The circadian patterns of spontaneous seminal emission, sexual activity and penile reflexes in the rat.

Spontaneous seminal emission (SSE) by sexually naive and experienced rats occurred almost exclusively in the light period of a 14:10 LD cycle. The circadian pattern of SSE slowly shifted following an LD reversal and was completely reversed by three weeks. The diurnal variation in parameters of sexual activity which are associated with sexual arousal shifted much more readily such that it was reversed within one week of the LD reversal. In contract, parameters of sexual behavior which are associated with the ejaculatory mechanism were altered following the LD shift with a phase-shifting pattern more similar to that exhibited for SSE, such that the diurnal variation seen before the LD shift was not reestablished until the third week after the shift. The characteristic pattern of SSE in 14:10 LD lighting was disrupted with two weeks of a shift to constant illumination, but the number and weight of spontaneously produced plugs did not change. Finally, there were no differences in any component of the display of penile reflexes by 29 rats tested in the dark period compared to 19 rats tested in the light period, despite significant circadian variation in the copulatory activity of these animals.