The effects of substance P and met5-enkephalin in dog ileum

Substance P initiated tonic contraction of dog ileum when administered in doses from 1 pg to 20 micrograms intraarterially (ED50 = 67 ng). Low doses acted to excite cholinergic postganglionic neurones since atropine or tetrodotoxin (TTX) increased the ED50 of substance P about 25-fold, while hexamethonium and local field stimulation had only a small effect to increase the ED50. Also atropine and tetrodotoxin effects were not additive. Higher doses apparently acted to stimulate smooth muscle directly, but no evidence was obtained that local field stimulation could release substance P to act on smooth muscle. Substance P tachyphylaxis prevented substance P actions on cholinergic nerves, but it did not affect responses to intraaterial acetylcholine or block distal inhibition from proximal distention or field stimulation. Met-enkephalin given intraarterially, was also excitatory in doses from 1 ng to 20 micrograms; the amplitude of tonic and phasic contractions produced was significantly decreased by TTX and atropine but was not diminished by hexamethonium or substance P tachyphylaxis. Partial tachyphylaxis to met-enkephalin was produced but was not diminished by hexamethonium or substance P tachyphylaxis. Partial tachyphylaxis to met-enkephalin was produced without affecting the ED50 for substance P. We conclude that substance P acts in small amounts on receptors in myenteric nerves to release acetylcholine by a mechanism, presumably involving postganglionic cholinergic nerves, while met-enkephalin also apparently may act at least in part through a similar TTX- and atropine-sensitive mechanism. These peptides also caused activation of other receptors, probably on smooth muscle by noncholinergic. TTX-insensitive mechanisms. Also the receptors for each peptide which are located on nerves were distinct and independent since tachyphylaxis could be produced to each without affecting the response to the other.     

Neurotransmitters in the intestine of the Atlantic cod, Gadus morhua

The effects of the putative neurotransmitters acetylcholine, adrenaline, adenosine, ATP, bombesin, 5-hydroxytryptamine, met-enkephalin, neurotensin, somatostatin, substance P and VIP have been investigated in the perfused intestine of the cod, Gadus morhua. The presence and distribution of the different types of nerves was investigated with immunohistochemistry and Falck-Hillarp fluorescence histochemistry. A spontaneous rhythmic activity of the perfused preparations usually occurred within a few minutes from the start of the experiment. This activity was diminished or abolished by addition of atropine, methysergide or tetrodotoxin to the perfusion fluid. Acetylcholine, 5-hydroxytryptamine or substance P caused a contraction of the intestinal wall. The response to acetylcholine was blocked by atropine but not by tetrodotoxin, while the response to 5-hydroxytryptamine was blocked by methysergide and usually also by tetrodotoxin. This indicates that the effect of acetylcholine is direct on the muscle cells, while the effect of 5-hydroxytryptamine may be at least partly via a second neuron. All adrenergic agonists (adrenaline, isoprenaline and phenylephrine) had a dominating inhibitory effect on the intestine. Experiments with antagonists showed that the inhibition is due to stimulation of both alpha-adrenoceptors and beta-adrenoceptors. ATP, adenosine and somatostatin also caused a relaxation of the intestinal wall, often followed by a contraction. Met-enkephalin produced variable responses, either a relaxation, a contraction or both. Bombesin caused a weak inhibition, if anything. Neurotensin and VIP did not visibly affect the intestinal motility. 5-HT-, substance P- and VIP-like immunoreactivity and catecholamine fluorescence were observed in the myenteric plexus, submucosa and muscle layers in all parts of the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Projection pathways,co-existence of peptides and synaptic organization of nerve fibers in the inferior mesenteric ganglion of the guinea-pig

