Thyrotropin-releasing hormone facilitates display of reproductive behavior and locomotor behavior in an amphibian

Abstract

In the amphibian brain, thyrotropin-releasing hormone (TRH) is present in many regions outside the hypothalamus. The functions of this extrahypothalamic TRH however are unknown. We sought to determine whether TRH or its metabolites altered reproductive behaviors (amplectic clasping behavior) or locomotor behaviors of the male South African clawed frog, Xenopus laevis. TRH-injected (100 μg; dorsal lymph sac injection) male Xenopus displayed significantly fewer amplectic clasp attempts and longer clasp durations than saline-injected controls. The TRH metabolites, TRH acid and histidylproline diketopiperazine, similarly altered clasping behavior. Several hormones released by TRH, including thyroid-stimulating hormone, melanocyte-stimulating hormone, prolactin, and dopamine, had no significant effect on clasp frequency or duration. Locomotor activity in Xenopus males was increased significantly after 15 min following TRH injection (150 μg); this effect persisted for at least 1 hr. The metabolites did not alter locomotion. These studies indicate that TRH can facilitate the display of two behaviors in the South African clawed frog. Effects of TRH on locomotor and reproductive behaviors thus appear in several vertebrate classes. These behavioral actions of TRH likely occur through different mechanisms or at different sites.