Testosterone and 17β-estradiol regulate hippocampal area CA3 sharp waves in male and female rats.

Sharp wave-ripples (SPW-Rs) are critical to hippocampal function, and the same is true of gonadal steroids, but the interactions are unclear. We find that surgical removal of the gonads greatly reduces SPW rates in both sexes. Ripples are greatly reduced also. Testosterone treatment rescues SPW and ripple rates in males, and 17β-estradiol restores SPW rates in females. We also find that male SPW rates are higher than females but have less power. Furthermore, in intact females, SPW rates fluctuate with the stage of the ovarian cycle. These data demonstrate that hippocampal SPWs are significantly affected by gonadal removal, testosterone, and 17β-estradiol. In addition, there are sex differences. The data are consistent with past demonstrations that testosterone and 17β-estradiol play central roles in hippocampus and significantly expand the views of hormone action and SPW-Rs.