Postganglionic, direct axo-axonal contacts on the splenic nerve

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. All rights reserved.