Development of tolerance to and physical dependence on ethanol: daily versus repeated cycles treatment with ethanol

Timing Eclipses Amount: The Critical Importance of Intermittency in Alcohol Exposure Effects

Frequency and duration of ethanol (EtOH) exposures influence the consequences of those experiences, with evidence building from basic science studies in rats and mice that intermittent alcohol access (IAA) typically produces a greater escalation of EtOH intake than more continuous alcohol access (CAA). IAA also better simulates human use patterns where alcohol levels typically clear from the body between periods of use. A variety of mechanisms have been proposed to contribute to the enhanced intake of EtOH induced by IAA, including a possible attenuation in the aversive effects of EtOH, although further studies are needed to address this and other possibilities. Neural differences include indications of an IAA-associated increase in NR2B receptors that is not evident with CAA; although little studied, alterations in other neural and neurotransmitter systems are evident as well. Many gaps in understanding of IAA/CAA effects remain. Further work is needed to characterize neural mechanisms underlying these effects, consequences of IAA/CAA on EtOH effects beyond intake, and the impact of stress and environmental variables on these differences. IAA/CAA studies to date have also largely been limited to males and to adult animals, and hence, more studies examining IAA/CAA across sex and age are needed. Such additional work is essential to determine unique contributors to IAA-induced elevations in EtOH intake that may provide important insights for the development of new prevention/intervention strategies for heavy alcohol use and abuse.

Impulsive choice and anxiety-like behavior in adult rats exposed to chronic intermittent ethanol during adolescence and adulthood

Binge drinking during adolescence and adulthood may have differential long-term effects on the brain. We investigated the long-term effects of chronic intermittent ethanol (CIE) exposure during adolescence and adulthood on impulsivity and anxiety-like behavior. Adolescent (adolescent-exposed) and adult (adult-exposed) rats were exposed to CIE/water on postnatal days (PND) 28-53 and PND146-171, respectively, and a 4-day ethanol/water binge on PND181-184 and PND271-274, respectively. During withdrawal from CIE and 4-day binge exposures, anxiety-like behavior and arousal were measured in the light-potentiated startle (LPS) and acoustic startle (ASR) procedures, respectively. Impulsive choice was evaluated in the delay discounting task (DDT) at baseline and after ethanol challenges. Independent of age, ASR and LPS were decreased during withdrawal from CIE exposure. In contrast, LPS was increased in adult-exposed, but not adolescent-exposed, rats during withdrawal from the 4-day ethanol binge. CIE exposure had no effect on preference for the large delayed reward at baseline, independent of age. During DDT acquisition, CIE-exposed, compared with water-exposed rats, omitted more responses, independent of age, suggesting the CIE-induced disruption of cognitive processes. Ethanol challenges decreased preference for the large reward in younger adolescent-exposed rats but had no effect in older adult-exposed rats, independent of previous CIE/water exposure. Taken together, the present studies demonstrate that CIE withdrawal-induced decreases in anxiety and arousal were not age-specific. CIE exposure had no long-term effects on baseline impulsive choice. Subsequent ethanol exposure produced age-dependent effects on impulsivity (increased impulsivity in younger adolescent-exposed rats) and anxiety-like behavior (increased anxiety-like behavior in older adult-exposed rats).

Acoustic startle at baseline and during acute alcohol withdrawal in replicate mouse lines selectively bred for high or low alcohol preference

BACKGROUND

Previous data in both rat and mouse genetic models suggest that there is a genetic relationship between acute alcohol withdrawal responses and innate alcohol drinking behavior. The purpose of the present study was to examine whether acute alcohol withdrawal responses, as measured by acoustic startle and prepulse inhibition (PPI) of acoustic startle, may be genetically related to innate differences in alcohol preference in 2 mouse lines selectively bred for high (HAP1 and HAP2) or low (LAP1 and LAP2) alcohol preference. Line differences in startle responses at baseline, prior to alcohol or saline treatment, were also measured.