Summary The presence of immunoreactive enkephalin, dynorphin, vasoactive intestinal polypeptide, cholecystokinin, substance P and neuropeptide Y in nerve fibers that project to the guinea-pig inferior mesenteric ganglion was analysed, after different denervation and ligation procedures. A quantitative analysis demonstrates that enkephalin- and substance P fibers reach the ganglion mainly via lumbar splanchnic and partly via intermesenteric nerves. Dynorphin-, vasoactive intestinal polypeptide- and cholecystokinin fibers reach the ganglion mainly via colonic and partly via hypogastric or intermesenteric nerves. Neuropeptide Y fibers enter via intermesenteric, lumbar splanchnic and hypogastric nerves and pass through the ganglion. Analysis of serial 0.5 m sections tends to confirm co-existence: of dynorphin, vasoactive intestinal polypeptide and cholecystokinin in fibers projecting from the colon; of dynorphin with substance P in the lumbar splanchnic nerves; and of neuropeptide Y with substance P in the hypogastric and colonic fibers. Synaptic contacts, predominantly axodendritic, onto the ganglion cells from enkephalin-, vasoactive intestinal polypeptide-, and substance P-containing terminals were revealed by electron microscopy. Enkephalin-immunoreactive axon varicosities are filled with small, clear vesicles with a few large, cored vesicles and form asymmetric synapses; dynorphin-, vasoactive intestinal polypeptide- and cholecystokinin-immunoreactive axon varicosities are rich in large, dense-cored vesicles and form symmetric synapses.     

Neuropeptide modification of chloride secretion in guinea pig distal colon

This study examined the effects of electrically stimulating submucosal neurons in the guinea pig isolated distal colonic mucosa and determined the effects of several peptides that are present in these neurons. Electrical field stimulation of muscle-stripped segments of guinea pig distal colonic mucosa, set up in Ussing flux chambers, evoked an increase in short-circuit current (Isc), of 371 +/- 31 MicroA.cm-2. The response to electrical stimulation was abolished by tetrodotoxin and significantly reduced by serosal furosemide. Atropine reduced, but did not abolish, the neurally evoked response. Addition of neuropeptide Y and galanin to the serosal bath had no effect on baseline Isc, but both evoked a concentration-dependent decrease in the neurally evoked secretory response. Vasoactive intestinal polypeptide evoked a concentration-dependent increase in basal (unstimulated) Isc that was reduced by furosemide and unaltered by tetrodotoxin. Neuropeptide Y, but not galanin, significantly reduced the secretory responses to vasoactive intestinal polypeptide and bethanechol. Somatostatin 201-995 and human calcitonin gene-related peptide had no effect on basal Isc nor did either alter the neurally evoked response. These results suggest that acetylcholine and non-cholinergic neurotransmitter(s) stimulate chloride secretion in the guinea pig distal colonic mucosa. This neurosecretory response may be modulated by neuropeptide Y and galanin that are found within submucosal neurons.     

Central 5-hydroxytryptamine (5-HT) mediates colonic motility by hypothalamus oxytocin-colonic oxytocin receptor pathway

Gut-derived 5-hydroxytryptamine (5-HT) is well known for its role in mediating colonic motility function. However, it is not very clear whether brain-derived 5-HT is involved in the regulation of colonic motility. In this study, we used central 5-HT knockout (KO) mice to investigate whether brain-derived 5-HT mediates colonic motility, and if so, whether it involves oxytocin (OT) production in the hypothalamus and OT receptor in the colon. Colon transit time was prolonged in KO mice. The OT levels in the hypothalamus and serum were decreased significantly in the KO mice compared to wild-type (WT) controls. OT increased colonic smooth muscle contraction in both KO and WT mice, and the effects were blocked by OT receptor antagonist and tetrodotoxin but not by hexamethonium or atropine. Importantly, the OT-induced colonic smooth muscle contraction was decreased significantly in the KO mice relative to WT. The OT receptor expression of colon was detected in colonic myenteric plexus of mice. Central 5-HT is involved in the modulation of colonic motility which may modulate through its regulation of OT synthesis in the hypothalamus. Our results reveal a central 5-HT - hypothalamus OT - colonic OT receptor axis, providing a new target for the treatment of brain-gut dysfunction.     

Cholinergic neurons are involved in the effect of substance P on the circular muscle of the guinea pig small intestine.

