The electrophysiological effects of vasoactive intestinal polypeptide in the guinea-pig inferior mesenteric ganglion

A ganglionic intestinointestinal reflex activated by acute noxious challenge

To investigate noxious stimulation-responsive neural circuits that could influence the gut, we recorded from intestinally directed (efferent) nerve filaments dissected from mesenteric nerves close to the small intestine in anesthetized rats. These exhibited baseline multiunit activity that was almost unaffected by vagotomy (VagX) and reduced only slightly by cutting the splanchnic nerves. The activity was halved by hexamethonium (Hex) treatment. When an adjacent gut segment received an intraluminal stimulus 2,4,6-trinitrobenzenesulfonate (TNBS) in 30% ethanol, mesenteric efferent nerve activity increased for more than 1 h. The increased activity was almost unaffected by bilateral vagotomy or splanchnic nerve section, indicating a lack of central nervous involvement, but it was 60% reduced by hexamethonium. Spike sorting discriminated efferent single and predominantly single-unit spike trains that responded to TNBS, were unaffected by splachnectomy but were silenced by hexamethonium. After noxious stimulation of one segment, the adjacent segment showed no evidence of suppression of gut motility or vasoconstriction. We conclude that luminal application of a noxious stimulus to the small intestine activates an entirely peripheral, intestinointestinal reflex pathway. This pathway involves enteric intestinofugal neurons that excite postganglionic sympathetic neurons via a nicotinic synapse. We suggest that the final sympathetic efferent neurons that respond to a tissue damaging stimulus are distinct from vasoconstrictor, secretomotor, and motility inhibiting neurons.NEW & NOTEWORTHY An intraluminal noxious chemical stimulus applied to one segment of small intestine increased mesenteric efferent nerve activity to an adjacent segment. This was identified as a peripheral ganglionic reflex that did not require vagal or spinal connections. Hexamethonium blocked most, but not all, ongoing and reflex mesenteric efferent activity. The prevertebral sympathetic efferent neurons that are activated likely affect inflammatory and immune functions of other gut segments.

Characterization of viscerofugal neurons in human colon by retrograde tracing and multi-layer immunohistochemistry

Background and Aims

Viscerofugal neurons (VFNs) have cell bodies in the myenteric plexus and axons that project to sympathetic prevertebral ganglia. In animals they activate sympathetic motility reflexes and may modulate glucose metabolism and feeding. We used rapid retrograde tracing from colonic nerves to identify VFNs in human colon for the first time, using ex vivo preparations with multi-layer immunohistochemistry.

Methods

Colonic nerves were identified in isolated preparations of human colon and set up for axonal tracing with biotinamide. After fixation, labeled VFN cell bodies were subjected to multiplexed immunohistochemistry for 12 established nerve cell body markers.

Results

Biotinamide tracing filled 903 viscerofugal nerve cell bodies (n = 23), most of which (85%) had axons projecting orally before entering colonic nerves. Morphologically, 97% of VFNs were uni-axonal. Of 215 VFNs studied in detail, 89% expressed ChAT, 13% NOS, 13% calbindin, 9% enkephalin, 7% substance P and 0 of 123 VFNs expressed CART. Few VFNs contained calretinin, VIP, 5HT, CGRP, or NPY. VFNs were often surrounded by dense baskets of axonal varicosities, probably reflecting patterns of connectivity; VAChT+ (cholinergic), SP+ and ENK+ varicosities were most abundant around them. Human VFNs were diverse; showing 27 combinations of immunohistochemical markers, 4 morphological types and a wide range of cell body sizes. However, 69% showed chemical coding, axonal projections, soma-dendritic morphology and connectivity similar to enteric excitatory motor neurons.

Conclusion

Viscerofugal neurons are present in human colon and show very diverse combinations of features. High proportions express ChAT, consistent with cholinergic synaptic outputs onto postganglionic sympathetic neurons in prevertebral ganglia.

Enteric Control of the Sympathetic Nervous System

The autonomic nervous system that regulates the gut is divided into sympathetic (SNS), parasympathetic (PNS), and enteric nervous systems (ENS). They inhibit, permit, and coordinate gastrointestinal motility, respectively. A fourth pathway, "extrinsic sensory neurons," connect gut to the central nervous system, mediating sensation. The ENS resides within the gut wall and its activities are critical for life; ENS failure to populate the gut in development is lethal without intervention."Viscerofugal neurons" are a distinctive class of enteric neurons, being the only type that escapes the gut wall. They form a unique circuit: their axons project out of the gut wall and activate sympathetic neurons, which then project back to the gut, and inhibit gut movements.For 80 years viscerofugal/sympathetic circuits were thought to have a restricted role, mediating simple sensory-motor reflexes. New data shows viscerofugal and sympathetic neurons behaving unexpectedly, compelling a re-evaluation of these circuits: both viscerofugal and sympathetic neurons transmit higher order, synchronized firing patterns that originate within the ENS. This identifies them as driving long-range motility control between different gut regions.There is need for gut motor control over distances beyond the range of ENS circuits, yet no mechanism has been identified to date. The entero-sympathetic circuits are ideally suited to meet this need. Here we provide an overview of the structure and functions of these peripheral sympathetic circuits, including new data showing the firing patterns generated by enteric networks can transmit through sympathetic neurons.

Control of colonic motility using electrical stimulation to modulate enteric neural activity

Electrical stimulation of the enteric nervous system (ENS) is an attractive approach to modify gastrointestinal transit. Colonic motor complexes (CMCs) occur with a periodic rhythm, but the ability to elicit a premature CMC depends, at least in part, upon the intrinsic refractory properties of the ENS, which are presently unknown. The objectives of this study were to record myoelectric complexes (MCs, the electrical correlates of CMCs) in the smooth muscle and 1) determine the refractory periods of MCs, 2) inform and evaluate closed-loop stimulation to repetitively evoke MCs, and 3) identify stimulation methods to suppress MC propagation. We dissected the colon from male and female C57BL/6 mice, preserving the integrity of intrinsic circuitry while removing the extrinsic nerves, and measured properties of spontaneous and evoked MCs in vitro. Hexamethonium abolished spontaneous and evoked MCs, confirming the necessary involvement of the ENS for electrically evoked MCs. Electrical stimulation reduced the mean interval between evoked and spontaneous CMCs (24.6 ± 3.5 vs. 70.6 ± 15.7 s, P = 0.0002, n = 7). The absolute refractory period was 4.3 s (95% confidence interval (CI) = 2.8-5.7 s, R2 = 0.7315, n = 8). Electrical stimulation applied during fluid distention-evoked MCs led to an arrest of MC propagation, and following stimulation, MC propagation resumed at an increased velocity (n = 9). The timing parameters of electrical stimulation increased the rate of evoked MCs and the duration of entrainment of MCs, and the refractory period provides insight into timing considerations for designing neuromodulation strategies to treat colonic dysmotility.NEW & NOTEWORTHY Maintained physiological distension of the isolated mouse colon induces rhythmic cyclic myoelectric complexes (MCs). MCs evoked repeatedly by closed-loop electrical stimulation entrain MCs more frequently than spontaneously occurring MCs. Electrical stimulation delivered at the onset of a contraction temporarily suppresses the propagation of MC contractions. Controlled electrical stimulation can either evoke MCs or temporarily delay MCs in the isolated mouse colon, depending on timing relative to ongoing activity.

Mast cell number, substance P and vasoactive intestinal peptide in irritable bowel syndrome with diarrhea

BACKGROUND

Recent studies have shown that mast cells play an important role in irritable bowel syndrome (IBS). We investigated the relationship between mast cells and the gut hormones substance P and vasoactive intestinal peptide (VIP) in irritable bowel syndrome with diarrhea (IBS-D).

