Distribution and projections of nerves with enkephalin-like immunoreactivity in the guinea-pig small intestine

Characterization of opioid receptors on isolated canine gallbladder smooth muscle cells

Smooth muscle cells were isolated from the fundus of the canine gallbladder and examined for the presence of opioid receptors. The cells contracted in a concentration-dependent manner in response to three opioid peptides (Met-enkephalin, dynorphin1-13 and Leu-enkephalin), which are known derivatives of opioid precursors present in myenteric neurons of the gut. The order of potency was Met-enkephalin greater than dynorphin1-13 greater than Leu-enkephalin. The contractile response to opioid agonists was selectively inhibited by opioid antagonists (naloxone and Mr2266) but not by muscarinic, CCK/gastrin or tachykinin antagonists. Equivalent responses to the three opioid peptides exhibited differential sensitivity to preferential antagonists of mu (naloxone) and kappa (Mr2266) opioid receptors consistent with the presence of the three main types of opioid receptors (mu, delta and kappa) on canine gallbladder muscle cells.

Return of nerve fibers containing gastrin-releasing peptide in rat small intestine after local removal of myenteric ganglia

Gastrin-releasing peptide is a neuropeptide with a wide distribution in the rat small intestine. Most of the GRP-containing fibers are intramural in origin. Local severing of myenteric GRP neurons by circumferential removal of the outer longitudinal muscle layer together with the adherent myenteric ganglia (myectomy) in a segment of the rat jejunum resulted in the disappearance of GRP fibers from the myectomized circular muscle and from myenteric ganglia and both muscle layers for approximately 10 mm anally to the lesion. As examined at different time intervals up to 60 weeks postoperatively fine-varicose GRP fibers of a normal appearance were found to return gradually to the portion anal to the lesion beginning at 20 weeks, first in the more distal portions and then (after 40-60 weeks) also in the more proximally located portions. Also the circular muscle in the myectomized segment became reinnervated during this time period. These fibers were notably coarse, more numerous than in control circular muscle, and arranged in thick bundles (hyperinnervation). Such nerve bundles were particularly frequent 40 weeks after the operation. The results indicate a remarkable plasticity of enteric neurons.

Neuromedin U--a study of its distribution in the rat

The distribution of neuromedin U, a novel peptide originally isolated from porcine spinal cord, was investigated in the rat using a recently developed radioimmunoassay. High concentrations of neuromedin U-like immunoreactivity were found in the pituitary gland and gastrointestinal tract. Significant concentrations of immunoreactivity were also found in several regions of the rat brain, spinal cord and both male and female genitourinary tracts. In the small intestine, neuromedin U-like immunoreactivity was restricted to the submucosal muscular layers, suggesting localization in neurones rather than in epithelial cells. Chromatographic analysis of pituitary, spinal cord and gut revealed a single peak of immunoreactivity which did not co-elute with either synthetic porcine neuromedin U-25 nor neuromedin U-8, indicating inter-species molecular heterogeneity.

Neuropeptides and the microcircuitry of the enteric nervous system

The discovery of neuropeptides in enteric neurons has revolutionized the study of the microcircuitry of the enteric nervous system. From immunohistochemistry, it is now clear that some individual enteric neurons contain several different neuropeptides with or without other transmitter-specific markers and that these markers occur in various combinations. There is evidence from experiments in which nerve pathways are interrupted that populations of enteric neurons with different combinations of markers have different projection patterns, sending their processes to distinct targets using different routes. Correlations between the neurochemistry of enteric neurons and the types of synaptic inputs they receive are also beginning to emerge from electrophysiological studies. These findings imply that enteric neurons are chemically coded by the combinations of peptides and other transmitter-related substances they contain and that the coding of each population correlates with its role in the neuronal pathways that control gastrointestinal function.

The source of the nerve fibres forming the deep muscular and circular muscle plexuses in the small intestine of the guinea-pig

A quantitative ultrastructural study was made of the neurites forming the deep muscular and circular muscle plexuses of the guinea-pig small intestine following microsurgical lesions designed to interrupt intrinsic and extrinsic nerve pathways within the intestinal wall. Removal of a collar of longitudinal muscle with attached myenteric plexus from the circumference of a segment of small intestine resulted in the underlying circular muscle. The few surviving neurites in the deep muscular plexus and circular muscle disappeared completely from lesioned segments that were, in addition, extrinsically denervated surgically. These results indicate that the majority of nerve fibres in the deep muscular and circular muscle plexuses of the guinea-pig small intestine is intrinsic to the intestine and originates from nerve cell bodies located in the overlying myenteric plexus. At the light-microscopic level, nerve bundles were traced from the myenteric plexus to the circular muscle.

