Effects of photoperiod and 6-methoxy-2-benzoxazolinone on male-induced estrus in prairie voles

Abstract

Prairie voles (Microtus ochrogaster) are characterized as facultative breeders with higher rates of reproductive activities observed during spring and summer than autumn and winter. The environmental factors regulating seasonal breeding in this species remain unspecified. Short day lengths inhibit reproductive organ development in male prairie voles in the laboratory, but these males remain fertile and capable of siring offspring; female prairie voles have been reported to be reproductively unresponsive to day length in the laboratory. The organization of estrus in this species is unusual in that females never display the cyclic changes associated with estrus; rather, female prairie voles require chemosensory stimuli associated with fertile males in order to be induced into estrus. The plant compound, 6-methoxy-2-benzoxazolinone (6-MBOA), is present in vegetatively growing grasses and sedges and acts to trigger reproduction in other rodent species exposed to short days. It was suspected that 6-MBOA present in the laboratory diet may have overridden the effects of photoperiod on female prairie voles in previous laboratory studies. In the present study, the effects of 6-MBOA and photoperiod on estrus induction were examined. Beginning at Week 0, female prairie voles were housed in long (LD 16:8) or short (LD 8:16) photoperiods for 9 weeks, then implanted subcutaneously either with an empty Silastic capsule or one packed with 6-MBOA. A special diet, devoid of 6-MBOA, was available ad lib from Week 5 to the end of the study. At the start of Week 11, a single drop of breeder male urine or distilled water was applied to the external nares of each female daily for 6 consecutive days. Neither exposure to male urine nor to 6-MBOA affected reproductive organ masses in short-day females. In long days, uterine and ovarian masses were elevated as compared to short-day voles. Treatment with male urine, but not 6-MBOA, further stimulated uterine development in long-day females. Taken together, these results document that the reproductive systems of female prairie voles respond to day length, but are not particularly responsive to short-term exposure to 6-MBOA.