Biomedical subjects

Raúl G Paredes

Publications and source records attributed to Raúl G Paredes.

13 recordsLinked to original sources

PubMed2006

Olfactory, partner preference and Fos expression in the vomeronasal projection pathway of sexually sluggish male rats.

Sexually sluggish (S) male rats take a long time to ejaculate or sometimes they don't achieve ejaculation when tested on repeated occasions with receptive females. In order to further understand what factors might contribute to the inconsistent display of sexual behavior in these animals and determine if S and non-copulating males have a different neurobiological profile, the present study was design to characterize sex-related behaviors of S male rats. We tested their preference to physically interact between a sexually receptive female and a sexually active male. We also tested whether S males have a preference to investigate soiled bedding from females in estrous, anestrous or clean bedding. We also evaluated if the serum hormonal levels of testosterone (T) and estradiol (E) are different between copulating (C) and S male rats. Finally, we compared the neuronal activity of the vomeronasal projection pathway of C and S male rats exposed to estrous bedding. The results indicate that S male rats increased the percentage of animals displaying mounts and intromissions after repeated testing with receptive females but no increased was observed in the percentage of animals displaying ejaculations (a total of nine tests were performed). Both C and S males had a clear preference to interact with a sexually receptive female. Both groups showed a clear preference for bedding from estrous females as opposed to anestrous or clean bedding. However, the time investigating the estrous bedding was significantly lower for the S in comparison to C rats. No differences in the serum levels of T and E were found. The structures of the vomeronasal projection pathway were equally activated by estrous bedding in C and S male rats. The results indicate that S male rats do not have hormonal alterations or deficient processing of sexually relevant olfactory cues. Although S males showed a reduced preference for estrous bedding, no changes in preference for a receptive female were observed.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

Prenatal blockade of androgen receptors reduces the number of intromissions needed to induce conditioned place preference after paced mating in female rats.

Estrous female rats pace their coital contacts to control the rate of cervical/vaginal stimulation. Females that receive at least 10 paced intromissions develop a reward state, evaluated by conditioned place preference (CPP), whereas females that do not pace their coital contacts do not develop CPP. We asked if the blockade of androgen receptors could modify the number of intromissions needed during paced mating to develop CPP. Pregnant females received daily injections of the androgen receptor antagonist flutamide from day 12 of pregnancy until pups were born. When adults, females exposed prenatally to flutamide or vehicle were ovariectomized and hormonally primed to evaluate if paced and non-paced mating induced CPP. The prenatal flutamide treatment did not affect the capacity of females to develop CPP to a systemic morphine injection. Flutamide-treated females that paced their sexual contacts developed CPP with fewer intromissions than control females. No effect on conditioning was observed when females were not allowed to pace their sexual contacts. The results suggest the existence of a threshold of cervical/vaginal stimulation that correlates with the induction of a reward state and that this threshold can be reduced by prenatal blockade of androgen receptors.

Androgen Antagonists↗

PubMed2004

Sexual experience and conditioned place preference in male rats.

We have previously shown that sexual behavior induces a reward state, as evaluated by conditioned place preference (CPP), only when males or females are able to control the rate of sexual interaction. In the present experiment, we evaluated if male rats that are repeatedly tested in a situation in which they are not able to control the sexual interaction eventually develop CPP. Three groups of sexually naïve male rats were used. One group never mated. A second group was tested once a week for 10 consecutive weeks in a chamber in which they controlled the rate of the sexual interaction. The third group was mated for the same number of weeks in a chamber in which the female, but not the male, controlled mating. The three groups were then tested for CPP. Only the group able to control the sexual interaction developed CPP. The group that had no control over the rate of the sexual interaction did not develop CPP even after 10 tests in which they consistently displayed sexual behavior. These results suggest that an estrous female and/or sexual behavior are powerful incentives that maintain mating even if the rewarding properties of the incentive are reduced.

Animals↗

PubMed2004

Has dopamine a physiological role in the control of sexual behavior? A critical review of the evidence.

