COLOCALIZATION OF ANGIOTENSIN-II AND GAMMA-AMINOBUTYRIC-ACID IN AXON TERMINALS IN THE RAT SUBFORNICAL ORGAN

Angiotensin II (Ag II) and gamma-aminobutyric acid (GABA) in the subfornical organ have been implicated in drinking and cardiovascular responses to changes in circulating hormones. We combined immunogold silver labeling of Ag II with immunoperoxidase detection of GABA to determine whether there might be common cellular sites for their physiological actions in this circumventricular region. Electron microscopy showed that numerous terminals in central portions of the rat subfornical organ contained both AgII and GABA immunoreactivity. These terminals as well as others exclusively labeled for AgII or GABA formed mainly symmetric, inhibitory type synapses with unlabeled dendrites. Immunogold-silver aggregates recognizing AgII were often detected near non-synaptic portions of the plasma membrane with or without apparent association with large dense core vesicles. In contrast, the GABA immunoperoxidase labeling was most intensely localized to membranes of small clear vesicles which were aggregated near the presynaptic junction. Our results indicate that in rat subfornical organ, neuronal AgII may modulate the inhibitory postsynaptic responses to GABA following release from single axon terminals.