Intrasexual interactions among female golden hamsters (Mesocricetus auratus) over the estrous cycle.

Examined social interactions of cycling female golden hamsters paired with ovariectomized animals (N?=?96) in large enclosures. Interactions were primarily agonistic and intense over the 4-day estrous cycle, as indicated by frequent occurrences of chase and flight behavior. Dominant and subordinate social ranks were established in the majority of pairs (96%) tested, and even Ss in sexual heat were capable of attacking and dominating their rivals. Furthermore, cycling Ss exhibited significantly more aggressive acts than ovariectomized opponents 1 day prior to sexual receptivity. No differences in fighting patterns were found between Ss on the other 3 days of the estrous cycle. Additional analyses revealed clear differences in agonistic elements, including flank marking, between dominant and subordinate Ss, regardless of whether they were gonadectomized or intact. Analyses also show that dominant Ss frequently chased and bit opponents during encounters within their nesting area. Data are examined for implications on the adaptive organization of female hamster agonistic behavior and the neuroendocrine regulation of species-typical behavior over the estrous cycle. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Shifting strategies for behavioral thermoregulation in developing golden hamsters.

Studied developmental changes in the golden hamster pup's capacity for behavioral temperature regulation. Groups of 3 pups aged 4-24 days were tested at room temperature (22°C), on a strong gradient (34-22°C), and on a mild gradient (30-22°C). The proportion of time engaged in the following behaviors was recorded: contact with the warm edge (thermotaxis), active huddling, and quiet huddling. Results show that Ss tested at 22° engaged in active huddling, and their temperature dropped rapidly. Only on Day 14 were they able to maintain their temperature constant with a combination of vigorous exploration and quiet huddling. On the strong gradient, Ss were able to regulate their temperature at all ages. Young Ss (4-5 days) depended on thermotaxis rather than huddling, separating when their temperature started to rise. With age, quiet huddling replaced thermotaxis as a dominant behavior. On the mild gradient, Ss combined active and quiet huddling with thermotaxis, so that their temperature dropped at a slow steady rate. It is concluded that hamster pups have a well-developed capacity for behavioral temperature regulation. Whether they attempt to keep their temperature constant or tolerate a slow rate of drop depends on the amount of exogenous heat available, which under natural conditions would be supplied predominantly by the mother. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physical and behavioral aspects of sexual maturation in male golden hamsters.

Male golden hamsters ( Mesocricetus auratus ) were examined from 3 to 9 wks of age for morphological, physiological, and behavioral indices of sexual maturation. Although each of the 8 variables (e.g., testis weight, seminal vesicle fluid, and rear mounts) selected for measurement displayed a unique developmental profile, a principal-components analysis of these variables resulted in the extraction of 2 principal components, one tentatively labeled physical and gross behavioral maturation (accounting for 66% of the total variance) and the other designated perfection of mounting orientation (accounting for an additional 12% of the variance). This result indicates that puberty in the male hamster is best viewed as 2 independent processes, rather than as a unitary process or as an arbitrary term applied to a variety of unrelated developmental phenomena. Advantages of using multivariate composite scores and selected univariate measurements are discussed, as are methods of comparing developmental changes in different variables. A 2nd experiment confirmed an unexpectedly early onset of androgen secretion and an unusual pattern of body weight gain. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial and nonspatial learning across the rat estrous cycle.

Recent evidence has demonstrated that there are fluctuations in both the anatomy and physiology of the hippocampus across the estrous cycle of the female rat. In the present study we examined the behavioral implications of these changes by testing females on either a hippocampal or nonhippocampal version of the Morris water maze during the various phases of the estrous cycle. Males were also tested on these tasks. Although there was little variance on the nonhippocampal cue task, females in proestrus performed significantly better than those in estrus. Optimal female performance on the spatial version of the task occurred during the phase of estrus, whereas the least efficient performance occurred during proestrus. These results do not support the traditional view that hippocampal long-term potentiation is positively correlated with spatial learning. (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)     

Aggressive behavior in female hamsters: The hormonal basis for fluctuations in female aggressiveness correlated with estrous state.

