Cesar A. Perez

Enhaced D2-type receptor activity facilitates the development of conditioned same-sex partner preference in male rats☆

Animal models have shown that the neural bases of social attachment, sexual preference and pair bonds, depend on dopamine D2-type receptor and oxytocin activity. In addition, studies have demonstrated that cohabitation can shape partner preference via conditioning. Herein, we used rats to explore the development of learned same-sex partner preferences in adulthood as a result of cohabitation during enhanced D2 activity. Experimental Wistar males (N=20), received saline or the D2 agonist (quinpirole) and were allowed to cohabitate during 24 h, with a stimulus male partner that bore almond scent on the back as conditioned stimulus. This was repeated every 4 days, for a total of three trials. Four days later they were drug-free tested for partner preference between the scented male partner and a sexually receptive female. Sexual partner preference was analyzed by measuring frequency and latency for appetitive and consummatory sexual behaviors, as well as non-contact erections. Social preference was also analyzed by measuring the frequency and latency of visits, body contacts and time spent together. Results indicated that only quinpirole-treated males displayed sexual and social preference for the scented male over the sexually receptive female. They spent more time together, displayed more body contacts, more female-like proceptive behaviors, and more non-contact erections. Accordingly, conditioned males appeared to be more sexually aroused and motivated by the known male than by a receptive female. We discuss the implications of this animal model on the formation of learned homosexual partner preferences.

Multiunit Recording of the Cerebellar Cortex, Inferior Olive, and Fastigial Nucleus During Copulation in Naive and Sexually Experienced Male Rats

The sexual behavior of male rats constitutes a natural model to study learning of motor skills at the level of the central nervous system. We previously showed that sexual behavior increases Fos expression in granule cells at lobules 6 to 9 of the vermis cerebellum. Herein, we obtained multiunit recordings of lobules 6a and 7 during the training period of naive subjects, and during consecutive ejaculations of expert males. Recordings from both lobules and the inferior olive showed that the maximum amplitude of mount, intromission, and ejaculation signals were similar, but sexual behavior during training tests produced a decrease in the amplitude for mount and intromission signals. The fastigial nucleus showed an inverse mirror-like response. Thus, the cerebellum is involved in the neural basis of sexual behavior and the learning of appropriate behavioral displays during copulation, with a wiring that involves the cerebellar cortex, inferior olive, and fastigial nucleus.

Histological modifications of the rat prostate following transection of somatic and autonomic nerves

It is known that hormones influence significantly the prostate tissue. However, we reported that mating induces an increase in androgen receptors, revealing a neural influence on the gland. These data suggested that somatic afferents (scrotal and genitofemoral nerves) and autonomic efferents (pelvic and hypogastric nerves) could regulate the structure of the prostate. Here we assessed the role of these nerves in maintaining the histology of the gland. Hence, afferent or efferent nerves of male rats were transected. Then, the ventral and dorsolateral regions of the prostate were processed for histology. Results showed that afferent transection affects prostate histology. The alveoli area decreased and increased in the ventral and dorsolateral prostate, respectively. The epithelial cell height increased in both regions. Efferent denervation produced dramatic changes in the prostate gland. The tissue lost its configuration, and the epithelium became scattered and almost vanished. Thus, afferent nerves are responsible for spinal processes pertaining to the trophic control of the prostate, activating its autonomic innervation. Hence, our data imply that innervation seems to be synergic with hormones for the healthy maintenance of the prostate. Thus, it is suggested that some prostate pathologies could be due to the failure of the autonomic neural pathways regulating the gland.

Influence of the paraventricular nucleus and oxytocin on the retrograde stain of pubococcygeus muscle motoneurons in male rats.

