Modification of in vitro neurotransmitter release from rat brain slices by hypophyseotropic factors

Abstract

This chapter discusses the ultrashort feedback effects of releasing hormones. Previous experiments had indicated that the subcutaneous administration of crude hypothalamic extracts containing follicle-stimulating hormone–releasing hormone (FSH-RH) and devoided of any FSH and sex steroid contamination may bring about a significant reduction of FSH-RH stores in the hypothalamus of castrated, hypophysectomized rats. These experiments suggested the possibility that the brain might contain receptors sensitive to circulating levels of FSH-RH, and that FSH-RH might directly regulate its own production via an “ultrashort” feedback effect. Subcutaneous or intracarotid treatments with repeated doses of synthetic LH-RH are able to bring back to normal the elevated levels of hypothalamic LH-RH in castrated, hypophysectomized animals. The data support the view that releasing hormones have direct effects on the brain and speak in favor of the existence of “ultrashort” feedback mechanisms controlling gonadotropin secretion In addition, the chapter also provides information on the modification of in vitro neurotransmitter release from rat brain slices by hypophyseotropic factors.