Marcela Arteaga-Silva

Hormonal responses to different sexually related conditions in male rats

Plasma levels of corticosterone (C) and testosterone (T) increase after sexual activity in males of several species. However, the physiological significance of these increases has not been elucidated. In the present study, hormonal response to different conditions linked to sexual activity was assessed. In the first experiment, plasma levels of C and T were assessed both in sexually experienced and naive male rats after the following conditions: (A) control group, without sexual stimulation; (B) males exposed to ovariectomized females; (C) males exposed to intact, non-receptive females; (D) males exposed to receptive females with the vagina obstructed, to avoid intromission; (E) males exposed to receptive females: but separated by a grid that prevents physical contact; (F) males exposed to receptive females during 30 min. In a second experiment, experienced male rats were allowed to repeatedly copulate until reaching the criteria for sexual exhaustion, and 24 h later, they were allowed to copulate. Once sexually related conditions ended, males were killed and their blood was obtained. C and T plasma levels were assessed by HPLC with ultraviolet (UV) detection. Results indicate that T did not increase significantly in naive male in any sexual condition, while in the experienced males, significant increases were observed with the mere presence of a receptive female and also after ejaculation. These increases were significantly larger in experienced males. On the other hand, C also increased in all sexual conditions, both in experienced and naive rats; however, the increase observed was larger in experienced males. Regarding sexual satiety, both C and T increased after copulating ad libitum to satiety. T increased almost three-fold compared to control, while C increased two-fold. No significant changes were observed in either one of the steroids 24 h after sexual exhaustion, even though males remained with a receptive female during an hour. These results show that sexual experience has an important influence on the hormonal response to sexual activity. C rises could be directly related to sexual arousal involved in the different sexual conditions, while T rises seem to have a direct relationship with both the motivation and execution aspects of masculine sexual behavior.

Effects of hormonal replacement with androgens and estrogens on male sexual behavior and plasma levels of these steroids in gonadectomized golden hamsters (Mesocricetus auratus)

Because the endocrine control of sexual behavior in male hamsters remains controversial, this study analyzed the influence of different androgens and estrogens in the regulation of masculine, sexual behavior (MBS). Aromatizable androgens: androstenedione (A) and testosterone (T), a non-aromatizable androgen: 5alpha-dihydrotestosterone (DHT), as well as estrogens (E2 and E1) alone or in combination with DHT, were administered in gonadectomized, sexually experienced males, for 3 weeks. In addition, plasma levels of these steroids were determined. Gonadectomy completely suppressed masculine sexual behavior (MSB) after 4 weeks. Both A and T replacements restored all the sexual behavior parameters in castrated hamsters by the 3rd week of treatment, with A being more potent in restoring all copulatory series and maintaining all MSB parameters, including long intromissions. Castrated males treated with DHT showed little interest in the female and did not display any copulatory behavior. Gonadectomized males treated with estrogens alone showed active anogenital investigation and displayed some mounts, but did not ejaculate. Males treated with estrogens combined with DHT had longer latencies and less number of ejaculations than males treated with aromatizable androgens. Long intromissions were observed only in males treated with T or A. Plasma levels of A were significantly higher than T levels in intact males. In males treated with A both androgens and estrogens were present in plasma. These results support the notion that aromatizable androgens, mainly A, but not non-aromatizable androgens or even estrogens in combination with DHT, play a relevant role in the endocrine regulation of MSB in the golden hamster.

Different functionality of the medial and orbital prefrontal cortex during a sexually motivated task in rats

This study was designed to analyze whether the electroencephalographic (EEG) activity of the medial (mPFC) and orbital prefrontal cortex (oPFC) was modified during the performance of male rats in a T maze under two different conditions, sexually motivated (with previous intromission and females in the goal boxes of the lateral arms) or sexually non-motivated (without previous intromission and with empty goal boxes). Relative power (RP) of three EEG band frequencies, and inter-hemispheric correlation (r) were calculated and a comparison was made between rats under motivated and non-motivated conditions. In the mPFC of sexually motivated males, an increase of the RP in the 6-7 Hz band as well as a decrease in the 8-11 Hz band was observed in relation to an awake-quiet state and during the walk in the maze stem. Similarly, an increase in the r of the 6-7 Hz band was observed during the walk in the maze stem and when remaining near to a receptive female, when compared to non-motivated males. In the oPFC, only the RP of the 6-7 Hz band was increased during the walk in the maze stem of the motivated males. These data suggest that, among sexually motivated males, the mPFC is involved both in anticipatory and motor execution during the performance of the T maze task, whereas the oPFC is only involved in the motor execution of the T maze. These results are in line with other studies suggesting that the mPFC and oPFC are functionally distinct, regions which may work together during certain behaviors and physiological conditions.

