GABA in the control of sympathetic preganglionic neurons

1. Amino acid neurotransmitters are critical for controlling the activity of most central neurons, including sympathetic preganglionic neurons (SPN), the spinal cord neurons involved in controlling blood pressure and other autonomic functions. 2. In studies reviewed here, SPN were identified either by retrograde tracing from a peripheral target (superior cervical ganglion or adrenal medulla) or by detection of immunoreactivity for choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme that is a marker for all SPN, in intact or completely transected rat spinal cord. 3. Postembedding immunogold labelling on ultrathin sections was then used to detect GABA and sometimes glutamate in nerve terminals on SPN or near them in the neuropil of the lateral horn. 4. In some cases, the terminals were prelabelled to show an anterograde tracer or immunoreactivity for ChAT or neuropeptide Y. 5. This anatomical work has provided information that is helpful in understanding how SPN are influenced by their GABAergic innervation. 6. Immunogold studies showed that the proportion of input provided by GABAergic terminals varies between different groups of SPN. For some groups, this input may be preferentially targeted to cell bodies. 7. Anterograde tracing demonstrated that supraspinal as well as intraspinal GABAergic neurons innervate SPN and investigations on completely transected cord suggested that supraspinal neurons may provide a surprisingly large proportion of the GABAergic terminals that contact SPN. 8. The double-labelling studies in which other amino acids, ChAT or neuropeptide Y were localized along with GABA indicate that GABAergic terminals contain other neurochemicals that could modulate the actions of GABA, depending on the complement of receptors that are present pre- and post-synaptically. 9. Taken together, these data indicate that GABAergic transmission to SPN may be much more complicated than suggested by the currently available electrophysiological studies.

Axons of sacral preganglionic neurons in the cat: I. Origin, initial segment, and myelination

Parasympathetic preganglionic neurons in the cat sacral spinal cord innervate intraspinal neurons and pelvic target organs. Retrograde tracing studies have revealed little of the morphology of their axons including their origin, initial segments, or their myelin, due to methodological limitations. Intracellular labeling of single neurons with neurobiotin or HRP has overcome these problems. Axons were studied in 24 preganglionic neurons. In 21 neurons the axon originated as a branch of a dendrite, without a detectable axon hillock, at distances from the soma ranging from 10 to 110 microm (average 34.1 microm ). In 3 neurons the axon was derived from the soma. Initial segments, present in all cells, ranged from 15 to 40 microm (average 26.8 microm). Nearly all axons followed the initial segment with unmyelinated segments that varied between 59 to 630 microm, followed by myelin and nodes of Ranvier. Internodal distances were variable and relatively short (average 93 microm). Axonal diameters measured over the intraspinal course in 18 axons averaged 1.3 microm (range 0.6-2.4 microm) and were relatively constant compared with other neurons. Spine-like protrusions were observed on the initial segments of 12 cells. Axon collaterals originated from unmyelinated sections and nodes of Ranvier. Antidromic action potentials showing initial segment, soma-dendritic inflections, did not differentiate between soma-derived and dendrite-derived axons. The data suggest that axons originating from a dendrite are the normal structure of preganglionic neurons in the lateral sacral parasympathetic nucleus. It is proposed that the particular structure of these axons may be part of a timing mechanism that coordinates preganglionic neurons with other spinal neurons involved in target organ reflexes.

Differential distribution of nerve terminals immunoreactive for substance P and cholecystokinin in the sympathetic preganglionic cell column of the filefish Stephanolepis cirrhifer

Immunoreactivity for substance P and cholecystokinin-8 was examined in the nerve fibers in the central autonomic nucleus, a cell column for sympathetic preganglionic neurons, in the filefish Stephanolepis cirrhifer. Substance P-immunoreactive fibers were distributed throughout the entire rostrocaudal extent, but were more abundant in the caudal part of the column, where substance P-immunoreactive varicosities sometimes made contacts with the sympathetic preganglionic neurons. Cholecystokinin-8-immunoreactive fibers were found almost entirely in the rostral part of the column, where a dense network of varicosities was in close apposition to a considerable number of the sympathetic preganglionic neurons. Double labeling immunohistochemistry showed that substance P fibers and cholecystokin-8 fibers were entirely different, and distinct from serotonin-immunoreactive fibers. By using immunoelectron microscopy, synaptic specialization was sometimes observed between the dendrites of preganglionic neurons and varicosities immunoreactive for substance P and cholecystokinin-8. Substance P- and cholecystokinin-8 fibers were seen from the descending trigeminal tract, through the dorsolateral funiculus and the ventral portion of the dorsal horn, to the central autonomic nucleus. After colchicine treatment, substance P-immunoreactive perikarya were found in the cranial and spinal sensory ganglia. These results suggest that the sympathetic preganglionic neurons of the filefish receive innervation by substance P fibers and cholecystokinin fibers, and that the former might be of primary sensory origin. Topographical distribution of cholecystokinin-8-immunoreactive terminals in the central autonomic nucleus along the rostrocaudal extent might underlie the differential regulation of sympathetic activity via a distinct population of sympathetic preganglionic neurons.

Reelin controls position of autonomic neurons in the spinal cord

Mutation of the reeler gene (Reln) disrupts neuronal migration in several brain regions and gives rise to functional deficits such as ataxic gait and trembling in the reeler mutant mouse. Thus, the Reln product, reelin, is thought to control cell-cell interactions critical for cell positioning in the brain. Although an abundance of reelin transcript is found in the embryonic spinal cord [Ikeda, Y. & Terashima, T. (1997) Dev. Dyn. 210, 157-172; Schiffmann, S. N., Bernier, B. & Goffinet, A. M. (1997) Eur. J. Neurosci. 9, 1055-1071], it is generally thought that neuronal migration in the spinal cord is not affected by reelin. Here, however, we show that migration of sympathetic preganglionic neurons in the spinal cord is affected by reelin. This study thus indicates that reelin affects neuronal migration outside of the brain. Moreover, the relationship between reelin and migrating preganglionic neurons suggests that reelin acts as a barrier to neuronal migration.

Effect of pulmonary C-fibre afferent stimulation on cardiac vagal neurones in the nucleus ambiguus in anaesthetized cats

It has been demonstrated previously that the vagal bradycardia evoked by activation of pulmonary C-fibres is not respiratory modulated. Experiments were carried out in alpha-chloralose anaesthetized cats to determine if these cardiac vagal preganglionic neurones (CVPNs) in the nucleus ambiguus (NA), which have respiratory modulated activity, can be activated when pulmonary C-fibre afferents are stimulated by right atrial injections of phenylbiguanide (PBG). Eleven CVPNs with B-fibre axons in the right cardiac vagal branches were identified and found to be localized within or ventrolateral to the nucleus ambiguus. Ionophoretic application of a high current of dl-homocysteic acid (DLH) induced a vagally mediated bradycardia and hypotension in six of eight sites from which CVPNs were recorded. The activity of B-fibre CVPNs, whether spontaneous (n = 4) or induced by ionophoresis of DLH (n = 7) was respiratory modulated, firing perferentially during post-inspiration and stage 2 expiration. This activity also correlated with the rising phase of the arterial blood pressure wave consistent with these CVPNs receiving an arterial baroreceptor input. Right atrial injections of PBG excited nine of eleven CVPNs tested. In eight of these activated neurones the onset latency of the excitation was within the pulmonary circulation time, consistent with being activated only by pulmonary C-fibre afferents. In two neurones the PBG-evoked excitation still occurred when central inspiratory drive was inhibited, as indicated by the disappearance of phrenic nerve activity. In conclusion, B-fibre respiratory modulated CVPNs can be activated following stimulation of pulmonary C-fibre afferents.

