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RISS 인기검색어
- 검색키워드
- 저자 : Donchan Choi (검색결과 39 건)
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Donchan Choi 한국발생생물학회 2013 발생과 생식 Vol.17 No.2
Golden hamsters reproduce in a limited time of a year. Their sexual activities are active in summer but inactive in winter during which day length does not exceed night time and environmental conditions are severe to them. The reproductive activities are determined by the length of light in a day (photoperiod). Melatonin is synthesized and secreted only at night time from the pineal gland. Duration of elevated melatonin is longer in winter than summer, resulting in gonadal regression. The present study aimed at the influences of continuous melatonin treatments impinging on the gonadal function in male golden hamsters. Animals received empty or melatonin-filled capsules for 10 weeks. They were divided into long photoperiod (LP) and short photoperiod (SP). All the animals maintained in LP (either empty or melatonin-filled capsules) showed large testes, implying that melatonin had no effects on testicular functions. Animals housed in SP displayed completely regressed testes. But animals kept in SP and implanted with melatonin capsules exhibited blockage of full regression by SP. These results suggest that constant release of melatonin prohibits the regressing influence of SP.
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The Consequences of Mutations in the Reproductive Endocrine System
Choi Donchan 한국발생생물학회 2012 발생과 생식 Vol.16 No.4
The reproductive activity in male mammals is well known to be regulated by the hypothalamus-pituitary-gonad axis. The hypothalamic neurons secreting gonadotropin releasing hormone (GnRH) govern the reproductive neuroendocrine system by integrating all the exogenous information impinging on themselves. The GnRH synthesized and released from the hypothalamus arrives at the anterior pituitary through the portal vessels, provoking the production of the gonadotropins(follicle-stimulating hormone (FSH) and luteinizing hormone (LH)) at the same time. The gonadotropins affect the gonads to promote spermatogenesis and to secret testosterone. Testosterone acts on the GnRH neurons by a feedback loop through the circulatory system, resulting in the balance of all the hormones by regulating reproductive activities. These hormones exert their effects by acting on their own receptors, which are included in the signal transduction pathways as well. Unexpected aberrants are arised during this course of action of each hormone. This review summarizes these abnormal phenomena, including various mutations of molecules and their actions related to the reproductive function.
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Choi, Donchan The Korean Society of Developmental Biology 2013 발생과 생식 Vol.17 No.2
Golden hamsters reproduce in a limited time of a year. Their sexual activities are active in summer but inactive in winter during which day length does not exceed night time and environmental conditions are severe to them. The reproductive activities are determined by the length of light in a day (photoperiod). Melatonin is synthesized and secreted only at night time from the pineal gland. Duration of elevated melatonin is longer in winter than summer, resulting in gonadal regression. The present study aimed at the influences of continuous melatonin treatments impinging on the gonadal function in male golden hamsters. Animals received empty or melatonin-filled capsules for 10 weeks. They were divided into long photoperiod (LP) and short photoperiod (SP). All the animals maintained in LP (either empty or melatonin-filled capsules) showed large testes, implying that melatonin had no effects on testicular functions. Animals housed in SP displayed completely regressed testes. But animals kept in SP and implanted with melatonin capsules exhibited blockage of full regression by SP. These results suggest that constant release of melatonin prohibits the regressing influence of SP.
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The Potential Regressive Role of Syzygium aromaticum on the Reproduction of Male Golden Hamsters
Choi, Donchan,Roh, Hyun Soo,Kang, Dong Won,Lee, Jong Seok The Korean Society of Developmental Biology 2014 발생과 생식 Vol.18 No.1
The flower buds of Syzygium aromaticum (clove) have been used as traditional medicine for the treatment of male sexual disorders in Asian countries. Recently, there are some reports about the effects of the clove on reproductive activities in mammals. Therefore, its effect on testicular function was examined in male golden hamsters whose reproductive activity is inhibited by photoperiod such as winter climate. The male animals were given by daily oral administrations (56 consecutive days) in three doses (4 mg, 20 mg, and 100 mg/kg BW) of the alcoholic extract of the clove. Generally lower dose (4 mg) of the extract continued to keep the reproductive activities of testes. The both middle and high doses (20 mg and 100 mg) of the extract completely inhibited the testicular activity in some animals. Taken together, these results suggest a possible biphasic action of alcoholic extract of Syzygium aromaticum flower bud on testicular function.
