Coexistence of immunoreactive substance P and serotonin in neurones of the gut

Alcohol and the Brain-Gut Axis: The Involvement of Microglia and Enteric Glia in the Process of Neuro-Enteric Inflammation

Binge or chronic alcohol consumption causes neuroinflammation and leads to alcohol use disorder (AUD). AUD not only affects the central nervous system (CNS) but also leads to pathologies in the peripheral and enteric nervous systems (ENS). Thus, understanding the mechanism of the immune signaling to target the effector molecules in the signaling pathway is necessary to alleviate AUD. Growing evidence shows that excessive alcohol consumption can activate neuroimmune cells, including microglia, and change the status of neurotransmitters, affecting the neuroimmune system. Microglia, like peripheral macrophages, are an integral part of the immune defense and represent the reticuloendothelial system in the CNS. Microglia constantly survey the CNS to scavenge the neuronal debris. These cells also protect parenchymal cells in the brain and spinal cord by repairing nerve circuits to keep the nervous system healthy against infectious and stress-derived agents. In an activated state, they become highly dynamic and mobile and can modulate the levels of neurotransmitters in the CNS. In several ways, microglia, enteric glial cells, and macrophages are similar in terms of causing inflammation. Microglia also express most of the receptors that are constitutively present in macrophages. Several receptors on microglia respond to the inflammatory signals that arise from danger-associated molecular patterns (DAMPs), pathogen-associated molecular patterns (PAMPs), endotoxins (e.g., lipopolysaccharides), and stress-causing molecules (e.g., alcohol). Therefore, this review article presents the latest findings, describing the roles of microglia and enteric glial cells in the brain and gut, respectively, and their association with neurotransmitters, neurotrophic factors, and receptors under the influence of binge and chronic alcohol use, and AUD.

NUMERICAL SIMULATION OF THE ROLE OF CO-TRANSMISSION BY ACETYLCHOLINE AND SEROTONIN ON MOTILITY OF THE GUT

Electrophysiological mechanisms of co-transmission by serotonin (5-HT) and acetylcholine (ACh), co-expression of their receptor types, i.e., 5-HT type 3 and 4, nicotinic cholinerginc (nACh) and muscarinic cholinergic (μACh), and effects of selective and non-selective 5-HT3 and 5-HT4 receptor agonists/antagonists, on electromechanical activity of the gut were studied numerically. Two series of numerical experiments were performed. First, the dynamics of the generation and propagation of electrical signals interconnected with the primary sensory (AH) neurons, motor (S) neurons and smooth muscle cells were studied in a one-dimensional model. Simulations showed that stimulation of the 5-HT3 receptors reduced the threshold of activation of the mechanoreceptors by 17.6%. Conjoint excitation of the 5-HT3 and 5-HT4 receptors by endogenous serotonin converted the regular firing pattern of electrical discharges of the AH and S neurons to a beating mode. Activation confined to 5-HT3 receptors, located on the somas of the adjacent AH and S type neurons, could not sustain normal signal transduction between them. It required ACh as a co-transmitter and co-activation of the nACh receptors. Application of selective 5-HT3 receptor antagonists inhibited dose-dependently the production of action potentials at the level of mechanoreceptors and the soma of the primary sensory neuron and increased the threshold activation of the mechanoreceptors. Normal mechanical contractile activity depended on co-stimulation of the 5-HT4 and μACh receptors on the membrane of smooth muscle cells. In the second series of simulations, which involved a spatio-temporal model of the functional unit, effects of co-transmission by ACh and 5-HT on the electromechanical response in a segment of the gut were analyzed. Results indicated that propagation of the wave of excitation between the AH and S neurons within the myenteric nervous plexus in the presence of 5-HT3 receptor antagonists was supported by co-release of ACh. Co-stimulation of 5-HT3, nACh and μACh receptors impaired propulsive activity of the gut. The bolus showed uncoordinated movements. In an ACh-free environment Lotronex (GlaxoSmithKline), a 5-HT3 receptor antagonist, significantly increased the transit time of the pellet along the gut. In the presence of ACh, Lotronex produced intensive tonic-type contractions in the longitudinal and circular smooth muscle layers and eliminated propulsive activity. The 5HT4 receptor agonist, Zelnorm (Novartis), preserved the reciprocal electromechanical relationships between the longitudinal and circular smooth muscle layers. The drug changed the normal propulsive pattern of activity to an expulsive (non-mixing) type. Treatment of the gut with selective 5HT4 receptor antagonists increased the transit time by disrupting the migrating myoelectrical complex. Cisapride (Janssen), a mixed 5HT3 and 5HT4 receptor agonist, increased excitability of the AH and S neurons and the frequency of slow waves. Longitudinal and circular smooth muscle syncytia responded with the generation of long-lasting tonic contractions, resulting in a "squeezing" type of pellet movement. Comparison of the theoretical results obtained on one-dimensional and spatio-temporal models to in vivo and in vitro experimental data indicated satisfactory qualitative, and where available, quantitative agreement.

