Effects of alcohol on visually evoked responses in rats during addiction and withdrawal

Modulation of responses to visual stimulus onset and offset by chronic alcohol consumption and withdrawal in the rat visual cortex and lateral geniculate nucleus

In the visual system, chronic alcohol consumption and subsequent abstinence strongly modulate processing of sensory information, which could interfere with the actions in our daily lives. Although previous studies showed histological and electrophysiological changes in the retina and visual cortex during chronic alcohol consumption and abstinence, there is still a lack of information related to the effect of alcohol on: 1) different stages of visual information processing; and 2) responses of stimulus onset (ON) and offset (OFF). In order to answer these questions, we recorded visual evoked potentials (VEPs), elicited by onset and offset of a 500-ms stimulus, following long-term alcohol consumption (8 weeks) and abstinence (3 weeks) in freely moving Wistar rats. Latency and amplitude of five components in the visual cortex (N1_VC, P2_VC, N2_VC, P3_VC, N3_VC) and three components in the lateral geniculate nucleus (P1_LGN, N1_LGN, P2_LGN) were analyzed. The results showed that long-term chronic alcohol consumption and abstinence have a strong long-term and, in some cases, irreversible impact on visual information processing. Both of these conditions modulate only the last stage of stimulus onset processing at the level of the visual cortex, but not at the level of the lateral geniculate body. Response to the stimulus offset is more susceptible to the effect of alcohol consumption and/or abstinence and is modulated at both the visual cortex and lateral geniculate nucleus levels. This modulation at different stages of the information processing chain can result in inaccurate processing of visual stimuli parameters and can lead to changes in perception of stimulus duration and intensity.

Alcohol reduces cross-frequency theta-phase gamma-amplitude coupling in resting electroencephalography

BACKGROUND

The electrophysiological inhibitory mechanism of cognitive control for alcohol remains largely unknown. The purpose of the study was to compare electroencephalogram (EEG) power spectra and cross-frequency phase-amplitude coupling (CFPAC) at rest and during a simple subtraction task after acute alcohol ingestion.

METHODS

Twenty-one healthy subjects participated in this study. Two experiments were performed 1 week apart, and the order of the experiments was randomly assigned to each subject. During the experiments, each subject was provided with orange juice containing alcohol or orange juice only. We recorded EEG activity and analyzed power spectra and CFPAC data.

RESULTS

The results showed prominent theta-phase gamma-amplitude coupling at the frontal and parietal electrodes at rest. This effect was significantly reduced after alcohol ingestion.

CONCLUSIONS

Our findings suggest that theta-phase gamma-amplitude coupling is deficiently synchronized at rest after alcohol ingestion. Therefore, cross-frequency coupling could be a useful tool for studying the effects of alcohol on the brain and investigating alcohol addiction.

The contribution of electrophysiology to knowledge of the acute and chronic effects of ethanol

This review describes the effects of ethanol on the components of neuronal transmission and the relationship of such effects to the behavioural actions of ethanol. The concentrations of ethanol with acute actions on voltage-sensitive ion channels are first described, then the actions of ethanol on ligand-gated ion channels, including those controlled by cholinergic receptors, 5-hydroxytryptamine receptors, the various excitatory amino acid receptors, and gamma-aminobutyric acid receptors. Acute effects of ethanol are then described on brain areas thought to be involved in arousal and attention, the reinforcing effects of ethanol, the production of euphoria, the actions of ethanol on motor control, and the amnesic effects of ethanol; the acute effects of ethanol demonstrated by EEG studies are also discussed. Chronic effects of alcohol on neuronal transmission are described in the context of the various components of the ethanol withdrawal syndrome, withdrawal hyperexcitability, dysphoria and anhedonia, withdrawal anxiety, craving, and relapse drinking. Electrophysiological studies on the genetic influences on the effects of ethanol are discussed, particularly the acute actions of ethanol and electrophysiological differences reported in individuals predisposed to alcoholism. The conclusion notes the concentration of studies on the classical transmitters, with relative neglect of the effects of ethanol on peptides and on neuronal interactions between brain areas and integrated patterns of neuronal activity.

Function of the auditory system, the visual system, and peripheral nerve and long-term combined exposure to toluene and ethanol in rats

Male pigmented rats (n = 36) were exposed to toluene and/or ethanol (1000 p.p.m. toluene in the inhaled air 21 hr/day, and 5.7-8.0% ethanol in the drinking water continuously) during 8 weeks. Electrophysiological recordings were made 1 week after the exposure. Auditory sensitivity (auditory brainstem response) was reduced only after exposures including toluene. At 20 kHz, ethanol antagonized toluene-induced loss of auditory sensitivity (P < 0.05). Flash evoked potentials were not affected in any group. In peripheral nerve, exposures containing ethanol were followed by increased amplitudes of nerve and muscle action potentials. Exposures including toluene were followed by an increase in liquid consumption.

