Coexistence of neuropeptides in sympathetic preganglionic neurons of the cat

Sympathetic preganglionic neurons: properties and inputs

The sympathetic nervous system comprises one half of the autonomic nervous system and participates in maintaining homeostasis and enabling organisms to respond in an appropriate manner to perturbations in their environment, either internal or external. The sympathetic preganglionic neurons (SPNs) lie within the spinal cord and their axons traverse the ventral horn to exit in ventral roots where they form synapses onto postganglionic neurons. Thus, these neurons are the last point at which the central nervous system can exert an effect to enable changes in sympathetic outflow. This review considers the degree of complexity of sympathetic control occurring at the level of the spinal cord. The morphology and targets of SPNs illustrate the diversity within this group, as do their diverse intrinsic properties which reveal some functional significance of these properties. SPNs show high degrees of coupled activity, mediated through gap junctions, that enables rapid and coordinated responses; these gap junctions contribute to the rhythmic activity so critical to sympathetic outflow. The main inputs onto SPNs are considered; these comprise afferent, descending, and interneuronal influences that themselves enable functionally appropriate changes in SPN activity. The complexity of inputs is further demonstrated by the plethora of receptors that mediate the different responses in SPNs; their origins and effects are plentiful and diverse. Together these different inputs and the intrinsic and coupled activity of SPNs result in the rhythmic nature of sympathetic outflow from the spinal cord, which has a variety of frequencies that can be altered in different conditions.

Intrathecal neurotensin is hypotensive, sympathoinhibitory and enhances the baroreflex in anaesthetized rat

BACKGROUND AND PURPOSE

The neuromodulatory effects of the gut-neuropeptide neurotensin on sympathetic vasomotor tone, central respiratory drive and adaptive reflexes in the spinal cord, are not known.

EXPERIMENTAL APPROACH

Neurotensin (0.5 µM-3 mM) was administered into the intrathecal (i.t.) space at the sixth thoracic spinal cord segment in urethane-anaesthetized, paralysed, vagotomized male Sprague-Dawley rats. Pulsatile arterial pressure, splanchnic sympathetic nerve activity (sSNA), phrenic nerve activity, ECG and end-tidal CO(2) were recorded.

KEY RESULTS

Neurotensin caused a dose-related hypotension, sympathoinhibition and bradycardia. The maximum effects were observed at 3000 µM, where the decreases in mean arterial pressure (MAP), heart rate (HR) and sSNA reached -25 mmHg, -26 beats min(-1) and -26% from baseline, respectively. The sympathetic baroreflex was enhanced. Changes in central respiratory drive were characterized by a fall in the amplitude of the phrenic nerve activity. Finally, administration of SR 142948A (5 mM), a potent, selective antagonist at neurotensin receptors, caused a potent hypotension (-35 mmHg), bradycardia (-54 beats min(-1) ) and sympathoinhibition (-44%). A reduction in the amplitude and frequency of the phrenic nerve activity was also observed.

CONCLUSIONS AND IMPLICATIONS

The data demonstrate that neurotensin plays an important role in the regulation of spinal cardiovascular function, affecting both tone and adaptive reflexes.

B-Afferents: A fundamental division of the nervous system mediating homeostasis?

The peripheral nervous system (PNS) has classically been separated into a somatic division composed of both afferent and efferent pathways and an autonomic division containing only efferents. J. N. Langley, who codified this asymmetrical plan at the beginning of the twentieth century, considered different afferents, including visceral ones, as candidates for inclusion in his concept of the “autonomic nervous system” (ANS), but he finally excluded all candidates for lack of any distinguishing histological markers. Langley's classification has been enormously influential in shaping modern ideas about both the structure and the function of the PNS. We survey recent information about the PNS and argue that many of the sensory neurons designated as “visceral” and “somatic” are in fact part of a histologically distinct group of afferents concerned primarily autonomic function. These afferents have traditionally been known as “small dark” neurons or B-neurons. In this target article we outline an association between autonomic and B-neurons based on ontogeny, cell phenotype, and functional relations, grouping them together as part of a common reflex system involved in homeostasis. This more parsimonious classification of the PNS, made possible by the identification of a group of afferents associated primarily with the ANS, avoids a number of confusions produced by the classical orientation. It may also have practical implications for an understanding of nociception, homeostatic reflexes, and the evolution of the nervous system.

