9728581 Horvath All animals studied to date possess endogenous biological clocks that mediate biological rhythms. In rats and other mammals, pulsatile hormone release from the anterior pituitary is essential for normal growth, metabolism, and reproduction. The interaction between visual, circadian and neuroendocrine systems underlies rhythmic anterior pituitary hormone secretions, including prolactin and luteinizing hormone (LH). The suprachiasmatic nucleus (SCN) is the critical brain structure underlying biological rhythms and a monosynaptic pathway between this hypothalamic nuclei and the principle neuronal populations regulating LH and prolactin release has been documented. Recently, it has become clear that pure visual signals may directly or indirectly via the intergeniculate leaflet of the lateral geniculate nucleus influence endocrine mechanisms and these pathways may be functioning in parallel with the biological clock that itself is under the influence of light. This indicates a more complex integration of visual signals into the neuroendocrine hypothalamus than previous suspected. Dr. Horvath, through a series of elegant neuroanatomical studies, will determine the morphological relationship between subcortical visual efferents and hypothalamic neurons responsible for the regulation of endocrine mechanisms. By using tract tracing methods in combination with degeneration and light and electron microscopic immunocytochemical approaches, and using biochemical assays, he will also assess the role of subcortical visual pathways in the regulation of pituitary gonadotrophs underlying ovulation. The delineation of the pathways via which visual and circadian signals are integrated into the neuroendocrine hypothalamus will enhance our understanding of how rhythmic anterior pituitary hormones secretions are regulated and this is critical for understanding reproduction and behavior.
