The origin of catecholaminergic nerve fibers in the subdiaphragmatic vagus nerve of rat.
ABSTRACT It is known that the vagus nerve contains catecholaminergic fibers. However, the origin of these fibers has not been systematically examined. In this study, we addressed this issue using retrograde tracing from the subdiaphragmatic vagus nerve combined with immunocytochemistry. The cervical and thoracic sympathetic trunk ganglia, the nodose ganglia and the dorsal motor nucleus of the vagus nerve were examined following injection of Fluoro-Gold or cholera toxin horseradish peroxidase conjugate into the trunks of the subdiaphragmatic vagus nerve of rats. Numerous retrogradely labeled neurons were seen in the nodose ganglion and the dorsal motor nucleus of the vagus nerve. Very few labeled neurons were found in the sympathetic ganglia (less than 0.06% of the neurons in either superior cervical ganglion or cervicothoracic ganglion were retrogradely labeled). Double labeling with immunofluoresence for catecholamine synthesizing enzymes revealed that: (1) 92% of all Fluoro-Gold retrogradely labeled tyrosine hydroxylase immunoreactive neurons were found in parasympathetic sources (75% in the dorsal motor nucleus of the vagus nerve and 17% in the nodose ganglia), and only 8% in the cervicothoracic sympathetic ganglia; (2) 12% of the retrogradely labeled catecholaminergic neurons in the dorsal motor nucleus of the vagus nerve were also dopamine-beta-hydroxylase immunopositive neurons; (3) 70% of the retrogradely labeled neurons in the sympathetic ganglia were tyrosine hydroxylase immunopositive and 54% of these catecholaminergic neurons contained dopamine-beta-hydroxylase, while 30% of the retrogradely labeled neurons were non-catecholaminergic neurons. These results indicate that catecholaminergic fibers in the abdominal vagus nerve are primarily dopaminergic and of parasympathetic origin, and that only an extremely small number of these fibers, mostly noradrenergic in nature, arise from postganglionic sympathetic neurons.
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ABSTRACT: Dopamine is a putative enteric neurotransmitter that has been implicated in exocrine secretory and motility functions of the gastrointestinal tract of several mammalian species including man. This study was designed to determine the presence of dopamine binding sites in human gastric and duodenal mucosa and to describe certain biochemical characteristics of these enteric receptor sites.The binding assay was performed in triplicate with tissue homogenates obtained from healthy volunteers of both sexes using 3H-dopamine as a ligand. The extent of nonspecific binding was determined in the presence of a 100-fold excess of unlabeled dopamine.Scatchard analysis performed with increasing concentrations of 3H-dopamine (20–500 nM) revealed a single class of saturable dopamine binding sites in gastric and duodenal mucosa. Binding parameters obtained from the regression lines of the Scatchard plots of gastric mucosa of males were Bmax = 73.4±4.0 pmoles/mg protein; KD = 154±20 nM and Bmax = 95±13.6 pmoles/mg protein and KD = 826±200 nM in females. In duodenal mucosa of males these parameters were Bmax = 63.9±15.9 pmoles/protein; KD = 235±53 nM and Bmax = 83.2±19.4 pmoles/mg proteinKD = 568±104 nM in females.The results of this report demonstrate the presence of specific dopamine receptors in human gastric and duodenal mucosa. These biochemical data suggest that molecular abnormalities of these receptor sites may be operative in the pathogenesis of important gastrointestinal disorders.The view that the autonomic innervation of the mammalian gastrointestinal tract is provided by parasympathetic (cholinergic) excitatory and sympathetic (adrenergic) inhibitory fibers has been expanded by the findings that these fibers contain not only acetylcholine and norepirephrine, but also several other aminergic and peptidergic neurotransmitters (1,2).Immunohistochemical studies have shown, for example, that the vagus nerve (in addition to acetylcholine) contains important amounts of serotonin, norepinephrine, gastrin, somatostatin, enkephalin, substance P and vasoactive-intestinal peptide (3). These findings suggest that the neural control of the gut is considerably more complex than originally thought, and raise the possibility that exocrine secretory and motility functions of the gut may be regulated by multiple enteric neurotransmitters.Recent evidence suggests that dopamine may be an important transmitter in enteric synapses, as well as a precursor molecule in the biosynthesis of norepinephrine in peripheral adrenergic terminals (4). Although, specific immunohistochemical demonstration of tyrosine hydroxylase in gastric