METHODS

Colonoscopic biopsies were performed on the rectal mucosa of 43 subjects (IBS-D patients: 22, healthy volunteers: 21) diagnosed according to the Rome III criteria. Mast cells, and substance P & VIP were evaluated by quantitative immunohistology and image analysis. Mast cells were counted as tryptase-positive cells in the lamina propria, and substance P and VIP levels were expressed as percentages of total areas of staining.

RESULTS

Mast cell counts were higher in IBS-D patients than healthy volunteers (9.6 ± 3.3 vs. 5.7 ± 2.5/high power field (HPF), p < 0.01). Substance P was also elevated (0.11 ± 0.08% vs. 0.03 ± 0.02 %, p < 0.01) while VIP was only high in women with IBS-D. Mast cell counts were positively correlated with levels of substance P & VIP in women but not men (women: r = 0.625, p < 0.01 for substance P and r = 0.651, p < 0.01 for VIP). However, mast cell counts were not correlated with IBS symptoms including abdominal pain.

CONCLUSION

Mast cells are activated leading to the raised levels of substance P & VIP in IBS-D patients. However, the correlation between mast cells and levels of substance P & VIP differs according to gender.

The enteric nervous system and neurogastroenterology

Neurogastroenterology is defined as neurology of the gastrointestinal tract, liver, gallbladder and pancreas and encompasses control of digestion through the enteric nervous system (ENS), the central nervous system (CNS) and integrative centers in sympathetic ganglia. This Review provides a broad overview of the field of neurogastroenterology, with a focus on the roles of the ENS in the control of the musculature of the gastrointestinal tract and transmucosal fluid movement. Digestion is controlled through the integration of multiple signals from the ENS and CNS; neural signals also pass between distinct gut regions to coordinate digestive activity. Moreover, neural and endocrine control of digestion is closely coordinated. Interestingly, the extent to which the ENS or CNS controls digestion differs considerably along the digestive tract. The importance of the ENS is emphasized by the life-threatening effects of certain ENS neuropathies, including Hirschsprung disease and Chagas disease. Other ENS disorders, such as esophageal achalasia and gastroparesis, cause varying degrees of dysfunction. The neurons in enteric reflex pathways use a wide range of chemical messengers that signal through an even wider range of receptors. These receptors provide many actual and potential targets for modifying digestive function.

PACAP modulation of the colon-inferior mesenteric ganglion reflex in the guinea pig

We investigated the effect of pituitary adenylate cyclase activating peptide (PACAP) on the colon-inferior mesenteric ganglion (IMG) reflex loop in vitro. PACAP27 and PACAP38 applied to the IMG caused a prolonged depolarization and intense generation of fast EPSPs and action potentials in IMG neurones. Activation of PACAP-preferring receptors (PAC1-Rs) with the selective agonist maxadilan or vasoactive intestinal peptide (VIP)/PACAP (VPAC) receptors with VIP produced similar effects whereas prior incubation of the IMG with selective PAC1-R antagonists PACAP6-38 and M65 inhibited the effects of PACAP. Colonic distension evoked a slow EPSP in IMG neurones that was reduced in amplitude by prolonged superfusion of the IMG with either PACAP27, maxidilan, PACAP6-38, M65 or VIP. Activation of IMG neurones by PACAP27 or maxadilan resulted in an inhibition of ongoing spontaneous colonic contractions. PACAP-LI was detected in nerve trunks attached to the IMG and in varicosities surrounding IMG neurones. Cell bodies with PACAP-LI were present in lumbar 2-3 dorsal root ganglia and in colonic myenteric ganglia. Colonic distension evoked release of PACAP peptides in the IMG as measured by radioimmunoassay. Volume reconstructed images showed that a majority of PACAP-LI, VIP-LI and VAChT-LI nerve endings making putative synaptic contact onto IMG neurones and a majority of putative receptor sites containing PAC1-R-LI and nAChR-LI on the neurones were distributed along secondary and tertiary dendrites. These results suggest involvement of a PACAP-ergic pathway, operated through PAC1-Rs, in controlling the colon-IMG reflex.

Elevated vasoactive intestinal peptide concentrations in patients with irritable bowel syndrome

The aim was to assess the roles of gut hormones and immune dysfunction in irritable bowel. In Study I, rectal mucosal samples examined blindly showed no histological evidence of inflammation in 16 irritable bowel patients compared to 17 healthy controls. The proinflammatory mediators interleukin-1beta and prostaglandin E2 also failed to show evidence of inflammation. Vasoactive intestinal peptide was elevated in irritable bowel (P = 0.01), but substance P, calcitonin gene-related peptide, and somatostatin levels were similar to control values. In Study II, 30 irritable bowel patients had elevated (P = 0.002) plasma concentrations of vasoactive intestinal peptide compared to 30 controls, and peptide levels were unrelated to whether the patient's predominant bowel habit was constipation, diarrhea, or both in alternation. In conclusion, no evidence of inflammation was detected in irritable bowel patients, but elevated vasoactive intestinal peptide concentrations were observed in both studies and might represent a potential diagnostic tool for irritable bowel syndrome.

Synaptic density, convergence, and dendritic complexity of prevertebral sympathetic neurons

Prevertebral sympathetic ganglia contain a unique population of final motor neurons receiving convergent synaptic inputs not only from spinal preganglionic neurons, but also from peripheral intestinofugal neurons projecting from the gut. We used quantitative confocal and ultrastructural immunohistochemistry to determine how this increased synaptic convergence is accommodated by sympathetic final motor neurons in the celiac ganglion of guinea pigs. Terminals of intestinofugal neurons were identified by their immunoreactivity to vasoactive intestinal peptide. Stereologic analyses were based on transects and point counts at confocal and ultrastructural levels. The relative amount of dendritic neuropil in the medial regions of the ganglion was approximately 2.5 times greater than in the lateral regions of the ganglion, consistent with the 2 to 3 times difference in average dendritic field size of neurons in these regions. The total numbers of boutons and synaptic profiles showed significant positive correlations with the relative amount of neuropil in a region. However, the overall density of synaptic boutons was twice as high in the medial region of the ganglion compared with the lateral regions. Because the relative density of preganglionic synapses was similar in each region, this difference was due to the selective projection of intestinofugal inputs to neurons in the medial celiac ganglion, where they provided 45% of synaptic contacts. These results show that, compared with vasoconstrictor neurons, sympathetic neurons regulating gastrointestinal activity support a higher number of convergent inputs in two ways: in addition to having larger dendritic fields, they also have a twofold higher density of synapses.

Serotonin receptor subtypes that depolarize guinea pig inferior mesenteric ganglion neurons

Our previous studies indicated that serotonin (5-HT) depolarized a majority of guinea pig inferior mesenteric ganglion (IMG) neurons and may be another transmitter for the noncholinergic late slow excitatory postsynaptic potential (ls-EPSP) in the IMG. However, the subtypes of 5-HT receptor mediating these responses have not yet been identified. Using intracellular recording, we examined the effect of 5-HT receptor antagonists with specificity to various 5-HT receptor subtypes on the 5-HT-mediated depolarization and ls-EPSP in IMG neurons in vitro. Cyproheptadine, a 5-HT(1/2) receptor antagonist, reversibly inhibited the slow, but not the fast, depolarization and ls-EPSP in the 5-HT-sensitive neurons. Both mianserin and spiperone, 5-HT(2) and 5-HT(1A) receptor antagonists, did not significantly alter either the fast or slow depolarizing responses or the ls-EPSP. The 5-HT(3) receptor antagonist MDL 72222 (Bemesetron) completely inhibited the fast depolarization with little diminution of the slow depolarization and ls-EPSP. Superfusion of putative 5-HT(1P) receptor antagonist, BRL 24924 (Renzapride), reversibly attenuated both the depolarization and ls-EPSP. However, 5-HT-insensitive neurons with ls-EPSP were found to be insensitive to both cyproheptadine and BRL 24924. In most 5-HT-sensitive neurons, the 5-HT(3) receptor agonist, 2-methyl-5-HT, and the selective 5-HT(1P) agonist, MCPP or 5-OHIP, evoked a fast and a slow depolarization in 55.6 and 71.4% of the neurons, respectively, without a significant effect on the membrane potential in 85.7 and 100% of the 5-HT-insensitive neurons. In 5-HT-sensitive neurons, MDL 72222 reversibly abolished the fast depolarization induced by 2-methyl-5-HT; BRL 24924 significantly inhibited the slow depolarization induced by MCPP or 5-OHIP, but not by SP. Prolonged superfusion of 5-HT-sensitive neurons with MCPP abolished the evoked ls-EPSP without inhibition of action potential. These results suggest that the fast and slow depolarizations in these neurons are mediated by 5-HT(3) and 5-HT(1P) receptor subtypes, respectively. The latter may also mediate the ls-EPSP in 5-HT-sensitive neurons.

