Differential effects of ageing on the EEG during pentobarbital and ketamine anaesthesia

Pentobarbital and ketamine are commonly used in animal experiments, including studies on the effects of ageing on the central nervous system. The electroencephalogram is a sensitive measure of brain activity. The present study investigated, under anaesthesia induced by the two drugs, whether cortical electroencephalogram in aged rats differs from that in young rats.

Electroencephalogram was recorded for young (2-3 months) and aged (15-17 months) rats before and during pentobarbital (40 mg kg (-1))or ketamine (100 mg kg (-1)) anaesthesia. The relative power in five frequency bands (delta: 2-4 Hz; theta: 4-8 Hz; alpha: 8-12 Hz; beta: 12-20 Hz; gamma: 20-100 Hz) was analysed, and then compared between the two age groups.

In both age groups, pentobarbital anaesthesia induced an increase in relative power in alpha and beta bands and a decrease in the theta band, but the degree of these power variations was more marked in aged rats. Ketamine anaesthesia increased relative power in the delta band and decreased that in the theta band; these effects were significantly different between the two age groups, with aged rats showing more markedly decreased power in the theta band.

(a) Pentobarbital and ketamine modified cortical electrical activity in a different manner as a function of age; (b) the modification of electroencephalogram relative power with anaesthesia was identical in young and aged rats but quantitatively more marked in aged rats. These findings will be useful in designing experiments that assess pathological changes in the central nervous system during ageing.