THE SUPRACHIASMATIC AREA IN THE FEMALE HAMSTER PROJECTS TO NEURONS CONTAINING ESTROGEN-RECEPTORS AND GNRH

THIS Study investigated whether the circadian regulation of luteinizin g hormone (LH) release may be through direct input of the suprachiasma tic nucleus (SCN) to estrogen receptor (ER)- and/or gonadotropin relea sing hormone (GnRH)-immunoreactive neurons. We used Phaseolus vulgaris leucoagglutinin (PHA-L) as an anterograde tracer of SCN efferents and performed double label immunocytochemistry for PHA-L and ER or GnRH. Between 8 and 30% of ER cells and 11-13% of the GnRH cells showed appo sitions with SCN efferents. Efferent projections of the subparaventric ular hypothalamic nucleus and the retrochiasmatic area, relay stations of the circadian system, also made appositions with these two cell ty pes. Results suggest that the circadian system could regulate the timi ng of the LH surge via two pathways, through input to GnRH and to ER c ells.