Distinct localization and target specificity of galanin-immunoreactive sympathetic preganglionic neurons of a teleost, the filefish Stephanolepis cirrhifer

Immunoreactivity for galanin was examined in the sympathetic preganglionic neurons in the spinal cord, adrenal glands, sympathetic ganglia, and some sensory ganglia of the filefish Stephanolepis cirrhifer. Galanin-immunoreactive neurons were found only in the rostral part, but not in the caudal part of the central autonomic nucleus (a column of sympathetic preganglionic neurons of teleosts). Many galanin-immunoreactive nerve terminals were found in contact with neurons in the celiac ganglia and the cranial sympathetic ganglia on both sides of the body. Most neurons encircled by galanin-immunoreactive nerve fibers were negative for tyrosine hydroxylase. Galanin-immunoreactive nerve fibers were very sparse in the spinal sympathetic paravertebral ganglia. No galanin-immunoreactive nerve fibers were found in the adrenal glands. No sensory neurons of the trigeminal, vagal, or spinal dorsal root ganglia were positive for galanin-immunoreactivity. These results suggest that galanin-immunoreactive sympathetic preganglionic neurons have distinct segmental localization and might project specifically to a population of non-adrenergic sympathetic postganglionic neurons in the celiac and cranial sympathetic ganglia.

Expression of Fos protein in adrenal preganglionic neurons following chemical stimulation of the rostral ventrolateral medulla of the rat

The ventrolateral medulla is known to be involved in the regulation of arterial blood pressure, especially via its connections with sympathetic preganglionic neurons (SPNs) mainly located in the intermediolateral nucleus of the spinal cord. It has been shown that stimulation of the rostral part of the ventrolateral medulla (RVLM) elicits a release of catecholamines from the adrenal medulla. The aim of the present study was to demonstrate the existence of a functional pathway between the RVLM and adrenal SPNs using the combination of a retrograde tract tracing technique (cholera toxin B subunit) with the immunohistochemical detection of Fos protein following the chemical stimulation of RVLM. The data obtained showed that: (1) chemical stimulation of the RVLM induced Fos immunoreactivity in the intermediolateral nucleus and particularly in SPNs projecting to the adrenal medulla; (2) along the thoracic segments T2-T12, 26.1% of retrogradely identified adrenal SPNs were Fos-immunoreactive with the greatest percentage (30.9%) in the T8 segment. These results favored a functional control of the RVLM on adrenal SPNs which may contribute to a substantial activation of the cardiovascular system via the release of adrenal catecholamines.

Chemically distinct preganglionic inputs to iris-projecting postganglionic neurons in the rat: A light and electron microscopic study

Individual autonomic postganglionic neurons are surrounded by pericellular baskets of preganglionic terminals that are easily identifiable with the light microscope. It has been assumed that the target cell of a pericellular basket of preganglionic terminals is the neuron at the centre of the basket. This assumption has enabled the connectivity of preganglionic neurons to be determined at the light microscopic level. However, if the preganglionic terminals in a pericellular basket make synapses with the dendrites of nearby, but functionally different, postganglionic neurons, then the conclusions of light microscopic studies are far less certain. We have used a serial section ultrastructural study to determine the target of the preganglionic pericellular basket in a situation where the apparent target cell is surrounded by neurons of dissimilar function. In the rat superior cervical ganglion, postganglionic neurons projecting to the iris were identified, using retrograde tracers, as single neurons (i.e., not in clusters). We have used immunohistochemistry to show that iris-projecting neurons are surrounded by preganglionic nerve terminals containing calcitonin gene-related peptide (CGRP). We have demonstrated that the pericellular basket of CGRP-immunoreactive preganglionic terminals provides inputs only to the soma at the centre of the basket and not to the dendrites of surrounding neurons. This suggests that, in autonomic ganglia, light microscopic identification of the preganglionic terminal baskets is likely to be a reliable method for identifying the targets of subclasses of preganglionic neurons.

CNS innervation of vagal preganglionic neurons controlling peripheral airways: a transneuronal labeling study using pseudorabies virus

The CNS cell groups that project to vagal preganglionic neurons which innervate the most distal part of the airways were identified by the viral retrograde transneuronal labeling method. Pseudorabies virus (PRV) was injected into the lung parenchyma of C8 spinal rats and after 5 days survival, brain tissue sections from these animals were processed for immunohistochemical detection of PRV. Retrogradely labeled parasympathetic preganglionic cells (first-order neurons) were seen mainly in the ventral medulla oblongata: the compact portion of the nucleus ambiguus and the area ventral to it. Occasionally, a few labeled cells were seen within the rostral part of the dorsal vagal nucleus. This labeling pattern correlated well with the retrograde cell body labeling seen following cholera toxin beta-subunit (CT-b) injections in the lung parenchyma. PRV transneuronally labeled neurons (second-order and/or presumed third-order neurons) were found throughout the CNS with the characteristic labeling in the brainstem. Labeled neurons were identified along and just beneath the ventral medullary surface, and in nearby areas: the parapyramidal, retrotrapezoid, gigantocellular and lateral paragigantocellular reticular nuclei, as well as the caudal raphe nuclei (raphe pallidus, obscurus, and magnus). Several nucleus tractus solitarius (nTS) regions contained labeled cells including the commissural, medial, and ventrolateral nTS subnuclei. The A5 cell group and a small number of locus coeruleus neurons were also labeled. PRV-infected neurons were present in the Kölliker-Fuse and Barrington's nuclei. In the mesencephalon, neurons within the ventral periventricular gray matter were labeled. Labeling was present in the dorsal, lateral and paraventricular hypothalamic nuclei, and within the amygdaloid complex. In summary, the parasympathetic preganglionic neurons that innervate the peripheral airways are controlled by networks of lower brainstem and suprapontine neurons that lie in the same regions known to be involved in central regulation of autonomic functions.

Endogenous lectin (RL-29) expression of the autonomic preganglionic neurons in the rat spinal cord

Rat spinal neurons expressing lectin RL-29 are visualized immunohistochemically. RL-29 immunoreactive (RL-29 IR) neurons are found in the lateral parts of laminae V-VII, designated as the intermediolateral cell column (IML) in the thoracic cord, the sacral parasympathetic nucleus (SPN) in the lumbosacral cord, and the dorsomedial nucleus (DMN) of the ventral horn. The majority of RL-29 IR neurons in the SPN are also labeled by a retrograde tracer DAPI applied to the cut L6-S1 ventral roots. These data indicate that the majority of RL-29 IR neurons in the SPN are autonomic preganglionic neurons, thus suggesting that RL-29 can be a useful tool in marking this subpopulation of neurons. In addition, the presence of previously described RL-29 IR primary afferent fibers and terminals in the dorsal parts of the cord are confirmed.

Glutamate receptor subunits associated with rat sympathetic preganglionic neurons

The purpose of this study was to determine what subunits of the glutamate (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)) receptor are expressed by sympathetic preganglionic neurons in the spinal cord of adult rats. Preganglionic neurons were retrogradely labelled with Fluorogold, double-labelled with choline acetyltransferase immunofluorescence, and examined with confocal microscopy for evidence of immunoreactivity for GluR1, GluR2, GluR2/3 and GluR4 subunits. Quantitative analysis revealed that 92, 63 and 85% of preganglionic cells in the T8 segment express GluR1, GluR2 and GluR2/3 subunits, respectively. Cells were not immunoreactive for the GluR4 subunit. This evidence is consistent with the idea that most sympathetic preganglionic neurons form heteromeric AMPA receptors. Cells with GluR2 subunits will assemble receptors which are impermeable to calcium ions and may be resistant to excitotoxic cell death.

Identification of CNS neurons innervating the rat prostate: a transneuronal tracing study using pseudorabies virus

The spinal and brain neurons that innervate the rat prostate were identified using the transneuronal tracing technique. Three groups of rats were prepared: (1) nerve intact, (2) bilateral pelvic nerve cut and right hypogastric nerve cut and (3) bilateral hypogastric nerve cut and right pelvic nerve cut. Pseudorabies virus (PRV) was injected into the ventral prostate on the left side. After 2-4 days, the rats were perfused transcardially under deep anesthesia and the spinal cord and brain removed. PRV-labelled cells were identified using immunohistochemistry. After 3 days survival, sympathetic and parasympathetic preganglionic neurons were labelled with PRV. In addition, spinal interneurons were found in the dorsal gray commissure (DGC) of T13-S1. Rats with only one hypogastric nerve intact resulted in spinal labelling of sympathetic preganglionic neurons in the DGC and ipsilateral intermediolateral cell column (IML). In addition, many spinal interneurons were found from L1 to L6 in the medial gray. Rats with only one pelvic nerve intact displayed PRV-labelled cells in the parasympathetic preganglionic nucleus ipsilateral to the injection site. Spinal interneurons were present in the region of the IML and in the medial cord. In the brain, areas predominately labelled with PRV included the nucleus gigantocellularis and paragigantocellularis, raphe magnus, raphe pallidus, A5, Barrington's nucleus, central gray, ventral tegmental area, the paraventricular nucleus of the hypothalamus, lateral hypothalamus and medial preoptic area. These data demonstrate the sympathetic and parasympathetic spinal circuits and demonstrate the overlap of supraspinal innervation of the spinal interneurons.

