Comparison of the neurophysiological effects of allopregnanolone and ethanol in rats.

RATIONALE: The central nervous system actions of allopregnanolone (3 alpha-hydroxy-5 alpha-pregnan-20-one) and ethanol are at least partially mediated by modulation of gamma-aminobutyric acid (GABA)-A receptors. Although ethanol and allopregnanolone have similar behavioral effects, their macro-electrophysiological profiles have not been directly compared. OBJECTIVE: The purpose of this study was to compare the effects of allopregnanolone and ethanol on the electroencephalogram (EEG) and event-related potentials (ERPs). METHODS: Male Wistar rats were implanted with cortical and amygdalar electrodes. The rats were then administered allopregnanolone (0.0-10 mg/kg), ethanol (0.0-1.0 g/kg), or a combination of the two before recording. RESULTS: Allopregnanolone and ethanol had similar effects on ERPs. When administered alone, both decreased cortical P1-N1 ERP amplitude by 25-50% and N1 amplitude in the amygdala by 75-80%. Combined administration of ethanol (0.50 g/kg) and allopregnanolone (5.0 mg/kg), doses which were ineffective alone, decreased N1 amplitude in the amygdala by 60%. Allopregnanolone and ethanol had dissimilar EEG effects. Allopregnanolone increased high frequency power in the cortex and amygdala by 25-30%. Ethanol decreased cortical and amygdalar power in the same high frequency bands by 25-45%. Allopregnanolone, but not ethanol, also shifted cortical frequency in the 32- to 50-Hz band. Combined administration of allopregnanolone and ethanol had no effect on EEG power but enhanced allopregnanolone's effect on cortical frequency. CONCLUSIONS: These data suggest that allopregnanolone's macro-electrophysiological profile resembles barbiturates and benzodiazepines more than ethanol. Further, the interactions of allopregnanolone and ethanol appear complex, with multiple effects observed (enhancement or reversal) depending on the neurophysiological variable assessed.

Neuropeptide Y administration into the third ventricle does not increase sucrose or ethanol self-administration but does affect the cortical EEG and increases food intake.

RATIONALE: Several studies have provided indirect evidence that neuropeptide Y (NPY) may play a role in the regulation of ethanol consumption. However, the direct effects of central NPY administration on ethanol drinking are unclear. OBJECTIVE: This study examined the effects of NPY on ethanol, sucrose, and food consumption as well as its concomitant effects on the cortical EEG. METHODS: Wistar rats were implanted with cortical recording electrodes and a cannula in the third ventricle after using a sucrose substitution procedure to establish ethanol self-administration. NPY (0-15 microg/3.0 microl) was infused into the third ventricle prior to drinking sessions, when 10% ethanol (10E), 2% sucrose (2S), 0.5% sucrose (0.5S), or food were available. Behavior and cortical EEG were monitored during the sessions. RESULTS: NPY had no effect on the intake of 10E, 2S, or 0.5S, but NPY (15 microg/3.0 microl) significantly increased food intake. Under baseline drinking conditions, EEG power in the 6-8 Hz range was significantly greater when 2S was consumed compared to 10E. NPY decreased power in the 8-16 Hz range, decreased peak frequency in the 6-8 Hz range, and increased peak frequency in the 32-50 Hz range when 10E or 2S was available. CONCLUSIONS: These data suggest that NPY administration into the third ventricle preferentially regulates feeding compared to ethanol or sucrose drinking. In addition, since NPY significantly altered the cortical EEG in the absence of effects on ethanol and sucrose consumption, these data may indicate that NPY's cortical EEG effects are more related to its sedative or anxiolytic properties, rather than any effect on consumption.

Neurophysiological effects of intracerebroventricular administration of urocortin.