METHODS

Alcohol-naive, male and female HAP1 (n = 35) and LAP1 (n = 32) and HAP2 (n = 43) and LAP2 (n = 40) mice were tested under baseline conditions and during withdrawal from a single injection of 4.0 g/kg alcohol or equal volume of saline at 4, 8, and 12 hours post-injection.

RESULTS

On most trial types, baseline startle responses and PPI were greater in both HAP lines than in both LAP lines, and startle responses were greater in males than in females. During acute alcohol withdrawal, both male LAP lines, and LAP1 females, showed reduced startle responses at the 4-hour time point during acute alcohol withdrawal. In contrast, both HAP1 males and females showed a trend toward enhanced startle at 4 hours in withdrawal. No clear differences in PPI during withdrawal were evident.

CONCLUSIONS

These findings indicate good evidence for a genetic relationship between greater baseline acoustic startle responses and PPI and high alcohol preference. Modest support for a genetic correlation between low alcohol preference and reduced startle responses at 4 hours in withdrawal was found in male mice. The suppression in acoustic startle during acute alcohol withdrawal in male LAP lines but not in male HAP lines suggests that a genetic propensity toward low alcohol preference may be related to greater sensitivity to alcohol as measured by acoustic startle responses during acute alcohol withdrawal.

Effect of duration and pattern of chronic ethanol exposure on tolerance to the discriminative stimulus effects of ethanol in C57BL/6J mice

This study was conducted to examine whether amount and/or pattern (intermittent or continuous) of chronic ethanol exposure subsequently alters sensitivity to the discriminative stimulus effects of ethanol. Adult male C57BL/6J mice were trained to discriminate between 1.5 g/kg ethanol and saline in a two-lever food-reinforced operant procedure. Once ethanol discrimination was successfully acquired, generalization testing was conducted using a cumulative dosing procedure to generate a baseline dose-response function (0-2.5 g/kg ethanol). Discrimination training was then suspended while mice received chronic ethanol vapor or air exposure in inhalation chambers. The total amount of ethanol exposure was systematically increased, but it was delivered in an intermittent or continuous manner. At 24 or 16 h after inhalation treatment, ethanol discriminability was reassessed using the same generalization testing procedures. Results indicated that discrimination performance in control (air-exposed) mice was similar to baseline. However, sensitivity to the discriminative cue of ethanol following chronic ethanol treatment was reduced (as evidenced by rightward shifts in the dose-response functions and increased ED(50) values). The magnitude of this tolerance effect increased as a function of the number of chronic ethanol exposures as well as the total duration of ethanol exposure. In addition, tolerance was more robust when generalization testing was conducted earlier (16 versus 24 h) after chronic ethanol treatment was halted (2- to 3-fold increase in ED(50) values). These results may have important clinical implications, because blunted sensitivity to the discriminative cue of ethanol may contribute to enhanced ethanol self-administration behavior observed in these mice following similar chronic ethanol treatment.

Intermittent presentations of ethanol sipper tube induce ethanol drinking in rats

AIMS

Intermittent presentations of the ethanol sipper have been reported to induce more ethanol drinking in rats than when the ethanol sipper was continuously available during the session. This intermittent sipper effect was observed in a social drinking situation, in which subjects experienced intermittent opportunities to interact briefly with a conspecific rat. The objective of this study was to evaluate the effects of the intermittent sipper procedure in situations providing for intermittent presentations of food, and, in addition, in situations that do not provide for intermittent presentations of another rewarding event.

METHODS

Four groups of male Long-Evans hooded rats, arranged in a 2 x 2 factorial design with two levels of Sipper Procedure (Intermittent vs Continuous) and two levels of Food procedure (Food vs No Food), were trained in drinking chambers. During each daily session, Intermittent Sipper groups received access to the ethanol sipper during each of 25 trials of 10 s each, while Continuous Sipper groups had access to the ethanol sipper during the entire session (approximately 30 min). During each session, Food groups received 25 presentations of food pellets while No Food groups received no food pellets. Ethanol concentrations in the sipper [3, 4, 6, 8, and 10% (vol./vol.)] increased across sessions.

