Identification of ending containing dopamine and vasopressin in the rat posterior pituitary by a combination of radioautography and immunocytochemistry at the ultrastructural level.

In order to study the morphological relationship between the dopaminergic and the vasopressinergic endings in the rat posterior pituitary, a combination of radioautography and immunocytochemistry techniques was applied to the same ultrathin section of the posterior pituitary. Immunocytochemical localization (peroxidase-antiperoxidase technique) of vasopressin was first applied, followed by the radioautography detection of [3H] dopamine that had been injected 30 and 60 min before fixation. This double labeling technique has established that the dopaminergic endings that contain both dense core vesicles (60-100 nm in diameter) and small clear vesicles are always found in close proximity to vasopressinergic neurosecretory endings, suggesting an interaction between these two systems. This relatively easy approach should be very useful to study the connections between different neurotransmitter systems in the nervous system.