Genital Sensation: CNS Targets and Functions in Females

comments on Erskine and Lee paper

Barry R. Komisaruk

Dear Mary and Jeung-Woon,
I enjoyed your paper and am happy to see that you, too, find analgesia to mating, although short-lived.  In our study  (Gomora, Beyer, Gonzalez-Mariscal and Komisaruk, 1994: Momentary analgesia produced by copulation in female rats. Brain Research, 656:52-58), we also found a strong analgesia (in the female, at the males' ejaculation, the magnitude of the females' analgesia was equivalent to more than 15mg/kg body weight of morphine sulfate, calibrated using the same, tail shock-induced vocalization threshold).  However, in determining the duration of this strong analgesia, we found that when measured 10-15 SECONDS later, the vocalization thresholds had returned to pre-mating baseline.  The threshold was measured instantaneously (i.e. probability of vocalizing to a measured intensity of 100 msec-duration tail shock).  Perhaps your latency to measure tail flick latency after matings was at or more than 15 seconds, and this could well have reduced the likelihood of finding analgesia.  We had initially tried using the tail flick latency measure, but found little, if any, effect.  The during-intromission and during-ejaculation threshold determination measure that we used showed much clearer effects, the during-intromission analgesia being equivalent to about 10mg/kg morphine sulfate.  

In addition, with repeated vaginocervical stimulation we see an "exhaustion" of analgesia, which is consistent with the hyperalgesia that you observe after repeated matings.  

Do you think it is possible that the decrease in fos expression that you see in the spinal cord is due to inhibition of A-delta afferents which carry not only nociceptive, but also pressure afferent activity?
That could account for at least some of the attenuation of response that you see.

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