The excitatory effect of ethanol: absence in rats, no tolerance and increased sensitivity in mice.

Three questions related to ethanol's stimulating effect (ESE) were studied. The first referred to the reported absence of tolerance to ESE in mice. It was determined whether tolerance would develop if the period of ethanol treatment were extended significantly beyond those normally found in the literature. No evidence of tolerance to ESE was found over a 5-month period of treatment. The second issue related to the possibility that mice not only do not develop tolerance but actually become more responsive to ESE after chronic exposure. A dose of ethanol that acutely did not produce a significant activating effect did induce a marked excitation after the animals were chronically treated with ethanol. Finally, the issue was addressed of whether the absence of ESE in some strains of rats could in part be due to a masking effect by the depressant component of this drug. To test this possibility rats were treated with ethanol for a 4-month period. Tolerance to the depressant effect was observed but no ESE was detected.