The role of nitric oxide synthase in mediating androgenic gating of male-typical copulatory behavior in whiptail lizards

Abstract

Male-typical copulatory behaviors such as mounting and intromission are dependent on testicular androgens in most vertebrates, being eliminated by castration and re-instated by administration of exogenous testosterone. Testosterone implants in the preoptic area (POA) can re-instate behavior as effectively as systemic testosterone replacement, implicating this area as a critical locus of hormonal gating. The cellular mechanisms underlying this gating phenomenon are not well understood, but according to one model, testosterone induces an up-regulation of nitric oxide synthase (NOS) in the POA, increasing nitric oxide synthesis following exposure to a sexual stimulus. Nitric oxide in turn, possibly through its effect on catecholamine turnover, influences the way the stimulus is processed and enables the appropriate copulatory behavioral response. The experiments described in this Dissertation were designed to test this model as it pertains to hormonal gating in Cnemidophorus lizards. Specifically, experiments were conducted to test the predictions that nitric oxide synthesis inhibition would suppress the expression of behavior; that preoptic nitric oxide synthesis would be greater in animals expressing copulatory behavior; and that preoptic NOS expression, at both the mRNA and the protein levels, would be greater in animals exposed to testosterone than in animals deprived of hormone. All three of these predictions were upheld, offering support to the model as described.