Reflexive testosterone release: a model system for studying the nongenomic effects of testosterone upon male behavior

Abstract

Male mammals of many species exhibit reflexive testosterone release in mating situations. In house mice (Mus musculus), the dramatic robustness of such release, occurring primarily in response to a novel female, suggests some function. The resulting testosterone elevations typically peak during copulatory behavior and may serve to activate transitory motivational and physiological responses that facilitate reproduction. However, such a function requires that testosterone be working through either nongenomic, or very quick genomic, mechanisms. The first part of the review describes reflexive sex hormone release in house mice. The second part summarizes research implicating testosterone's fast actions in affecting anxiety, reward, learning, analgesia, and penile reflexes in rodents, all of which could optimize male mating success. The review concludes with a speculative model of how spontaneous and reflexive hormone release might interact to regulate reproductive behavior and why mice appear to be an ideal species for examining testosterone's quick effects.

Figure 1

A representative depiction of changes in plasma hormone levels during spontaneous testosterone and LH release in a male house mouse. While interpulse intervals are quite variable, the figure illustrates the dramatic plasma hormone changes during male mouse pulsatile release. Adapted from data collected by Coquelin and Desjardins [4]. See text for more explanation.

Figure 2

A representative depiction of reflexive sex hormone release in a male house mouse during a mating encounter. Encountering a female causes anticipatory release, while ejaculation causes ejaculatory release. The timing of LH release in relation to ejaculation is adapted from Coquelin and Bronson [8], the approximate timing of copulatory behavior and postejaculatory interval (PEI) in relation to ejaculation adapted from Nyby [27] and the testosterone titers inferred from the time between LH and testosterone release reported by Coquelin and Desjardins [4]. See text for more explanation.

Figure 3

A hypothetical model of how spontaneous and reflexive testosterone release might affect adult male reproductive physiology and behavior. See the text for an explanation of the various events (A-K) are hypothesized to be involved.