First Geoffrey Harris Memorial lecture. Some recent developments in brain-pituitary-ovarian physiology.

Figure 14 summarizes some of the brain-pituitary-ovarian relationships which we have been discussing. Neurons in the arcuate nucleus of the hypophysiotropic area produce LRH which is secreted into the proximal capillary plexus of the hypophysio-portal system in the median eminence. LRH production is modulated in the rat and possibly also in the monkey by direct input from the preoptic region and less directly by facilitatory and inhibitory projections from the amygdala, hippocampus and midbrain. Electrophysiological evidence has been presented for "ultrashort' feedback action of LRH on arcuate neurons as well as the "short' feedback loop of LH. Gonadal steroids are pictured as feeding back directly to the pituitary and to several sites in the brain where positive and negative influences are exerted on both pituitary-ovarian function and sexual behavior. Evidence has been presented that adrenergic mechanisms influence LRH release with norepinephrine facilitatory and dopamine inhibitory to the process; dopaminergic neurons may be more intimately related to the control of prolactin secretion, and some consider dopamine and prolactin inhibiting factor to be identical. Finally, immunological methods as represented by immunohistochemistry and radioimmunoassay promise further important developments in this field in the near future. I am sure that Geoffrey Harris would have been pleased with the progress made in answering the questions which he raised in his Dale lecture.