Differential vulnerability of autonomic and somatic motor neurons to N-methyl-D-aspartate-induced excitotoxicity

Two closely-related subsets of spinal motor neurons are differentially vulnerable in the degenerative neurological disease amyotrophic lateral sclerosis. Autonomic motor neurons (i.e. preganglionic sympathetic neurons) survive in this disorder, whereas most spinal somatic motor neurons do not. The present study was undertaken in order to begin to understand the phenotypic differences between the two motor neuronal subsets which might contribute to this differential survival. Organotypic slice cultures of postnatal rat thoracic spinal cord were maintained in defined medium for one to 12 days in the presence or absence of N-methyl-D-aspartate or its antagonist, D-amino-phosphonopentanoic acid. Autonomic motor neurons that were stained for either nicotinamide adenine dinucleotide phosphate reduced diaphorase or choline acetyltransferase only were both able to tolerate 50 microM N-methyl-D-aspartate treatment for over seven days in culture with no apparent adverse effects. In contrast, cultures maintained for only one day in medium containing 50 microM N-methyl-D-aspartate showed a dramatic and highly significant decrease in the numbers of neurofilament-positive somatic motor neurons, as well as nicotinamide adenine dinucleotide phosphate reduced diaphorase-positive interneurons. These N-methyl-D-aspartate-induced effects were dose-dependent and blockable. The results of this investigation indicated that autonomic motor neurons and somatic motor neurons were differentially susceptible to N-methyl-D-aspartate-induced excitotoxicity, and that the resistance of autonomic motor neurons to this insult appeared to be independent of the nicotinamide adenine dinucleotide phosphate reduced diaphorase phenotype.

Spinal and vagal projections to the sympathetic trunk of the wrasse, Halichoeres poecilopterus

The sympathetic preganglionic neurons of the teleost, Halichoeres poecilopterus, were identified by retrograde axonal tracing. After horseradish peroxidase was applied to the sympathetic trunk, labeled neurons were found at the caudalmost level of the medulla, in the spinal cord near the fourth spinal nerve root (rostral spinal group), and in the spinal cord from rostral to the sixth spinal nerve root to caudal to the tenth spinal nerve root (caudal spinal group). The rostral spinal group has three cell columns segregated mediolaterally from the central gray zone to the lateral funiculus. Labeled neurons were found predominantly on the side ipsilateral to the application. In the caudal spinal group, labeled neurons were found bilaterally in the central gray zone. This condition is different from that previously reported in the puffer fish and filefish. The labeling in the medulla suggests that the preganglionic neurons in the brainstem may send fibers to the sympathetic trunk of this fish, although their peripheral targets are unknown.

Periaqueductal gray matter projection to vagal preganglionic neurons and the nucleus tractus solitarius

The periaqueductal gray matter (PAG) has been implicated in a variety of different functions, including autonomic regulation. Chemical stimulation of the lateral PAG produces hypertension and tachycardia while activation of the ventrolateral PAG produces the opposite effect. While these effects are the result of alterations in sympathetic activity, little is known about whether the PAG can modulate vagal functions as well. The anterograde axonal tracing method using the plant lectin Phaseolus vulgaris leucoagglutinin (PHA-L) was used to determine whether both of the lateral and ventrolateral PAG columns project to vagal preganglionic neurons and/or to the nucleus tractus solitarius (NTS). Highly restricted PHA-L injections were made in all four PAG columns throughout their rostrocaudal extent in rats. Labeled fibers were visualized by immunohistochemistry and studied in relationship with choline acetyltransferase (ChAT) immunostained parasympathetic preganglionic neurons of the dorsal motor vagal nucleus (DMV) and nucleus ambiguous (NA). The lateral PAG projects to the lateral DMV and to the caudal part of the external NA. The ventrolateral PAG innervates the same regions and also projects to the rostral part of the external NA -- a site that contains cardiac parasympathetic preganglionic neurons. Both the lateral and ventrolateral PAG project to the NTS in a similar fashion innervating the medial, ventrolateral and commissural subnuclei. In summary, the lateral and ventrolateral PAG have similar patterns of innervation of the NTS and DMV, but their projection to the NA is different: the rostral external NA receives innervation only from the ventrolateral PAG and the lateral PAG innervates the caudal part.

Electrophysiological evidence for multiple glycinergic inputs to neonatal rat sympathetic preganglionic neurons in vitro

The time pattern of glycinergic inhibitory postsynaptic currents (IPSCs) in sympathetic preganglionic neurons was studied in thin transverse spinal cord slices of neonatal (1-10 days postnatal) rats by means of the patchclamp technique. Three time patterns could be distinguished: (i) large events [mostly > 400 pA (30-36 degrees C)] occurring at regular intervals, (ii) small events occurring at irregular intervals, and (iii) small events occurring in transient (1.5-10 s), high-frequency (> 15 Hz) bursts of synaptic activity. The large regular events had uniform kinetics which was consistent with the idea of a proximal site of origin for all of these events. They were reversibly inhibited in amplitude and frequency by extracellular application of a high concentration of acetylcholine (200 microM) or the specific nicotinic acetylcholine receptor agonist dimethylphenylpiperazinium iodide (DMPP; 1 mM), but unaffected by glutamate (100 microM). IPSCs occurring in bursts had slower and less uniform kinetics, suggesting a more diverse site of origin. The frequency of events decreased during a burst. Similar bursts could be induced by extracellular application of glutamate receptor agonists. These results indicate that sympathetic pregnanglionic neurons in a thin, transverse spinal cord slice receive at least two different glycinergic inputs.

Cytochrome oxidase staining in the major pelvic ganglion of the male rat

Cytochrome oxidase staining was used as a marker of metabolic activity in neural elements in the rat major pelvic ganglion. Many neurons in the ventral pole of the ganglion have little cytochrome oxidase activity, while neurons in other locations show gradations in staining intensity. Punctate staining around principal neurons may represent preganglionic terminals, since it was greatly reduced after denervation of the ganglion. Image analysis was used to compare neuronal size to staining intensity. There was a negative correlation between cell size and staining intensity; the largest neurons were only lightly stained for cytochrome oxidase, while the medium and the small neurons showed a full range of metabolic activity. To study metabolic activity of an identified neuronal population, the seminal vesicles were injected with a retrograde tracer. The largest seminal vesicles neurons (1500 to 3200 microns2) had low enzyme activity, whereas the majority of neurons to this organ were smaller with gradations in staining. These results are indicative of the metabolic activity of the autonomic innervation to various pelvic tissues. Cytochrome oxidase histochemistry should prove valuable in assessing the demands placed on autonomic ganglia in differing functional and dysfunctional states.

Vagal preganglionic projections to the enteric nervous system characterized with Phaseolus vulgaris-leucoagglutinin

The patterns and extent of vagal preganglionic divergence and convergence within the gastrointestinal tract of the rat were characterized with the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Three weeks after tracer was iontophoretically injected into two to four sites within the dorsal motor nucleus of the vagus, wholemounts of perfused gut organs (stomach, duodenum, cecum) were prepared, counterstained with Cuprolinic blue, and processed for PHA-L using the avidin biotin complex with diaminobenzidine. Controls included animals injected with PHA-L after intracranial deafferentations. Well-positioned injections labeled an extremely dense and intricate network of varicose efferent axons throughout the gastric myenteric plexus (including that of the fundus). Individual fibers collateralized extensively, forming a variety of pericellular arborizations and terminal complexes made up of both en passant and end swellings. Single axons frequently innervated subsets of neurons within ganglia. Most enteric neurons were contacted by varicosities of more than one vagal fiber. The patterns of vagal preganglionic fibers in the duodenal and cecal myenteric plexuses resembled the organization in the stomach in many aspects, but the projections in each organ had distinctive characteristics, and label was less dense in the intestines than in the stomach. Vagal preganglionic fibers directly innervated submucosal ganglia, although sparsely. Brainstem injections of PHA-L retrogradely labeled a few myenteric neurons in the corpus, fundus, and duodenum: These "gastrobulbar" and "duodenobulbar" neurons received reciprocal vagal preganglionic innervation. Finally, the PHA-L that spread to the nucleus of the solitary tract occasionally produced transganglionic labeling of afferent intramuscular arrays (gastric fundus). The results of this paper provide strong evidence that the traditional "command neuron" or "mother cell" hypotheses of vagal-enteric organization should be abandoned for an integrative neural network model.

