Sex differences and hormone influences on tyrosine hydroxylase immunoreactive cells in the leopard frog

Abstract

We examined sex differences in tyrosine hydroxylase immunoreactive (TH-ir) cell populations in the preoptic area (POA), suprachiasmatic nucleus (SCN), posterior tuberculum (TP), and caudal hypothalamus (Hy) in the leopard frog (Rana pipiens), in addition to the effects of natural variation in sex steroid hormones on these same populations in both sexes. All four of these populations have been shown to be dopaminergic. Gonadal sex, androgens, and estrogen all influenced TH-ir cell numbers, but in a complicated pattern of interactions. After factoring out the effects of sex steroids by multiple regression, TH-ir cell numbers in all four areas differed between the sexes, with males having a greater number of TH-ir cells. The influence of androgens and estrogen differed by region and sex of the animals. Androgens were the main influence on TH-ir cell numbers in the POA and SCN. Plasma androgen concentrations were positively correlated with TH-ir cell numbers in both areas in males. In females, androgen concentration was negatively correlated with TH-ir cell numbers in the POA; there was no significant relationship in the SCN in females. In the more caudal populations, estrogen (E2) levels were positively correlated with TH-ir cell numbers in the TP of both males and females. In the caudal hypothalamus, E2 levels were positively correlated with TH-ir cell numbers in females, but there was no significant correlation in males. The results indicate that gonadal sex imposes a baseline sex difference in the four TH-ir (dopamine) populations, resulting in a higher number of such cells in males. Individual and sex-linked differences in gonadal steroid hormones lead to variation around this baseline condition, with androgens having a greater influence on rostral populations and estrogen on caudal populations. Last, an individual's gonadal sex determines the effect that androgens and estrogen have on each population.

Hormonal state influences aspects of female mate choice in the Túngara Frog (Physalaemus pustulosus)

“…Although our assays are unable to discern whether the androgen pattern is due to a change in testosterone, dihydrotestosterone or both, previous studies have reported that reproductively active female anurans exhibit significantly higher circulating levels of testosterone than dihydrotestosterone (Harvey et al, 1997;Wilczynski et al, 2003;Medina et al, 2004). In addition, levels of testosterone in some female anurans are comparable to male levels and are generally higher than the concentration of estrogen in the plasma (d 'Istria et al, 1974;Licht et al, 1983;Harvey et al, 1997;Wilczynski et al, 2003;Medina et al, 2004).…”

Current research in amphibians: Studies integrating endocrinology, behavior, and neurobiology

“…Circulating plasma testosterone levels are as high in reproductive females as in males (although in males dihydrotestosterone is higher) and higher than estrogen levels in many anuran species (d 'Istria et al, 1974;Licht et al, 1983;Iela et al, 1986;Itoh and Ishii, 1990;Harvey et al, 1997;Wilczynski et al, 2003;Medina et al, 2004;. The behavioral relevance of this, if any, is unclear.…”

Characterization of the Dopamine System in the Brain of the Túngara Frog, <i>Physalaemus pustulosus</i>

“…We describe here the dopaminergic system in P. pustulosus compared with the brains of other anurans, including the African clawed frog ( X. laevis [González et al, 1993]), the marsh frog ( R. ridibunda [González and Smeets, 1991]), the fire-bellied toad ( B. orientalis [Endepols et al, 2006]), and the northern leopard frog ( R. pipiens [Wilczynski et al, 2003]). Overall the distribution of dopaminergic neurons and fibers is highly conserved across amphibians [González and Smeets, 1994] ( table 1 ).…”

“…The distribution of dopamine-producing cells in the amphibian brain in particular has been well studied in several species including the African clawed frog ( Xenopus laevis [González et al, 1993]), the marsh frog ( Rana ridibunda [González and Smeets, 1991]), the fire-bellied toad ( Bombina orientalis [Endepols et al, 2006]), and the northern leopard frog ( Rana pipiens [Wilczynski et al, 2003]). However, it has recently become apparent that all vertebrates except mammals have 2 paralogs encoding TH: th1 and th2 [Filippi et al, 2010;Yamamoto et al, 2010].…”

“…Marín and colleagues [1995] have described the mesolimbic reward system in anurans as dopaminergic projections originating from the posterior tuberculum to the nucleus accumbens. Dopaminergic neurons in the posterior tuberculum are required for phonotaxis behavior in female grey tree frogs [Endepols et al, 2004] and vary in number with sex and gonadal hormone levels in Northern leopard frogs [Chu and Wilczynski, 2002;Wilczynski et al, 2003].…”