Kisspeptin neurons as a key player bridging the endocrine system and sexual behavior in mammals.

Reproductive behaviors are sexually differentiated: for example, male rodents show mounting behavior, while females in estrus show lordosis behavior as sex-specific sexual behaviors. Kisspeptin neurons govern reproductive function via direct stimulation of gonadotropin-releasing hormone (GnRH) and subsequent gonadotropin release for gonadal steroidogenesis in mammals. First, we discuss the role of hypothalamic kisspeptin neurons as an indispensable regulator of sexual behavior by stimulating the synthesis of gonadal steroids, which exert "activational effects" on the behavior in adulthood. Second, we discuss the central role of kisspeptin neurons that are directly involved in neural circuits controlling sexual behavior in adulthood. We then focused on the role of perinatal hypothalamic kisspeptin neurons in the induction of perinatal testosterone secretion for its "organizational effects" on masculinization/defeminization of the male brain in rodents during a critical period. We subsequently concluded that kisspeptin neurons are key players in bridging the endocrine system and sexual behavior in mammals.

The age-dependent effect of pre-pubertal castration on anxiety-like behaviour in male rats.

Adolescence is considered to be a critical period of sex hormone action (re)organising the brain and determining the behavioural phenotype. Such organisational effects in the brain might be the cause of sex differences in some behavioural features. In this experiment, we aimed to examine the role of pubertal sex hormones in development of anxiety in male rats. Male rats underwent gonadectomy prior to puberty onset, and were tested for explorative and anxiety-like behaviour in adolescence as well as in young adulthood. In adolescence, but not in adulthood, gonadectomised rats spend by 50% more time (p < .05) in the centre zone of the open-field than sham-operated counterparts. Young adult gonadectomised rats showed approximately 1.5-fold greater exploratory activity, in both open field (p < .001) and elevated plus maze (p < .01), in comparison with young adult control rats. Our results indicate that pre-pubertal castration may have test-specific anxiolytic effect in adolescent male rats, and it may attenuate the decline in explorative behaviour in young adult males. These differences in short- and long-term effects of gonadectomy could explain some contradictory results of previous studies on the role of testosterone in anxiety-like behaviour of male rodents. Thus, the age-specific consequences of pre-pubertal hormone deprivation should be considered.

An exploration of the hypothesis that testosterone is implicated in the psychological functioning of women with polycystic ovary syndrome (PCOS).

One of the diagnostic features of polycystic ovary syndrome (PCOS) is elevation of the androgen, testosterone. It is known that women with PCOS are more likely to suffer from psychological problems, especially anxiety and depression, than other women. However, little is known of how much of this is due to testosterone, and if so, what the mechanism(s) might be. This study explores the hypothesis that testosterone impacts women with PCOS both directly and indirectly, via testosterone currently in the bloodstream and through prenatal exposure. It is hypothesised that direct effects occur when testosterone acts directly upon receptors; indirect effects occur where the impact of testosterone is mediated via another variable; activational effects are ephemeral and are caused by testosterone in the bloodstream; organizational effects occur prenatally and cause permanent changes. Four pathways are hypothesised in this paper: 1/ a direct and activational pathway which improves mental rotation ability; 2/ an indirect and activational pathway, whereby distress is caused when the physiological symptoms of testosterone are experienced as embarrassing or otherwise disturbing; 3/ an indirect and organizational effect on mood, where elevated prenatal testosterone predisposes women with PCOS to low blood sugar levels and thus low mood; 4/ and finally, it is suggested that the pathway from biology to psychology can be travelled in reverse, with a direct activational effect of relaxation training on the reduction of adrenal androgens. Testing these hypotheses has important implications for our understanding of PCOS, and our ability to treat this condition more effectively.

Testosterone influences song behaviour and social dominance - but independent of prenatal yolk testosterone exposure.

In the last two decades, maternally derived yolk androgens have been shown to significantly alter offspring development, and a number of these effects persist into adulthood. However, little is known about their underlying mechanisms. Mechanisms that have been suggested are changes in the endogenous androgen production post-hatching or changes in the sensitivity towards circulating androgens. We tested the effects of yolk testosterone on the plasma testosterone levels and the sensitivity to testosterone in 5months old male canaries that hatched from eggs that were either injected with testosterone (yT-males) or with a control solution (yC-males). Changes in sensitivity were investigated via the behavioural response to an experimental elevation of the plasma testosterone levels. We performed the experiment in fall (low endogenous testosterone production), focusing on testosterone dependent response traits (aggression and song). Before implantation, there was a non-significant trend that the plasma testosterone levels were lower in yT-males than in yC-males. Elevating the plasma testosterone concentrations increased aggressiveness, song bout length and similarity of repeated song elements (=consistency), with the latter likely being a consequence of testosterone-driven song crystallization. However, these effects were not different among yT- or yC-males in any of the parameters. Thus, our findings render it unlikely that changes in the sensitivity to testosterone post-hatching would form the main underlying mechanism of hormone-mediated maternal effects in birds. Further experiments are urgently needed in order to understand the nature of the phenotypic effects resulting from embryonic exposure to maternal yolk testosterone.