Effects of ethanol on the dorsal raphe nucleus and its projections to the caudate putamen.

The objective of this study was to examine the effects of intraperitoneal injection of ethanol on the activity of the dorsal raphe nucleus (DRN) serotonin (5-hydroxytryptamine [5-HT]) system and its projections to the rostral caudate putamen (CPu) and determine whether rapid tolerance to the effects of ethanol develops in this system. Adult, male, Wistar rats were used in these experiments. In experiment 1, a microdialysis procedure was used to determine (a) the effects of acute intraperitoneal administration of ethanol (1.75 and 2.5 g/kg) on the extracellular levels of 5-HT in the rostral CPu and (b) whether rapid tolerance develops to these effects. In experiment 2, firing rates of 5-HT neurons were determined in the DRN after intraperitoneal administration of 2.5 g/kg of ethanol. The results of the microdialysis experiments indicated that the 2.5-g/kg dose significantly (P < .005) increased the extracellular levels of 5-HT to 150%-160% of baseline. Compared with findings for rats pretreated with saline 24 h earlier, prior treatment 24 h earlier with 2.5 g/kg of ethanol had no effect on the extracellular levels of 5-HT produced by a challenge dose of 2.5 g/kg of ethanol. Contrary to the effects in the CPu, intraperitoneal administration of 2.5 g/kg of ethanol significantly (P<.005) decreased the firing rates of 5-HT neurons in the DRN to approximately 50% of control. Overall, the results suggest to us that there is a dissociation between the effects of acute administration of ethanol on 5-HT cell body neuronal activity and 5-HT synaptic activity. The higher extracellular levels of 5-HT in the CPu may be due to increased release of 5-HT from a direct or an indirect action of ethanol, a result of inhibiting 5-HT reuptake, or related to both of these mechanisms. In addition, the findings suggest to us that rapid tolerance did not develop to the effects of ethanol on the 5-HT system within the CPu.

A preliminary study of acute responses to clamped alcohol concentration and family history of alcoholism.

BACKGROUND: The clamping method of alcohol administration was combined with a battery of dependent measures of frontal lobe brain function, and a novel index of acute adaptation, in a preliminary study in order to explore the paradigm's sensitivity to a familial history of alcoholism (FHA). METHODS: Ten family history-positive (FHP) and 10 family history-negative (FHN) adult social drinkers of both genders underwent alcohol clamping. Twenty minutes after the start of an intravenous infusion of alcohol, the breath alcohol concentration was clamped at a target of 60+/-5 mg/dl for 150 min. Initial and adaptive responses to alcohol were assessed using scalar indices of change. One index assessed initial improvements or impairments in brain function after alcohol. The other index assessed acute adaptation (tolerance or sensitization) to alcohol while the brain's exposure to alcohol was held constant. The battery of dependent measures included subjective perceptions, neuropsychological tests, saccadic eye-movement tasks, and event-related potential (ERP) tasks. Effect sizes for FHA were estimated for 10 dependent variables that showed adequate baseline test-retest reliability (r>0.6). RESULTS: FHP subjects showed less intense initial responses to alcohol in subjective perceptions, but greater changes in the latency of volitional saccades and ERP P3 components than did the FHN controls. FHP subjects generally showed greater acute tolerance to alcohol than did controls, who showed more instances of acute sensitization at this moderate breath alcohol concentration. Effect sizes for FHA exceeded 0.4 in more than half of the indices. CONCLUSIONS: The BrAC clamping paradigm assesses initial and adaptive responses of a battery of behavioral and electrophysiological measures of frontal lobe function to ethanol that appear both reliable and sensitive to FHA.

Serotonergic neuronal activity in the dorsal raphe nucleus of selectively bred alcohol-preferring and alcohol-nonpreferring rats and unselected wistar rats.

