Microfluorimetric study of adrenergic structures in nerve plexuses of the cat pelvic cavity following decentralization and in the normal

Microfluorimetric techniques were used to investigate catecholamine concentration in small, intensely fluorescent cells and adrenergic fibers of the cat pelvic plexus ganglia and intramural ganglia of the urinary bladder and rectum in the control and following sympathetic and parasympathetic denervation. The cells examined could be divided between catecholamine- and serotonin-containing types. Parasympathetic denervation brought about an increase in the number of cells displaying serotinergic fluorescence and heightened fluorescence in the adrenergic fibers of the pelvic plexus ganglia and intramural ganglia of the urinary bladder, without affecting degree of fluorescence in those of the rectal intramural ganglia. Sympathetic denervation failed to change fluorescence level in the cells and adrenergic fibers in pelvic plexus and urinary bladder ganglia but caused the almost complete disappearance of the adrenergic fibers in the rectal intramural ganglia.Institute of Physiology, Academy of Sciences of the Belorussian SSR, Minsk. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 496–502, July–August, 1986.     

Myenteric plexus is differentially affected by infection with distinct Trypanosoma cruzi strains in Beagle dogs

Chagasic megaoesophagus and megacolon are characterised by motor abnormalities related to enteric nervous system lesions and their development seems to be related to geographic distribution of distinct Trypanosoma cruzi subpopulations. Beagle dogs were infected with Y or Berenice-78 (Be-78) T. cruzi strains and necropsied during the acute or chronic phase of experimental disease for post mortem histopathological evaluation of the oesophagus and colon. Both strains infected the oesophagus and colon and caused an inflammatory response during the acute phase. In the chronic phase, inflammatory process was observed exclusively in the Be-78 infected animals, possibly due to a parasitism persistent only in this group. Myenteric denervation occurred during the acute phase of infection for both strains, but persisted chronically only in Be-78 infected animals. Glial cell involvement occurred earlier in animals infected with the Y strain, while animals infected with the Be-78 strain showed reduced glial fibrillary acidic protein immunoreactive area of enteric glial cells in the chronic phase. These results suggest that although both strains cause lesions in the digestive tract, the Y strain is associated with early control of the lesion, while the Be-78 strain results in progressive gut lesions in this model.     

Projections of neurochemically specified neurons in the porcine colon

The intramural projections of nerve cells containing serotonin (5-HT), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and nitric oxide synthase or reduced nicotinamide adenine dinucleotide phosphate diaphorase (NOS/NADPHd) were studied in the ascending colon of 5- to 6-week-old pigs by means of immunocytochemistry and histochemistry in combination with myectomy experiments. In control tissue of untreated animals, positive nerve cells and fibres were common in the myenteric and outer submucous plexus and, except for 5-HT-positive perikarya, immunoreactive cell bodies and fibres were also observed in the inner submucous plexus. VIP- and NOS/NADPHd-positive nerve fibres occurred in the ciruclar muscle layer while VIP was also abundant in nerve fibres of the mucosal layer. 5-HT- and CGRP-positive nerve fibres were virtually absent from the aganglionic nerve networks. In the submucosal layer, numerous paravascular CGRP-immunoreactive (IR) nerve fibres were encountered. Myectomy studies revealed that 5-HT-, CGRP-, VIP- and NOS/NADPHd-positive myenteric neurons all displayed anal projections within the myenteric plexus. In addition, some of the serotonergic myenteric neurons projected anally to the outer submucous plexus, whereas a great number of the VIP-ergic and nitrergic myenteric neurons send their axons towards the circular muscle layer. The possible function of these nerve cells in descending nerve pathways in the porcine colon is discussed in relation to the distribution pattern of their perikarya and processes and some of their morphological characteristics.     

Morphometric investigations of the colon mucosa in chronic Trypanosoma cruzi infected rats.

The objective of this investigation was to study the morphometry of the epithelial mucosa in the chronic phase of T. cruzi infection. Nine young female Wistar rats were inoculated with T. cruzi. Ten months after inoculation the animals were sacrificed and the proximal colon was collected for morphometric measurements of the thickness of the muscle layers, the number of neurons in the myenteric plexus, the crypt cell population (CCP), crypt cell production per crypt (CCPC) and turnover time (TT) of the epithelium. There was no muscle layer hypertrophy but there was significant denervation in the group inoculated with T. cruzi, which also showed hyperplasia of the epithelium. The data suggest that denervation of the myenteric plexus did not induce hypertrophy of the propria muscle layer itself but altered the morphometry of the colonic epithelium in T. cruzi-infected animals, with increased development of CCP and TT. It is possible that this epithelial hyperplasia, as a consequence of a longer crypt cell TT, increased the absorption and secretion activities of the colon, which in turn may participate in the genesis of the enteromegalies observed in the chronic phase of Chagas' Disease.     

