Effects of adolescent ethanol exposure on event-related oscillations (EROs) in the hippocampus of adult rats

Abstract

Electrophysiological studies have shown that adolescent ethanol (EtOH) exposure can produce long-term changes in hippocampal EEG and ERP activity. Recently, evidence has emerged suggesting that event-related oscillations (EROs) may be good indices of alcoholism risk in humans, however, have not been evaluated for their ability to index the effects of EtOH exposure. The objective of the present study was to characterize EROs generated in hippocampus in adult rats exposed to EtOH during adolescence. Adolescent male Sprague-Dawley rats were exposed to EtOH vapor for 12h/d for 10 days. A time-frequency representation method was used to determine delta, theta, alpha and beta ERO energy and the degree of phase variation in the hippocampus of adult rats exposed to EtOH and age-matched controls. The present results suggest that the decrease in P3 amplitudes, previously observed in adult rats exposed to EtOH during adolescence, is associated with increases in evoked theta ERO energy. These studies suggest that EROs are suitable for characterizing the long-term effects of adolescent EtOH exposure. Further studies are needed to determine the relationship between the mechanisms that regulate these neurophysiological endophenotypes and the consequences of adolescent EtOH exposure.

Figure 1

Mean amplitude values of ERO energy for the theta band in response to standard, rare and noise stimuli in the hippocampus. Adult rats exposed to EtOH during adolescence showed greater hippocampal theta ERO energy than control rats in the 250-450 ms time window in response to noise tones. * Significant differences between control and EtOH-exposed rats (P < 0.05).

Figure 2

Time-frequency representation of evoked delta, theta, alpha and beta band energy distribution of noise stimuli in the hippocampus of adult control and adult rats exposed to EtOH during adolescence. Time-frequency responses of evoked theta (a) band energy distribution to noise stimuli in control (A) and EtOH-exposed (B) groups in the hippocampus. Time-frequency ROI window used was 250-400 ms (white squares). The inset shows representative ERP grand averages in control (black line) and EtOH (gray line) groups from the hippocampus in response to the noise tones.