Identification of serotonin- and vasopressin immunoreactivities in the suprachiasmatic nucleus of four mammalian species.

The distribution of serotonin- and vasopressin immunoreactivities in the suprachiasmatic nucleus (SCN) of four mammalian species was studied with the use of the modified peroxidase-antiperoxidase (PAP) method and antisera to serotonin and vasopressin. In the SCN of the rat, hamster and cat, we noted a large number of serotonin-immunoreactive nerve fibers particularly in the ventral area, where these fibers containing small varicosities (less than 1 micron in diameter) formed a dense plexus. In the monkey (Macaca fuscata), however, only few serotonin-containing fibers were evident throughout the SCN. Vasopressin-immunoreactive somata and fibers were distributed in large numbers in the SCN of the rat, hamster, cat and monkey, especially in the dorsal nuclear area. Regional and species-related differences of serotonin- and vasopressin distribution in the SCN were elucidated; possible functional differences between the ventral and dorsal areas of the SCN are discussed.