Effect of chemical ablation of myenteric neurons on neurotransmitter levels in the rat jejunum

We have quantified neurotransmitter changes in the rat jejunum in which the myenteric neurons were ablated by serosal application of benzalkonium chloride. Within 2 days after benzalkonium chloride treatment, there was a 40% reduction in the activity of choline acetyltransferase, a specific marker for cholinergic neurons, and a 25% reduction in the amount of vasoactive intestinal peptide per centimeter length of jejunum. By 15 days, levels were comparable to those in control segments, and by 45 days after myenteric neuronal ablation, levels in treated tissues were twice those in controls. In contrast, we observed no reduction in the amount of leucine-enkephalin per centimeter length of jejunum at early times after benzalkonium chloride treatment, although by 45 days, levels of this neurotransmitter in treated segments of jejunum were more than twice those in controls. Significant increases in muscle thickness and tissue weight were also observed at 15, 30, and 45 days after myenteric neuronal ablation. Thus we have observed that in response to chemical ablation of myenteric neurons in the rat jejunum, there is a thickening of the smooth muscle layers and a compensatory increase in the production of certain neurotransmitters by the surviving neuronal elements in the gut.

Opioids and opioid receptors in peripheral tissues

Opioid peptides belonging to the enkephalin, beta-endorphin or dynorphin family, acting on specific opiate receptors may be found in peripheral tissues. Enkephalins have a widespread peripheral distribution, while beta-endorphin and dynorphin may be found locally in the enteric nervous system. The peptides of the various families are formed from specific precursor molecules. Apart from the enteric nervous system, opioids are also found in the adrenal medulla as well as in several autonomic ganglia. There is some evidence of three different classes of opioid receptors in peripheral tissues, i.e. mu-, delta- and kappa-receptors. These receptors are not only found on enteric nervous and mucosa cells but also on various cells in the immune system where opioid peptides seem to have important actions and appear to link the neuroendocrine and immune systems to control immunological functions. The physiological as well as the pathophysiological role of opioid peptides in the periphery is gradually being elucidated and, based on such knowledge, new therapeutic implications in gastrointestinal or immune diseases may be developed.

Sources of excitatory synaptic inputs to neurochemically identified submucous neurons of guinea-pig small intestine

The locations of the cell bodies of axons responsible for synaptic potentials evoked in neurochemically identified submucous neurons of the guinea-pig small intestine were investigated using a combination of intracellular recording, immunohistochemical and lesioning techniques. The myenteric plexus was removed from an 8-15 mm wide ring of small intestine in 15 anaesthetized guinea-pigs. After the operations, the animals were allowed to recover for 3-7 days so that nerve terminals that were disconnected from their cell bodies would degenerate. Preparations of submucous plexus were then made from the region under the lesion. Submucous neurons were impaled with electrodes containing a mixture of KCl and the fluorescent dye, Lucifer yellow CH, and their electrophysiological properties determined. They were then filled with the dye for subsequent reidentification after processing for immunohistochemical localization of vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY). The synaptic inputs to 33 neurons were characterized: 19 of these were found to be VIP-reactive, 7 were NPY-reactive and 7 were negative for both VIP and NPY. These results were compared to those obtained from 43 neurons in control preparations: 25 VIP-reactive, 9 NPY-reactive and 9 negative for both VIP and NPY. Removal of the myenteric plexus caused a significant reduction in the number of inputs providing fast excitatory synaptic potentials to each of the neurochemically defined classes of neurons. The lesions also caused a significant reduction in the number of VIP-reactive neurons that exhibited slow excitatory synaptic potentials (other neurochemical types do not normally exhibit such responses).(ABSTRACT TRUNCATED AT 250 WORDS)

