Medial amygdala involvement in discrimination of same-species and closely-related-species male stimuli in estrous female Mesocricetus hamsters.

Efficient discrimination between individuals of closely related species is important to maximize reproductive potential. Some studies using males as subjects have indicated that the medial amygdala (MeA) is involved in discrimination between odors of conspecific females and females from distantly related species. The authors investigated the involvement of the MeA in discrimination by females between odors of conspecific males and odors of males of a closely related species. The authors exposed estrous or diestrous female hamsters (Mesocricetus auratus) to saline, conspecific male odors, or heterospecific (M. brandti) male odors and quantified the expression of c-fos–related antigens in the anterior and posterior MeA. They found that estrous (but not diestrous) females investigated conspecific male odors longer than heterospecific male odors. Neural activity in both the anterior and the posterior MeA was higher in estrous than in diestrous females. In the anterior MeA, there were no significant differences in response to odors of conspecific and heterospecific males. In the posterior MeA, however, neural activity was higher when estrous females were exposed to conspecific odors than when they were exposed to heterospecific odors. No such difference was observed in diestrous females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial amygdaloid lesions and the regulation of sociosexual behavioral patterns across the estrous cycle in female golden hamsters.

Two experiments were conducted to examine the behavioral effects of medial amygdaloid (M) lesions during the estrous cycle in female golden hamsters. In Experiment 1, males were paired with gonadally intact M-lesioned, sham-operated, or ovariectomized M-lesioned females and tested in large enclosures. Medial amygdaloid lesions reduced, significantly, the occurrence of precopulatory biting attack and vaginal scent-marking behavior in females. In contrast, M lesions produced a significant increase in the duration of copulation. Mating behavior was also observed for a brief period of time in 1 M-lesioned female during the diestrus period and in 2 ovariectomized animals. After copulation, M-lesioned females attacked their mating partner less frequently than did sham-lesioned animals, which suggests that M lesions may modulate the reduction of both pre- and postcopulatory aggressive behavior by common processes. The attenuation in aggressive responsiveness was further documented in Experiment 2, which shows that during intrasexual fights, M-lesioned females exhibited significantly fewer offensive agonistic responses than did sham-operated opponents. Collectively, the results demonstrate that M lesions produce significant alterations in both social and sexual response patterns and suggest that M may be a neural component of a forebrain inhibitory system regulating the display of feminine copulatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory basis for the delayed onset of maternal behavior in virgin female rats: Experimental effects.

A previous study showed that intranasal zinc sulfate (ZnSO4) treatment shortens the latencies for the onset of maternal behavior in nonpregnant rats. The present study attempted to determine whether after recovery from the effects of ZnSO4 treatment, the latencies for maternal behavior increased. In Exp I, with 28 Charles River female rats, nonpregnant Ss were intranasally infused with ZnSO4 or air were left untreated and exposed to pups starting 48 hr later. Olfactory discrimination tests using chocolate bits were done simultaneously. The ZnSO4 treatment resulted in short latency maternal behavior (1.1 days) compared with latencies of control Ss (3.8 days), but neither group showed any loss of olfactory discrimination. 3 wks later, ZnSO4-treated Ss showed increased latencies for all but retrieving, while control groups showed decreased latencies for all maternal behaviors. In Exp II, with 13 nulliparous Charles River females, intranasal ZnSO4- and air-treated Ss were given olfactory discrimination tests under food deprivation, using chocolate bits and guinea pig pellets. Choice of guinea pig pellets was more severely affected than choice of chocolate bits, but recovery of the discriminations was complete in 4-5 days. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neonatal androgenic stimulation and adult sexual behavior in male and female golden hamsters.

In an experiment with 48 male and 48 female golden hamsters, neonatally and adult castrated males as well as neonatally androgenized and nonandrogenized females were tested for both mounting and lordosis behaviors during treatment with either testosterone or ovarian hormones. Neonatal androgenization facilitated mounting behavior in adult Ss administered either testosterone or ovarian hormones and suppressed lordosis behavior in adult ovarian-hormone-treated Ss. Early androgen effects on the display of lordosis behavior during adult testosterone treatment were complex and varied with the exact timing of perinatal endogenous or exogenous androgenization. Species differences in hormone-behavior relationships and the possible role of perinatal androgenization in the development of rodents' ability to aromatize androgens are discussed. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of testosterone propionate administered neonatally on puberty and bisexual behavior in female hamsters.

