Photoperiodic and temporal influences on chemosensory induction of brain fos expression in female prairie voles.

Prairie voles (Microtus ochrogaster) typically stop breeding during winter. Male prairie voles respond to winter day lengths with gonadal regression, whereas female voles are relatively unresponsive to photoperiod. Unlike commonly studied laboratory rodents, female prairie voles do not exhibit spontaneous oestrous cycles. Instead, females are induced into oestrus by chemosensory cues from conspecific male urine. The present study investigated the interaction among day length, chemosensory cues and the initial brain responses during oestrus induction in female voles. A single drop of male conspecific urine, saline or skimmed milk was applied to the nares of female prairie voles housed for 9 weeks in either long (LD 16 : 8 h) or short (LD 8 : 16 h) days. Animals were killed 0.5, 1, 2 or 24 h after chemosensory treatment and their brains were processed for Fos immunocytochemistry. Body mass and ovarian fat pad mass were higher, but uterine and ovarian mass were lower, in short-day compared to long-day females. Regardless of photoperiod, Fos- immunoreactivity increased in the granule layer of the accessory olfactory bulb (AOB), the supraoptic nucleus and bed nucleus of the stria terminalis (BNST) (anterior medial) in females treated with male urine compared to the two control groups. Fos staining intensified in the AOB, medial and posterocortical medial amygdala and BNST (posterior ventral), 1 h and 2 h after urine treatment. In the medial preoptic area, anterior and lateral hypothalamus, and ventromedial nucleus of the hypothalamus, Fos-immunoreactivity was elevated in females 2 h after receiving urine. Overall, long-day females displayed higher Fos expression in response to urine than females maintained in short days. These results identify a putative neural circuitry of oestrus induction in this species, and provide an approximate time line of activation in the brain circuit responsible for oestrus induction in prairie voles.

Social environment and steroid hormones affect species and sex differences in immune function among voles.

Testosterone has bipotential effects on male fitness; that is, it both suppresses immune function and maintains characteristics important for reproductive success. Presumably, these effects of testosterone may be more pronounced among polygynous species because testosterone concentrations are generally higher among polygynous than monogamous males. The present study examined sex and species differences in cell-mediated immunity among four arvicoline rodents. The role of mating system and sex steroids in sex differences in immune function was examined in individually housed polygynous meadow (Microtus pennsylvanicus) and montane (M. montanus) voles and monogamous prairie (M. ochrogaster) and pine (M. pinetorum) voles in Experiment 1. No sex differences in splenocyte proliferation were observed among the four species and circulating testosterone concentrations did not correlate with immune function of individuals within each species. The contribution of social isolation to these results was examined in Experiment 2, in which meadow and prairie voles were housed individually, or with same- or opposite-sex conspecifics in either pairs or groups of four per cage for 28 days. Overall, prairie voles exhibited more robust immune responses than meadow voles when housed in pairs or in same-sex groups. Sex differences in immune function were also apparent; male meadow voles had higher immune responses than female conspecifics when housed in pairs, whereas female prairie voles had higher responses than male conspecifics when housed in same-sex pairs. Circulating sex steroid hormones and corticosterone appear to mediate some, but not all, of the changes in immune function evoked by differential housing conditions. Taken together, these results suggest that social factors have significant effects on immunity and should be considered in studies of sex differences in immunity at both proximate and ultimate levels.

Characterization of sensorimotor performance, reproductive and aggressive behaviors in segmental trisomic 16 (Ts65Dn) mice.

In the present study, segmental trisomy 16 (Ts65Dn) mice, an animal model of Down Syndrome (DS), were examined for sensorimotor, reproductive, and aggression abnormalities associated with DS. The Ts65Dn mice exhibited no sensorimotor deficits in olfactory sensitivity, visual abilities, orientation reactions, forelimb strength, postural skills, balance/ coordination, climbing, or locomotion compared to genetically matched control B6EiC3HF1 mice. In mating tests, the percentage of Ts65Dn mice displaying intromissions when paired with estrous females was significantly less than that in controls. Although the percentage of Ts65Dn mice that mounted and ejaculated with an estrous female was marginally less than in controls, there were no significant differences on the other measures of reproductive behavioral performance. In aggression tests, Ts65Dn males showed increased offensive aggression in a neutral arena both when paired and among grouped males. Conversely, Ts65Dn mice exhibited less offensive aggression against an intruder in their home cage than control males. In sum, these mice possess some of the adaptive behavior abnormalities observed in DS patients; however, because the Ts65Dn mice do not have any observed sensorimotor deficits that could interfere with behavioral assessments, they may serve as a useful model for the study of behavioral impairments associated with DS.