Choline acetyl transferase and neuropeptide immunoreactivities are colocalized in somata, but preferentially localized in distinct axon fibers and boutons of cat sympathetic preganglionic neurons

Cholinergic sympathetic preganglionic neurons (SPN) coexpress the biosynthetic enzyme for acetylcholine, choline acetyl-transferase (ChAT), and neuropeptides such as enkephalin (ENK) in their cell bodies. However, it is not clear whether they also coexpress ChAT and neuropeptides in axon fibers and boutons. To explore coexpression of ChAT and neuropeptides in somata and axon processes of SPN, we investigated, using immunohistochemistry, retrograde labeling, confocal analysis, and tridimensional reconstruction, whether ChAT and the peptides neurotensin, methionine-ENK, somatostatin, calcitonin gene-related peptide, and vasoactive intestinal peptide colocalize in somata, axons fibers, and boutons of cat SPN. Practically, complete colocalization for these peptides and ChAT was observed in SPN somata. Conversely, in most instances we observed independent localization of immunoreactivity (IR) for ChAT and the peptides in axon fibers and boutons. The minor colocalization between ChAT- and peptide-IR in preganglionic fibers could correspond to a sequential axonal transport of ChAT and peptides, since we observed coexistence of these transmitters after blocking axonal transport. Contrary to Dale's principle, our results suggest that SPN can synthesize ChAT and peptides in their cell bodies and route them to distinct axon boutons or terminals in sympathetic ganglia. Presence of axon boutons containing either ChAT or neuropeptides lead us to suggest a new neurochemical pattern of cotransmission in sympathetic ganglia based on the concurrent release of transmitters and cotransmitters from distinct presynaptic boutons, rather than in the corelease of these mediators from the same axon process. The possibility that cellular segregation could be transient and depend on functional requirements is considered.

A neglected 'accessory' vasomotor pathway: implications for blood pressure control

1. Distinct from 'regular' sympathetic preganglionic neurons, there exists a population of 'accessory' preganglionic neurons. The latter are distinguishable by their unmyelinated axons and their different functional properties. They synapse on the same ganglion cells. 2. Ongoing sympathetic activity is driven by 'regular' preganglionic neurons. 3. 'Accessory' preganglionic neurons drive hexamethonium-resistant ganglionic transmission: part of this is muscarinic and part not (possibly peptidergic or nitrergic). 4. 'Accessory' preganglionic neurons supply cardiovascular (vasomotor, cardiac, adrenal), but apparently not other, sympathetic pathways. 5. 'Accessory' preganglionic neurons are activated by arterial chemoreceptors. 6. Brief activation of 'accessory' preganglionic neurons potentiates ongoing post-ganglionic activity for tens of minutes by an action at the ganglion. This is probably by enabling previously subthreshold excitatory post-synaptic potentials to trigger action potentials. 7. Evidence is presented that microinjections of GABA into the rostral ventrolateral medulla activate the 'accessory' pathway while inhibiting the 'regular' pathway. 8. A role for this 'accessory' pathway in the long-term control of blood pressure in health and disease is predicted, but still untested.

