Two discrete enkephalinergic neuron systems in the superior cervical ganglion of the guinea pig: an immunoelectron microscopic study

Localization, regulation and functions of neurotransmitters and neuromodulators in cervical sympathetic ganglia

Cervical sympathetic ganglia represent a suitable model for studying the establishment and plasticity of neurochemical organization in the nervous system since sympathetic postganglionic neurons: (1) express several neuromediators, i.e., short acting transmitters, neuropeptide modulators and radicals, in different combinations; (2) receive synaptic input from a limited number of morphologically and neurochemically well-defined neuron populations in the central and peripheral nervous systems (anterograde influence on phenotype); (3) can be classified morphologically and neurochemically by the target they innervate (retrograde influence on phenotype); (4) regenerate readily, making it possible to study changes in neuromediator content after axonal lesion and their possible influence on peripheral nerve regeneration; (5) can be maintained in vitro in order to investigate effects of soluble factors as well as of membrane bound molecules on neuromediator expression; and (6) are easily accessible. Acetylcholine and noradrenaline, as well as neuropeptides and the recently discovered radical, nitric oxide, are discussed with respect to their localization and possible functions in the mammalian superior cervical and cervicothoracic (stellate) paravertebral ganglia. Furthermore, mechanisms regulating transmitter synthesis in sympathetic neurons in vivo and in vitro, such as soluble factors, cell contact or electrical activity, are summarized, since modulation of transmitter synthesis, release and metabolism plays a key role in the neuronal response to environmental influences.

An immunoelectron microscopic study of methionine-enkephalin structures in cat prevertebral ganglia

Methionine-enkephalin-like immunoreactivity was detected in presynaptic nerve fibers and SIF cells in cat prevertebral ganglia. The immunoreactive nerve fibers contained a mixture of numerous small clear vesicles and a few large vesicles; the immunoreactivity was only confined to the large vesicles. Most of the immunoreactive fibers were in apposition with non-immunoreactive neuronal profiles, without any detectable synaptic membrane specializations. The other immunoreactive fibers formed synaptic contacts mainly with non-immunostained dendrites and to a lesser extent with axons and neuronal soma. The characterization at the ultrastructural level of the enkephalin-like immunoreactive structures is discussed as regards the modalities whereby opiates may be involved in sympathetic ganglionic transmission.

Comparison of immunohistochemical localization of [Met5]enkephalin-Arg6-Gly7-Leu8, [Met5]enkephalin, neuropeptide Y and vasoactive intestinal polypeptide in the superior cervical ganglion of the rat

The localization of [Met5]enkephalin-Arg6-Gly7-Leu8 and [Met5]enkephalin immunoreactivities was studied in the rat superior cervical ganglion. The distribution of these enkephalin-containing peptides in the ganglion was correlated to that of neuropeptide Y and vasoactive intestinal polypeptide. Three different populations of peptide-containing postganglionic neurons were demonstrated. (1) A minor population (10-20%) of principal neurons was immunoreactive for [Met5]enkephalin-Arg6-Gly7-Leu8 but not immunoreactive for neuropeptide Y nor vasoactive intestinal polypeptide. (2) The major population (about 50-70%) was immunoreactive for neuropeptide Y but not for [Met5]enkephalin-Arg6-Gly7-Leu8. (3) Few vasoactive intestinal polypeptide-immunoreactive principal neurons (less than 2% of all principal neurons) were observed in the ganglion. All vasoactive intestinal polypeptide-immunoreactive neurons were also immunoreactive for neuropeptide Y but not for [Met5]enkephalin-Arg6-Gly7-Leu8. [Met5]enkephalin-Arg6-Gly7-Leu8- and [Met5]enkephalin-immunoreactive nerve fibers had a similar distribution. These enkephalin immunoreactive nerve fibers were seen to enclose both neuropeptide Y-containing principal neurons and neurons devoid of neuropeptide Y immunoreactivity. Furthermore, there were enkephalin-immunoreactive fiber baskets around vasoactive intestinal polypeptide-immunoreactive neurons and sometimes also around solitary enkephalin-immunoreactive neurons. Previously reported diverse role of enkephalins in the rat superior cervical ganglion is supported by this study.

