Gonadotrophin-releasing hormone (GnRH) release in marmosets I: in vivo measurement in ovary-intact and ovariectomised females.

In vivo hypothalamic gonadotrophin-releasing hormone (GnRH) release was characterised for the first time in a New World primate. A nonterminal and repeatable push-pull perfusion (PPP) technique reliably measured GnRH in conscious common marmoset monkeys. Nineteen adult females (n = 8 ovary-intact in the mid-follicular phase; n = 11 ovariectomised) were fitted with long-term cranial pedestals, and a push-pull cannula was temporarily placed in unique locations within the pituitary stalk-median eminence (S-ME) 2 days prior to each PPP session. Marmosets underwent 1-3 PPPs (32 PPPs in total) lasting up to 12 h. Plasma cortisol levels were not elevated in these habituated marmosets during PPP, and PPP did not disrupt ovulatory cyclicity or subsequent fertility in ovary-intact females. GnRH displayed an organised pattern of release, with pulses occurring every 50.0 +/- 2.6 min and lasting 25.4 +/- 1.3 min. GnRH pulse frequency was consistent within individual marmosets across multiple PPPs. GnRH mean concentration, baseline concentration and pulse amplitude varied predictably with anatomical location of the cannula tip within the S-ME. GnRH release increased characteristically in response to a norepinephrine infusion and decreased abruptly during the evening transition to lights off. Ovary-intact (mid-follicular phase) and ovariectomised marmosets did not differ significantly on any parameter of GnRH release. Overall, these results indicate that PPP can be used to reliably assess in vivo GnRH release in marmosets and will be a useful tool for future studies of reproductive neuroendocrinology in this small primate.

Gonadotrophin-releasing hormone (GnRH) release in marmosets II: pulsatile release of GnRH and pituitary gonadotrophin in adult females.

Unlike other mammals, including rodents, Old World primates and humans, common marmosets and probably all other New World primates synthesise and release chorionic gonadotrophin (CG), and not luteinising hormone (LH) from pituitary gonadotrophs. However, little is known about the physiological dynamics of gonadotrophin-releasing hormone (GnRH)-regulated CG release from gonadotrophs and whether such CG release has pulsatile release characteristics similar to those of LH in other mammalian species. Consequently, we performed a series of in vivo and in vitro studies in ovariectomised laboratory rats and female marmosets to compare GnRH-induced pituitary LH and CG release characteristics, respectively. Exogenous GnRH stimulated a slower onset of release of marmoset pituitary CG, both in vivo and in vitro, and induced an approximately 400% greater increase in the duration of marmoset pituitary CG release compared to that for rat LH. Not surprisingly, hypothalamic pulsatile release of GnRH in vivo was not obviously concordant with endogenous episodic changes in circulating levels of CG in marmosets, in contrast to the clear concordance observed between in vivo GnRH and LH release previously demonstrated in rats and other mammals. Pituitary CG release in marmosets thus demonstrates considerable divergence from the timely hypothalamic GnRH-regulated LH release in other female mammals, implying potentially different physiological dynamics in gonadotrophin regulation of marmoset ovarian function.

Novel restraint system for neuroendocrine studies of socially living common marmoset monkeys.

We describe a novel soft jacket and sling-harness restraint that permits species-typical postures for small-bodied primates, such as the common marmoset (Callithrix jacchus), during long-term (>6 h), continuous restraint. The restraint system is straightforward to use and manipulate, it is easily repaired, and the materials used are readily available. The soft jacket allows for increased versatility and longevity, and the sling-harness provides for greater movement and much longer duration of continuous restraint (up to 3 days) compared to a previously described, more conventional chair restraint for small-bodied primates. The new restraint system prevents the normal diurnal decrease in plasma cortisol levels across the daylight hours; however, it does not disrupt ovulatory cycles. Unlike the previously available techniques, therefore, this new restraint system is applicable to many neurobiological and neuroendocrine studies involving small-bodied, non-human primates and is especially suited to investigations requiring the maintenance of relationships within social groups.

Functional imaging of brain activity in conscious monkeys responding to sexually arousing cues.

Olfactory cues can elicit intense emotional responses. This study used fMRI in male common marmoset monkeys to identify brain areas associated with sexual arousal in response to odors of ovulating female monkeys. Under light anesthesia, monkeys were secured in a specially designed restrainer and positioned in a 9.4 T magnetic resonance spectrometer. When fully conscious, they were presented with the scents of both ovariectomized and ovulating monkeys. The sexually arousing odors of the ovulating monkeys enhanced signal intensity in the preoptic area and anterior hypothalamus compared to the odors of ovariectomized monkeys. These data corroborate previous findings in monkeys based on invasive electrical lesion and stimulation techniques and demonstrate the feasibility of using non-invasive functional imaging on fully conscious common marmosets to study cue-elicited emotional responses.

Peak occurrence of female sexual initiation predicts day of conception in rhesus monkeys (Macaca mulatta).