The mode of action of the excitatory neuropeptide substance P was studied on the circular muscle of the guinea pig ileum in vitro. Atropine or tetrodotoxin strongly inhibited substance P-induced phasic contractions. The atropine-resistant part of the circular response was blocked by tetrodotoxin. A newly-developed method for quantitative evaluation revealed a rightward displacement of the substance P concentration-response curve, as well as a strong depression of the maximum effect, in the presence of atropine. These results indicate that cholinergic (and probably also non-cholinergic) excitatory neurons mediate phasic contractions due to substance P. The tonic component of the substance P-induced contraction was slightly reduced by atropine.     

Involvement of different mechanisms in the stimulatory effects of cholecystokinin octapeptide on gastrointestinal and colonic motility in dogs

The effects of an intravenous infusion of cholecystokinin octapeptide (CCK-8, 1 microgram.kg-1.h-1) were investigated in conscious fasted dogs chronically fitted with strain-gauge transducers on the antrum, the jejunum, and the colon. Attempts to antagonize the increase of motility appearing at the three levels during CCK infusion were made using different blockers to elucidate the mechanisms involved. Asperlicin (a specific CCK antagonist) blocked the effects of CCK-8 at the three levels, while atropine and somatostatin were only effective in the jejunum and colon. Methyl-levallorphan (a mu-opiate antagonist that poorly crosses the blood-brain barrier) antagonized the CCK-induced colonic stimulation when intracerebroventricularly administered. Serotonin, histamine, substance P, and K-antagonists as well as a benzodiazepine did not modify the CCK-8 induced stimulation. It was concluded that the stimulatory effect of CCK-8 resulted from (a) a direct stimulation of the smooth muscle cells at gastric level, (b) a cholinergic activation of the jejunum and the colon, and (c) the involvement of a mu-opioid central component in the colonic response only.     

Cholecystokinin stimulates neuronal receptors to produce contraction of the canine colon

The motor effects of cholecystokinin 26-33-amide (CCK octapeptide; CCK-OP) and several purported CCK receptor antagonists on canine colonic circular muscle were determined in pentobarbital anesthetized dogs. Intravenous injections of CCK-OP had no effect on colonic motility at doses that contracted the gallbladder, stomach and duodenum. CCK-OP delivered by intraarterial injection to a small segment of the proximal colon produced a dose related increase in colonic motility with one-half maximum response at 12 ng/Kg and maximum response at 50 ng/Kg. The effects of intraarterial injections of several established CCK-receptor antagonists on proximal colonic responses to intraarterial injections of CCK-OP were determined. Proglumide, 10 mg/Kg, did not produce colonic contractions itself, but antagonized CCK-OP-induced responses. Carbobenzyloxy (CBZ)-CCK27-32-amide antagonized CCK-OP-induced colonic responses and also had no effect on basal colonic motility (0.1-1 and 5 micrograms/Kg). Neither compound antagonized acetylcholine- induced colonic responses. Butoxycarbonyl (BOC)-CCK31-33-amide increased basal colonic motility, but did not alter CCK-OP-induced responses at doses of 0.1 and 0.2 mg/Kg. Dibutyryl-cGMP at a dose of 0.1 mg/Kg did not affect basal motility or CCK-OP-induced contractions. At a dose of 1.0 mg/kg it increased basal colonic motility but did not affect CCK-OP-induced contractions. Pentagastrin increased colonic motor activity only at a dose of 5 micrograms/Kg, i.a., a much higher dose than effective doses of CCK-OP. The mechanism of CCK-OP-induced colonic motor effects also was determined. Atropine sulfate, 100 micrograms/Kg, i.v. significantly reduced both intraarterial acetylcholine-and CCK-OP-induced maximum colonic contractions. Tetrodotoxin, at intravenous doses that completely block neuronal activity, did not affect maximum acetylcholine-induced contractions but practically eliminated maximum CCK-OP-induced maximum colonic responses. In conclusion, intraarterial CCK-OP produces circular muscle contraction of the canine proximal colon that is mediated by stimulation of specific CCK receptors which produce the release of acetylcholine from cholinergic enteric neurons. Proglumide and CBZ-CCK27-32-amide are effective CCK receptor antagonists at these colonic neuronal receptors.     

