advantage for climbers, supporting the holding force of their flexor muscles but may also increase the susceptibility to injury.

Increase in NADPH-Diaphorase-Positive and Neuronal NO Synthase Immunoreactive Neurons in the Rat Spinal Trigeminal Nucleus Following Infusion of a NO Donor—Evidence for a Feed-Forward Process in NO Production Involved in Trigeminal Nociception

Nitric oxide (NO) donors, which cause delayed headaches in migraineurs, have been shown to activate central trigeminal neurons with meningeal afferent input in animal experiments. Previous reports indicate that this response may be due to up-regulation of NO-producing cells in the trigeminal brainstem. To investigate this phenomenon further, we determined nitric oxide synthase (NOS)-containing neurons in the rat spinal trigeminal nucleus (STN), the projection site of nociceptive trigeminal afferents, following infusion of the NO donor sodium nitroprusside (SNP). Barbiturate anaesthetized rats were infused intravenously with SNP (50 μg/kg) or vehicle for 20 min or 2 h, and after periods of 3–8 h fixed by perfusion. Cryostat sections of the medulla oblongata containing the caudal STN were histochemically processed for detection of nicotineamide adenine dinucleotide phosphate (NADPH)-diaphorase or immunohistochemically stained for NOS isoforms and examined by light and fluorescence microscopy. The number of neurons positive for these markers was determined. Various forms of neurons positive for NADPH-diaphorase or immunoreactive to neuronal NOS (nNOS) were found in superficial and deep laminae of the STN caudalis and around the central canal. Neurons were not immunopositive for endothelial (eNOS) or inducible (iNOS) NOS isoforms. The number of NADPH-diaphorase-positive neurons increased time dependently after SNP infusion by a factor of more than two. Likewise, the number of nNOS-immunopositive neurons was increased after SNP compared with vehicle infusion. Around the central canal the number of NADPH-diaphorase-positive neurons was slightly increased and the number of nNOS+ neurons not changed after SNP treatment. NO donors increase the number of neurons that produce NO in the STN, possibly by induction of nNOS expression. Increased NO production may facilitate neurotransmitter release and promote nociceptive transmission in the STN. This mechanism may explain the delayed increase in neuronal activity and headache after infusion of NO donors.

Cell death induced by uridine 5'-triphosphate (UTP) in contrast to adenosine 5'-triphosphate (ATP) in human epidermoid carcinoma cells (A-431)

OBJECTIVE

Extracellular ATP has been reported as an important signaling molecule mediating quite divergent specific biological effects. Recent clinical trials suggest a potential role of ATP in cancer treatment. The aim of our study was to analyze the mechanisms of UTP in comparison to ATP-mediated cell death in an established cell line model (A-431).

METHODS

Cell culture and proliferation assays, separation of nucleotides by thin-layer technique, measurement of cytosolic free Ca(2+), flow cytometry analysis (annexin V), ultra structure, semi-quantitative RT-PCR, standard statistics.

RESULTS

ATP, when added as a single dose between 100 and 500 microM to A-431 cell cultures, showed increasing cytotoxicity, mainly as apoptosis, with a paradoxically decreasing effect at higher concentrations up to 1500 microM. Doses exceeding 1500 microM again led to increasing cytotoxicity. UTP at doses between 500 and 3000 microM resulted in increasing cell death following a normal sigmoid dose-response model. ATP and UTP were degraded by membrane-bound ectoenzymes. ATP degradation products, e.g. adenosine, also induced cell death. Dipyridamole, an adenosine uptake inhibitor, was able to abolish ATP toxicity, which was also counteracted by the addition of uridine. In addition, we found functional and transcriptional evidence for P2 receptors on A-431 cells.

CONCLUSION

Extracellular ATP seems to act via degradation to adenosine and consecutive induction of apoptosis. In contrast, we were not able to demonstrate analogous mechanisms for cell death mediated by extracellular UTP, but were able to provide some evidence of classical ligand-receptor action of uncleaved UTP on A-431 cells.

