STUDIES ON THE EFFECT OF ANOXIC ANOXIA ON THE CENTRAL NERVOUS SYSTEM

Abstract

Studies on the effect of lowered barometric pressure on unanesthetized rats have shown that when the ascent is carried out rapidly a period of temporary silence of the cortex occurs at a level of 190 mm. Hg from which the animals recover spontaneously in spite of continued lowered barometric pressure. During the period of cortical silence righting reflexes are absent. Recovery is accompanied by the appearance of large spin-dles of a frequency of 8 to 10/sec. Righting reflexes reappear during this period but the animals remain depressed. Rats injected with benzedrine show similar changes in EEG as far as the period of cortical silence is concerned, but they show during the subsequent recovery a normal'' EEG without spindles and without any other signs of depression of activity. If the pressure is gradually lowered to 190 mm. Hg, the periods of temporary silence may be absent, but spindles accompanied by a general depression of the animals are found. The occurrence of spindles is confined mostly to barometric pressures varying between 280 mm. Hg and 160 mm. Hg. If the pressure is lowered to 110 to 140 mm. Hg, a period of electrical silence occurs from which no recovery at that barometric pressure is possible. As the gasping and slowing of pulse show, the medulla is involved under these conditions. Benzedrine which increases the resistance of rats to anoxia as indicated by the EEG at moderate degrees of anoxia does not increase the resistance or the survival time of rats under conditions of extreme anoxia. Conversely, rats fed with carrots although showing an increased survival time under lethal conditions do not show any improvement in performance or in EEG under conditions of more moderate anoxia.