The frequency and sequencing of aggressive behaviors by naive female hamsters has been found to change during series of brief encounters, probably because of the lack of stable dominance relations. Such initial encounters seem most representative of interactions likely in free-ranging hamsters and have been emphasized in studies of the hormonal mediation of female aggression. The present 4 experiments, conducted with a total of 72 random-bred female hamsters, found that nonestrous females exhibited intense aggression toward conspecifics of either sex. Estrous females were not aggressive and spent much time in lordosis, indicative of sexual receptivity. While oil-injected adrenalectomized-ovariectomized females fought at high levels, comparable with intact nonestrous females, the combination of 17-β-estradiol benzoate and progesterone suppressed fighting completely. In contrast, replacement of estradiol, progesterone, or testosterone propionate individually had no consistent effect. Hypophysectomized females also fought at high levels, indicating that pituitary hormones are not required for vigorous aggression. Further, individual anterior pituitary hormones did not produce marked changes in fighting. Results emphasize the roles of estrogen and progesterone in synchronizing aggression with current reproductive state. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flank-marking behavior and the neural distribution of vasopressin innervation in golden hamsters with suprachiasmatic lesions

In golden hamsters, microinjections of arginine-vasopressin (AVP) within the anterior hypothalamus trigger a stereotyped scent-marking behavior, flank marking. Our experiment was carried out to test the contribution of AVP neurons within the suprachiasmatic nucleus (SCN) in the control of this behavior. Our results suggest that the SCN does not contribute to flank-marking behavior. Whereas SCN lesions disrupted circadian rhythms of wheel running, the same lesions did not disrupt flank-marking. The results also suggest that neurons located outside the SCN contribute significantly to the vasopressinergic innervation of the brain and the expression of AVP-dependent behaviors, such as flank-marking behavior. Although AVP-immunoreactive fibers were severely (ca. 95%) depleted from several forebrain areas in SCN-lesioned hamsters, the effect of the lesions was much more limited within the forebrain areas involved in flank-marking behavior as well as within the midbrain and hindbrain.     

Medial septal lesions: Disruptions of microregulatory patterns and circadian rhythmicity in rats.

Examined the microregulatory patterns of food and water intake in 10 male and 10 female Long-Evans rats bearing medial septal lesions and in sham-operated controls. Medial septal ablation, although not affecting the total amount of food or water ingested, resulted in a profound disruption of the pattern of intake. Circadian rhythmicity was disrupted for a period, returning to normal by 25 days postlesion. Permanent disruptions occurred in feeding patterns in that Ss with septal lesions ingested more frequent but smaller meals. There was also a marked increase in food-intake-associated drinking and a decrease in non-food-intake-associated drinking. Results reflect 2 separate independent effects, a general circadian disruption and an alteration in regulatory behavior produced by a chronic depletion of body fluid. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Allopregnanolone concentration in hippocampus of prepubertal rats and female rats throughout estrous cycle

Hippocampus plays an important role in cognition, neuroendocrine function and sexual behaviour. Changes of hippocampal neuropeptide and neurotransmitter concentrations are associated to behavioural changes occurring throughout reproductive life. The present study focused the attention on the presence of a neurosteroid, 5 alpha-pregnan-3 alpha-ol-20-one (termed allopregnanolone) in hippocampus. In particular, hippocampal allopregnanolone concentration in male and female prepubertal rats and in female rats throughout estrous cycle were evaluated. Hippocampal extracts were eluted on high pressure liquid chromatography and allopregnanolone concentration was measured by radioimmunoassay. Prepubertal male and female rats (15 days old) showed highest values which significantly decreased with advancing age (25 and 60 days) (p < 0.01); the lowest hippocampal concentration of allopregnanolone was found in adult rats. Female rats on proestrus morning and afternoon showed an hippocampal allopregnanolone concentration significantly higher than on diestrus or on estrus (p < 0.01), while rats on estrus showed hippocampal allopregnanolone concentration significantly lower than during other days of estrus cycle (p < 0.01). These data indicate differences in hippocampal concentration of allopregnanolone between prepubertal and adult rats and throughout estrous cycle in female rats. This finding suggest a putative role of neurosteroids in the modulation of behavioral changes occurring throughout reproductive life.     

Comparative metabolism and disposition of gemfibrozil in male and female Sprague-Dawley rats and Syrian golden hamsters

Antibodies (Abs) can contribute to the cure of a viral infection, in principle, in two ways by: (1) binding to infected cells and thereby reducing the production of progeny virus [here termed cell-targeting (CT) activity] and (2) reacting with released progeny virus and thereby inhibiting the spread of the infection [termed virus neutralizing (VN) activity]. We have previously shown that a pulmonary influenza virus infection in severe combined immunodeficient mice could be cured by treatment of these mice with hemagglutinin (HA)-specific monoclonal Abs (mAbs) that mediated both of the above activities. Although the therapeutic activity of these mAbs correlated with their VN activity, it remained unclear how much their CT activity contributed to the Ab-mediated recovery process. To clarify this point, we tested the therapeutic efficacy of two mAbs of IgG2a isotype that mediated CT but no VN activity: one specific for the viral neuraminidase and the other for matrix protein 2. Both mAbs reduced pulmonary virus titers by 100- to 1000-fold but they failed to clear the infection, even when administered in combination and at therapeutically saturating concentrations. The results suggest that CT activity contributes significantly also to the therapeutic activity of HA-specific mAbs and further support the notion that VN-activity is required for Ab-mediated virus clearance.     