Treated female golden hamsters with oil, 3-mg, 30-mg, or 300-mg testosterone propionate (TP) as neonates in Exp I. Neonatal TP treatment delayed the onset of puberty by 4.5 days to an age near that previously reported for the male hamster. In addition, neonatal TP altered genital morphology, induced the capacity for mounting behavior, and at the highest dosage, disrupted the ability to bear and rear young. Vaginal and behavioral estrous cycles, however, were not influenced by neonatal TP. In Exp II 600-mg TP administered neonatally blocked estrous cyclicity but did not eliminate the capacity to display feminine sexual behavior. Results imply that masculinization and defeminization are separate aspects of neurobehavioral sexual differentiation, and that defeminization includes several independent physiological processes. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal aspects of ventromedial hypothalamic progesterone action in the facilitation of estrous behavior in the female rat.

Examined the temporal parameters of progesterone (P) action in the ventromedial nucleus of the hypothalamus (VMN) in the facilitation of estrous behavior in estrogen-primed female Long-Evans rats stereotaxically outfitted with guide cannulae directed towards the VMN. Crystalline P was applied directly to the brain tissue via bilateral insert cannulae. Ss were ovariectomized and estrogen primed with 5% estradiol Silastic capsules. They received a counterbalanced series of 2 experimental tests: one involving a manipulation with a P-filled implant, and another with a blank implant. In Exp I, a significant increase in estrous responsiveness occurred only after 2 hr exposure of the VMN to P, whereas 4 hr were required for a full display of estrous behavior, including solicitation. In Exp II, P was lowered into the brain for either 1, 2, or 4 hr, and testing took place 4 hr after the lowering of the implant. It was found that 2 hr of P exposure was sufficient to facilitate full estrous responsiveness at 4 hr. In Exp III, it was revealed that the duration of estrous responsiveness was directly related to the time the P implant remained in the brain. In Exp IV, the time course of P retention in brain tissue, revealed by determination of –3H-progesterone levels in hypothalamus, agreed with the behavioral findings. Progesterone levels in the region of the VMN remained high while a P implant was in place, but declined rapidly after removal. A dual mechanistic hypothesis for P action in the facilitation of estrous behavior is presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Forebrain sites of estradiol-17!b action on sexual behavior and aggression in female Syrian hamsters.

The effects of intracranial implants of estradiol in the ventromedial hypothalamus (VMH), the anterior hypothalamus (AH), or the medial amygdala (AMG) on aggression, sexual behavior, and serum estradiol were examined in female Syrian hamsters. Estradiol implants in the VMH, followed by systemic progesterone, stimulated sexual behavior and inhibited aggression. Estradiol implants in other intracranial sites activated sexual behavior but did not reliably inhibit aggression. Intracranially implanted and systemically treated animals had equivalent peripheral estradiol concentrations at sacrifice. Results suggest that (1) the VMH is an important neural site for estradiol actions on sexual and aggressive behavior, (2) the caudal AH and AMG may also be sites of estradiol action on sexual behavior, and (3) intracranial implants may only be effective given systemic estradiol exposure or the concurrent stimulation of multiple brain areas. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The habenular complex mediates hormonal stimulation of maternal behavior in rats.

The role of the habenular complex (Hbc) in the hormonal onset and nonhormonal maintenance of maternal behavior in rats was examined. In Exp 1, bilateral lesions were produced in the Hbc on Gestational Day (GD) 12. On GD 16, animals were hysterectomized/ovariectomized and given estradiol benzoate; they were then tested for maternal behavior 48 hrs later. Hbc lesions delayed the appearance of all components of maternal behavior for several days. In Exp 2, large Hbc lesions that were produced on Postpartum Day 4 caused only 1- or 2-day deficits in maternal behavior. These data suggest that the Hbc mediates the hormonal onset of maternal behavior. During the postpartum period, however, the importance of the Hbc for maternal behavior diminishes as the hormones of pregnancy become less important. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pup cannibalism: One aspect of maternal behavior in golden hamsters.

