REGULATION OF THE SECOND (ESTROUS) RELEASE OF FOLLICLE-STIMULATING HORMONE IN HAMSTERS BY THE MEDIAL BASAL HYPOTHALAMUS2

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Abstract
In female proestrous hamsters (1800 h), bilateral electrocoagulative lesions in the arcuate-median eminence (Arc-ME) region blocked the pituitary FSH [follicle stimulating hormone] release that normally would have begun in late proestrus and continued until the afternoon of estrus. This 2nd (estrous) FSH elevation, which is not accompanied by LH release, was unaffected by neural disconnection of the medial preoptic area (MPOA) from the medial basal hypothalamus (MBH) or by production of MBH-pituitary islands. After gonadotropin-releasing hormone was injected into Arc-ME-lesioned hamsters, LH was released. These results suggest that the Arc-ME does not require the MPOA for initiation of the estrous release of FSH.