IMMUNOCYTOCHEMICAL LOCALIZATION OF A GROWTH-ASSOCIATED PROTEIN (GAP-43) IN RAT ADRENAL-GLAND

We have localized at light and electron-microscopic level the growth-a ssociated protein GAP-43 in adrenal gland using single and double labe lling immunocytochemistry. Clusters of GAP-43-immunofluorescent chroma ffin cells and many immunofluorescent fibres were observed in the medu lla. GAP-43-immunoreactive fibres also formed a plexus under the capsu le, crossed the cortex and ramified in the zona reticulata. Double lab elled sections showed the coexpression of GAP-43 with a subpopulation of tyrosine hydroxylase- and of dopamine-beta-hydroxylase-immunoreacti ve chromaffin cells. Dual colour immunofluorescence for GAP-43 and cal citonin gene-related peptide (CGRP) revealed that some of the GAP-43-i mmunoreactive fibres also express CGRP. Pre-embedding electron microsc opy showed GAP-43 immunoreactivity associated with the plasma membrane s and cytoplasm of noradrenaline-producing chromaffin cells, and with processes of nonmyelin-forming Schwann cells. Immunoreactive unmyelina ted axons and terminals were also observed. The immunostained terminal s made symmetrical synaptic contacts with chromaffin cells. Immunoreac tive unmyelinated fibres and small terminals were present in the corte x. Our results show that GAP-43 is expressed in noradrenergic chromaff in cells and in various types of nerve fibres that innervate the adren al. Likely origins for these fibres include preganglionic sympathetic fibres which innervate chromaffin cells, postganglionic sympathetic fi bres in the cortex, and CGRP containing sensory fibres.