Projections of peptide-containing neurons in rat small intestine

The distribution, origin and projections of nerve fibers containing vasoactive intestinal peptide, neuropeptide Y, somatostatin, substance P, enkephalin and calcitonin gene-related peptide were studied in the rat jejunum by immunocytochemistry and immunochemistry. Their origin was determined by the use of various procedures for extrinsic denervation (chemical sympathectomy, bilateral vagotomy or clamping of mesenterial nerves). The terminations of the different types of intramural nerve fibers were identified by examination of the loss of nerve fibers that followed local disruption of enteric nervous pathways (intestinal myectomy, transection or clamping). The majority of the peptide-containing nerve fibers in the gut wall were intramural in origin, each nerve fiber population having its own characteristic distribution and projection pattern. Nerve fibers emanating from the myenteric ganglia terminated within the myenteric ganglia and in the smooth muscle layers: those storing vasoactive intestinal peptide/neuropeptide Y, somatostatin and substance P were descending, those storing enkephalin were ascending and those containing calcitonin gene-related peptide projected in both directions. Nerve fibers emanating from the submucous ganglia terminated mainly within the submucous ganglia and in the mucosa: those storing calcitonin gene-related peptide or vasoactive intestinal peptide/neuropeptide Y were ascending and those storing substance P or somatostatin were both ascending and descending. Enkephalin nerve fibers could not be detected in the mucosa.

The immunohistochemical distribution of neuropeptide Y in lumbar pre- and paravertebral sympathetic ganglia of the guinea pig

Neuropeptide Y (NPY)- like immunoreactive nerve cell bodies and nerve fibres have been studied in normal and colchicine-treated ganglia of the caudal lumbar sympathetic chain (LSC) and the inferior mesenteric ganglion (IMG) of the guinea pig. The great majority of noradrenergic ganglion cells in the LSC (defined as containing tyrosine hydroxylase immunoreactivity), but less than 20% of those in the IMG, were NPY-positive. These proportions correspond well to the proportions of neurones that have been found to discharge phasically in electrophysiological experiments on the same ganglia. As noradrenergic terminals innervating blood vessels contain NPY, the data are consistent with the idea that phasic discharge is a characteristic of vasoconstrictor neurones.

Autoradiographic localization of mu- and delta-type opioid receptors in the gastrointestinal tract of the rat and guinea pig

The distribution of delta- and mu-type opioid binding sites in the gastrointestinal tract of the rat and guinea pig was studied by autoradiography after in vitro incubation of tissue slices with 3H-D-Ala2,D-Leu5-enkephalin, and 3H-naloxone or 3H-dihydromorphine to locate delta- and mu-type opioid receptors, respectively. In the gastric fundus, both mu- and delta-type binding sites were found to occur associated with the circular muscle, muscularis mucosae, and submucosal plexus, whereas in the corpus and antrum, binding was located primarily in the submucosal plexus, deep muscular plexus, and mucosa. Some mu-type opioid receptor sites were present in the myenteric plexus. A dense distribution of both mu- and delta-type binding sites was observed throughout the mucosa of the duodenum and ileum of the rat. In guinea pig ileal tissue, however, only mu-type binding could be demonstrated, occurring in the submucosal plexus and diffusely over the muscle layers. Endogenous opioid peptides, acting at these receptors sites, might be involved in the control of gastrointestinal motility, endocrine and exocrine secretions, as well as intestinal fluid and electrolyte transport.

Electron microscopic study of neuropeptide Y-containing nerve elements of the guinea pig small intestine

Neuropeptide Y-containing nerve cell bodies and processes were identified by electron microscopic immunocytochemistry in the guinea pig small intestine. Labeled nerve processes were numerous in the myenteric plexus. However, a few immunoreactive nerve fibers were found in all layers of the small intestine. Some of the immunoreactive nerve processes were found in close apposition to the epithelial cells of the crypts of Lieberkühn and to endothelial and smooth muscle cells. The neuropeptide Y-containing nerve cell bodies were preferentially located in the submucous ganglia. In the myenteric plexus many synaptic connections were observed between the neuropeptide Y-immunoreactive nerve fibers and unlabeled nerve cell bodies and other nerve fibers. These findings provide a morphologic basis for the possibility that neuropeptide Y may act as a transmitter and exert postsynaptic effects on intrinsic neurons, in addition to participating in the regulation of smooth muscle activity and epithelial cell functions.