Immunocytochemical localization of the neurons in the superior mesenteric ganglion innervating the small intestine of the cat

Retrograde tracing was used to determine the localization of neuronal perikarya and fibres in the feline superior mesenteric ganglion (SMG), projecting to the small intestine. In the distal part of the ileum, a retrograde neuronal tracer Fast Blue (FB) was injected and after approximately thirty five to forty days the animals were killed by perfusion. The SMG were removed and the neuropeptide contents of the neurons, projecting to the distal ileum, were determined by means of immunofluorescence with antisera to neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), substance P (SP), somatostatin (SOM), and vasoactive intestinal polypeptide (VIP). Neurons innervating the small intestine were located in the upper part of the SMG and all of them were NPY-immunopositive. The group of CGRP-immunoreactive (IR) cells was less numerous (73.33%). Probably the FB-labeled fibres, containing the same neuropeptides, arise from these perikarya. SP- or VIP-immunopositive neuronal processes were found to surround immunonegative ganglionic cells but their origin is not in the ganglion. Only single FB-marked cells were VIP-immunopositive. SP- and SOM-immunoreactive amounted respectively to 2.28% and 3.01% of all the neuronal population, but only a few of these cells were FB-labelled.

Tachykininergic synaptic transmission in the coeliac ganglion of the guinea-pig

1. The responses of coeliac ganglion neurones of the guinea-pig to electrical stimulation of the mesenteric nerves and applications of tachykinin receptor agonists were investigated by use of intracellular recording techniques. 2. Ganglion neurones were classified into three groups based on firing patterns in response to a depolarizing current pulse: phasic (38% of the population), tonic (39%) and atypical (23%). In the majority of phasic neurones (91%) a long after-hyperpolarization (LAH) lasting 5-8 s followed action potentials induced by a train of depolarizing current pulses. In contrast, LAH was rarely observed in tonic neurones (5%). 3. In most of tonic neurones (90%) slow excitatory post-synaptic potentials (e.p.s.ps) lasting 3-10 min were evoked by repetitive electrical stimulation of the mesenteric nerves. Prolonged depolarizations were also evoked in most tonic neurones by applications of substance P (SP), neurokinin A (NKA) or senktide, a tachykinin NK3 receptor agonist. 4. In most of phasic neurones (73%), mesenteric nerve stimulation did not induce an obvious depolarization but induced a prolonged inhibition of LAH lasting 3-10 min. Bath-applied tachykinin receptor agonists similarly induced an inhibition of LAH without causing depolarization in most of the phasic neurones. 5. GR 71251 (5 microM), a tachykinin NK1 receptor antagonist, partially depressed the nerve-evoked slow e.p.s.ps in tonic neurones and the nerve-evoked LAH inhibition in phasic neurones. 6. Capsaicin (0.1-5 microM) induced a prolonged depolarization in tonic neurones and an inhibition of LAH in phasic neurones. 7. A mixture of peptidase inhibitors potentiated the depolarization and the LAH inhibition evoked by nerve stimulation, SP and NKA, but not those evoked by senktide. 8. It is concluded that tonic neurones respond to repetitive mesenteric nerve stimulation preferentially with slow e.p.s.ps and that phasic neurones respond preferentially with LAH inhibition. The present study further suggests that SP and NKA, released from axon collaterals of primary afferent neurones, produce slow e.p.s.ps in tonic neurones and the LAH inhibition in phasic neurones via NK1 receptors.

The mammalian sympathetic prevertebral ganglia: integrative properties and role in the nervous control of digestive tract motility

The prevertebral ganglia which are a constitutive part of the sympathetic system have long been considered as a simple relay on this efferent pathway. In fact, these ganglia must be considered as true peripheral nervous centres. They possess various integrative properties, such as projections of central and peripheral inputs onto the ganglionic neurones, gating of these projections and pacemaker activity of the ganglionic neurones. These properties explain the ability of these ganglia to participate in the regulation of various visceral functions, including digestive tract motility.

Modulation by opioid peptides of mechanosensory pathways supplying the guinea-pig inferior mesenteric ganglion

1. Radioimmunological techniques were used in isolated guinea-pig inferior mesenteric ganglion (IMG)-colon preparations to determine whether opioid peptides and neurotensin8-13 (NT8-13), the C-terminal region of NT1-13 recognized by neurotensin receptors, modulate distension-induced release of substance P (SP)- and vasoactive intestinal polypeptide (VIP)-like immunoreactive (LI) material. 2. Colonic distension significantly increased the amount of SP- and VIP-LI material released in the ganglionic superfusate. A low-Ca2+ (0.1 mM), high-Mg2+ (15 mM) solution blocked their release. 3. In vivo capsaicin pretreatment abolished release of SP-LI material during colonic distension but had no significant effect on distension-induced release of VIP-LI material. 4. The addition of [Leu5]enkephalin, [Met5]enkephalin, PL017 (a mu-receptor agonist) and DPDPE (a delta-receptor agonist) to the ganglion side of a two-compartment chamber blocked distension-induced release of SP-LI material. The addition of naloxone and ICI-174,864 (a delta-receptor antagonist) to the ganglion compartment reversed the inhibitory effect of the mu- and delta-receptor agonists. 5. Addition of [Leu5]enkephalin and [Met5]enkephalin to the ganglion compartment had no significant effect on release of VIP-LI material during colonic distension. 6. Addition of NT8-13 to the ganglion compartment significantly increased in the amount of SP-LI material released during colonic distension but had no affect on distension-induced release of VIP-LI material. 7. The results suggest the hypothesis that under in vivo conditions, enkephalinergic nerves decrease and neurotensinergic nerves increase the release of SP from peripheral branches of primary afferent sensory nerves.

Chemical coding of neurons that project from different regions of intestine to the coeliac ganglion of the guinea pig

The chemical codings of neurons that project from the small intestine, caecum, proximal colon, distal colon and rectum to the coeliac ganglion of the guinea pig were investigated. The coeliac ganglion was injected with the retrogradely transported dye Fast Blue, and each of the regions was examined 6 days later in wholemounts that had been prepared for immunohistochemical localisation of pairs of antigens. In both the small and large intestines, all intestinofugal neurons were immunoreactive (IR) for choline acetyltransferase (ChAT). In each region of the large intestine, the largest population, representing 50-60% of retrogradely labelled neurons in each region, was immunoreactive for ChAT, bombesin (BN), calbindin (Calb) and nitric oxide synthase (NOS). Most intestinofugal neurons in the small intestine contain bombesin and VIP-IR along with ChAT-IR but none contain either Calb or NOS. Thus, nerve endings of enteric origin in the coeliac ganglion that contain NOS-IR or Calb-IR come from the large intestine and those with bombesin-IR but not NOS-IR are from the small intestine. The gastric wall was injected with Fast Blue in order to label noradrenergic (NA) neurons in the coeliac ganglion and to determine, by localisation of NOS and bombesin-IR, whether they receive inputs from the small and large intestine. Some NA neurons received inputs from the large intestine (and perhaps also from the small intestine) and some received inputs exclusively from the small intestine. Most NA neurons that received intestinofugal inputs had the chemical code NA/-; some were immunoreactive for somatostatin (NA/SOM neurons), but those with IR for neuropeptide Y (NA/NPY) rarely received intestinofugal inputs.