tissue has not been provided, significant amounts of dopamine have been found in the gastrointestinal mucosa and muscle of several mammalian species (5) and in human gastric juice (6,7).In addition, it is also important to indicate that DOPA decarboxylase activity has been detected in a specific enterochromaffin-like cell system in the gastric mucosa (8). There is also evidence that dopamine levels in gastric mucosa but not in muscle are regulated independently of either parasympathetic or sympathetic control (9). Furthermore, neurophysiological studies indicate that dopamine, like norepinephrine, exerts an inhibitory effect on cholinergic neurotransmission by including hyperpolarization of the post-synaptic membrane (10).Inhibitory actions of dopamine and dopamine-related compounds on acid secretion (11–14), gastric emptying (15), antral activity (16), and intragastric pressure have been demonstrated in rats, dogs and man (17).Specific high-affinity dopamine receptors and different molecular species of these receptor sites have been extensively studied in rat and human brain tissue (18,19). Similar, but less extensive studies, have been performed with gastrointestinal tissue. Szabo et al. (20) provided an initial description of dopamine receptors in rat stomach and duodenum, and suggested that they may be involved in the pathogenesis of experimental duodenal ulceration. More recently, we have provided a detailed biochemical characterization of specific receptor sites for dopamine in rat gastric mucosa and muscle and suggested that these molecular entities may play a critical role in the onset of stress ulcers (21).This body of evidence indicates that dopamine and dopamine receptors may play an important role in gastrointestinal physiology and suggest that similar dopamine receptors may also be present in human gastrointestinal tissue.The study described below was specifically designed to determine the presence of dopamine binding sites in human gastric and duodenal mucosa.Life Sciences. 01/1987;
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ABSTRACT: It is often necessary to obtain unbiased estimates of neuronal or synaptic numbers. In the past, estimates were almost always done by counting profiles of these structures in single histological sections. Assumptions were then made and calculations were done to determine particle numbers or ratios. To the extent that the assumptions deviated from reality, the conclusions will be biased. That these biases are, in fact, serious has recently become apparent. To obtain unbiased particle counts, the presently available methods are serial-section reconstructions (which are accurate but cumbersome), and the recently developed disector method. The disector method, because it is unbiased and easy to use, is becoming the method of choice. The goals of this paper are to show why previous methods are biased and to describe the rationale behind the disector method so that neuroscientists can consider its appropriateness for their work.Trends in Neurosciences 02/1992; 15(1):9-13. · 13.58 Impact Factor
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ABSTRACT: The location of the extrinsic efferent and afferent nerve cell bodies to the mucosa, submucosa, and tunica muscularis of the cardiac, gastric, and pyloric gland regions of the ventral stomach and to the mucosa-submucosa alone of these 3 glandular gastric regions was determined using the horseradish peroxidase technique. All animals of the study demonstrated labeling bilaterally in the rostrocaudal extent of the dorsal motor nucleus of the vagus nerve (DMV) although mucosa-submucosa injections resulted in fewer labeled cells in the DMV. There was no evidence of viscerotopic organization within the DMV for the different gastric regions. However, the left nucleus generally contained a greater number of labeled cells than the right nucleus. Injection of the mucosa, submucosa, and tunica muscularis of the cardiac gland region also resulted in labeling in the nucleus ambiguus in 4 of 5 animals. The vast majority of labeled postganglionic sympathetic neurons were found in the celiacomesenteric ganglion. Labeled cells were also located variously in the stellate ganglion, middle cervical ganglion, and sympathetic trunk ganglia for the different groups. There was no discernible pattern of localization of labeled cells within a sympathetic ganglion. For the stomach, afferent labeled cells were located in the range of the first thoracic to fourth lumbar spinal ganglia and the nodose ganglia, bilaterally. As with sympathetic neurons, there was no discernible pattern of localization of labeled cells within a sensory ganglion.Journal of the Autonomic Nervous System 11/1989; 28(1):1-14.