Bicuculline infusion advances the timing of Fos expression in LHRH neurons in the preoptic area of proestrous rats

The effect of bicuculline (BIC) on Fos expression in lutenizing hormone-releasing hormone (LHRH) neurons was examined by immunocytochemistry. Proestrous rats were infused with saline (SAL 1400, n = 4) or BIC (BIC 1400, n = 5) for 3 h (10.00-13.00 h) and were killed at 1400 h. Three control rats (SAL 1700), which received saline infusion, were killed at 1700 h. In both the BIC 1400 group and the SAL 1700 group, many LHRH neurons in the preoptic area expressed Fos, but those in the SAL 1400 group did not. The distribution and proportion of LHRH neurons expressing Fos in the BIC 1400 group were identical to those in the SAL 1700 group. We conclude that GABAergic neurons play a critical role in inducing LH surge by controlling LHRH neuronal activity.