Colocalization of NADPH-diaphorase activity and certain neuropeptides in the esophagus of opossum (Didelphis virginiana)

Nitric oxide and various neuropeptides in the myenteric plexus regulate esophageal motility. We sought colocalization of nitric oxide synthase and neuropeptides in frozen sections of mid-portion of smoothmuscled opossum esophagus using NADPH-diaphorase activity to mark the synthase and immunoreactivity to detect peptides. The peptides, all with demonstrated physiological activity in this organ, were calcitonin generelated peptide, galanin, neuropeptide Y, substance P, and vasoactive intestinal polypeptide. The ExtrAvidin Peroxidase immunostain for each peptide was carried up to the final peroxidase reaction with 3-amino-9-ethylcarbazole. The NADPH-diaphorase reaction was applied with short incubation to provide light staining just before the peroxidase reaction was performed. We examined sections for the proportions of singly and dually labeled nerve cells in the myenteric plexus. NADPH-diaphorase activity was highly colocalized with calcitonin gene-related peptide (59%), galanin (54%), and vasoactive intestinal polypeptide (53%). It showed little colocalization with neuropeptide Y (10%) and substance P (8%). The proportions of all nerve cells containing each of the substances were: NADPH-diaphorase-33%, calcitonin gene-related peptide-30%, galanin-55%, neuropeptide Y-16%, substance P-35%, and vasoactive intestinal polypeptide-58%. We conclude that the nerves responsible for peristalsis in the esophagus may act by releasing nitric oxide along with other inhibitory substances, calcitonin gene-related peptide, galanin, and vasoactive intestinal polypeptide, but not excitatory substances, neuropeptide Y and substance P.     

Effects of cholera toxin on the potential difference and motor responses induced by distension in the rat proximal small intestine in vivo

Cholera toxin (CT) may induce uncontrolled firing in recurrent networks of secretomotor neurons in the submucous plexus. This hypothesis was tested in chloralose-anesthetized rats in vivo. The secretory reflex response to graded intestinal distension was measured with or without prior exposure to luminal CT. The transmural potential difference (PD) was used as a marker for electrogenic chloride secretion. In controls, distension increased PD, and this response was reduced by the neural blocker tetrodotoxin given serosally and the vasoactive intestinal peptide (VIP) receptor antagonist [4Cl-d-Phe(6),Leu(17)]VIP (2 mug.min(-1).kg(-1) iv) but unaffected by the serotonin 5-HT(3) receptor antagonist granisetron, by the nicotinic receptor antagonist hexamethonium, by the muscarinic receptor antagonist atropine, or by the cyclooxygenase inhibitor indomethacin. Basal PD increased significantly with time in CT-exposed segments, an effect blocked by granisetron, by indomethacin, and by [4Cl-d-Phe(6),Leu(17)]VIP but not by hexamethonium or atropine. In contrast, once the increased basal PD produced by CT was established, [4Cl-d-Phe(6),Leu(17)]VIP and indomethacin had no significant effect, whereas granisetron and hexamethonium markedly depressed basal PD. CT significantly reduced the increase in PD produced by distension, an effect reversed by granisetron, indomethacin, and atropine. CT also activated a specific motility response to distension, repeated cluster contractions, but only in animals pretreated with granisetron, indomethacin, or atropine. These data are compatible with the hypothesis that CT induces uncontrolled activity in submucous secretory networks. Development of this state depends on 5-HT(3) receptors, VIP receptors, and prostaglandin synthesis, whereas its maintenance depends on 5-HT(3) and nicotinic receptors but not VIP receptors. The motility effects of CT (probably reflecting myenteric activity) are partially suppressed via a mechanism involving 5-HT(3) and muscarinic receptors and prostaglandin synthesis.     

Phenazine methosulfate induces a neurally-mediated contraction of the guinea-pig ileum

Phenazine methosulfate (PMS) and related phenazines are widely used in biochemistry and histochemistry and act as anti-bacterial agents, however, there is little information on their pharmacological actions. In the present paper the guinea-pig ileum was used as a model for studying the effects of PMS on nerve cells. PMS was found to contract intestinal muscle. This action appeared to be mediated by the activation of muscarinic receptors since it was blocked by atropine. Neostigmine potentiated the response to PMS. The nerve blocker tetrodotoxin prevented the effect of PMS and it is concluded that PMS causes the release of acetylcholine from nerve elements. The action of PMS on nerves is not mediated by nicotinic receptors. Receptors for serotonin, substance P or cholecystokinin also appear not to be involved. Of all the phenazines tested PMS was found to be the most potent and reversible.     