Alterations in cortical visual evoked response following ethanol feeding in adult rats

A study was performed on the visual-evoked response (VER) in adult rats that were given an ethanol containing liquid diet for 2 months and examined directly after the exposure period or subjected to a gradual decrease in ethanol over 3 days and total abstinence for 1 week. Control rats showed a first negative peak (N1) directly following the first positive peak (P1). In ethanol-exposed rats examined without withdrawal, the VER showed an increase in onset latency and a marked distorsion of the N1 region. The existing N1 potential was very sensitive to high-frequency stimulation. The alterations were partly normalized 1 week after withdrawal. There was no increase in latency to onset of the response or to P1. There remained an increase of latency and a reduced relative amplitude upon high-frequency stimulation of the N1 peak in ethanol-exposed rats compared with controls. The mechanisms underlying the changes in the cortical potentials are not clear, but they may be related to the cholinergic, glutamatergic/NMDA and/or noradrenergic cortical systems. The lack of persistent changes in onset and P1 latency may be related to the circumstance that the retinogeniculate impulses are transmitted over glutamatergic kainate receptors, which are relatively resistant to ethanol.

Event-related potential evidence of dysfunction in automatic processing in abstinent alcoholics

The preattentive automatic processing of 63 alcoholics and 27 controls was evaluated with an auditory inattentive event-related oddball paradigm. We examined the mismatch negativity and the N2-P3 complex. Results showed significantly greater amplitude for N2, P3 and the N2-P3 complex for controls but no individual lead (Fz, Cz, Pz) differences by group. A group-by-lead interaction was found for N2 and for the N2-P3 complex. There were no significant latency differences between groups; however, a significant age-by-group interaction effect on latency was greatest at the Cz electrode. Results reflect a possible aberration of automatic processing in alcoholics because of a defect in the mnemonic template necessary to match with an infrequent deviant stimuli. We also found suggestive evidence of a relative weakness of frontal cortical organization in alcoholics. Future studies are suggested that would help clarify these differences in alcoholics.

Late auditory evoked potentials in alcoholics. Identifying those with a history of epileptic seizures during withdrawal

The N1-P2 wave of the auditory evoked potential was studied in 19 alcoholics, six of whom had withdrawal seizures on previous admissions. The recordings were made at 1 and 5 days after cessation of drinking. Eight nonalcoholic volunteers were used as controls. The latencies of N1 and P2 were slightly prolonged in alcoholics, but during the detoxification period they frequently shortened (p less than 0.05), occasionally attaining the values of the controls. One day after withdrawal, the amplitude of N1-P2 was consistently reduced in the alcoholics compared to the controls (p less than 0.05 and p less than 0.01), but higher in alcoholics with a seizure history compared to alcoholics without seizures (p less than 0.05 and p less than 0.001). Five days after cessation of drinking, the amplitude in the alcoholic groups always increased from the admission values (p less than 0.05 and p less than 0.01). By that time, the alcoholics with a history of withdrawal seizures had significantly (p less than 0.05 and p less than 0.01) higher amplitudes than those of the controls or the alcoholics without seizures. Large N1-P2 amplitude during alcohol withdrawal may reflect increased cerebral excitability and contribute to the identification of alcoholics with high risk for withdrawal seizures.

EEG and ERP response to chronic ethanol exposure in rats

Chronic ethanol exposure has been described in humans to produce a series of long and short term electrophysiological consequences. Interpretation of the electrophysiological findings in human subjects, however, is made difficult due to concomitant factors, such as nutritional status, premorbid functioning and differences in genetic susceptibility to the effects of ethanol. In the present study, electroencephalograms (EEGs) and auditory event related potentials (ERPs) were utilized to explore the short and longer term effects of chronic ethanol exposure in rats. Rats were continuously exposed to ethanol vapors for a period for 1 month. This treatment produced a mean blood ethanol level of 178 +/- 13.86 mg%. EEGs and ERPs were subsequently collected at 10 min, 24 h, and 2 weeks following termination of ethanol exposure. Significant changes in the EEGs and ERPs of these rats could be demonstrated. EEG amplitude increases, as quantified by spectral analysis, were most prominent at the 24 h time period, perhaps reflecting a state of "rebound excitability". EEG responses were normalized in ethanol-treated rats by 2 weeks post-withdrawal. In contrast, reductions in the N1 and P2 amplitudes of the rat ERPs were prominent after chronic ethanol exposure and following 2 weeks withdrawal, suggesting that ethanol may produce some longer term effects on response to ERP stimuli. Taken together, these studies suggest that ethanol may produce differential effects on EEG and ERPs and that this model may provide a useful substrate for the evaluation of the mechanisms underlying the effects of chronic ethanol exposure.

