Immunocytochemical demonstration of close relationships between neuropeptidergic nerve fibers and hormone-producing cell types in the adenohypophysis of the sea bass (Dicentrarchus labrax).

Light microscopic double immunocytochemical stainings, performed on sea bass hypothalamo-hypophysial sections, revealed the projection of different neuropeptide-immunoreactive neurons innervating the hormone-producing cell populations in the pituitary gland. In the rostral pars distalis (PD) the ACTH cells were found in close proximity to fibers immunoreactive for somatostatin (SRIF), growth hormone-releasing hormone (GRF), corticotropin-releasing hormone (CRF), vasotocin (VT), isotocin (IT), substance P (SP), neurotensin, and galanin (GAL), while the PRL cell zone seemed only innervated by nerve fibers immunopositive for GAL. In the proximal PD, fibers immunoreactive for SRIF, GRF, VT, IT, cholecystokinin, SP, neuropeptide Y, and GAL formed a close relationship with the growth hormone cells. The gonadotrophs were observed near nerve fibers immunostained for gonadotropin-releasing hormone, IT, and less obviously GRF and VT, while fibers positive for GRF, CRF, VT, IT, SP, and GAL penetrated between and formed a close association with the thyrotrophs. In the pars intermedia the MSH cells and the PAS-positive (PAS+) cells seemed both innervated by separate nerve fibers immunoreactive for GRF, CRF, melanin concentrating hormone, VT, IT, and SP. All these results suggest a functional role of the neuropeptides in the adenohypophysis of the sea bass, possibly in the synthesis and/or release of hypophysial hormones from the different cell types.