Peptides and self-stimulation of the medial prefrontal cortex in the rat: effects of intracerebral microinjections of substance P and cholecystokinin

The effects of intracerebral microinjections of substance P and cholecystokinin on self-stimulation of the medial prefrontal cortex of the rat were studied. Intracerebroventricular administration of substance P at doses of 2.5, 5, 10 and 20 micrograms produced a dose-related decrease in self-stimulation of the medial prefrontal cortex; spontaneous motor activity, measured as a control, was not affected. Unilateral microinjections into the medial prefrontal cortex of substance P at doses of 10 and 20 micrograms produced a decrease of self-stimulation of the ipsilateral side, but self-stimulation of the contralateral cortex, used as a control, was not affected. On the contrary, cholecystokinin in both intracerebroventricular administration at doses of 100, 200 and 400 ng, or intracortical microinjections into the medial prefrontal cortex at doses of 200, 400 and 800 ng, had no effect on self-stimulation of this cortical area. These results suggest that substance P, but not cholecystokinin, could be part of the neurochemical substrate underlying self-stimulation of the medial prefrontal cortex in the rat.     

Intracisternal administration of cholecystokinin-8 counteracts the central cardiovascular effects of adrenaline and NPY. A study based on the coexistence of cholecystokinin, phenylethanolamine N-methyltransferase and neuropeptide Y immunoreactivity in neurons of the nucleus tractus solitarius

(1) In the present study the occlusion method was employed to evaluate the overall coexistence of neuropeptide Y and phenylethanolamine-N-methyl transferase, neuropeptide Y and tyrosine hydroxylase as well as cholecystokinin and phenylethanolamine-N-methyl transferase immunoreactivity in nerve cell bodies of the dorsal subnuclei of the nucleus tractus solitarius of the male rat. A high degree of coexistence was established for neuropeptide Y/phenylethanolamine-N-methyl transferase, cholecystokinin/phenylethanolamine-N-methyl transferase and for tyrosine hydroxylase/neuropeptide Y immunoreactivity. (2) Sulfated [¹²I]cholecystokinin-8 was used as radioligand to study the densities of cholecystokinin-8 binding sites in the dorsal medulla oblongata by means of quantitative receptor autoradiography. High densities of binding sites were observed in parts of the nucleus tractus solitarius and in the area postrema. Labeling was also observed in the dorsal motor nucleus of the vagus. (3) In the physiological studies adrenaline (0.15–1.0 nmol), neuropeptide Y (0.075–0.75 nmol) and sulfated cholecystokinin-8 (0.3–3.0 nmol) were administered alone or in combination with neuropeptide Y or adrenaline intracisternally into -chloralose anaesthetized male rats. Especially the hypotensive and bradycardic responses of adrenaline were counteracted in the adrenaline/cholecystokinin co-treated animals, whereas the cardiovascular effects of neuropeptide Y when co-administered with cholecystokinin-8 (0.3 nmol) appeared to be more resistant to the antagonistic effect of cholecystokinin 8. In addition, cholecystokinin-8 further enhanced the neuropeptide Y-induced bradynpnea and increase in the tidal volume.

The present results indicate the existence of neuropeptide Y, adrenaline and cholecystokinin-8 immunoreactivity in the same neurons of the dorsal subnuclei of the nucleus tractus solitarius. Furthermore, binding sites for cholecystokinin-8 seem to at least partly co-distribute with -2 adrenergic and neuropeptide Y binding sites in the nucleus tractus solitarius. In the functional analysis, an antagonistic interaction between cholecystokinin-8 and adrenaline as well as between cholecystokinin and neuropeptide Y is demonstrated opening up the possibility that cholecystokinin peptides act as intrinsic modulators in the putative cholecystokinin/neuropeptide Y/adrenaline synapses in the nucleus tractus solitarius.     

