The neuroendocrine regulation of ovarian cyclicity in a seasonally breeding species is the theme of this project. Studies will be performed to identify signals pertinent to photoperiodic, pineal, hypothalamic and steroidal regulation of pulsatile LH secretion and response to estradiol negative feedback in the female sheep. Particularl emphasis will be placed on the importance of patterning of these signals to generation of responses. The patterns of hypothalamic GnRH and pineal melatonin signals will be of special interest and will be studied using a portable back-pack infusion system. Stereotaxically placed knife-cuts in the hypothalamus and immunocytochemical localization of GnRH in neurons of the sheep brain will be used to examine the neural processing of photoperiodic and steroidal signals which regulate pulsatile LH secretion. Radioimmunoassays will be used to measure serum LH, FSH, GnRH, melatonin, estradiol and progesterone. It is expected that these findings will lead to new insight concerning ovarian cyclicity and seasonal breeding, an natural process of reversable fertility.