Met5-enkephalin-Arg6-Gly7-Leu8 immunoreactivity in the human gut

The presence of the proenkephalin A-derived peptide Met5-enkephalin-Arg6-Gly7-Leu8 was demonstrated throughout the human gastrointestinal tract. Highest concentrations of Met5-enkephalin-Arg6-Gly7-Leu8, as assessed by radioimmunoassay, were measured in the separated muscularis externa, while lower levels were found in the submucosa and only small amounts in the mucosa. The results are consistent with a neuronal location of this peptide in the human gut. Over 65% of total immunoreactivity coeluted with the authentic peptide in both molecular exclusion chromatography and HPLC, while most of the remainder activity eluted earlier on gel filtration. The latter material probably represents N-terminally extended Met5-enkephalin-Arg6-Gly7-Leu8. Taken together with previous studies, our results appear to indicate that there are important species differences in post-translational processing of proenkephalin A in gut nerves.

Effects of noradrenaline and somatostatin on basal and stimulated mucosal ion transport in the guinea-pig small intestine

Noradrenaline (NA) and somatostatin (SOM) stimulate intestinal water and ion absorption and are found in mucosal nerve fibres and nerve terminals in submucous ganglia of the guinea-pig small intestine. As the main projection of submucous neurons is to the mucosa, NA and SOM might alter mucosal transport either by a direct effect on the epithelium or indirectly, by affecting submucous neurons. In this study these two possible sites of action of NA and SOM have been investigated in mucosa-submucosa preparations of guinea-pig ileum. In addition, the actions of NA and SOM on the secretory responses caused by stimulation of different populations of submucous neurons have been studied. The stimulants of secretion used were a nicotinic agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP, 10(-5) M), 5-hydroxytryptamine (5-HT, 10(-7) M) and electrical field stimulation (EFS), which activate cholinergic, noncholinergic and mixed populations of submucous secretomotor neurons, respectively. Segments of intestine were dissected free of external muscle and myenteric plexus and mounted in Ussing chambers. Short-circuit current (Isc) was measured as an indication of net active ion transport across the tissue. NA (greater than or equal to 10(-8) M) and SOM (greater than 10(-10) M) each caused a decrease in Isc, indicating a net increase in ion absorption. The NA response was abolished and the magnitude of the SOM response was reduced to 20% by tetrodotoxin (10(-7) M). DMPP, 5-HT and EFS each stimulated nerves that increased Isc and each of these responses was significantly diminished by NA and SOM.(ABSTRACT TRUNCATED AT 250 WORDS)

Actions of morphine and enkephalins on the internal anal sphincter of the cat: relevance for the physiological role of opiates

The effects of Leu-enkephalin, Met-enkephalin and morphine on the electrical activity of the internal anal sphincter were studied in anesthetized spinalized cats and in vitro on sphincteric muscle strips. All the effects of enkephalins and morphine were antagonized by naloxone (2 mg/kg, i.v. in vivo and 10(-6)M in vitro). In vivo, the enkephalins (0.01 mg/kg i.v.) and morphine (2 mg/kg, i.v.) decreased the amplitude of the excitatory responses evoked in the sphincter by stimulation of the hypogastric nerves. Opiates presumably act on the sympathetic nerve endings by reducing the release of noradrenaline. In vitro, the enkephalins (10(-6)M) and morphine (10(-6)M) had a similar inhibitory effect, indicating that opiates act, at least partly, at intramural level. In vivo, the enkephalins and morphine produced an inhibition of the spontaneous electrical activity of the internal anal sphincter. This inhibition occurs also in vitro; it is thus due to a peripheral effect of opiates acting either directly on the sphincteric smooth muscle cells, or through the nervous structures controlling sphincteric motility. In addition, the distribution of nerves containing enkephalin-like immunoreactivity, using whole mount preparations of cat internal anal sphincter, indicates that this area is supplied with a dense Leu- and Met-enkephalinergic innervation. Met- and Leu-enkephalin-like immunoreactive axons were detected within the circular and longitudinal muscles.

Selective presence of opiate receptors on intestinal circular muscle cells

Smooth muscle cells isolated separately from the longitudinal and circular muscle layers of guinea pig and human intestine exhibited a unique pattern of response to derivatives of proenkephalin and prodynorphin present in the myenteric plexus. Receptors for other myenteric transmitters (acetylcholine, the octapeptide of cholecystokinin and substance P) capable of mediating contraction, were present on both circular and longitudinal muscle cells, whereas opiate receptors were present on circular muscle cells and selectively absent from longitudinal muscle cells in both species. The opiate myoreceptors belonged to the three main subclasses (kappa, delta and mu) and exhibited a rank order of sensitivity similar to that of opiate neuroreceptors. The distribution of these receptors parallels the distribution of opioid nerve fibers and appears to reflect the role of opioids in the regulation of neuromuscular activity.