BACKGROUND: Selectively-bred alcohol-preferring (P) rats have fewer serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) than do alcohol-nonpreferring (NP) rats. The present study was designed to test the hypothesis that the remaining 5-HT neurons in P rats compensated for their reduced number by increasing neuronal activity. METHODS: Spontaneous activity was recorded from single-spiking and bursting 5-HT neurons in the DRN of unanesthetized paralyzed, alcohol-naive P, NP, and Wistar rats. Firing frequencies, the percentages of action potentials in bursts, and the percentages of bursting neurons were evaluated. RESULTS: There were no significant differences among the three groups of rats in any of the parameters measured. Power analyses were performed on preliminary data to determine the sample sizes necessary for detection of significant differences. The mean firing frequencies of single-spiking 5-HT neurons averaged 1.8 (37 neurons), 1.7 (17 neurons), and 1.8 (41 neurons) spikes per second in P, NP, and Wistar rats, respectively. For bursting 5-HT neurons, the percentages of action potentials in bursts for P, NP, and Wistar rats were 55.0% (24 neurons), 49.7% (18 neurons), and 55.1% (21 neurons). The mean percentages of bursting 5-HT neurons encountered per electrode penetration were 44% for P rats (n = 28), 44% for NP rats (n = 14), and 34% for Wistar rats (n = 26). CONCLUSIONS: The results indicate that the sample of 5-HT neurons recorded in the DRN of P rats had not compensated for a reduced number by altering neuronal activity.

A twin study of genetic influences on the acute adaptation of the EEG to alcohol.

A two-dose alcohol challenge protocol was used to study genetic influences on the acute adaptation of the EEG to alcohol in 53 monozygotic and 38 same-sex dizygotic Caucasian twin pairs averaging 30 years of age. Equal doses of alcohol were administered at 10:00 and 11:00 AM, yielding mean peak breath alcohol concentrations of 0.057% and 0.099%, respectively. Eyes-closed, resting EEG was recorded four times: at baseline; on the ascending limb of the overall experiment at a breath alcohol concentration (BrAC) near 0.06%; on the descending limb at a BrAC near the value when the subject's EEG was obtained on the ascending limb; and, finally, when the BrAC fell to 0.02%. Genetic analyses of log-transformed values of total spectral power (L10TSP) and spectral band power (L10SBP) were performed on EEG spectra averaged across all 17 scalp lead locations. After adjusting for body weight, a significant fraction of population variance in L10TSP was attributable to genetic influence: H2 values for TSP were 0.73, 0.72, and 0.73 at the three postalcohol EEG recordings, respectively. Similar findings pertained to each L10SBP at each postalcohol recording, except forthe delta band. The change in postethanol EEG power was examined for evidence that genes influence acute adaptations in brain function. Descending-minus-ascending limb L10TSP was normalized by the individual's ascending limb L10TSP to minimize nonalcohol-related effects that can influence both measurements. Earlier analyses of the same sample's initial EEG response to alcohol noted a substantial increase in the ascending limb EEG power, compared with baseline. Thus, positive values of the postethanol change denote a progression away from baseline attributable to acute sensitization to alcohol; negative values signify a return toward baseline values suggesting acute tolerance to alcohol. Genetic analysis of the normalized difference in L10TSP had a highly significant H2 value of 0.70, indicating that both acute tolerance and acute sensitization to alcohol may represent adaptations reflecting substantial heritable influence. Slightly smaller, but significant values of H2 for the normalized difference in L10SPB were observed for delta, alpha-slow and beta-slow frequency bands. In contrast, H2 for the differences between the final and ascending limb EEG power were not significant, except for the theta band. Thus, heritable drowsiness may have contributed to detection of genetic influences on acute adaptation, but represent a potential confound only in the theta band.

VTA dopamine neuron activity distinguishes alcohol-preferring (P) rats from Wistar rats.