Neurochemical bases of visceral nociception: mathematical model

A mathematical model of visceral perception was constructed, comprising primary sensory, motor, intestinofugal and principal neurons, interstitial cells of Cajal and smooth muscle elements that are arranged in a functional circuit through chemical synapses. The mathematical description of constructive elements was based on detailed morphological, anatomical, electrophysiological and neuropharmacological characteristics of cells and chemical processes of electrochemical coupling. Emphasis was given to signal transduction mechanisms that involved multiple neurotransmitters and receptor polymodality. The role of co-transmission by acetylcholine (ACh), serotonin (5-HT), noradrenalin (NA), N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and their corresponding receptors-muscarinic and nicotinic type ACh receptors, beta-adrenoceptors, 5-HT(3/4) type serotonergic receptors, NMDA and AMPA receptors in pathogenesis of nociception was studied numerically. Results of computer simulations reproduced patterns of electrical activity of neurons and mechanical responses of the smooth muscle similar to those observed in in vivo and in vitro experiments when ACh, 5-HT, NA, NMDA and AMPA were acting either alone or co-jointly. The results provide neurochemical bases for explanation of pathophysiological mechanisms of visceral nociception, which cannot be elucidated by existing experimental methods. Care should be taken though when extrapolating the numerical results onto the actual system because of limiting assumptions of the model.

Chronotropic action of 5-hydroxytryptamine (5-HT) on colonic migrating motor complexes (CMMCs) in the isolated mouse colon

The effects of 5-hydroxytryptamine (5-HT) and related drugs on colonic migrating motor complexes (CMMCs) were evaluated in isolated colons from the heterozygotes of pie-bald lethal mice. 5-HT produced a dose-related increase in the frequency of CMMCs without any change in the amplitude or duration of the CMMC contractions themselves. The 5-HT(2) agonist, alpha-methyl 5-HT, (100 nM-1 microM) increased the frequency of CMMCs whilst the 5-HT(3) agonist, 2-methyl 5-HT, did so at 10 microM. The 5-HT(4) agonist, 5-methoxy dimethyl tryptamine oxalate did not alter the frequency of CMMCs in the concentration range 1 nM-10 microM. The 5-HT(3) receptor antagonist, ondansetron, increased the interval between CMMCs in the concentration range 100 nM-1 microM, whilst the 5-HT(1) receptor antagonist, methiothepin, the 5-HT(2) receptor antagonist, cyproheptadine and the 5-HT(4) receptor antagonist, SDZ 205 557, had no significant effects on the interval between CMMCs in the concentration range 1 nM-10 microM. The effects of 5-HT did not appear to be altered by the presence of ondansetron (1 microM) or cyproheptadine (1 microM). However, in the presence of ondansetron (1 microM), the further addition of cyproheptadine (1 microM) effectively abolished CMMCs. Furthermore, in the combined presence of these antagonists the effects of 5-HT were severely diminished. It is suggested that the frequency of CMMCs may be under the influence of endogenously released 5-HT in this preparation

Immunohistochemical colocalization of serotonin, substance P and Met-enkephalin-Arg6-Gly7-Leu8 in the endocrine cells of the ruminant duodenum

The duodenum of various ruminants was examined by immunohistochemical staining for serotonin, substance P and Metenkephalin-Arg6-Gly7-Leu8 (MENK8). Serotonin- and substance P-immunoreactive endocrine cells were detected in samples from cow, calf, sheep, goat, and barbary sheep, MENK8-immunoreactive endocrine cells were detected exclusively in samples from cow and calf. Substance P and MENK8 immunoreactivity was found in serotonin-immunoreactive endocrine cells of cattle. Substance P- and MENK8-immunoreactive nervous elements were detected in all ruminants examined. The present results suggest that the expression and/or the mechanism that controls the expression of each peptide might differ between endocrine cells and nerve cells and might also depend on animal species.

Investigation into the 5-hydroxytryptamine-induced atropine-resistant neurogenic contraction of guinea-pig proximal colon