Nitric oxide synthase neurons in the rodent spinal cord: distribution, relation to Substance P fibers, and effects of dorsal rhizotomy

The indirect immunofluorescent method was employed to investigate the distribution of neuronal nitric oxide synthase-like immunoreactivity(nNOS-LI) in the spinal cord of the golden hamster and to compare it to data obtained from rats. Immunoreactive neurons were found throughout the cervico-sacral extent in the dorsal horn (mainly in laminae I-III) and in the preganglionic autonomic regions, i.e., the sympathetic intermediolateral nucleus (IML), lateral funicle (LF), intercalated region (IC), the area surrounding the central canal (CA), and the sacral preganglionic parasympathetic cell group. While the distribution of immunoreactive cells was generally similar in both species, some differences were observed. For example in the hamster LF, a higher percentage of stained neurons was seen than in the IML, while the situation was rather inverse in the rat. In order to study the coincidence of nNOS-LI in the population of preganglionic sympathetic neurons (PSN) that innervate the superior cervical ganglion (SCG), these were identified by retrograde axonal transport of fluoro-gold (FG) following unilateral injection into the SCG. PSN were localized ipsilateral to the injection site mainly in the IML and LF of spinal segments C7-Th4. The portion of double-labeled neurons of the IML were lower in hamster (17% in C7, 34% in C8) of FG-labeled cells) than in rat (47% in C8, 77% in Th2), while in the LF of segments C8-Th2 in both species the majority of FG-neurons contained nNOS. While only very few double-labeled neurons were detected in the IC in hamster and rat, a striking difference was observed in the CA, where no double-labeled neurons were found in hamster, but up to 50% in rat. Double immunofluorescence detection of nNOS and substance P (SP) showed that in both the autonomic regions and the dorsal horn, SP-LI fibers and puncta were present in close spatial relationship to nNOS-LI cell bodies. These results were basically identical in the hamster and rat. Unilateral transection of the dorsal roots of segments C6-Th2 in rats resulted in a clear reduction of SP-LI structures in the dorsal horn 5 days after rhizotomy, but not in the autonomic regions. Compared to the unlesioned side, the numbers of nNOS-LI neurons in the superficial laminae of the dorsal horn were reduced to 32-46% in the lesioned segments, and to 53% and 87%, respectively, in the two segments cranial to the rhizotomized segments but remained unchanged caudally to the lesion. Numbers of nNOS-LI cell bodies in the autonomic regions were not altered following dorsal root transection. The present study provides data on the widespread distribution of nNOS in the spinal cord of golden hamster and describes the partial coincidence of the enzyme in PSN. The effects of dorsal rhizotomy on nNOS-LI neurons in the dorsal horn reveal that primary-afferent fibers provide a stimulatory influence on neurons of the dorsal horn to generate the gaseous neuroactive substance, nitric oxide.

Methods of sympathetic degeneration and alteration

The role of the sympathetic nervous system in health and disease has often been elucidated by inducing changes in, or degeneration of sympathetic neural pathways. Several methods of inducing peripheral lesions have been created from surgical removal, NGF depletion, auto-immune and chemical destruction to novel approaches using immunotoxins and transgenic animals. This review compares these methods in terms of their mechanism and specificity. The advantages and disadvantages of these techniques are discussed.

Segmental restriction and target specificity of bullfrog preganglionic neurons that exhibit galanin-like immunoreactivity

These experiments were designed to examine the distribution of galanin-like peptide immunoreactivity (GAL-IR) in bullfrog sympathetic preganglionic neurons and to identify the peripheral target organs affected by these neurons. Cells expressing GAL-IR were observed in the intermediolateral column of segments 7 and 8 only. Apparent GAL-IR innervation is present, but rare, in sympathetic chain ganglia. Double-labelling with retrogradely transported fast blue and galanin antiserum demonstrated that most GAL-IR neurons project via splanchnic nerves to innervate the adrenal gland, which receives a dense plexus of GAL-IR fibers surrounding chromaffin cells. The adrenal gland is also innervated by preganglionic neurons in segments 5 and 6 that do not express GAL-IR. Because nitric oxide is expressed in sympathoadrenal preganglionic neurons in mammals (Anderson, C.R., Neurosci. Lett., 139 (1992) 280), we examined whether it is expressed in bullfrog preganglionic neurons. Nicotinamide adenine dinucleotide phosphate-diaphorase positive neurons are present in bullfrog spinal grey at segments 5 through 8. These neurons were not double-labelled with fast blue retrogradely transported from the sympathetic chain, celiac ganglion, or adrenal gland; nor were they double-labelled with GAL-antiserum. Thus nitric oxide is apparently not expressed in bullfrog sympathetic preganglionic neurons.