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Potency of Melatonin in Living Beings
Choi, Donchan The Korean Society of Developmental Biology 2013 발생과 생식 Vol.17 No.3
Living beings are surrounded by various changes exhibiting periodical rhythms in environment. The environmental changes are imprinted in organisms in various pattern. The phenomena are believed to match the external signal with organisms in order to increase their survival rate. The signals are categorized into circadian, seasonal, and annual cycles. Among the cycles, the circadian rhythm is regarded as the most important factor because its periodicity is in harmony with the levels of melatonin secreted from pineal gland. Melatonin is produced by the absence of light and its presence displays darkness. Melatonin plays various roles in creatures. Therefore, this review is to introduce the diverse potential ability of melatonin in manifold aspects in living organism.
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Identification of a Partial Melatonin Receptor in Golden Hamster(Mesocricetus auratus)
Choi,Donchan 용인대학교 자연과학연구소 1998 自然科學硏究所論文誌 Vol.3 No.1
Reproductive activity is regulated by the photoperiod in golden hamsters (Syrian hamster, Mesocricetus auratus). They are sexually active in summer and inactive in winter. A major key that controls the seasonal reproductive activity is the length of the light per day, which is transmitted to the pineal gland, secreting the hormone melatonin. Melatonin is known to mediate circadian rhythm and sexual activities in seasonal breeding animals. Melatonin receptor was recently cloned in several animal species including human. But nothing has been known about it in golden hamster. By using reverse transcription polymerase chain reaction (RT-PCR) methods, a portion of the melatonin receptor gene (309 nucleotides) was for the first time identified in golden hamster. The nucleotide sequence analysis of melatonin receptor of golden hamster shows a homology of 96%, 92%, 88%, 83%, and 80% with stripped hairy-footed hamster, house mouse, Norway rat, human, and sheep, respectively . The amino acid sequence deduced displays a homology of 98%, 91%, 91%, 84%, and 81% with the same order of animals mentioned above. Melatonin receptors were obviously detected in hypothalamus, pituitary containing pars tuberalis, blood, spleen, and adrenal gland. A part of melatonin receptor identified in the GT1-1 cells, which release gonadotropin-release hormone (GnRH), was identical to the reported mouse melatonin receptor. these findings favor molecular insight to investigate the effect of melatonin on reproductive activity that is established in the golden hamster and to examine other possible functions. Furthermore, the presence of melatonin receptor in GT1-1 cell suggests putative function to regulate the synthesis or release of GnRH.
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Choi, Donchan 용인대학교 자연과학연구소 1997 自然科學硏究所論文誌 Vol.2 No.2
Serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin (PRL) levels and the effects of naloxone on the pituitary hormone release were examined in melatonin-implanted male Syrian hamsters housed in either long (LP) or short photoperiod (SP). Adult male hamsters received Silastic capsules filled with crystalline melatonin and were either transferred to SP (12L:12D) or remained on LP (14L:10D). Non-implanted animals served as controls. Testicular weights were determined from measurement by laparotomy performed at 0, 6, 15, and 20 weeks. At 26 weeks, all animals were killed by decapitation and testes were weighed. Serum LH, FSH, and PRL concentrations were measured from blood withdrawn by cardiac puncture 15 minutes after subcutaneous injection of saline or naloxone at 5, 10, 15, 20, and 25 weeks. Controls in SP had regressed testes followed by recrudescence. Animals with melatonin implants had large testes regardless of photoperiod. Serum LH, FSH, and PRL levels were decreased by SP exposure at week 10, week 5, and weeks 5, 10, and 15, respectively. Continuously released melatonin by implantation prevented the reductions of the pituitary homones caused by SP. Naloxone increased LH and decreased PRL, and had no effect on FAH levels in LP control hamsters. The effects of naloxone were eliminated at weeks 5, 10, 15, and 20 for LH and at weeks 5, 10, and 15 PRL in SP control hamsters. In melatonin-implanted hamsters housed in both LP and SP, naloxone increased LH concentrations at 5, 10, and 25 weeks but was without effect at 15 and 20 weeks. Serum PRL levels were consistently decreased by naloxone in melatonin-implanted hamsters without respect to photoperiod. Unexpectedly naloxone caused serum FSH levels to decrease in melatonin-implanted SP animals. These observations indicate that in SP the continuous presence of melatonin prolongs the function of opioidergic neurons and maintains gonadal activity. These results suggest that opioidergic neurons may mediate the progonadotropic effect of exogenous melatonin.
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