IMMUNOHISTOCHEMICAL CORRELATION OF HUMAN ADRENAL NERVE-FIBERS AND THORACIC DORSAL-ROOT NEURONS WITH SPECIAL REFERENCE TO SUBSTANCE-P

Applying a double-labelling immunofluorescence technique, six types of substance P-containing nerve fibres were distinguished in the human a drenal gland according to the immunohistochemical colocalization of (I ) calcitonin gene-related peptide (CGRP), (II) cholecystokinin, (III) nitric oxide synthase, (IV) dynorphin, (V) somatostatin, and (VI) vaso active intestinal polypeptide. Fibre populations I to IV in their medi ator content resembled the respective subpopulations of primary sensor y neurons in human thoracic dorsal root ganglia, while populations V a nd VI revealed no correspondence with dorsal root neurochemical coding . Nerve fibres with the combination substance P/nitric oxide synthase occurred only in the adrenal cortex, whereas all other fibre types wer e present in both cortex and medulla. As revealed by immune-electron m icroscopy, substance P-immunolabelled axon varicosities (a) exhibited synaptic contacts with medullary chromaffin cells or with neuronal den drites, (b) were directly apposed to cortical steroid cells and (c) we re separated from fenestrated capillaries only by the interstitial spa ce. These findings provide immunochemical support for an assumed senso ry innervation of the human adrenal gland, and additionally suggest pa rticipation of substance P in efferent autonomic pathways. Furthermore , the results are indicative for a differentiated involvement of subst ance P in the direct and indirect regulation of neuroneuronal and neur oendocrine interactions.