Testosterone, androstenedione, and 5α-dihydrotestosterone on male sexual behavior and penile spines in the hamster

The expression of masculine sexual behavior (MSB) in male hamsters is optimally stimulated by aromatizable androgens like androstenedione (AD) and testosterone (T), while the non-aromatizable androgen, 5alpha-dihydrotestosterone (DHT), exerting potent androgenic peripheral effects, only in high doses maintains MSB after castration. No data exist on the ability of these androgens to restore long intromissions after castration. In this study, AD, T, and DHT were administered to four-week gonadectomized, sexually experienced male hamsters, for three weeks, in doses of 25 microg/day or up to 1000 microg/day to compare their potency in restoring MSB, penile size, and penile spines growth. Plasma levels of these steroids and the metabolites estrone and estradiol, were determined at the end of the treatment period. Gonadectomy completely suppressed MSB and induced a regression of penile spines. AD was more potent than T in restoring MSB, ejaculatory behavior being displayed by most castrated subjects with a lower dose of AD (50 microg/day) than of T (300 microg/day), and long intromissions being shown by all AD-treated castrated hamsters but only by 20% of T-treated ones, when doses of 1000 microg/day were given. DHT did not stimulate any copulatory response. The three androgens, even at the lowest dose, partially stimulated penis and penile epithelium growth, DHT showing the highest potency. Treatment of castrated hamsters with AD (50 microg/day), restored steroid levels to similar values as those of intact animals. These results show that AD and T restored MSB even with a partial stimulation of penile spines growth, AD being more potent than T. In contrast, DHT did not restore MSB in the hamster in spite of its peripheral androgenic potency.

Taenia crassiceps infection disrupts estrous cycle and reproductive behavior in BALB/c female mice

Previously, it has been shown that parasitic infections are able to alter the normal mammal physiology, at several extents. Thus, we investigated the effects on estrous cycle and sexual behavior induced by intraperitoneal infection with Taenia crassiceps in female host mice. Along the weeks of infection, parasites were collected from the peritoneal cavity of female mice, showing the maximum parasite load at 16 weeks. No parasites were found outside peritoneal cavity. Vaginal estrous cycle was monitored daily for 4, 8, 12 and 16 weeks of infection, and results compared against age-matched female mice. Female sexual behavior (FSB) tests were performed, one test per week. Immediately after the last behavioral test, blood was collected by cardiac puncture for steroid determinations. First of all, there was a strong tissular damage in the female reproductive tract in all infected females. The phases of the estrous cycle were interrupted at 12 and 16 weeks, with increased leukocytes and the presence of a few cornified epithelial cells and nucleated epithelial cells. The FSB decreased starting 6 weeks post infection. On the 16th week, all infected female mice ceased to exhibit sexual responses, and estradiol levels showed a significant decrease. Control mice continued showing FSB and the different phases of the estrous cycle throughout the observation period. Our results strength the notion that parasites may be considered as an evolutionary force in the reproductive ability of mammals.

Mesquite pod extract modifies the reproductive physiology and behavior of the female rat.

Phytoestrogens are non steroidal compounds that can bind to estrogen receptors, mimicking some effects of estradiol (E(2)). These compounds are widespread among legumes, which are used as pasture, and their importance in animal agriculture has increased. Mesquite (Prosopis sp) is a widespread legume, widely used to feed several livestock species in Mexico. The main product of mesquite is the pod, which is considered high quality food. As a legume, it could be assumed that mesquite contains some amounts of phytoestrogens which might induce potential estrogenic effects. However, to our knowledge, there are no reports regarding the possible estrogenic activity of this legume either in livestock or in animal models such as the rat. Therefore, in this study, we evaluated the potential estrogenic effects of mesquite pod extract on several aspects of behavior and reproductive physiology of the female rat. The effects of the extract were compared with those of E(2) and two isoflavones: daidzein (DAI) and genistein (GEN). The following treatments were given to groups of intact and ovariectomized (OVX) female rats: vehicle; mesquite pod extract; E(2); GEN; DAI. Compared to vehicle groups, mesquite pod extract, DAI, GEN, and E(2) increased uterine weight and induced growth in vaginal and uterine epithelia. In intact rats, mesquite pod extract, GEN and DAI altered estrous cyclicity, decreased lordotic quotient and intensity of lordosis. In OVX rats, mesquite pod extract, DAI and GEN induced vaginal estrus, increased vaginal epithelium height, and induced lordosis, although its intensity was reduced, compared with intact rats in estrus and E2-treated rats. These results suggest that mesquite pod extract could have estrogenic activity. However, the presence of phytoestrogens in this legume remains to be confirmed.