RESULTS

More rapid escalation of ethanol intake was observed in the Intermittent Sipper groups than in the Continuous Sipper groups, and this effect was observed in both the Food and No Food conditions (P's < 0.05), which did not differ from one another.

CONCLUSIONS

Intermittent Sipper procedures provide less access to the ethanol sipper, yet induced more ethanol drinking than Continuous Sipper procedures. The intermittent sipper effect is not dependent on presentations of food. Implications for schedule-induced polydipsia and Pavlovian autoshaping are discussed.

Alphaxalone and epiallopregnanolone in rats trained to discriminate ethanol

BACKGROUND

Neurosteroids with a 3 alpha-hydroxy orientation share pharmacological effects with ethanol, increase in brain after ethanol administration, and may mediate ethanol effects. 3beta-hydroxy neurosteroids antagonize in vitro and some, but not all in vivo effects of ethanol and 3 alpha-hydroxy neurosteroids.

METHODS

We assessed the discriminative stimulus and rate altering effects of alphaxalone, a 3 alpha-hydroxy neurosteroid, and epiallopregnanolone, a 3beta-hydroxy neurosteroid, in rats trained to discriminate either 0.8 g/kg or 1.2 g/kg ethanol. The ability of epiallopregnanolone to antagonize the discriminative stimulus or rate-altering effects of ethanol or alphaxalone was also assessed.

RESULTS

Ethanol had similar discriminative ED50s (0.5 g/kg) in both groups; however rats trained with the lower ethanol dose were more sensitive to rate-decreasing effects of ethanol. Alphaxalone occasioned ethanol-appropriate responding in both training groups, although less effectively in rats trained on the lower ethanol dose (maximum 65% versus 80% ethanol-appropriate responding). No difference in sensitivity to the rate-decreasing effects of alphaxalone was present between groups. Epiallopregnanolone did not reliably occasion ethanol-appropriate responding in either training group, and rats trained on the lower ethanol dose were slightly more sensitive to epiallopregnanolone rate decreasing effects. Epiallopregnanolone did not alter any effects of ethanol or alphaxalone.

CONCLUSIONS

Our results agree with previous reports that 3 alpha-hydroxy neurosteroids occasion ethanol-appropriate responding, while 3beta-hydroxy neurosteroids do not; as well as reports showing no antagonism of the discriminative stimulus or rate-suppressant effects of ethanol or 3 alpha-hydroxy neurosteroids by 3beta-hydroxy neurosteroids. Results of the present study demonstrate that ethanol and 3 alpha-hydroxy neurosteroids share discriminative stimulus effects. However, these results are inconsistent with the hypothesis that such neurosteroids mediate the discriminative stimulus of ethanol.

Enhanced prepulse inhibition following adolescent ethanol exposure in Sprague-Dawley rats

OBJECTIVES

Recent studies have demonstrated that ethanol exposure differentially affects adolescents and adults. The current studies were designed to compare the effects of 2-week exposure to ethanol during adolescence or adulthood on the acoustic startle response (ASR) and prepulse inhibition (PPI) METHODS: Male Sprague-Dawley rats were exposed to ethanol vapor 12 hr/d (on from 6 pm to 6 am) for 14 days during adolescence or adulthood. Six days after the cessation of ethanol vapor exposure, the ASR and PPI were assessed.

RESULTS

During ethanol treatment, overall blood alcohol levels averaged 230 to 250 mg/dl in the adolescent and adult treatment groups. Assessment of the ASR revealed that latency to startle was more rapid in adolescents than in adults, but ASR latency was not altered by ethanol exposure. In addition, ASR magnitude was lower in adolescents and was decreased in ethanol-exposed rats on startle trials. Ethanol exposure significantly enhanced PPI, but only after adolescent exposure

CONCLUSIONS

These data further demonstrate a differential sensitivity of adolescents and adults to the effects of ethanol exposure. Specifically, a 2-week period of ethanol exposure during adolescence selectively enhanced PPI, a neurobehavioral index of sensorimotor gating. However, ASR magnitude was decreased by ethanol exposure regardless of age. On the basis of previous studies, the effects of ethanol exposure on PPI data could indicate that adolescent rats exposed to ethanol are more likely to exhibit behavioral inflexibility and that ethanol exposure acts as a more potent physical stressor in adolescent rats.