EEG, visually evoked and event related potentials in young abstinent alcoholics

EEG, visually evoked potentials (VEP), and event related potentials (P300) were recorded from 60 males aged 25-40 (20 abstinent alcoholics, 20 social drinkers, and 20 lifetime nondrinkers). Alcoholics were at least 1 month abstinent, medication free, and neuropsychologically normal. Residual effects of alcohol abuse were not detected in EEG power and cortical coupling analyses, or VEP amplitude, latency, and amplitude/intensity slope measures. Only P300 measures, recorded while subjects were actively engaged in a visual oddball task (20% targets), differentiated alcoholics from nonalcoholics. Alcoholics had reduced N2-P3 amplitude and delayed N2 latencies compared to social drinkers and nondrinkers. Because P300 abnormalities have been reported for individuals with positive family history for alcoholism, it is not clear whether these results reflect familial influence or residual effects of alcohol abuse. Issues relating to age, health and medication status of abstinent alcoholics, and use of social drinkers as comparison groups in studies of brain dysfunction in "recovering" alcoholics are also discussed.

Influence of acute and chronic administration of ethanol on photic-evoked response in rats

The effect of acute and chronic administration of ethanol on photic-evoked response was studied in rats. Acute administration of ethanol (1-3 g/kg, i.p.) produced behavioural depression, EEG synchronization and a biphasic effect on the amplitude of the photic evoked responses (PER) recorded from the frontal cortex (FC) and optic cortex (OC), while a reduction in amplitude was observed in the midbrain reticular formation (MBRF). The amplitude of the averaged PER in the FC and OC was increased in chronic ethanol-treated rats, while in the MBRF, a reduction in amplitude was observed. Abrupt discontinuation of ethanol produced behavioural excitation and increase in amplitude of the averaged evoked responses recorded from the three brain areas studied. These observations suggest that the neural hyperexcitability that characterizes ethanol withdrawal may affect both cortical and subcortical structures.

Naloxone-induced augmentation of the photically evoked afterdischarge in conscious rats

Naloxone, at subconvulsive dose levels, from 1 to 15 mg/kg were administered to conscious rats. Significant increases in photically evoked afterdischarge occurrence were seen at naloxone dose levels above 5 mg/kg with no clinical evidence of seizure activity being observed. Typically photically evoked afterdischarge augmentation is only observed following the administration of convulsive drugs.

The study of brain function impairment in fetal alcohol syndrome: some fruitful directions for research

Fetal alcohol syndrome (FAS) is the most prevalent known preventable health hazard to the human fetus by a noxious agent. It is associated with impairments of the central nervous system that are expressed in the forms of mental retardation of varying severity, learning disabilities, attentional deficits and an increased vulnerability to stress. Results of psychophysiological studies of the effects of ethanol on the central nervous system are reviewed, with the aim of exploring how conclusions derived from them can serve as testable hypotheses in FAS research. The experimental methods used in such studies are examined for their applicability to FAS research. It is concluded that FAS research effort will benefit from the inclusion of psychophysiological studies.

Acute effects of alcohol on photic evoked potentials of albino rats: visual cortex and superior colliculus

Photic evoked potentials were recorded from the primary visual cortex (VC) and superior colliculus (SC) of chronically implanted rats. Animals were given intraperitoneal injections of saline, 1.5 and 2.5 g ethyl alcohol/kg body weight on separate days. Evoked potentials were recorded at 5, 20, 40 and 60 min following injection. The amplitudes of all of the VC components except P2 (latency of 52 msec) were depressed to some extent by both doses of alcohol. In contrast, the amplitude of component P2 was increased by both alcohol doses. In the SC, the peak amplitudes of two individual components of the early positive complex were diminished by both doses of alcohol, as was a later negative component. A series of late oscillatory potentials recorded from the SC were minimally depressed by the 1.5 g/kg dose of alcohol, but showed a more prolonged depressant effect at the higher dose. Both doses of alcohol produced reliable increases in peak latency for the primary components in the VC and SC.