Effects of axotomy, deafferentation, and reinnervation on sympathetic ganglionic synapses: a comparative study

The main physiological and morphological features of the synapses in the superior cervical ganglia of mammals and the last two abdominal ganglia of the frog sympathetic chain are summarized. The effects of axotomy on structure and function of ganglionic synapses are then reviewed, as well as various changes in neuronal metabolism in mammals and in the frog, in which the parallel between electrophysiological and morphological data leads to the conclusion that a certain amount of synaptic transmission occurs at "simple contacts." The effects of deafferentation on synaptic transmission and ultrastructure in the mammalian ganglia are reviewed: most synapses disappear, but a number of postsynaptic thickenings remain unchanged. Moreover, intrinsic synapses persist after total deafferentation and their number is strongly increased if axotomy is added to deafferentation. In the frog ganglia, the physiological and morphological evolution of synaptic areas is comparable to that of mammals, but no intrinsic synapses are observed. The reinnervation of deafferented sympathetic ganglia by foreign nerves, motor or sensory, is reported in mammals, with different degrees of efficiency. In the frog, the reinnervation of sympathetic ganglia with somatic motor nerve fibers is obtained in only 20% of the operated animals. The possible reasons for the high specificity of ganglionic connections in the frog are discussed.

Neuropeptides in the sympathetic system: presence, plasticity, modulation, and implications

Neuropeptides are ubiquitous in the sympathetic system and modulate transmission at the levels of the intermediolateral cell column, sympathetic ganglia, and neuroeffector junctions. Several neuropeptide-containing pathways from the hypothalamus and medulla modulate excitability of preganglionic neurons. Neuropeptides coexist with norepinephrine or acetylcholine in subpopulations of chemically coded, target-specific sympathetic ganglion neurons. Neuropeptide Y is colocalized in adrenergic vasoconstrictor neurons, whereas vasoactive intestinal polypeptide is colocalized in cholinergic sudomotor neurons. Neuropeptide expression is plastic; during development, neurons that switch from a noradrenergic to a cholinergic phenotype increase expression of vasoactive intestinal polypeptide, somatostatin, and substance P. Preganglionic inputs increase neuropeptide Y and inhibit substance P expression. Sympathetic denervation produces sprouting of sensory fibers containing substance P and calcitonin gene-related peptide in target tissues. Neuropeptides from preganglionic fibers (e.g., enkephalin) and primary afferents (e.g., substance P, vasoactive intestinal polypeptide) modulate transmission in sympathetic ganglia. Neuropeptide Y produces vasoconstriction, prejunctional inhibition of norepinephrine release, and postjunctional potentiation of norepinephrine effects. Plasma neuropeptide Y increases during intense sympathoexcitation, hypertension, and pheochromocytoma. Dystrophic neurites containing neuropeptide Y occur in human sympathetic ganglia during aging, diabetes, and dysautonomia. Sympathetic neuropeptides may thus have important clinical implications.

Activity following colonic distension in enteric sensory fibres projecting to the inferior mesenteric ganglion in the guinea pig

In this investigation the characteristics of the response to colonic distension of afferent fibres projecting to the inferior mesenteric ganglion (IMG) of the guinea pig were studied in vitro. Intracellular membrane potential recordings were made from neurons in the IMG. Post-synaptic potentials arising from activity in afferent fibres were recorded in these cells following distensions of a small segment of colon placed in a separate and independently perfused organ bath. These afferent fibres showed both transient and sustained responses to distension. Application of a solution containing 0.25 mM Ca2+ and 10 mM2+ Mg2+ to the colon (but not to the IMG) reduced the overall response but did not abolish the activity in these fibres. It is concluded that some afferent fibres which respond to colonic distension project directly to the IMG.

New insights into the organization of a gastroduodenal inhibitory reflex by the coeliac plexus

The mechanisms involved at the prevertebral ganglionic level in a gastroduodenal inhibitory reflex were investigated in the rabbit on an in vitro preparation of the coeliac plexus connected to the stomach and duodenum. Intraluminal gastric and duodenal pressures were measured using water-filled balloons. Gastric distension inhibited duodenal motility via a nerve reflex which was abolished by section of the nerves connecting the coeliac plexus to the viscera. Superfusion of the coeliac plexus with a low Ca(2+)-high Mg2+ solution abolished the gastroduodenal inhibitory reflex, indicating a synaptic link at the ganglion level. The reflex was unaffected by superfusion of the coeliac plexus with hexamethonium and tubocurarine, ruling out a nicotinic mechanism. The reflex persisted when the coeliac plexus was superfused with tetrodotoxin or when the nerves connecting the coeliac plexus to the viscera were superfused with a Na(+)-free solution; these results indicate that the reflex does not involve sodium-dependent action potentials. Moreover, superfusion of the nerves connecting the coeliac plexus to the viscera with a calcium blocker or with a Ca(2+)-free solution also failed to abolish the reflex, suggesting that calcium-dependent action potentials are not involved. Our study demonstrates that a gastrointestinal inhibitory reflex via the coeliac ganglion is not based on fast synaptic inputs or action potentials. These results provide new insights concerning the physiology of the sympathetic prevertebral ganglia.

The electrophysiological effects of endogenous GABA in the guinea-pig inferior mesenteric ganglion

1. GABA receptor-modulating drugs and intracellular recording techniques were used to determine the functional significance of peripheral afferent GABA-containing nerves projecting from the distal colon to sympathetic neurones in the inferior mesenteric ganglion of the guinea-pig. 2. GABAA receptor-modulating drugs added selectively to the inferior mesenteric ganglion side of a two-compartment bath had pronounced effects on on-going colonic afferent cholinergic synaptic input. Bicuculline (20 microM) decreased the amplitude and frequency of fast excitatory postsynaptic potentials (EPSPs) by 40% whereas diazepam (5 microM) increased cholinergic input by 43%. Neither drug had any effect on the resting membrane potential or membrane input resistance of ganglion cells. 3. Bicuculline (20 microM) significantly reduced, whereas diazepam (5 microM) significantly enhanced, distension-induced increases in nicotinic fast EPSPs and action potentials. 4. Slow EPSPs evoked by colonic distension were not affected by bicuculline or diazepam. 5. Manual voltage clamp of the postsynaptic depolarizing response to exogenous GABA revealed GABA-induced presynaptic facilitation of colonic afferent but not central preganglionic efferent cholinergic synaptic input. 6. The data suggest that endogenously released GABA participates in on-going colo-colonic reflex activity by acting on presynaptic GABAA receptors to facilitate release of acetylcholine from colonic mechanosensory nerves.

The origin and distribution of neurons with projections passing through the inferior mesenteric ganglion of the guinea-pig

Retrograde tracing with the fluorescent dye, Fast Blue, was used to examine the origin and distribution of neurons whose axons project through the inferior mesenteric ganglion (IMG) of the guinea-pig. These studies were performed by applying the tracer to (a) the rostral cut-end of the hypogastric nerves and (b) the caudal cut-end of the inter-mesenteric nerve (IMN). After application of tracer to the hypogastric nerves retrogradely labelled cell profiles were observed in the IMG and the superior mesenteric ganglion (SMG). The number of labelled cell profiles in the SMG was consistently about 15% of the number in the IMG. In only one of seven animals tested were labelled cells seen in the wall of the colon. Application of tracer to the IMN labelled cells in the IMG and in the wall of the colon. The distribution of the labelled enteric neurons was skewed towards the anal end of the colon. These results confirm that postganglionic sympathetic neurons in the SMG project axons through the guinea-pig IMG and describe the colonic distribution of enteric neurons that project through the IMG and into the IMN.

