Effect of pentobarbital on uptake of horseradish peroxidase by rabbit cortical synapses

The presynaptic membrane response of rabbit cortical synapses to different doses of pentobarbital anesthesia was studied ultrastructurally by measuring the uptake of an extracellular marker, horseradish peroxidase, into presynaptic bouton vesicles. Uptake of peroxidase after a pentobarbital dose of 25 mg/kg was virtually unchanged from uptake observed in the absence of barbiturate anesthesia. After a pentobarbital dose of 40 mg/kg, however, a significant decrease in the number of peroxidase labeled vesicles was observed. Further increment in the barbiturate dose resulted in fewer labeled vesicles and at a dose of 150 mg/kg, no labeled presynaptic organelles were detected. These observations suggest that pentobarbital exerts an inhibitory effect on vesicular membrane transport and synaptic vesicle turnover; thus, one way it may alter synaptic transmission in rabbit cortex is by a direct action on the presynaptic bouton.