The development of somatostatin immunoreactivity in the interpeduncular nucleus of the cat

Somatostatin (SS) immunoreactivity was localized in a population of neurons in the interpeduncular nucleus (IPN) of the developing and adult cat. SS-immunoreactive perikarya and fibers were found in several subdivisions of the IPN, but were most heavily concentrated in the central nucleus (IPC). Some immunoreactive fibers appeared to be associated with the ventral surface of the IPN where they may come in contact with the interpeduncular cistern. Bundles of immunoreactive fibers also appeared to leave the rostral pole of the IPN bilaterally. Still other SS-positive perikarya and fibers were associated with the tegmentopeduncular tract and the medial division of the dorsal tegmental nucleus. SS was present in both perikarya and fibers of the IPN at birth. The concentration of immunoreactivity increased dramatically during the first 100 days postnatal, but by 180 days the overall intensity of immunoreactivity had decreased to adult levels. These data indicate that SS may be present in the cat IPN in a specific population of neurons that is most active during early postnatal development. The data are consistent with previous suggestions that SS plays a special role in the development of certain neuronal systems and may be particularly important in the integration of behaviors during the neonatal period.