1. The aim of this study was to characterize the receptors mediating the atropine-resistant neurogenic contraction to 5-hydroxytryptamine (5-HT) in the longitudinal muscle of the guinea-pig proximal colon and to determine the type of tachykinin receptors involved in the contractile response to 5-HT by the use of selective antagonists. 2. In the presence of atropine (0.3 microM), guanethidine (5 microM), hexamethonium (100 microM), ketanserin (0.1 microM) and indomethacin (3 microM), 5-HT (0.01-3 microM) produced concentration-dependent neurogenic contractions of colonic strips and at 0.3 microM produced a maximal effect (pEC50 = 7.39 +/- 0.09, n = 18). The 5-HT4 receptor stimulant, 5-methoxytryptamine (5-MeOT, 0.03-10 microM) also produced neurogenic contractions with similar maximum effect to those of 5-HT (pEC50 = 6.89 +/- 0.16). 3. The 5-HT4 receptor antagonist, DAU 6285 (3 microM) shifted the concentration-response curves to both 5-HT and 5-MeOT to the right without significant depression of the maximum, but the 5-HT1/5-HT2 receptor antagonist, metitepine (0.1 microM) and the 5-HT3 receptor antagonist, ondansetron (0.3 microM) had no effect on the control curves to 5-HT and 5-MeOT. 4. The selective NK1 receptor antagonist, FK 888 (1 microM) markedly attenuated the contractions to 5-HT and 5-MeOT. In contrast, the selective NK2 receptor antagonist, SR 48968 (10 nM) and the selective NK3 receptor antagonist, SR 142801 (10 nM) had no effect on the contractions to 5-HT and 5-MeOT. 5. These results indicate that the 5-HT-induced atropine-resistant neurogenic contraction of guinea-pig proximal colon is due to activation of 5-HT4 receptors, presumably located on excitatory motor neurones, innervating the longitudinal muscle. The contraction evoked by activation of the 5-HT4 receptors is mediated primarily via NK1 receptors but not NK2 or NK3, suggesting that the 5-HT4 receptor-mediated contraction is evoked indirectly via tachykinin release from tachykinin-releasing excitatory neurones.

Projections of 5-hydroxytryptamine-immunoreactive neurons in guinea-pig distal colon

The presence of 5-hydroxytryptamine in enteric neurons of the guinea-pig distal colon was demonstrated by immunohistochemistry and the projections of the neurons were determined. 5-Hydroxytryptamine-containing nerve cells were observed in the myenteric plexus but no reactive nerve cells were found in submucous ganglia. Varicose reactive nerve fibres were numerous in the ganglia of both the myenteric and submucous plexuses, but were infrequent in the longitudinal muscle, circular muscle, muscularis mucosae and mucosa. Reactivity also occurred in enterochromaffin cells. Lesion studies showed that the axons of myenteric neurons projected anally to provide innervation to the circular muscle and submucosa and to other more anally located myenteric ganglia. The results suggest that a major population of 5-hydroxytryptamine neurons in the colon is descending interneurons, most of which extend for 10 to 15 mm in the myenteric plexus and innervate both 5-hydroxytryptamine and non-5-hydroxytryptamine neurons.

Uptake of 5-hydroxydopamine into non-sympathetic nerves of guinea-pig uterine artery in late pregnancy

Perivascular nerve fibres of the uterine artery of virgin and late pregnant guinea-pigs were examined under the electron microscope following loading with 5-hydroxydopamine, a marker for catecholamine uptake, and immunohistochemistry for dopamine beta hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, substance P and calcitonin gene-related peptide. Varicosities, loaded with 5-hydroxydopamine labelled vesicles, and immunoreactive axons were counted in whole transverse sections of uterine arteries. Localization of the immunoreactivities in 5-hydroxydopamine-labelled vesicles was also studied. Colocalization of substance P and dopamine beta hydroxylase immunoreactivities was investigated at the light microscopic level. Both total and relative number of varicosities with 5-hydroxydopamine-labelled vesicles in a whole section of the artery increased in late pregnancy (61.2 +/- 10.2 versus 24.5 +/- 3.2 in virgin, representing 35% and 27% respectively, of all varicosities). Also the number of neuropeptide Y, vasoactive intestinal polypeptide, substance P and calcitonin gene-related peptide-immunoreactive axons increased, but their relative proportion remained unchanged. In virgin guinea-pigs only calcitonin gene-related peptide and neuropeptide Y immunoreactivities were associated with varicosities loaded with small dense-cored vesicles, while in late pregnancy 5-hydroxydopamine-labelled vesicles were also seen in a number of vasoactive intestinal polypeptide, substance P and calcitonin gene-related peptide-immunoreactive axons. Double immunolabelling for dopamine beta hydroxylase and substance P immunoreactivity showed that substance P immunoreactivity was not present in dopamine beta hydroxylase-immunoreactive axons of the uterine artery, of neither virgin nor late pregnant guinea-pigs. It is concluded that vascular hypertrophy of the uterine artery in late pregnancy is associated with an increase in the number of perivascular nerve fibres, that involves many, if not all of the subpopulations of neurons supplying the uterine artery. Also 5-hydroxydopamine-labelled varicosities were increased, but the results of the present study indicate that some of the nerve fibres that are able to take up 5-hydroxydopamine in late pregnancy are not sympathetic (i.e. are sensory and/or parasympathetic in origin). The relevance of these findings in pregnancy is discussed.

