BARBITURATE DEPRESSES SIMPLE SPIKE ACTIVITY OF CEREBELLAR PURKINJE-CELLS AFTER CLIMBING FIBER INPUT

1. Some scientists reported that the simple spike (SS) activity was transiently depressed after climbing fiber input, but others reported that predominant population of Purkinje cells increased their SS activity after the complex spike (CS). In the present study, SS activity after spontaneous CS was compared before and after the administration of pentobarbital sodium and of ketamine in high decerebrate cats. 2. Frequencies of spontaneous CS and SS firing were reduced (P < 0.001, t test) after pentobarbital administration of a total dose of 20-30 mg/kg. 3. In the peri-CS time histogram, the SS activity during a post-CS period of 10-110 ms with respect to that during a pre-CS period of -100-0 ms was reduced (P < 0.001) after the pentobarbital administration from, on average, 132.4 to 81.9%. In contrast, the SS activity during a post-CS period of 110-210 ms remained unchanged (P > 0.2). 4. In the pre-CS time histogram constructed after the pentobarbital administration, there were no significant differences (P > 0.01) between the SS activity during a pre-CS period of -600 to -500 ms and that during each of other pre-CS periods, suggesting that the barbiturate had little effect on the SS activity preceding the CS. 5. Analysis of raster diagrams revealed the variability of individual SS activity after the CS. The occurrence probability of the transient increase in SS number in individual raster traces during a post-CS period of 0-100 ms compared with that during a pre-CS period of -100-0 ms was reduced (P < 0.001) by the pentobarbital administration from 72.5 to 43.9%. 6. In the frequency distribution of SS pause duration after the CS in 100 raster traces, the median was prolonged (P < 0.001) by the pentobarbital administration from 19.4 to 57.8 ms. 7. The ketamine administration (total dose 20-30 mg/kg) decreased both spontaneous CS (P < 0.01) and SS (P < 0.001) firing rates but did not alter the transient increase in SS activity after the CS (P > 0.5). The results suggest that the decrease in SS activity after the CS under the pentobarbital anesthesia is induced by specific effects of the barbiturate but not by secondary effects of the decrease in the spontaneous SS activity. 8. It is concluded that the barbiturate (but not the ketamine) contributes to the transient depression of SS activity after climbing fiber input. This conclusion prompts us to reevaluate the reported results obtained in preparations anesthetized with barbiturate. 9. It is suggested that 1) the climbing fiber input would contribute to the short-term (less-than-or-equal-to 100 ms) modulation of SS activity by activating both facilitation and depression mechanisms of SS activity, and 2) the facilitation mechanism would predominate over the depression mechanism in unanesthetized preparations, and vice versa in preparations anesthetized with barbiturate.