Sympathetic Ganglia Of Guinea-pigs Research Articles

Pathway-specific expression of PKC and PKA in sympathetic neurons

We used multiple-labelling immunofluorescence, intracellular dye injection, electrophysiological recording and confocal microscopy to examine the expression of immunoreactivity to protein kinase C (PKC) and protein kinase A (PKA) in sympathetic ganglia of guinea-pigs. PKCalpha and PKCgamma were widespread in vasoconstrictor and pilomotor neurons. High levels of PKA RIIalpha and RIIbeta were restricted to neurons that lacked significant expression of PKC, including somatostatin-containing neurons projecting to the gut, and non-noradrenergic vasodilator neurons. In coeliac ganglia, most neurons with PKC contained neuropeptide Y and displayed phasic patterns of action potential firing, often with a long after-hyperpolarization. Tonically firing neurons lacked both neuropeptide Y and PKC. These results show remarkably pathway-specific expression of protein kinases in functionally identified populations of sympathetic neurons.

Synaptic organisation of lumbar sympathetic ganglia of guinea pigs: Serial section ultrastructural analysis of dye-filled sympathetic final motor neurons

The authors serially sectioned seven dye-filled neuronal somata and more than 1.6 mm of their dendrites from the lumbar sympathetic ganglia of guinea pigs and examined them ultrastructurally to determine the distribution of preganglionic synaptic inputs to their dendrites and cell bodies. Most of the surface of the neurons was covered with Schwann cells. Apposing boutons were rare, with an average density of one axosomatic bouton per 125 microm2 of somatic membrane and one axodendritic bouton per 25 microm of dendrite. Many dendritic segments that were more than 50 microm long completely lacked any apposing boutons. Although the average density of apposing boutons was low, local densities could be high, so that clusters of up to four adjacent boutons occurred on cell bodies and dendrites alike. The spatial arrangement of the apposing boutons for each of the cells examined here was not significantly different from a random distribution. Consequently, the number of apposing boutons observed for any neuron was simply proportional to the amount of neuronal surface sampled in the serial section run. About 50% of boutons directly apposing the neurons lacked any detectable presynaptic specialisations. When they were present, the presynaptic densities had a mean length of about 220 nm, with no difference between boutons that made axosomatic or axodendritic appositions. By applying these data to complete reconstructions of the dendritic trees of dye-filled sympathetic neurons at the light microscopic level, the authors estimated that few neurons in the lumbar sympathetic chain of guinea pigs would receive more than 200 synapses or apposing boutons and that many of them would receive less than 100 synapses. Up to 50% of these boutons would be predicted to make axosomatic contacts. These new observations provide a strong morphological framework for a better understanding of how sympathetic final motor neurons process their preganglionic synaptic inputs.

Synaptic organisation of neuropeptide-containing preganglionic boutons in lumbar sympathetic ganglia of guinea pigs.

Within the lumbar sympathetic ganglia of guinea pigs, the endings of different populations of neuropeptide-containing preganglionic neurons form well-defined pericellular baskets of boutons around target neurons in specific functional pathways. We have used multiple-labelling immunofluorescence, confocal microscopy, and ultrastructural immunocytochemistry to investigate synaptic organisation within pericellular baskets labelled for immunoreactivity to calcitonin gene-related peptide (CGRP), substance P (SP), or the pro-enkephalin-derived peptide, met-enkephalin-arg-gly-leu (MERGL) in relation to their target neurons. Different functional populations of neurons, identified by their neurochemical profile, showed a significant degree of spatial clustering and predicted well the distribution of specific classes of pericellular baskets. Most of the boutons in a basket were completely surrounded by Schwann cell processes and did not form synapses. The synapses that were present were made mostly onto dendrites enclosed by the Schwann cell sheath surrounding the neuron within the basket. These dendrites probably originated from neurochemically similar neighbouring neurons. Nevertheless, some of the boutons in the baskets did form synapses with the cell body or proximal dendrites of the neuron they surrounded. Occasionally, cell bodies received a relatively high number of synapses and close appositions from boutons in a pericellular basket. Synaptic convergence of two immunohistochemically distinct types of preganglionic inputs was found in baskets of SP-immunoreactive or MERGL-immunoreactive, but not CGRP-immunoreactive, boutons. Taken together, our results show that the appearance of pericellular baskets is primarily due to the packing of the target neurons. The grouping of functionally similar classes of neurons with their pathway-specific projections of peptide-containing preganglionic neurons suggests that peptides could exert their effects in relatively well-defined zones within the ganglia.