Grafting in acute spinal cord injury: morphological and immunological aspects of transplanted adult rat enteric ganglia

We have studied allogeneic transplants of adult rat enteric ganglia in order to evaluate their use as donor tissue for eventual autografts in rodent spinal cord injury models. Female Sprague-Dawley rats of similar weights served either as transplant donors or as recipients. A glass micropipette of 0.8 mm diameter was used to create a local penetrating injury of the lower thoracic spinal cord and the transplant material was pressure injected through the pipette within the neural parenchyma. Ganglia of the myenteric plexus adhering to the stratum longitudinal muscularis were dissected from portions of the jejunum and ileum. Following partial enzymatic digestion and mechanical disruption of the myenteric plexus and muscle tissue (labeled with adherent rhodamine conjugated microbeads), reaggregates of myenteric plexus and muscle were suspended in growth medium and cultured in vitro for one to two days prior to transplantation. Transplants were examined at three, four, six, and eight weeks after surgery. Some of the donor tissue was grown in vitro, in order to determine its cellular composition. These cultured explants were fixed after 10 days, and like myenteric plexus and muscle grafts, were stained histochemically for acetylcholinesterase and observed by fluorescence and light microscopy. At the earlier post-transplantation periods, grafts contained several clusters of enteric ganglion cells that were positive for acetylcholinesterase and exhibited ultrastructural features characteristic of the enteric nervous system. They had well-defined boundaries. Reactive astrocytes and their processes remained located within the host spinal cord adjacent to the boundary region of the grafts. Likewise, macrophages were located in areas abutting the graft. Newly formed vasculature penetrated the graft interior and appeared to be continuous with the host vessels. Grafts grown for at least eight weeks were characterized by interdigitating boundaries. Finger-like protrusions of graft tissue containing fibroblasts and collagen intermixed with adjacent gray and white matter of the host cord. Such transplants also had reactive astrocytes and ED1-positive macrophages. At this later stage, several groups of ganglion cells were identified that were intensely acetylcholinesterase-positive; however, only two of four grafts were recovered, whereas two of the transplants degenerated. We postulate that degeneration of allogeneic grafts may occur as a result of ongoing immune responses of the host which could be prevented by use of autogeneic enteric ganglia. Our studies show that fully differentiated enteric ganglia can survive transplantation to acutely injured spinal cord of adult rats.

[Role of substance P in the nervous system control of digestive motility]

Substance P is a 11 amino-acids peptide which belongs to the tachykinins, a family of peptide which induces a rapid contraction of the smooth muscle of the digestive tract. The occurrence of substance P has been demonstrated by immunohistochemical and radioimmunological techniques in most parts of the central and peripheral nervous system. Substance P exerts on the smooth muscle of all the areas of the digestive tract a strong excitatory effect which is either direct or relayed by the cholinergic intramural neurones. Numerous electrophysiological, pharmacological and immunohistochemical data lead to the conclusion that substance P is released by intrinsic neurones of the digestive tract or by extrinsic nerves (vagus and splanchnic nerves, etc...). This release is enhanced by acetylcholine, cholecystokinin, serotonin and neurotensin, it is reduced by opioid peptides and noradrenaline. Substance P participates in the intestinal peristaltic reflex by the activation of the smooth muscle cells of the intestine, either directly or through the activation of the cholinergic intrinsic neurones. Substance P is also involved in the genesis of a non-cholinergic ascending excitatory activity likely occurring during vomiting. Lastly, substance P participates in the reflex contraction of the lower oesophageal sphincter following acidification of the distal part of the oesophagus.

Biogenic amine localization in cardiac ganglion intrinsic neurons: electron microscopic histochemistry of SIF cells

The parasympathetic cardiac ganglion in the mudpuppy, N. maculosus, contains postganglionic nerve cells and intrinsic neurons, many of which are small intensely fluorescent (SIF) cells. Several bioactive substances have been localized in the intrinsic nerve cells which may have integrative effects at synapses within the ganglion. Ganglionic intrinsic neurons can be identified electron microscopically by the presence of numerous cytoplasmic granular vesicles 80-120 nm in diameter. Throughout the ganglion there are bundles of unmyelinated fibers some of which are filled with granular and agranular vesicles and axosomatic terminals with similar vesicles synapsing on principal parasympathetic nerve cells. To understand the aminergic contribution to ganglionic synaptic circuitry the chromaffin reaction was used. The intrinsic neurons (i.e., SIF cells) were readily identified by their characteristic intracellular granule population. All intrinsic nerve cells identified showed granules which were positively labelled by the chromaffin reaction. Granular vesicles in synaptic profiles on principal cells (P cells) were also labelled indicating a direct aminergic synaptic innervation to these cells. The cell bodies of intrinsic neurons, ensheathed with supportive glial-like cellular processes, rarely received synapses. Elemental microanalysis was used to verify the chromium content of the electron dense product within the granular vesicles. These studies demonstrated direct aminergic synaptic input to at least a subpopulation of principal parasympathetic cells in the cardiac ganglion of mudpuppy.