The recently isolated Corticotropin Releasing Factor (CRF) related peptide, urocortin, has been reported to elicit a different behavioral profile than that of CRF. CRF is a potent anxiogenic agent and stimulant of motor activity whereas under similar conditions urocortin is a potent anorectic and mild locomotor stimulant. The neurophysiological effects of this newly synthesized peptide have not yet been examined. The present study evaluated the effects of intracerebroventricular administration of 3 doses of urocortin on the electroencephalogram (EEG) and on Event-Related Potentials (ERPs) in rats. Twenty male Wistar rats were implanted with electrodes in the amygdala and dorsal hippocampus, a cannula into the lateral ventricle, and skull surface electrodes over the frontal and parietal cortices. Following recovery from surgery, urocortin (0.01-1.0 microg) was infused into the lateral ventricle 5 min prior to the recording of EEG (10 min) and ERPs (10 min). Urocortin at any of the doses, did not produce any electrographic or behavioral signs of seizure activity. The predominant effect of urocortin infusion on EEG spectral activity was an increase in mean power in the 4-16 Hz range in the frontal cortex and a decrease in EEG stability in the frontal cortex and amygdala. Urocortin administration also decreased the latency of the P3 component of the ERP in the amygdala and hippocampus. These neurophysiological effects, that only partially overlap with those of CRF, are consistent with the behavioral profile described following urocortin administration in rats. Overall, these data further support the assertion that urocortin functions as a mild CNS stimulant enhancing arousal, as measured by EEG, and modulating the speed of stimulus evaluation as measured by ERPs.

Periadolescent alcohol exposure has lasting effects on adult neurophysiological function in rats.

Most individuals have their first experience with ethanol (EtOH) consumption as adolescents. Episodes of high EtOH drinking, lasting from hours to days (i.e. binges), are not uncommon. Thus, adolescent EtOH drinking has become a significant health concern due to the possible protracted effects of high doses of EtOH on behavior and the developing brain. This study assessed the effects of brief high levels of EtOH during periadolescence on subsequent behavior and electrophysiology in adult rats. Male Sprague-Dawley rats were exposed to EtOH vapor for 5 days (i.e. postnatal days 35-40) or 10 days (i.e. postnatal days 30-40) for 12 h/day. Locomotor activity, EEG activity, and event-related potentials (ERPs) were then assessed at 1 and 6-7 weeks post EtOH exposure. Significant differences in locomotor activity were not observed at 1 week or 6-7 weeks post-ethanol exposure. However, EtOH exposure did have long-term electrophysiological effects. EtOH exposure increased the frequency of the EEG in the 1-2 Hz range in the parietal cortex and the 16-32 Hz range in the hippocampus. EtOH exposure also increased hippocampal N2 amplitude, decreased hippocampal P3 amplitude, and decreased cortical and hippocampal P2 amplitudes. While these findings are generally similar to those reported following long-term ethanol exposure during adulthood, alcohol exposure during adolescence appears to produce more robust hippocampal effects following shorter periods of exposure. In addition, these data indicate that, in the absence of overt behavioral differences, there are long-lasting changes in the functional brain activity of adult rats briefly exposed to high levels of EtOH during the periadolescent period.

Effects of prolonged ethanol exposure on neurophysiological measures during an associative learning paradigm.

Long-term ethanol exposure has been reported to produce electrophysiological and cognitive impairments in some alcoholics. This study assessed the effects of chronic ethanol exposure on neurophysiological indices of associative learning in rats. Male Wistar rats (46) were exposed to ethanol vapor (EtOH group) or air (control group) for 6 consecutive weeks. After the animals were withdrawn from ethanol, electrodes were implanted in the frontal and parietal cortices and in the amygdala. Following a prolonged abstinence from ethanol (10-15 weeks), rats were exposed to a classical conditioning paradigm in which a food pellet was paired with the presentation of an auditory stimulus. During the first five sessions (conditioning phase), food pellet presentation was paired with the presentation of an infrequently presented tone. During the second five sessions (extinction phase), the association between food pellet presentation and the infrequently presented tone was weakened by no longer presenting food pellets following the infrequent tone. During selected test sessions, event-related brain potentials (ERPs) elicited by each tone (i.e. food-paired tone, non-paired tone) were recorded and analyzed. These analyses revealed differences in ERP responses between the groups. The latency of the N1 and P2 ERP components in the cortex of the control group, but not the EtOH group, increased during sessions when the association between food pellet delivery and tone presentation was being established or extinguished. These data support the hypothesis that chronic ethanol treatment results in a loss of responsivity in ERP components sensitive to changes in food-tone associations, even following a prolonged period of withdrawal from ethanol.