Electroacupuncture at ST-36 accelerates colonic motility and transit in freely moving conscious rats

Acupuncture is useful for functional bowel diseases, such as constipation and diarrhea. However, the mechanisms of beneficial effects of acupuncture on colonic function have scarcely ever been investigated. We tested the hypothesis that electroacupuncture (EA) at ST-36 stimulates colonic motility and transit via a parasympathetic pathway in conscious rats. Hook-shaped needles were inserted at bilateral ST-36 (lower limb) or BL-21 (back) and electrically stimulated at 10 Hz for 20 min. We also studied c-Fos expression in response to EA at ST-36 in Barrington's nucleus of the pons. EA at ST-36, but not BL-21, significantly increased the amplitude of motility at the distal colon. The calculated motility index of the distal colon increased to 132 +/- 9.9% of basal levels (n = 14, P < 0.05). In contrast, EA at ST-36 had no stimulatory effects in the proximal colon. EA at ST-36 significantly accelerated colonic transit [geometric center (GC) = 6.76 +/- 0.42, n = 9, P < 0.001] compared with EA at BL-21 (GC = 5.23 +/- 0.39, n = 7). The stimulatory effect of EA at ST-36 on colonic motility and transit was abolished by pretreatment with atropine. EA-induced acceleration of colonic transit was also abolished by extrinsic nerve denervation of the distal colon (GC = 4.69 +/- 0.33, n = 6). The number of c-Fos-immunopositive cells at Barrington's nucleus significantly increased in response to EA at ST-36 to 8.1 +/- 1.1 cells/section compared with that of controls (2.4 +/- 0.5 cells/section, n = 3, P < 0.01). It is concluded that EA at ST-36 stimulates distal colonic motility and accelerates colonic transit via a sacral parasympathetic efferent pathway (pelvic nerve). Barrington's nucleus plays an important role in mediating EA-induced distal colonic motility in conscious rats.     

Effects of ciliary neurotrophic factor (CNTF) and depolarization on neuropeptide expression in cultured sympathetic neurons.

We examined the effects of ciliary neurotrophic factor (CNTF) and depolarization, two environmental signals that influence noradrenergic and cholinergic function, on neuropeptide expression by cultured sympathetic neurons. Sciatic nerve extract, a rich source of CNTF, increased levels of vasoactive intestinal peptide (VIP), substance P, and somatostatin severalfold while significantly reducing levels of neuropeptide Y (NPY). No change was observed in the levels of leu-enkephalin (L-Enk). These effects were abolished by immunoprecipitation of CNTF-like molecules from the extract with an antiserum raised against recombinant CNTF, and recombinant CNTF caused changes in neuropeptide levels similar to those of sciatic nerve extract. Alterations in neuropeptide levels by CNTF were dose-dependent, with maximal induction at concentrations of 5-25 ng/ml. Peptide levels were altered after only 3 days of CNTF exposure and continued to change for 14 days. Depolarization of sympathetic neuron cultures with elevated potassium elicited a different spectrum of effects; it increased VIP and NPY content but did not alter substance P, somatostatin, or L-Enk. Depolarization is known to block cholinergic induction in response to heart cell conditioned medium and we found that it blocked the induction of choline acetyltransferase (ChAT) and peptides by recombinant cholinergic differentiation factor/leukemia inhibitory factor (CDF/LIF). In contrast, it did not antagonize the effects of CNTF on either ChAT activity or neuropeptide expression. Thus, while CNTF has effects on neurotransmitter properties similar to those previously reported for CDF/LIF, the actions of these two factors are differentially modulated by depolarization, suggesting that the mechanisms of cholinergic and neuropeptide induction for the two factors differ. In addition, in contrast to CDF/LIF, CNTF did not alter levels of ChAT, VIP, substance P, or somatostatin in cultured dorsal root ganglion neurons. These observations indicate that CNTF and depolarization affect the expression of neuropeptides by sympathetic neurons and provide evidence for an overlapping yet distinct spectrum of actions of the two neuronal differentiation factors, CNTF and CDF/LIF.     

