Differential organization of male copulatory patterns in high- and low-yawning-frequency sublines versus outbred Sprague-Dawley rats.

The temporal organization of masculine sexual behavior in rats is highly stereotyped; involving a sequence of mounts, intromissions and ejaculations. Sexual behavior has been described in exogamic and genetically manipulated rodent species. In this work, we compare the male sexual behavior of outbred Sprague-Dawley (SD) to those of rats inbred for high (HY)- and low (LY)- spontaneous yawning frequency. In the first experiment, the percentage of inexperienced rats' ejaculatory behavior is significantly lower in the HY and LY respect to Sprague-Dawley rats. The latency to ejaculate for inexperienced HY was shorter than the LY and SD rats. In the second experiment, we examined the differences between inbred sublines and Sprague-Dawley rats once the subjects had become sexually experienced after four copulatory sessions. HY rats still have slower proportion of ejaculators respect to LY and SD rats. Additionally, postejaculatory latencies were longer for HY rats, with longer intercopulatory intervals and higher number of copulatory bouts that delayed ejaculation. Both sublines show lower copulatory efficiency respect to SD rats. In conclusion, both sublines show alterations in the temporal organization of sexual motor pattern that are due at least partially to strong inbreeding process to select them.

Behavioral differences between selectively bred rats: D1 versus D2 receptors in yawning and grooming.

We used SKF 38393 and quinpirole for determining whether activation of D(1) and D(2) receptors, respectively, is involved in behaviors of rats selectively bred for high or low rates of yawning. After injection of SKF 38393, yawning diminished more markedly in high-yawning (HY) than in low-yawning (LY) rats, whereas this drug increased the number and duration of grooming episodes similarly in both strains. After injection of quinpirole, yawning increased more markedly in HY than in LY rats, whereas this drug decreased the number and duration of grooming episodes similarly in both rat strains. After coadministration of SKF 38393 and quinpirole, yawning increased similarly in both rat strains, whereas the combination of drugs failed to reliably affect grooming behavior. We interpret our findings as indicating that D(2) receptors are more important than D(1) receptors for differences in yawning behavior between HY and LY rats.