Effect of amphetamine on behavior maintained by sucrose: interaction of reinforcement schedule and food restriction.

A multiple schedule (Mult FR 10 VI 30") was employed to examine the interaction of reinforcement schedule and food restriction on amphetamine's effects on lever pressing behavior. High response rates were observed in fixed ratio (FR) 10 components. Significantly lower response rates were observed under the variable interval (VI) 30" schedule. In the nonrestricted feeding condition, significant decreases in high rate FR 10 responding occurred after administration of 1.0 mg/kg amphetamine while lower rates under the same schedule were increased by 0.30 and 1.0 mg/kg amphetamine. In contrast, VI 30" responding was minimally effected at any amphetamine dose. Food restriction resulted in significant increases in responding in both schedule components. Under food restriction, significant decreases in responding were observed only in the FR 10 components at the highest amphetamine dose. The data indicate that amphetamine produced rate-convergent effects and the susceptibility of the animal to these effects was dependent on the schedule of reinforcement and food restriction.

Intranucleus accumbens amphetamine infusions enhance responding maintained by a stimulus complex paired with oral ethanol self-administration.

Six male Long-Evans rats were trained to self-administer 10% ethanol (v/v) during 30 min operant sessions. A licking response on an empty drinking tube resulted in the presentation of reinforcement from an automatic dipper. During the initiation of ethanol self-administration, a tone-light stimulus complex was paired with all ethanol presentations. When 10% ethanol maintained responding, guide cannulae aimed at the nucleus accumbens (NAcc) were implanted into the brain. The ability of the paired stimulus complex to reinforce a new operant response (i.e., a lever press) was then examined. To test for the development of the new response, responding on one lever resulted in presentation of only the paired tone-light stimulus complex (contingency-associated lever) while responding on an alternate lever had no programmed consequences (no contingency-associated lever). Prior to some new response sessions, amphetamine (5-20 microg/microl) was infused into the NAcc to examine the influence of dopamine on responding maintained by the stimulus complex. Ethanol intake during the sessions prior to new response testing averaged 0.49 +/- 0.07 g/g. During new response sessions no significant differences in lever pressure during no-drug conditions (control, sham, injection or vehicle injection) were observed between the contingency-associated and no contingency-associated levers. Intra-NAcc infusion of amphetamine (5-20 microg/microl) resulted in significant increases in lever pressing only on the contingency-associated lever. These data suggest that increasing NAcc dopamine levels with amphetamine enhanced the ability of the stimulus complex to function as a reinforcer. Further studies examining the ability of potentially more salient stimuli (i.e., taste of ethanol) to function as conditioned reinforcers associated with ethanol self-administration are warranted due to the apparent inability of the paired tone-light stimulus complex to function as a reinforcer without amphetamine-induced activation of the NAcc.

Presentation of an ethanol-paired stimulus complex alters response patterns during extinction.

It has been hypothesized that environmental stimuli previously paired with ethanol consumption play a role in excessive ethanol intake. This study examined the ability of orally self-administered ethanol to establish a tone-light stimulus complex as a conditioned reinforcer (CSR). Male Long-Evans rats were trained to orally self-administer 10% ethanol (10E) using the sucrose-substitution procedure. During training, a tone-light stimulus complex was paired with ethanol presentation in a stimulus complex paired (SC-paired) group but not in a control group. Responding during extinction in the presence and absence of the stimulus complex was then examined. Following the initiation of ethanol self-administration, 10E maintained greater responding in the SC-paired group compared to the control group. When the stimulus complex was presented contingent on responding during extinction, the rate of extinction was slightly attenuated in the SC-paired group but not in the control group. The altered rate of extinction in the SC-paired group was characterized by: 1) a slight decrease in total session responding over successive days of extinction and 2) a transient attenuation of extinction burst response rate during the first extinction session. These data suggest the stimulus complex could function as a weak CS(R), but overall its ability to maintain lever pressing was minimal.