Effects of vasoactive intestinal polypeptide, substance P, 5-hydroxytryptamine, met-enkephalin and neurotensin on the swimbladder smooth muscle of two teleost species,Gadus morhua andAnguilla anguilla

The effects of vasoactive intestinal polypeptide (VIP), substance P (SP), 5-hydroxytryptamine (5-HT), neurotensin (NT) and met-enkephalin (mEnk) on the smooth muscles of the teleost swimbladder were studied in two teleost species, the Atlantic cod (Gadus morhua) and the eel (Anguilla anguilla). The study was made on isolated strip preparations of the muscularis mucosae, using putative transmitters corresponding to the immunoreactive materials that have previously been localized by immunohistochemical methods in nerves or endocrine/paracrine cells of the teleost swimbladder and/or the gastrointestinal canal. VIP was relaxatory on both cod and eel swimbladder smooth muscle, SP and 5-HT were constrictory in both species, and mEnk was excitatory on the eel swimbladder smooth muscle. Clear effects of these agents were usually seen at a concentration ofca. 10 nM in cumulative concentration/effect experiments. NT had no effect in either species. In the eel, the effects on the pneumatic duct were generally greater than on the swimbladder proper. The study indicates that the 5-HT and peptides previously observed by immunohistochemistry have physiological functions in the swimbladder.

Sensory-motor neuromodulation of sympathetic vasoconstriction in the rabbit central ear artery

Histochemical and pharmacological studies were performed on the rabbit central ear artery. In perivascular nerves, positive immunoreactivity for calcitonin gene-related peptide and substance P was demonstrated. Calcitonin gene-related peptide-like immunoreactivity was also found to be colocalised with substance P-like immunoreactivity in a subpopulation of perivascular nerves. In vitro incubation with 6-hydroxydopamine did not alter the intensity and/or density of either the calcitonin gene-related peptide- or substance P-like immunoreactive fibres, whereas incubation with capsaicin significantly reduced both. In pharmacological studies, calcitonin gene-related peptide reduced the vasoconstrictor responses to exogenous noradrenaline and alpha, beta-methylene ATP and to electrical field stimulation in a concentration-dependent manner. In segments of the central ear artery preconstricted with noradrenaline, relaxation mediated by calcitonin gene-related peptide was endothelium-independent. These results shed new light on the innervation and nervous control of the rabbit central ear artery previously thought to be exclusively under sympathetic (adrenergic and purinergic) control. Further, the results suggest that calcitonin gene-related peptide localised in sensory nerves in the rabbit central ear artery may act as an inhibitory modulator of excitatory sympathetic vascular neurotransmission.

Neuropeptide release from isolated myenteric nerve endings derived from the guinea pig myenteric plexus

Isolated myenteric nerve varicosities prepared from the myenteric plexus of the guinea pig ileum were investigated as a suitable model system with which to study the release of several neuropeptide-like immunoreactivities (-LI). Basal release of substance P-LI, neurokinin A-LI, Leu-enkephalin-LI and Met-enkephalin-LI was determined, and clear depolarization-induced release of the enkephalin-LI's and neurokinin A-LI was obtained using this preparation, providing further support for their roles as putative mediators in the enteric nervous system. Evoked-release of these peptides was dependent on the presence in the incubation mixture of certain antagonists to known endogenous neuronal mediators. In the absence of such antagonists, no unequivocal evidence of release was seen. Clear evoked release of Leu-enkephalin-LI occurred only in the presence of the adenosine receptor antagonist 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX), atropine and naloxone. Release of Met-enkephalin-LI occurred in the presence of either atropine or naloxone. The release of neurokinin A-LI was evident in the presence of DPSPX. These findings suggest the existence of either distinct subpopulations of nerve varicosities or distinct neuronal pools containing each peptide and that these peptides may be under differential regulation by endogenous inhibitory mediators. It is concluded that, under suitable conditions, isolated myenteric nerve varicosities provide a useful model system for the study of release, and the modulation of release, of endogenous neuropeptides.

Metabolic origins of 5-hydroxytryptamine in enteric neurons in a teleostean fish (Platycephalus bassensis), a toad (Bufo marinus) and the guinea-pig

1. 5-Hydroxytryptamine (5-HT) content and synthesis in mucosa-free intestine of guinea-pig, the teleost Platycephalus bassensis and the amphibian Bufo marinus was studied by HPLC with electrochemical detection or by TLC. 2. The 5-HT content of small intestine was: guinea-pig 0.58; Bufo: 1.23; Platycephalus: 26.88 nmol/g. 3. Intestine from each species synthesized 5-HT from exogenous 5-HTP. 4. Platycephalus preparations synthesized labelled 5-HT from 14C-tryptophan, but no labelled 5-HT was detected after similar incubation of guinea-pig or Bufo preparations. 5. Incubation of guinea-pig preparations with tryptophan did not increase tissue 5-HT or 5-HIAA content. 6. 5-HT in Platycephalus enteric neurons may be synthesized from tryptophan in situ; 5-HT in Bufo and guinea-pig neurons may be synthesized elsewhere, perhaps in enterochromaffin cells.

