Testosterone Stimulates Mounting Behavior and Arginine Vasotocin Expression in the Brain of both Sexual and Unisexual Whiptail Lizards

Abstract

In nonmammalian vertebrates the abundance of arginine vasotocin (AVT) neurons in the brain is sexually dimorphic, a pattern that is modulated by testicular androgen. This peptide is thought to be involved in the control of male-typical mounting behaviors. The all-female desert-grasslands whiptail (Cnemidophorus uniparens) reproduces by obligate parthenogenesis and in nature no males exist, but eggs treated with aromatase inhibitor hatch into individuals (called virago C. uniparens) having testes, accessory sex structures, high circulating concentrations of androgens, and exhibiting only male-like copulatory behavior. To examine the ‘sexual’ dimorphism of AVT-containing neurons in these animals, we compared AVT immunoreactivity in gonadectomized control and virago C. uniparens, with that of gonadectomized male and female Cnemidophorus inornatus, a sexual species that is the maternal ancestor to the parthenogenetic species. Mounting behavior is elicited in both species and both sexes by testosterone, and it was predicted that the distribution and abundance of AVT cell bodies and fibers would reflect the propensity of males and females of the two species to display male-typical copulatory behavior. Since both this propensity and AVT abundance are controlled by androgens, we compared testosterone-implanted and control animals within each group. Testosterone treatment generally increased AVT abundance, except in lab-reared parthenoforms, in which testosterone treatment was the least effective in inducing male-like copulatory behavior.

Sexually Dimorphic Effects of Melatonin on Brain Arginine Vasotocin Immunoreactivity in Green Treefrogs <b><i>(Hyla cinerea)</i></b>

“…For example, increased androgen concentrations during the breeding season may regulate changes in the production and/or release of AVT in this and other socially breeding vertebrates. Indeed, increased AVT/AVP levels in the brain are associated with increased androgen concentrations in males across many species [Goodson and Bass 2001; De Vries and Panzica 2006; Hillsman et al 2007; Kabelik et al 2008]. However, decreased AVP immunoreactivity occurs in male mice lacking a functional gene for aromatase, the enzyme that metabolizes androgens to estrogens [Plumari et al 2002].…”

Sex and species differences in plasma testosterone and in counts of androgen receptor-positive cells in key brain regions of Sceloporus lizard species that differ in aggression

“…In prairie voles, the lateral habenula also receives arginine-vasopressin (AVP) projections from the bed nucleus of the stria terminalis, and these projection are sexually-dimorphic [42]. The vasotocinergic system plays diverse roles in vertebrate social behavior [50], including reptiles [e.g., 32] and should also be exampled in Sceloporus . Differences in brain estrogen receptors may also contribute to species differences in aggression [67, 70], and should be explored in this system.…”

Possible hormonal interaction for eliciting courtship behavior in the male newt, Cynops pyrrhogaster

“…AVT neurons that play an active role in the expression of male-typical sexual behaviors in many vertebrate species exhibit a sexual dimorphism, with males having a greater number of AVT cells than females in various brain areas involved in regulating the sexual behaviors (Boyd et al, 1992;Boyd, 1994;Marler et al, 1999;Moore et al, 2000;Goodson and Bass, 2001). Sexual dimorphism develops and is maintained by androgen (Panzica et al, 2001;Hillsman et al, 2007;Kabelik et al, 2008), and androgen also enhances the expression of AVT precursor mRNA (Panzica et al, 1999;Aste et al, 2013). It is likely, therefore, that the flutamide-induced suppression of the tail vibration behavior as observed in our experiments is, at least partly, due to a shortage of AVT.…”