The splenic nerve is made up almost exclusively of adrenergic fibers. Conse
quently it was used as a model system in the study of autonomic sympathetic
neurotransmission. The splenic nerve regulates the vasoconstriction and vo
lume reduction of the spleen. Brain-immune interactions via modulation of t
he splenic nerve activity may regulate peripheral cellular immunity. An inh
ibition of noradrenaline release by alpha (2)-adrenoceptor activation has b
een reported. As we were interested in a structurally detailed distribution
of synaptophysin, immunocytochemical methods were applied to splenic nerve
axons. In 1 mum plastic sections a network of synaptophysin-positive varic
osities could be observed all along the splenic nerve. They were also posit
ive for dopamine-beta -hydroxylase and cytochrome b561. At the ultrastructu
ral level the varicosities were seen to establish direct contact with the s
plenic axons. In normal morphology the varicosities revealed small synaptic
vesicles and several dense granules. It is demonstrated that a network of
direct symmetric contacts of adrenergic nature is present all along thp ner
ve These terminals may have nn inhibitory effect nn the splenic nerve activ
ity via axonal receptors. This finding opens new perspectives for the study
of the splenic nerve in general and more particularly for its role in the
regulation of peripheral cellular immunity. (C) 2001 Elsevier Science B.V.
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