The present study investigated whether peaks in female sexual initiation could accurately predict conception in group-living female rhesus monkeys. Behavioral observations, 4 or 5 days per week in large, stable, social groups of monkeys, provided frequencies of female initiation of proximity, sexual solicitation, mounts, and ejaculations. Since a preovulatory peak in female sexual initiation is likely linked to the preovulatory oestradiol surge, we used the third day after a peak in behavior as the behavioral estimate of conception date. For each pregnancy, an independent estimate of conception date was derived from ultrasound determination of fetal length. Estimates of conception based on female initiation of proximity with adult males were accurate for more than 90% of pregnancies, whereas observation of ejaculations by males predicted conception in fewer than 60% of pregnancies. Behavioral and ultrasound estimates of conception date were highly correlated and differed by less than I day on average. Accordingly, predictions of delivery date based on behavioral estimates of conception date were as accurate as those based on ultrasound-derived estimates. These data suggest that female-initiated sexual behavior can be used in rhesus monkeys as a practical, non-invasive tool for producing timed matings in social groups of monkeys, providing accurate estimates of conception date, gestational age, and predicted date of birth.

Adaptations to subordinate status in female marmoset monkeys.

In singular cooperatively breeding mammals, social status is a key determinant of female reproductive success. Usually only one dominant female breeds in a social group. In the common marmoset (Callithrix jacchus), a cooperatively breeding primate, adaptations to nonbreeding subordinate status appear to parallel those found in social insect societies which demonstrate similar skew to the marmoset in female reproductive success. Female marmosets exhibit rank-related polyethism in behavior, reproductive neuroendocrinology and non-reproductive physiology, and subordinates participate in alloparental care and territory defense. Olfactory, visual and behavioral cues from dominant female marmosets provide important proximate cues regulating ovarian inhibition in female subordinates. Cooperatively breeding marmosets, therefore, appear to have developed specific neural and neuroendocrine adaptations to subordinate social status analogous to those found in social insects such as the lower wasps, bees and termites. Such parallel developments probably reflect the outcome of repeated convergent evolutionary attempts at adapting to environmental conditions not readily conducive to dispersal and independent breeding.

Neonatal testicular suppression with a GnRH agonist in rhesus monkeys: effects on adult endocrine function and behavior.

Male rhesus monkeys secrete adult levels of androgen for 3 months postnatally. The role of this neonatal testicular secretion in sexual development was investigated by suppressing luteinizing hormone (LH) and testosterone (T) in neonatal male rhesus (n = 6) by administering a gonadotropin-releasing hormone agonist (Ag) for the first 4 months of postnatal life. Controls (n = 4) received vehicle. Six years later, endocrine function and sexual behavior were examined with ovariectomized females (n = 6) receiving periodic estradiol (E2) treatment during the breeding and nonbreeding seasons. During the breeding season, there were no differences between Ag-treated and control males in levels of LH and T or in frequency of copulatory behavior. However, Ag-treated males masturbated less frequently than controls when the females were not on E2. During the nonbreeding season, Ag-treated males had lower T levels than controls when the females were not receiving E2 and copulated less when the females received E2, even though T levels were comparable. During both E2 and non-E2 treatments, Ag-treated males secreted less T per unit of LH than controls. Neonatal Ag treatment had no effect on social rank. These data demonstrate that neonatal testicular suppression, or the Ag treatment itself, altered systems regulating sexual motivation and neuroendocrine control of these males and suggest that the early neonatal period in male rhesus monkeys is another point when the developing central nervous system is sensitive to the organizing actions of androgens.

Antide (Nal-Lys GnRH antagonist) suppression of pituitary-testicular function and sexual behavior in group-living rhesus monkeys.

The ability of a Nal-Lys gonadotropin releasing-hormone antagonist (Antide) to suppress pituitary-testicular function and male sexual behavior was studied in seven group-living adult male rhesus monkeys. Each male received a single 15 mg/kg b.wt. subcutaneous injection of Antide dissolved in equal volumes of propylene glycol and sterile water. Prior to Antide treatment, and at two, four, and eight weeks after Antide, males received an IV bolus of GnRH (50 ng/kg) to assess pituitary and testicular function. For four weeks before and eight weeks after Antide treatment, blood samples and behavioral observations were collected three times weekly in a 74-member heterosexual group. Antide levels increased to more than 150 ng/ml 24 h postinjection and remained above 15 ng/ml for 30 days postinjection. Circulating LH and T were significantly reduced within 24 h following Antide, and remained significantly lower than pretreatment levels in all males for 5 weeks after Antide. T levels rose above 1 ng/ml while Antide levels were still significantly elevated in four males. Both LH and T returned to pretreatment levels by seven weeks post-Antide and then showed a second significant decrease during the eighth study week. Pituitary responsiveness to exogenous GnRH was reduced by Antide and remained below pretreatment levels eight weeks after Antide treatment. Testosterone secretion in response to exogenous GnRH was significantly reduced at two and four weeks post-Antide, but was at pretreatment levels by eight weeks after Antide. Male sexual behavior declined significantly within one week after Antide treatment, almost ceased completely by four weeks after Antide, and returned to pretreatment levels by seven weeks post-Antide.(ABSTRACT TRUNCATED AT 250 WORDS)