Lumbosacral cord motoneurons innervating the pubococcygeus muscle (Pcm) at the pelvic floor of male rats were analyzed. We showed previously that these motoneurons participate in sexual functions and are sensitive to fluctuations of systemic androgen and estrogen. Though estrogen receptors have not been identified in Lamina IX at these spinal areas, the release of oxytocin from the paraventricular nucleus of the hypothalamus (PvN) has been found to control pelvic sexual physiology. We therefore worked on the hypothesis that steroid hormones in the PvN induce the release of oxytocin at the lumbosacral level to modulate the function of Pcm motoneurons. Four experiments were developed, and results were observed with the retrograde staining of motoneurons with horseradish peroxidase. Data indicated that morphometric parameters of Pcm motoneurons were significantly reduced after castration or blocking of the steroids at the PvN site, or following complete transection of the spinal cord at the T8 level. In each case, the reduction of the stain was recovered after intrathecal treatment with oxytocin. Thus, present results show that Pcm motoneurons respond to spinal oxytocin. The conclusive model that we propose is that steroids stimulate the PvN, causing the nucleus to release oxytocin at the level of the lumbosacral spinal cord, and the release of the peptide regulates the spread of the stain of Pcm motoneurons. This work also shows that motoneurons distal to a transected area in the spinal cord could respond to exogenous oxytocin, an important finding for the research of spinal cord lesioned subjects.

Sexual behavior and locomotion induced by sexual cues in male rats following lesion of Lobules VIa and VII of the cerebellar vermis.

The cerebellum is an important contributor to the neural basis of sexual behavior, but the specific cerebellar regions underlying different aspects of reproduction are still unknown. Here, we used experimental lesions of Lobules VIa and VII of the vermis to investigate their specific role, both in locomotion stimulated by sexual cues and the execution of sexual behavior. Sexually experienced male rats and receptive females were used, and experimental males received an electrolytic lesion of either lobule. Before and after the lesion, males were tested for sexual behavior, and for locomotion on a horizontal or ascending bar to reach an estrous female. The lesion of Lobule VIa produced impairments in intromission-related behaviors during copulation, and produced slippery footsteps that increased the time to cross the bars with a stronger effect on the ascending bar. The lesion of Lobule VII produced a dramatic arrest of respiration that precluded further behavioral tests. These results suggested that Lobule VIa is involved in the integration of sensory inputs coming from in-copula penile stimulation, implying the existence of a penis-cerebellum neural pathway for a proprioception-like process involved in the proper spatial orientation of the erected penis. Walking on bars showed an alteration of the stepping cycle that suggests the role of Lobule VIa in the fine tuning of locomotion spinal reflexes. The lesion of Lobule VII suggested its role in the physiology of respiration, a topic that deserves further research.

Olfactory conditioned same-sex partner preference in female rats: Role of ovarian hormones

ABSTRACT The dopamine D2‐type receptor agonist quinpirole (QNP) facilitates the development of conditioned same‐sex partner preference in males during cohabitation, but not in ovariectomized (OVX) females, primed with estradiol benzoate (EB) and progesterone (P). Herein we tested the effects of QNP on OVX, EB‐only primed females. Females received a systemic injection (every four days) of either saline (Saline‐conditioned) or QNP (QNP‐conditioned) and then cohabited for 24 h with lemon‐scented stimulus females (CS +), during three trials. In test 1 (female‐female) preference was QNP‐free, and females chose between the CS + female and a novel female. In test 2 (male‐female) they chose between the CS + female and a sexually experienced male. In test 1 Saline‐conditioned females displayed more hops & darts towards the novel female, but QNP‐conditioned females displayed more sexual solicitations towards the CS + female. In test 2 Saline‐conditioned females displayed a clear preference for the male, whereas QNP‐conditioned females displayed what we considered a bisexual preference. We discuss the effect of dopamine and ovarian hormones on the development of olfactory conditioned same‐sex preference in females. HIGHLIGHTSConditioned same‐sex partner preference (CSSP) has been reported in naïve male ratsCSSP is formed during same‐sex cohabitation under enhanced D2‐type activityCSSP does not occur in ovariectomized, hormone‐primed (EB + P) femalesHerein, we induced CSSP in ovariectomized EB‐only treated femalesWe discuss the role of ovarian hormones and dopamine in the development of CSSP