Lordosis behavior in castrated male rats treated with estradiol benzoate or testosterone propionate in combination with an estrogen antagonist, MER-25, and in intact male rats

Lordosis behavior could be elicited by manual stimulation in castrated male rats after treatment with estradiol benzoate (15 μg for 10 days) or testosterone propionate (1 or 3 mg for 10 days). The effect was antagonized by treatment with the estrogen antagonist MER-25 (10mg for 10 days). Prolonged treatment with testosterone propionate (1 mg for 26 days) resulted in display of male (nine of ten rats) as well as female (seven of ten rats) sexual behavior. Eleven of 32 intact male rats (age 120 days) and 22 of 37 other intact males (age 75 days) displayed lordosis in response to manual stimulation without hormonal treatment. Seven intact males which showed lordosis without hormone treatment were injected with MER-25 (10 mg/day × 10 days) and lordosis was abolished in six cases. The results suggest that estrogen is involved in the regulation of lordosis behavior in TP-treated and intact male rats.     

Lordosis behavior in male rats after lesions in different regions of the corticomedial amygdaloid nucleus

The aim of the experiment was to study the effects of stereotaxic lesions of the anterior and the posterior regions of the corticomedial amygdaloid nucleus (CMN) on the display of lordosis behavior by the male rat. Animals were orchidectomized as adults and given estradiol benzoate and progesterone (P) sequentially. Sexual behavior testing was performed by 9 +/- 1 hr after P injection. Lesions placed into the posterior region of the CMN significantly decreased the proportion of animals showing lordosis behavior as compared to sham-operated and control animals. By contrast lesions in the anterior region of the CMN did not cause any changes in the proportion of animals displaying lordosis but markedly increased the lordosis quotient (LQ) of responding animals. The CMN was then concluded to exert a dual control in the display of lordosis behavior in the male rat with a posterior region regulating the willingness of animals to display lordosis behavior and rostral region subserving inhibitory mechanisms related to the sexual performance (LQ values).     

Lordotic behavior in male rats: genetic and hormonal regulation of sexual differentiation

The male offspring of Long-Evans rats treated with the aromatization inhibitor ATD (1,4,6-androstatriene-3,17-dione) during pregnancy show high levels of lordotic behavior when treated with estrogen and progesterone in adulthood. The male offspring of Sprague-Dawley dams treated in the same way show only a slight facilitation of lordotic potential. These strain differences could reflect strain differences in gestation length and therefore differences in the timing of the sensitive period of sexual differentiation; they could reflect differences in the sensitivity to the defeminizing actions of gonadal hormones; or they could reflect differences in the sensitivity to ATD treatment. We therefore directly compared the effects of prenatal and early postnatal treatment with ATD on the potential of male Long-Evans and Sprague-Dawley rats to show lordosis when given estrogen and progesterone in adulthood. In both strains ATD treatment facilitated adult lordotic behavior. Treatment appeared to have a greater effect in the Long-Evans strain. However, control Long-Evans males were substantially more responsive to hormone treatment in adulthood than were Sprague-Dawley males. In the Long-Evans strain short-term ATD treatment (Days 20-23 of pregnancy) was as effective as long-term treatment (Days 10-23). In the Sprague-Dawley strain, ATD treatment was most effective when given prenatally and postnatally. Strain differences in hormonal sensitivity best account for the present findings.     

MMP-2 and TIMP-2 in the prostates of male and female mongolian gerbils: effects of hormonal manipulation

TIMPs in the prostates of male and female gerbils and evaluated the effects of testosterone on the expression of these enzymes. Ventral prostates from male gerbils that were either intact or had been castrated for 7 or 21 days, along with prostates from female gerbils that were either intact or had been treated with testosterone for 7 or 21 days, were submitted to histological, stereological and immunohistochemical analyses. Stereology of prostatic components showed significant alterations of tissue compartments in the ventral male prostate after castration, especially after 21 days, with a significant increase in stroma. Administration of testosterone led to disorganization in the female prostate, with a significant increase in collagen fibers and smooth muscle cells after 21 days, along with the development of epithelial lesions such as PINs. MMP-2 increased after 21 days of castration in males; however, the TIMP-2 immunoreaction for this group was weak or absent. In females, the expression of MMP-2 appeared to decrease after 7 days of treatment with testosterone, but after 21 days, both epithelium and stroma showed a stronger reaction for MMP-2 than the controls. The expression of TIMP-2 in the treated females was similar to its expression in the castrated males. We conclude that the distribution of MMPs and TIMPs in both male and female prostates is altered by androgen manipulation, but the mechanism of stromal regulation appears to be distinct between genders because both the lack of T in castrated males and the excess levels of T in treated females lead to the same effect.     