Opioid inhibition of synaptic transmission in the guinea-pig myenteric plexus

Intracellular recordings were made from neurones in the myenteric plexus of the guinea-pig ileum. Presynaptic nerves were excited by a focal stimulating electrode on an interganglionic strand. Fast excitatory postsynaptic potentials (e.p.s.ps) were depressed in amplitude by morphine and [Met5]enkephalin in the concentration range of 1 nM-1 microM. Nicotinic depolarizations evoked by exogenously applied acetylcholine (ACh) were not affected by these opioids. Hyperpolarization of the presynaptic fibres probably contributed to the depression of the fast e.p.s.p. because fast e.p.s.ps evoked by low stimulus voltages were more depressed than those evoked by high stimulus voltages and fast e.p.s.ps resulting from activation of a single presynaptic fibre were blocked in a non-graded manner. Opioids depressed the slow e.p.s.p. in those neurones in which they did not change the resting membrane potential. The slow e.p.s.p. was increased in amplitude in those neurones hyperpolarized by opioids. Depolarizations resulting from application of barium, substance P or ACh were also enhanced by opioids. Equivalent circuit models in which opioids increase, and substance P or ACh decrease, the same potassium conductance could account for this enhancement. The actions of opioids were prevented or reversed by naloxone (1 nM-1 microM). It is concluded that morphine and enkephalin inhibit the release of ACh and a non-cholinergic transmitter from fibres of the myenteric plexus, and that this may involve a hyperpolarization of presynaptic fibres. Additionally, opioids can interact postsynaptically with other substances which affect membrane potassium conductances.

Peptide neurons in the canine small intestine

The distributions of peptide-containing nerve fibers and cell bodies in the canine small intestine were determined with antibodies raised against seven peptides: enkephalin, gastrin-releasing peptide (GRP), neuropeptide Y, neurotensin, somatostatin, substance P, and vasoactive intestinal peptide (VIP). Immunoreactive nerve cell bodies and fibers were found for each peptide except neurotensin. In the muscle layers there were numerous substance P, VIP, and enkephalin fibers, fewer neuropeptide Y fibers, and very few GRP or somatostatin fibers. The mucosa contained many VIP and substance P fibers, moderate numbers of neuropeptide Y, somatostatin, and GRP fibers and rare enkephalin fibers. Nerve cell bodies reactive for each of the six neural peptides were located in both the myenteric and submucous plexuses. The distributions of nerve cell bodies and processes in the canine small intestine show many similarities with other mammals, for example, in the distributions of VIP, substance P, neuropeptide Y, and somatostatin nerves. There are some major differences, such as the presence in dogs of numerous submucosal nerve cell bodies with enkephalinlike immunoreactivity and of GRP-like immunoreactivity in submucous nerve cell bodies and mucosal fibers.

Heterogeneity of ganglia of the guinea pig myenteric plexus: an in vitro study of the origin of terminals within single ganglia using a covalently bound fluorescent retrograde tracer

Experiments were done to test the hypothesis that individual ganglia of the myenteric plexus of the guinea pig small intestine are heterogeneous with respect to the location of the neurons that provide terminals to them. The myenteric plexus, attached to the longitudinal layer of smooth muscle, was maintained in vitro. Individual ganglia were injected with a variety of potential retrograde tracers by pressure microejection from the tip (20-micron diameter) of a glass micropipette. The fluorescent dye 4-acetoamido, 4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) was found to be an effective tracer, labeling neuronal perikarya, evidently by retrograde transport. SITS has previously been shown not to cross plasma membranes, but to be covalently bound to the outer surface of that membrane, and to be taken up by nerve terminals to be retrogradely transported to label neuronal cell bodies. SITS fluorescence was found in about 12% of the neurons within the ganglion into which it was injected and also in approximately ten times more neurons in discretely located distant ganglia. No labeling of neurons was found when SITS was injected into the bath or into the smooth muscle below the myenteric plexus. Damage to neural connectives obstructed the labeling of neurons in ganglia distal to the injection site. Individual SITS-injected myenteric ganglia were found to vary greatly in the ratios of intraganglionic SITS-labeled neurons to the total number of neurons within the injected ganglion. The ratios of the number of intraganglionic SITS-labeled neurons to SITS-labeled neurons in distant ganglia projecting to the injected ganglion from elsewhere in the myenteric plexus also varied greatly. More strikingly, individual ganglia differed over a wide range with respect to whether the neurons in distant ganglia that provided them with terminals were situated in the oral, anal, or circumferential direction. Although the majority of projections were found to be from orally located ganglia, individual ganglia were observed that received predominantly or exclusively anal or oral projections. Others received mixtures of terminals from ganglia that were anal, oral, or circumferential. This anatomical heterogeneity in the location of afferent inputs to individual myenteric ganglia is probably reflected in a functional heterogeneity as well and will have to be taken into account in further studies of the physiology of the myenteric plexus. Individual ganglia of the plexus can no longer be taken as anatomically and functionally equivalent to one another.