Electrical and integrative properties of rabbit sympathetic neurones re-evaluated by patch clamping non-dissociated cells

1. Voltage recordings were performed on non-dissociated sympathetic neurones from rabbit coeliac ganglia using the whole-cell configuration of the patch clamp technique. 2. Cells were classified depending on their firing pattern as silent cells (63%) producing either phasic (24%) or tonic (76%) spike discharge in response to depolarizing currents, and pacemaker cells (37%). 3. All the cells produced large overshooting spikes and prolonged postspike after-hyperpolarization. The peak-to-peak spike amplitude was 113.8 +/- 1 mV. Spikes were shortened and the after-hyperpolarization was suppressed when calcium channel blockers (Cd2+ and La3+) were added. 4. Silent cells have a resting potential of -58.8 +/- 1.5 mV. At potentials ranging from -50 to -90 mV, the input impedance was 490 +/- 27 M omega at 22-24 degrees C and 426 +/- 47 M omega at 35-36 degrees C. The time constant at voltages corresponding to the high input impedance region was 126 +/- 7 ms at 22-24 degrees C and 86 +/- 7 ms at 35-36 degrees C. 5. The firing frequency of the pacemaker cells was 3.2 +/- 0.5 Hz at 35-36 degrees C in the presence of nicotinic blockers. Evidence is given that the firing did not result from cell injury but was induced by an intrinsic pacemaker mechanism. Input impedance of pacemaker neurones was 580 +/- 47 M omega at 22-24 degrees C and 473 +/- 56 M omega at 35-36 degrees C. 6. Most of the pacemaker cells (63%) were motoneurones, since they were antidromically fired by stimulating post-ganglionic nerves. In addition, they received synaptic inputs from both preganglionic fibres (splanchnic nerves) and the periphery (postganglionic nerves). Long-lasting depolarizations were induced in either silent or pacemaker cells by single shocks applied to pre- and postganglionic nerves. 7. Slowly rising voltage ramps revealed the presence of an N-shaped current-voltage relationship in voltage clamped pacemaker cells. The negative slope was located in a subthreshold voltage range, between -83.4 +/- 1.4 and -59.0 +/- 1.8 mV. It was induced by the activation of a low threshold persistent inward current. Although it was tiny (22 +/- 3 pA at its peak level) this current brought the null-current voltage up to -41.0 +/- 1.4 mV, which resulted in continuous firing. 8. Due to the instability introduced by the N-shaped I-V relationship, pacemaker cells can display bistable behaviour characterized by hyperpolarizing responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of enteric nerve cells that project to the coeliac ganglion of the guinea-pig

The digestive tract of the guinea-pig, from the esophagus to the rectum, was examined in detail to determine the distribution and relative abundances of neurons in these organs that project to the coeliac ganglion and the routes by which their axons reach the ganglion. A retrogradely transported neuronal marker, Fast Blue, was injected into the coeliac ganglion. The esophagus, stomach, gallbladder, pancreas, duodenum, small intestine, caecum, proximal colon, distal colon and rectum were analysed for labelled neurons. Retrogradely labelled neurons were found only in the myenteric plexus of these organs, and in the pancreas. No labelled neurons were found in the gallbladder or the fundus of the stomach, or in the submucous plexus of any region. A small number of labelled neurons was found in the gastric antrum. An increasing density of labelled neurons was found along the duodenum. Similarly, an increasing density of labelled neurons was found from proximal to distal along the jejuno-ileum. However, the greatest densities of labelled neurons were in the large intestine. Many labelled neurons were found in the caecum, including a high density underneath its taeniae. An increasing density of labelled neurons was found along the length of the proximal colon, and labelled neurons were found in the distal colon and rectum. In total, more labelled cell bodies occurred in the large intestine than in the small intestine. The routes taken by the axons of viscerofugal neurons were ascertained by lesioning the nerve bundles which accompany vessels supplying regions of the digestive tract. Viscerofugal neurons of the caecum project to the coeliac ganglion via the ileocaeco-colic nerves; neurons in the proximal colon project to the ganglion via the right colic nerves, and neurons in the distal colon project to the ganglion via the mid colic and intermesenteric nerves. Neurons in the rectum project to the coeliac ganglion via the intermesenteric nerves. These nerves (except for the intermesenterics) all join nerve bundles from the small intestine that follow the superior mesenteric artery. All viscerofugal neurons of the caecum were calbindin-immunoreactive (calb-IR) and 94% were immunoreactive for vasoactive intestinal peptide (VIP-IR). In the proximal colon, 49% of labelled neurons were calb-IR and 85% were VIP-IR. In the distal colon, 80% of labelled neurons were calb-IR and 71% were VIP-IR.

Vasoactive intestinal polypeptide presynaptically enhances the synaptic transmission in cultured sympathetic neurons

We studied the effects of vasoactive intestinal polypeptide (VIP) on the cholinergic synaptic transmission that was developed between rat sympathetic neurons in culture. Electrophysiological examinations revealed that the amplitude of fast excitatory postsynaptic potential (fast EPSP) was increased by VIP (0.2-0.8 microM) reversibly and dose-dependently, whereas transient nicotinic depolarization evoked by pressure application of acetylcholine (ACh) was not affected by VIP. In most of the cells examined, VIP depolarized membrane potential by a few millivolts with concomitant increases in membrane conductance. Furthermore, the VIP-induced depolarization was suppressed by Co2+ but not by hexamethonium or atropine. Hence it is highly likely that the peptide augmented the amplitude of fast EPSPs by increasing ACh release from the presynaptic cell. These results demonstrate that VIP influences the presynaptic phase of cholinergic synaptic transmission between sympathetic neurons.

The neuropeptide VIP modulates the neurotransmitter phenotype of cultured chick sympathetic neurons

The present report provides evidence for a novel function for the neuropeptide vasoactive intestinal peptide (VIP). We demonstrate that VIP increases the cholinergic and the noradrenergic properties of cultured chick sympathetic neurons without changing neuronal survival and metabolism. VIP induces a 10- to 15-fold increase in the activity of choline acetyltransferase and an approximately twofold increase in the activity of tyrosine hydroxylase. Forskolin, an activator of adenylate cyclase, mimics all the effects of VIP on these cells. In addition, the effects of forskolin and VIP at optimal concentrations are not additive. Furthermore, VIP induces a rapid increase in the intracellular cAMP levels. Thus VIP acts via a cAMP-dependent pathway to enhance the cholinergic and noradrenergic properties of cultured chick sympathetic neurons.

Calbindin-immunoreactive nerve terminals in the guinea pig coeliac ganglion originate from colonic nerve cells

Previous work has shown that calbindin-immunoreactive (calbindin-IR) nerve terminals are numerous in guinea pig prevertebral ganglia. A high proportion of those colonic nerve cells that project to the inferior mesenteric ganglia are calbindin-IR, but none of the neurons that project from the small intestine to the coeliac ganglion are immunoreactive for calbindin. The present work was designed to determine the source of the calbindin-IR fibres and the pathways by which they reach the coeliac ganglion. Sections through the major nerve trunks that connect with the coeliac ganglion revealed numerous calbindin-IR fibres in the inferior coeliac nerves and in the intermesenteric nerves, while there were very few fibres in the splanchnic or superior coeliac nerves. When all peripheral nerve connections to a lobe of the coeliac ganglion were cut, all calbindin-IR terminals degenerated. Cutting the ileo-caeco-colic nerves caused a substantial reduction in the density of nerve fibres in the coeliac ganglion, whereas no significant reduction could be detected when the intermesenteric nerves were cut. However, lesion of both the ileo-caeco-colic and intermesenteric nerves caused all the calbindin-IR nerve fibres in the coeliac ganglion to degenerate. It is concluded that most or all of the calbindin-reactive nerve terminals in the coeliac ganglion originate from the large intestine and that most reach the ganglion via the ileo-caeco-colic nerves. Thus many colonic intestinofugal neurons, supplying both the coeliac and inferior mesenteric ganglia, are immunoreactive for calbindin, whereas small intestinal intestinofugal neurons are not immunoreactive for this protein.

