LHRH EFFECTS ON HIPPOCAMPAL-NEURONS ARE MODULATED BY ESTROGEN IN RATS

The effect of luteinizing hormone releasing hormone (LHRH) on the neur onal activity of CA1 and CA3 regions of the hippocampus was studied by means of extracellular recordings in the castrated male, intact male, castrated female, and castrated female injected s.c. with 20 mu g est radiol benzoate (EB) for 3 days. The basal firing rate of the CA3 neur ons of castrated EB-treated female rats was significantly lower than t hat of the neurons in castrated EB-untreated female rats as well as ma le rats, either intact or castrated, whereas that of the CA1 neurons w as not significantly different from castrated EB-untreated female rats . Iontophoretically applied LHRH predominantly resulted in facilitatio n of the neuronal firing in most of the animal groups. In the CA3 regi on of castrated EB-treated female rats, however, inhibition occurred i n a large percentage of neurons, and the ratio of facilitation, inhibi tion and no response was significantly different from that in castrate d EB-untreated female rats. In the CAI region of castrated EB-treated female rats, the predominant effect of LHRH was facilitation and the r atio of facilitation, inhibition and no response was not significantly different from that in castrated EB-untreated female rats. These resu lts suggest that LHRH is involved in increasing the neuronal activity of the CA3 region in the hippocampus, and estrogen reduces this LHRH a ction.