AROUSAL EFFECT OF AFFERENT DISCHARGES FROM MUSCLE SPINDLES URON ELECTROENCEPHALOGRAMS IN CATS

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Abstract
In order to investigate effects of afferent discharges from muscle spindles upon EEGs electroencephalograms of the neocortex and hippocampus, succinyl-choline (Sch) was administered intravenously in 25 cats immobilized with Flaxedil on the basis of previous reports that Sch affects muscle spindles and produce profuse afferent discharges of group la and group II fibers at the doses at which neither its direct effect upon the spinal cord nor upon receptors in the skin was observed. EEG synchronization in the neocortex and irregular slow waves in the hippocampus were usually observed 20-40 min. after Flaxedil (2-4 mg/kg) administration and it lasted for 60-90 min. When Sch (40-200 [mu]g/kg) was injected intravenously at the above noted light sleep patterns of EEGs generally changed into low voltage, fast activities in the neocortex and into regular slow waves of 3-5/sec. in the hippocampus in 40-90 sec. from the onset of Sch administration and these changes lasted for 3-5 min. No appreciable change in blood pressure was observed in association with these EEG arousal response. Such an EEG arousal response was also obtained even after the cerebellum was removed. The EEG arousal response was recognized neither in the case of intracarotid injection of Sch (10-40 [mu]g/kg) in cats immobilized with Flaxedil nor in the case of intravenous injection of Sch (40-200 Mg/kg) in encephale isole preparations. On the basis of the above noted experimental results and of direct action of Sch to muscle spindles, the EEG arousal response following Sch administration may be attributable to the afferent discharges from muscle spindles. It was supposed that such arousal effect of Sch was relatively weak in comparison with other procedures usually employed for eliciting EEG arousal response, because the response was not obtained with Sch injection (40-200 [mu]g/kg) in cats lightly anesthetized with Nembutal (2-5 mg/kg) in which distinct responses were observed by stimulation of the mesencephalic reticular formation or sciatic nerve.