NEUROCHEMISTRY, CONNECTIVITY AND PLASTICITY OF SMALL INTENSELY FLUORESCENT (SIF) CELLS IN THE RAT SUPERIOR CERVICAL-GANGLION

Applying double-labelling immunofluorescence, the peptide content of s olitary and clustered small intensely fluorescent (SIF) cells, identif ied by an antiserum to a selective membrane glycoprotein marker, synap tophysin, was correlated with the presence of catecholamines in the ra t superior cervical ganglion. Most of synaptophysin-immunoreactive sol itary and clustered SIF cells apparently contained dopamine (indicated by tyrosine hydroxylase - TH) but not noradrenaline (indicated by dop amine-beta-hydroxylase-DBH). Frequently, immunoreactivities for substa nce P or rarely, neuropeptide Y were colocalized in TH-immunolabelled cells of both types. Immunostaining for vasoactive intestinal polypept ide was found only in solitary SIF cells and was visible in TH-immunor eactive, as well as in TH-nonreactive cells. Very few solitary SIF cel ls were TH- and DBH-immunoreactive. Solitary and clustered SIF cells, as a rule, were encircled by leu-enkephalin-positive fibres which were also met-enkephalin-arg6-phe7-immunoreactive, indicating pro-enkephal in as precursor. SIF cells were additionally approached by varicose fi bres which contained immunoreactivity for calcitonin gene-related pept ide (CGRP) but not for enkephalins. As observed by immuno-electronmicr oscopy, fibres that were immunostained for leu-enkephalin or CGRP, dee ply invaginated into SIF cell somata. In addition to close membrane ap positions, CGRP-immunolabelled fibres exhibited efferent synaptic cont acts with elements of SIF cell clusters. SIF cells were non-reactive t o enkephalin-antisera in control ganglia and after transection of the postganglionic nerves (axotomy); but both types exhibited leu-enkephal in in preganglionically transected ganglia (decentralization) in which enkephalin-immunoreactive fibre baskets were absent. Synthesis of enk ephalin in SIF cells after decentralization was confirmed by in situ h ybridization demonstrating intracyto-plasmic proenkephalin messenger-R NA. The findings are indicative for a differential neurochemical equip ment of SIF cells in the rat superior cervical ganglion, which mainly is independent to a topographical classification. Moreover, they demon strate the involvement of two neuropeptides in preganglionic SIF cell innervation. Finally, the observations indicate the capacity of SIF ce lls for proenkephalin-expression in response to preganglionic denervat ion.