Intrinsic Neurons of the Septal Area are Involved in Reproductive Development of the Female Rat

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Abstract
Three experiments were conducted using intracranial infusion of kainic acid (KA) to lesion the medial septal (MS) neurons and dorsal hippocampal (DH) neurons in 25-day-old female rats. Rats of experiment 1 were allowed to develop until vaginal opening (VO) after which vaginal lavages were taken to monitor the vaginal cycle. Rats of experiment 2 received estradiol benzoate (EB) subcutaneously immediately after KA infusion. Blood was obtained at 11.00 and 16.00 h, 2 days after EB and measured for luteinizing hormone (LH) by radioimmunoassay. Rats of experiment 3 received MS KA lesions and 2 days later tested for pituitary responsiveness to LHRH-induced LH release. In experiment 1, MS KA-lesioned rats exhibited a significant delay in VO when compared to the sham-lesioned or the unoperated control groups. Hippocampal KA-lesioned rats in contrast, showed no difference in the age of VO from the control groups. Septal KA-lesioned rats also showed disrupted vaginal cycles after the onset of puberty. In experiment 2, all the EB-treated animals exhibited the expected rise in serum LH on the afternoon 2 days following EB with the exception of the septal KA-lesioned rats. In every case, KA infusion into the medial septum abolished the ability of EB to induce an LH increase at 16.00 h 2 days after EB administration. DH KA lesion on the other hand had no effect on the EB-induced LH increase. The block of LH secretion by MS KA infusion shown in experiment 2 is not a result of decreased pituitary gland sensitivity to LH-releasing hormone (LHRH) as shown in experiment 3. These results indicate that MS neurons play a vital role in the feedback mechanism whereby EB induces an LH increase in the prepuberal female rat, and that they play a role in the timing of VO.