Immunocytochemical localisation of neuropeptide Y and 5-hydroxytryptamine in a subpopulation of amine-handling intracardiac neurones that do not contain dopamine beta-hydroxylase in tissue culture

The colocalisation of neuropeptide Y (NPY)- and 5-hydroxytryptamine (5-HT)-immunoreactivities in intracardiac neurones in dissociated cultures from the atria and interatrial septum of newborn guinea pig heart was demonstrated by the sequential application of specific antisera which were visualised by two different fluorochromes. In this way it was observed that most 5-HT-immunoreactive neurones also contained NPY-immunoreactivity (approximately 40% of identified neurones), some neurones were 5-HT-immunoreactive alone (approximately 10%), while neurones that were NPY-immunoreactive only were rarely seen. No dopamine beta-hydroxilase (DBH)-immunoreactive intracardiac neurones were demonstrated in any of the culture preparations studied, although DBH-immunoreactive neurons could be detected in sections of the newborn guinea pig heart containing intracardiac ganglia. The possible implications of the colocalisation of 5-HT, that has been taken up from the culture medium, with NPY in a population of intracardiac neurones are discussed; and reasons for the loss of expression of DBH by these neurones under the conditions of culture are considered.

Substance P-like immunoreactivity and the effects of tachykinins in the intestine of the Atlantic cod, Gadus morhua

The substance P (SP)-like peptides present in the intestine of the cod, Gadus morhua, were studied by immunochemical techniques. The amount of SP-like material in extracts of the intestine was quantified using radioimmunoassay (RIA). Immunohistochemistry indicated that the SP-like material detected in nerve fibres and endocrine cells of the intestine is more closely related to SP than to the other tachykinins used in the study. The excitatory response of SP on the vascularly perfused cod intestine was reduced or abolished by treatment with atropine, methysergide or tetrodotoxin. The results indicate that SP acts partly via cholinergic and serotonergic neurons and partly directly on the smooth muscle cells of the intestine. The effect of SP was compared to the effects of 5 other tachykinins. No great difference was found between the potencies of the tachykinins, suggesting that the receptors present are most similar to the SP-P type of receptor.

Regulatory mechanisms in endoluminal release of serotonin and substance P from feline jejunum

The mechanisms controlling vagally induced 5-HT and SP release into the jejunal lumen were studied in the cat. In control animals, electrical vagal nerve stimulation doubled the rate of endoluminal secretion of 5-HT and SP. Propranolol pretreatment did not alter luminal secretion of these hormones. Atropine suppressed motor function and induced dose-related inhibition of vagal release of endoluminal 5-HT, but not of SP; the response to hexamethonium pretreatment was similar to that of atropine. In contrast, superior cervical ganglionectomy did not alter stimulated endoluminal 5-HT release but it completely abolished release into the portal vein. The portal 5-HT release was not affected by ganglionic blockade. The data suggest that vagally mediated 5-HT release into the lumen and the portal circulation are mediated by different neural mechanisms, the former cholinergic, the latter presumably adrenergic; and release of feline 5-HT and SP are independent, suggesting two intestinal sources, the EC cell for 5-HT and peptidergic neurons for SP.

Substance P and vasoactive intestinal peptide in serotonin-induced nasal secretions in normal subjects

The aim of this study was to examine if nasal secretions contained substance P and/or vasoactive intestinal peptide. Serotonin nasal challenge was performed in 14 normal subjects 15 min after intranasal pretreatment (double-blind) with atropine, methysergide, chlorpheniramine or isotonic saline. Serotonin induced a dose dependent increase in secretion (P less than 0.05), and only pretreatment with atropine reduced the secretion (P less than 0.02). Substance P, measured by radioimmunoassay, was found in all of the examined secretions (n = 100) with a median concentration of 13.7 pmol/l (range 1.7-125.0). Serotonin challenge increased the concentration or content of substance P in a dose-related fashion (P less than 0.01). The different pretreatments did not affect the concentration of substance P. Vasoactive intestinal peptide was found in low concentration in 37% of the secretions with a median concentration of 0 pmol/l (range 0-50.0).