Topographic relationship of neurotensin-containing axon terminals with cardiac and noncardiac principal ganglion cells in the stellate ganglia of the cat

The pattern of association between neurotensin (NT)-immunoreactive (NTIR) preganglionic nerve terminals and cardiac and noncardiac neurons in the stellate ganglion of the cat is analyzed, based on the finding of an excitatory modulation effect of exogenous NT on cardiac functions. For this purpose, NT-containing terminals were labeled by immunohistochemistry, and ganglion cells were detected by retrograde labeling of cardiac and vertebral nerves to identify cardiac and noncardiac neurons. To determine a possible regional localization of NTIR terminals and ganglion cells, the ganglia were divided into four areas: caudal, dorsomedial, cranial, and ventromedial, related to the two major afferent nerves (thoracic white rami 3 [T3WR] and 2 [T2WR]) and the two efferent nerves (vertebral and cardiac). NTIR terminals were widespread in the complete ganglion tissue; they covered practically all the regions explored, although two clusters of high concentration of NTIR terminals were detected in the cranial and caudal areas. By retrograde labelling it was found that cardiac cells were arranged around the exit of the cardiac nerve and that the vertebral neurons were extended from the exit of the vertebral nerve to the entrance of T3WR. The finding of association of NTIR terminals with cardiac neurons may account for the cardioregulatory effect of NT; however, since the presence of NTIR terminals close to the noncardiac neurons is notorious, other regulatory functions of NT must be considered.

Voltage-dependent potassium currents of sympathetic preganglionic neurons in neonatal rat spinal cord thin slices

Voltage-dependent potassium currents were analyzed in the visually identified sympathetic preganglionic neurons (SPNs) of neonatal rat spinal cord thin slices by the whole-cell patch-clamp technique. Some of the SPNs were identified by the presence of retrogradely transported fluorescent dye, DiI, injected into the superior cervical ganglion several days prior to experimentation. In a tetrodotoxin (TTX)-containing solution, a step depolarization from the holding potential of -72 mV generated a slow outward current that was suppressed by tetraethylammonium (TEA) and by Ca(2+)-free/2.5 ImM Co2+ solution. Ca(2+)-dependent current consisted of a transient and a sustained components. In a Ca(2+)-free (substituted with Mg2+) solution with TTX and TEA, a step depolarization from a hyperpolarized potential evoked a transient outward current that was blocked by 4-aminopyridine (4-AP). A step hyperpolarization evoked a voltage-dependent inward current, the conductance of which was dependent not only on the membrane potential, but also on the extracellular K+ concentration. Tail current analyses revealed that all of these currents were carried by K+ ions. These results indicate that SPN possesses at least five types of voltage-dependent K+ current, including the delayed rectifier current (IK), Ca(2+)-dependent transient current (IC), Ca(2+)-dependent sustained current (IAHP), A-current (IA) and inward rectifying current (Iu), which may be targets of putative transmitters released from various descending and segmental inputs impinging upon the SPN.

Voltage-gated currents in identified parasympathetic cardiac neurons in the nucleus ambiguus

Heart rate is normally dominated by the activity of the cardioinhibitory parasympathetic nervous system, while abnormally low levels of parasympathetic cardiac activity have been implicated in many cardiovascular diseases including hypertension, heart failure and sudden cardiac death. In this study we have examined the voltage-gated currents in parasympathetic cardiac neurons that were identified with a retrograde fluorescent tracer in visualized sections (250 microns) of nucleus ambiguus. Depolarization of parasympathetic cardiac neurons to potentials more positive than -50 mV evoked a rapidly activating and inactivating inward current which could be blocked by tetrodotoxin (TTX), although in some neurons up to 10 microM was required for complete block. The voltage-dependent inactivation properties of this Na current showed relatively broad inactivation characteristics, a characteristic of TTX-resistant Na channels. Depolarization also elicited biphasic outward currents, which were separated into a transient IA type K current using the specific channel antagonist 4-aminopyridine and a long-lasting delayed rectified K current. These voltage-gated Na and K currents define the action potential firing patterns of parasympathetic cardiac neurons, such as frequency adaptation and spike delay, and also determine the activity of these neurons in response to depolarizing and hyperpolarizing synaptic innervation.

Brainstem origin of preganglionic cardiac motoneurons in the muskrat

The muskrat, and aquatic rodent with a brisk and reliable diving response, shows a remarkable bradycardia after nasal stimulation. However, the medullary origin of cardiac preganglionic motoneurons is unknown in this species. We injected fat pads near the base of the heart of muskrats with a WGA-HRP solution to label retrogradely preganglionic parasympathetic neurons that project to the cardiac plexi. Results showed that the preponderance of labeled neurons was in ventrolateral parts of the medulla from 1.5 mm caudal to the obex to 2.0 mm rostral. Eighty-nine percent of the labeled neurons were located bilaterally in the external formation of the nucleus ambiguus, 5.6% were in the lateral extreme of the dorsal motor nucleus of the vagus nerve and 5.3% were found in the intermediate area in between these two nuclei. Although controversy still exists concerning the medullary origin of preganglionic cardiac motoneurons, our results from muskrats agree with those from most other species where preganglionic cardiac motoneurons were located just ventral to the nucleus ambiguus.

Visceral afferent and efferent columns in the spinal cord of the teleost, Ictalurus punctatus

In tetrapod vertebrates, neural circuitries subserving visceral and somatic reflexes are each represented in distinct columns of cells within the gray area of the spinal cord. To determine the location of visceral elements of the spinal cord of a teleost fish, crystals of the carbocyanine dye 1,1'dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI), were placed on either the abdominal sympathetic (mesenteric) nerves, the coeliac ganglia, or on the rostral three somatic spinal nerves, in fixed specimens of the channel catfish, Ictalurus punctatus. In fish in which DiI had been placed on the mesenteric nerves, labeled fibers coursed along the lateral margin of the dorsal horn within the first and second spinal segments, and appeared to terminate in a region at the base of the dorsal horn. In contrast, when DiI crystals were placed on the somatic spinal nerves, labeled primary afferents terminated in the dorsalmost two thirds of the dorsal horn, as well as in ventral and ventromedial areas of the medial funicular nuclear complex. Labeled somata (motor neurons) were situated in the ventral horn. When DiI crystals were placed bilaterally on the coeliac ganglia, labeled piriform and fusiform preganglionic neurons occurred in intermediate positions adjacent to the central canal, corresponding to the paracentral nucleus of Herrick, and in the lateral funiculus. These results demonstrate that somatic and visceral afferent and efferent functional columns are distinct in a teleost fish as they are in amniote vertebrates.

The spinal sympathetic preganglionic cell column in the puffer fish, Takifugu niphobles

Little is known about the spinal sympathetic organization in teleosts. We examined the location of the sympathetic preganglionic neurons with horseradish peroxidase (HRP) labeling. After HRP application to the sympathetic trunk or celiac ganglion, labeled neurons were found just dorsal - dorsolateral to the central canal. They form a cell column (central autonomic nucleus) at the level of the posterior rootlet of the first spinal nerve to the third spinal nerve. HRP application to the sympathetic trunk produced labeling in almost the entire central autonomic nucleus, but HRP application to the celiac ganglion produced labeling in only the rostral half of the central autonomic nucleus. These results suggest that there is some topographical arrangement in the rostrocaudal part of the central autonomic nucleus. On the other hand, the fact that the sympathetic preganglionic neurons are within a single cell column and have no mediolateral segregation means that the target-related or function-associated mediolateral arrangement found in tetrapods is lacking in this species. We also found some labeling in the central autonomic nucleus after HRP application to the cranial nerves. This may indicate that the preganglionic neurons project to the cranial nerves.