Blood pressure of sinoaortic-denervated dogs is not increased by cardiac denervation

Although blood pressure rises markedly after acute sinoaortic denervation, animals with chronic sinoaortic denervation have normal or only slightly elevated mean arterial pressures. The present study was performed to determine whether reflexes from cardiac receptors exert antihypertensive effects and thereby lower blood pressure in animals with chronic sinoaortic denervation. We made multiple measurements of blood pressures in dogs with chronic sinoaortic denervation before and after their hearts were denervated surgically. Mean arterial pressure after cardiac denervation (100.3 +/- 4.2 mm Hg) was not significantly different from the mean pressures recorded before cardiac denervation in these sinoaortic-denervated dogs (104.8 +/- 3.1 mm Hg). Also, mean heart rate after cardiac denervation (107.4 +/- 5.5 beats/min) did not differ significantly from the mean heart rate recorded before cardiac denervation (107.2 +/- 5.9 beats/min). Cardiac denervation did, however, appear to reduce the lability of both blood pressure and heart rate in sinoaortic-denervated dogs. We conclude that cardiac receptors are not responsible for maintaining arterial pressure within essentially normal limits in animals with chronic sinoaortic denervation.     

Denervation, but Not Decentralization, Reduces Nerve Growth Factor Content of the Mesenteric Artery

Abstract: In the present study we applied an improved nerve growth factor (NGF) extraction method to examine the effects of denervation and sympathetic decentralization on NGF levels in vascular tissue. Adult male Wistar Kyoto rats underwent mesenteric arterial denervation or splanchnic nerve transection. Four days after operation, animals were killed, and the mesenteric artery and coeliac-superior mesenteric ganglia were removed. The arterial adventitia was stripped from the media to measure NGF levels in nerve and smooth muscle separately. A high concentration of NGF was detected in the normal artery, 90% of which was in the adventitial layer. Surgical denervation significantly reduced the NGF levels in the artery and ganglia by 78 and 71%, respectively. However, within the artery the level of NGF was reduced in the adventitia but not in the media. Thus, the large reduction of NGF content resulted from the loss of nerve plexus from the artery. In contrast, decentralization did not alter the NGF content in the artery, in either the adventitia or media. Our results are in marked contrast to previous studies reporting elevated levels of NGF following denervation. This discrepancy is explained by the ability of our new procedure to extract much greater amounts of NGF from the tissue.     

Morphometric investigations of the colon mucosa in chronicTrypanosoma cruzi infected rats

The objective of this investigation was to study the morphometry of the epithelial mucosa in the chronic phase ofT. cruzi infection. Nine young female Wistar rats were inoculated withT. cruzi. Ten months after inoculation the animals were sacrificed and the proximal colon was collected for morphometric measurements of the thickness of the muscle layers, the number of neurons in the myenteric plexus, the crypt cell population (CCP), crypt cell production per crypt (CCPC) and turnover time (TT) of the epithelium. There was no muscle layer hypertrophy but there was significant denervation in the group inoculated withT. cruzi, which also showed hyperplasia of the epithelium. The data suggest that denervation of the myenteric plexus did not induce hypertrophy of the propria muscle layer itself but altered the morphometry of the colonic epithelium inT. crwzi-infected animals, with increased development of CCP and TT. It is possible that this epithelial hyperplasia, as a consequence of a longer crypt cell TT, increased the absorption and secretion activities of the colon, which in turn may participate in the genesis of the enteromegalies observed in the chronic phase of Chagas’ Disease.     