Immuno-electron-microscopic localization of enkephalin in the secretory granules of C cells in the chicken ultimobranchial glands

In the chicken, enkephalin-immunoreactive cells and nerve fibers are distributed in the ultimobranchial glands, which consist of C-cell groups and cyst structures. Ultrastructural features of the enkephalin cells and nerve fibers were examined by immuno-electron microscopy using both the streptavidin-biotin-peroxidase method and the protein A-colloidal gold method. Immunoreactivity for enkephalin was located on the secretory granules of C cells. In 1-day-old chickens, three types of C cells were distinguished on the basis of their granule size. Type-I cells were filled with large secretory granules (200-600 nm in diameter). These elements represented a majority of the C-cell population. Type-II cells contained medium-sized granules (100-280 nm in diameter). Type-III cells displayed small secretory granules (60-200 nm in diameter). The latter cells were elongate or irregular in shape and frequently extended cytoplasmic processes into the connective tissue stroma or contacted other C cells. Enkephalin-immunoactivity was revealed by dense deposits of immunogold particles on the secretory granules of type-II and type-III cells. There were only a few type-I cells showing immunoreactivity for enkephalin. A double immunogold labeling procedure demonstrated that calcitonin and enkephalin were colocalized in the same secretory granules of type-I and type-II cells. Type-III cells were devoid of immunoreactivity for calcitonin. Enkephalin-immunoreactive nerve fibers were characterized by the presence of granular vesicles, 60-160 nm in diameter, and frequently established direct contact with the surface of C cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathetic and parasympathetic ganglia express non-NMDA type glutamate receptors: distinct receptor subunit composition in the principle and SIF cells

The presence of non-NMDA glutamate receptors in the rat sympathetic and parasympathetic ganglia was examined by immunocytochemistry using specific antibodies against AMPA-type excitatory amino acid receptor subunits (GluR1-4). Three kinds of antibodies specific to the GluR1, GluR2 and 3, and GluR4 subunits were used. The superior cervical ganglion and pterygopalatine ganglion were examined as representatives of sympathetic and parasympathetic ganglia. In the superior cervical ganglion, GluR1- and GluR2/3-like immunoreactivity was observed in most principal neurons and SIF cells. In contrast, GluR4-like immunoreactivity was not observed in the principal cells; however, SIF cells exhibited intense immunoreactivity of GluR4. In the pterygopalatine ganglion, the profile of the immunoreactivity was similar to that seen in the superior cervical ganglia. The subunit compositions between the principal cells and SIF cells were different, whereas the compositions in cell species involved in the autonomic ganglia, sympathetic and parasympathetic ganglia were identical. This suggests that glutamate is another important preganglionic transmitter together with acetylcholine, and the responses elicited in the principal cells and SIF cells might be different because of the difference in subunit composition.

Ultrastructural connectivity of [leu]5-enkephalin-immunoreactive synapses in the guinea-pig stellate ganglion: involvement of spines and triads

The ultrastructure of [leu]5-enkephalin-immunoreactive (ENK-IR) nerve fibres in the guinea-pig stellate ganglion was studied by means of pre-embedding immunohistochemistry. ENK-immunoreactivity was primarily contained within large dense core vesicles (91 +/- 21 nm in diameter; n = 259) but was absent from small clear vesicles (47 +/- 9 nm; n = 488) within the same nerve terminal that were concentrated at presynaptic regions. Thus, fast synaptic transmission mediated by ENK-IR terminals most probably does not involve [leu]5-enkephalin which may be released parasynaptically. Evaluating a total number of 123 synapses involving an ENK-IR presynaptic nerve ending, 47% terminated upon a spine, 46% upon a dendritic shaft, and 7% directly addressed a soma of a postganglionic neuron. In 30% of axo-dendritic synapses and 33% of axo-somatic synapses, non-immunoreactive dendrites or somata being postsynaptic to an ENK-IR terminal were in direct but non-synaptic contact to another dendrite/soma. Such arrangements are termed "triads". In view of the current hypotheses concerning the function of spines and triads, these findings indicate that ENK-IR terminals within the guinea-pig stellate ganglion may be involved in the generation of long-lasting synaptic events and modulation of non-synaptic intraganglionic communication.

