INFLUENCE OF IMMOBILIZATION STRESS UPON THE PARADOXICAL SLEEP (EEG AFTERREACTION) IN THE RABBIT

Abstract

The influence of immobilization stress upon the incidence of the episode of paradoxical sleep (PS) was studied both in mature ovariectomized and immature New Zealand White rabbits with electrodes implanted chronically in several parts of the brain.The characteristic EEG changes of PS and animal's behavior as well as remarkable diminutions of electromyographic discharges from m. trapeziuspars cervicalis and m. scutuloauricularis superior were employed as indicators of the PS appearance, and the following sequences of PS have been observed. 1. The distribution of spontaneous PS episodes was markedly increased for 4-8 hours soon after the release of a 12 hours insomnia, reaching 2.1-5.5 times as large as that of pre-insomnia. In case of insomnia lasting nearly 24 hours, however, there was observed the merely 1.3-1.7 times increased distribution for 4-8 hours immediately after its release as compared with that of preinsomnia.2. In the mature rabbit with immobilization stress imposed for 6 hours, the PS episode was depressed in a marked degree for 4-8 hours soon after its release; especially for the first 4 hours after release, almost no PS distribution was made. On the other hand, in case of the immature rabbit, there was hardly observed any blocking effect upon the distribution of PS.3. Only a slight or almost no PS blocking phenomenon induced by the stress was observed in the rabbit implanted with minute amount of hydrocortisone in various regions of the brain such as the ant. median eminence, supraoptic region and the ventromedial hypothalamus.4. The spontaneous PS was blocked nearly two hours after the intravenous administration of ACTH (0.5-1.0 u. s. p. u.), and the threshold of the electricallyinduced PS was also elevated about 10 times as high as that of pre-injection.On the other hand, the PS was not blocked with hydrocortisone (0.8-2.0mg) or desoxycorticosterone (0.8-2.0mg) injected intravenously. Moreover, in case of adrenalectomized animals, there was observed the lesser distribution of the PS than the non-adrenalectomized without the administration of hydrocortisone and desoxycorticosterone. Further, from the facts that the distribution of PS episode was promoted by adrenalin (5-10γg), oxytocin (0.3-1.0 u.) and vasopressin (0.3-0.5 u.), the blocking effect of stress upon the PS appearance seems to be based not on increased ACH, but on the increase of ACTH in the blood.5. Both in the intact and supracollicular transectioned rabbit, the blocking effect of insulin (1.0-2.0 u.) was exerted upon the spontaneous PS episode for 85-101 minutes after intravenous injection and the PS threshold from electrically stimulating the septum had significantly risen over 10 times as high as the initial level within one hour following administration of 1.0u. of insulin.6. Repeated immobilization stress resulted in almost no PS blocking phenomenon after release from the 5th or 6th stress.