Differential effects of bromocriptine treatment on LH release and copulatory behavior in hyperprolactinemic male rats

Hyperprolactinemia (hyperPRL) induced by grafting four pituitary glands under the kidney capsule suppresses copulatory behavior in male rats and sexually naive male mice. In mice sexual experience attenuates the suppressive effects of hyperPRL on mating behavior, thus a comparison of the behavioral consequences of inducing hyperPRL in sexually naive and experienced male rats was undertaken. Hyperprolactinemia had a significant suppressive effect on mating behavior in both groups of animals. Experienced animals showed deficits in all parameters studied except mount frequency and postejaculatory interval, while naive animals differed from respective controls only in mount latency, intromission latency, and intromission frequency. To determine if the inhibition of chronically elevated prolactin (PRL) levels would reverse the suppression of gonadotropin secretion and copulatory behavior in hyperprolactinemic animals, the effects of bromocriptine (CB-154) administration on plasma hormone levels and mating behavior were examined in pituitary-grafted and control rats. Bromocriptine treatment (1 mg/day for 14 days) led to increases in sexual activity in both the sham-operated and grafted animals. In the grafted animals, plasma PRL was reduced and plasma LH significantly increased in the CB-154-treated animals when compared to oil-treated controls. In sham-operated animals, CB-154 produced no significant changes in plasma LH or FSH despite the suppressed PRL levels. These results indicate that (1) hyperPRL induced by pituitary grafts can cause deficits in mating behavior in male rats despite previous sexual experience, and (2) while CB-154 may be acting through other mechanisms to stimulate copulatory behavior, the reduction of chronically elevated PRL levels due to CB-154 treatment is responsible for reversal of the suppressive effects of hyperPRL on LH secretion.     

To forage,mate, or thermoregulate: Influence of resource manipulation on male rattlesnake behavior

Male animals should preferentially allocate their time to performing activities that promote enhancing reproductive opportunity, but the need to acquire resources for growth and survival may compete with those behaviors in the short term. Thus, behaviors which require differing movement patterns such as ambushing prey and actively searching for mates can be mutually exclusive. Consequently, males that succeed at foraging could invest greater time and energy into mate searching. We radio‐tracked sixteen male massasauga rattlesnakes (Sistrurus catenatus) and supplemented the diets of half the snakes with mice across an active season. We tested the predictions that reduced foraging needs would allow fed snakes to move (i.e., mate search) more, but that they would consequently be stationary to thermoregulate less, than unfed controls. Contrary to our first prediction, we found no evidence that fed snakes altered their mate searching behavior compared to controls. However, we found controls maintained higher body temperatures than fed snakes during the breeding season, perhaps because fed snakes spent less time in exposed ambush sites. Fed snakes had higher body condition scores than controls when the breeding season ended. Our results suggest the potential costs incurred by devoting time to stationary foraging may be outweighed by the drive to increase mating opportunities. Such instances may be especially valuable for massasaugas and other temperate reptiles that can remain inactive for upwards of half their lives or longer in some cases, and for female rattlesnakes that generally exhibit biennial or more protracted reproductive cycles.     

Impairment of olfactory perception in male rats by treatment with p-chlorophenylalanine and hydrocortisone.

p-Chlorophenylalanine treatment eliminated the normal male rat preference for the female preputial gland odor. Oral administration of hydrocortisone had a similar effect on dimethyl sulfite preference, which slowly reappeared after the discontinuance of the treatment. These changes of behavior are discussed in relation to possible serotonin alterations resulting from the treatments.     

Effect of chronic treatment with phenobarbital or 3-methylcholanthrene on the male reproductive system in rats

Treatment of rats for 4 weeks with phenobarbital (PB) did not inhibit the growth of the seminal vesicles, nor did it affect the biosynthesis of testosterone by testis microsomes. Moreover, neither the concentration of cytochrome p-450 or the 17 α-hydroxylase activity in testis microsomes were affected. In contrast, treatment with 3-methylcholanthrene (3-MC) for 4 weeks markedly decreased the weights of the seminal vesicles. The decrease was probably related to an impairmant of testosterone formation in the gonads, since testosterone biosynthesis as well as the concentration of cytochrome p-450 and the activity of 17 α-hydroxylase in testis microsomes were significantly decreased in the 3-MC treated rats. No histopathological changes were seen in testes from any of the PB or 3-MC treated rats.     

Different olfactory system deficits affect the antigonadal action of light deprivation differently in male rats

Twenty-eight day-old male rats were subjected to: Blinding-olfactory bulbectomy, Blinding-peripheral anosmia, Blinding-accessory olfactory bulbectomy and Blinding-sham olfactory operation. A set of rats remained intact. Six weeks later, their pituitary-gonads-accessory sex organs were studied. Bulbectomy as well as peripheral anosmia exaggerated the antigonadal effects of blindness, while the accessory olfactory system impairment did not. It is suggested that olfactory bulbectomy potentiation of the antigonadal effects of light deprivation is due to a lack of sensory function rather than to bulbectomy itself and that the accessory olfactory system which is involved in the priming pheromonal effects does not play any role in the inhibition of the antigonadal effects of blindness.     

