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Ultrastructural localization of NGF receptors in satellite cells of the rat spinal ganglia.

Data on the presence of NGF receptors in the satellite cells of spinal ganglia are scanty and contradictory. In the present study we used immunocytochemistry to examine the distribution of these receptors in spinal ganglia of the adult rat by light and electron microscopy. We found that (1) all satellite cells were immmunoreactive to p75 and the mean density of gold particles (mean number per microm2) was significantly greater in the satellite cell sheath than in the nerve cell body; (2) numerous satellite cells were immunoreactive for trkA with a mean density of gold particles slightly greater in the satellite cell sheath than in the nerve cell body, although the difference was not statistically significant; (3) both p75 and trkA immunoreactivity were confined to the cytoplasm. We suggest that the p75 receptor may be involved in the NGF-induced outgrowth of slender projections from the nerve cell body surface. With regard to the trkA receptor, satellite cells might be supported trophically by NGF released from the neuron with which they are associated; alternatively, satellite cells might internalize NGF to constitute a reservoir for later release to the neuron.

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Expression of fibroblast growth factor-2 and fibroblast growth factor receptor 1 messenger RNAs in spinal ganglia and sciatic nerve: regulation after peripheral nerve lesion.

In order to determine functional roles of basic fibroblast growth factor (FGF-2) in the peripheral nervous system we have analysed the expression of FGF-2 and FGF receptor 1 (FGFR1) in spinal ganglia and the sciatic nerve under normal conditions and after nerve crush using RNAse protection assay and in situ hybridization. In intact spinal ganglia, both FGF-2 and FGFR1 messenger RNAs are expressed, albeit at different levels. In situ hybridization identifies satellite cells as the source of FGF-2 and sensory neurons as the source of FGFR1 suggesting a paracrine mode of action of FGF-2 on sensory neurons. One day after crush lesion FGF-2 is significantly up-regulated in sensory ganglia L4-L6. Highest levels are found at day 7; control levels are approached after 28 days. FGFR1 messenger RNA, which is strongly expressed in intact spinal ganglia, displays no significant change after lesion. In the intact sciatic nerve, FGFR1 messenger RNA is detected at higher levels than FGF-2 messenger RNA. After injury, both transcripts display a time-dependent up-regulation in both the proximal and distal nerve stump. Schwann cells, as a putative source of the sciatic nerve-derived FGF-2, express both FGF-2 and FGFR1 messenger RNAs in vitro. The FGFR1 transcript level is increased in the presence of forskolin. FGF-2 does not affect expression of FGFR1 messenger RNA but stimulates its own expression. These results show that during peripheral nerve regeneration FGF-2 is up-regulated in both the crushed nerve and the respective spinal ganglia suggesting a possible physiological function of FGF-2 during the regeneration process.

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Freeze-fracture aspects of the perineurium of spinal ganglia.

The internal portion of the capsule of the spinal ganglia of rabbit is composed of continuous superimposed layers of flattended cells (perineurium). In replicas, extensive meshworks of strands, presumably forming zonulae occludentes, are found between the perineurial cells of the same layer. Adjacent layers are joint by maculae occludentes located on the lateral processes of the perineurial cells. Occasionally small gap junctions lie within the meshes of the zonulae occludentes.

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Differential regulation of fibroblast growth factor (FGF)-2 and FGF receptor 1 mRNAs and FGF-2 isoforms in spinal ganglia and sciatic nerve after peripheral nerve lesion.

To study the functional role of endogenous basic fibroblast growth factor-2 (FGF-2) during degeneration and regeneration of the sensory system, we have determined the expression and regulation of FGF-2 and FGF receptor (FGFR)-1 mRNAs in spinal ganglia and sciatic nerve during experimental transection and crush injury of the sciatic nerve. In contrast to levels of the FGFR-1 transcript, which is not altered, the level of FGF-2 mRNA is dramatically up-regulated in spinal ganglia after injury. In the proximal and distal nerve stumps both transcript levels are significantly elevated, albeit at different time points. The FGF-2 isoforms are differently up-regulated in spinal ganglia and sciatic nerve following peripheral nerve lesion. The differential response of FGF-2 mRNA and protein and of FGFR-1 mRNA in spinal ganglia and sciatic nerve after lesion is suggestive of different physiological functions: a local reaction at the lesion site where axonal regrowth occurs and a trophic reaction for the degenerating/regenerating sensory neurons.

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