Peptide-immunoreactive neurons and nerve fibres in lumbosacral sympathetic ganglia: selective elimination of a pathway-specific expression of immunoreactivities following sciatic nerve resection in kittens

The distributions of peptide-immunoreactive nerve fibres and cell bodies in lumbosacral paravertebral sympathetic ganglia of young cats were analysed with antibodies to calcitonin gene-related peptide, enkephalin, neurotensin, somatostatin, substance P, galanin, neuropeptide Y and vasoactive intestinal polypeptide. Fairly dense networks of nerve fibres showing enkephalin-, neurotensin-, somatostatin- or substance P-like immunoreactivity were observed in the ganglia. Double-staining experiments revealed that enkephalin- and somatostatin-immunoreactive nerve fibres preferentially surrounded calcitonin gene-related peptide- and/or vasoactive intestinal polypeptide-immunoreactive cell bodies. Neurotensin- and substance P-immunoreactive nerve fibres were mainly associated with neurons showing neuropeptide Y and/or galanin-like immunoreactivity. Occasional nerves containing calcitonin gene-related peptide-, galanin-, neuropeptide Y- or vasoactive intestinal polypeptide-like immunoreactivity were observed. These fibres did not seem to have any direct regional distribution within the ganglia. In kittens surviving for three months after early postnatal sciatic nerve resection, no calcitonin gene-related peptide-immunoreactive cell bodies could be detected in ganglia ipsilateral to the operation. In contrast, vasoactive intestinal polypeptide-like immunoreactivity, which partly co-exists with calcitonin gene-related peptide, was observed to the same extent as in control ganglia. Furthermore, almost all of the somatostatin-immunoreactive varicose nerve fibres had disappeared, whereas a fairly dense network of calcitonin gene-related peptide-immunoreactive nerve fibres could be observed. This change was paralleled by an increased content of nerve fibres that were immunoreactive to antibodies against the growth-associated protein GAP-43 (also known as B-50). The present findings suggest that experimental perturbations where postganglionic neurons are separated from their target areas by axotomy, not only induce differential changes in neurotransmitter expression in the principal ganglion cells, but also in preganglionic sympathetic neurons projecting to the ganglia. One possible explanation for the occurrence of an axotomy-induced network of calcitonin gene-related peptide-immunoreactive nerve fibres, is that extrinsic sensory nerve fibres grow into the ganglia after the sciatic nerve lesion. Thus, these findings seem to suggest one additional possibility with regard to the question of a possible interaction between sympathetic and sensory neurons after peripheral nerve injury.

Essential organization of the sympathetic nervous system

The sympathetic nervous system consists of efferent neurones supplying the viscera. The cell bodies of preganglionic neurones are located in four areas in the thoracolumbar cord; however, the majority are found in the IML. Various tracing techniques have provided information concerning the location of the cell bodies of sympathetic preganglionic neurones projecting into various nerves and ganglia and regulating the adrenal gland, the kidney and the sympathetic supply to skeletal muscle. Numerous supraspinal neurones project to the neuropil surrounding sympathetic preganglionic neurones and may form synaptic contacts with these neurones. The areas of the brain that project to the IML appear to be part of a network of reciprocally connected supraspinal cell groups. Although much emphasis has been placed on the importance of the RVLM in the mediation of tonic and phasic inputs to sympathetic preganglionic neurones, it appears that other areas are of significant import; the RVLM should not be considered to be 'the vasomotor centre'. Spinal and cranial afferents influence the sympathetic nervous system. Baroreceptor afferents terminate in the NTS and may utilize an excitatory amino acid as their neurotransmitter. However, a number of neuropeptides are also associated with these afferents. Neurones within the NTS project to a number of brain stem areas thought to be involved in the regulation of sympathetic activity; consequently the baroreceptor reflex may be mediated over a number of parallel pathways involving both supraspinal and spinal sites of inhibition. Many neurotransmitters are thought to regulate the activity of sympathetic preganglionic neurons: monoamines, peptides and amino acids. Matching the chemical content of the cell bodies of neurones within a particular cell group with physiological characteristics is a challenging task; some barosensitive neurones of the RVLM do not appear to be adrenergic although they are in the midst of the C1 adrenergic cell group. Besides acetylcholine and noradrenaline, neurotransmission in the periphery appears to involve numerous peptides and ATP.

