Sexual Experience Modulates Partner Preference and mPOA Nitric Oxide Synthase in Female Rats

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Abstract

Sexually experienced female rats return to the male more quickly after intromissions, exhibit shorter interintromission intervals, and spend more time with the male rat during a test of paced mating behavior in comparison to naïve rats. The present study tested whether these changes reflect heightened sexual motivation independent of receipt of vaginocervical stimulation and/or neurochemical changes in the medial preoptic area (mPOA). Ovariectomized, female rats were given estradiol benzoate and progesterone, and then received either 6 paced mating encounters (experienced) or 6 control exposures to an empty paced mating arena (naïve). Experienced and naïve rats received a no-contact partner preference test under oil vehicle and then under hormone on a different day. Hormonal status and sexual experience led to significantly higher preference for the male. Brains were collected 1 hr after both experienced and naïve rats received paced mating to compare mPOA levels of Fos, a marker of neural activity, in response to copulation and nitric oxide synthase (NOS), the enzyme responsible for production of nitric oxide (NO). Expression of NOS was higher in experienced relative to naïve rats, whereas Fos was comparable between the groups. The data are consistent with the idea that both sexual motivation and changes to the mPOA contribute to the shift in paced mating behavior induced by sexual experience.

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