Immunohistochemical identification of cholinergic neurons in the myenteric plexus of guinea-pig small intestine

It is well established that acetylcholine is a neurotransmitter at several distinct sites in the mammalian enteric nervous system. However, identification of the cholinergic neurons has not been possible due to an inability to selectively label enteric cholinergic neurons. In the present study an immunohistochemical method has been developed to localize choline acetyltransferase, the synthetic enzyme for acetylcholine, in order that cholinergic neurons can be visualized. The morphology, neurochemical coding and projections of cholinergic neurons in the guinea-pig small intestine were determined using double-labelling immunohistochemistry. These experiments have revealed that many myenteric neurons are cholinergic and that they can be distinguished by their specific combinations of immunoreactivity for neurochemicals such as calretinin, neurofilament protein triplet, substance P, enkephalin, somatostatin, 5-hydroxytryptamine, vasoactive intestinal peptide and calbindin. On the basis of their previously described projections, functional roles could be attributed to each of these populations. The identified cholinergic neurons are: motorneurons to the longitudinal muscle (choline acetyltransferase/calretinin); motorneurons to the circular muscle (choline acetyltransferase/neurofilament triplet protein/substance P, choline acetyltransferase/substance P and choline acetyltransferase alone); orally directed interneurons in the myenteric plexus (choline acetyltransferase/calretinin/enkephalin); anally directed interneurons in the myenteric plexus (choline acetyltransferase/somatostatin, choline acetyltransferase/5-hydroxytryptamine, choline acetyltransferase/vasoactive intestinal peptide); secretomotor neurons to the mucosa (choline acetyltransferase/somatostatin); and sensory neurons mediating myenteric reflexes (choline acetyltransferase/calbindin). This information provides a unique opportunity to identify functionally distinct populations of cholinergic neurons and will be of value in the interpretation of physiological and pharmacological studies of enteric neuronal circuitry.

Morphological and chemical identification of neurons that project from the colon to the inferior mesenteric ganglia in the guinea-pig

Labelled nerve cells were located in the distal colon of the guinea-pig 4-5 days after the retrograde tracing agent, Fast blue, was injected into the inferior mesenteric ganglia. Labelled neurons were only found in the myenteric plexus. Their frequency increased from oral to anal and was greater towards the mesenteric border, compared with the anti-mesenteric aspect, of the colon. Many retrogradely labelled neurons were immunoreactive for vasoactive intestinal peptide or calbindin. In the inferior mesenteric ganglia, vasoactive intestinal peptide and calbindin immunoreactive nerve fibres surrounded the same clumps of nerve cell bodies. Almost all calbindin and vasoactive intestinal peptide immunoreactive terminals degenerated after the nerves running from the large intestine to the inferior mesenteric ganglia were cut. It is concluded that the great majority of calbindin and vasoactive intestinal peptide immunoreactive terminals in the inferior mesenteric ganglia arise from nerve cell bodies in the myenteric plexus of the large intestine.

The role of serotonin in non-cholinergic excitatory transmission in the guinea pig inferior mesenteric ganglion

The non-cholinergic late slow excitatory postsynaptic potential (ls-EPSP) of the guinea pig inferior mesenteric ganglion (IMG) was previously believed to be mediated by substance P (SP) or several other neuropeptides. Yet, the pharmacological evidence presented here indicates that serotonin (5-HT) may be another transmitter for the ls-EPSP in the guinea pig IMG. Repetitive stimulation of the presynaptic nerves elicited ls-EPSP in about half of the IMG neurons. Application of 5-HT or SP caused, in a portion of the IMG neurons, a slow depolarization similar to ls-EPSP. Fifty-six out of 88 (63.6%) neurons with ls-EPSP and 13 out of 35 (37.1%) neurons with ls-EPSP were sensitive to 5-HT and SP, respectively. Superfusion of the ganglia with 5-HT markedly suppressed the ls-EPSP evoked in 5-HT sensitive neurons. Similarly, exogenously applied SP attenuated the ls-EPSP of SP-sensitive neurons. However, prolonged superfusion of 5-HT or SP had no effect on the ls-EPSP elicited in 5-HT or SP-insensitive neurons, respectively. Furthermore, the ls-EPSPs elicited in 5-HT-sensitive neurons as well as the 5-HT-induced depolarization were reversibly suppressed by cyproheptadine, a 5-HT antagonist, and enhanced by fluoxetine, a 5-HT reuptake inhibitor. In contrast, the ls-EPSP of 5-HT insensitive neurons and SP-induced depolarization were not appreciably changed by those two drugs. Pretreatment with p-chlorophenylalanine, a 5-HT biosynthesis inhibitor, did not change the general electrophysiological characteristics of the neurons and did not suppress nicotinic neurotransmission, but markedly reduced the occurrence rate of ls-EPSP from 53.8% to 15.1% (P less than 0.005). Collectively, our results indicate that, besides SP, 5-HT may be involved in mediating the ls-EPSP in a subpopulation of neurons in the guinea pig IMG. The type of transmitter mediating ls-EPSP is apparently not limited to 5-HT and SP, as about 30% of the neurons with ls-EPSP were found to be insensitive to both 5-HT and SP and prolonged superfusion with both did not affect appreciably the ls-EPSP elicited in these neurons.

Direct evidence for the involvement of vasoactive intestinal polypeptide in the motor response of the human isolated ileum to capsaicin

Capsaicin (1 microM) produced complex motor responses in longitudinal and circular muscle strips from the human isolated small intestine (jejunum and ileum). In the longitudinal muscle, inhibition of the nerve-mediated contractions (electrical field stimulation) was the dominant response, while capsaicin had a weak and inconsistent effect on tone and spontaneous activity. In contrast, relaxation and decreased spontaneous activity were the responses of the circular muscle to capsaicin. These effects of capsaicin were not reproduced by a second application of capsaicin, indicating desensitization, a feature of the specific action of this drug on sensory nerves. All the effects of capsaicin in the longitudinal and circular muscle were closely mimicked by exogenous vasoactive intestinal polypeptide (VIP). Further, the inhibitory motor effect of capsaicin in both muscle layers was blocked by an anti VIP serum. In the longitudinal muscle, VIP, like capsaicin, inhibited the electrically evoked nerve-mediated contractions but not the tetrodotoxin-resistant myogenic contractions, suggesting a prejunctional site of action. The inhibitory effect of both capsaicin and VIP in the circular muscle was tetrodotoxin-resistant suggesting direct inhibition of muscle cells. Capsaicin (1 microM) evoked a tetrodotoxin-resistant release of VIP-like immunoreactivity from the human small intestine. On high pressure liquid chromatography, a major peak of the immunoreactive material released by capsaicin co-eluted with authentic VIP and a minor, unidentified peak eluted shortly afterward. We conclude that authentic VIP is involved in the local motor response to capsaicin in the human small intestine. These findings raise the possibility that VIP might be present in sensory nerves of the human gut from which it is released by capsaicin.

