Reproductive responses of male Microtus montanus to photoperiod, melatonin, and 6-MBOA.
Juvenile male Microtus montanus were examined for the effects of photoperiod, melatonin, and the naturally occurring reproductive stimulant 6-MBOA on growth and sexual maturation. 6-MBOA, present in sprouting grass, is an important environmental cue used for the initiation of reproduction in natural populations of this species. Long photoperiod (16:8) was stimulatory to body, testes, and seminal vesicle growth, while short photoperiod (8:16) inhibited these parameters. The pineal hormone melatonin, administered via daily afternoon injections (5 micrograms), was also inhibitory to all of the above parameters as well as to serum testosterone. 6-MBOA, administered via injection (0.0001-100 micrograms) or dietary means (0.1 or 1.0 microgram/gm unsifted chow), appeared unable to augment the rate of maturation in long-photoperiod-stimulated animals. When short-photoperiod animals were treated with high doses of the compound (100 micrograms injected or 1.0 micrograms/gm sifted chow), body and gonadal growth was inhibited to a greater extent than when animals were exposed to short photoperiod alone, and serum LH was reduced. Lower doses of the compound had no effect. Melatonin-treated animals experienced less maturational inhibition when simultaneously given a low dose of 6-MBOA-coated chow (1.0 micrograms/gm unsifted chow). A higher dose of 6-MBOA (1.0 micrograms/gm sifted chow) was ineffective in preventing the response to melatonin. These results indicate that 1) male M. montanus utilize photoperiod, rather than 6-MBOA, as a primary environmental cue, 2) high doses of 6-MBOA can be inhibitory under short photoperiod, 3) juvenile male voles are highly sensitive to the inhibitory effects of exogenously administered melatonin, and 4) 6-MBOA can partially prevent the inhibitory effects of melatonin on growth and sexual maturation.
Department of Biology, University of Utah, Salt Lake City 84112.
B A
BA
Gower
P J
PJ
Berger
D000704:Analysis of Variance; D000818:Animals; D003411:Arvicolinae; D001583:Benzoxazoles / Q000494:pharmacology*; D001835:Body Weight / Q000187:drug effects; D004338:Drug Combinations; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009929:Organ Size / Q000187:drug effects; D010507:Periodicity; D011863:Radioimmunoassay; D012098:Reproduction / Q000187:drug effects / Q000502:physiology*; D013737:Testis / Q000187:drug effects / Q000502:physiology; D013739:Testosterone / Q000097:blood
D001583:Benzoxazoles; D004338:Drug Combinations; D013739:Testosterone; C031896:6-methoxybenzoxazolinone; D007986:Luteinizing Hormone; D008550:Melatonin