In 5 experiments with a total of 157 golden hamsters (Mesocricetus auratus), examination of the role of 6 factors (e.g., extreme litter size, illness of pups, and lack of maternal experience) generally held to affect incidence of litter cannibalism in the golden hamster revealed little influence of any of them on frequency of pup destruction. More than 75% of mothers in all conditions examined cannibalized a portion of their litters during the 1st few days postpartum. Termination of cannibalism was found to result both from reduction in litter size, consequent upon destruction of young, and from changes in the internal state of the mother following parturition. The outcome of additional studies indicated that mothers maintain litter size at an individually determined value, behaviorally compensating for experimental alterations in pup number. Results are interpreted as indicating that pup cannibalism in hamsters is an organized part of normal maternal behavior which allows an individual female to adjust her litter size in accord with her capacity to rear young in the environmental conditions prevailing at the time of her parturition. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recovery of masculine copulatory behavior from lesions of the medial preoptic area: Effects of age versus hormonal state.

Two experiments tested the hypothesis that one consequence of the hormonal activation of the onset of copulation in male rats is a reduction in the plasticity of the medial preoptic area (MPOA) with respect to its role in copulation. In Exp I, 31 male rats received 1 mg of testosterone propionate daily from 10 to 45 days of age, and 30 Ss received oil injections. Ss in each of these groups received either bilateral MPOA lesions (MPOAX) or a sham operation as juveniles (28–31 days of age). The proportions of MPOAX Ss copulating as adults did not differ for Ss previously injected with oil or testosterone. In Exp II, 33 male rats were castrated at 15 days of age. These castrated Ss as well as 34 gonadally intact males received bilateral MPOA lesions or a sham operation in adulthood. Following testosterone replacement, MPOAX Ss displayed copulatory impairments regardless of hormonal state during development. Taken together, the results of these experiments suggest that the plasticity (with respect to copulation) of the neural system encompassing the MPOA is a function of some aspect of chronological age unrelated to the rat's developmental hormonal condition prior to the time of the lesion. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Localization of hypothalamic sites for the estrogen-priming of sexual receptivity in female hamsters.

Ovariectomized female hamsters received small unilateral implants of estradiol at a variety of anterior-posterior levels of the medial preoptic area and hypothalamus. The results of an initial experiment using 27-ga. implants showed that females with estradiol implants in the ventromedial hypothalamus (VMN) or nearby anterior hypothalamus consistently showed higher levels of sexual receptivity than did females with implants farther rostral, in the preoptic area, or farther caudal, in the posterior hypothalamus. A second experiment used smaller, 28-ga. implants to compare directly the two areas at which implants were effective in the first experiment. The results confirm the findings of other recent studies of hamsters and rats by identifying the VMN as the most effective hypothalamic site for the estrogen priming of sexual receptivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of endocrine state on sociosexual behavior of female rats tested in a complex environment.

Examined the influence of both natural and artificially induced endocrine states on the sociosexual behavior of female Long-Evans rats during 15-min behavioral observations in a complex testing apparatus that allowed Ss to control their contacts with sexually active and passive males and ovariectomized (OVX) females. Ss were either intact and in various stages of the estrous cycle or OVX and treated with estradiol benzoate (5–20 μg), estradiol plus progesterone (0.5 mg/kg), or vehicle. Factor analysis of the behavioral measures indicated separate loadings on a lordotic behavior factor, a factor for Ss' preference for proximity to OVX females or passive males; and a factor for Ss' locomotion between portions of the testing apparatus. Behavioral variables loading on these factors were influenced by endocrine state, but the nature of the relation between behaviors and endocrine state varied between factors. The utility of the present testing situation in investigations of the neuroendocrine substrates underlying the motivational aspects of feminine reproductive behavior is discussed. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odor preferences of female Peromyscus maniculatus bairdi for male mouse odors of P. m. bairdi and P. leucopus noveboracensis as a function of estrous state.

Tested 20 sexually naive mature P. m. bairdi female mice for male mouse (P. m. bairdi and P. l. noveboracensis) odor preferences during natural estrous and diestrous conditions in a 2-choice Plexiglas olfactorium. The homospecific odor side was chosen 76% of the time by estrous Ss and 43% of the time by diestrous Ss. Only the estrous group differed significantly from the expected 50:50 distribution. High intratest reliability coefficients suggested stable modes of responding within test sessions. These findings suggest female P. m. bairdi reactions to male mouse odors are influenced by gonadal state, and that olfaction conceivably plays a role in sexual isolation between these species. (29 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateral habenula neurons are necessary for the hormonal onset of maternal behavior and for the display of postpartum estrus in naturally parturient female rats.

