Relationship between serum levels and fast EEG activities in rats by a single administration of phenobarbital

Three groups of 6 rats each were given a single dose of 20, 50, or 100 mg/kg phenobarbital. The EEG was recorded for 15 min before and 1, 2, 4, 8 and 24 h after phenobarbital administration. Serum levels of phenobarbital in all rats were assayed at 1, 2 and 4 h. In the 20 mg/kg group, the beta 2 band was significantly increased from 2 to 4 h following phenobarbital administration. In the 50 mg/kg group, the beta 2 band significantly increased from 2 to 8 h (P < 0.01), and the theta band decreased at 8 h (P < 0.01). In the 100 mg/kg group, the beta 2 band was significantly increased during 24 h (P < 0.01) and the theta band was significantly decreased during 2 and 8 h (P < 0.05, P < 0.01). As for phenobarbital concentrations, in all rats, serum phenobarbital levels became gradually higher with time. When serum levels became more than 25 micrograms/ml, the beta 1 and beta 2 bands showed a significant increase. Whereas, above 35 micrograms/ml, theta waves decreased significantly. These results suggest that the significant increase of fast waves resulted from inhibition of reticular activating system and theta waves mainly resulted from depression of the cortex.