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Altered EEG responses to ethanol in adult rats exposed to ethanol during adolescence.

BACKGROUND
Adolescent ethanol (EtOH) exposure is a significant health concern due to the potential long-term effects of EtOH on the developing brain. However, few studies have assessed how exposure to EtOH during adolescence influences the response of adults to EtOH after a long period of withdrawal. This study was designed to assess long-term changes in EEG activity after EtOH challenge in adult rats exposed to EtOH during adolescence.


METHODS
Male Sprague Dawley rats (n = 24) were exposed to EtOH vapor for 5 days (12 hr/day) between postnatal days 35 and 40. After maturing to adulthood, rats were implanted with cortical, amygdalar, and hippocampal electrodes. Then EEG activity after EtOH challenge (0.0-1.5 g/kg) was assessed.


RESULTS
There were no EEG differences between groups under baseline or vehicle conditions, but EtOH did have differential behavioral and electrophysiological effects when adolescent ethanol-exposed rats were compared with controls. After 1.5 g/kg EtOH, ethanol-exposed rats displayed decreased behavioral indexes of intoxication. In addition, EtOH significantly increased 4 to 6 Hz power in the hippocampus and parietal cortex of the control group but had no effect on 4 to 6 Hz power in the ethanol-exposed group in either of these brain regions. EtOH produced maximal increases in cortical EEG variability in control rats after 1.5 g/kg EtOH but produced maximal increases in cortical EEG variability in ethanol-exposed rats after 1.0 g/kg EtOH. As a result, ethanol-induced increases in EEG variability after 1.5 g/kg ethanol were blunted in the ethanol-exposed group compared with the control group.


CONCLUSIONS
These data demonstrate persistent and brain-region-specific changes in the neurobehavioral effects of acute EtOH challenge in adult rats exposed to EtOH during adolescence in the absence of baseline neurophysiological differences. Decreased EEG responses to high doses of EtOH combined with decreased behavioral measures of intoxication suggest that adolescent ethanol exposure produces long-lasting tolerance to the sedative effects of ethanol.