Motor response of the human isolated colon to capsaicin and its relationship to release of vasoactive intestinal polypeptide

The aim of this study was to obtain indirect evidence of the presence of capsaicin-sensitive afferents in the human colon by studying the motor response to capsaicin of longitudinal strips from the human isolated taenia coli in parallel to the ability of capsaicin or KCl to induce peptide release from the human superfused colon. Capsaicin (1 microM) evoked a relaxation of the taenia, approaching 60-80% of the response to isoprenaline. Tachykinins evoked contractions of the taenia, while calcitonin gene-related peptide induced a relaxation. Neither tachyphylaxis to calcitonin gene-related peptide nor preincubation with an anti-calcitonin gene-related peptide serum did block the response to capsaicin which was also unaffected by tetrodotoxin, apamin, naloxone or an anti-galanin serum. Vasoactive intestinal polypeptide produced a concentration-dependent tetrodotoxin-resistant relaxation which was shifted rightward in the presence of anti-vasoactive intestinal polypeptide serum. The anti-vasoactive intestinal polypeptide serum reduced the response to capsaicin and application of capsaicin prevented the ability of anti-vasoactive intestinal polypeptide serum to block exogenous vasoactive intestinal polypeptide. Capsaicin (1 microM) evoked a significant release of vasoactive intestinal polypeptide-like immunoreactivity from the superfused muscle but not mucosa of the human colon. A significant vasoactive intestinal polypeptide-like immunoreactivity release was also observed in response to KCl (80 mM). KCl but not capsaicin evoked a significant release of neurokinin A-like immunoreactivity from colonic muscle and mucosa. No significant release of either substance P-, neuropeptide Y-, galanin- or calcitonin gene-related peptide-like immunoreactivity was detected in response to capsaicin or KCl although detectable levels of each peptide were evident in tissue extracts.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitation of locus coeruleus neurons by vasoactive intestinal peptide: evidence for a G-protein-mediated inward current

Vasoactive intestinal polypeptide (VIP) caused a reversible increase in the firing rate of locus coeruleus (LC) neurons. Voltage-clamp at -60 mV revealed that VIP induced an inward current associated with a small increase in conductance. The inward current persisted in the presence of Co2+ (to block Ca2+ channels) or tetrodotoxin (to block fast voltage-dependent Na+ channels). Substitution (80%) of Na+ with choline or Tris reduced the VIP-elicited inward current by approximately 75%. Changing external K+ concentrations did not alter the effect of VIP. The inward current induced by VIP became irreversible after the intracellular administration of GTP gamma S, a hydrolysis-resistant analog of GTP which can cause a prolonged activation of G-proteins. The intracellular application of GDP beta S, which can interfere with G-protein activation, attenuated the effect of VIP. Pertussis toxin, an inactivator of certain G-proteins, did not block the effect of VIP. We conclude that VIP directly excites LC neurons by inducing a largely Na-dependent inward current. As this effect became irreversible in the presence of intracellular GTP gamma S, was attenuated by GDP beta S, and was not eliminated by pertussis toxin, mediation through a pertussis toxin-insensitive G-protein is suggested.

Synaptic potentials induced by postganglionic stimulations in cat bladder parasympathetic neurones

Intracellular recording techniques were used to examine and compare synaptic potentials evoked by stimulating pre- and postganglionic nerve trunks in cat bladder parasympathetic ganglia. In the 76 ganglion cells examined, two types of responses were recorded on stimulating the postganglionic nerve: an antidromic action potential (type PostNS1; n = 30) or a fast excitatory postsynaptic potential (f-EPSP; type PostNS2; n = 46) which resulted in an orthodromic-like action potential. In some of the cells exhibiting a PostNS1 response (n = 19), a fast depolarization was superimposed on the antidromic spike. This depolarization was due to the synaptic activation of nicotinic receptors. In many of the cells exhibiting either PostNS1 or PostNS2 responses, repetitive stimulation of the postganglionic nerve induced a slow hyperpolarization. Applying nicotinic (hexamethonium, 0.5-1 mM) receptor muscarinic (atropine, 1 microM), alpha-adrenergic (phentolamine, 1 microM) and purinergic (caffeine, 0.5-1 mM) receptor antagonists completely inhibited the tetanus-induced slow hyperpolarization in some cells (n = 5). In other cells (n = 15), a slow hyperpolarization persisted in the presence of these antagonists. These results indicate that stimulation of the postganglionic nerve trunk of cat bladder parasympathetic ganglia can elicit not only an antidromic action potential, but also synaptic potentials which are mediated by the activation of cholinergic (nicotinic and muscarinic), noradrenergic and purinergic receptors, as well as non-cholinergic, non-alpha-adrenergic and non-purinergic synaptic potential.

Release of VIP- but not CGRP-like immunoreactivity by capsaicin from the human isolated small intestine

Exposure to capsaicin (1 microM) produced a prompt and sustained release of vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) from mucosa-free strips of human small intestine (jejunum and ileum). A second application of capsaicin, 60 min later, had no effect indicating complete desensitization, a specific feature of the action of capsaicin on sensory nerves. By contrast no release of calcitonin gene-related peptide (CGRP)-LI was produced upon the first or second application of capsaicin.

Central neurotensin nerves modulate colo-colonic reflex activity in the guinea-pig inferior mesenteric ganglion

1. The effects of neurotensin and of stimulation of preganglionic nerves on peripheral afferent synaptic input from segments of distal colon to neurones in the inferior mesenteric ganglia of guinea-pigs were studied using intracellular recording techniques in vitro. 2. Electrical stimulation of colonic afferent nerve fibres evoked fast, nicotinic synaptic responses (fast EPSPs or action potentials) followed by a slow depolarizing response (slow EPSP). 3. Neurotensin (1 microM) increased the amplitude and duration of slow EPSPs evoked by stimulation of colonic afferents. 4. Distention of a segment of distal colon left attached to an inferior mesenteric ganglion evoked a slow depolarization. Neurotensin (1 microM) increased the amplitude and duration of distention-induced depolarizations. 5. Electrical stimulation of central preganglionic nerve fibres present in the third and fourth lumbar ventral roots increased the amplitude and duration of slow EPSPs evoked by electrical stimulation of colonic afferent nerves. This facilitatory effect was abolished after desensitization to neurotensin. 6. Slow depolarizations evoked by neurotensin and by stimulation of central preganglionic nerves converted subthreshold fast EPSPs due to mechanosensory synaptic input from an attached segment of distal colon to action potentials. This increase in firing rate of sympathetic ganglion cells led to a decrease in colonic intraluminal pressure. 7. Taken together these data support the hypothesis that neurotensin or a closely related substance contained in central preganglionic nerves facilitated release of a non-cholinergic excitatory transmitter from colonic mechanosensory nerves. The slow depolarization evoked by the non-cholinergic transmitter converted on-going subthreshold fast EPSPs to action potentials thereby increasing sympathetic output to the colon. 8. It is suggested that under normal in vivo conditions, central preganglionic fibres containing neurotensin or a closely related peptide modulate peripheral reflex activity through prevertebral ganglia in guinea-pigs.

Neurotensin facilitates release of substance P in the guinea-pig inferior mesenteric ganglion

1. Intracellular, electrophysiological techniques were combined with radio-immunological, chromatographic and pharmacological techniques to determine if nerve terminals containing substance P mediated transient depolarizing responses of principal ganglion cells induced by neurotensin. Experiments were performed in vitro on guinea-pig inferior mesenteric ganglia. 2. In 61% of principal ganglion cells tested in normal ganglia, neurotensin caused a transient membrane depolarization. In ganglia which were removed from animals which had been pre-treated with capsaicin, transient responses to neurotensin were virtually abolished. 3. In normal ganglia, neurotensin increased the amplitude and duration of noncholinergic slow EPSPs evoked by electrical stimulation of the lumbar colonic nerve. Such increases were absent in ganglia obtained from animals pre-treated with capsaicin. 4. In guinea-pigs pre-treated with capsaicin, the content of substance P-like material was significantly reduced in inferior mesenteric and coeliac ganglia, dorsal root ganglia and lumbar spinal cord, compared to control animals. The content of substance P-like material in segments of distal colon was slightly reduced. The content of vasoactive intestinal polypeptide-, cholecystokinin- and bombesin-like material in the same tissues from animals pre-treated with capsaicin was not significantly different from control animals. 5. Chromatographic analysis using HPLC (high-performance liquid chromatography) techniques revealed that the material depleted from inferior mesenteric and coeliac ganglia, dorsal root ganglia and lumbar spinal cord by capsaicin pre-treatment co-eluted with synthetic substance P. 6. Electrical stimulation of the lumbar colonic nerve released substance P-like material from isolated inferior mesenteric ganglia as determined by radioimmunoassay of samples of superfusate. Exogenous administration of neurotensin caused a significant increase in the amount of substance P-like material released during nerve stimulation. 7. Transient depolarizing responses evoked by neurotensin were markedly attenuated when ganglion cells were postsynaptically desensitized to exogenously administered substance P. 8. Taken together, these findings suggest that transient depolarizations mediated by an indirect action of neurotensin and facilitation of electrically evoked non-cholinergic slow EPSPs by neurotensin involved presynaptic release of substance P from collateral nerve terminals of primary afferent nerve fibres in the inferior mesenteric ganglion. 9. It was suggested that under normal in vivo conditions, neurotensin or a C-terminal-related peptide contained in central preganglionic nerve endings might function as an excitatory neuromodulator to enhance the release of substance P from primary afferent nerve terminals thereby facilitating non-cholinergic peripheral afferent synaptic input to prevertebral ganglion cells.