Decreased density of amygdaloid parvalbumin-positive interneurons and behavioral changes in dystonic hamsters (Mesocricetus auratus).

The dtsz hamster represents a model of primary paroxysmal nonkinesiogenic dyskinesia in which dystonic episodes can be induced by stress and anxious stimuli. This disease is regarded as a basal ganglia disorder. In fact, a deficit of striatal interneurons could play a key role in the pathophysiology in dystonic hamsters. Because the involvement of limbic structures cannot be excluded so far, the density of parvalbumin-immunoreactive (PV+) interneurons was determined in the basolateral amygdala in the present study. Compared with nondystonic hamsters, the density of PV+ interneurons was moderately decreased in the dtsz mutant. The functional consequence of this finding was examined by behavioral analyses. Examinations in the elevated plus maze and in a modified open field failed to disclose an enhanced anxiety-related behavior in dtsz hamsters (Mesocricetus auratus). A lower acoustic startle response and a stronger habituation in mutant hamsters than in controls correlated with a decreased body weight. Interestingly, prepulse inhibition was absent in mutant hamsters. The latter finding suggests a disturbed sensorimotor gating that can be related to alterations in both the basal ganglia nuclei and in limbic structures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavior of attack-primed and attack-satiated female golden hamsters (Mesocricetus auratus).

In 3 experiments with 50 female hamsters, "priming" the S by allowing it one biting attack on a smaller, methotrimeprazine-treated target hamster significantly decreased its latency to attack a subsequently presented probe target. Conversely, the latency of attacks on the probe was increased, and the number of attacks decreased, if the S was first "satiated" by allowing it 1 hr of ad-lib access to a target followed by a series of briefer target presentations until a criterion of 3 successive presentations without attack was met. The respective aggression-increasing and aggression-decreasing effects of these manipulations were also demonstrated in more naturalistic, unrestrained encounters between pairs of Ss that had just been exposed to the same manipulation. Neither manipulation affected the nonaggressive behaviors of sunflower seed acceptance and wheel running, which suggests that the effects of attack priming and satiation may be specific to aggression. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Immunolocalization of 11beta-hydroxysteroid dehydrogenase types 1 and 2 in rat uterus: variation across the estrous cycle and regulation by estrogen and progesterone

Glucocorticoid hormone action in several target tissues is dependent not only on the expression of the glucocorticoid receptor, but also on that of the 11beta-hydroxysteroid dehydrogenase (11betaHSD) enzymes, 11betaHSD-1 and -2. In the uterus, glucocorticoids can exert inhibitory effects on a range of important functions, particularly in relation to the effects of estrogen. Therefore, the present study examined immunolocalization of the two 11betaHSD enzymes in the rat uterus at each stage of the estrous cycle and after ovariectomy with or without estrogen/progesterone replacement. In cycling rats 11betaHSD-1 was localized to luminal and glandular epithelial cells and to eosinophils in both the endometrial stroma and myometrium. In contrast, 11betaHSD-2 immunostaining was localized to endometrial stromal cells and myometrial cells, with no staining evident in epithelial cells or eosinophils. Immunostaining for both enzymes was cycle dependent, being maximal at proestrus and minimal at diestrus. Western blot analysis of whole uterus at proestrus showed the presence of 34- and 40-kDa immunoreactive species for 11betaHSD-1 and -2, respectively. These immunoreactive signals were almost abolished by ovariectomy, but this effect was reversed for both enzymes by estrogen replacement with or without progesterone. These effects of ovariectomy and steroid replacement were confirmed by immunocytochemical analysis, with the exception that progesterone appeared to enhance the stimulatory effects of estrogen on 11betaHSD-2 specifically within the endometrial stroma. In conclusion, these results establish the presence of both 11betaHSD-1 and -2 in the nonpregnant rat uterus and show distinct distributions for the two enzymes and cyclic variation related to positive regulation by ovarian steroids. The physiological implications of these patterns of 11betaHSD expression will ultimately depend on the reaction direction for each enzyme, but 11betaHSD-2 is likely to limit disruptive effects of glucocorticoids on the endometrial stroma, and 11betaHSD-1 may then serve to selectively reactivate glucocorticoids in epithelial cells.     