Neuropeptides in the human celiac/superior mesenteric ganglionic complex: an immunohistochemical study

The occurrence of vasoactive intestinal polypeptide (VIP), peptide histidine-isoleucine (PHI), calcitonin gene-related peptide (CGRP), substance P (SP), somatostatin (SOM), galanin (GAL) and enkephalins (ENK) is studied in the human celiac/superior mesenteric ganglionic complex of pre- and full-term newborns, and adult subjects by means of immunohistochemistry. The antisera used labelled nerve fibres and terminal-like networks for each examined peptide, as well as VIP- and SOM-positive postganglionic neurons. Differences in the relative amount and density of the structures immunoreactive to the various peptides were observed. Moreover, variations in the amount and type of labelled elements were appreciable for each peptide when specimens from subjects at perinatal and adult ages were compared. Double-labelling immunofluorescence for SP and each other peptide showed that co-localization with SP is very frequent for CGRP, moderate to scarce for GAL and SOM, and rare to absent for PHI, VIP and ENK. VIP-, ENK- and CGRP-immunolabeled perikarya bearing the morphological features of the small intensely fluorescent (SIF) cells occurred in the organ. The presence of a paraganglion in one of the specimens examined allowed the detection of VIP- and ENK-positive cell bodies and VIP-, ENK-, SP- and GAL-like immunoreactive varicose nerve fibres in it. The results obtained provide substantial morphological data in support of the involvement of the examined peptides in the chemical interneuronal signalling in the human celiac/superior mesenteric ganglia.

CRF-like immunoreactivity selectively labels preganglionic sudomotor neurons in cat

Immunohistochemical and neuronal tracing methods were used in cats to determine which type of postganglionic sympathetic neuron is innervated by preganglionic neurons which contain corticotrophin releasing factor-like immunoreactivity (CRF-LI). Preganglionic neurons with CRF-LI have their cell bodies at two restricted levels of the spinal cord and terminate in the stellate and lower lumbar ganglia. CRF-LI terminal baskets in stellate and lumbar ganglia surrounded cell bodies, 96-99% of which showed no tyrosine hydroxylase (TH)-LI (presumptive cholinergic neurons). Calcitonin gene-related peptide (CGRP)-LI was used to label the cholinergic ganglion cells which innervate sweat glands: 96-99% of those were confirmed as lacking TH-LI, while the remainder showed weak staining. Every one of over 6000 CRF-LI terminal baskets counted in 4 stellate and 6 lumbar ganglia was found to surround a cell body with CGRP-LI; conversely, 81-86% of the cell bodies showing CGRP-LI were surrounded by CRF-LI terminal baskets. In 3 cats, the retrograde tracer fluorogold was used to label postganglionic neurons projecting to the paw pads (a population which includes both cholinergic sudomotor neurons and noradrenergic vasoconstrictor neurons). Between 26 and 38% of the retrogradely labelled ganglion cells were surrounded by CRF-LI terminal baskets. We conclude that in cats, preganglionic sympathetic neurons with CRF-LI are sudomotor in function.

