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M R Gorman

Publications and source records attributed to M R Gorman.

24 records · Page 2Linked to original sources
PubMed1994

Melatonin influences sex-specific prenatal mortality in meadow voles.

Meadow voles exhibit seasonal changes in litter size, ovulation rates, and prenatal mortality. To investigate the proximate bases of seasonal changes in reproductive effort, adult female voles, maintained in long photoperiods (14 h of light/day), were injected daily with 10 micrograms melatonin 2 h before light offset to extend the duration of the nighttime melatonin pulse. At parturition the number, sex, and weight of offspring were assessed. The number of ovarian corpora lutea (CL), an index of potential litter size, was used to calculate rates of prenatal survival (i.e., pups per CL). Prenatal survival rates were reduced in female but not male pups of dams that had been injected before blastocyst implantation (Days 1-6 of pregnancy) with melatonin as compared with saline. Melatonin injections initiated after blastocyst implantation (Days 7-21 of pregnancy) did not affect prenatal survival, nor were birth weights of pups affected by either pre- or postimplantation melatonin treatment. We conclude that sex-specific prenatal survival is a labile feature of vole reproduction that may be under proximate control of photoperiod and melatonin before blastocyst implantation.

Animals↗
PubMed1992

Photoperiod and gonadal hormones influence odor preferences of the male meadow vole, Microtus pennsylvanicus.

Male meadow voles housed in a long photoperiod (14 h light/day, LP) preferred female to male odors, whereas males maintained in a short photoperiod (10 h light/day, SP) did not display preferences for odors of either sex. These odor-preference patterns matched those of free-living males during spring and autumn, respectively. The preference of LP male voles for female over male odors was eliminated by gonadectomy and reinstated by treatment with testosterone. In SP males, although gonadectomy did not affect odor choices, a preference for female odors was induced by testosterone treatment. Treatment with estradiol did not alter odor preferences of LP or SP males. In conjunction with previous result, the present findings suggest that hormonal responsiveness of neural substrates that control odor preferences are sexually dimorphic and may reflect sex differences in reproductive strategies.

Animals↗
PubMed1992

Influence of gonadal hormones on odours emitted by male meadow voles (Microtus pennsylvanicus).

Free-living male meadow voles (Microtus pennsylvanicus) emit odours that are attractive to females at the beginning, but not at the end, of the breeding season. The effect of gonadal hormones on female-attractant cues was examined in males born and reared in long (14 h light day-1) and short (10 h light day-1) photoperiods that simulate daylengths in the breeding and nonbreeding seasons, respectively. Gonadectomy affected the attractant properties of odours emitted by long photoperiod, but not short photoperiod, males. Long photoperiod females preferred odours of intact rather than those of gonadectomized long photoperiod males, and odours of gonadectomized long photoperiod males rather than those of intact short photoperiod males. Females did not show a preference between the odours of intact and castrated short photoperiod males. Gonadal hormone replacement in males affected female responses to the odours emitted by long photoperiod, but not short photoperiod, gonadectomized males. Long photoperiod females did not display a preference between odours of intact long photoperiod males and gonadectomized long photoperiod males treated with testosterone or oestradiol. We conclude that in spring and summer gonadal hormones increase attractiveness of male odours; this effect may require aromatization of testosterone to oestradiol. Substrates that control attractiveness of odour cues in male voles appear to be unresponsive to androgens during the nonbreeding season.

Animals↗
PubMed1991

Ovarian hormones influence odor cues emitted by female meadow voles, Microtus pennsylvanicus.

During the spring-summer breeding season female meadow voles emit odors that are preferred by males, whereas in the autumn-winter season of reproductive quiescence females emit odors that are not preferred by males, but are attractive to females. The effects of daylength and ovarian hormones on salience of female odors were determined by assaying male responses to odors. Females housed in long and short photoperiods transmitted odors that elicited responses similar to those of spring and autumn female voles, respectively. The odor cues emitted by ovariectomized (OVX) females, irrespective of photoperiodic history, were similar to those generated by females during the nonbreeding season. In the absence of ovarian hormones, long daylengths were not sufficient to induce females to broadcast the spring odors preferred by males. Spring-type odor cues were, however, emitted by OVX voles housed in either photoperiod and treated with estradiol. Ovarian hormones appear necessary and sufficient to generate breeding season odor cues and sufficient to induce production of such cues during the nonbreeding season. We conclude that daylength affects odor cues emitted by females by altering ovarian hormone activity.

Animal Communication↗