The differentiation of cytotoxic T lymphocytes in vitro

Summary Previous neurohistological studies have been extended to include the structures contained solely or mainly within the junctional esophageal segment which may play an important role in the sphincter mechanism. The main findings were: 1) a progressive cranio-caudal thickening of the muscularis mucosae; 2) a conspicuous thickening of the circular muscle layer; 3) abundant and close interconnections between the esophageal striated fibres and gastric smooth muscle cells; 4) presence of annulo-spiral elastic fibres coiled around bundles of striated musculature; 5) increase of the intramural nerve component, particularly Auerbach's plexus, which consisted of a continuous nervous layer containing twice as many neurocytes as found in the upper esophageal segments; 6) presence of numerous interconnected motor endplates often possessing ultraexpansional fibres and secondary endplates. The findings are discussed with emphasis on functional correlations in order to attain a unitary morpho-functional view.Abbreviations used LES lower esophageal sphincter - HPZ high pressure zone; mm: muscularis mucosae - CNS central nervous system - CCK-PZ cholecystokinin-pancreozymin Dedicated to Prof. Dr. Wolfgang Bargmann for his fundamental contributions to Comparative Morphology     

Colocalization of dynorphin-A(1-17) and dynorphin-A(1-8) within some perikarya of rat duodenum: immunohistochemical evidence for the presence of two separate dynorphinergic systems

Adjacent serial sections through the rat duodenum were alternately stained for immunofluorescence microscopic studies with specific anti-sera directed to the opioid peptides dynorphin-A(1-17) and dynorphin-A(1-8), respectively. This resulted in the evidence that two separate dynorphinergic neuron populations are present there: intramural neurons, revealing a colocalization of dynorphin-A(1-17) and dynorphin-A(1-8), were round, contained a large and round nucleus and were lying sporadically in the longitudinal muscle layer as well as bulb-shaped neurons expressing only a dynorphin-A(1-8) immunoreactivity. The latter were recognized abundantly in the myenteric plexus. Myenteric plexus nerve fibres and terminals were immunoreactive for dynorphin-A(1-8), but not for dynorphin-A(1-17). Dynorphin-A(1-8) immunostained nerve terminals formed close contacts with large non-dynorphinergic myenteric plexus perikarya. These findings might indicate that dynorphin-A(1-8) is processed directly from its prodynorphin ('preproenkephalin B') precursor within myenteric plexus perikarya and indirectly via dynorphin-A(1-17) within intramural perikarya, indicating the presence of two separate dynorphinergic systems in the rat duodenum.     

Lines of transformed murine thymus cells. I. Production of the lines

Supernatant of activated cells of human T-leucosis line "Jurkat" enriched with interleukin-2 (IL-2) was injected to Balb/c mice. After a number of injections the animals were sacrificed and the thymus cells were cultured in vitro. Transformed cell clones were formed on days 3-4. Two stable T-cell strains of the reproduced primary cells were obtained (TC.SC-1/1.1. and TC.SC-1/2.0). The strains corresponded to the transitional stage of pre-T-lymphocytes and consisted of tumour cells. A possible mechanism of malignant transformation of these cells is discussed.     

Effects of denervation on the glycogen content and on the activities of enzymes of glucose and glycogen metabolism in rat diaphragm muscle

1. Changes in the content and concentration of glycogen and in the activity of a number of enzymes involved in glucose and glycogen metabolism were studied in the rat hemidiaphragm after unilateral denervation. 2. After nerve section the tissue hypertrophies; this hypertrophy is said to be confined to the smaller red fibres and not to the white. 3. The total hexokinase activity increases, whereas that of total glycogen phosphorylase decreases. The specific activity of phosphorylase a, determined after Halothane anaesthesia, remains fairly constant. 4. In fed animals the denervated tissue stores less glycogen, but in the early stages its glycogen content does not fall on starvation. 5. The effect of denervation on the specific activities of several other characteristically white-fibre enzymes are not consistent with the response of glycogen phosphorylase; the increase in content of glyceraldehyde 3-phosphate dehydrogenase and lactate dehydrogenase is thought to be related to proliferation of the sarcoplasmic reticulum. 6. The ratio of lactate dehydrogenase M/H subunits increases at the height of the hypertrophy, but then declines as the mass of the tissue falls. 7. The chronology of these changes in enzyme activities suggests a multiplicity of distinct responses after nerve section not consistent with any one model, either specific fibre development or reversion to de-differentiated, foetal-type metabolism.     