Effects of galanin on smooth muscle and mucosa of porcine jejunum.

The enteric neuropeptide galanin (GAL) increased the amplitude of spontaneous contractions in longitudinally oriented muscle strips and inhibited short-circuit current (Isc) elevations induced by transmural electrical stimulation (ES) of mucosal sheets from porcine jejunum in vitro. GAL-induced contractions (GAL EC50 = 9 nmol/l) were maximally 25% of those elicited by 10 mumol/l carbamylcholine and remained unaffected by atropine, tetrodotoxin, or tachyphylaxis to substance P. The presynaptic Ca2+ channel blocker, omega-conotoxin (0.1 mumol/l), inhibited GAL-induced contractions by 66%. GAL attenuated mucosal Isc elevations induced by ES with an IC50 = 13 nmol/l and at 0.1 mumol/l produced rapid decreases in basal Isc averaging 8 +/- 2 microA cm-1 in 77% of tissues examined. The alpha-adrenoceptor blocker phentolamine or the opiate antagonist naloxone did not alter tissue Isc responses to GAL. These results suggest that GAL modulates neuronal activity linked to secretomotor function in the porcine small intestine.     

Clostridium difficile suppresses colonic vasoactive intestinal peptide associated with altered motility

We investigated whether Clostridium difficile toxin alters colonic tissue levels of vasoactive intestinal peptide (VIP) at the expense of changes in colonic motility in the isolated perfused rabbit left colon. Colonic inflammation was induced by the intracolonic administration of 10(-8) M C. difflcile toxin. Strain gauge transducers were sewn onto the serosal surface of the colon to evaluate colonic motility. C. difflcile administration produced histologic changes consistent with epithelial damage. This was associated with an increased production of prostaglandin E(2) and thromboxane B(2). Tissue levels of VIP but not substance P were significantly reduced. This was associated with an increased number of contractions per minute and an average force of each colonic contraction. These results suggest that tissue levels of VIP are suppressed by C. difflcile and may participate in colonic dysmotility during active inflammation.     

Peptidergic modulation of efferent sympathetic neurons in intrathoracic ganglia regulating the canine heart

When either substance P or vasoactive intestinal peptide was injected into an acutely decentralized intrathoracic sympathetic ganglion, short-lasting augmentation of cardiac chronotropism and inotropism was induced. These augmentations were induced before the fall in systemic arterial pressure occurred which was a consequence of these peptides leaking into the systemic circulation in enough quantity to alter peripheral vascular resistance directly. When similar volumes of normal saline were injected into an intrathoracic ganglion, no significant cardiac changes were induced. When substance P or vasoactive intestinal peptide was administered into an intrathoracic ganglion, similar cardiac augmentations were induced either before or after the intravenous administration of hexamethonium. In contrast, when these peptides were injected into an intrathoracic ganglion in which the beta-adrenergic blocking agent timolol (0.1 mg/0.1 ml of normal saline) had been administered no cardiac augmentation occurred. These data imply that in the presence of beta-adrenergic blockade intraganglionic administration of substance P or vasoactive intestinal peptide does not modify enough intrathoracic neurons to alter cardiac chronotropism and inotropism detectably. When neuropeptide Y was injected into an intrathoracic ganglion, no cardiac changes occurred. However, when cardiac augmentations were induced by sympathetic preganglionic axon stimulation these were enhanced following the intraganglionic administration of neuropeptide Y. As this effect occurred after timolol was administered into the ipsilateral ganglia, but not after intravenous administration of hexamethonium, it is proposed that the effects of neuropeptide Y are dependent upon functioning intrathoracic ganglionic nicotinic cholinergic synaptic mechanisms. Intravenous administration of either morphine or [D-ala2,D-leu5]enkephalin acetate did not alter the capacity of the preganglionic sympathetic axons to augment the heart when stimulated. Following the intravenous administration of naloxone, the positive inotropic cardiac responses induced by efferent preganglionic sympathetic axonal stimulation were enhanced minimally in control states and significantly following hexamethonium administration. Thus, it appears that enkephalins are involved in the modulation of intrathoracic ganglion neurons regulating the heart, perhaps via modification of beta-adrenergic receptors. Taken together these data indicate that substance P, vasoactive intestinal peptide, neuropeptide Y, or enkephalins modify intrathoracic ganglionic neurons which are involved in efferent sympathetic cardiac regulation.     