An NK1 receptor antagonist affects the circadian regulation of locomotor activity in golden hamsters

The objective of this study was to evaluate the impact of a feeding supplementation program on the growth of undernourished children younger than 5 years in the city of Guariba, state of S?o Paulo, Brazil. The sample consisted of 469 malnourished children enrolled in a feeding supplementation program sponsored by the State Health Secretariat. The children were divided into four groups according to how long they had been enrolled in the program: in group 1, the children had been enrolled for up to 12 months; in group 2, from 12 to 24 months; in group 3 from 24 to 36 months; and in group 4 the children had been enrolled for more than 35 months. Percentiles for weight/age, height/age and weight/height were calculated for each child. To assess the impact of the program, reference curves for the anthropometric profile were constructed based on expected variations in population percentiles. The changes observed in each group were analyzed statistically (McNemar). Groups 1 and 2 presented weight recovery and gains in the weight/height ratios for the most severely malnourished children; in group 3, the weight/height ratio was maintained and there was a discrete tendency towards weight recovery, which was reversed in group 4, in which the weight was again low in relation to height. The feeding supplementation program temporarily minimized severe nutritional deficiencies but was not sufficient to recover and maintain normal growth.     

Effects of neonatal (Day 10) olfactory bulb lesions on social behavior of female golden hamsters (Mesocricetus auratus).

Found that, after neonatal (Day 10) bilateral olfactory bulbectomy (BOB; n = 16), adult female golden hamsters' scent marking and defense behavior to males was reduced relative to sham (n = 13) or neocortically lesioned (n = 11) littermate controls. The BOB aggressive and sexual behavior appeared grossly normal-15 were successfully mated, but 5 destroyed their litters. After mating, controls became more aggressive but BOB aggression decreased and had disappeared by the 2nd wk. of pregnancy. All groups ceased scent marking after mating, but controls returned to premating levels during lactation. The BOB Ss showed no scent marking, defense, or aggression throughout lactation. Unilateral olfactory bulbectomy of 6 Ss also eliminated normal social behavior during lactation, suggesting that not all the behavioral effects of olfactory damage can be attributed to anosmia. (29 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory sensitive periods in albino rats and golden hamsters.

Examined odor preferences of 72 infant, juvenile, and adult Sprague-Dawley rats and 119 Syrian hamsters in a 2-choice situation following 3–10 days of differential olfactory exposure. Exposure increased preferences for a simple botanical odor in infants and juveniles but not adults of both species. Preference differences between exposure groups were greatest for infants, moderate for juveniles, and insignificant for adults, suggesting that olfactory sensitive periods occur in these altricial rodent species. Age of exposure differentially influenced responses to combinations of conspecific and botanical odors. Results suggest that olfactory experience has a similar impact on responses of rats and hamsters to botanical but not conspecific odors. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neonatal androstenedione and adult sexual behavior in golden hamsters.

Notes that male rats castrated and given androstenedione neonatally can show high levels of both masculine and feminine copulatory behavior in adulthood. In the present study, 24 intact female and 30 intact male hamsters castrated at birth were treated for their 1st 20 days with oil, free testosterone, or androstenedione. All neonatal androgen treatments mimicked the naturally occurring developmental process of the male in that all androgenized groups were capable of high levels of male behavior (males but not females showing ejaculation patterns) as well as moderate levels of lordotic receptivity. There were no significant differences in effect among neonatal androgen treatments. Results are discussed as they relate to species differences, sex differences, hamster "bisexuality," and posthormone copulatory performance. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The regulation mechanism of the female menstrual cycle

The hormonal patterns during menstrual cycle, which consist of cyclic alterations in gonadotropins, estradiol, and progesterone, are controlled by hypothalamic-pituitary-ovarian feedback mechanism. GnRH produced in hypothalamus acts on the pituitary cells to secrete FSH and LH, which stimulate the follicular development. The developed follicles secrete estradiol, progesterone, inhibin, activin, and follistatin. Estradiol and progesterone, at different concentrations and/or ratios, either positively or negatively control the feedback of hypothalamic-pituitary axis in regulating the secretion of GnRH, FSH and LH. Inhibin and follistatin selectively suppress, whereas activin enhances the secretion of FSH in the pituitary. Recently, various additional factors produced by the ovary have been identified to contribute to the follicular development by paracrine and/or autocrine regulation as well as to feedback on hypothalamic-pituitary unit.