Kinetics of A-currents in sympathetic preganglionic neurones and glial cells

Transient outward currents (A-currents; IA) were recorded in sympathetic preganglionic neurones (SPNs) and glial cells of the intermediolateral cell column (IML) by whole-cell recordings in rat spinal cord slices. In both cell types IA activated at around -45 mV and the time-course of decay was monoexponential, but faster in glial cells than in neurones. In both cases decay time constants displayed the same increase with depolarization above -30 mV. In neurones, the activation curve was shifted to more negative value along the voltage axis and was steeper than the activation curve for glial cells whereas inactivation curves were similar. Recovery from inactivation followed a double and monoexponential decay in neurones and glial cells, respectively.

Expression of GAP-43 mRNA in preganglionic sympathetic neurones of the adult rat spinal cord

In situ hybridization combined with intraperitoneal injection of the tracer Fluoro-Gold was used to study the distribution of GAP-43 mRNA in autonomic cell groups of the rat spinal cord. In the thoracic cord, numerous cells expressing GAP-43 mRNA were present in the central autonomic nucleus (lamina X) and in the intermediolateral cell column (IML). In the IML, all Fluoro-Gold-labelled preganglionic neurones were heavily labelled for GAP-43 mRNA. In contrast, Fluoro-Gold-labelled motoneurones were unlabelled or only lightly labelled. Our results indicate that preganglionic sympathetic neurones express GAP-43, a conclusion that is consistent with studies showing that GAP-43 immunoreactive terminals are present in autonomic ganglia. GAP-43 in these neurones may play a role in their continuing anatomical remodelling.

Oxytocinergic innervation to the upper thoracic sympathetic preganglionic neurons in the rat. A light and electron microscopical study using a combined retrograde transport and immunocytochemical technique

A combination of retrograde cell body labeling and immunohistochemistry was employed to elucidate how oxytocinergic fibers make contact with sympathetic preganglionic neurons (SPNs) in the rat spinal cord from T1 to T4. SPNs were labeled retrogradely using cholera toxin subunit B (CTb) or horseradish peroxidase-conjugated CTb. Oxytocin-immunoreactive (ir) fibers were found in the intermediate zone, including the sympathetic preganglionic subnuclei. In the central autonomic nucleus and the intercalated nucleus, brown-stained oxytocin-ir varicosities or terminals were frequently observed to stud black-stained dendrites of SPNs. Electron microscopical observations showed that oxytocin-ir terminals form synapses with dendrites or soma of the sympathetic preganglionic neurons. The terminals contained numerous small clear round vesicles and a few large, cored vesicles. These results clearly show that a large proportion of SPNs are innervated by oxytocin-containing fibers. The origin of these fibers is discussed, and it is concluded that they are probably descending fibers from the paraventricular nucleus of the hypothalamus.

A comparative study of NADPH-diaphorase in the sympathetic preganglionic neurons of the upper thoracic cord between spontaneously hypertensive rats and Wistar-Kyoto rats

With retrograde tracing using fluorogold injection into the superior cervical ganglion and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry, the present comparative study revealed that the retrogradely labelled neurons in n. intermediolateralis pars funicularis (ILf) and n. intermediolateralis pars principalis (ILp) of the autonomic region in the upper thoracic cord exhibited a much stronger reactivity for NADPH-diaphorase in Wistar-Kyoto (WKY) rats than those in spontaneously hypertensive rats (SHR). It was found that in ILf in WKY rats, 77.62% of the fluorogold-labelled neurons were NADPH-d positive, while in SHR, only 56.43% of the labelled neurons were NADPH-d positive. The frequency distribution of NADPH-d positive retrogradely labelled neurons was significantly reduced in ILf of the spinal cord of SHR (U-test: P < 0.01). In ILp in WKY rats, 65.25% of fluorogold-labelled neurons were NADPH-d positive in WKY rats, while in SHR, only 56.28% of the labelled neurons were NADPH-d positive. Although the difference (P > 0.05) in the frequency of NADPH-d positive neurons in ILp between the two strains of rats was not significant, the reductions in SHR seemed considerable. Examination of the preganglionic sympathetic trunk and the superior cervical ganglion between SHR and WKY rats revealed that virtually all the NADPH-d positive fibers were derived from the sympathetic preganglionic neurons. In SHR, the NADPH-d positive fibers were not as intensely stained as those of WKY rats. This preliminary results suggest that nitric oxide, as an inhibitory neurotransmitter, may be implicated in the onset of hypertension.

Vagal preganglionic neurons innervating the different gastric regions in the Japanese quail (Coturnix japonica)

The cytoarchitecture and distribution patterns of the vagal preganglionic neurons within the dorsal motor nucleus of the vagus nerve (DMNX) innervating the proventriculus and the gizzard of the Japanese quail were examined by Nissl staining and the horseradish peroxidase (HRP) method. A 30% solution of HRP was injected into nine different gastric regions: the ventral and dorsal parts of the proventriculus, the caudodorsal and cranioventral thick muscles, the craniodorsal and caudoventral thin muscles, and the pylorus, and the ventral and dorsal tendons of the gizzard. Nissl preparations showed that the DMNX is composed of two cell groups, the dorsal magnocellular and mediocellular subnucleus (Xd) and the ventral parvicellular subnucleus (Xv). After injection of HRP into the ventral and dorsal parts of the proventriculus, HRP-labeled cells were predominantly observed in the left and right DMNX, respectively. The rostrocaudal distribution patterns of HRP-labeled cells in the Xd and Xv were symmetric on the left and right sides. The distribution patterns of labeled cells following the injection of HRP into each region of the gizzard showed that there was very little difference in the number of neurons between the left and right DMNX, and no topographic localization was found in the Xd and Xv. The vagal preganglionic neurons projecting to the gizzard lay more caudal than the ones for the proventriculus. This study suggested topographic localization in the distribution patterns of the vagal preganglionic neurons innervating the proventriculus and the gizzard.

Chemical mediators of spinal inhibition of rat sympathetic neurones on stimulation in the nucleus tractus solitarii

1. This study was undertaken to gain more direct evidence of the pathways and neurochemical mediators of a spinally mediated baroreceptor inhibition of sympathetic preganglionic neurones (SPNs). 2. For this purpose, single-pulse electrical stimulation within identified vasodepressor regions of the nucleus tractus solitarii (NTS) was used together with extracellular recordings of single antidromically identified SPNs in the T2 segment of the spinal cord of anaesthetized rats. 3. The actions of agonists and antagonists of inhibitory amino acids on the NTS-induced inhibitions were determined, when they were iontophoretically applied in the vicinity of SPNs via a multibarrel micropipette assembly. 4. Extracellular recordings were made from sixty-nine SPNs. In forty-four SPNs, NTS stimulation elicited a period of inhibition of activity in both spontaneous and 'D,L-homocysteic acid-driven' SPNs with a latency to onset of 60 +/- 6 ms and a magnitude of 80 +/- 3%. 5. In six out of eight neurones, the NTS-induced inhibition was reduced by 74 +/- 16% during the application of the glycine antagonist strychnine (0-10 nA, 5-10 min) with doses that selectively blocked the inhibitory effect of iontophoretically applied glycine. 6. In nine out of nine neurones, the NTS-induced inhibition was reduced by 38 +/- 6% during the application of the GABAA antagonist bicuculline (5-15 nA, 4-14 min) with doses that selectively blocked the inhibitory effect of iontophoretically applied GABA. 7. In two SPNs, the actions of strychnine and bicuculline were shown to be additive in blocking the NTS inhibition. 8. The selective GABAB antagonists, CGP 35348 (20-50 nA, 6-25 min) and CGP 55845A (10 nA, 11 min) did not antagonize the NTS-induced inhibition. 9. It is suggested that GABA and glycine interneurones are activated by a baroreceptor bulbospinal pathway to inhibit sympathetic preganglionic neurones in the spinal cord.