Corticotropin-releasing factor: immunohistochemical colocalization with adrenocorticotropin and beta-endorphin, but not with Met-enkephalin, in subpopulations of duodenal perikarya of rat

By the use of two different double-staining techniques (simultaneous staining of adjacent serial sections and the double-staining elution method) it was possible to demonstrate that a corticotropin-releasing factor (CRF) immunofluorescence co-existed with an adrenocorticotropin (ACTH) and beta-endorphin (beta-END) immunoreactivity, but not with a Met-enkephalin (Met-ENK) immunostaining, within perikarya subpopulations of both the myenteric and submucousal plexus of the rat duodenum. Not a single Met-ENK-positive neuronal cell body was stained also for CRF, ACTH or beta-END. Even nerve fibres, localized in both the myenteric plexus and closely to submucousal blood vessels (probably arterioles), revealed a CRF immunofluorescence, which is also colocalized with an beta-END staining. These results are quite different to the recent observations in the mammalian hypothalamus, suggesting that some myenteric and submucousal plexus neurons may synthesize CRF as well as beta-END and ACTH, but not Met-ENK. The colocalized peptides might be concomitantly released into the synaptic cleft after terminal stimulation.

Dynorphin-A (1-8) is contained within perikarya, nerve fibres and nerve terminals of rat duodenum

By the use of well-characterized antibodies against porcine dynorphin-A(1-8), an endogenous opioid peptide, and the use of a modified immunofluorescence microscopic technique, dynorphin-A(1-8) stained perikarya, nerve fibres, and nerve terminals were visualized in the rat duodenum. Dynorphin-A(1-8) immunoreactive perikarya were revealed with certainty only in the myenteric plexus, while dynorphinergic nerve fibres could bee seen in the myenteric plexus and circular muscle layer, but not in the longitudinal muscle layer and submucous plexus. Dynorphin-A(1-8) immunofluorescent nerve endings were in close contacts with submucosal blood vessels, probably arterioles, and Brunner's gland cells. These findings suggest that the opioid peptide dynorphin-A(1-8) might be synthetized within myenteric plexus perikarya of the rat duodenum and that it might modulate the peristaltic activity, intestinal blood pressure, and production of mucopeptides synthetized within Brunner's gland cells.

Separate populations of opioid containing neurons in the guinea-pig intestine

Double staining immunofluorescence techniques were applied to investigate the co-existence of enkephalin, dynorphin and vasoactive intestinal peptide immunoreactivity in the guinea-pig enteric nervous system. Segments of guinea-pig small intestine were incubated for 24h in a culture medium with colchicine. Several subpopulations with overlapping immunoreactivities were found, i.e. neurons with enkephalin and vasoactive intestinal peptide, with enkephalin and dynorphin and with all three neuropeptides. It is probable that subpopulations with dynorphin and vasoactive intestinal peptide and with each neuropeptide only are also present. These subpopulations of enteric neurons with multiple neurochemical subcoding are likely to have different connections and functions.

Autoradiographic localization of opioid receptors in the rat stomach

The distribution of opioid receptors in the stomach has been studied using autoradiography of slide-mounted tissue sections incubated with [3H]D-Ala2,D-Leu5-enkephalin. The major sites of binding were the mucosa and the submucosal and deep muscular plexi. Other regions did not exhibit significant binding. These locations suggest that endogenous delta-opioid receptors may regulate mucosal ion transport and smooth muscle motility in the stomach.

