Persistence of brain hyperexcitability following chronic alcohol exposure in rats

Eighteen hooded Long-Evans rats were implanted with monopolar electrodes for the purpose of recording visual evoked potentials (VEP's) at the following brain sites: visual cortex, reticular formation and thalamus. Baseline VEP's were obtained to flashes for all animals, and subsequently twelve rats were intubated daily with a progression of increasing quantities of 20% (V/V) alcohol (3-8 g/kg), while the remaining six rats received an equivalent amount of water in the same fashion. Beginning 4 1/2 hours after the last dose of intubated alcohol, withdrawal VEP's were sampled every half-hour up to 8 hours, and 24-27 hours postwithdrawal. All experimental animals manifested their greatest brain hyperexcitability at visual cortex, which peaked sharply between 7-8 hours after alcohol withdrawal. Following two weeks of abstinence, half of the experimental rats (N = 6) and half of the controls (N = 3) received an alcohol challenge dose (2 g/kg i.p.), while the remaining animals received the same challenge dose after five weeks. Marked hyperexcitability was observed in the two-week challenge dose animals that had been previously subjected to alcohol; no such increase in VEP amplitude was apparent for control rats. There is also some evidence of hyperexcitability after five weeks of abstinence from alcohol at visual cortex. The data indicates that the neurophysiological responses of post-addict rats to challenge doses of alcohol are readily distinguishable from those of naive animals, even five weeks after alcohol removal. Furthermore, alcohol seems to act differently at different sites of the brain.