Membrane peptidases in the peripheral nervous system of the pig: their localization by immunohistochemistry at light and electron microscopic levels

The presence and cellular localization of five membrane peptidases has been investigated in peripheral nerves, including those of the autonomic nervous system, in the pig. Endopeptidase-24.11 ("enkephalinase") peptidyl dipeptidase A, aminopeptidase N, aminopeptidase W and dipeptidyl peptidase IV were studied by both enzymic assays of membranes prepared from samples of nerve and by immunoperoxidase histochemistry at light and in two cases, endopeptidase-24.11 and aminopeptidase W, at electron microscopic levels. All five peptidases could be quantified by enzymic assay, though the activities were about 1% of those in renal microvilli and less than those of choroid plexus membranes. Endopeptidase-24.11 was associated with Schwann cell membranes in all types of nerve examined, including major nerves containing predominantly myelinated fibres as well as autonomic nerves, such as the vagus and splenic nerves and the sympathetic chain, staining being observed in membranes associated with myelinated and unmyelinated fibres. The Schwann cell location of endopeptidase-24.11 was confirmed by correlation with immunostaining for glial fibrillary acidic protein and by electron microscopy. This peptidase is known to have a wide repertoire of susceptible substrates among neuropeptides which was here shown to include vasoactive intestinal polypeptide (Km 268 microM, kcat 568 min-1), one of a number of neuropeptides present in peripheral nerve fibres. Three of the peptidases, peptidyl dipeptidase A, aminopeptidase N and dipeptidyl peptidase IV, were associated with microvessels of peripheral nerves. Aminopeptidase N was also observed in connective tissue elements, including the perineurium. Aminopeptidase W was unique among the five peptidases in having a neuronal localization. This was observed in unmyelinated and myelinated nerves and was supported by comparison with the pattern of staining observed for neurofilament protein and by electron microscopic immunoperoxidase staining. This observation was unexpected since aminopeptidase W has not been detected as a neuronal marker in the brain. Some possible roles for the membrane peptidases in peripheral nerves are discussed.

Evidence that some preganglionic sympathetic neurons in the rat contain vasoactive intestinal peptide- or peptide histidine isoleucine amide-like immunoreactivities

Physiological studies have established that preganglionic sympathetic nerve fibers innervating the rat superior cervical ganglion release a second transmitter, in addition to acetylcholine. Based on pharmacological and histochemical investigations, possible candidates for this non-cholinergic neurotransmitter include vasoactive intestinal peptide and peptide histidine isoleucine amide. For example, previous immunohistochemical studies have demonstrated that antisera raised against both of these peptides stain neural processes in the rat preganglionic cervical sympathetic trunk and in the superior cervical ganglion. In the present study, it was found that, when the cervical sympathetic trunk was ligated, vasoactive intestinal peptide- and peptide histidine isoleucine amide-like immunoreactivities built up on both sides of the ligature. In addition, examination of the thoracic spinal cord in colchicine-treated animals revealed vasoactive intestinal peptide- and peptide histidine isoleucine amide-like immunoreactivies in neuronal cell bodies in the intermediolateral cell column and in the region of the lateral funiculus adjacent to it. In a second group of animals in which retrograde tracing techniques were used, these two regions of the spinal cord were shown to contain most of the cell bodies of the preganglionic neurons that project to the superior cervical ganglion. Smaller numbers of retrogradely labeled neurons were found dorsal to the central canal and in the nucleus intercalatus. When either vasoactive intestinal peptide- or peptide histidine isoleucine amide-like immunostaining and retrograde labeling were examined in the same animals, double-labeled neurons were found in the intermediolateral cell column and in the lateral funiculus. These data demonstrate that vasoactive intestinal peptide- and peptide histidine amide-like immunoreactivities are present in certain of the preganglionic neurons that project to the superior cervical ganglion, supporting the hypothesis that vasoactive intestinal peptide and peptide histidine isoleucine amide are released in the ganglion when these preganglionic neurons are activated.

Ultrastructural identification of neuropeptides in the central nervous system

A number of different neuropeptides have been described within presynaptic terminals at the ultrastructural level in the central nervous system. The majority of these neuropeptides share a common morphology with one another. Terminals containing neuropeptides have a population of small, clear vesicles associated with the active zone of the synapse and a lesser number of large, granular vesicles that are located at a distance from the active site of the synapse. It is believed that the large, granular vesicles act as a mechanism for the transport/storage of the neuropeptides, while the small, clear vesicles are thought to be acting as structures responsible for the release of the neurotransmitter/neuropeptide into the synaptic cleft. The neuropeptide containing terminals most often have asymmetrical junctions associated with their presynaptic membranes, although symmetrical junctions have been described with peptide containing terminals in a number of areas in the central nervous system. Neuropeptide containing terminals contact every part of the neuronal membrane; however, the majority of synaptic contacts involve portions of the dendritic shafts. Evidence is beginning to accumulate to indicate that for certain neuropeptides there is a specific spatial arrangement to their termination along the neuronal membrane.

