CHEMICAL CODES OF SENSORY NEURONS INNERVATING THE GUINEA-PIG ADRENAL-GLAND

Retrograde neuronal tracing in combination with double-labelling immun ofluorescence was applied to distinguish the chemical coding of guinea -pig primary sensory neurons projecting to the adrenal medulla and cor tex. Seven subpopulations of retrogradely traced neurons were identifi ed in thoracic spinal ganglia T1-L1. Five subpopulations contained imm unolabelling either for calcitonin gene-related peptide (CGRP) alone ( I), or for CGRP, together with substance P (II), substance P/dynorphin (III), substance P/cholecystokinin (IV), and substance P/nitric oxide synthase (V), respectively. Two additional subpopulations of retrogra dely traced neurons were distinct from these groups: neurofilament-imm unoreactive neurons (VI), and cell bodies that were nonreactive to ei ther of the antisera applied (VII). Nerve fibres in the adrenal medull a and cortex were equipped with the mediator combinations I, II, IV an d VI. An additional meshwork of fibres solely labelled for nitric oxid e synthase was visible in the medulla. Medullary as well as cortical f ibres along endocrine tissue apparently lacked the chemical code V, wh ile in the external cortex some fibres exhibited code III. Some intram edullary neuronal cell bodies revealed immunostaining for nitric oxide synthase, CGRP or substance P, providing an additional intrinsic adre nal innervation. Perikarya, immunolabelled for nitric oxide synthase, however, were too few to match with the large number of intramedullary nitric oxide synthase-immunoreactive fibres. A non-sensory participat ion is also supposed for the particularly dense intramedullary network of solely neurofilament-immunoreactive nerve fibres. The findings giv e evidence for a differential sensory innervation of the guinea-pig ad renal cortex and medulla. Specific sensory neuron subpopulations sugge st that nervous control of adrenal functions is more complex than hith erto believed.