The role of dopaminergic systems in the control of sexual behavior has been a subject of study for at least 40 years. Not surprisingly, reviews of the area have been published at variable intervals. However, the earlier reviews have been summaries of published research rather than a critical analysis of it. They have focused upon the conclusions presented in the original research papers rather than on evaluating the reliability and functional significance of the data reported to support these conclusions. During the last few years, important new knowledge concerning dopaminergic systems and their behavioral functions as well as the possible role of these systems in sexual behavior has been obtained. For the first time, it is now possible to integrate the data obtained in studies of sexual behavior into the wider context of general dopaminergic functions. To make this possible, we first present an analysis of the nature and organization of sexual behavior followed by a summary of current knowledge about the brain structures of crucial importance for this behavior. We then proceed with a description of the dopaminergic systems within or projecting to these structures. Whenever possible, we also try to include data on the electrophysiological actions of dopamine. Thereafter, we proceed with analyses of pharmacological data and release studies, both in males and in females. Consistently throughout this discussion, we make an effort to distinguish pharmacological effects on sexual behavior from a possible physiological role of dopamine. By pharmacological effects, we mean here drug-induced alterations in behavior that are not the result of the normal actions of synaptically released dopamine in the untreated animal. The conclusion of this endeavor is that pharmacological effects of dopaminergic drugs are variable in both males and females, independently of whether the drugs are administered systemically or intracerebrally. We conclude that the pharmacological data basically reinforce the notion that dopamine is important for motor functions and general arousal. These actions could, in fact, explain most of the effects seen on sexual behavior. Studies of dopamine release, in both males and females, have focused on the nucleus accumbens, a structure with at most a marginal importance for sexual behavior. Since accumbens dopamine release is associated with all kinds of events, aversive as well as appetitive, it can have no specific effect on sexual behavior but promotes arousal and activation of non-specific motor patterns. Preoptic and paraventricular nucleus release of dopamine may have some relationship to mechanisms of ejaculation or to the neuroendocrine consequences of sexual activity or they can be related to other autonomic processes associated with copulation. There is no compelling indication in existing experimental data that dopamine is of any particular importance for sexual motivation. There is experimental evidence showing that it is of no importance for sexual reward.

Animals↗

PubMed2004

Progestins and place preference conditioning after paced mating.

When female rats pace their coital interaction, a reward state evaluated by conditioned place preference is induced. Progesterone (P) is essential for the expression of proceptive behavior and for the induction of CPP. However, the functional significance of ring A reduction of P for the induction of this state during estrous is unsettled. In the present study, we evaluated whether ring A-reduced metabolites of P are involved in the reward state induced when the females are allowed to pace their sexual contacts. Ovariectomized (ovx) female rats treated with estradiol benzoate (EB, 5 microg) and P (13 microg), Megestrol acetate (MA; 13 microg ), 5 alpha-pregnan-20 dione (5 alphaDHP; 3 microg), or 5 beta-pregnan-3 alpha-ol-20-one (5 beta,3 alpha-Pgl; 3 microg) were used. Progestins were dissolved in propylene glycol and intravenously (iv) injected through an indwelling jugular catheter before females were tested for pacing behavior. After 15 intromissions or one ejaculation, females were gently placed in the nonpreferred compartment of a CPP box. Paced mating in all groups treated with progestins induced a clear change of preference. The administration of progestins alone did not induce CPP. These results suggest that P and ring A-reduced metabolites facilitate the reward state following pacing.

5-alpha-Dihydroprogesterone↗

PubMed2004

Sexual incentive motivation, olfactory preference, and activation of the vomeronasal projection pathway by sexually relevant cues in non-copulating and naive male rats.

There are some apparently healthy male rats that fail to mate after repeated testing with receptive females. We have previously shown that these "non-copulator (NC)" males show no partner preference for a receptive female when given the opportunity to physically interact with a sexually receptive female or a sexually active male. We also demonstrated that although NC males prefer odors from estrous females to odors from anestrous females, this preference is significantly reduced in comparison to the preference displayed by copulating (C) males. The aim of the present study was to evaluate in NC males sexual incentive motivation, that is, the approach behavior of male rats to either a sexually receptive female or a sexually active male in a test where the subjects can smell, hear, and see the stimulus animal but prevents their physical interaction. In addition, we determined whether NC rats have alterations in their ability to detect odors from conspecifics or odors related to food. In the detection of odors from conspecifics, we determined if these NC males are sexually attracted toward odors from receptive females or sexually active males. For food-related odors, we quantified the time it took the subjects to locate a hidden a piece of apple. Finally, using the induction of Fos-immunoreactivity (Fos-IR) as an index of neuronal activation, we compared the response of the vomeronasal projection pathway (VN pathway) of C and NC male rats exposed to estrous bedding. Males without sexual experience (WSE) were included in all experiments to determine the importance of previous heterosexual experience in the different behavioral tests and in the activity of the VN pathway. In the sexual incentive motivation test, we found that C and WSE male rats have a clear preference for estrous females over sexually active males, whereas NC male rats showed no preference. In odor tests, our results showed that C males had a clear preference for odors from estrous females as opposed to odors from sexually active males. Although NC and WSE male rats showed a preference for estrous female odors, this preference was significantly reduced compared to that shown by C males. No differences were found between WSE, C, and NC males in the detection of stimuli associated with food-related odors. A significant increase in Fos-IR was observed in the mitral cell layer of the accessory olfactory bulb in all groups when exposed to estrous bedding. However, only the C male rats exposed to estrous female bedding showed an increase Fos-IR in all structures of the VN pathway. An increase in Fos-IR was observed in the medial preoptic area (MPOA) of WSE males exposed to estrous bedding. No increases in Fos-IR were detected along the VN pathway in NC male rats. We proposed that NC male rats do not display sexual behavior due to a reduced sexual motivation that could be caused by alterations in the neuronal activity of the VN pathway during the processing of estrous odors.