Further evidence of an inverse genetic relationship between innate differences in alcohol preference and alcohol withdrawal magnitude in multiple selectively bred rat lines

BACKGROUND

We have previously shown that a genetic association exists between low alcohol drinking and high alcohol withdrawal magnitude after acute alcohol exposure in alcohol-naïve rats. However, the behavioral rating scale used in this prior study was not optimal for assessing the magnitude of mild alcohol withdrawal. The present study examined whether a genetic relationship is again found between alcohol preference and alcohol withdrawal magnitude when a sensitive measure is used to index mild alcohol withdrawal in rats.

METHODS

Alcohol-naïve, male rats selectively bred for alcohol preference (P, HAD1, HAD2) or nonpreference (NP, LAD1, LAD2) received a single intragastric infusion of alcohol (4.0 g/20.3 ml/kg body weight; 25% v/v) or water followed by acoustic startle testing.

RESULTS

Startle probability and magnitude was greater in water-treated P than in water-treated NP rats. During alcohol withdrawal, startle probability and magnitude was suppressed in P rats and elevated in NP rats relative to water-treated controls. Startle probability and magnitude was greater in water-treated LAD1 rats than in water-treated HAD1 rats. During alcohol withdrawal, startle probability and magnitude was suppressed in HAD1 and elevated in LAD1 rats relative to water-treated controls at 20 hr after acute alcohol exposure. Startle probability and magnitude did not differ between water-treated HAD2 and water-treated LAD2 rats. During alcohol withdrawal, there was a trend toward decreased startle probability and magnitude in HAD2 rats compared with water-treated controls.

CONCLUSIONS

The acoustic startle response to a tone stimulus is a sensitive measure of mild alcohol withdrawal in rats. Rats selectively bred for low alcohol intake showed greater alcohol withdrawal magnitude than did rats selectively bred for high alcohol intake. These results provide further evidence that an inverse genetic association exists between alcohol withdrawal magnitude and propensity toward alcohol drinking in rats.

Uncoupling protein 2 (UCP2) lowers alcohol sensitivity and pain threshold

Abuse of ethanol is a major risk factor in medicine, in part because of its widespread effect on the activity of the central nervous system, including behavior, pain, and temperature sensation. Uncoupling protein 2 (UCP2) is a mitochondrial protonophore that regulates cellular energy homeostasis. Its expression in mitochondria of axons and axon terminals of basal forebrain areas suggests that UCP2 may be involved in the regulation of complex neuronal responses to ethanol. We employed a paradigm in which acute exposure to ethanol induces tolerance and altered pain and temperature sensation. In UCP2 overexpressing mice, sensitivity to ethanol was decreased compared to that of wild-type animals, while UCP2 knockouts had increased ethanol sensitivity. In addition, UCP2 expression was inversely correlated with the impairment of pain and temperature sensation induced by ethanol. Taken together, these results indicate that UCP2, a mitochondrial uncoupling protein previously associated with peripheral energy expenditure, is involved in the mediation of acute ethanol exposure on the central nervous system. Enhancement of UCP2 activation after acute alcohol consumption might decrease the time of recovery from intoxication, whereas UCP2 inhibition might decrease the tolerance to ethanol.

Monoaminergic changes associated with audiogenic seizures in ethanol-dependent rats

1. A previous report demonstrated the efficacy of combining dopaminergic and serotonergic agonists in suppressing audiogenic seizures induced in ethanol-dependent rats undergoing withdrawal. Moreover, an increase in dopamine and a reduction in serotonin levels in the striatum were associated with such seizures. 2. The present study was designed to examine neurochemical changes in the striatum associated with repeated episodes of ethanol withdrawal seizures in untreated ethanol-dependent rats as well as in those treated with amphetamine and fenfluramine in combination. 3. Ethanol-dependent rats undergoing audiogenic seizures exhibited an increase in striatal dopamine and a reduction in striatal serotonin as compared to control and ethanol-dependent rats not undergoing seizures. Amphetamine and fenfluramine in combination effectively suppressed the audiogenic seizures by reversing the neurochemical changes in the striatum in ethanol-dependent rats. However, increased dopamine but decreased serotonin levels in the striatum were observed in rats undergoing one episode of ethanol withdrawal, but not in those experiencing multiple episodes of ethanol withdrawal. 4. Thus, alterations in striatal dopamine and serotonin levels were, at best, necessary but not sufficient to predispose audiogenic seizure susceptibility in ethanol-dependent rats.