Development of 5-hydroxytryptamine-like immunoreactive neurones in cultures of the myenteric plexus from the guinea-pig caecum

5-Hydroxytryptamine (5-HT)-like immunoreactive neurones were studied during the development of myenteric plexus explant cultures from the guinea-pig taenia coli over a period of 3 weeks in vitro, using immunofluorescence histochemistry. Brightly fluorescent 5-HT-like immunoreactive neuronal cell bodies and fibres were found in all ages of cultures examined. In mature cultures, where the histotypic organization resembles that of the plexus in vivo, the pattern of immunoreactivity was strikingly similar to that previously described for in situ preparations. These culture preparations may therefore be useful models for the study of the development of putative serotonergic neurones. High-performance liquid chromatography was used to measure 5-HT levels in fetal calf serum, a supplement of the culture medium used in this study. 5-HT levels of 0.48 X 10(-5) M to 1.74 X 10(-4) M were found in 4 batches of this serum, indicating that some of the immunoreactive neurones observed in the cultures may have selectively taken up 5-HT during development in vitro.

Electrophysiology and enkephalin immunoreactivity of identified myenteric plexus neurones of guinea-pig small intestine

Intracellular injection of the fluorescent dye, Lucifer Yellow CH, revealed the shapes of neurones in the myenteric plexus of the guinea-pig ileum, and these shapes were correlated with the electrophysiological properties and enkephalin immunoreactivity of the neurones. A total of eighty-three neurones were filled using electrodes containing a 5% solution of the dye. Forty-six cells had many short processes and a single long process (Dogiel type 1) and twenty-four cells had essentially smooth somas and one to eight long processes (Dogiel type II). Thirteen cells could not be put into either group. Enkephalin-like immunoreactivity was detected in twenty-two of the forty-six Dogiel type I cells. Eighteen of these had club-like short processes. No other cells of the eighty-three showed enkephalin-like immunoreactivity. Electrodes filled with a 0.5% solution of Lucifer Yellow in 0.5 M-KCl were used to record from and simultaneously to inject dye into 240 neurones. Eighty-six nerve cells had a slow after-hyperpolarization following the action potential (AH cells) and forty-six nerve cells had no after-hyperpolarization but exhibited a fast excitatory synaptic potential (S cells). The other cells could not be unequivocally identified by their observed electrophysiological characteristics. Almost all S cells (forty-two of forty-six) were Dogiel type I, while eighty-two of the eighty-six AH cells were Dogiel type II. Fifty S cells (eight located geometrically, forty-two by dye injection) and ninety-one AH cells (twenty-six located geometrically, sixty-five by dye injection) were examined for enkephalin immunoreactivity. Fifteen of the S cells were reactive, whereas all of the AH cells were unreactive. It appears that prolonged impalements reduce immunoreactivity so that the proportion of reactive neurones in this series is an underestimate of the true proportion of S cells with enkephalin-like immunoreactivity. The results suggest that a substantial proportion of the S cells in myenteric ganglia contain enkephalin immunoreactivity while none of the AH cells do. The enkephalin neurones have a distinctive shape and are all Dogiel type I cells. AH cells are nearly always Dogiel type II.

Immunocytochemical localization of substance P, methionine-enkephalin and somatostatin in the cat intestinal wall

The localization of substance P-(SP-), methionine-enkephalin (met-Enk-) and somatostatin (SOM-)like immunoreactivity was studied in the cat pyloric sphincter, ileum, ileocecal sphincter and proximal colon. The enteric plexuses in all regions examined contained SP-, met-Enk- and SOM-like immunoreactive varicose nerve fibres. A large number of especially SP- and met-Enk-containing varicosities were often seen to encircle the nerve cell bodies and processes in the two ganglionic plexuses. The SOM-like immunoreactive perikarya were the only peptide-containing nerve cells, preferentially located in the submucous ganglia. The predominant localization of the SOM-like immunoreactive neurons in the two enteric plexuses of the ileum was the most pronounced regional difference in the distribution pattern of the peptides. Among the layers of the cat intestinal wall the circular muscle contained the most peptide-immunoreactive fibres in contrast to the longitudinal muscle. Evidence was obtained for the occurrence of single peptide-immunoreactive varicose nerve fibres in muscularis mucosae as well as around the glands and the blood vessels. Immunoreactive endocrine cells occurred mainly in the ileum mucosa.

