Sarah H. Meerts

Female rats exhibit a conditioned place preference for nonpaced mating

Paced, but not nonpaced, mating behavior is reported to induce a conditioned place preference (CPP) in female rats. Contrary to these previous findings, Experiment 1 showed that female rats that received 15 intromissions from a single male rat during each of five conditioning sessions exhibited a CPP for the compartment associated with mating when the intromissions were delivered via a paced or nonpaced paradigm. Experiment 2 demonstrated that nonpaced mating induced a CPP when a single male delivered the 15 intromissions but not when the male was replaced following ejaculation and a new male allowed to complete the requisite number of intromissions. These findings invite reevaluation of the reinforcing aspects of mating behavior in female rats.

Artificial vaginocervical stimulation induces a conditioned place preference in female rats.

Female rats express a conditioned place preference (CPP) for a context paired with mating. During a mating encounter, the female rat is exposed to several different types of stimuli, including, but not limited to, vaginocervical stimulation and social contact. The present experiment tested the hypothesis that two components of the mating interaction, vaginocervical stimulation or social contact, each induce a CPP in female rats. During conditioning rats received nonpaced mating, artificial vaginocervical stimulation, social interaction or a control treatment. Rats expressed a CPP for the context paired with nonpaced mating or artificial vaginocervical stimulation whereas social interaction and the control treatment did not induce a CPP. The present findings highlight the important role that vaginocervical stimulation plays in the reinforcing effects of mating in female rats.

Sex-and age-specific effects of anabolic androgenic steroids on reproductive behaviors and on GABAergic transmission in neuroendocrine control regions

Illicit use of anabolic androgenic steroids (AAS) has become a prevalent health concern not only among male professional athletes, but, disturbingly, among a growing number of women and adolescent girls. Despite the increasing use of AAS among women and adolescents, few studies have focused on the effects of these steroids in females, and female adolescent subjects are particularly underrepresented. Among the hallmarks of AAS abuse are changes in reproductive behaviors. Here, we discuss work from our laboratories on the actions of AAS on the onset of puberty and sexual behaviors in female rodents, AAS interactions and sex- and age-specific effects of these steroids on neural transmission mediated by gamma-aminobutyric acid receptors within forebrain neuroendocrine control regions that may underlie AAS-induced changes in these behaviors.

Conditioned place preference for mating is preserved in rats with pelvic nerve transection.

Female rats exhibit a conditioned place preference (CPP) for a context paired with mating. The present experiment tested the hypothesis that the activation of the pelvic nerve mediates the reinforcing effects of mating for female rats. Rats underwent bilateral pelvic nerve or sham transection and then received paced mating, nonpaced mating, or the control treatment during a CPP procedure. Pelvic nerve transection did not affect the CPP for paced or nonpaced mating. In tests of paced mating behavior, contact-return latencies following intromissions were significantly shorter in rats with pelvic nerve transection than they were in rats with sham transections. These results show that the pathway conveying the reinforcing effects of mating stimulation does not depend on the integrity of the pelvic nerve, but that activation of the pelvic nerve contributes to the display of paced mating behavior.

Lesions of the medial preoptic area interfere with the display of a conditioned place preference for vaginocervical stimulation in rats.

The present study examined the effect of ibotenic acid lesions of the medial preoptic area (mPOA) on the expression of a conditioned place preference (CPP) for vaginocervical stimulation. Rats with bilateral lesions of the mPOA failed to display the CPP for vaginocervical stimulation shown by rats with sham or incomplete lesions. These findings provide additional support for the role of the mPOA in the neural circuitry underlying the reinforcing effects of female sexual behavior and raise the possibility that the altered pattern of approach and withdrawal behavior observed following lesions of the mPOA may be attributable in part to a diminution of the reinforcing effects of vaginocervical stimulation.

Stimulus animal characteristics do not modulate the expression of partner preference by female rats

The stimulus animals used in tests of partner preference in female rats vary. To test the hypothesis that the alternative stimulus animal modulates the preference for an intact male, gonadectomized (GDX) female rats received estradiol benzoate plus progesterone or the oil vehicle and were tested for partner preference with either an intact male paired with a GDX hormone-primed female or an intact male paired with a GDX male. Rats were tested under conditions that limited physical contact (No Contact) or allowed sexual interaction (Contact). Stimulus animal condition was not a primary determinant of partner preference. In contrast, contact condition and hormone treatment modulated preference, as well as activity levels and the display of proceptive behaviors. Our findings demonstrate that the characteristics of the alternative stimulus animals tested here do not play a significant role in modulating partner preference in female rats.

Zaprinast, a Phosphodiesterase Type-5 Inhibitor, Alters Paced Mating Behavior in Female Rats

Nitric oxide (NO) is the primary mediator of blood flow in female genital tissues and drugs that enhance the activity of nitric oxide, such as phosphodiesterase type-5 (PDE-5) inhibitors, increase vaginal blood flow in anesthetized rats. The goal of the present study was to test the effects of one PDE-5 inhibitor, zaprinast, on the display of sexual behaviors in gonadectomized, estrogen- and progesterone-treated female rats. Experiment 1 demonstrates that zaprinast alters paced mating behavior by lengthening the contact-return latency to ejaculation; there is a significant relationship between dose of zaprinast (range 1.5-6 mg/kg) and contact-return latency to ejaculation. Experiment 2 illustrates that zaprinast has no effect on preference for an intact male as measured in a No Contact partner preference test. Rats receiving zaprinast tend to exhibit reduced locomotor activity in both experiments. Collectively, these findings demonstrate that modulation of the NO-cGMP pathway using a PDE-5 inhibitor alters the display of paced mating behaviors in rats.

Paced mating behavior persists in rats with vaginocervical Lidocaine.

The present study tested whether the topical application of a local anesthetic (Lidocaine) to the vaginocervical region altered the pattern of paced mating behavior displayed by gonadectomized, hormone-primed female rats. Both rats receiving Lidocaine and rats receiving vehicle exhibited the expected lengthening of contact-return latency as the intensity of the mating stimuli increased (mount<intromission<ejaculation). Although rats given Lidocaine versus vehicle received a greater number of intromissions, no other group differences were observed. The present study found no evidence for a change in behavioral responsiveness following the vaginocervical application of Lidocaine.

Genitosensory nerve modulation of paced mating behavior: evidence for pelvic, but not hypogastric, nerve influence.

The pelvic nerve is known to play a role in the behavioral and neurochemical responses exhibited during paced mating behavior. The present study extended the analysis of the contribution of the genitosensory nerves to the display of paced mating behavior to include bilateral hypogastric nerve transection, bilateral pelvic nerve transection, or transection of both the hypogastric and pelvic nerves. Rats with pelvic nerve transection were less likely to exit the male compartment, took longer to exit the male compartment following intromissions, and returned to the male more quickly following intromissions compared to rats with an intact pelvic nerve. In contrast, hypogastric nerve transection alone did not affect paced mating and had no modulating effect on the paced mating behavior of rats with pelvic nerve transection. Our results support the view that key aspects of paced mating behavior are modulated by signals transmitted via the pelvic nerve, without any discernable contribution from the hypogastric nerve.

Sexual experience modulates partner preference and mPOA nitric oxide synthase in female rats.

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. (PsycINFO Database Record