Increases in sucrose consumption, but not ethanol consumption, following ICV NPY administration.

Neuropeptide Y (NPY) is a centrally acting neuromodulator that influences both consummatory behaviors and anxiety. NPY's effects on feeding are primarily regulated through Y5 receptors in hypothalamic sites, whereas NPY-induced anxiolysis appears to be mediated by Y1 receptors in the amygdala. Recently, NPY has been postulated to play a role in the regulation of ethanol consumption. The present study assessed the influence of intracerebroventricular (ICV) administration of NPY on the consumption of 10% ethanol or 2% sucrose in rats. Male Wistar rats were trained to self-administer 10% ethanol using the sucrose-substitution procedure and then implanted with an intracerebroventricular (ICV) cannula. The effects of NPY (0-15 microg) on ethanol consumption and sucrose consumption were then examined. ICV NPY infusion had no significant effects on the consumption of 10% ethanol, however, NPY significantly increased the consumption of 2% sucrose, [F(1, 11) = 6.18, p = 0.03]. These data suggest that ethanol intake and sucrose intake are differentially regulated by NPY. It is hypothesized that ICV infusion of NPY may be affecting both Y1 and Y5 receptors producing increased consummatory drive and anxiolysis, two factors that have opposing effects on subsequent ethanol consumption. Therefore, additional studies including site specific injection of NPY will be necessary to provide further insight into the role of NPY on ethanol consumption.

Neonatal nicotine exposure alters hippocampal EEG and event-related potentials (ERPs) in rats.

A consensus is forming that nicotine can damage the developing rat central nervous system. However, few studies have assessed the electrophysiological effects of neonatal nicotine exposure in rodents in brain regions known to be sensitive to the teratogenic properties of nicotine. In a previous study it was reported that 1.0 and 4.0 mg/kg/day nicotine exposure from postnatal days 4-9, a developmental period corresponding to human third-trimester exposure, significantly altered hippocampal event-related potentials (ERPs) but did not effect cortical ERPs, cortical EEG, or hippocampal EEG. Because alterations in behavior and cortical/hippocampal neurochemistry and morphology have been reported following nicotine exposure, the present study used a higher dose of nicotine during the postnatal period (6.0 mg/kg/day) determine if functional changes in the EEG of these regions might contribute to behavioral changes that have been observed. Male Sprague-Dawley rats were exposed to 6. 0 mg/kg/day nicotine via gastric infusion using an artificial rearing, "pup-in-the-cup," technique for 6 consecutive days (postnatal days 4-9). At adulthood, EEG and auditory ERPs were recorded from the cortex and hippocampus. There were no significant differences in EEG or ERPs recorded from the cortex between nicotine-treated and control subjects. Examination of the hippocampal EEG revealed significantly decreased power in the 1-2-Hz frequency band of nicotine-treated rats. In addition, there was a significantly attenuated P300 ERP response to a noise tone in the nicotine-treated rats compared to controls. These data indicate that neonatal nicotine exposure alters functional activity in the hippocampus of adult rats. These effects are likely to be the result of synaptic disorganization in the hippocampus, and indicate that neonatal nicotine exposure exerts teratogenic effects on the developing central nervous system, particularly the hippocampus, which persist into adulthood.

Nicotine exposure during the neonatal brain growth spurt produces hyperactivity in preweanling rats.

Despite warning labels and increases in evidence of the adverse effects of tobacco use, women continue to use tobacco products during pregnancy. Cigarette smoking has been linked to increased prenatal mortality, increased incidence of SIDS, reductions in birth weight, and disruptions in CNS and behavioral development. Animal model systems have critically established the causal relationship between nicotine and adverse developmental outcome. The present study examines the behavioral effects of nicotine exposure in the rat during the third trimester equivalent of the human brain growth spurt, a period of rapid development of the cholinergic systems and a period during which the CNS is particularly vulnerable to a number of insults. Sprague-Dawley rat pups were exposed to nicotine (6.0 mg/kg/day) from postnatal days (PD) 4-9 via an artificial rearing procedure. This procedure ensures that observed effects are not due to nutritional deficits. Two control groups were employed, an artificially reared control group and a normally reared control group. Activity level was measured on PD 18-19. Nicotine-exposed subjects were significantly overactive compared to both control groups, which did not differ significantly from one another. This behavioral alteration was observed in the absence of nicotine-induced body weight deficits. These results suggest that women who use tobacco products during late gestation may place their fetuses at risk for hyperactivity later in life, particularly during early adolescence.