In 16-day pregnant, hysterectomized-ovariectomized and estradiol benzoate-treated rats, cytotoxic lesions of the lateral habenula (Lhb) produced severe deficits in maternal behavior (K. P. Corodimas, J. S. Rosenblatt, M. E. Canfield, & J. I. Morrell, 1993). To determine if deficits could be found in parturient rats, females were bilaterally injected with kainic acid (KA) to produce cytotoxic lesions of the Lhb. Controls either received bilateral KA-induced lesions to the hippocampus or were unoperated. All females maintained their pregnancies, underwent parturition, and were tested for maternal behavior (pup retrieval, nursing, and nestbuilding), general activity, and oromotor carrying. Females with lesions of the Lhb had severe disruptions of all components of maternal behavior and postpartum estrus. These results extend previous findings that the Lhb is involved in the hormonal onset of maternal behavior and also demonstrate that the Lhb supports the display of postpartum estrus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Male hamster preference for odors of female hamster vaginal discharges: Studies of experiential and hormonal determinants.

In a study with 21 male hamsters, it was found that Ss approached sources of odors from female hamster vaginal discharges and spend significantly more time around these odor sources than around control locations in the test box. This preference for female vaginal odors appeared in sexually inexperienced as well as experienced males even in Ss isolated from females since the time of weaning. Castration significantly reduced the sex odor preference, and treatment with testosterone propionate partially restored it. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurochemical basis of conditioned partner preference in the female rat: II. Disruption by flupenthixol.

The effects of the dopamine receptor antagonist flupenthixol were examined on the development of conditioned partner preference induced by paced copulation in female rats. In Experiment 1, ovariectomized, hormone-primed rats were conditioned to associate scented and unscented males with paced and nonpaced copulation, respectively. Females in Experiment 2 associated albino or pigmented males with paced or nonpaced copulation. Flupenthixol or saline was administered before each conditioning trial. During a final drug-free preference test, females could choose to copulate with either a pacing-related or nonpacing-related male. Saline-trained females copulated preferentially with the pacing-related male, whereas flupenthixol disrupted odor but not strain conditioning. The role of dopamine in conditioned partner preference depends on the type of stimuli to be learned. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurochemical basis of conditioned partner preference in the female rat: I. Disruption by naloxone.

The effects of the opioid antagonist naloxone were examined on the development of conditioned partner preference induced by paced copulation in female rats. In Experiment 1, ovariectomized, hormone-primed rats were conditioned to associate scented and unscented male rats with paced and nonpaced copulation, respectively. Female rats in Experiment 2 associated albino or pigmented male rats with paced or nonpaced copulation. Naloxone or saline was administered before each conditioning trial. During a final drug-free preference test, female rats could choose to copulate with either a pacing related or unrelated male. Saline-trained female rats in the paired group copulated preferentially with the pacing-related male rat, whereas naloxone-trained female rats did not show a preference. The authors concluded that opioids mediated the conditioned partner preference induced by paced copulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential inhibition of sexual behavior by progesterone in female rats: Comparison with a synthetic antiestrogen.

Findings from 6 experiments show that when a large dose of progesterone was administered to ovariectomized Sprague-Dawley rats 24 hrs after a 2-μg injection of estradiol benzoate (EB), sexual receptivity was inhibited at 54 hrs (sequential inhibition). Larger doses of progesterone (1 mg) were required to inhibit the induction of sexual receptivity when tested at 54 hrs than were necessary to facilitate at 30 hrs. This inhibition was not due to copulatory stimuli from the 1st test, because inhibition occurred even when the 1st test was omitted. The inhibition was dose dependent on estradiol; increasing the EB priming dose offset the inhibition caused by 1 mg of progesterone. The results of an experiment that behaviorally dissociated the antiestrogenic action of progesterone from that of a synthetic antiestrogen, CI-628, are consistent with the notion that progesterone and synthetic antiestrogens inhibit the neural effects of estradiol by separate mechanisms of action. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)