Abstract
Individual male rats may systematically display or not copulatory behavior when paired with receptive females. Although these phenotypes are associated with differences in brain organization and function, they might also do so at the level of the reproductive organs. We then used high performance liquid chromatography to quantify serotonin concentration and the activity of tryptophan hydroxylase in the reproductive organs of copulator and non-copulator males. Sexual behavior display was compared between groups and parameters of fertility and reproductive fitness were determined for copulator males. Copulator males had higher concentrations of serotonin in the epididymis, testicle and ventral prostate than their non-copulator counterparts, as it was found for epididymal and testicular tryptophan hydroxylase activity. However, preliminary data shows that serotonin elevation occurs in copulator males only until they have accumulated several sexual encounters, so it might be a response to genital gratification or sexual rewarding. Interestingly, only epididymal serotonin concentration correlated with reproductive fitness, offspring number, mating success and seminal plug volume in copulator males. Our results support that copulator and non-copulator male rats feature a phenotype-specific serotoninergic tone in the epididymis, testicle and ventral prostate gland. The observation documenting that epididymal serotonin concentration correlated with parameters that monitor male fertility and reproductive fitness in copulator males predicts that epididymal factors increase their chances of parenting offspring.
Highlights
Copulatory or consummatory behavior in male rats is displayed as a stereotyped motor pattern that comprises mounts, intromissions and ejaculation [1]
We report data that shows that copulator males have elevated testicular, epididymal and prostatic serotonin concentration and TPH activity as compared with non-copulator males
Differences in copulatory abilities among male rats may be inherent, our results suggest that the increment of the serotoninergic tone in some reproductive organs of copulator males is an acquired trait
Summary
Copulatory or consummatory behavior in male rats is displayed as a stereotyped motor pattern that comprises mounts, intromissions and ejaculation [1]. This pattern suits well the majority of male rats, a small percentage of them exhibit either none or incomplete copulatory behavior when repeatedly paired with sexually receptive females [2]. The present work evaluated possible differences of the serotoninergic tone in reproductive organs of males displaying or not normal copulatory behavior. Studying the serotoninergic tone seems an adequate election because this parameter shifts across genital/reproductive organs as sexual maturation progresses, with reproductive status or photoperiod length and along the breeding season in various different species [7,8,9]. Among other important reproductive processes, ejaculation, seminiferous tubule fluid transit, production and clearance, sexual accessory glands contraction, epididymal fluid composition, testicular steroidogenesis and spermatogenesis [10,11,12,13,14,15]
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