The mesolimbic dopamine (DA) system is innately deficient in rats selectively bred for high alcohol drinking behavior compared with rats selectively bred for low alcohol drinking and unselected rats. In alcohol-preferring (P) rats, compared with alcohol-nonpreferring (NP) rats, this is evidenced by fewer DA neurons in the ventral tegmental area (VTA) projecting to the nucleus accumbens (ACB). Yet, despite this deficiency, DA release in the ACB is similar in P, NP, and Wistar rats. DA release is regulated by DA neuronal activity, and DA neurons fire tonically as well as in bursts. Burst firing has been shown to substantially enhance DA release compared with tonic firing. The present study was designed to test the hypothesis that the remaining VTA DA neurons in P rats have faster firing frequencies and/or burst fire more frequently than VTA DA neurons in Wistar rats. The spontaneous activity of VTA DA neurons was recorded in unanesthetized alcohol-naive P and Wistar rats. A conventional burst analysis on 500 consecutive action potentials revealed that P rats had a significantly (p < 0.05) greater percentage of action potentials in bursts when compared with Wistar rats (P: 50.9%, Wistar: 34.4%). Firing frequency and other burst parameters (burst interspike interval, burst length, interburst interval, and the number of action potentials per burst) did not distinguish the two groups of rats. The increased burst activity in P rats may represent a compensatory mechanism to maintain adequate basal levels of DA despite the deficiency in the mesolimbic DA system.

Clamping breath alcohol concentration reduces experimental variance: application to the study of acute tolerance to alcohol and alcohol elimination rate.

An oral loading dose was combined with intravenous infusion of 6% alcohol at rates adjusted on-line to close the gap between measurements of breath alcohol concentration (BrAC) and a target of 50 mg%. The goal was to minimize the deviation from a prescribed course of BrAC over time. In a pilot study of 10 young men, subjects underwent three experimental sessions: twice at 50 mg% and once in a 0 mg% control condition. The pilot study assessed the performance of the BrAC clamp, its potential utility in studies of acute tolerance to alcohol, and the retest reliability of directly measuring the alcohol elimination rate (AER) calculated from the steady-state infusion rate. Reduced variance was demonstrated in 4 of 5 experimental parameters, compared with results of an earlier approach using a split-dose oral administration procedure. Subjects' perceptions about alcohol effects were measured in one BrAC clamping session, using Schuckit's Subjective High Assessment Scale: 3 of 15 Schuckit's items demonstrated statistically significant indices of acute tolerance to alcohol. Within-subject AERs calculated in the steady-state had a coefficient of variation of 6.5%. Details of the BrAC clamping procedure are provided. The pilot study demonstrated the ability to prescribe experimental parameters of the brain's exposure to alcohol while preserving experimental flexibility in studies of acute tolerance to alcohol and AER.

P300 topography of amplitude/latency correlations.

The correlational association from 19 electrode sites between peak amplitude and latency for the P3(00) event-related brain potential (ERP) for n = 80 homogeneous subjects was assessed using a simple auditory discrimination task. The correlation strength varied systematically across scalp topography in different ways for the various ERP components. For the target stimuli, P3 amplitude and latency were negatively correlated and most tightly coupled over the frontal-central and right medial/lateral recording sites. In contrast, the N1 produced negative correlations that were strongest over the left and right central/lateral locations; P2 demonstrated a positive correlation that was strongest frontally and centrally; N2 demonstrated a positive correlations that was strongest over the central and parietal sites. ERPs from the standard stimuli produced generally similar patterns for the P3 and P2 components, with only weak or no reliable effects observed for the N1 and N2 potentials. Taken together, the findings suggest that analysis of amplitude/latency correlational relationships can provide information about ERP component generation. Theoretical implications are discussed.

Alcohol effects on the heritability of EEG spectral power.

