Evidence that short photoperiod-induced gonadal regression in the Mongolian gerbil is mediated by the action of melatonin in the medial hypothalamus.
The present study was undertaken to examine the effects of exposure to short photoperiod (SD) and treatment with subcutaneous (s.c.) or intrahypothalamic melatonin-containing beeswax implants on reproduction in the Mongolian gerbil Meriones unguiculatus. Exposure of adult female gerbils to SD (8 h light: 16 h dark) caused a significant decrease in weight of the reproductive tract (ovaries, oviducts, uterus and vagina; RTW) compared to animals maintained under stimulatory photoperiod (12 h light: 12 h dark; 81.4 +/- 8.0 mg vs 151.8 +/- 16.0 mg, respectively (P less than 0.01]. Treatment with two large s.c. implants, each containing 3 mg melatonin, mimicked the antigonadal effect of SD (68.7 +/- 3.9 mg vs 118.1 +/- 19.5 mg for the blank (melatonin-free) implant controls; P less than 0.05). Gerbils with a small melatonin-beeswax pellet (containing 0.2 mg melatonin) in the anterior hypothalamus (AH) underwent a significant reduction in RTW compared to gerbils with a blank intrahypothalamic implant (73.0 +/- 5.7 mg vs 134.6 +/- 14.5 mg, respectively; P less than 0.01). Melatonin pellets in the mediobasal hypothalamus (MBH) also induced gonadal regression, but to a lesser degree (88.7 +/- 12.6 mg; P less than 0.05 vs blank controls). Small melatonin pellets placed elsewhere in the hypothalamus or s.c. had little effect on RTW (143.4 +/- 20.9 mg and 129.2 +/- 19.7 mg, respectively). Only 25% of the gerbils with melatonin pellet in the AH or MBH had a corpus luteum compared to 73% of the blank controls (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Devries
M J
MJ
Department of Biological Sciences, Kent State University, OH 44242.
Ferreira
S A
SA
Glass
J D
JD
D000818:Animals; D004343:Drug Implants; D005260:Female; D005849:Gerbillinae / Q000378:metabolism / Q000502:physiology*; D007033:Hypothalamus, Middle / Q000187:drug effects / Q000502:physiology*; D008550:Melatonin / Q000494:pharmacology*; D010053:Ovary / Q000187:drug effects / Q000502:physiology*; D012621:Seasons
D004343:Drug Implants; D008550:Melatonin