Biochemical, neural, endocrine and behavioral rhythms play a central role in many different aspects of the reproductive process in animals. These rhythms provide the basis for temporal organization of the reproductive functions of individual animals. In this paper, I introduce our results about the relationship of biological clock to reproductive function, analysis of mechanisms in biological clock, and manipulation of circadian rhythms. Main contents are as follows: 1) The ovulation is induced between 14 and 16 hr after stimulation dissociating entirely with solar hours in light estrous rat. The effectiveness of the cervical stimulation for induction of ovulation in light estrous rats is related to not only the duration of light estrus but also the time after transfer to LL. 2) Both nocturnal and diurnal prolactin surges are controlled by a circadian system. 3) Pseudopregnancy is induced by a single injection of progesterone at a special time. 4) The time of parturition and of pre-partum progesterone decrease is closely associated with an endogenous circadian system. 5) Food restriction is more potent zeitgaber than light in circadian adrenocortical rhythms. 6) The circadian rhythms of blinded rat pups is entrained by the nursing dam. 7) Social cues have a profound effect on the synchronization of the free-running period of adrenocortical rhythm. 8) Carbachol, an acetylcholine agonist, shortens the free-running period of circadian activity rhythm. 9) Melatonin accelerates the re-entrainment of the circadian rhythm to shifted LD cycle. 10) Light signals increase the acetylcholine concentration in suprachiasmatic nucleus, but not the other control site. 11) The cAMP levels in rat suprachiasmatic nucleus show an endogenous circadian rhythm. 12) Long term cultured neuron from rat suprachiasmatic nucleus retain the capacity for circadian oscillation of vasopressin release. 13) Inhibitors of protein synthesis phase shift the circadian clock in chick pineal cells.

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The aim of the present study was to develop an automatic and reliable ice nucleation method by using silver iodide (AgI) as the ice nucleating agent. The effect of the introduction of ice nucleation by AgI was examined by observing the temperature rise due to the release of latent heat of fusion at temperatures where spontaneous freezing did not yet occur. AgI in distilled water was loaded into a plastic straw, and was separated from the freezing solution by air bubbles. By using a copper-constantan thermocouple to measure temperature of latent heat released, it was confirmed that AgI could be used for effective ice nucleation in freezing solutions. Rabbit morulae and bovine Day 7 to 8 embryos were frozen by the AgI seeding method. It became clear that AgI was an effective ice nucleating agent for freezing rabbit and bovine embryos. The original method was improved for practical application by immobilizing AgI in alginate gel. This method makes it possible to immerse AgI with embryos in any kind of freezing vessels. The reliability of seeding increased when this method was used, judging from the high post thaw survival of the bovine embryos. The process of ice crystal growth germinating from AgI alginate gel droplets was observed under a cryomicroscope. The droplets suspended in a solution containing 10% glycerol or 11% dimethyl sulfoxide germinated ice crystals at approximately -8°C. The start of freezing in the straw used to be detected indirectly with a thermocouple as a temperature increase due to the emission of the latent heat. Thus, it was uncertain whether the freezing was induced through the aid of AgI alginate gel droplets or not. This problem appeared to be clarified by the cryomicroscopic observation.

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