To estimate the effects of a moderate dose of alcohol on heritability of the EEG power spectrum, 53 monozygotic and 38 like-sexed dizygotic Caucasian twin pairs (aged 30.0 +/- 7.0 years) were studied. Subjects were asked not to drink alcohol for 2 days and to fast after midnight before a protocol of: (1) a low fat meal at 8:00 AM; (2) a baseline EEG recording; (3) ingestion of alcohol over 10 min, which raised the breath alcohol concentration to 0.057 +/- 0.017% (SD); followed by (4) a postalcohol EEG recording 35.1 +/- 5.7 (SD) min after the start of drinking. One previous study (Propping, P., Hum. Genet. 35: 309-334, 1977) found that heritability (H2), the fraction of total variance in the EEG power that is attributable to genetic influences, increased after alcohol administration. In the current study, H2 of log-transformed, body-weight-adjusted spectral band power increased after alcohol for the theta-, alpha-slow, alpha-fast, beta-slow, and beta-fast bands (from an average of 0.47 to an average of 0.80). The increase in heritability was accompanied by a significant decrease in the within-pair differences of monozygotic cotwins for all of the same frequency bands except beta-fast. Because within-pair differences are expected to contain only environmental factors for the genetically identical individuals, it was concluded that alcohol decreases environmental variation of EEG power spectral density, causing the increase in H2.

Genetic analysis of the resting electroencephalographic power spectrum in human twins.

Most twin studies have provided evidence for genetic effects on the electroencephalogram (EEG). In two twin studies, monozygotic (MZ) cotwin covariance for EEG power was greater than expected for additive gene actions, as compared with dizygotic (DZ) cotwin covariance. These findings were attributed to complex gene interactions, termed emergenesis. In the present study of 53 MZ and 38 DZ twin pairs departures from the additive genetic model were tested on resting EEG power. Total spectral power and the quotient of (beta band power)/(total power) both fit gene interaction models significantly better than did additive genetic models. These findings support the previous findings of MZ covariance for EEG power as much greater than DZ covariance; these findings can be explained entirely by the additive effects of genes. This pattern of twin covariances could be due to gene interactions but also to greater MZ than DZ environmental covariance.

Innate differences in medial septal area burst firing neurons and the hippocampal theta rhythm during ambulation in selectively bred rat lines.

Previous studies have demonstrated a higher mean peak frequency of the hippocampal (HPC) theta rhythm during REM sleep in alcohol-nonpreferring (NP) rats when compared with alcohol-preferring (P) rats. Burst firing neurons of the medial septal area (MS/VDB) are thought to pace the HPC theta rhythm during REM sleep and ambulation. Therefore, extracellular action potentials of MS/VDB burst firing neurons and HPC-CA1 field potentials were recorded simultaneously in ambulating P and NP rats. These recordings revealed that the mean peak frequency of the HPC theta rhythm during ambulation was higher in NP rats (7.62 +/- 0.12 Hz) as compared with P rats (7.21 +/- 0.14 Hz) (P < 0.05). Consistent with the difference in the HPC theta rhythm, the burst pattern of MS/VDB neurons exhibited a shorter inter-burst interval in the NP rats (NP 82.4 +/- 5.4 ms, P 97.4 +/- 8 1 ms P < 0.05). The difference in the inter-burst interval was confirmed by the distribution of inter-spike intervals in cumulative inter-spike interval histograms and the frequency of peaks in the mean cumulative autocorrelation histograms for P and NP rats. The mean cumulative autocorrelation histograms for P and NP rats also revealed that the regularity of the burst pattern in NP rats was sustained over a longer time period as determined by the decay constant. The cross-correlation of MS/VDB burst activity and the HPC theta rhythm showed a strong relationship between the two signals in P and NP rats. In both P and NP rats, two similar phase relationships were observed between MS/VDB bursting neurons and the HPC theta rhythm. These findings are in agreement with the hypothesis that MS/VDB burst firing neurons are responsible for the variation in the HPC theta rhythm between the two lines. Other mechanisms consistent with these findings are also discussed.

Hemispheric differences for P300 amplitude from an auditory oddball task.

The P3(00) event-related potential (ERP) was elicited in 80 normal, right-handed male subjects using a simple auditory stimulus discrimination task, with electroencephalographic (EEG) activity recorded at 19 electrodes. P300 amplitude was larger over the right compared to left hemisphere electrode sites primarily at anterior-medial locations (F3/4, C3/4) for both target and standard stimuli. The N100, P200, and N200 components also demonstrated several similar, albeit less robust, hemispheric asymmetries. No hemispheric effects for P300 latency were observed, with few consistent latency findings for any of the other components obtained. The results suggest that the discrimination process underlying P300 generation may originate with right frontal activation.