Relating acoustic startle reactivity and plasticity to alcohol consumption in male Wistar rats

The purpose of this study was to investigate the relationship between the startle response and ethanol. Aspects of the startle response, including initial and average startle, habituation, and prepulse inhibition (PPI) were studied. The startle response was measured to detect potential predictors of voluntary ethanol consumption and to observe whether ethanol ingestion would affect startle in subsequent tests. Rats were tested three times in a standard startle chamber. After the initial startle test, rats categorized as showing high or low PPI were allocated in a balanced way to a free-choice ethanol-water regime or to the water-regime control group. At the end of the ethanol period (lasting for 16 days, including access to ethanol for 10 days), the rats were tested again in the startle chamber 24 h after ethanol removal. After 5 weeks of ethanol abstinence, rats were exposed to a final startle test. The response to the first 120-dB stimulus showed an inverted U-shaped, curvilinear relationship to later ethanol consumption. Startle habituation appeared to have predictive value regarding ethanol consumption, with rats showing the most efficient habituation drinking most. Data showed no relationship between PPI and ethanol intake. Rats given access to ethanol showed greater habituation in the post-ethanol test than did the water controls. After 5 weeks of abstinence, low ethanol-consuming rats showed lower startle responses to the first 120-dB stimulus than did high ethanol-consuming rats. The present data suggest a two-way relationship between startle response characteristics and alcohol.

Chronic ethanol self-administration in a continuous-access operant situation: the use of a sucrose/ethanol solution to increase daily ethanol intake

The addition of sucrose to an ethanol solution increases both limited- and continuous-access ethanol consumption. The present study examined if the increased intakes in a continuous-access condition could produce withdrawal signs indicating physical dependence on ethanol. Rats were maintained in a continuous-access operant situation in which one lever press on one lever resulted in the presentation of a food pellet, whereas one lever press on a second lever presented 0.1 ml of fluid in a dipper. Water was available from a drinking spout. Ten rats received a 10% sucrose/20% ethanol mixture in the dipper and six rats 10% sucrose. After 30 days the animals were tested for withdrawal signs after 8 h without ethanol using an activity test and response to key shaking. They were then given an additional 30 days of access to the solutions and retested for withdrawal. This was followed by a final 30 days of access and a third withdrawal test. Over the 90 days, the sucrose/ethanol group consumed 8-10 g of ethanol per kilogram of body weight per day. Over this time both groups gained weight. At the third withdrawal test, a significant reduction in activity occurred in the ethanol-drinking group, compared with the sucrose group. No severe withdrawal effects were observed to the key shake test. The results suggest that the higher ethanol intakes previously observed using this sucrose/ethanol solution can be maintained over long periods of time. Although this intake was not sufficient to produce severe withdrawal signs, the results suggest that longer exposure might result in more severe ethanol dependence.

Lack of tolerance to ethanol-induced motor impairment on accelerod performance in rats

The effect of ethanol on rats was investigated at increasing rates of acceleration for bar rotation speed. Ethanol was given to rats by a liquid diet starting with 2.4% ethanol (v/v) for 3 days. Then the ethanol concentration was increased to 4.8% (v/v) for 3 days and finally to 7.2% (v/v) for 15 days. Accelerod performance was recorded before and throughout 20 days of ethanol intake. Mean blood ethanol levels were 266.34+/-13.11 and 285.20+/-9.77 mg/dl on the 7th and 15th days of ethanol (7.2% v/v) consumption, respectively, as measured in a parallel group of animals. Ethanol produced significant concentration-dependent impairments in the accelerod performance of rats. The motor impairment effect of ethanol was most prominent in the test using the greatest rate of acceleration (from 0 to 79 rpm within 2 min). The impairment effect of ethanol on accelerod performance occurred throughout the period of ethanol exposure. Our results indicate that motor impairment on the accelerod performance test produced by an ethanol liquid diet depends on the concentration of ethanol and the rate of acceleration. In addition, under free-access conditions accelerod performance may not be a suitable behavioral test for detecting tolerance development to ethanol in rats.

