Sexual behavior of female rats in a multiple-partner preference test.

In this study, sexually experienced female rats were tested in a multiple-partner preference test (MPPT) in which they were allowed to pace their sexual contacts with four sexually active males. Four cylinders, with a small hole through which only the female could move freely from one cylinder to another, were assembled forming in the center an empty compartment. An intact female was placed in the central compartment and a sexually active male in each cylinder. Female sexual behavior was analyzed throughout the estrus cycle in four consecutive days. Each daily test lasted 15 min. The percentage of exits after intromission or ejaculation was significantly higher than the percentage of exits after each mount. The female spent significantly longer time with one of the males. We designated this male as the preferred male (PM). Although in each of the 4 days studied, females spent significantly longer time with the PM, however, the male selected was not the same throughout the estrus cycle. The number of entries into the compartment of the PM was significantly higher and increased around proestrus. Compared to previous studies, pacing behavior was notably lower in the conditions of the MPPT. No significant differences were observed during the estrous cycle concerning the other parameters recorded. The present results suggest that the MPPT could be a good model to study partner preference in the female rat.

Monoaminergic and cholinergic stimulation of masculine sexual behavior in neonatally demasculinized male rats.

Sexual behavior during adulthood largely depends upon hormonal events that take place around birth. Administration of the antiestrogen Tamoxifen (Tx) to males immediately after birth induces a marked decrease of masculine sexual behavior during adulthood. On the other hand, it is well known that masculine sexual behavior can be stimulated by the administration of drugs acting specifically on the monoaminergic or the cholinergic systems. This study was performed to analyze if masculine sexual behavior can be pharmacologically stimulated in adult male rats neonatally demasculinized by the administration of Tx. Neonatal administration of Tx induced clear impairments of masculine sexual behavior during adulthood. Administration of oxotremorine (OXO), 8-OH-DPAT (8-hydroxy-2(di-n-propylaminotetraline)), yohimbine (YH), and apomorphine (APO), drugs that normally elicit a stimulation of masculine sexual behavior were unable to fully restore it in demasculinized males. Only slight improvements of some behavioral parameters were observed with 8-OH-DPAT and YH. OXO seems to induce a worsening of sexual behavior impairments. Results obtained with APO were not significantly different from saline controls. Data suggest that neonatal treatment with Tx induces permanent impairments of the neural circuitry regulating masculine sexual behavior not only limited to morphological changes but also functional alterations of the neurotransmitter systems.

Masculine sexual behavior features in the Flinders sensitive and resistant line rats.

The Flinders sensitive (FSL) and resistant (FRL) lines of rats have been selectively bred for their differences in cholinergic sensitivity. The FSL rats display hypersensitive responses to agonists of muscarinic receptors. In addition, the FSL rats display behavioral alterations that support the notion that this strain could be useful as an animal model of depression. These abnormalities include increase in rapid eye movement sleep, decrease of saccharin consumption after stress, and reduced exploratory behavior in a novel open field. On the other hand, sexual behavior is a pleasure-seeking behavior that should be altered in a mood disorder characterized by anhedonia. In the present study, spontaneous masculine sexual behavior features were analyzed, both during 30-min tests as well as during a satiety test. Results showed that, compared to outbred Sprague-Dawley (SD) rats, both the FSL and the FRL rats displayed some behavioral impairment, like a marked decrease of the ejaculatory frequency. During the satiety tests, both the FSL and the FRL rats became exhausted sooner than their SD controls. In addition to considering the present results in terms of alterations in specific neurotransmitter systems, endogamy is proposed as a possible source of the behavioral alterations.