Neuroplasticity in the smooth muscle of the myenterically and extrinsically denervated rat jejunum

The objective of this study was to examine the effects of two different denervation procedures on the distribution of nerve fibers and neurotransmitter levels in the rat jejunum. Extrinsic nerves were eliminated by crushing the mesenteric pedicle to a segment of jejunum. The myenteric plexus and extrinsic nerves were eliminated by serosal application of the cationic surfactant benzyldimethyltetradecylammonium chloride (BAC). The effects of these two denervation procedures were evaluated at 15 and 45 days. The level of norepinephrine in whole segments of jejunum was initially reduced by more than 76% after both denervation procedures, but by 45 days the level of norepinephrine was the same as in control tissue. Tyrosine hydroxylase (nor-adrenergic nerve marker) immunostaining was absent at 15 days, but returned by 45 days. However, the pattern of noradrenergic innervating axons was altered in the segment deprived of myenteric neurons. Immunohistochemical studies showed protein gene product 9.5 (PGP 9.5)-immunoreactive fibers in whole-mount preparations of the circular smooth muscle in the absence of the myenteric plexus and extrinsic nerves. At 45 days, the number of nerve fibers in the circular smooth muscle increased. Vasoactive intestinal polypeptide (VIP)-immunoreactive fibers, a subset of the PGP 9.5 nerve fibers, were present in the circular smooth muscle at both time points examined. Choline acetyltransferase (CAT) activity and VIP and leucine enkephalin levels were measured in separated smooth muscle and submucosa-musosal layers of the denervated jejunum. VIP and leucine-enkephalin levels were no different from control in tissue that was extrinsically denervated alone. However, the levels of these peptides were elevated two-fold in the smooth muscle 15 and 45 days after myenteric and extrinsic denervation. In the submucosa-mucosa, VIP and leucine enkephalin levels also were elevated two-fold at 15 days, but comparable to control at 45 days. CAT activity was equal to control in the smooth muscle but elevated two-fold in the submucosa-mucosa at both times. These results provide evidence for innervation of the circular smooth muscle by the submucosal plexus. Moreover, these nerve fibers originating from the submucosal plexus proliferate in the absence of the myenteric plexus. Furthermore, the myenteric neurons appear to be essential for normal innervation of the smooth muscle by the sympathetic nerve fibers. It is speculated that the sprouting of the submucosal plexus induced by myenteric plexus ablation is mediated by increased production of trophic factors in the hyperplastic smooth muscle.     

In Vitro Selection of High-Infectious, Leukemogenic Virus from Low-Infectious, Non-Leukemogenic Type C Virus from a Malignant ST/a Mouse Cell Line

Low-infectious, nontransforming type C virus was isolated from an in vitro spontaneously transformed ST/a mouse cell line, ST-L1. The virus released by ST-L1 cells was NB-tropic and XC(-). It gave rise to very small peroxidase antibody plaques (PAP) in cultures which initially were nonproducing. Sodium dodecyl sulfate (SDS)-polyacrylamide gels of the structural proteins of the ST-L1 virus showed an envelope glycoprotein with an apparent mass of 65 kilodaltons (kdal). The mouse cells SC-1, BALB/3T3, and NIH/3T3 could be productively infected with cell-free supernatants from the ST-L1 cell line; however, virus was detected in supernatant fluids only after two to four subcultures of the infected cells. The virus thus produced was XC(+) and a large plaque former. The virus released from infected SC-1 cells was N-tropic, whereas the viruses from infected NIH/3T3 and BALB/3T3 cells were NB-tropic. The structural proteins of the N- and NB-tropic viruses could be distinguished on SDS polyacrylamide gels, the major dissimilarity being a difference in the mobility of the p30. All these viruses had an envelope glycoprotein with an apparent mass of 70 kdal. The infectivity of the viruses, measured as PAP per nanogram of p30, was 30- to 60-fold lower for the virus released from the ST-L1 cell line than that of the viruses after passage in SC-1, NIH/3T3, and BALB/3T3 cells. None of the viruses could infect rabbit or mink cells. Inoculation of the viruses into newborn mice showed that the ST-L1 virus was non-leukemogenic, whereas the NB-tropic virus selected from this after passage in BALB/3T3 or NIH/3T3 cells was highly leukemogenic. Viruses isolated from leukemic animals were indistinguishable with respect to host range and protein mobilities in SDS gels from the ones with which the mice were inoculated. Although the SC-1-selected virus was highly infectious in vitro, it was only weakly, if at all, leukemogenic.     