Lordosis: Inhibiting effects of progesterone in the female rat

Progesterone has two types of inhibitory effects on female sexual behavior that have been well-documented in the guinea pig. The first occurs when high levels of progesterone are present around the start of the estrogen-priming process (“concurrent inhibition”). The second occurs immediately after the display of an estrogen-progesterone-induced period of estrous behavior (“sequential inhibition”). In the present set of experiments, we show that the rat, like the guinea pig, is capable of exhibiting both of these inhibitory effects of progesterone. However, rats require higher doses of progesterone than guinea pigs, at least for concurrent inhibition to be evident. In addition, we show that the dose of progesterone required in a single injection to produce concurrent inhibition is higher than the dose required to produce sequential inhibition in rats. A theory of how progesterone may be accomplishing its inhibitory effects on female sexual behavior in rodents is presented.     

Exogenous androgen during development alters adult partner preference and mating behavior in gonadally intact male rats

In the rat, neonatal administration of testosterone propionate to a castrated male causes masculinization of behavior. However, if an intact male is treated neonatally with testosterone (hyper-androgen condition), male sexual behavior in adulthood is disrupted. There is a possibility that the hyper-androgen treatment is suppressing male sexual behavior by altering the male's partner preference and thereby reducing his motivation to approach the female. If so, this would suggest that exposure to supra-physiological levels of androgen during development may result in the development of male-oriented partner preference in the male. To test this idea, male rats were treated either postnatally or prenatally with testosterone, and partner preference and sexual behavior were examined in adulthood. The principal finding of this study was that increased levels of testosterone during early postnatal life, but not prenatal, decreased male sexual behavior and increased the amount of time a male spent with a stimulus male, without affecting the amount of time spent with a stimulus female during partner preference tests. Thus, the reduction in male sexual behavior produced by early exposure to high levels of testosterone is not likely due to a reduction in the male's motivation to approach a receptive female.     

Central effects of yohimbine on copulatory behavior in aged male rats

It is well known that yohimbine has a history of popular use because of its supposed aphrodisiac properties. The present study was done to determine whether yohimbine can modify the copulatory behavior of aged male rats. Adult male rats of the Wistar-Imamichi strain, 52 weeks of age and weighing 600-650g, were injected intracerebroventricularly with yohimbine hydrochloride (5, 10 micrograms/10 microliters/rat) or vehicle. Each male was then given the opportunity to mate with a receptive female for 30 min after administration of yohimbine or vehicle. Yohimbine produced significant decreases in the latency to initial mounting and significant increases in the number of mountings. However, there was no ejaculation in the yohimbine-and vehicle-treated males. This study is the first to clearly establish an important modulator of sexual arousal for yohimbine in aged male rats.     

Studies on feminine sexual behavior in the male rat: Influence of olfactory stimuli

The aim of this study was to determine if the display of lordosis behavior in the male rat could be influenced by the olfactory environment. Unexperienced adult male rats were orchidectomized (ORCH). They were primed with 75 μg estradiol benzoate and 1 mg progesterone was injected at an interval of 39 hr following long-term (LT = 3 weeks) or short-term (SHT = 8 hr 30 min) exposure to the odor of male or female urine. For 10 min they were placed in the presence of a “stimulus” male of proven sexual vigor 9 hr 30 min ± 1 hr after progesterone injection. Both LT and SHT exposure to the odor of male urine caused a significant increase in the number of ORCH rats which showed lordosis response to male mounts compared to either the ORCH rats exposed to the odor of female urine or to the controls. Following complete olfactory bulb removal (COBR), no difference was observed in the occurrence of lordosis behavior between the ORCH rats whether or not exposed to the odor of urine. For the ORCH-COBR rats exposed to male urine the proportion of animals responding to mounts did not differ from that of their nonbulbectomized counterparts. In comparing the effects of COBR vs anterior olfactory bulb removal (AOBR) lordosis behavior occurred more frequently in COBR than in AOBR-ORCH rats. The lordosis quotient (LQ) was not affected by exposure to the odor of male urine in the nonbulbectomized ORCH rats. In contrast, it appeared to be higher in both COBR and AOBR animals than in their nonbulbectomized counterparts. The olfactory bulbs were then concluded to inhibit the display of lordosis behavior in the male rat. It was also thought that the olfactory stimuli originating from male urine were capable of releasing the hypothalamic structures involved in the control of lordosis behavior of the male rat from an olfactory inhibitory influence.     

Masculine sexual behavior in male and female rats following perinatal manipulation of androgen: Effects of genital anesthetization and sexual experience

Androgenized females, Day 1 male castrates, normal males, and normal females were tested for mounting behavior as adults following TP administration (1 mg/day). Genital anesthetization was used to eliminate all intromission and ejaculation behavior. Results showed that sexually-naive normal males and androgenized females mounted significantly more then Day 1 male castrates, while the Day 1 male castrates mounted significantly more than normal females. Sexually-experienced normal males and androgenized females displayed a significant facilitation of mounting behavior as compared to the sexually-naive animals. Tests of masculine copulatory behavior without genital anesthetization also were conducted with androgenized females and normal males. In these tests, androgenized females were indistinguishable from normal males in all aspects of the complete masculine pattern. The present results provide evidence that during perinatal development androgen acts directly on neural systems which will later regulate adult masculine sexual behavior.