Structural and functional aspects of acetylcholine peptide coexistence in the autonomic nervous system

The present article is an attempt to briefly review acetylcholine and peptide coexistence in the ANS. For more detailed information the reader is referred to the book by Furness and Costa (1987) and books edited by Elfvin (1983) and Björklund et al. (1988). Acetylcholine is the "classical" transmitter substance between preganglionic and post-ganglionic neurons in both the sympathetic and parasympathetic nervous system but also between postganglionic parasympathetic neurons and effector cells. ENK and NT were early on shown to be present in preganglionic sympathetic neurons whereas SP and SOM have more recently been associated with these cells. Physiological experiments have shown that ENK may presynaptically inhibit cholinergic transmission in sympathetic ganglia. The cholinergic postganglionic parasympathetic neurons contain VIP/PHI. These peptides may be responsible for the atropine-resistant vasodilation seen after stimulation of parasympathetic nerves. In salivary glands VIP has been shown to potentiate the salivatory volume response to ACh. A number of postganglionic sympathetic neurons innervating exocrine sweat glands in the skin are also cholinergic. In addition to VIP/PHI, these neurons contain CGRP and probably also SP. The functional significance of acetylcholine coexisting with four vasodilatory peptides in this cell population is at present unclear. In the enteric ganglia the coexistence situation is very complex. Thus, in the myenteric plexus cholinergic SP-containing excitatory motor neurons seem to be present. In the myenteric plexus other cholinergic neurons may contain at least six different neuronal peptides. These latter neurons seem to be part of the peripheral intestino-intestinal reflex arc which is involved in regulation of gastrointestinal motility and mucosal functions. In the submucous plexus three populations of cholinergic neurons are present, one of which has secretomotor properties and contains CGRP, CCK, GAL, NPY and SOM. In vivo and in vitro studies have shown that developing sympathetic neurons can "change" the "classical" transmitter they-use and alter their neuropeptide expression. If dissociated sympathetic neurons are grown in cultures without any non-neuronal elements they differentiate into a noradrenergic phenotype. However, if the cultures also contain non-neuronal cells, both noradrenergic and cholinergic properties will develop. These changes may also by induced by a conditioned medium, containing a diffusible factor secreted from the non-neuronal cells. In conclusion, the present article underlines the complexity of the chemical neuroanatomy of the ANS and emphasizes the abundance of the peptides in both noradrenergic and cholinergic neurons. Although these peptides can be shown to exert a number of interesting effects in various experimental paradigms, much work is needed to define their exact role in nervous system function.

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.

Central neurotensin nerves modulate colo-colonic reflex activity in the guinea-pig inferior mesenteric ganglion

