Male Hamster Brain Research Articles

De novo assembly, annotation, and characterization of the whole brain transcriptome of male and female Syrian hamsters

Hamsters are an ideal animal model for a variety of biomedical research areas such as cancer, virology, circadian rhythms, and behavioural neuroscience. The use of hamsters has declined, however, most likely due to the dearth of genetic tools available for these animals. Our laboratory uses hamsters to study acute social stress, and we are beginning to investigate the genetic mechanisms subserving defeat-induced behavioural change. We have been limited, however, by the lack of genetic resources available for hamsters. In this study, we sequenced the brain transcriptome of male and female Syrian hamsters to generate the necessary resources to continue our research. We completed a de novo assembly and after assembly optimization, there were 113,329 transcripts representing 14,530 unique genes. This study is the first to characterize transcript expression in both female and male hamster brains and offers invaluable information to promote understanding of a host of important biomedical research questions for which hamsters are an excellent model.

Facilitation of Male Sexual Behavior in Syrian Hamsters by the Combined Action of Dihydrotestosterone and Testosterone

BackgroundTestosterone (T) controls male Syrian hamster sexual behavior, however, neither of T's primary metabolites, dihydrotestosterone (DHT) and estradiol (E2), even in highly supraphysiological doses, fully restores sexual behavior in castrated hamsters. DHT and T apparently interact with androgen receptors differentially to control male sexual behavior (MSB), but whether these two hormones act synergistically or antagonistically to control MSB has received scant experimental attention and is addressed in the present study.Methodology/Principal FindingsSexually experienced male Syrian hamsters were gonadectomized and monitored 5 weeks later to confirm elimination of the ejaculatory reflex (week 0), at which time they received subcutaneous DHT-filled or empty capsules that remained in situ for the duration of the experiment. Daily injections of a physiological dose of 25 µg T or vehicle commenced two weeks after capsule implantation. MSB was tested 2, 4 and 5 weeks after T treatment began. DHT capsules were no more effective than control treatment for long-term restoration of ejaculation. Combined DHT + T treatment, however, restored the ejaculatory reflex more effectively than T alone, as evidenced by more rapid recovery of ejaculatory behavior, shorter ejaculation latencies, and a greater number of ejaculations in 30 minute tests.Conclusions/SignificanceDHT and T administered together restored sexual behavior to pre-castration levels more rapidly than did T alone, whereas DHT and vehicle were largely ineffective. The additive actions of DHT and T on MSB are discussed in relation to different effects of these androgens on androgen receptors in the male hamster brain mating circuit.

Distribution of methionine and leucine enkephalin neurons within the social behavior circuitry of the male Syrian hamster brain

Enkephalin plays a role in the social behaviors of many species, but no corresponding role for this peptide has been investigated in the male Syrian hamster, a species in which brain nuclei controlling social behaviors have been identified. Previous studies have shown the distribution of dynorphin and beta-endorphin throughout social behavior circuits within the male hamster brain. To date, the only studies of enkephalin in the hamster brain address the distribution of this peptide in the olfactory bulb and hippocampus. The present study provides a complete map of enkephalinergic neurons within the forebrain and midbrain of the male Syrian hamster and addresses the question of whether enkephalin immunoreactive (Enk-ir) cells are found within brain regions relevant to male hamster social behaviors. Following immunocytochemistry for either methionine enkephalin (met-enkephalin) or leucine enkephalin (leu-enkephalin), we observed enkephalin localization consistent with data that have previously been reported in the rat, with notable exceptions including lateral septum, ventromedial nucleus of the hypothalamus and cingulate gyrus. Additionally, met- and leu-enkephalin localization patterns largely overlap. Consistent with the post-translational processing of preproenkephalin, met-enkephalin was more abundant than leu-enkephalin both within individual cells (darker staining), and within given brain nuclei (more met-enkephalin immunoreactive cells). Two exceptions were the posterointermediate bed nucleus of the stria terminalis, containing more neurons heavily labeled for leu-enkephalin, and the main olfactory bulb, where only met-enkephalin was observed. Of most interest for this study was the observation of Enk-ir cells and terminals in areas implicated in both sexual and agonistic behaviors in this species.