Autonomic renal denervation ameliorates experimental glomerulonephritis

Increasing evidence indicates that inflammation of visceral organs is significantly affected by the autonomic nervous system. Such neuroimmune interactions have not been studied in the kidney. Here, we show that the rat kidney is innervated by both tyrosine hydroxylase-positive sympathetic efferent nerve fibers and calcitonin gene-related peptide-positive primary afferent nerve fibers, both of which are found in proximity to macrophages and dendritic cells. Complete surgical bilateral renal denervation was performed 2 d before glomerulonephritis was induced by injecting the monoclonal anti-Thy-1.1 antibody OX-7. Denervation significantly reduced albuminuria, mesangiolysis, formation of microaneurysms, deposition of glomerular collagen IV, and expression of TGF-beta compared with sham-operated controls. Accordingly, inflammation, identified by accumulation of interstitial macrophages and renal expression of TNF-alpha, and mesangial cell proliferation were significantly reduced. These findings indicate that autonomic renal denervation ameliorates and, by inference, innervation exacerbates acute inflammation in the kidney; therefore, neurotransmitters or neuropeptides and their receptors might represent novel targets for the treatment of acute glomerulonephritis.

Inducible knockout mutagenesis reveals compensatory mechanisms elicited by constitutive BK channel deficiency in overactive murine bladder

The large-conductance, voltage-dependent and Ca(2+)-dependent K(+) (BK) channel links membrane depolarization and local increases in cytosolic free Ca(2+) to hyperpolarizing K(+) outward currents, thereby controlling smooth muscle contractility. Constitutive deletion of the BK channel in mice (BK(-/-)) leads to an overactive bladder associated with increased intravesical pressure and frequent micturition, which has been revealed to be a result of detrusor muscle hyperexcitability. Interestingly, time-dependent and smooth muscle-specific deletion of the BK channel (SM-BK(-/-)) caused a more severe phenotype than displayed by constitutive BK(-/-) mice, suggesting that compensatory pathways are active in the latter. In detrusor muscle of BK(-/-) but not SM-BK(-/-) mice, we found reduced L-type Ca(2+) current density and increased expression of cAMP kinase (protein kinase A; PKA), as compared with control mice. Increased expression of PKA in BK(-/-) mice was accompanied by enhanced beta-adrenoceptor/cAMP-mediated suppression of contractions by isoproterenol. This effect was attenuated by about 60-70% in SM-BK(-/-) mice. However, the Rp isomer of adenosine-3',5'-cyclic monophosphorothioate, a blocker of PKA, only partially inhibited enhanced cAMP signaling in BK(-/-) detrusor muscle, suggesting the existence of additional compensatory pathways. To this end, proteome analysis of BK(-/-) urinary bladder tissue was performed, and revealed additional compensatory regulated proteins. Thus, constitutive and inducible deletion of BK channel activity unmasks compensatory mechanisms that are relevant for urinary bladder relaxation.

Quantitative estimation of putative primary afferent neurons in the myenteric plexus of human small intestine

This study aimed at estimating the proportion of human myenteric Dogiel type II neurons, putative intrinsic primary afferent neurons (IPANs), in relation to the entire myenteric neuron population. Since, at present, there is no known single marker, which specifically labels these neurons, we tried to identify the most appropriate marker combination based on the results of an earlier study. For this purpose, 10 wholemounts derived from human small intestinal segments were immunohistochemically triple-stained for calretinin (CALR), somatostatin (SOM) and neurofilaments (NF) and 9 were stained for substance P (SP), SOM and NF. In each wholemount, 15 ganglia selected randomly were evaluated. On the basis of their NF-reactivity, neurons reactive for one or co-reative for both of the other two markers, respectively, were morphologically classified as type II or non-type II neurons. We found that the majorities of neurons co-reactive for CALR/SOM and SP/SOM, respectively, were type II neurons whereas this was not the case for neurons, which were reactive for only one of the two markers. One of the statistical parameters estimated was the positive predictive value, the probability that a neuron displaying CALR/SOM- or SP/SOM-co-reactivity, respectively, is a type II neuron. This value was 97% in case of CALR/SOM- and 95% in case of SP/SOM-co-staining. Although the difference of the statistical parameters between the two stainings was not significant, CALR and SOM were used to estimate indirectly the proportion of type II neurons, in wholemounts co-stained with the pan-neuronal marker neuronal protein HuC/HuD (HU). In these wholemounts, altogether 9.1% of neurons were coreactive for CALR/SOM. We suggest that the proportion of myenteric type II neurons in the human small intestine is related to the proportion of CALR/SOM-co-reactive neurons and may be near to one tenth of the total myenteric neuronal population.