Use-dependent fade and two-rate recovery of a naloxone-sensitive inhibition in the cat superior cervical ganglion

In anaesthetized cats, a short train to the cervical sympathetic trunk (CST), of frequency between 0.5 and 5.0 Hz, inhibited the postganglionic compound action potential (CAP) evoked by a test shock to the CST. When the CST was split into two bundles, the inhibition was obtained both homosynaptically and heterosynaptically. The inhibition was antagonized by naloxone and enhanced by peptidase inhibitors. Leu-enkephalin (ENK), injected into the arterial supply of the superior cervical ganglion (SCG) depressed the CAP. The ENK-evoked inhibition was antagonized by naloxone, enhanced by peptidase inhibitors and was occluded by the train-evoked inhibition. After prolonged stimulation of the CST (5-20 min at 5 Hz), the inhibition produced by a short train was depressed (faded). The fade was greater the longer the stimulation. After 20 min of stimulation the inhibition was absent. At this time the depressant effect of ENK was unchanged. When only one bundle of the split CST was stimulated at 5 Hz for 20 min, only the inhibition produced by that bundle faded, although both bundles converged onto a common set of ganglion cells. Thus, the fade is not due to receptor desensitization but more likely to failure to release the inhibitory mediator by the overstimulated axons. When, after 20 min of 5 Hz stimulation, no further stimuli were applied, the inhibition recovered in 60 min (fast recovery). However, recovery was slower when stimulation lasted longer than 20 min. Recovery took three days when stimulation lasted 80 min (slow recovery). The inhibition was markedly depressed after application of colchicine to the CST three days earlier.(ABSTRACT TRUNCATED AT 250 WORDS)

Naloxone-sensitive inhibition of nicotinic transmission in the superior cervical ganglion of the cat

In anesthetized, artificially ventilated cats, pretreated with the muscarinic antagonist scopolamine, the effect of naloxone on the efficacy of nicotinic transmission in the superior cervical ganglion was used as a test of endogenous opioid release by the preganglionic axons. The cervical sympathetic trunk (CST) was split into two bundles. The compound action potential (CAP), evoked by supramaximal low-frequency stimulation (0.25 Hz) of one CST bundle, was recorded from a postganglionic nerve of the superior cervical ganglion. Partial block with hexamethonium was used to reduce the 'safety factor' of nicotinic transmission. A conditioning train (5 Hz, 40 s, supramaximal) to the other CST bundle (heterosynaptic conditioning) inhibited the CAP. At the peak of the inhibition the CAP was attenuated by 51 +/- 4%. Recovery was 90% complete in 201 +/- 28 s. The inhibition was antagonized in a dose-dependent manner by i.v. naloxone with an apparent IC50 of 60 +/- 12 micrograms/kg. The maximum effect obtained with naloxone was an 80% decrease in the magnitude of the inhibition. Magnitude and duration of the heterosynaptic inhibition were related to frequency, duration and intensity of the conditioning train. Naloxone-sensitive inhibition was observed with frequencies of the conditioning train as low as 0.5 Hz. A train (5 Hz, 40 s) to the postganglionic nerves produced a naloxone-insensitive depression of the orthodromic test CAP which was of smaller amplitude and duration than when the conditioning train was applied to the preganglionic axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Met5-enkephalin-Arg6-Gly7-Leu8-like immunoreactivity in the pelvic ganglion of the male rat: a light and electron microscopic study

By using both light and electron microscopic immunocytochemical methods, Met5-Enkephalin-Arg6-Gly7-Leu8 (MEAGL)-like immunoreactive structures were detected in the pelvic ganglion of male rats. Denervation studies were carried out to determine the origin of these immunoreactive fibers and the projection of immunoreactive neurons within the pelvic ganglion. MEAGL-like immunoreactivity was found in numerous axon boutons, some small, intensely fluorescent (SIF) cells, and a few principal ganglion neurons. Most of the immunoreactive nerve fibers formed pericellular plexuses surrounding the ganglion cells. In addition, there were a few scattered varicose fibers. These fiber plexuses could be classified into two types: type I (approximately 90% of fibers), which consisted of 80-120 small boutons that synapsed on either the dendrites (80% of cases) or somata (20% of cases) of principal neurons; and type II (approximately 10% of fibers), which consisted of 20-40 larger boutons that formed axodendritic synapses exclusively. After transection of the hypogastric and pelvic nerves, virtually all of the pericellular fiber plexuses disappeared, whereas the scattered varicose fibers remained. According to their ultrastructure, these remaining fibers were considered to arise from SIF cells. Following the injection of Fast Blue into the bladder wall, some of the MEAGL-like immunoreactive principal neurons were retrogradely labeled. The results of this study indicate that there are two origins for the MEAGL-like immunoreactive fibers detected in the pelvic ganglion: most arise from preganglionic neurons in the spinal cord, and a small proportion may originate from intraganglionic MEAGL-like immunoreactive SIF cells or principal neurons. Some MEAGL-like immunoreactive principal neurons may project to the urinary bladder.