Animals↗

PubMed2004

Dopamine antagonists do not block conditioned place preference induced by paced mating behavior in female rats.

The authors assessed the behavioral effects of dopamine (DA) receptor antagonists, Cis (Z) flupentixol and S(+)-raclopride L-tartrate, on conditioned place preference (CPP) induced by paced mating behavior. Ovariectomized female rats of the Wistar strain were used. The administration of amphetamine (1 mg/kg) induced a clear CPP that was completely blocked by the DA antagonists flupentixol (0.25 mg/kg) or raclopride (0.125 mg/kg). These doses had no effect on motor coordination. Female rats that mated in a pacing chamber developed a clear CPP. Neither flupentixol nor raclopride blocked the reward state induced by paced mating behavior. These results indicate that DA is not involved in the reward state induced by paced mating behavior in female rats.

Animals↗

PubMed2003

Facilitation of male-like coital behavior in female rats by kindling.

Kindling is a model of epilepsy and brain plasticity. When applied to the medial preoptic area (MPOA) of non-copulating male rats kindling induces masculine sexual behavior. In order to test if kindling could facilitate male-like coital behavior in female rats, sexually naive females were ovariectomized and kindled in the amygdala (AMG) or the MPOA until an intermediate stage (between 1 and 3, MPOA1-3) or until stage 5 (MPOA5 group). Once kindling was established, females were treated with 2.5 mg/Kg of testosterone propionate (TP) for 15 days. Male-like coital behavior was evaluated on days 5, 10 and 15 of treatment. Subjects were then injected with a TP dose of 5 mg/kg for 15 days and tested in the same way as with the lower dose. The number of mounts was significantly increased and the mount latency was significantly reduced in the MPOA1-3 group when tested 5 days after treatment with the low dose of TP. The same facilitation was observed in MPOA1-3 and MPOA5 groups on day 10 of treatment with the low dose of TP. When the animals were under the high dose of TP treatment, the number of intromissions was increased in all experimental groups (including the AMG kindled group) in comparison to sham animals. In a second experiment we evaluated if the facilitation of male-like coital behavior induced by kindling was produced by a modification of the response of the vomeronasal system to sexually relevant cues. Ovariectomized females were stimulated until they reached kindling stage 2, then they were treated with 2.5 mg/kg of TP for 5 days. After animals were exposed for 90 min to clean sawdust or sawdust soiled by estrous females they were perfused. Fos was detected by immunocytochemistry along the vomeronasal pathway. No differences were found in Fos responses between sham and MPOA kindled females. The facilitation of masculine sexual behavior observed in AMG kindled females may be a consequence of the propagation of the AD to other brain regions involved in the expression of masculine sexual behavior. We propose that masculine sexual behavior is facilitated in MPOA kindled female rats by local neural changes produced by this kind of stimulation without modifying the response of the vomeronasal system to sexually relevant cues.

Amygdala↗

PubMed2003

Permanent changes in sexual behavior induced by medial preoptic area kindling-like stimulation.

Kindling is a model of neuronal plasticity in which repeated electrical stimulation of certain brain areas leads to the progressive development of motor seizures. We have previously shown that medial preoptic area (MPOA) kindling induces sexual behavior in non-copulating male rats. In the present experiment, we found that previously non-copulating male rats display sexual behavior even 8 months after kindling stimulation had ceased. In addition, elicitation of an afterdischarge (AD) or stimulation until an intermediate stage was sufficient to induce sexual behavior in previously non-copulating male rats. These results suggest that kindling like stimulation, without seizure development, can induce permanent behavioral changes.

Animals↗

PubMed2003

Sexual and olfactory preference in noncopulating male rats.