Excitatory synaptic potentials due to activation of neurons with short projections in the myenteric plexus

Intracellular microelectrodes have been used to examine the effects, on excitatory inputs to myenteric nerve cells, of lesions of intrinsic pathways in the myenteric plexus of the guinea-pig small intestine. The lesions consisted of circumferential cuts (myotomies) which severed the external musculature to the depth of the submucosa and thus interrupted pathways in the myenteric plexus. Sufficient time was allowed between creating the lesions and recording from the neurons for the endings of severed neurites to degenerate and this was confirmed histochemically by examining the distribution of varicose fibres with 5-hydroxytryptamine immunoreactivity in myenteric ganglia from which recordings were made. Two types of excitatory input, eliciting fast and slow excitatory post-synaptic potentials, respectively, were demonstrable in response to focal stimulation of nerves in the ganglia from which recordings were made. There were no differences in the proportions of neurons in which fast or slow excitatory synaptic potentials were evoked in unoperated preparations (controls), in islands 1.5-4 mm wide between myotomies, or within 1 mm on the oral or anal sides of myotomies. Possible differences in the amplitudes, durations at half amplitude, and threshold numbers of stimuli for initiation of slow excitatory synaptic potentials were analyzed. The only significant differences were found when data from control and oral areas were pooled and compared with combined data from island and anal areas (this assessed differences that could arise from severing nerve fibres running from oral to anal).(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution, pathways and reactions to drug treatment of nerves with neuropeptide Y- and pancreatic polypeptide-like immunoreactivity in the guinea-pig digestive tract

Pancreatic polypeptide-like immunoreactivity (PPLI) has been localized in nerves of the guinea-pig stomach and intestine with the use of antibodies raised against avian, bovine and human pancreatic polypeptide (PP), the C-terminal hexapeptide of mammalian PP, and against the related peptide, NPY. Each of the antibodies revealed the same population of neurones. Reactive cell bodies were found in both myenteric (5% of all neurones) and submucous ganglia (26% of all neurones) of the small intestine, and varicose processes were observed in the myenteric plexus, circular muscle, mucosa and around arterioles. The nerves were unaffected by bilateral subdiaphragmatic truncal vagotomy, but the staining of the periarterial nerves disappeared after treatment of animals with reserpine or 6-hydroxydopamine and was also absent after mesenteric nerves had been cut and allowed to degenerate. Vascular nerves showing immunoreactivity for dopamine beta-hydroxylase and PPLI had the same distribution. It is concluded that PPLI is located in periarterial noradrenergic nerves. However, other noradrenergic nerves in the intestine do not show PPLI, and PPLI also occurs in nerves that are not noradrenergic. Analysis of changes in the distribution of terminals after microsurgical lesions of pathways in the small intestine showed that processes of myenteric PP-nerve cells provide terminals in the underlying circular muscle and in myenteric ganglia up to about 2 mm more anal. Submucous PP-cell bodies provide terminals to the mucosa.

The origins, pathways and terminations of neurons with VIP-like immunoreactivity in the guinea-pig small intestine

We have analyzed changes in the distributions of terminals with vasoactive intestinal polypeptide (VIP)-like immunoreactivity, and accumulations in severed processes, that occur after lesions of intrinsic and extrinsic nerve pathways of the guinea-pig small intestine. The observations indicate that enteric vasoactive intestinal polypeptide immunoreactive neurons have the following projections. Nerve cell bodies in the myenteric plexus provide varicose processes to the underlying circular muscle; the majority of these pathways, if they extend at all in the anal or oral directions, do so for distances of less than 1 mm. Nerve cell bodies of the myenteric plexus also project anally to provide terminals to other myenteric ganglia. The lengths of the majority of these projections are between 2 and 10 mm, with an average length of about 6 mm. Processes of myenteric neurons also run anally in the myenteric plexus and then penetrate the circular muscle to provide varicose processes in the submucous ganglia at distances of up to 15 mm, the average length being 9-12 mm. In addition, there is an intestinofugal projection of myenteric neurons whose processes end around nerve cell bodies of the coeliac ganglia. A similar projection from the colon supplies the inferior mesenteric ganglia. The nerve cell bodies in submucous ganglia give rise to a subepithelial network of fibres in the mucosa and also supply terminals to submucous arterioles. It is concluded that vasoactive intestinal polypeptide is contained in neurons of a number of intrinsic nerve pathways, influencing motility, blood flow and mucosal transport. The myenteric neurons that project to prevertebral sympathetic ganglia may be involved in intestino-intestinal reflexes.