Distribution of peptidergic nerves in the choroid plexus, focusing on coexistence of neuropeptide Y, vasoactive intestinal polypeptide and peptide histidine isoleucine

Choroid plexus from rat, guinea-pig, rabbit and pig was investigated by light-microscopic immunohistochemistry and by radioimmunoassay for the presence of neuropeptides. A moderately dense supply of nerve fibers containing neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), respectively, was found around blood vessels and in close relation to the secretory epithelium in both pig and rabbit, while lower densities of nerve fibers were found in rat and guinea-pig. Peptide concentrations ranged from 10-40 pmolequivalents/g (pmoleqv/g) for NPY and 0.5-6 pmoleqv/g for VIP in all four species. Peptide histidine isoleucine (PHI) immunoreactive nerve fibers were present in pig choroid plexus at a lower density than NPY and VIP but with a similar distribution. Low concentrations of substance P (0.3-3 pmoleqv/g) and calcitonin gene-related peptide (0.1-3 pmoleqv/g) were found to a varying degree in choroid plexus tissue from the different species, while immunohistochemical investigation was unable to detect any immunoreactive nerve fibers. NPY was often found to coexist with VIP and PHI in pig choroid plexus, while a lesser amount of nerve fibers showed coexistence of NPY and the noradrenaline synthetizing enzyme, dopamine-beta-hydroxylase. Surgical sympathetic denervation by excision of the superior cervical ganglion in the rabbit abolished NPY-containing nerve fibers, as revealed by immunohistochemistry, but only decreased NPY levels by one third, which may be due to different identity of the peptide being detected by the two techniques. It is concluded that NPY-containing nerve fibers have a dual origin in the choroid plexus and coexist with either noradrenaline or VIP/PHI.     

Experimental induction of the two-host life cycle of Sarcocystis cruzi between dogs and Korean native calves

Eight dogs were experimentally infected with Sarcocystis by oral inoculation of cardiac muscle from naturally infected cattle. The infected dogs commenced discharging of sporocysts in the feces after 10 to 12 days of inoculation, and continued until 20 and 35 days after inoculation. Three dogs were reinfected with cardiac muscle from the naturally infected cattle. Sporocysts reappeared in the feces on 12 to 13 days after reinfection. Sarcocystis sporocysts collected from the experimentally infected dogs were fed to each of the two 30-day-old Korean native calves. The infected calves remained clinically normal, except for the high fever (> or = 40 degrees C) and decreased hematocrit values on day 30 to 40 post inoculation. Muscular cysts of Sarcocystis were found from infected calves on day 40 post inoculation. Proliferative forms of Sarcocystis were also observed in the muscle of infected calves. These results suggest that the Sarcocystis cruzi found in Korean native cattle has a 2-host life cycle with dogs as the definitive host and Korean native calves as the intermediate host.     

Staphylococci Isolated from Carriage Sites and Infected Sites of Dogs as a Reservoir of Multidrug Resistance and Methicillin Resistance

The aim of this study was to compare the spread of multidrug-resistant (MDR) and methicillin-resistant (MR) staphylococci in healthy dogs and in dogs with evident symptoms of infection. The samples from 172 healthy and 197 infected dogs were examined. The staphylococci were identified with conventional methods and by means of the polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) method (MboI). Susceptibility to 15 antibiotics from 10 different antimicrobial classes was tested. Resistance to methicillin was confirmed by the presence of Staphylococcus aureus mecA and S. sciuri mecA genes. Multidrug resistance was defined as resistance to three or more antimicrobial classes. The oral mucosa to be the most frequent site of staphylococcal colonization (55.8 %), followed by nasal cavity (44.2 %), and anus (32.6 %). The prevalence of MDR staphylococci in infected dogs was significantly higher than in the healthy animals (74/137 vs. 34/95, P = 0.006). The MR strains of S. pseudintermedius (2.9 %) originated solely from infected dogs. In contrast, the MR coagulase-negative strains (7.4 %) were isolated solely from healthy dogs. S. aureus strains originated from nasal swabs, MRSA strains were not isolated. MDR staphylococci and MR S. pseudintermedius are more common among infected dogs, but coagulase-negative staphylococci (mostly S. sciuri) seem to be a reservoir of methicillin resistance in healthy dogs.     