Neuronal pathways in the guinea-pig lumbar sympathetic ganglia as revealed by immunohistochemistry

Tyrosine hydroxylase (TH)- and peptide-immunoreactivity of postganglionic neurons and of nerve fibres in guinea pig lumbar paravertebral sympathetic ganglia 2-4 after transection of the communicating rami and the visceral branches, respectively, were investigated by single- and double-labelling techniques. Six subpopulations of postganglionic neurons were discriminated immunohistochemically: two cell types, which were immunoreactive to only one of the applied antisera - TH, and vasoactive intestinal polypeptide (VIP); and four cell types in which immunoreactivity was colocalized - TH/neuropeptide Y (NPY), NPY/VIP, dynorphin/alpha-neoendorphin and dynorphin (alpha-neoendorphin)/NPY. Small intensely fluorescent (SIF) cells dependent on their location exhibited differential immunobehaviour to NPY-/dynorphin-(alpha-neoendorphin-) and TH-antisera. Immunoreactivity to substance P (SP), calcitonin gene-related peptide (CGRP), met-enkephalin-arg-phe (MEAP) and leu-enkephalin was present in nerve fibres but not in postganglionic neurons with frequent colocalization of SP/CGRP- and MEAP/leu-enkephalin- and, sometimes leu-enkephalin/SP- and dynorphin/SP-immunoreactivity. TH-immunoreactive intraganglionic nerve fibres were numerically more increased after cutting the visceral branches, than after transection of the communicating rami. Vice versa, NPY-, VIP-, dynorphin- and alpha-neoendorphin-immunoreactive nerve fibres were particularly increased in number after cutting the communicating rami. Many but not all of the nerve fibres exhibited colocalization of two of these peptides. SP-, CGRP-, and enkephalin-immunoreactive nerve fibres were not visibly affected by cutting the visceral branches but virtually disappeared after lesioning the communicating rami.

Immunocytochemical analysis of [Met5]enkephalin-Arg6-Gly7-Leu8 immunoreactive structures in the rat superior cervical ganglion

Indirect immunofluorescence and immunoelectron microscopy were employed to analyze the enkephalinergic systems in the rat superior cervical ganglion (SCG). These systems were identified using specific antiserum against [Met5]Enkephalin-Arg6-Gly7-Leu8 (ENK-8), a peptide which is derived only from proenkephalin A. Abundant ENK-8 like immunoreactive (ENK-8-LI) neurons and fibers were observed in the SCG, but their distribution patterns were heterogenous; ENK-8-LI neurons were localized preferentially in the caudal two-thirds of the SCG, while immunoreactive fibers were found to be distributed more densely in the rostral one-third than in the remaining part of the SCG. Most of the ENK-8-LI neurons were large and had ultrastructural features resembling those of principal cells, some were identified electron microscopically as small intensely fluorescent (SIF) cells. ENK-8-LI fibers were varicose in appearance and surrounded the perikarya of neurons. Since most of these fibers were not detected after experimental decentralization of the SCG and since ENK-8-LI terminals were seen to contain small lucent vesicles, most of the former were thought to be preganglionic fibers. Immunoreactive fibers mainly formed synaptic contacts with the dendrites of non-immunoreactive principal cells, but a small proportion of ENK-8-LI principal cells also received synaptic input from them. Occasionally, immunoreactive fibers formed synapses with the processes or the soma of both ENK-8-LI and non-immunoreactive SIF cells. On the basis of these findings, we conclude that: (1) preganglionic ENK-8-LI fibers terminate mainly on the principal cells, which are devoid of ENK-8-LI structures; (2) the majority of ENK-8-LI neurons are principal cells, while the remainder are SIF cells; (3) inputs to these cells mainly involve structures lacking ENK-8 immunoreactivity; and (4) there are, however, a small number of ENK-8-LI preganglionic fibers which terminate on ENK-8-LI principal cells and SIF cells.