Acamprosate and alcohol: II. Effects on alcohol withdrawal in the rat

The suppressing effect of acamprosate (calcium-acetyl homotaurinate) on alcohol drinking is well established; however, little is known about its effects upon the alcohol-induced withdrawal syndrome. Male Wistar rats received as a sole drinking fluid a 20% (v/v) alcohol solution for one week. Animals consumed on average 5.3 +/- 0.3 g/kg per day alcohol, which resulted in blood alcohol levels of 38 +/- 14 mg/dl. For the quantification of alcohol withdrawal we used a new radio-telemetric system which enabled us to monitor body temperature, locomotor activity, food and water intake patterns constantly during alcohol withdrawal. Although alcohol intake and the resulting blood alcohol levels were low, clear signs of withdrawal could be observed. Thus, hyperthermia and hyperlocomotion occurred 18 h after the termination of forced alcohol drinking. Food intake was initially enhanced but dropped significantly below basal food intake in control animals one day after the termination of forced alcohol drinking. Acamprosate given twice a day (200 mg/kg, i.p., 8 a.m. and 8 p.m.) reduced hyperlocomotion and food intake significantly in the alcohol withdrawal animals, however, it did not change withdrawal-induced hyperthermia. When acamprosate was given to alcohol-naive animals, it increased locomotor activity and body temperature transiently, in particular during the rats' active night phase. In summary, (i) the radio-telemetric system used in the present study proved to be a very sensitive method for quantifying alcohol-induced withdrawal symptoms; (ii) acamprosate reduced alcohol-induced physical signs of withdrawal, however, this effect could not be observed for all parameters measured, which might be explained by the fact that (iii) acamprosate exerts a slight, transient psychomotor stimulant effects by itself.

Reversible inhibition by ethanol of Mg(2+)-dependent phosphatidate phosphohydrolase: an in vitro study in the rat reticulocyte

By using a tracer method, we demonstrate that short-term in vitro exposure of intact rat reticulocytes to ethanol elicits a biphasic response of cell-bound Mg(2+)-dependent phosphatidate phosphohydrolase (PAP). An initial concentration-dependent (200-750 mM) activity decrease is rapidly (< 10 min) followed by reversal of the inhibition in the presence of ethanol, suggesting the development of a cell resistance to the inhibitory agent. Addition to the cell suspension of propranolol (100 microM), a known PAP inhibitor, does elicit PAP inhibition but unlike ethanol, inhibition is not followed by a return with time to control value. Ethanol-induced inhibition of cell-bound PAP was also demonstrated in cell-free extracts, where the Mg(2+)-dependent activity was decreased both in the particulate and soluble fractions. In the intact cells, the transient PAP inhibition occurs in concomitance with an overall increase in total glycerolipid biosynthesis, which is constant over 60-min incubation. We suggest that the biphasic mode of response to ethanol of Mg(2+)-dependent PAP activity may play a role in the mechanism of membrane adaptation to ethanol, and thereby to the pathogenesis of alcoholism.