An immunohistochemical study of serotonin-containing nerves in the colon of rats

The localization of the serotonin-like immunoreactive nerves of the rat colon was investigated by means of immunohistochemistry, utilizing an antibody against serotonin. In non-treated colons, serotonin-positive neuropils were consistently detected around the myenteric plexus. In pargyline-treated colons, serotonin-like fibres were demonstrated in association with either the small intramural blood vessels of the submucosa or the extramural nerve bundles. Treatment with 5-hydroxytryptophan (5-HTP) permitted the visualization of additional serotonin-immunoreactive fibres around the large extramural blood vessels. Immunoreactive nerve cell bodies were demonstrated in the myenteric plexus of colons treated with 5-HTP or colchicine. From these observations, it is suggested that the serotoninergic nerves of the rat colon comprise both intrinsic and extrinsic elements.     

Enteric Neuronal Damage,Intramuscular Denervation and Smooth Muscle Phenotype Changes as Mechanisms of Chagasic Megacolon: Evidence from a Long-Term Murine Model of Tripanosoma cruzi Infection

We developed a novel murine model of long-term infection with Trypanosoma cruzi with the aim to elucidate the pathogenesis of megacolon and the associated adaptive and neuromuscular intestinal disorders. Our intent was to produce a chronic stage of the disease since the early treatment should avoid 100% mortality of untreated animals at acute phase. Treatment allowed animals to be kept infected and alive in order to develop the chronic phase of infection with low parasitism as in human disease. A group of Swiss mice was infected with the Y strain of T. cruzi. At the 11^th day after infection, a sub-group was euthanized (acute-phase group) and another sub-group was treated with benznidazole and euthanized 15 months after infection (chronic-phase group). Whole colon samples were harvested and used for studying the histopathology of the intestinal smooth muscle and the plasticity of the enteric nerves. In the acute phase, all animals presented inflammatory lesions associated with intense and diffuse parasitism of the muscular and submucosa layers, which were enlarged when compared with the controls. The occurrence of intense degenerative inflammatory changes and increased reticular fibers suggests inflammatory-induced necrosis of muscle cells. In the chronic phase, parasitism was insignificant; however, the architecture of Aüerbach plexuses was focally affected in the inflamed areas, and a significant decrease in the number of neurons and in the density of intramuscular nerve bundles was detected. Other changes observed included increased thickness of the colon wall, diffuse muscle cell hypertrophy, and increased collagen deposition, indicating early fibrosis in the damaged areas. Mast cell count significantly increased in the muscular layers. We propose a model for studying the long-term (15 months) pathogenesis of Chagasic megacolon in mice that mimics the human disease, which persists for several years and has not been fully elucidated. We hypothesize that the long-term inflammatory process mediates neuronal damage and intramuscular and intramural denervation, leading to phenotypic changes in smooth muscle cells associated with fibrosis. These long-term structural changes may represent the basic mechanism for the formation of the Chagasic megacolon.     

Susceptibility of experimental animals to reinfection with Clonorchis sinensis

The present study observed the resistance to reinfection with Clonorchis sinensis in various experimental animals including mice, guinea pigs, rabbits, and dogs, as well as rats and hamsters. The resistance rates to reinfection in rats, mice, hamsters, guinea pigs, rabbits, and dogs were 79.7%, 58.0%, -12.6%, 54.8%, 62.6%, and 6.0%, respectively. Worms recovered from reinfected rats and mice were immature, and significantly smaller than those from the primarily infected (P < 0.01), whereas those from other animals were fully matured to adults. These findings indicate that the protective response against reinfection with C. sinensis is prominent in rats and mice, and that they may be a good animal model to investigate the mechanism of resistance to reinfection with C. sinensis.     

An immunohistochemical study of serotonin-containing nerves in the colon of rats

Summary The localization of the serotonin-like immunoreactive nerves of the rat colon was investigated by means of immunohistochemistry, utilizing an antibody against serotonin. In non-treated colons, serotonin-positive neuropils were consistently detected around the myenteric plexus. In pargyline-treated colons, serotonin-like fibres were demonstrated in association with either the small intramural blood vessels of the submucosa or the extramural nerve bundles. Treatment with 5-hydroxytryptophan (5-HTP) permitted the visualization of additional serotonin-immunoreactive fibres around the large extramural blood vessels. Immunoreactive nerve cell bodies were demonstrated in the myenteric plexus of colons treated with 5-HTP or colchicine. From these observations, it is suggested that the serotoninergic nerves of the rat colon comprise both intrinsic and extrinsic elements.