Effects of chronic ethanol exposure on sleep in rats.

Sleep disturbance is a common complaint in alcoholics. When polysomnographic studies are performed in alcoholics, reductions in slow wave sleep are a common finding; however, few studies have evaluated the effects of chronic alcohol exposure on sleep in animal models. In the present study, the sleep EEG was evaluated in 40 Wistar rats who were exposed to chronic alcohol or control conditions in vapor chambers. Rats were exposed to ethanol vapors or control chambers for 6 weeks and then withdrawn. Sleep EEG was recorded before exposure (baseline), immediately following exposure, and 5 weeks after withdrawal from the ethanol/control chambers. In the ethanol-exposed animals, blood ethanol levels averaged 192 mg/dL over 6 weeks of exposure. Chronic ethanol exposure and withdrawal was not found to affect either slow wave sleep latency or slow wave sleep duration; however, overall spectral power as well as power in the delta, theta, and beta frequencies were significantly reduced following chronic exposure (2-4 Hz, [F(1, 17) = 18.11, p = 0.001], 4-6 Hz, [F(1, 17) = 15.98, p = 0.001], 6-8 Hz [F(1, 17) = 15.52, p = 0.001], 8-16 Hz band [F(1, 17) = 18.73, p < 0.0001], 16-32 Hz [F(1, 17) = 10.13, p = 0.005], and 1-50 Hz [F(1, 17) = 17.03, p = 0.001]. After 5 weeks of withdrawal, significant decreases still persisted in the delta and theta frequencies (2-4 Hz [F(1, 16) = 6.21, 0.024], 4-6 Hz [F(1, 16) = 6.26, 0.024], and 6-8 Hz [F(1, 16) = 4.84, p = 0.043]). These findings suggest that spectral analysis of the EEG is a highly sensitive measure of the effects of ethanol on sleep. These findings additionally demonstrate that chronic ethanol exposure can produce persistent diminution in the systems that generate cortical slow waves in the rat and thus may provide a model for understanding the mechanisms underlying sleep disturbances associated with alcoholism.

Exposure to sucrose-quinine solutions does not increase ethanol consumption.

The taste of ethanol can be aversive or preferred based on prior experience with ethanol consumption. A preference for ethanol's taste is thought to result from the association of ethanol's taste with its neuropharmacological activity. However, acclimation to ethanol's aversive taste may also play a role in increased ethanol consumption following prolonged exposure. The present study examined if acclimation to a bitter-sweet tastant, which has been suggested to share similar taste qualities with ethanol, would increase ethanol intake with only minimal prior experience of an association of ethanol intake with its neuropharmacological activity. Male Long-Evans rats were trained to drink 10% sucrose during 20-min sessions. The consumption of 0-20% ethanol was then determined before and after exposure to a sucrose-quinine solution. Before the sucrose-quinine taste acclimation procedure, the initial intake of sucrose-quinine was low and similar to 5% ethanol. After the acclimation procedure, increases in sucrose-quinine intake, but not ethanol intake, were observed. These data could indicate that any similarity in the taste qualities of sucrose-quinine and ethanol solutions are diminished following exposure to sucrose-quinine. Alternatively, the differential changes in sucrose-quinine and ethanol intake could be the result of being differentially regulated by a combination of taste and postingestive factors. Overall, these data indicate that exposure to sucrose-quinine, which resulted in increased intake of sucrose-quinine, was not sufficient to alter ethanol intake. Rather, exposure to taste and postingestive factors associated with ethanol may be necessary to increase ethanol intake.

