The differential expression of male sexual behavior in the Lewis, Fischer and Sprague-Dawley rat strains.

Several indices of sexual behavior were characterized for male rats of the Lewis (LEW), Sprague-Dawley (SD) and Fischer (F344) strains. Males were permitted access to a receptive female of their own strain for five 50-min sessions every fifth day. LEW males emitted longer latencies (first mount, intromission, ejaculation and post-ejaculatory interval) and lower frequencies (mounts, intromissions, ejaculations, intromission ratio) relative to F344 males, with the SD strain in general, lying intermediate. Following this assessment, males of each strain were randomly assigned to females of their own or another strain to ascertain whether differences were due to differential female receptivity. Although there were no significant differences during this phase indicative of differential receptivity, the sample size may preclude a definitive interpretation of such results. The data were discussed in the context of other behavioral differences between the strains and the possible neurobiological mechanisms underlying these differences.