Synaptic contact of neuropeptide-and amine-containing axons on parasympathetic preganglionic neurons in the superior salivatory nucleus of the rat

Parasympathetic preganglionic neurons in the superior salivatory nucleus (SSNNs) projecting to the pterygopalatine ganglion were labeled by retrograde transport of cholera toxin B subunit (CTB) in the rat. Morphological interactions between SSNNs and afferent fibers immunoreactive (IR) for neuropeptide and amine were examined with light and electron microscopes by double-immunostaining techniques. SSNNs were found in the ipsilateral ventrolateral part of the rostral medulla oblongata. Around SSNNs, substance P-, enkephalin-, neuropeptide Y-and somatostatin-IR nerve fibers were very rich and tyrosine hydroxylase (TH)-, serotonin (5-HT)-, vasoactive intestinal polypeptide- and calcitonin gene-related peptide (CGRP)-IR axons showed moderate density. Thyrotropin-releasing hormone-containing axons were scarce in this region. The electron microscopic examinations revealed that CTB-IR structures directly received synaptic input from axon varicosities IR for TH, 5-HT and all neuropeptides except for CGRP. These findings suggest that catecholamine, 5-HT and the neuropeptides directly influence the activity of SSNNs and are concerned with the autonomic regulation of nasal and palatal mucosa, lacrimal glands and cerebral blood vessels of the rat.

Postsynaptic gephyrin immunoreactivity exhibits a nearly one-to-one correspondence with gamma-aminobutyric acid-like immunogold-labeled synaptic inputs to sympathetic preganglionic neurons

Peripheral regulation of cardiovascular function is fundamentally influenced by central excitation and inhibition of sympathetic preganglionic neurons in thoracic spinal cord. This electron microscopy study investigated whether the gamma-aminobutyric acid (GABA)-ergic and glycinergic inhibitory innervation of sympathetic preganglionic neurons arises from mutually exclusive afferent populations. Sympathetic preganglionic neurons were retrogradely labeled with cholera beta subunit. GABAergic terminals were identified using strict quantitative statistical analyses as those boutons containing significantly elevated levels of GABA-like immunogold labeling (GABA+). Glycinergic terminals were classified as those boutons opposite postsynaptic gephyrin immunostaining containing background levels of GABA-like immunogold labeling (gephyrin+/GABA- association). Approximately 43% of the synaptic terminals that contacted sympathetic preganglionic somata and proximal dendrites and that were opposite gephyrin were GABA-; the remaining 57% were GABA+. Only two GABA+ boutons (4%) that synapsed on identified sympathetic preganglionic neuron (SPN) processes were not opposite gephyrin immunostaining (GABA+/gephyrin- association). GABA-/gephyrin+ associations were anticipated given prior anatomical, physiological, and pharmacological data. The observed nearly one-to-one correspondence between postsynaptic gephyrin immunoreactivity and GABA+ boutons was unexpected. Prior physiological and pharmacological experiments suggest that the postsynaptic effects of GABAergic inputs to sympathetic preganglionic neurons are mediated by activation of GABAA receptors. Those data, the present results, and other molecular, biochemical, and anatomical studies of gephyrin in the central nervous system (CNS) are consistent with two hypotheses: 1) Postsynaptic gephyrin is associated with GABAA receptors in the membranes of sympathetic preganglionic neurons, and 2) GABA+/gephyrin+ associations do not necessarily predict colocalization of GABA and glycine within single boutons synapsing on sympathetic preganglionic somata and dendrites.

Synapses on axons of sympathetic preganglionic neurons in rat and rabbit thoracic spinal cord

Axosomatic and axodendritic synapses occur on sympathetic preganglionic neurons, but it is not yet known whether their axons receive synaptic input, which could be particularly effective at regulating sympathetic outflow. Here, we examined retrogradely labelled sympathetic preganglionic axons to see if they received synapses. Cholera toxin B subunit (CTB) or CTB conjugated to horseradish peroxidase (CTB-HRP) was used to label neurons projecting to the rat or rabbit superior cervical ganglion, the rat adrenal medulla, or the rabbit stellate ganglion. At the light microscopic level, small groups of CTB-immunoreactive axons travelled through the ventral horn near its lateral boundary, with occasional axons taking a more medial course. The axons passed through the ventrolateral funiculus to exit at the ventral roots. In parasagittal section, a few axons branched within the ventral horn, sending processes rostrally and caudally for short distances before they turned ventrally to exit the spinal cord. At the ultrastructural level, CTB-immunoreactive rat and rabbit sympathetic preganglionic axons were almost exclusively unmyelinated. In contrast, labelling with CTB-HRP revealed both myelinated and unmyelinated axons in the ventral horn, the ventrolateral white matter, and the ventral roots. CTB-HRP also allowed the detection of the initial segment of a sympathetic preganglionic axon. Synapses, with vesicles clustered presynaptically and membrane specializations postsynaptically, were found on some unmyelinated CTB-immunoreactive axons. Occasional axons received several synapses. Synapses were most common on CTB-containing axons just ventral to the intermediolateral cell column. One synapse was found on an axon within 2 microns of its origin from a proximal dendrite. Rare synapses were found several hundred micrometers ventral to the intermediolateral cell column. One branching axon had synapses just below the branch point on both the main axon and the axonal branch. These findings indicate an extensive synaptic input to the axons of at least some sympathetic preganglionic neurons. These axoaxonic synapses could have a profound effect on sympathetic activity.

Glycine induces two distinct membrane currents in neonatal rat sympathetic preganglionic neurones in vitro

1. The effects of glycine (Gly) on neonatal (12- to 16-day-old) rat sympathetic preganglionic neurones (SPNs) in transverse (500 microns) thoracolumbar spinal cord slices were studied by whole-cell patch-clamp techniques. 2. Gly elicited three types of membrane currents when applied to SPNs by pressure ejection (100 mM; 20-180 ms pulse duration): (1) an outward current (20/94 cells); (2) an inward current (30/94); and (3) a biphasic response (44/94) consisting of an outward followed by an inward current. 3. The Gly-induced outward current (IGly,(out)) had a mean reversal potential of -67 mV, was reversed in a low (5.7 mM) chloride Krebs solution, and was reversibly eliminated by strychnine (0.1-1 microM). 4. The Gly-induced inward current (IGly,(in)) had a mean reversal potential of -41 mV, was reduced in a Na(+)-free and increased in a high (15 mM) K+ solution; strychnine at the high concentration of 1 microM reduced the response by an average of 53%. 5. The electrophysiological and pharmacological characteristics of the biphasic response suggest that it was a combined response of outward and inward currents. 6. The results show that Gly elicits two distinct membrane currents, a Cl(-)-dependent outward current and a cationic inward current, which are mediated by strychnine-sensitive and strychnine-resistant Gly receptors. Functionally, activation of both types of Gly receptors reduces neuronal excitability and attenuates synaptic transmission.

Sympathetic preganglionic neurons contain nitric oxide synthase and project to the superior cervical ganglion: combined application of retrograde neuronal tracer and NADPH-diaphorase histochemistry

Nitric Oxide (NO), which was initially identified as an endothelium-derived relaxing factor, has recently been demonstrated to be a neuronal messenger in central and peripheral nervous systems. In the present study, we examined the possibility of NO producing neurons in teh intermediolateral (IML) cell collum of the thoracic spinal cord (Th) project to the superior cervical ganglion (SCG). First, we observed the NADPH-diaphorase-positive/nitric oxide synthase (NOS)-immunoreactive neurons of the IML and the dorsal part of the central canal at the level of Th1-Th3, and numerous fiber-stainings in the superior cervical ganglion. Second, after injecting WGA-HRP (wheat germ agglutinin-horse radish peroxidase complex), a retrograde neuronal tracer, into the SCG, and developing WGA-immunohistochemistry and the NADPH-diaphorase histochemistry in the same sections, we detected double-labeled neurons in the IML. These findings provide evidence that sympathetic preganglionic NO producing neurons directly innervate to the SCG.

