ZOOLOGICAL SCIENCE 5: 1137-1139 (1988) ? 1988 Zoological Society of Japa [COMMUNICATION] Effects of Adult Male Cohabitation on Precocious Puberty in Early Weaning Female Guinea Pigs Tadashi Kosaka, Masaki Obata, Toru R. Saito and Kazuaki W. Takahashi 1 Toxicology Division, Institute of Environmental Toxicology, Suzuki-cho 2-772, Kodaira-shi, Tokyo 187, and ' Department of Laboratory Animal Science, Nippon Veterinary & Zootechnical College, Kyonan-cho 1-7-1, Musashino-shi, Tokyo 180, Japan ABSTRACT? The effects of adult male cohabitation with infant female guinea pigs weaned at 2 days or 4 days of age on the onset of puberty were investigated. The females weaned at 4 days had no growth abnormalities, while 2 of 20 females weaned at 2 days died due to developmental abnormalities. Cohabitation with an adult male significantly advanced the day of vaginal opening in the females weaned at 4 days. During the first vaginal opening, 4 of 9 and 7 of 10 females with male cohabitants in the groups weaned at 2 and 4 days old, respectively, copulated, became pregnant and delivered normally. These results indicated that advancement of female puberty was produced by continuous exposure to an adult male even in infant female guinea pigs weaned at 4 days. INTRODUCTION Social stimuli that operate primarily through olfactory mechanisms, including presence of males, influence reproductive biology in mice [1- 4]. Similar sensory mechanisms are undoubtedly involved in modifying animal reproduction. Pre- vious reports have shown that the presence of an adult male accelerates the sexual maturation of female mice [1, 2, 5-9], rats [3], pigs [10] and human beings [11]. In guinea pigs, our previous work [12] indicated that a similar advancement in puberty was caused by adult male cohabitation from the day of normal weaning (1 or 2 weeks of Accepted February 15, 1988 Received October 28, 1987 age). It is known that newborn babies of guinea pigs are well-developed compared with other rodents, i.e., the babies have a fully developed coat, walk immediately and eat food; their teeth are useful and their eyes are open. Thus, it seems possible that social stimuli can play a useful role in infant guinea pigs weaned earlier than normal. The present study, therefore, was designed to investigate the influence of continuous exposure to an adult male on the onset of female sexual maturation in infant female guinea pigs weaned early. MATERIALS AND METHODS Albino guinea pigs of the Hartley strain were used. They were kept in a controlled semi-barrier system room with a temperature of 22?2?C, a photoperiod of 14 hr light/10 hr dark (lights on from 05:00 to 19:00hr) and ventilation 12 times an hour. The females were housed individually, either alone or with an adult male cohabitant in an aluminum cage (260Wx400Dx200H mm), and given commercial pellets (GB-1, Funabashi Farm Inc.) and tap water ad libitum. Infant female guinea pigs were weaned at the age of 2 days (group A) and 4 days (group B). Each group was then divided into two subgroups. One subgroup of females was continuously ex- posed to an adult male (5 to 12 months old) with proven fertility from the time of weaning until the
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ZOOLOGICAL SCIENCE 5: 1137-1139 (1988) ? 1988 Zoological Society of Japa [COMMUNICATION] Effects of Adult Male Cohabitation on Precocious Puberty in Early Weaning Female Guinea Pigs Tadashi Kosaka, Masaki Obata, Toru R. Saito and Kazuaki W. Takahashi 1 Toxicology Division, Institute of Environmental Toxicology, Suzuki-cho 2-772, Kodaira-shi, Tokyo 187, and ' Department of Laboratory Animal Science, Nippon Veterinary & Zootechnical College, Kyonan-cho 1-7-1, Musashino-shi, Tokyo 180, Japan ABSTRACT? The effects of adult male cohabitation with infant female guinea pigs weaned at 2 days or 4 days of age on the onset of puberty were investigated. The females weaned at 4 days had no growth abnormalities, while 2 of 20 females weaned at 2 days died due to developmental abnormalities. Cohabitation with an adult male significantly advanced the day of vaginal opening in the females weaned at 4 days. During the first vaginal opening, 4 of 9 and 7 of 10 females with male cohabitants in the groups weaned at 2 and 4 days old, respectively, copulated, became pregnant and delivered normally. These results indicated that advancement of female puberty was produced by continuous exposure to an adult male even in infant female guinea pigs weaned at 4 days. INTRODUCTION Social stimuli that operate primarily through olfactory mechanisms, including presence of males, influence reproductive biology in mice [1- 4]. Similar sensory mechanisms are undoubtedly involved in modifying animal reproduction. Pre- vious reports have shown that the presence of an adult male accelerates the sexual maturation of female mice [1, 2, 5-9], rats [3], pigs [10] and human beings [11]. In guinea pigs, our previous work [12] indicated that a similar advancement in puberty was caused by adult male cohabitation from the day of normal weaning (1 or 2 weeks of Accepted February 15, 1988 Received October 28, 1987 age). It is known that newborn babies of guinea pigs are well-developed compared with other rodents, i.e., the babies have a fully developed coat, walk immediately and eat food; their teeth are useful and their eyes are open. Thus, it seems possible that social stimuli can play a useful role in infant guinea pigs weaned earlier than normal. The present study, therefore, was designed to investigate the influence of continuous exposure to an adult male on the onset of female sexual maturation in infant female guinea pigs weaned early. MATERIALS AND METHODS Albino guinea pigs of the Hartley strain were used. They were kept in a controlled semi-barrier system room with a temperature of 22?2?C, a photoperiod of 14 hr light/10 hr dark (lights on from 05:00 to 19:00hr) and ventilation 12 times an hour. The females were housed individually, either alone or with an adult male cohabitant in an aluminum cage (260Wx400Dx200H mm), and given commercial pellets (GB-1, Funabashi Farm Inc.) and tap water ad libitum. Infant female guinea pigs were weaned at the age of 2 days (group A) and 4 days (group B). Each group was then divided into two subgroups. One subgroup of females was continuously ex- posed to an adult male (5 to 12 months old) with proven fertility from the time of weaning until the
Effects of Adult Male Cohabitation on Precocious Puberty in Early Weaning Female Guinea Pigs : COMMUNICATION : Reproductive Biology
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