SOMATOTROPIN RELEASE-INHIBITING FACTOR AND GALANIN INNERVATION IN THEHYPOTHALAMUS AND PITUITARY OF SEABREAM (SPARUS-AURATA)

The distribution of galanin (GAL) and somatotropin-release-inhibiting- factor (SRIF) immunoreactivity in the hypothalamus and pituitary of th e sea bream (Sparus aurata) was studied by immunocytochemistry. An ext ensive system of neurons immunoreactive with antisera to the two pepti des was identified throughout the brain with staining particularly in the hypothalamus. In the hypothalamus, GAL immunoreactive perikarya we re detected principally in the nucleus preopticus and nucleus tuberis. Major nerve tracts were observed to sweep down from the hypothalamic nuclei and reached the pituitary via the preoptico-hypophysial tract. Many of the fibers had varicose swellings indicating they were secreto ry. SRIF immunoreactivity was distributed similarly to GAL but the net work of nerve fibers was less dense; no colocalization of these two pe ptides was seen. SRIF immunoreactive perikarya were present in the pre optic nucleus, the tuberal nucleus, and the basolateral hypothalamus. These perikarya were large and densely staining and were predominately bipolar, although some multipolar perikarya were observed. In the pit uitary GAL and SRIF immunoreactivities were confined principally to th e pars distalis where fibers infiltrated between growth hormone, prola ctin, and adreno cortico trophic cells. More of the fibers were immuno reactive for SRIF than for GAL. There was no immunoreaction for GAL or SRIF in any of the pituitary cells. There is thus morphological evide nce for a neuroendocrine control of the pars distalis by GAL and SRIF and for a possible functional interaction between these two systems. ( C) 1996 Academic Press, Inc.