Positive relationship between the number of prior ethanol withdrawal episodes and the severity of subsequent withdrawal seizures

One factor that has been shown to influence the severity of an ethanol withdrawal syndrome is a history of prior experience with episodes of ethanol withdrawal. It has been hypothesized that the progressive intensification of withdrawal symptoms following repeated bouts of ethanol intoxication and withdrawal may represent the manifestations of a "kindling-like" process. In mice, repeated episodes of ethanol withdrawal potentiate the severity of subsequent withdrawal seizures, even when the total amount of ethanol intoxication is equated across groups. In the current experiments, mice received 16-h bouts of continuous exposure to ethanol vapor in inhalation chambers separated by 8-h periods of abstinence. The withdrawal response was assessed by scoring handling-induced convulsions. The results demonstrated that a positive relationship exists between the number of prior episodes of ethanol withdrawal and the severity of subsequent withdrawal seizures. This conclusion was supported by both between-subject and within-subject comparisons. The difference in withdrawal severity does not appear to be related to differences in the level of intoxication, since blood ethanol levels immediately preceding withdrawal testing were similar for all groups. Further, the differential withdrawal response exhibited by multiple and single withdrawal groups cannot be explained by a difference in the rate of ethanol elimination. Although the mechanism(s) remain to be determined, taken together, these results provide support for the "kindling" hypothesis of ethanol withdrawal.

Long-term effects of intermittent versus continuous ethanol exposure on hippocampal synapses of the rat

The hippocampus is known to be very sensitive to a large spectrum of different neurotoxins including ethanol. Ethanol administered continuously or intermittently may affect the hippocampus in different ways. Intermittent administration of ethanol has many features in common with the low level electrical stimulation protocols which lead to the functional changes associated with the phenomenon of kindling. In this study, the differential effects of intermittent intraperitoneal ethanol injections (3 g/kg twice daily) and continuously administered ethanol in drinking water (20%) on hippocampal synapses in the rat were studied using ethanolic phosphotungstic acid staining and electron microscopy. After 1 month of intermittent exposure a significant reduction (18%) of synapses was seen in the stratum lucidum of the CA3 region. Continuously treated animals showed no significant change over this time despite a higher total ethanol intake. In the dentate gyrus, a compensatory increase in supragranular synaptic number was seen only in continuously treated animals. These findings demonstrate the sensitivity of synapses of the hippocampus to the presence of ethanol and the larger effects of peaking ethanol concentrations compared to more constant levels. These results emphasize the need to consider the differential effects of various types of ethanol consumption also on the human brain.

The kindling model of alcohol dependence: similar persistent reduction in seizure threshold to pentylenetetrazol in animals receiving chronic ethanol or chronic pentylenetetrazol

Rats on a chronic intermittent ethanol (CIE) regimen showed a persistent reduction in seizure threshold to the convulsant drug pentylenetetrazol (PTZ). CIE rats were given ethanol by intubation on an alternate day schedule and tested at selected intervals for seizure threshold with PTZ. A significant reduction in seizure threshold, a sign of withdrawal, was observed 20 hr after the first dose. The severity of withdrawal intensified on repetition of the ethanol administration and depression-hyperexcitability cycle, with the seizure threshold reaching a maximum decrease after 12 doses and remaining reduced up to 60 doses. The reduction in seizure threshold persisted for at least 40 days of no alcohol following the 60th dose. The long-lasting decrease in seizure threshold following CIE treatment resembled the "kindling" phenomenon produced by chronic administration of PTZ (25 mg/kg, 3 times/week). The CIE rats developed, in addition, a tolerance to the anticonvulsant action of ethanol, which occurred well after the decrease in PTZ seizure threshold, and a tolerance to the hypothermic effect of ethanol, which developed rapidly. PTZ kindled rats that had never been exposed to ethanol also exhibited tolerance to the hypothermic effect of ethanol. We propose that kindling contributes to the mechanism of the development of dependence on central nervous system depressants like benzodiazepines, barbiturates, and alcohol, drugs that act on the gamma-aminobutyric acid-A receptor chloride ion channel complex. Repeated episodes of depression and withdrawal hyperexcitability are postulated to produce kindling during the repeated withdrawal episodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated episodes of ethanol withdrawal potentiate the severity of subsequent withdrawal seizures: an animal model of alcohol withdrawal "kindling"