Immunohistochemical localization of substance P, vasoactive intestinal polypeptide and gastrin-releasing peptide in vas deferens and seminal vesicle, and the effect of these and eight other neuropeptides on resting tension and neurally evoked contractile activity

Immunohistochemical studies of the vas deferens and seminal vesicle of mouse, guinea-pig, and rabbit showed the presence of nerve fibres containing vasoactive intestinal polypeptide (VIP), substance P (SP), and gastrin-releasing peptide (GRP) supplying the smooth muscle layers as well as blood vessels. The nerve supply was better developed in the seminal vesicle than in the vas deferens. The motor activity of the vas deferens and seminal vesicle of the guinea-pig was studied in vitro. The vas deferens responded to transmural electrical stimulation with a twitch followed by a slow contraction. The twitch was blocked by guanethidine and tetrodotoxin, but not by atropine, propranolol, phenoxybenzamine, or fluphenazine. The slow contraction exhibited features of an alpha-receptor-mediated response. SP, physalaemin and eledoisin contracted the smooth muscle and also potentiated the twitch response to electrical nerve stimulation in a concentration-dependent manner. The SP blocking agent, (D-Pro2,D-Trp7,9)-SP, affected neither the resting tension nor the response to electrical stimulation. It is therefore suggested that the SP fibres act mainly prejunctionally. VIP, Leu-enkephalin, cholecystokinin octapeptide (CCK-8), angiotensin II, vasopressin, neurotensin, bombesin, and GRP had no effect on either the resting tension or the response to electrical nerve stimulation. The seminal vesicle responded to electrical stimulation with a contraction which was unimpaired by atropine, propranolol, phenoxybenzamine, and guanethidine, but abolished by tetrodotoxin. Hence, this contraction is mediated by a non-adrenergic, non-cholinergic neurotransmitter. Bombesin, GRP, SP, physalaemin and eledoisin contracted the smooth muscle and potentiated the response to electrical stimulation. VIP, Leu-enkephalin, CCK-8, angiotensin II, vasopressin, and neurotensin had no effect on the resting tension or on the response to transmural electrical stimulation. The SP antagonist abolished the contraction elicited by SP but did not influence the response to nerve stimulation. The results suggest that the SP and GRP nerves may have prejunctional and facilitating postjunctional effects in the seminal vesicle.     

The effects of cholecystokinin-octapeptide and pentagastrin on electrical and motor activities of canine colonic circular muscle

The effects of cholecystokinin-octapeptide (CCK-OP) and pentagastrin on electrical and motor activities of circular muscle of the canine colon were studied with the sucrose gap technique. Additional organ bath experiments were performed to further characterize the motor response to the peptides and to elucidate their site of action. The electrical activity consisted of slow waves having an initial potential followed by a plateau potential, at a regular frequency of 4.5 cycles/min. Both peptides prolonged the duration and increased the amplitude of the plateau phase of the slow waves. Concomitantly, the slow wave frequency was reduced. In addition, CCK-OP increased spiking activity. Both spiking activity and the prolonged plateau potential generated contractile activity, prolonged phasic contraction occurring with slow waves with a prolonged plateau. In organ bath experiments, both CCK-OP and pentagastrin increased the basal tone of the muscle strips and prolonged the duration of the phasic contractions. The prolongation of the duration of the contractions was not antagonized by tetrodotoxin (TTX) and atropine. CCK-OP but not pentagastrin increased the force of contractions, this action was not affected by atropine but was reduced in the presence of TTX, suggesting that the increase in force may be partially mediated by noncholinergic excitatory nerves. The increase in basal tension by the peptides was enhanced in the presence of TTX indicating that myenteric inhibitory neurones were tonically active under our experimental conditions. The results provide the electrophysiological basis for CCK-OP and pentagastrin induced changes in colonic motility.