1. The effects of neurotensin and of stimulation of preganglionic nerves on peripheral afferent synaptic input from segments of distal colon to neurones in the inferior mesenteric ganglia of guinea-pigs were studied using intracellular recording techniques in vitro. 2. Electrical stimulation of colonic afferent nerve fibres evoked fast, nicotinic synaptic responses (fast EPSPs or action potentials) followed by a slow depolarizing response (slow EPSP). 3. Neurotensin (1 microM) increased the amplitude and duration of slow EPSPs evoked by stimulation of colonic afferents. 4. Distention of a segment of distal colon left attached to an inferior mesenteric ganglion evoked a slow depolarization. Neurotensin (1 microM) increased the amplitude and duration of distention-induced depolarizations. 5. Electrical stimulation of central preganglionic nerve fibres present in the third and fourth lumbar ventral roots increased the amplitude and duration of slow EPSPs evoked by electrical stimulation of colonic afferent nerves. This facilitatory effect was abolished after desensitization to neurotensin. 6. Slow depolarizations evoked by neurotensin and by stimulation of central preganglionic nerves converted subthreshold fast EPSPs due to mechanosensory synaptic input from an attached segment of distal colon to action potentials. This increase in firing rate of sympathetic ganglion cells led to a decrease in colonic intraluminal pressure. 7. Taken together these data support the hypothesis that neurotensin or a closely related substance contained in central preganglionic nerves facilitated release of a non-cholinergic excitatory transmitter from colonic mechanosensory nerves. The slow depolarization evoked by the non-cholinergic transmitter converted on-going subthreshold fast EPSPs to action potentials thereby increasing sympathetic output to the colon. 8. It is suggested that under normal in vivo conditions, central preganglionic fibres containing neurotensin or a closely related peptide modulate peripheral reflex activity through prevertebral ganglia in guinea-pigs.

Postnatal ontogeny of enkephalin fibers in spinal sympathetic nuclei

The postnatal distribution of enkephalin (Enk) fibers is described in preganglionic containing sympathetic nuclei in the rat thoracolumbar spinal cord. In high thoracic spinal cord, at birth, Enk fibers are present in moderate numbers in the intermediolateralis nucleus, pars principalis (ILp), and nucleus intercalatus spinalis (IC). Enkephalin fibers first appear in the dorsal commissural nucleus (dcn) on postnatal day 2. Postnatal day 6 represents a pivotal timepoint when the basic Enk innervation pattern is established. From postnatal day 11 through day 20 there is a gradual accumulation of Enk fibers within each of the sympathetic nuclei such that the density and distribution of immunoreactive fibers approaches the adult appearance by postnatal day 20. An adult pattern is achieved by postnatal day 30. There is a rostral-caudal gradient in the developmental appearance of Enk fibers in sympathetic nuclei such that the ILp nucleus contains Enk fibers on postnatal day 0 in the high thoracic spinal levels compared to postnatal day 6 in low thoracic-high lumbar spinal levels. Examination of the location of Enk fibers during ontogeny highlighted several additional features of the distribution of Enk fibers in the adult animal. Enkephalin fibers delineate two subdivisions of the IC nucleus; a thin dense core of Enk fibers contained within a broader band of moderate numbers of Enk fibers. We also report variations in the general overall pattern of the Enk fiber distribution in high thoracic, middle thoracic, and lwo thoracic-high lumbar spinal cord levels.

Light- and electron-microscopic evidence of costoring of immunoreactive enkephalins and substance P in dorsal horn neurons of rat

The topographical localization of substance P (SP) and methionine-enkephalin-octapeptide (Enk-8) was examined immunohistochemically in the surface layer of the dorsal horn of rat cervical spinal cord. Although a few neurons were immunoreactive for Enk-8 in the intact animals, after an intracisternal administration of colchicine, immunoreactive Enk-8 neurons were numerous, and half of them indicated immunoreactivity also for SP. Some immunoreactive SP neurons appeared to show no immunoreactivity for Enk-8. Immuno-reactive nerve fibers, on the other hand, were numerous, and many of them contained both peptides. Electron-microscopic examination of the nerve fibers in tissue prepared by a freeze-drying procedure and stained by a postembedding procedure, revealed the costoring of both peptides in the same cored vesicles. The physiological significance of this costoring is discussed.

Coexistence of substance P and neurotensin-like peptides in single neurons of the rat hypothalamus

The coexistence of substance P with neurotensin-like immunoreactivity in certain neurons of the hypothalamus were demonstrated by the double immunofluorescence method. Substance P and neurotensin-like immunoreactivity coexisted within single neurons of some hypothalamic areas such as the medial preoptic area, perifornical area, anterior hypothalamic area, lateral hypothalamic area, periventricular nucleus and posterior hypothalamic nucleus, although they did not coexist in the majority of immunoreactive cells.