Neuroendocrinological study on the initial process of photostimulated LH release.

• Project/Area Number: 60540480
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 動物形態・分類学
• Research Institution: Tokyo Medical and Dental University
• Principal Investigator: WADA Masaru Tokyo Medical and Dental University, Department of General Education, 教養部, 助教授 (40100953)
• Project Period (FY): 1985 – 1986
• Project Status: Completed (Fiscal Year 1986)
• Budget Amount: ¥1,700,000 (Direct Cost: ¥1,700,000); Fiscal Year 1986: ¥500,000 (Direct Cost: ¥500,000); Fiscal Year 1985: ¥1,200,000 (Direct Cost: ¥1,200,000)
• Keywords: Gonadotropin release / Luteinizing hormone / Testosterone / Melatonin / Japanese quail / 分泌パターン / 神経内分泌

Research Abstract

The aim of this research project is to investigate an initial process of luteinizing hormone (LH) secretion induced by phtostimulation in Japanese quail (Coturnix coturnix japonica).
1. As already clarified by many preceding investigations, a change of photoperiods from 8L16D to 16L8D induces a rapid LH release in photosensitive birds. However, a precise profile of LH secretion is not fully inestigated. A previous project supported by a Grant-in-Aid from the Ministry of Education, Science and Culture (1984) revealed that LH increase is attained by abrupt release rather than gradual increase in the initial process, if a sampling interval is reduced. The profile of abrupt LH release is similar to the release pattern of LH found with ovulatory cycle. However, administration of either pentobarbital or phenobarbital could not block photoinduced LH secretion both in males and females, injected either at, before or after the photoinducible phase. Phenobarbital injection 10 hours before the exp ected LH surge completely blocked LH release and subsequent ovulation while control injection did not. Several drugs that inhibit neurotransmitter release or synthesis also did not block LH secretion. These results indicate that photostimulated LH secretin is very different from LH surge in which the neural triggering is involved and that dependent more directly on photic information.
2 After several days of photostimulation, LH levels have increased and these high levels are maintained thereafter; it becomes difficult to detect a rhythm of LH secretion. Plasma levels of testosterone (T) gradually increase on day 3 to day 4 of photostimulation. However, T implants did not enhance LH secretion, rather it suppress LH release. In vitro experiment indicated that continuous and frequenet exposures of LHRH did not induce and maintain LH release except the first release. LHRH applied every 60 minutes maintained LH release suggesting an optimum interval of LHRH stimulation for LH release.
3 Melatonin is knownw to be involved in control of breeding in shortday mammals, such as sheep and goat. Melatonin injection or implantation did not interfare photoperiodic stimulation LH release.