Orchiectomy modifies the antidepressant-like response of nicotine in the forced swimming test

Several studies have demonstrated that nicotine (NIC) exhibits antidepressant-like effects. In addition, it has been suggested that sexual hormones participate in the antidepressant actions of antidepressives. The present study was designed to analyze the effect of orchiectomy and the supplementation of testosterone propionate (TP) or 17β-estradiol (E(2)) on the antidepressant properties of NIC using the forced swimming test (FST), as well as to determine possible changes in the FST during different time periods after orchiectomy. In order to evaluate the influences of orchiectomy on the effects of NIC, the study first evaluated the effects of different time periods on orchiectomized rats (15, 21, 30, 45 and 60 days) that were subjected to the FST. Then, different doses of NIC (0.2, 0.4, 0.8, 1.6 mg/kg, sc) were administered for 14 days to both intact and orchiectomized rats (after 21 day) which were then also subjected to the FST. Finally, the influence of the TP or E(2) supplementation on the antidepressant-like effect of NIC on orchiectomized rats (after 21 days) was also analyzed. Results reveal that orchiectomy significantly increased immobility behavior and decreased swimming and climbing up to 60 days after castration. In contrast, NIC decreased immobility behavior and increased swimming in intact rats; whereas orchiectomy suppressed this antidepressant effect of NIC. Only with E(2) supplementation was it possible to restore the sensitivity of the castrated rats to NIC. These results suggest that E(2) was able to facilitate the antidepressant response of NIC in orchiectomized rats.

Circadian activity of corticosterone in an animal model of depression: Response to muscarinic cholinergic stimulation

Neonatal treatment with clomipramine (CMI) in rats induces multiple behavioral alterations during adulthood that resemble certain symptoms of human depression, such as impairments of pleasure-seeking behaviors. CMI may also induce permanent changes in the reactivity of the hypothalamic-pituitary-adrenocortical axis (HPA) to different stimuli; however, the endocrinal changes induced by this treatment are still a matter of debate. In the present study, we evaluated the levels of corticosterone in rats treated in the neonatal period with CMI in basal conditions (0, 6, 12 and 18 h after lights on) and after treatment with the antidepressant fluoxetine (FLX; 5mg/kg for 14 days). To evaluate the response of the HPA axis to a cholinergic agonist, we analyzed the effect of oxotremorine administration (OXO; 0.4, 0.8 mg/kg) on plasma levels of corticosterone. Administration of OXO took place at the beginning of each one of the two phases of the light-dark cycle (time points 0 and 12h, respectively). Results showed an increase in basal plasma levels of corticosterone in CMI-treated rats at time point zero and at 6h after the onset of the light period. While treatment with FLX reversed the increase in corticosterone plasma levels in CMI-treated rats, the results regarding cholinergic stimulation indicate that those rats do not respond to the administration of a low dose of OXO (0.4 mg/kg) at the onset of the dark phase (time point 12h). In conclusion, this study supports the hypothesis that neonatal treatment with CMI induces a hypersecretion of corticosterone in adulthood that was reversed through treatment with the antidepressant FLX. The CMI-treated rats showed a hyporesponse to cholinergic stimulation with OXO at low doses and at the beginning of the dark phase. Thus, the present results do not support the assumption that an increased sensitivity of the muscarinic cholinergic system is one of the possible correlates of the behavioral alterations seen in CMI-treated rats.

Hormone replacement with 17β-estradiol plus dihydrotestosterone restores male sexual behavior in rats treated neonatally with clomipramine

Male sexual behavior (MSB) in rodents, in both its consummatory and motivational components, is regulated by hormones such as testosterone, 17β-estradiol and 5-α-dihydrotestosterone. In experiments, neonatal treatment with clomipramine (CMI; a serotonin reuptake inhibitor) reproduces some of the signs of depression in adult age, including reduced sexual behavior manifested in a lower percentage of subjects that mount, intromit and ejaculate, although their testosterone levels were not altered. However, the effect of this treatment on estrogen levels and the consequences of hormone substitution using 17β-estradiol and 5-α-dihydrotestosterone on the expression of male sexual behavior are still unknown. Therefore, the objective of the present study was to analyze the effect of neonatal treatment with CMI on plasma testosterone and 17β-estradiol levels, and the role of testosterone, 17β-estradiol and 5-α-dihydrotestosterone in altering the consummatory and motivational components of sexual behavior in male rats. To this end, it analyzed the copulatory parameters and sexual incentive motivation (SIM) of rats treated with CMI under two conditions: basal and post-hormone replacements. Neonatal treatment with CMI did not affect plasma testosterone or 17β-estradiol concentrations, but did decrease both the consummatory component and sexual motivation according to the results of the SIM test. These aspects were recovered after administering 17β-estradiol +5-α-dihydrotestosterone, but not testosterone.

Postnatal testicular development in the Chinchilla rabbit

The Chinchilla rabbit is a breed with high commercial value and nowadays is increasingly used in various fields of biomedical research, however, its postnatal reproductive biology has been little studied. The aim of the present study was to investigate the postnatal development of the testis in this rabbit breed to determine both the proliferative periods and apoptosis. 30 rabbits aged 3-100 days old were used in the study. Determination of the period of differentiation of gonocytes to spermatogonia (50dpp), the periods of proliferation and apoptosis of their cells, as well as the beginning of spermatogenesis (60dpp) and the different stages of the seminiferous epithelium cycle were made. We found that these testicular developments were closer to that of humans when compared with rats, a species commonly employed in reproductive research. On comparing these results with those obtained from other breeds, there are clear differences favoring the use of this species as a research model in the field of male reproductive biology.