5-Hydoxytryptamine evokes depolarizations and membrane potential oscillations in rat sympathetic preganglionic neurones

1. Whole-cell recordings were made from seventy-seven identified rat sympathetic preganglionic neurones (SPN) in spinal cord slices. Perfusion of 5-HT (0.5-30 microM) strongly depolarized 90% of neurones. The response was slow in onset, could last over 10 min and was associated with an increase in input resistance. 5-HT could also evoke rhythmical membrane potential oscillations in a population of previously quiescent neurones. 2. The 5-HT response persisted in TTX and also in low-Ca(2+)-high-Mg2+ artificial cerebrospinal fluid (ACSF), suggesting that the receptors are on SPN. The 5-HT uptake inhibitor 6-nitroquipazine potentiated the 5-HT-induced depolarization. 3. The 5-HT-induced depolarization was reduced and then abolished by membrane hyperpolarization to potentials of about -100 mV, but was not reversed in sign by further hyperpolarization. In voltage clamp, 5-HT evoked inward currents associated with the reduction of an outwardly rectifying potassium conductance. 4. The 5-HT2 receptor agonist alpha-methyl-5-HT mimicked the 5-HT response on all neurones, as did the 5-HT1 receptor agonist 5-carboxamidotryptamine (5-CT) on 71% of SPN. The responses to 5-HT, alpha-methyl-5-HT and 5-CT were inhibited by the 5-HT2 antagonists ketanserin and ritanserin. 5. Pressure ejection of 5-HT over the central canal region could evoke a biphasic inhibitory-excitatory response. This response persisted in TTX, suggesting that an inhibitory 5-HT receptor may be located on the medial dendrites. 6. SPN are powerfully depolarized by 5-HT acting at 5-HT2 receptors, via the closure of an outwardly rectifying potassium conductance. The long duration of the response and the ability of 5-HT to induce rhythmical oscillations suggest that 5-HT may have an important role in regulating SPN excitability.

Spinal cord lamina V and lamina VII interneuronal projections to sympathetic preganglionic neurons

This light and electron microscopic study sought to localize spinal cord interneurons that contribute to the normal and abnormal physiological regulation of spinal sympathetic preganglionic function. Sympathetic preganglionic neurons in caudal C8 through T4 of rat spinal cord were retrogradely labeled with wheat germ agglutinin (WGA) and/or cholera beta subunit (CT beta) following injections into the superior cervical ganglion (SCG). With two exceptions, the observed locations of retrogradely WGA- and CT beta-labeled sympathetic preganglionic neurons were as expected from previous studies. The exceptions were restricted populations of cells in caudal C8 and rostral T1 spinal segments. These neurons were classified as ventrolateral (vlSPN) and ventromedial (vmSPN) sympathetic preganglionic neurons; their somata and dendrites encircled dorsolateral lamina IX motoneurons. Only WGA was transported transneuronally following the retrograde labeling of sympathetic preganglionic neurons. Transneuronally WGA-labeled spinal interneurons were located principally in the reticulated division of lamina V and dorsolateral lamina VII. A strict segmental organization was observed. All transneuronally labeled interneurons were ipsilateral to, and coextensive with, retrogradely WGA-labeled sympathetic preganglionic neurons. Electron microscopic observations suggested that retrograde transsynaptic passage of WGA occurred within the sympathetic preganglionic neuropil and showed further that similar classes of organelles were WGA immunoreactive in retrogradely labeled sympathetic preganglionic neurons and in transneuronally labeled lamina V and lamina VII neurons: 1) cisternae and vesicles at the trans face of the Golgi apparatus, 2) large endosomes/dense bodies, and 3) multivesicular bodies. The data are consistent with two hypotheses: 1) Somatic and visceral primary afferent inputs to thoracic spinal cord modify segmental sympathetic preganglionic function through activation of a disynaptic pathway involving lamina V and/or lamina VII interneurons, and 2) long-loop propriospinal pathways access sympathetic preganglionic neurons through symmetrical, segmental interneuronal circuitry.

Segmental patterning of rat and chicken sympathetic preganglionic neurons: correlation between soma position and axon projection pathway

The segmental organization of midthoracic rat and chicken sympathetic preganglionic neurons was examined by retrograde labeling in vivo and in vitro. The results demonstrate that individual sympathetic preganglionic neurons project only rostrally or caudally within the sympathetic chain, even though the spinal segment in which they reside provides innervation to both rostral and caudal ganglia. In addition, there is both a segmental and an intrasegmental pattern in the thoracic sympathetic column, in which the position of preganglionic neurons is related to the direction they project in the sympathetic chain. Thoracic sympathetic preganglionic neurons are organized into discrete segmental units, each of which exhibits an internal rostrocaudal polarity with respect to the direction of axon projection in the sympathetic chain. The rostrocaudal bias of this internal polarity is graded from segment to segment along the longitudinal axis. Since there is minimal overlap between thoracic segments, the transition from one segment to another entails a sharp change in the pathway choice of the preganglionic neurons. The organization of the preganglionic projections thus includes (1) segmental periodicity, (2) intrasegmental gradients of neuronal identity, and (3) an axial gradient of segment identity. The significance of these findings is twofold. First, they suggest a functional organization that may be related to the specificity of sympathetic reflex action. Second, they reveal a cellular organization that suggests an underlying segmental pattern in the developing spinal cord.

CNS cell groups regulating the sympathetic outflow to adrenal gland as revealed by transneuronal cell body labeling with pseudorabies virus

The CNS cell groups that innervate the sympathoadrenal preganglionic neurons of rats were identified by a transneuronal viral cell body labeling technique combined with neurotransmitter immunohistochemistry. Pseudorabies virus was injected into the adrenal gland. This resulted in retrograde viral infections of the ipsilateral sympathetic preganglionic neurons (T4-T13) and caused retrograde transneuronal cell body infections in 5 areas of the brain: the caudal raphe nuclei, ventromedial medulla, rostral ventrolateral medulla, A5 cell group, and paraventricular hypothalamic nucleus (PVH). In the spinal cord, the segmental distribution of virally infected neurons was the same as the retrograde cell body labeling observed following Fluoro-gold injections in the adrenal gland except there was almost a 300% increase in the number of cells labeled and a shift in cell group distribution. These results imply there are local interneurons that regulate the sympathoadrenal preganglionic neurons. In the medulla oblongata, serotonin (5-HT)-, substance P (SP)-, thyrotropin-releasing hormone-, Met-enkephalin-, and somatostatin-immunoreactive neurons of the raphe pallidus and raphe obscurus nuclei and the ventromedial medulla were infected. In the ventromedial and rostral ventrolateral medulla, immunoreactive phenylethanolamine-N-methyltransferase, SP, neuropeptide Y, somatostatin, and enkephalin neurons were infected. The A5 noradrenergic cells were labeled, as were some somatostatin-immunoreactive neurons in this area. In the were infected. The A5 noradrenergic cells were labeled, as were some somatostatin-immunoreactive neurons in this area. In the hypothalamus, tyrosine hydroxylase- and SP-immunoreactive neurons of the dorsal parvocellular PVH were infected. Only a few immunoreactive vasopressin, oxytocin, Met-enkephalin, neurotensin, and somatostatin PVH neurons were labeled.

Calcitonin gene-related peptide containing sympathetic preganglionic and sensory neurons projecting to the superior cervical ganglion of the rat

The origin of calcitonin gene-related peptide (CGRP)-containing fibers observed in the superior cervical ganglia (SCG) of the rat was investigated by a combined technique of retrograde axonal tracing and indirect immunofluorescence. Following the injection of Fast blue (FB) into the SCG, labeled neurons were observed in the C8-T5 spinal cord segments, with the highest density in T1-T3 (5-8 neurons per section). More than 90% of them were located in the ipsilateral intermediolateral cell column (IML) and the rest were found in the central autonomic area (CA) and intercalated region (IC) between the IML and CA. CGRP-like immunoreactive (IR) neurons were detected in these areas in animals pretreated with colchicine. About one-fourth of FB-labeled cells were CGRP-IR, which corresponded to three-fourths of the CGRP-IR neurons in the above-mentioned autonomic areas of these spinal cord segments. Most of these double-labeled cells were found in the IML (95%). A few FB-labeled cells were also observed in dorsal root ganglia (C8-T5) and 30% of them were CGRP-IR. These findings suggested that the CGRP-IR fibers in the rats SCG are supplied from both sympathetic preganglionic neurons in the spinal cord and sensory ganglion cells, although the latter projection is quite rare.

