The influence of acute hypoxia and sleep states on the electrical activity of the cerebellum in the sheep fetus.
The experiments were designed to examine (1) the effects of acute hypoxia and (2) the influence of sleep states on the electrical activity of the cerebellum in the fetus. Five fetal sheep were instrumented between 106 and 133 days of gestation and survived in utero until term (140-146 days). Insulated stainless steel electrodes (75 microns diam.) were introduced into the cerebellar cortex and cemented in place. Electrodes were also implanted into 4 fetuses to monitor the electrocorticogram, rapid eye movements and the EMG of the dorsal neck (nuchal) muscles. Recordings of cerebellar activity were made for 252 h in 4 fetuses. The recordings were derived from many units (probably Purkinje cells) with a high level of basal discharge. The mean firing frequency was related to fetal sleep state. The highest frequencies coincided with episodes of rapid eye movements with low-voltage electrocortical activity and the lowest occurred during high-voltage electrocortical activity when rapid eye movements are absent. Acute hypoxaemia (fetal pa O2 6-10 mm Hg for up to 30 min) abolished rapid eye movements and caused a marked reduction in cerebellar activity. High-voltage electrocortical activity and nuchal EMG activity were maintained indicating that the effects of hypoxia on the cerebellum were not due simply to a general CNS depression. Cerebellar neural activity returned to normal at the termination of the hypoxic stimuli demonstrating that fetal Purkinje cells can withstand short episodes of severe hypoxia.
D000818:Animals; D002531:Cerebellum / Q000503:physiopathology*; D004569:Electroencephalography; D005333:Fetus / Q000503:physiopathology*; D002534:Hypoxia, Brain / Q000503:physiopathology*; D012756:Sheep; D012894:Sleep Stages / Q000502:physiology*