[Immunocytochemical studies on the possible involvement of the classical neurosecretory system in the cerebral processes of cardiovascular regulation].

The distribution and the cytomorphology of neurophysin- and oxytocin-producing cells of the classic neurosecretory system of the rabbit were investigated at light microscopic level using the peroxidase-antiperoxidase (PAP) technique. Our results show that the neurons are distributed not only in the paraventricular and supraoptic nuclei, but as constituents of the suprachiasmatic nucleus and different cell clusters in the diencephalon they have a broader distribution than hitherto has been assumed. The light microscopic analysis of the exohypothalamic hypothalamo-rhombencephalic pathway shows that its fibres are closely related to neurons of the nucleus of the tractus solitarii and the dorsal motor nucleus of vagus. Following light microscopic observations suggesting that these fibres terminate on neurons in these nuclei, an immuno-electron microscopic study was undertaken. Using the pre-embedding technique, specific reaction products were observed indicating both neurophysin and oxytocin in axo-dendritic and axo-somatic synapses. These peptide-containing terminals do not seem to differ in any way from classic transmitter-containing synapses in the brain. The synaptic contacts between hypothalamo-rhombencephalic fibres on the one hand and neurons of the nucleus tractus solitarii and the dorsal motor nucleus of vagus on the other might be the morphological representation of an involvement of the paraventricular nucleus in cerebral cardiovascular regulation.