EJACULATION INDUCED CHANGES IN ESCAPE LATENCY IN THE HOT PLATE TEST -PHARMACOLOGICAL ANALYSIS OF ANXIOLYTIC VERSUS ANALGESIC EFFECT

The possible changes in nociception at various stages of male sexual b ehaviour were explored in the hot plate test. Although other authors h ave reported an antinociceptive effect of mating, we failed to find th is effect on the hot plate test after several sexual behaviour events. To further explore the possible antinociceptive action of copulation we administered a suboptimal analgesic dose of morphine (0.3 mg/kg i.p .). No change in nociception were observed in animals treated with a s ubthreshold dose of morphine and tested in the nociception test after ejaculation were observed. Since previous reports have refered that ej aculation produces hypoalgesia when measured in the hot plate test, we attempted to replicate these findings. We found that one ejaculation produces an increase in the latency to escape in male rats previously habituated to the hot plate test. These results suggest a hypoalgesic effect. However, such changes could also be interpreted as alterations in the animals' emotionality. Thus, a group of habituated animals was tested on the switched off plate. An important increase in the escape latency behaviour after ejaculation was observed, while no difference s between control animals, without sexual behaviour display, tested on switched on and snitched off plate were observed. The participation o f the benzodiazepine and opiod systems in the ejaculation effect on th e switched off plate was explored. A similar increase in escape latenc y to that induced by ejaculation was caused by diazepam (1.0 and 2.0 m g/kg). The increase in escape latency induced by ejaculation was preve nted by the benzodiazepine antagonist, flumazenil (20.0 mg/kg). Conver sely, the opiate antagonist, naloxone (1.0 mg/kg), was unable to rever se the increase in escape latency provoked by ejaculation. Morphine (O .5 mg/kg) did not elicit an increase in the escape latency behaviour. All data support the idea that the hot plate test might reveal false d ata respect a putative algesic change after ejaculation in male rats.