Effects of microiontophoretic and intravenous application of gonadotrophic hormones on the discharge of medial-basal hypothalamic neurones in rats.

In ovariectomized rats, the responses of medial-basal hypothalamic neurones to gonadotrophic hormones have been recorded. The luteinizing and follicle stimulating hormones (LH and FSH) were applied to neurones both by microiontophoresis and by intravenous injection. Although LH was the more frequently effective, both hormones caused either excitation or inhibition of neurones, and the effects were consistently repeatable on the same neurones. Iontophoretic and intravenous application of the same hormones to the same neurone gave identical responses. Responsive neurones were found throughout the medial-basal hypothalamus and hormones were effective both on neurones which could be antidromically activated from the median eminence and on those which could not be activated. Treatment of rats with oestradiol, either during the experiment or 24 h earlier, did not significantly alter neuronal responses to the gonadotrophins. The results are discussed in terms of possible feedback by gonadotrophic hormones on the brain and it is suggested that such a feedback may not be concerned with control of gonadotrophic hormone secretion.