Differential distribution of substance P binding sites in guinea-pig sympathetic ganglia

We have used a combination of autoradiographic and immunohistochemical techniques to investigate the distribution of binding sites for substance P in relation to the distribution of substance P-immunoreactive nerve fibres and specific functional populations of neurons in the sympathetic ganglia of guinea-pigs. There was considerable heterogeneity in the density of binding sites for Bolton Hunter labelled 125 I−substance P (BHSP). Binding sites were more dense in the prevertebral ganglia, such as the coeliac and inferior mesenteric ganglia, than in the paravertebral ganglia, such as the superior cervical or lumbar chain ganglia. The binding sites tended to be clumped within the ganglia. Within the prevertebral ganglia, they were associated predominantly with neurons projecting to the enteric plexuses. Many of these neurons contained somatostatin immunoreactivity. In the lumbar sympathetic chain ganglia, there was a weak association of binding sites with neurons containing immunoreactivity to vasoactive intestinal peptide. Overall, the density of binding sites matched the density of nerve fibres containing immunoreactivity to substance P in different ganglia. However, within particular ganglia, there was little, if any, correlation between the distribution of binding sites and nerve fibres containing substance P. Most of the binding sites in the ganglia had the pharmacological characteristics of NK 1 receptors. Our results show that there is considerable heterogeneity in the expression of NK 1 receptors in the sympathetic ganglia of guinea-pigs. However, given the relatively poor spatial correlation between the distribution of binding sites and potential sites of substance P release from intraganglionic nerve fibres, we suggest that substance P may diffuse for relatively large distances through the ganglia, with actions only on those neurons selectively expressing NK 1 receptors.

Immunoreactive substance P in sympathetic ganglia: Distribution and sensitivity towards capsaicin

The distribution of immunoreactive substance P was studied in sympathetic ganglia of guinea-pigs and rats. In both species the highest concentration was found in the coeliac-superior mesenteric ganglion. Guinea-pigs had three times higher concentrations of immunoreactive substance P than rats in all ganglia studied. Pretreatment of guinea-pigs with capsaicin (125 mg/kg; s.c.), an agent shown to deplete immunoreactive substance P only from primary sensory neurons, caused a 63–96% depletion of immunoreactive substance P in sympathetic ganglia and the splanchnic nerve. Superfusion of coeliac ganglia with capsaicin (3.3 × 10 −5M) in vitro led to a calcium-dependent release of immunoreactive substance P. The findings that capsaicin causes release and depletion of immunoreactive substance P from sympathetic ganglia support the hypothesis that substance P-containing fibers in sympathetic ganglia are primary sensory neurons.

The ultrastructure of junctions between satellite cells in mammalian sympathetic ganglia as revealed by freeze-etching

Intercellular junctions and other membrane specializations of the satellite cells in the superior cervical ganglion of rabbit and guinea pig, as well as in prevertebral sympathetic ganglia of guinea pig, have been revealed in a study of freeze-fractured material. In all ganglia the satellite cells are united by gap junctions varying in size from 0.1 to 0.5 μm and containing intramembranous particles, 80–90 A in diameter. In about half of the junctions the particles are closely packed and arranged in an ordered hexagonal pattern. In the others, the particles are arranged in rows displaying a varying degree of organization and are separated by particle-free aisles. Tight junctional elements between satellite cells are also present in the guinea pig ganglia. Orthogonal arrays of 60- to 70-A particles are frequently observed in the satellite cell membranes, particularly in the guinea pig ganglia. In certain regions of the satellite cell membrane in the rabbit superior cervical ganglion, accumulations of aggregates consisting of two to four membrane particles 60–100 A in diameter are found.

Interactions between autonomic nerves and smooth and cardiac muscle cells in tissue culture

Specific interactions occur between nerve fibers from cultured sympathetic ganglia of guinea pigs and rats and single muscle cells from vas deferens and heart. The associations are long-lasting and resemble the pattern of autonomic neuromuscular relations in situ. In contrast, any associations formed between sympathetic nerve fibers and fibroblasts appear to be temporary. The results are discussed in relation to the normal innervation of smooth muscle and the reinnervation of explants.