Priming of experimental anxiety by repeated subthreshold GABA blockade in the rat amygdala.

Blockade of GABAA receptor function in the area of the anterior basolateral amygdala of rats elicits physiological (increases in heart rate and blood pressure) and behavioral changes similar to symptoms of human anxiety states. Repeated subthreshold blockade of GABAA receptors in this region appears to result in a long-term 'priming' of these anxiety-like responses. The present study was conducted to characterize the 'priming' of the heart rate and blood pressure responses and to test if these 'primed' animals would show increases in anxiety responses. Male Wistar rats with arterial catheters placed for physiological measurements were implanted with chronic microinjection cannulae in the anterior basolateral amygdaloid nucleus (BLA) under pentobarbital anesthesia. Repeated daily injections of a subthreshold dose of bicuculline methiodide (GABAA receptor antagonist; BMI) into the BLA elicited 'priming' of physiological responses after 3-5 injections and this response was maintained for at least 6 weeks. The primed animals also showed increased anxiogenic responses to GABAA blockade in the BLA. The 'priming' of anxiety responses were clearly elicited before kindling of seizures as measured by EEG. These results suggest that this 'priming' phenomenon may be similar to kindling and long-term potentiation. This could be one potential mechanism for developing pathological emotional responses, such as chronic, high levels of anxiety.

P300 hemispheric amplitude asymmetries from a visual oddball task.

The P3(00) event-related potential (ERP) was elicited in 80 normal, right-handed male subjects using a simple visual discrimination task, with electroencephalographic (EEG) activity recorded at 19 electrodes. P3 amplitude was larger over the right than over the left hemisphere electrode sites primarily at anteromedial locations (F3/4, C3/4) for target, novel, and standard stimuli. The N1, P2, and N2 components also demonstrated hemispheric asymmetries. The strongest P3 hemispheric asymmetries for all stimuli were observed at anterior locations, suggesting a frontal right hemisphere localization for initial stimulus processing, although target stimuli produced larger P3 amplitudes at parietal locations that did novel stimuli. The relationships of hemispheric asymmetries to anatomical variables, background EEG activity, and neurocognitive factors are discussed.

P300 from an auditory oddball task: inter-laboratory consistency.

Event-related potentials (ERPs) were recorded from normal subjects for the purpose of evaluating measurement consistency among six laboratories located in different cities within the United States. At each laboratory location 15 male subjects were tested using a simple auditory stimulus discrimination task and identical electrophysiological equipment and recording methods. Assessment of the N1, P2, N2, and P3(00) potentials from both the target and standard stimuli resulted in no reliable differences among laboratories for component amplitudes, latencies, and scalp distributions. Quantitative evaluation of overall waveform and specific component morphology yielded good to excellent agreement across laboratories. The findings suggest that large-scale inter-laboratory human electrophysiological studies are feasible and may prove of value when using ERPs to evaluate cognitive function in humans.

Comparison of innate EEG parameters in rat lines selected for ethanol preference.

Through bidirectional selective breeding, lines of rats that differ greatly in their voluntary alcohol drinking behavior have been developed--namely, the alcohol-preferring (P) and high-alcohol-drinking (HAD) lines and the alcohol-nonpreferring (NP) and low-alcohol-drinking (LAD) lines. The present experiments were designed to determine if an association exists between ethanol preference and features of the electroencephalogram (EEG) during various sleep-wake behaviors. Of the EEG parameters measured, only theta activity in the hippocampus revealed differences in the lines. However, these differences were not generally associated with ethanol preference. The peak frequency and distribution mean of hippocampal theta activity during REM sleep were significantly higher in NP rats than in P, HAD, and LAD rats. In addition, theta frequency during alert immobility tended to be higher in NP rats than in P, HAD, and LAD rats. A qualitative comparison of these data with published data from unselected rats further suggested that the NP rats are uniquely different with respect to theta frequency.

