Female Prairie Voles Research Articles

Males increase serum estrogen and estrogen receptor binding in brain of female voles

Sexual development of female prairie voles does not occur unless females are exposed to stimuli from an unfamiliar male. Three experiments were conducted to determine whether a saturable high-affinity estradiol binding site (ERN) is present in cell nuclei of brain tissue from females exposed to male stimuli and whether serum estradiol and brain ERN are correlated with the duration of male exposure. Brain ERN were detected and found to be correlated with serum estradiol levels. Significant increases in brain ERN were observed within 18 hours after females were exposed to a male for either a continuous (uninterrupted) or transient ( 1 1 4 hour) period. A significant increase in serum estradiol was observed for females given continuous male exposure. The rate of increase of ERN in brain was significantly higher for females given continuous as opposed to transient male exposure. The results suggest that the continued presence of a male can accelerate the rate of increase of ERN in the brain, presumably through increases in circulating estradiol.

Familiarity and female mate choice in two species of voles ( Microtus ochrogaster and Microtus montanus)

The effect of familiarity on female mate choice was examined in prairie voles ( Microtus ochrogaster) and montane voles ( M. montanus). In experiment I females were given simultaneous access to a male with which they had just mated and to a novel male. Prairie vole females mated preferentially and spent more time with the familiar males; montane voles showed no preference. Experiment II consisted of two tests in which familiarity was established by housing a female across a wire mesh barrier from a male for 2 weeks. Female prairie voles showed no preference based on familiarity. Overriding any effect of adjacent housing was a preference in the second test for the male from which they received their first ejaculate in test 1. Montane voles spent more time with the unfamiliar male. Therefore, in prairie but not montane voles, copulation and/or the receipt of an ejaculate appears to be responsible for the ‘stamping in’ of a preference for a particular male. These results suggest that finely tuned differences in a female's reproductive responses to familiar and unfamiliar males may be proximate behavioural processes underlying species differences in mating systems.

The neuronal activity of the monkey preoptic hypothalamus during thermoregulatory and feeding behavior

It is well established that social environment, particularly isolation, has a significant impact on social behaviors and neuroendocrine responses. Estrogen receptor alpha (ERα) expression in limbic structures and associated nuclei is related to the display of social behaviors. We hypothesized that the stress of isolation would cause changes in the pattern of ERα expression in the brain. Using a highly social (typically monogamous and biparental) rodent species, the prairie vole (Microtus ochrogaster), we housed juvenile voles with a sibling, stranger or in isolation for either 4 days or 21 days. Housing manipulations began following weaning from parents and group housed siblings. Rodents may be especially sensitive to manipulations of their social environment during this juvenile period. In particular, female prairie voles are induced ovulators, reliant upon exposure to an unrelated male (male urine) to become reproductively active. ERα immunoreactivity was quantified in the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BST), ventromedial nucleus of the hypothalamus (VMH) and medial amygdala (MeA). Significantly fewer ERα immunoreactive (ERα-ir) cells were labeled in the MPOA and BST of females isolated for 21 days compared with stranger housed females. Non-significant differences were shown in the VMH and MeA of females. No differences were found in voles isolated for 4 days. These results suggest that female prairie voles may be more sensitive than males to manipulations of their social environment during the juvenile period.

Home Range Overlap and Nest Cohabitation of Male and Female Prairie Voles

The degree of association between male and female prairie voles Microtus ochrogaster was assessed using radiotelemetry. Nine sets of males and females caught together in live traps were fitted with transmitters and monitored for 3-4 days; an additional three sets of voles were radiotracked for 10 days. Eleven of the 12 male-female pairs remained together during the radiotracking period. The areas used by the male and female of each of these pairs overlapped greatly. Furthermore, each pair cohabited in a nesting burrow. On an average of 34.6% of the occasions when simultaneous readings were taken for a male and female, they were together in a nest. These results contrast markedly with field studies of M. pennsylvanicus and M. montanus which have revealed no nest cohabitation by adult males and females. The results of this study support laboratory evidence and live-trapping data suggesting pair-bonding in M.

Male-female interactions in prairie voles

Dyadic encounters between virgin female prairie voles ( Microtus ochrogaster) and males with various reproductive histories were analysed using observational techniques and sequential analysis. Unfamiliar, sexually inexperienced males interacted in a manner that would permit physical contact, pheromone transfer and the subsequent induction of female sexual behaviour. Low levels of olfactory investigation were seen among sibling males and females, which may account for the failure of such pairs to reproduce. Agonistic encounters were common between females and unfamilar sexually-experienced males, suggesting that fighting could also provide a behavioural barrier to reproduction.

Male Vole Urine Changes Luteinizing Hormone-Releasing Hormone and Norepinephrine in Female Olfactory Bulb

Female prairie voles (Microtus ochrogaster) exposed to a single drop of male urine on the upper lip showed changes in concentrations of luteinizing hormone-releasing hormone (LHRH) and norepinephrine in olfactory bulb tissue; no such changes occurred in dopamine concentration. The changes were measured in the posterior but not the anterior olfactory bulb tissue of females within 1 hour after they were exposed to urine. These females also showed rapid increases in serum concentrations of luteinizing hormone. Females exposed to water on the upper lip showed none of these changes. These results suggest that in this species LHRH and norepinephrine in the olfactory bulb may mediate luteinizing hormone release in response to external (pheromonal) chemical cues.

Opiate use and sexual function.

Although opiate addicts often equate the drug experience with sexual orgasm, diminished libido and impaired sexual performance are common sequelae of chronic use. Early clinical studies suggested that opiates may interfere with sex hormone secretion. The authors carried out three sequential studies which demonstrated that heroin use in man results in acute suppression of luteinizing hormone (LH) release from the pituitary followed by a secondary drop in plasma testosterone levels. The time course of these neuroendocrine events correlates well with the tension-reducing effects of heroin and suggests that drive reduction is an important component of opiate reinforcement.

Ovarian hormones regulating sexual and social behaviors in female prairie voles, Microtus ochrogaster

In the induced ovulator, Microtus ochrogaster (the prairie vole), daily injections of estradiol benzoate (EB 0.5 μg or 5.0 μg) facilitated high levels of sexual receptivity in ovariectomized females withing 48 hr of the onset of treatment. A lower level of EB (0.05 μg) with or without progesterone (0.5 mg) for five days did not induce lordosis. Four hr after sexually receptive EB-primed females received progesterone (0.5 mg) they either continued to show lordosis (EB 5.0 μg group) or showed an inhibition of lordosis (EB 0.5 μg group). Within 24 hr lordosis was markedly reduced in both groups. Progesterone-associated inhibitions were no longer apparent 48 hr after progesterone was discontinued. This general pattern of response to ovarian hormones is consistent with data described for other induced ovulators.

Male copulatory behavior and the induction of ovulation in female voles: A quest for species specificity

Two experiments were conducted to investigate species specificity in the neuroendocrine responsiveness of female prairie voles to the copulatory patterns of males. In Experiment 1, prairie vole males mated for one ejaculatory series were not significantly more effective in inducing ovulation in prairie vole females than montane voles mated with prairie vole females for one series, two series, or to satiety. Mating with conspecific males did result in significantly more implanted embryos than did heterospecific matings. In Experiment 2, it was found that, when the amount of vaginal stimulation was both low and equated across groups, prairie vole males were significantly more effective in triggering ovulation in female prairie voles than were either meadow voles or montane voles. Although there appears to be some species specificity to the “vaginal codes” of these congeneric species, its biological significance is unclear.