Effects of Retinal Gonadotropin-Releasing Hormone on Reproductive Behavior and Retinal Activity in the Cichlid Fish, Astatotilapia burtoni

Many animals use visual signals to evade predators, forage for food, and communicate with conspecifics. Some animals that shift into and out of breeding stages, such as fish, can modulate their visual sensitivity to better adapt to changing internal and external conditions. Previous work in our lab demonstrated that females of the cichlid fish Astatotilapia burtoni have improved visual sensitivity when they enter reproductive readiness. However, little is known about how fish and vertebrates more broadly modulate visual sensitivity across their reproductive cycle. We hypothesized that the hormone and neuromodulator gonadotropin-releasing hormone (GnRH) could modulate visual sensitivity because GnRH is a regulator of the reproductive cycle, and some GnRH neurons in the brain project to the retina. To examine the role of GnRH in modulating retinal activity in ovulated female A. burtoni, I first used calcium imaging to observe neural activity. Bath application of GnRH on live retina slices decreased outer nuclear layer fluorescence but increased inner nuclear layer and ganglion cell layer fluorescence. Antide, a GnRH receptor antagonist, following the GnRH had little effect. These data illustrate that GnRH can affect retinal activity. I also injected ovulated female eyes with GnRH or antide and measured changes in reproductive behavior in the presence of a courting male. Sham, GnRH, or antide eye injections in already ovulated females did not affect male courtship behavior, but antide eye injections reduced female responsiveness to courtship overall. In trials where spawning did not happen, GnRH-injected females often chose to intentionally avoid courtship whereas antide-injected females were more likely to not respond to courtship at all. This suggests that the GnRH system in the retina may ultimately impact reproductive decision-making. Lastly, the retinas of the fish from the behavior study were labeled for the neural activation marker, pS6. Higher quantities of cells expressing pS6 were observed in GnRH eye-injected females across all quantified layers (inner nuclear, amacrine cell, and ganglion cell layer). Overall, this study is the first to integrate behavioral and neural activation analyses to show the importance of GnRH in regulating retinal activity and reproductive communication in fish.