Heritable features of the auditory oddball event-related potential: peaks, latencies, morphology and topography.

Baseline auditory ERP data from a larger study of the genetic determinants of the response to alcohol were collected from 59 monozygotic (MZ) twin pairs and from 39 same-sex dizygotic (DZ) twin pairs who drank socially. Three methods for measuring genetic influence on the ERPs were applied. First, based on maximum-likelihood estimates, the heritability of conventional peak amplitude and latency of N1 and P3 components was computed for each of 16 lead locations using tests of the significance of heritability based on intraclass correlations. P3 amplitude provided the strongest results, distributed symmetrically over caudal leads, and implied gene dominance as the mode of genetic transmission for the P3 component. A substantial genetic influence on N1 latency suggested a mixture of additive and dominance effects in the left fronto-temporal regions. N1 amplitude measures trended towards significant heritability, but none was observed for P3 latency. The second method used the maximum of the cross-correlation function to compare wave form shape in a lead-by-lead analysis of data from cotwins. Genetic influence was apparent in both target and non-target ERP responses, with a fronto-central topography of significant results. The third method reduced all spatial and temporal ERP differences from a pair of twins to a single scalar number for each response. Distributions of this global measure revealed significant genetic influence on both non-target and target ERPs. A post hoc analysis of the effect of gender on the heritability of N1 or P3 peaks and latencies revealed no statistically significant observations in this sample of young adult twins.

The effect of TRH on ethanol-induced sedation in alcohol-preferring and -nonpreferring rats.

TRH antagonism of ethanol sedation was evaluated in selectively-bred alcohol-preferring (P) and -nonpreferring (NP) rats. Intracerebroventricular (i.c.v.) infusions of TRH significantly reduced sleep time in the NP rats. In the P rats, TRH tended to reduce sleep, but this reduction was not significant. TRH had no significant effect on peripheral blood alcohol concentrations. The present results show that NP rats are more sensitive to the analeptic effect of TRH compared to P rats. These data support and extend those of others who have demonstrated a TRH antagonism on drug-induced sedation. Differential sensitivity to TRH may reflect differences in TRH receptor activity and/or TRH metabolism. Sensitivity to TRH analepsis may be associated with sensitivity to ethanol.

Septal TRH in alcohol-naive P and NP rats and following alcohol challenge.

Regional brain content of TRH was evaluated in selectively bred alcohol-preferring (P) and -nonpreferring (NP) rats before, during, and upon awakening from ethanol sedation. TRH content was significantly lower in both the medial and lateral septum of alcohol-naive P rats compared with alcohol-naive NP rats. Following a sedating dose of ethanol, P rats righted themselves sooner than NP rats. TRH content in the medial septum of P and NP rats was significantly higher when the rats regained their righting reflex. While sedated, TRH in the medial septum of P rats was insignificantly increased. These data are the first to show that endogenous TRH in the medial septum may be involved in arousal from drug-induced sedation and that the events preceding arousal may occur sooner in P than in NP rats. In addition, innate differences in septal TRH may be associated with preference for ethanol.

Analysis of rat EEG using autoregressive power spectra.

The main objective of this paper is to make the auto regressive (AR) power spectrum estimation method accessible to electrophysiologists and present some typical applications. The AR method is explained, choices of various parameters are explored and examples from the analysis of rat hippocampal EEG are given. We also provide the pseudocode for the computation of the AR coefficients and the AR spectrum. We compare the results from the AR method to the FFT-based power spectrum method and demonstrate the superiority of the AR method. We also show the differences in the spectra of the EEG of alcohol-preferring (P) and non-preferring (NP) rats in the baseline condition when no alcohol is infused. We found a statistically significant difference in peak theta frequency which was at 6.96 Hz for the P rats and at 7.74 Hz for the NP rats. There were also other observable differences in the shape of the spectra of the EEG of the P and NP rats.