Conversion of Testosterone to Estradiol May Not Be Necessary for the Expression of Mating Behavior in Male Syrian Hamsters (Mesocricetus auratus)

Male sexual behavior is mediated in part by androgens, but in several species, mating is also influenced by estradiol formed locally in the brain by the aromatization of testosterone. The role of testosterone aromatization in the copulatory behavior of male Syrian hamsters is unclear because prior studies are equivocal. Therefore, the present study tested whether blocking the conversion of testosterone to estradiol would inhibit male hamster sexual behavior. Chronic systemic administration of the nonsteroidal aromatase inhibitor Fadrozole (2.0 mg/kg/day) for 5 or 8 weeks did not significantly increase mount latency or reduce mount frequency, intromission frequency, ejaculation frequency, or anogenital investigation relative to levels shown by surgical controls. However, Fadrozole effectively inhibited aromatase activity, as evidenced by the suppression of estrogen-dependent progesterone receptor immunoreactivity in the male hamster brain. The JZB39 anti-progesterone receptor antibody labeled significantly more neurons in brains of sham-treated hamsters than in brains of Fadrozole-treated hamsters. These data suggest that aromatization of testosterone to estradiol is not necessary for normal mating behavior in Syrian hamsters.

Distribution of androgen receptor-like immunoreactivity in the brains of intact and castrated male hamsters

The distribution of androgen receptor-like (AR) immunoreactivity was mapped in brains of (a) intact, sham-castrated and (b) castrated male hamsters. The pattern of AR-immunoreactive (AR-ir) staining was, in general, similar to that reported for gonadal steroid autoradiography of the male hamster brain. Moreover, with one exception, AR-like staining was similar in intact and castrated males, and occurred in the medial preoptic area, bed nucleus of stria terminalis, amygdala, hippocampus, thalamus, and several hypothalamic nuclei including the periventricular, supraoptic, and ventromedial nuclei, and median eminence. However, while AR-ir labeling was virtually absent in the lateral septum of intact males, it was clearly present in the lateral septum of castrated males. The view that androgen receptors in brain generally decline after castration received no support from this study.

Substance P and Luteinizing Hormone-Releasing Hormone Levels in the Brain of the Male Golden Hamster Are Both Altered by Castration and Testosterone Replacement

The effects of castration and testosterone (T) replacement on levels of substance P (SP) and luteinizing hormone-releasing hormone (LHRH) were assessed in discrete areas of the male hamster brain. The animals were either castrated, castrated and given a chronically low or high dose of T by Silastic implant, or sham-operated. Brain tissues and trunk blood were collected 3 weeks after surgery. Plasma T levels were maintained within the normal range by the implants but at significantly lower or higher levels than the mean for sham-operated males. Levels of SP and LHRH were quantified in the olfactory bulbs, rostral basal forebrain, anterior hypothalamic and preoptic area, medial basal hypothalamic area, medial basal hypothalamic area and median eminence, and brain stem. In general, castration and T replacement effected opposite changes in levels of SP and LHRH. In the medial basal hypothalamic area and median eminence SP levels were found to be inversely related to the chronic T levels, whereas the LHRH levels were directly correlated. In the anterior hypothalamic and preoptic area, castration reduced levels of SP. Conversely, castration elevated levels of LHRH in this area. This inverse dynamic relationship between changing peptide levels was also observed in the rostral basal forebrain but not in the olfactory bulbs. In most of these forebrain regions, the dose-response curves for the experimental groups could not incorporate the peptide levels in the sham-operated control group. SP levels in the brain stem showed a monotonic inverse relationship to circulating T levels which did include the control group values.(ABSTRACT TRUNCATED AT 250 WORDS)

LHRH-systems in the brain of the golden hamster.

Vibratome sections of male hamster brains were treated immunohistochemically with LHRH antiserum, and the anatomical distribution of LHRH immunoreactive cells and nerve fibers was assessed. LHRH-cell bodies are found in the ventral hypothalamus that includes its preoptic, anterior and central parts, in the septum, the olfactory tubercle, the main and accessory olfactory bulb, and the prepiriform cortex. In addition, extracerebral LHRH-neurons and ganglia exist in LHRH-positive nerves at the ventromedial surface of the olfactory tubercle and bulb as well as in olfactory nerves. Dense networks of LHRH-immunoreactive fibers are found in all regions where LHRH-cell bodies exist. Intraseptal connections reach the organum vasculosum of the lamina terminalis, the subfornical organ, and the lateral ventricle. Dorsolateral projections from the septum can be traced via the fimbria hippocampi and alveus to the ventral hippocampus, via the stria terminalis to the amygdala and piriform cortex. Ventrolateral projections extend from the level of the olfactory tubercle and preoptic-anterior hypothalamic area via the ventral amygdalofugal pathway to the prepiriform and piriform cortex as well as the amygdala. Dorsal supracallosal projections via the stria longitudinalis are seen in the induseum griseum and the cingulate cortex. Caudal efferents reach the havenula, interpeduncular nucleus, midbrain raphe, and central gray of the rostral fourth ventricle via the stria medullaris and fasciculus retroflexus and by a ventral projection via the periventricular and subventricular hypothalamus. A major portion of this ventrocaudal projection gives rise to a dense network in the median eminence. Anatomical relationships of LHRH-fibers to certain regions of the inner ventricular and outer brain surface are noted.