Dopaminergic and opiate agonists and antagonists differentially decrease multiple schedule responding maintained by sucrose/ethanol and sucrose.

Similar neurobiological mechanisms are hypothesized to influence ethanol- and food-related reinforcement processes. This study examined the ability of compounds with dopaminergic or opiate activity to selectively alter responding maintained by a sucrose/ethanol solution in comparison to a sucrose solution. Long-Evans rats were trained to press a lever using 5% sucrose/10% ethanol and 5% sucrose as the reinforcers on a multiple Fixed Ratio 4 Fixed Ratio 4 schedule of reinforcement. When stable responding was established, the effects of intraperitoneally administered amphetamine (0.0-3.0 mg/kg), haloperidol (0.0-1.0 mg/kg), morphine (0.0-10.0 mg/kg), and naloxone (0.0-10.0 mg/kg) were examined on total session reinforcer presentation and presentation of each reinforcer within individual multiple schedule components. Prior to drug treatment, the total number of reinforcer presentations of the sucrose/ethanol solution was significantly greater than sucrose reinforcer presentations, suggesting the sucrose/ethanol solution was a more efficacious reinforcer. All agents administered decreased responding maintained by sucrose/ethanol and sucrose. The dose-effect curves for sucrose/ethanol were shifted to the left compared to sucrose, suggesting that although the compounds did not selectively impact sucrose/ethanol-maintained responding, sucrose/ethanol-maintained responding was more sensitive to the effects of these compounds.

Substance P and neurokinin levels are decreased in the cortex and hypothalamus of alcohol-preferring (P) rats.

OBJECTIVE: Central tachykinin levels (i.e., substance P [SP], neurokinin A [NKA], neurokinin B [NKB] and neurokinin K [NKK]) have been reported to fluctuate in association with stress and anxiety. Ethanol can also modulate stress and anxiety. Further, ethanol intake can change as a result of stress and anxiety. This suggests possible interactions between ethanol and central tachykinins, i.e., changing tachykinin levels could influence ethanol intake and vice versa. However, to date few studies have assessed the potential relationship between tachykinin levels in the brain and ethanol preference. The present study was designed to determine if rodent lines selectively bred for differences in alcohol preference (i.e., alcohol-preferring [P] and non-preferring [NP] rats) have different tachykinin levels in the brain. METHOD: Tissue samples from the brains of ethanol-naive P and NP rats were collected from the frontal cortex, caudate, hippocampus, amygdala and hypothalamus. Using radioimmuno assays, concentrations of SP-like immunoreactivity (SP-LI) and neurokinin-like immunoreactivity (NK-LI, i.e., neurokinin A, B and K) in P and NP rats were determined. RESULTS: In P rats, SP-LI was significantly lower in the frontal cortex (F= 12.80, 1/26 df, p = .001) while NK-LI was significantly lower in the frontal cortex (F = 7.36, 1/26 df, p = .012) and hypothalamus (F = 5.32, 1/26 df, p = .029) compared with NP rats. CONCLUSIONS: These data indicate that endogenous SP and neurokinin levels are reduced in discrete brain regions of P rats compared with NP rats. These decreases may be associated with decreased serotonergic innervation of these brain regions in P rats compared with NP rats.

Changes in oral ethanol self-administration patterns resulting from ethanol concentration manipulations.

