The influence of some neurotransmitter agonists and antagonists on the response of hippocampal units and the cortical EEG to ethanol in the awake rat

A novel electroencephalographic analysis method discriminates alcohol effects from those of other sedative/hypnotics

Here we describe a mathematical and statistical signal processing strategy termed event resolution imaging (ERI). Our principal objective was to determine if the acute intoxicating effects of ethanol on spontaneous EEG activity could be discriminated from those of other sedative/hypnotics. We employed ERI to combine and integrate standard analysis methods to learn multiple signal features of time-varying EEG signals. We recorded cortical EEG, electromyographic activity, and motor activity during intravenous administration of saline, ethanol (1.0 g/kg), chlordiazepoxide (10 mg/kg), pentobarbital (6 mg/kg), heroin (0.3 mg/kg), and methamphetamine (2 mg/kg) administered on separate days in six rats. A blind treatment of one of the drugs was readministered to validate the efficacy of ERI analysis. Significant changes in spontaneous EEG activity produced by all five drugs were detected by ERI analysis with a time resolution of 5-10 s. ERI analysis of spontaneous EEG activity also discriminated, with 90-95% accuracy, an ataxic dose of ethanol versus equivalent ataxic doses of chlordiazepoxide or pentobarbital, as well as the effects of saline, a reinforcing dose of heroin, or a locomotor activating dose of methamphetamine. ERI correctly matched the 'blind drug' as ethanol. These findings indicate that ERI analysis can detect the central nervous system effects of various psychoactive drugs and accurately discriminate the electrocortical effects of select sedative/hypnotics, with similar behavioral endpoints, but with dissimilar mechanisms of action.

Effects of ethanol on hippocampal place-cell and interneuron activity

Mounting evidence suggests that ethanol exerts effects on learning and memory by altering cellular activity in the hippocampus and related structures. However, little is actually known regarding ethanol's effects on hippocampal function in awake, freely-behaving animals. The present study examines the effects of ethanol on hippocampal place-cell and interneuron activity in freely-behaving rats. Signals from individual hippocampal neurons were isolated while subjects traversed a symmetric Y-maze for food reward. Following 15 min of baseline recording, subjects were injected with one of four doses of ethanol (0.0, 0.5, 1.0 and 1.5 g/kg), and cellular activity was monitored for a 1-h time period. Following sufficient time for recovery (minimum of 3 h post injection), cellular activity was monitored for an additional 15-min period. Both 1.0 and 1.5 g/kg ethanol potently suppressed the firing of hippocampal place-cells without altering place-field locations. Ethanol did not significantly suppress out-of-field firing rates, leading to a decrease in spatial specificity (i.e. the ratio of in-field/out-of-field firing rates). Interneuron activity was not altered by 1.0 g/kg ethanol, but was occasionally suppressed by 1.5 g/kg ethanol. Results are interpreted in light of recent behavioral and electrophysiological studies examining the effects of ethanol on hippocampal function.

Effects of ethanol inhalation on EEG in rats

Effects of ethanol on duration of stages of sleep-wake cycle and EEG power spectra were measured during a 2-h exposure in a dynamic inhalational chamber in rats. Rats were exposed to one of four graded concentrations (approx. 100, 400, 800 and 1600 ppm) of ethanol on different days. Ethanol was found to increase the duration of waking (W) with a decrease in duration of rapid eye movement (REM) sleep at 100 and 400 ppm. No effect was observed at 800 and 1600 ppm on the stages of sleep-wake cycle or at 100-1600 ppm on EEG power spectra from the somatosensory or visual cortices. Results indicate that ethanol administered by inhalation could produce arousal action at low doses, but did not have any effect on EEG power spectrum at the concentrations used.

Circadian variations in vigilance states in the alcohol-dependent rat

Waking and sleep states were studied in the alcohol-dependent rat after administration of ethanol (416 mg/kg/hr) by indwelling intragastric catheter (IGC) for 13 days. Electropolygraphic recordings performed for a total of 24 hr from the start of withdrawal were compared with those of control rats receiving water by IGC and showed 1) that rapid eye movement sleep was the most sensitive of the four vigilance states studied. A decrease was noted both for the total duration of recording and for the light period; 2) that nonactive wakefulness was the only vigilance state to show an inversion of percentages between the light and dark period; 3) that the light period was the best time for studying changes in vigilance states. Changes included increased percentages of active and nonactive wakefulness and decreased percentages of slow-wave and rapid eye movement sleep. This was due to a change in the number of episodes rather to a change in their mean duration. No significant change occurred during the dark period.

Ethanol effects on EEG spectra in monkeys: comparison to morphine and diazepam

The effects of oral administration of 3 doses of ethanol (0.75, 1.0 and 1.5 g/kg) and single doses of morphine (2.5 mg/kg) and diazepam (2.5 mg/kg) on spectral components of the EEG were investigated in the squirrel monkey Saimiri sciureus. Comparisons of mean spectral power in the 4 frequency bands (2-4 Hz, 4-8 Hz, 8-16 Hz, 16-32 Hz) revealed that the lowest dose of ethanol (0.75 g/kg) produced some increase in power in all 4 frequency bands with significant increases in the 8-16 Hz band. Morphine also produced some increase in power in all bands; however, significant increases were prominent in the 16-32 Hz range. Moderate doses of ethanol (1.0, 1.5 g/kg) produced dose-dependent decreases in the lower frequencies which were significant in the 2-4 Hz band. Diazepam also produced significant decreases in the lower frequencies (2-4, 4-8 Hz) but also produced significant decreases in 8-16 Hz and increases in the 16-32 Hz band. The distribution of these power changes as a function of time (power spectral band time series) was also studied. Evaluation of fluctuations in the 8-16 Hz band which is a measure of the periodic shifts in alertness demonstrated that ethanol and diazepam slowed the dominant frequency of the time series; whereas, morphine caused an increase in the frequency. This study suggests that two EEG measures, mean EEG spectral profiles and power spectral band time series analysis, can successfully discriminate the electrophysiological actions of ethanol, and that these markers may provide a means for uncovering ethanol's mechanisms of action.