Chemical coding of myenteric neurons with different axonal projection patterns in the porcine ileum

The aim of this study was to perform an immunohistochemical characterization of two different myenteric neuron types of the pig displaying opposite axonal projections. These were type I neurons equipped with lamellar dendrites that projected mainly orally, and type VI neurons that displayed typical axonal dendrites and projected anally. Double immunostainings of longitudinal muscle/myenteric plexus wholemounts from ileal segments of four pigs were performed to visualize neurofilaments (NF) in combination with calcitonin gene-related peptide (CGRP), leu-enkephalin (ENK) and substance P (SP), respectively. Triple immunostainings of wholemounts, using antibodies against neuronal nitric oxide synthase (nNOS) and vasoactive intestinal peptide (VIP) as well as against VIP and galanin (GAL), were performed. We found that 78% of type I neurons immunoreacted to ENK, 21% to CGRP and 24% to SP. The NF-positive type I neurons co-reactive for one of the three above markers displayed mostly frayed outlines of both their somal contours and their broadened dendritic endings. By contrast, most of the non-coreactive type I neurons displayed rather sharply outlined somata and dendrites. No type I neuron immunoreacted to nNOS, VIP or GAL and none of the type VI NF-reactive neurons reacted to CGRP, ENK or SP. All type VI neurons investigated displayed immunoreactivity for nNOS, 92% of which were co-reactive for VIP. Co-reactivity for VIP and GAL was found in 69% of type VI neurons, 21% were positive for VIP but negative for GAL, 9% were negative for both GAL and VIP, and 1% were positive for GAL but negative for VIP. We conclude that there are two subpopulations of morphological type I neurons. One of these displays mainly oral projections and could not be further characterized in this study. The other, which may correspond to neurons innervating the longitudinal and circular muscle layers, were partly immunoreactive for ENK, CGRP and/or SP. Type VI neurons are immunoreactive for nNOS frequently co-localized with VIP and, partly, also GAL. These may be inhibitory motor neurons and are different from VIP/GAL-coreactive minineurons described earlier.

Chemical coding of submucosal type V neurons in porcine ileum

In this study, we attempted to determine the proportion of type V neurons relative to the putative whole neuron population in the two submucosal plexuses of pigs identified by their neurofilament immunoreactivity. The total neuron number was estimated in cuprolinic blue (CB)/anti-Hu protein (HU) costained wholemounts as the sum of the number of CB+/HU+, CB+/HU- and CB-/HU+ neurons. In the external submucosal plexus (ESP), HU labelled 98.6% and CB 97.3% of neurons. In the internal submucosal plexus, HU labelled 98.3%, whereas CB only marked 92.5% of neurons. Furthermore, we investigated the chemical coding of submucosal type V neurons and searched for submucosal, non-type V neurons displaying the same chemical coding as the myenteric type V neurons described earlier, i.e. the colocalization of calcitonin gene-related peptide (CGRP) and somatostatin (SOM). In order to facilitate immunohistochemical detection of neuroactive peptides, ileal segments were pretreated with colchicine prior to fixation. Type V neurons in the ESP occurred either as single cells displaying one or few prominent dendrite(s) or within aggregates displaying a dendritic tangle. In this plexus, type V neurons amounted to between 0.9 and 1.6% of all CB-stained neurons. ESP type V neurons displayed immunoreactivities for choline acetyl transferase (95.8%) and leucine-enkephalin (73.9%). All type V neurons were negative for neuronal nitric oxide synthase. Fifty-eight percent of ESP CGRP/SOM co-immunoreactive neurons displayed type V morphology, whereas 42% were non-type V neurons. Thus, the chemical coding of ESP type V neurons is in principal similar to that of the myenteric type V neurons described earlier. In the internal submucosal plexus, we found no type V neurons. In this plexus, 0.2% of all neurons counterstained with HU displayed CGRP/SOM coreactivity. As had been observed earlier concerning the myenteric type V neurons, ESP type V neurons were also closely apposed by conspicuous accumulations of boutons reactive for the same markers as the neurons themselves. Although we cannot exclude that axons of CGRP/SOM-reactive enteric, non-type V or extrinsic neurons end synaptically on type V neurons, we suggest that the main synaptic input to type V neurons originates from other type V neurons. This presents an argument for an interneuronal role of type V neurons.