Comparative effects of almitrine and raubasine, singly and in combination, on electroencephalographic activity in young and old rats.

A new method for quantification of electroencephalographic (EEG) signals was used to study the effects of almitrine and raubasine, alone and in combination, in two groups of six unanesthetized rats, aged 8 months (young) and 22 months (old). Coadministration of almitrine (7.5 mg/kg-1 i.p.) and raubasine (2.5 mg/kg-1 i.p.) induced an increased EEG power from 7 to 30 Hz; the frequencies concerned were identical in young and old rats, but the degree of their power variations was more marked in old rats. Almitrine induced a 20 to 50% increase in EEG power in young rats on nearly all spectral components. The effects of almitrine were only seen in the low-frequency range in old rats. Raubasine increased the EEG power in the 10 to 20 Hz frequency range; these effects were significantly greater in old rats. In both age groups, the effects on EEG power observed with coadministration of almitrine and raubasine were significantly different from those expected if raubasine and almitrine add their individual effects. These results show that a) almitrine and raubasine modify cortical electrical activity in a different manner as a function of age; b) the modification of the EEG activity induced by the coadministration is suggestive of an interaction between the cortical effects of each drug; and c) the modification of EEG power induced by the coadministration is qualitatively identical in young and old rats but quantitatively more marked in old rats.