A variety of initiation procedures have been used to develop oral ethanol consumption. Using the sucrose-substitution procedure, oral self-administration of ethanol-water solutions with ethanol concentrations as high as 40% can be initiated in food- and fluid-sated rats. An important question for these models is the relationship between ethanol concentration and self-administration patterns after initiation. This study examined the differential patterns of ethanol self-administration maintained by a range of ethanol solutions (10 to 30%) over a 5-week period, compared with rats maintained on 10% ethanol for 5 weeks. In 43 male Long Evans rats, the sucrose-substitution procedure was used to initiate responding maintained by 10% ethanol on a Fixed Ratio 4 schedule of reinforcement. The ethanol concentration presented was then increased to 30% in stepwise fashion and then returned to 10% [Ethanol Concentration Manipulation (ECM) group, n = 32], or 10% ethanol was maintained as the reinforcer for 5 weeks [Control (Con) group, n = 11]. Significant increases in ethanol intake and decreases in responding were associated with increased ethanol concentration. Although no overall differences in total session responding were observed in either group between week 1 and week 5 (10E vs. 10E), examination of changes in initial low responders of the ECM group revealed significant increases in responding that were not observed in the initial low responders of the Con group. Significant increases in momentary response rates were observed on both the ECM and Con groups, independent of the ethanol concentration presented. Increases in response rate in the ECM group were the result of increases in initial low rate and high rate responders; however, the increased response rates in the Con group were the result of increases only in the initial low rate responders. These data suggest that the ECM procedure can aid in the initiation of ethanol self-administration and may be particularly useful in rats of heterogeneous stock.

Neurophysiological profiles of replicate line 2 high-alcohol-drinking (HAD-2) and low-alcohol-drinking (LAD-2) rats.

RATIONALE: A select number of electrophysiological findings have been demonstrated to differentiate rat lines selectively bred for high and low ethanol preference. OBJECTIVE: In the present study, EEGs and event-related potentials (ERPs) of high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats from replicate line 2 (HAD-2 and LAD-2) were assessed to determine if their neurophysiological profiles are similar to selected lines previously evaluated. METHODS: Rats obtained from Indiana University were implanted with cortical and amygdalar recording electrodes. Baseline EEG and ERPs were assessed in ethanol-naïve HAD-2 and LAD-2 rats. Animals subsequently were trained to self-administer ethanol by using a sucrose-substitution procedure. RESULTS: Compared with LAD-2 rats, HAD-2 rats displayed greater parietal cortical power in the 6 to 32 Hz frequency range of the EEG. Greater parietal cortical peak frequency in the 2 to 4 Hz range and decreased frontal, parietal, and amygdalar peak frequencies in the 16 to 32 Hz frequency range were also seen. Compared with LAD-2 rats, HAD-2 rats had decreased P2 latency of ERPs recorded in the parietal cortex. HAD-2 rats also had greater frontal, parietal, and amygdalar P2 amplitudes, greater frontal and parietal cortical P1 amplitudes, and greater parietal cortical P3 amplitudes compared with LAD-2 rats. As anticipated, HAD-2 rats consumed significantly greater levels of sucrose, sucrose-ethanol, and ethanol over the course of the sucrose-substitution procedure compared with LAD-2 rats. CONCLUSIONS: These data suggest that increased cortical power is associated with high ethanol preference in a number of selectively bred rat lines. However, unique electrophysiological characteristics may index alcohol preference in each line.

Differential changes in sucrose/ethanol and sucrose maintained responding by independently altering ethanol or sucrose concentration.

Increased reinforcing efficacy of sucrose/ethanol solutions in comparison to sucrose solutions has been previously demonstrated. However, the contribution of the components of the sucrose/ethanol solution is not well defined. The present study used a multiple schedule of reinforcement to evaluate the differential changes in reinforcer presentations as sucrose or ethanol concentrations were altered. Male Long-Evans rats were trained to press a lever on a multiple fixed ratio 4-fixed ratio 4 schedule which was composed of alternating 2-min components. During one component, 5% sucrose/10% ethanol was presented as the reinforcer and, in the second component, 5% sucrose was presented. Independent manipulations of the ethanol concentration (0, 5, and 20%) in the sucrose/ethanol solution or sucrose concentration (0, 10, and 20%) in the sucrose solution were then performed. Increasing the ethanol concentration in the sucrose/ethanol solution resulted in decreases in reinforcer delivery but increases in ethanol intake (grams per kilogram) and total session caloric intake. Increasing the sucrose concentration in the sucrose solution resulted in significant increases in sucrose reinforcer delivery and total session caloric intake. During the concentration manipulations, the number of reinforcers presented of the unchanged reinforcer was not affected. Differential changes in the pattern of reinforcer presentation after ethanol and sucrose concentration manipulations during successive access periods suggest that sucrose and sucrose/ethanol maintained responding are differentially regulated. Changes in sucrose maintained responding after increases in the sucrose concentration were observed early in the session suggesting a strong influence of taste in regulating intake. Changes in sucrose/ethanol maintained responding after increases in the ethanol concentration occurred later in the session and suggest that postingestive effects (i.e., pharmacology) play a major role in the regulation of sucrose/ethanol intake. In addition, the differential patterns of sucrose/ethanol and sucrose maintained behavior suggest that the ethanol component of the sucrose/ethanol solution plays an important role in maintaining sucrose/ethanol reinforced behavior.