Distribution of sympathetic preganglionic neurons and monoaminergic nerve terminals in the spinal cord of the rat

A study was made of the distribution of sympathetic preganglionic neurons identified by retrograde labeling with horseradish peroxidase from various peripheral nerve trunks and of the distributions of monoaminergic terminals in the spinal cord of the rat. Nerve terminals were stained immunohistochemically by using antisera raised against tyrosine hydroxylase, phenylethanolamine-N-methyl-transferase, neuropeptide Y, and 5-hydroxytryptamine and by using formaldehyde-induced fluorescence. The three-dimensional distribution of sympathetic preganglionic neurons was described by using computer reconstruction and compared with the arrangement of each population of immunohistochemically stained terminals in the intermediate zone. Although monoaminergic terminals are associated with most sympathetic neurons, particularly in the intermediolateral column, the relationship of many terminals to sympathetic neuron somata in other parts of the intermediate zone is tenuous. Some of the descending innervation may terminate on interneurons. The data are consistent with the coexistence of phenylethanolamine-N-methyl-transferase and neuropeptide Y in terminals arising from cell bodies in the C1 region in the ventrolateral medulla and with the presence of at least two populations of catecholaminergic terminals as well as the adrenergic one. Serotoninergic terminals are denser and have a different arrangement from those of catecholaminergic terminals in the intermediate zone.

Immunohistochemical distribution of serotonin in spinal autonomic nuclei: I. Fiber patterns in the adult rat

The differential distribution of serotonin (5HT) fibers in spinal laminae VII and X is described for the adult rat. The results indicate that descending 5HT fibers preferentially innervate those regions of lamina VII that contain sympathetic and parasympathetic neurons. In lamina X, especially the dorsal commissural nucleus, large numbers of 5HT fibers are observed throughout the spinal cord. Moreover, sympathetic nuclei are more richly innervated with 5HT than the spinal parasympathetic nuclei. Spinal cord hemisections reveal that spinal autonomic nuclei are differentially innervated: ipsilateral serotoninergic projections to the intermediolateral cell column are preferentially interrupted. In addition, a large crossed 5HT projection exists throughout the length of the spinal cord that decussates five to six spinal segments rostral to its termination. Both crossed and uncrossed 5HT fibers span many spinal segments and have large numbers of collaterals. Spinal cord transections show that the vast majority of spinal 5HT descends from the brainstem but that some 5HT fibers are of intrinsic origin.

Immunohistochemical distribution of serotonin in spinal autonomic nuclei: II. Early and late postnatal ontogeny in the rat

These studies reveal that the postnatal ontogeny of serotonin (5HT) in the sympathetic nuclei of the rat spinal cord is protracted; the adult complement of 5HT-immunoreactive fibers is not achieved until at least 60 days of age. As descending serotonin fibers innervate and demarcate the distribution of preganglionic sympathetic nuclei, rostral-caudal and temporal gradients exist. Additionally, a heterogeneous segmental 5HT ontogenetic pattern is observed in sympathetic nuclei. Most serotonin fibers in laminae VII and X are unorganized at birth except for some sympathetic nuclei in high thoracic regions where the 5HT sympathetic pattern is being initiated. By postnatal day 6 the framework of the 5HT pattern is established in all sympathetic nuclei, and by postnatal day 16 a pattern is formed, which develops into the compact adult state by postnatal day 60. The protracted period of sympathetic 5HT development corresponds with the length of time it takes for the autonomic nervous system to mature. In addition, 5HT intraspinal cell bodies are observed at all time points examined, except for the day of birth, and are found in the same regions as adult 5HT neurons, i.e., dorsal or lateral to the central canal in laminae VII and X and in all spinal segments except cervical levels. Many of the 5HT neurons are pericanalicular and bipolar in appearance. Multipolar 5HT neurons are first observed on postnatal day 45.

NPY-containing nerve terminals and fibers in close association with peptidergic sympathetic preganglionic neurons

The anatomical relationship between neuropeptide Y (NPY)-containing nerve terminals and fibers and peptidergic sympathetic preganglionic neurons (SPN) was studied immunohistochemically in cat spinal cord after colchicine administration. Terminals and fibers with NPY were found in apparent close apposition to SPN containing enkephalin-, neurotensin-, somatostatin- and substance P-like immunoreactivities along the entire thoracolumbar cord and to varying degrees. The results argue against involvement of NPY in peptide-specific pathways to peripheral organs and suggest, instead, that NPY and its association with peptidergic SPN play a more general role in the regulation of the autonomic nervous system.

Rostrocaudal location of sympathetic preganglionic neurones within the third thoracic segment of the cat spinal cord investigated by the retrograde transport of horseradish peroxidase and by recording of antidromic field potentials

The rostrocaudal location of sympathetic preganglionic neurones (SPNs) in the intermediolateral cell column of the third thoracic segment was studied in the cat by the retrograde transport of horseradish peroxidase and by recording of antidromic field potentials in the spinal cord in response to stimulation of white ramus T3. By both methods, the position of the rostral and caudal border of SPNs was determined in relation to the entry of segmental dorsal roots. It was found that SPN's are confined in the spinal cord to the length of one segment (9494 +/- 823 micron), but are shifted rostrally by about 3 mm with respect to the point of entry of the dorsal roots of segment T3.

Sympathetic preganglionic neurons in frog spinal cord

Sympathetic preganglionic neurons innervating the first sympathetic ganglion were identified in a frog (Rana pipiens). After wheat germ agglutinin conjugated horseradish peroxidase was implanted into this ganglion a homogeneous population of labeled sympathetic preganglionic neurones were identified ipsilaterally within the lateral field of the spinal gray at the level of the third spinal nerve. The total population of labeled cells (n = 324 +/- 62) extended in a rostrocaudal field for about 1800 micron as two distinct columns consisting of about equal numbers of cells. One group, at the lateral border of the intermediate zone, corresponds to the intermediolateral column, as also found in mammals, while the second group extends within the intercalated region, as the intercalated nucleus, lateral and slightly dorsal to the central canal. Transection of spinal nerves reveals that 65% of preganglionic axons leave the cord from the third spinal nerve with the remainder coursing through the first and second spinal nerves.

Location of cardiac vagal preganglionic cell bodies in the bullfrog

The bullfrog, Rana catesbeiana, provides a relatively simple model for study of the cardiac innervation. The present study located the origin of cardiac vagal preganglionic cell bodies in the frog with the retrograde tracer, horseradish peroxidase (HRP). HRP was injected subepicardially over the surface of atrial regions and along the major vessels exiting the heart. labeled cell bodies in the brainstem were confined to the nucleus of the glossopharyngeal-vagal complex, from approximately 1.5 mm caudal to 1.5 mm rostral to the calamus scriptorius (obex). Brainstem neurons were labeled ipsilateral to the intact vagus nerve when unilateral vagotomy was performed at the time of HRP injection. No labeled somata were identified in the spinal cord. Comparison of the cardiac pool of neurons with the population of neurons labeled after injection of HRP directly into the cervical vagus nerve demonstrated that cardiac preganglionic neurons are localized to the caudal region of the vagal neuron pool and that there are no dimensional differences between the two populations in terms of major and minor diameters.

Anatomic and physiologic evaluation of a link between the nucleus reticularis gigantocellularis and nucleus ambiguous in the rat

Localized microinjection of wheat germ agglutinin-conjugated horseradish peroxidase into the nucleus ambiguous (NA) of Sprague-Dawley rats retrogradely labeled neurons that were bilaterally located within the confine of the nucleus reticularis gigantocellularis (NRGC). These cells conformed with the Golgi description of cytoarchitectonic configurations and size distributions for neurons in this reticular nucleus. Furthermore, field potentials antidromically evoked at the NA by stimulating the vagus nerve were augmented by concurrent activations of bilateral NRGC sites that were themselves capable of eliciting hypotension and bradycardia. We conclude that the gigantocellular reticular nucleus may at least employ the cardiac vagal preganglionic neurons in the NA to exert its actions on the heart.