Dopaminergic cells in the superior cervical ganglion of the rat: light and electron microscopic study using an antibody against dopamine

So-called small intensely fluorescent (SIF) cells were visualized immunohistochemically using a newly developed anti-dopamine (DA) serum in the rat superior cervical ganglia (SCG), both light and electron microscopically. Specificity of the anti-DA serum was tested in a control test and enzyme-linked immunosorbent assay (ELISA). DA-immunoreactivity was found in a subpopulation of SIF cells, but not in principal neurons. Ultrastructurally, DA-immunoreactivity was noticed in the cytoplasmic matrix and vesicles of perikarya, dendritic processes and terminals of SIF cells. DA-labeled terminals made symmetrical synaptic contacts with unlabeled principal neurons. These findings provide a morphological basis for the role of dopaminergic SIF cells as interneurons.

Neuroneuronal interconnections in the rat superior cervical ganglion; possible anatomical bases for modulatory interactions revealed by intracellular horseradish peroxidase labelling

Electrophysiologically identified neurons of rat superior cervical ganglion were intracellularly injected with horseradish peroxidase and processed for light and electron microscopic observation. At light microscope level, neurons could be classified according to their dendritic arborization pattern in the vicinity of the soma into radiate, tufted and intermediate types. Upon electrical stimulation of the internal and external carotid nerves it was observed that radiate and intermediate neurons sent their axons into one or the other of these nerve trunks, whereas a majority of tufted neurons gave no response to stimulation of either of these postganglionic nerves. Electron microscopic exploration of horseradish peroxidase-labelled neurons revealed a surprisingly high prevalence of interconnectivity between ganglionic neurons. These contacts were both dendrosomatic and dendrodendritic, and were a universal feature of the labelled neurons explored. Twenty-two of the 23 labelled cells were found to receive direct dendritic appositions on their somata, and 13 of these 23 cells were seen each to send their dendrites into contact with at least one unlabelled neuronal soma. Dendrodendritic contacts were observed for 87% of the labelled neurons, and most of the cells (80%) were seen to form triadic contacts which included two dendrites and a preganglionic nerve ending. All these figures represent minimum incidences. None of the dendrosomatic or dendrodendritic appositions observed was overtly synaptic although several morphological features indicated the possibility of somatic and or dendritic release and uptake at sites of apposition. It is suggested that the observed appositions provide anatomical substrates for modulatory interactions between the ganglionic neurons, possibly involving slow potentials or the switching of metabolic pathways.

Interactions between prostaglandin E2 and D-ala2-met-enkephalinamide on adenylate cyclase activity in the guinea-pig superior cervical ganglion

Crude membrane fractions, obtained from superior cervical ganglia of normal and sympathectomized guinea-pigs, have been used to investigate the role of prostaglandin E2 and D-ala2-met-enkephalinamide in the modulation of ganglionic adenylate cyclase as well as their functional interrelationship. In ganglia from normal animals the enzyme activity was stimulated and inhibited, respectively, by the prostaglandin (10(-4)M) and by the opiate pentapeptide (10(-4)M), while little or no effects were observed in denervated preparations. When the two substances were tested in combination, a supra-additive stimulation of adenylate cyclase activity was obtained both in normal and denervated ganglia. In the latter preparation the opiate increased prostaglandin E2 specific binding, suggesting that the mechanism of supra-additivity could involve interactions at receptors level. Furthermore, the supra-additive stimulation of adenylate cyclase activity by the combination of the two drugs was obtained in a narrow range of concentrations since at low prostaglandin E2 doses (10(-7)-10(-6)M) or at very high doses of the opiate (10(-3)M), only the inhibitory effect of D-ala2-met-enkephalinamide was evidenced.

Corticotropin-releasing factor-like immunoreactive nerve fibers in the rat superior cervical ganglion and their fine structures

The existence of nerve fibers containing corticotropin-releasing factor (CRF)-like immunoreactivity (CRFI) in the rat superior cervical ganglion (SCG) was demonstrated by using immunocytochemistry. They were found to be extrinsic in origin, because no CRFI neurons were seen in the SCG and decentralization resulted in the disappearance of CRFI fibers in the SCG on the operated side. These findings were also confirmed by immunoelectron microscopic analysis; CRFI fibers contained a number of small clear synaptic vesicles but were devoid of large granular and agranular vesicles. These morphological characteristics are identical to those of the preganglionic fibers. The present immunoelectron microscopic analysis revealed that most of the CRFI fibers in the SCG make synaptic contact predominantly with the dendrites of the principal cells, partly with their somas and rarely with a non-CRFI terminal. Thus, the present study provides direct morphological evidence that CRF directly influences the function of the principal cells of the SCG and that CRFI fibers are preganglionic.