Norepinephrine and serotonin receptors in the paraventricular nucleus interactively modulate ethanol consumption.

The homeostatic function of the hypothalamus has long been recognized. In particular, the role of the paraventricular nucleus (PVN) in regulating ingestive behavior has been of interest. Infusions of serotonin and norepinephrine into the PVN are correlated with nutrient selective decreases and increases in consumatory behavior, respectively. Given the wide range of homeostatic functions of the hypothalamus, it is plausible that similar hypothalamic mechanisms may also be involved in the regulation of ethanol intake. This study examined the effects of PVN infusions of serotonin (5-HT) and norepinephrine (NE) on ethanol intake in a 1-hr limited-access two-bottle paradigm. When intake of 6% (v/v) ethanol versus water stabilized, male Wistar rats were implanted with stainless steel guide cannulae aimed at the PVN. After recovery, NE (20, 50, and 100 nmol), 5-HT (5 and 25 nmol), and their combination (NE 50 nmol + 5-HT 5 nmol) were microinjected into the PVN in a volume of 0.5 microliter/side over 1 min. Baseline ethanol intake was approximately 1.0 g/kg and ethanol preference (milliliters ethanol per total milliliters) was approximately 60%. Both 20 and 50 nmol of NE significantly increased absolute ethanol intake by 50% and relative ethanol intake by approximately 30%. Corresponding decreases were observed in water intake. Neither dose of 5-HT when administered alone altered ethanol or water consumption, but the 5-nmol dose of 5-HT attenuated the increase observed after NE (50 nmol) administration. These data demonstrate that NE and 5-HT receptors in the PVN interact in the modulation of ethanol ingestion. This finding suggests that homeostatic regulatory functions of the hypothalamus are involved in ethanol intake, and a perturbation of this system may influence excessive drinking.

Effects of chronic ethanol exposure on neurophysiological responses to corticotropin-releasing factor and neuropeptide Y.

Stress has been reported to influence ethanol consumption and relapse in abstinent alcoholics. The present study examined if prolonged alterations in neurophysiological responses to corticotropin-releasing factor (CRF) and neuropeptide Y (NPY), peptides known to influence stress responses, would persist during protracted ethanol abstinence. Male Wistar rats were chronically exposed to ethanol vapour (EtOH group) or air (control group) for 6 weeks. Upon removal from the vapour chambers, recording electrodes were implanted in the cortex and amygdala. The effects of intracerebroventricular infusions of CRF and NPY on electroencephalogram (EEG) and event-related potentials (ERPs) were then assessed 10-15 weeks after withdrawal from ethanol. Following abstinence from ethanol, the EtOH group displayed increased power in the 6-8 Hz frequency range and increased stability in the cortical EEG. In addition, in the EtOH group the amplitude of the P2 ERP component in the frontal cortex was decreased and the latency of the P3 ERP component in the parietal cortex was delayed, compared to the control group during baseline recording conditions. The EtOH group was also more responsive to CRF and NPY. CRF significantly increased cortical power (6-8 Hz) and increased cortical EEG stability in the EtOH group, compared to controls. Additionally, NPY significantly decreased the amplitude of the N1 ERP component in the amygdala of the EtOH group, but not in the control group. This enhanced sensitivity to CRF and NPY following chronic ethanol exposure and abstinence suggests that these peptidergic systems may play a role in the symptomatology of the prolonged abstinence syndrome.