Coexistence of neuropeptides in sympathetic preganglionic neurons of the cat

Coexistence of four neuropeptides in sympathetic preganglionic neurons (SPN) was investigated immunohistochemically in cats after intrathecal administration of colchicine. Neurons were studied for the coexistence of all combinations of enkephalin-, neurotensin-, somatostatin-, and substance P-like immunoreactivity (ENK, NT, SS, and SP, respectively) in the intermediolateral cell column (IML), nucleus intercalatus (IC), and central autonomic area (CA). The results indicate that SP coexists with all three other peptides, SS coexists with NT and SP, and ENK coexists only with SP. In all cases, SPN which contained two peptides were found in the IML in almost all levels of the thoraco-lumbar cord. Much smaller numbers of SPN which contained two peptides (in the same combinations as above) were found in the IC and not all segments contained such neurons. In the CA, only one neuron was found which contained two peptides (SP/SS). The distribution of SPN containing two peptides suggests that these neurons may participate in more general functions of the autonomic nervous system and that they are not likely involved in the innervation of specific visceral organs.

Immunoreactivity in Limulus. II. Studies of serotoninlike immunoreactivity, endogenous serotonin, and serotonin synthesis in the brain and lateral eye

Serotoninlike immunoreactivity was examined by the fluorescein-isothiocyanate-labeled secondary antibody technique in the lateral eye and brain of Limulus. Endogenous serotonin was measured with high-performance liquid chromatography and electrochemical detection. The synthesis of [3H]serotonin from [3H]tryptophan was measured in the presence and absence of reserpine. Fibers with serotoninlike immunoreactivity were found in the proximal stalks of the corpora pedunculata, in the neuropil of the central body, in the neuropils of the visual centers (lamina, medulla, and ocellar ganglion), in the optic tract that connects the ocellar ganglion with the posterior medial medulla, and in the central neuropil of the brain. Immunoreactive somata were found in four groups in the brain. Up to 50 somata were scattered through each side of the dorsal medial group that lies centered on the dorsal surface within the curve of the central body. These neurons innervate the central body neuropil and send processes into the central neuropil. Three or four reactive somata formed the ventral pole of each medullar group. These may provide the innervation of the proximal stalk of the corpora pedunculata. Five to ten reactive neurons were observed anteriorly in the ventral posterior lateral group #2 on each side that send processes into the central neuropil. Ten to 15 reactive somata were found on either side of the midline in the dorsal anterior part of the ventral medial group that contribute processes to the central neuropil. The remainder of the brain was not immunoreactive. No immunoreactive fibers or somata were found in the lateral eye or in the lateral optic nerve. Serotoninlike and substance P-like immunoreactivities were not found to be colocalized anywhere in the brain. Significant amounts of endogenous serotonin were detected in the lamina and medulla whose neuropils are rich in immunoreactive fibers and in the central body and dorsal medial group that are also rich in immunoreactive somata and fibers. No endogenous serotonin was detected in either the lateral eye or the lateral optic nerve. The lamina, medulla, and central body and dorsal medial group also synthesized and stored [3H]serotonin from [3H]tryptophan. It is likely that serotonin is a neurotransmitter in the brain, but not in the lateral eye of the horseshoe crab. In particular, it appears that serotoninergic neurons may play a role in central visual processing.

The glutamate decarboxylase-, leucine enkephalin-, methionine enkephalin- and substance P-immunoreactive neurons in the neostriatum of the rat and cat: evidence for partial population overlap

We have examined the populations of neurons in the neostriatum of both rat and cat that are immunoreactive for glutamate decarboxylase, [Leu]enkephalin, [Met]enkephalin and substance P. Neurons that were immunoreactive for glutamate decarboxylase made up 47% of the neurons in our samples from the rat and ranged from 39 to 49% of the neurons in the cat. Those immunoreactive for [Leu]enkephalin made up 44-49% of the neurons in rat neostriatum, and 38-47% in the cat, and those immunoreactive for [Met]enkephalin made up 36-41% of the neurons in rat and 43-49% of the neurons in the cat. Substance P-immunoreactive neurons made up 30-38% of neurons in rat and 32-39% in cat. Most substance P neurons (particularly the most darkly staining ones) were, however, clustered such that they were most numerous in the patch compartment of neostriatum; within the patches the substance P neurons comprised 59% of neurons in the rat and 55% in cat, but in the matrix substance P neurons comprised only 32% of neurons in the rat and 25% in the cat. Samples taken from sections processed for two-color double labeling immunocytochemistry revealed that 12% of neurons label for both glutamate decarboxylase and [Leu]enkephalin, 12% for both glutamate decarboxylase and [Met]enkephalin, 11-12% for both glutamate decarboxylase and substance P, and 17% for both [Met]enkephalin and substance P. These results provide evidence for chemical heterogeneity within the medium-sized neostriatal neurons, and provide the first evidence for coexistence of glutamate decarboxylase and substance P within a single neuron, and the first evidence for the coexistence for substance P and [Met]enkephalin within single neurons of the central nervous system.

