Figure 3.

Spontaneous electrical activity of GnRH1 neurons and the pituitary gonadotropin mRNA expression levels, and their time-of-day changes. (A) Spontaneous firing activities of GnRH1-GFP neurons for 1 min in the time period preceding the putative LH surge (at 1300 h) and just before or during the putative LH surge (at 1600 h). Bars above the traces indicate the lighting conditions of the aquarium room. (B) Time-of-day changes in median instantaneous frequency (Hz) of the GnRH1-GFP neurons. (C) Time-of-day changes in pituitary lhβ mRNA expression levels. (D) Working hypothesis for the temporal regulation of the ovulatory cycle in the female medaka. The GnRH1 neuronal activity increases in the evening of Day 1, which causes the release of GnRH. GnRH stimulates release of LH from pituitary gonadotropes to cause the LH surge, which triggers ovulation during the night. GnRH1 peptide simultaneously acts on the pituitary gonadotropes to up-regulate lhb mRNA expression over the course of several hours, and LH thus synthesized and stored will be released during the LH surge on Day 2 (11).