Immunohistochemical analysis of neurotransmitters of the subfornical organ

The localizations of peptides and putative neurotransmitters in the subfornical organ of the rabbit, rat and guinea pig were analyzed by using immunohistochemical methods. The variations that occurred in the three species were investigated. Immunoreactivities including serotonin (5-HT), neurotensin (NT), vasopressin (VP), luteinizing hormone releasing hormone (LHRH) and FMRFamide (Phe-Met-Arg-Phe-NH2) were examined in the subfornical organ. Nerve fibers that displayed 5-HT-positive immunoreactivity were observed in all species examined. Some immunoreactive perikarya were detected in guinea pigs and rabbits. Neurotensin-positive immunoreactivity was weak in the subfornical organ. LHRH immunoreactivity was detected in the rabbit only. Conspicuous vasopressin-positive immunoreactive cell bodies and fibers were detected in the subfornical organ of the rat, rabbit and guinea pig. Mild FMRFamide-positive immunoreactive fibers were observed in the rabbit and rat and no reaction was shown in the guinea pig by the PAP immunolabeling technique. Each neurotransmitter had a specific pattern of distribution in the SFO, though there were some overlapping reactive areas. Dramatic differences were demonstrated for fiber density among species.