Neurons reactive to antibodies against serotonin in the stomatogastric nervous system and in the alimentary canal of locust and crickets (Orthoptera, Insecta)

Immunoreactive neurons in the stomatogastric nervous system and in the alimentary tract of the locust Schistocerca gregaria and the crickets Gryllus bimaculatus and Acheta domesticus have been examined using antibodies against serotonin (5-hydroxytryptamine; 5-HT). For comparative anatomical analysis cobalt chloride infusion was applied. The innervation of the visceral muscles was studied electron microscopically. In all three species the majority of the 5-HT-immunoreactive cell bodies of the stomatogastric nervous system occur in the frontal ganglion in which 30-40% of the total number of cell bodies react with anti-5-HT. In the occipital ganglion only two to four cell bodies (1-2%) are 5-HT-immunoreactive. Single immunoreactive cell bodies were observed in the ventricular ganglia in only a few preparations. The 5-HT-immunoreactive neurons in the frontal ganglion are pseudounipolar or multipolar. The main process of the 5-HT-immunoreactive neurons of the frontal ganglion descend along the entire stomatogastric nervous system. Some arborizations of these processes ascend into the brain and others supply the neuropil of all stomatogastric ganglia. Side branches leave the stomatogastric nervous system and form a plexus along the surface of the entire intestinal tract from where 5-HT-immunoreactive fibers supply: all muscle layers of the muscularis; the external dilator muscles of the foregut and probably some somatic muscles, neurohaemal organs and Malpighian tubules (excretory system). Serotonin-immunoreactive fibers further proceed into salivary gland and the retrocerebral complex (corpora cardiaca and corpora allata). The retrocerebral glandular complex and the hindgut receive additional immunoreactive neurons from the central nervous system. Electron microscopic analysis of nerves innervating the muscle layers of the alimentary tract revealed one type of 5-HT-immunoreactive and one or two types of non-5-HT-immunoreactive fibers. All fiber types contact the sarcolemma of muscle fibers without any obvious synaptic membrane specializations. The 5-HT-immunoreactive fibers are in some regions in close contact with the haemolymph. These regions can be regarded as sites of neurohormonal release. The distribution of serotonin-immunoreactive neurons suggests that 5-HT acts as a neurotransmitter and/or modulator on intestinal muscles and some somatic muscles and glandular cells, and as a neurohormone released from neurohaemal sites into the body fluid.

Coexistence of pancreatic polypeptide and substance P in the chicken retina

The present immunohistochemical study using flat-mounted and frozen sections has revealed that in the chicken retina, pancreatic polypeptide (PP)-, such as avian pancreatic polypeptide (APP) and neuropeptide Y (NPY), and substance P (SP)-like immunoreactive (PPI and SPI) amacrine cells are composed of more heterogeneous subpopulations than has hitherto been supposed. Furthermore, using double-staining immunohistochemical procedures, we demonstrate that a substantial proportion of some subtypes of PPI cells contain SPI and that the ratio of both PPI and SPI cells to total immunoreactive cells differs according to the retinal portions and cell types.

Co-existence of glucagon- and substance P-like immunoreactivity in the chicken retina

This immunohistochemical study of chicken retina using flat-mounts shows that pancreatic glucagon- and substance P-like immunoreactive amacrine cells have more heterogeneous subpopulations than was previously understood to be the case. Using double-staining immunohistochemical procedures we demonstrate that a substantial proportion of all subtypes of glucagon-like immunoreactive cells contain substance P-like immunoreactivity and that the ratio of the amacrine cells containing both peptides to total immunoreactive cells varies according to position in the retinal and cell type. These results suggest that retinal cells may have different functions according to position or cell type.

On the nature of the contractile motor responses of the rat stomach elicited by serotonin or substance P in vitro

SP or 5-HT elicited contractile motor responses from strip preparations of the rat antrum and pylorus, effects which were efficiently antagonized by blockade directed against each substance (SP-receptors: tachyphylaxis or a SP analogue; 5-HT2 receptors: ketanserin). Indirect effects of SP or 5-HT, i.e. causing the release of other spasmogens such as histamine (from mast cells) and prostaglandins, were ruled out in separate experiments using pyrilamine or indomethacin. When the contractile effects of SP or 5-HT motor responses were studied after TTX no inhibition was demonstrated indicating that the effects were mediated via muscle receptors. Both SP- and 5-HT-responses were partially antagonized by blockade of muscarinic or nicotinic receptors, even in the presence of TTX, in favour of interaction at the receptor level of the smooth muscle membrane. One exception was the SP-induced pyloric contraction, which was partially atropine-sensitive but resistant to hexamethonium. Interestingly, blockade of 5-HT2 receptors (ketanserin) reduced the contractile response to SP. These observations indicate an interaction between SP and 5-HT receptors at the smooth muscle membrane. However, SP and 5-HT added together did no facilitate the response. Therefore, the interaction of ketanserin with the SP response may rather be sterical than due to binding to a common receptor site. These findings may be of importance, since SP and 5-HT have recently been shown to coexist in gut neurons.

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.