Prior experience with ethanol (EtOH) withdrawal may sensitize an individual to subsequent withdrawal episodes. It has been hypothesized that the progressive intensification of the EtOH withdrawal syndrome following repeated episodes of EtOH intoxication and withdrawal may represent the manifestations of a "kindling" mechanism. The purpose of this study was to develop an animal model of EtOH withdrawal that is sensitive to the effects of prior withdrawal experience. Adult male C3H mice were chronically exposed to EtOH vapor in inhalation chambers prior to withdrawal testing. A multiple withdrawal (MW) group received 3 cycles of 16 hr EtOH vapor separated by 8-hr periods of abstinence; a single withdrawal (SW) group received a single bout of EtOH exposure (16 hr); a third group (SW-CONT) experienced a single withdrawal episode after receiving the equivalent amount of EtOH intoxication as the MW group (16 x 3 = 48 hr), but in a continuous (uninterrupted) fashion; and a fourth group (C) served as controls, not receiving any EtOH exposure throughout the study. Severity of the withdrawal response was assessed by scoring handling-induced convulsions hourly for the first 10 hr and then at 24 hr postwithdrawal. The results indicated that the severity of EtOH withdrawal seizures was significantly greater in animals that had a prior history of withdrawal episodes (MW group) in comparison to a separate group of animals that were tested following a single withdrawal from the same 16-hr intoxication period (SW group).(ABSTRACT TRUNCATED AT 250 WORDS)

Daily dose of ethanol and the development and decay of acute and chronic tolerance and physical dependence in rats

Using behavioral and physiological measures, we compared the rates of development and decay of acute and chronic tolerance to ethanol (ET) and the severity of the withdrawal syndrome. Male rats were treated with 6, 9, or 12 g/kg/day ET or equicaloric dextrin maltose, delivered intragastrically. Although treatment duration varied, the total dose of ET was kept constant at 162 g/kg/rat for the three groups. The effects of a cumulative test dose of ET or equicaloric dextrin maltose, after exposure to a total of 0, 42, 83, 126, and 162 g/kg ET, and at 3, 5, and 7 days after termination of the chronic treatments, were evaluated on rectal temperature, dowel performance, and tail-flick and startle responses. After the initial five tolerance tests, chronic treatments were discontinued and rats were tested in a modified open-field apparatus and for their startle response to an auditory stimulus at 8, 12, 16, 20, 32, and 40 h later. With all measures, little tolerance developed in the 6-g/kg/day group. On the other hand, development of chronic tolerance was fastest in rats treated with the 12-g/kg/dose of ET. Chronic tolerance did not develop to ET's depressant effect on the startle response. Acute tolerance declined with chronicity of treatment in animals given the largest daily dose of ET. During withdrawal, and in contrast to the dextrin maltose-treated animals, there was impairment in all measures taken during the modified open-field test and hypersensitivity of the startle response for all three chronic ET-treated animals. Greatest behavioral impairment occurred in animals treated with 12 g/kg/day, and some impairment was still evident 40 h after the last dose of ET. Thus, the severity of the withdrawal syndrome was greatest in the group displaying the most acute and chronic tolerance.

Tolerance to ethanol's effects on operant performance in rats: role of number and pattern of intoxicated practice opportunities

Acquisition and retention of tolerance to ethanol's rate-decreasing effects on operant performance were examined in rats which received a 52-day regimen of ethanol or saline injections prior to and/or after each daily session. Eight groups of rats differed on: (a) number of days with intoxicated practice (pre-session ethanol); (b) intermittent (spaced) or daily (massed) intoxicated practice; and (c) post-session ethanol or saline on non-intoxicated practice days. Massed practice groups were given their presession saline days prior to their pre-session ethanol days. Ethanol dose-effect tests were given prior to, during, and after the chronic injection regimen. Under both spaced and massed practice conditions, the magnitude of tolerance developed increased directly with the number of pre-session ethanol days, even when absolute ethanol exposure was constant. No group showed complete tolerance loss. The post-session ethanol supplements (a) facilitated tolerance development in spaced practice groups and tolerance loss in massed practice groups, (b) blocked ethanol's low dose rate-increasing effects, and (c) produced an acute withdrawal-like performance disruption the next day. The results suggest that both intoxicated practice and practice during acute ethanol withdrawal influence the acquisition and retention of compensatory behaviors during ethanol tolerance development.