ABSTRACT
This chapter provides morphological evidence suggesting that estrogen or aromatizable androgen play significant roles in modulating neural circuit formation in sex steroid-sensitive hypothalamus. Attempts have been made to clarify the molecular mechanisms underlying sexual differentiation of synaptic connections. Activational effects of sex steroids on adult neuroendocrine brain are considered to be impermanent and reversible, and involving changes in neurophysiological and/or neurochemical events. R. A. Gorski et al. found an intensely staining neuron group with a striking sex difference in the rat medial preoptic area (POA) that is called the sexually dimorphic nucleus of the POA. Immunohistochemical studies have shown that there is sexual dimorphism in the distribution pattern of neuronal cell bodies and fibers containing several types of neurotransmitters and neuromodulators in the hypothalamus. Gonadotropin-releasing hormone (GnRH) neurons of the POA represent the final common pathway regulating gonadotropin secretion by the anterior pituitary.