In some species including rats, mice, gerbils, and rams, apparently normal males fail to copulate when repeatedly tested with receptive females. These animals are called "noncopulators (NC)," and the cause of this behavioral deficit is unknown. It has been shown that NC rats do not have hormonal alterations or deficits in the mechanisms that control penile function. The present study was designed to examine (Experiment 1) whether NC male rats prefer receptive females to sexually active males. In addition, the olfactory preference for bedding soiled from estrous or for anestrous bedding was investigated. These tests were performed in NC and copulating (C) male rats when the subjects were intact, gonadectomized (GDX), or GDX and treated with high doses of testosterone propionate (TP). Our results demonstrate that NC rats do not display sexual behavior even after high TP treatment. While C male rats have a clear preference for receptive females as opposed to a sexually active male, NC rats do not. In all hormonal conditions, the preference shown by NC rats for estrous bedding was significantly reduced in comparison to that seen in C rats. TP treatment in NC rats did not modify either partner or odor preference. In Experiment 2, we evaluated if NC rats are feminized and if it could be easier to induce feminine-like behavior by hormone treatment with estradiol benzoate (EB) or with EB plus progesterone (P) (EB+P). Odor preference for estrous or male bedding under these hormonal conditions was also compared. No differences between NC and C rats were found in feminine sexual behavior. In the olfactory test, we found that NC rats prefer odors from receptive females as opposed to male odors, but this preference is reduced compared to that of C rats. Males treated with EB or EB+P show no preference for female odors. These results demonstrate that treatment with EB or EB+P does not increase feminine sexual behavior in NC rats.

Animals↗

PubMed2003

Medial preoptic area/anterior hypothalamus and sexual motivation.

The medial preoptic area/anterior hypothalamus (MPOA/AH) is a brain site derived from proliferative zones from the diencephalon and telencephalon. It is probably this characteristic that makes this brain region participate in different physiological and behavioral functions. The present review addresses the role of the MPOA/AH in the control of male sexual behavior. It is clear that the MPOA/AH is a crucial site in the control of sexual behavior in males of all species studied to date. But although many different publications have followed the contribution of Heimer and Larsson there is no agreement as to what is specifically the role of the MPOA/AH in sexual behavior. At least three hypotheses have been presented. The first one suggests that this brain region is involved in the consummatory aspects (execution) of sexual behavior. The second indicates that the MPOA/AH is involved in the appetitive components (motivation) of masculine sexual behavior. The third hypothesis considers that MPOA/AH neurons are involved in the regulation of consummatory and appetitive aspects of sexual behavior. From the literature reviewed, it will become evident that the evidence supporting a role of the MPOA/AH in the execution of sexual behavior is based on a number of limited studies not easy to interpret. On the other hand, several lines of evidence using a variety of methodologies support the notion that the MPOA/AH is involved in the motivational aspects of male sexual behavior.

Animals↗

PubMed2002

Effect of prenatal androgen receptor antagonist or aromatase inhibitor on sexual behavior, partner preference and neuronal Fos responses to estrous female odors in the rat accessory olfactory system.

Many socially relevant odors are detected in rodent species by the vomeronasal organ and subsequently processed by the accessory olfactory system (AOS). We previously found that gonadectomized male and female rats treated in adulthood with testosterone propionate (TP) showed equivalent Fos responses in the AOS to odors derived from estrous females. Likewise, in contrast with numerous other mammalian species, gonadectomized female rats show surprisingly high levels of male-typical mounting behavior in response to adult TP. We tested the hypothesis that prenatal testosterone (T) exposure, acting via androgen receptors (ARs) or via estrogen receptors, masculinizes the AOS in rats of both sexes. Pregnant dams were treated with either the AR blocker, Flutamide, the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), or nothing (control) to assess the role of prenatal androgen and estradiol receptor activation, respectively, in this masculinization. Beginning at birth, male and female offspring were injected subcutaneously (sc) every other day with either ATD (pre- and neonatal ATD group) or oil vehicle (Flutamide and control groups) until postnatal Day 12. Subjects were gonadectomized as adults, hormonally treated and tested for different behaviors before having their AOS Fos responses to estrous female odors assessed. Prenatal treatment with Flutamide (but not ATD) significantly decreased anogenital distance and severely impaired intromissive and ejaculatory behaviors in males tested after TP replacement without disrupting mounting capacity in either sex. Pre- and neonatal treatment with ATD (but not Flutamide) enhanced lordosis responsiveness in males tested after sc injections of estradiol and progesterone, whereas these perinatal treatments had no effect on any aspect of masculine coital performance in either sex. After TP treatment, male and female control subjects preferred to approach a tethered stimulus female as opposed to a male, and prenatal Flutamide or perinatal ATD treatments did not modify this pattern of partner preference. Neuronal Fos responses to estrous odors were (as in previous studies) identical in the AOS of gonadectomized TP-treated control males and females. Prenatal Flutamide or perinatal ATD treatments failed to disrupt consistently this profile of Fos responses to estrous odors in the AOS of rats of either sex. These behavioral and neuroanatomical findings raise the possibility that the similar level of male-typical responsiveness to social odors that occurs in male and female rats after adult TP treatment results from nonsteroid-hormone-dependent, species-specific factors that act perinatally in the brains of rats of both sexes.

Androgen Antagonists↗