The electrophysiological effects of neurotensin on neurones of guinea-pig prevertebral sympathetic ganglia

1. The membrane effects of neurotensin on neurons of guinea-pig prevertebral ganglia were investigated by means of intracellular recording techniques in vitro. 2. Neurotensin (2-5 microM) applied by superfusion caused depolarizing responses in fifty-seven of seventy-four neurones tested in the inferior mesenteric ganglion and thirty-seven of forty-seven neurones tested in the coeliac plexus. The remaining neurones tested showed no membrane response. 3. Responses to neurotensin could be discriminated into two different types of membrane depolarizations on the basis of their different time courses and pharmacological characteristics: a steady-state type of depolarization and a transient type of depolarization. Seven of fifty-seven responsive neurones tested in the inferior mesenteric ganglion and ten of thirty-seven responsive neurones tested in the coeliac plexus responded to neurotensin with a depolarization which was maintained constant as long as neurotensin was superfused over the preparation (steady-state type). Forty-eight of fifty-seven responsive neurones tested in the inferior mesenteric ganglion and twenty of thirty-seven responsive neurones tested in the coeliac plexus responded with a transient depolarization which was followed by a repolarization in the maintained presence of neurotensin (transient type). A combination of both types of responses was observed in two neurones tested in the inferior mesenteric ganglion and in seven neurones tested in the coeliac plexus. 4. Steady-state type responses were characterized by a slowly developing membrane depolarization which reached a plateau and lasted throughout the presence of neurotensin. Amplitude and time course of this response were not altered in a solution containing hexamethonium (10 microM) and atropine (10 microM) or by a solution low in calcium (1 mM) and high in magnesium (15 mM). 5. Transient type depolarizations evoked by neurotensin were faster in reaching their maximum and were followed by a repolarization during the maintained presence of neurotensin. Responses similar in time course and amplitude were obtained in solutions containing hexamethonium (10-100 microM) and atropine (10 microM). However, transient responses were abolished in a solution low in calcium (1 mM) and high in magnesium (15 mM) and were markedly attenuated in ganglia treated with capsaicin (3 microM). 6. Both types of depolarizations were associated with increases in membrane input resistance. Both responses converted subthreshold depolarizing electrotonic potentials and subthreshold fast EPSPs to action potentials. 7. Both types of depolarizations were observed when the C-terminal hexapeptide fragment neurotensin 8-13 was used.(ABSTRACT TRUNCATED AT 400 WORDS)

Direct electrical stimulation of the superior ovarian nerve in rats causes an increase in neuronal activity in the ipsilateral ovarian plexus nerve

Ovarian blood flow and neuronal activity in the ovarian plexus nerve (OPN) were monitored before, during and after direct electrical stimulation of the central cut end of the ipsilateral superior ovarian nerve (SON). Blood flow did not change during the observation period. Stimulation of the SON increased the frequency of action potentials in the OPN, suggesting an ovarian reflex pathway mediated by the SON and the OPN.

Calcitonin gene-related peptide evokes distinct types of excitatory response in guinea pig coeliac ganglion cells

Pressure application of calcitonin gene-related peptide (CGRP) evoked in a population of guinea pig coeliac neurons 3 types of response: a fast, a slow and a biphasic depolarization. The responses were not appreciably affected in low Ca/high Mg or tetrodotoxin-containing Krebs solution. The fast depolarization was associated with a fall in membrane resistance; it was made larger on hyperpolarization and the estimated reversal potential was -24 mV. The fast response was reversibly blocked in a Na-free medium as well as by relatively high concentrations of d-tubocurarine (50-100 microM) but not by hexamethonium. The slow, CGRP-induced depolarization resistant to nicotinic and muscarinic antagonists, was associated with either a small increase or decrease of input resistance. Membrane hyperpolarization increased the slow response in the majority of coeliac neurons, with an estimated reversal potential of -44 mV. The biphasic depolarization displayed electrophysiological and pharmacological characteristics resembling the fast and slow responses. These results raise the possibility that CGRP acting via two distinct types of receptor elicits, respectively, a fast, Na-dependent excitatory response and a slow response, the mechanism of which remains to be established.

Modulation of synaptic transmission in the rabbit coeliac ganglia by gastric and duodenal mechanoreceptors

The involvement of duodenal and gastric mechanoreceptors in the modulation of synaptic transmission was investigated in a rabbit sympathetic prevertebral ganglion. The present study was performed in vitro on the coeliac plexus connected to the stomach and the duodenum. The electrical activity of ganglionic neurons was recorded using intracellular recording techniques. The patterns of synaptic activation of these ganglionic neurons in response to the activation of mechanoreceptors by gastric or duodenal distension were investigated. Although gastric or duodenal distension was unable to elicit any fast synaptic activity in ganglionic neurons, it produced either an inhibition or a facilitation of the fast nicotinic excitatory postsynaptic potentials elicited by stimulation of the thoracic splanchnic nerves. In addition, this distension triggered long-lasting (3-11 min) modifications in the electrical properties of the ganglionic neurons, i.e. slow depolarizations (6-18 mV) or slow hyperpolarizations (3-6 mV), which were sometimes associated with a decrease in the input membrane resistance. After cooling of the nerves connecting the coeliac ganglia to the stomach, the activation of gastric or duodenal mechanoreceptors was no longer able to modify the fast synaptic activation or the electrical properties of the ganglionic neurons. The results demonstrate that gastric and duodenal mechanoreceptors project onto neurons of the coeliac ganglia and change their excitability as well as the central inputs they receive. The long duration of these modifications suggests that gastric and duodenal mechanoreceptors can modulate the activity of the neurons of the coeliac ganglia.

Substance P-mediated membrane currents in voltage-clamped guinea pig inferior mesenteric ganglion cells

Responses to substance P (SP) and to hypogastric nerve stimulation were recorded from voltage-clamped guinea pig inferior mesenteric ganglion (IMG) neurons, and compared with those to muscarine. Muscarine produced a voltage-dependent inward current accompanied by a reduced input conductance and inhibition of IM a time- and voltage-dependent K+-current (Brown and Adams: Nature 283:673-676, 1980). SP also produced an inward current, accompanied by a fall in input conductance (20 out of 31 cells) or a rise in input conductance (7 out of 31 cells). The fall in input conductance was not accompanied by an inhibition of M-current (unlike frog ganglia: Adams et al.: British Journal of Pharmacology 79:330-333, 1983) or an inhibition of the inward rectifier current (unlike globus pallidus neurons: Stanfield et al.: Nature 315:498-501, 1985). Repetitive hypogastric nerve stimulation (10-20 Hz, 2-10 s) produced a slow inward postsynaptic current lasting 1-3 min, with decreases or increases of input conductance matching those produced by SP. The postsynaptic current did not show a consistent or reproducible change in amplitude on varying the holding potential between -90 and -25 mV. It is concluded that SP and hypogastric stimulation produce complex and variable changes in ionic conductance in IMG neurons.