Impact of ovariectomy and estradiol-17β (E2) replacement on the brain steroid levels of the Indian stinging catfish Heteropneustes fossilis

Abstract

In the present study, effects of ovariectomy (Ovx) and estradiol-17β (E2) replacement on the brain steroid levels were investigated in the resting and prespawning phases of the female catfish Heteropneustes fossilis. The study showed that Ovx resulted in significant decreases in plasma levels of estradiol-17β (E2) and its precursors, and the effect varied with the reproductive stage and duration. Our study showed that E2 supplementation reversed the effect of Ovx in 3-week Ovx fish group, either restored or increased according to the dose. In contrast, E2 levels increased in the brain after Ovx in the resting stage and produced a biphasic effect of significant decreases on week 1 and 2, and significant increases on week 3, 4 and 5 in the pre-spawning stage. The brain E2 levels significantly inhibited in E2 supplementation groups. The testosterone (T) levels showed biphasic effects, an initial decrease (up to 3 weeks Ovx) and an increase later (week 4, 5) in the resting stage. In the pre-spawning stage, the T levels increased significantly after Ovx. The E2 supplementation significantly inhibited the T levels, more severely in the low dose group in the resting and pre-spawning stages. Brain 17-hydroxyprogesterone(17-OHP4) levels increased (week 1, 2, 3) but decreased on week 4 and 5 of Ovx in the resting stage and increased throughout Ovx in the pre-spawning stage except in the 5th week (though compared to other steroids, level was very low; almost negligible). The E2 replacement significantly decreased the steroid levels further down compared to the Ovx control group. Brain progesterone (P4) and pregnenolone (P5) levels decreased initially (week 1 and 2 Ovx) and recovered later. The E2 replacement significantly decreased P4 levels in the Ovx fish in the pre-spawning stage and in the lower dose group in the resting stage. The P5 levels remained inhibited after the E2 supplementation in the resting stage but unchanged or increased it in the pre-spawning stage. Brain cortisol (F) levels were inhibited initially (1 and 2 weeks and later increased after OVX in the resting stage. In the pre-spawning stage, the F levels increased in the week 1, 2 and 3 of Ovx and decreased in the 4th and 5th weeks. The E2 supplementation inhibited the cortisol (F) levels in both phases. The results show that ovarian steroids influence neurosteroidogenesis in a reproductive stage-dependent manner.