Cycles Of Chronic Ethanol Exposure Research Articles

Lorazepam and MK-801 effects on behavioral and electrographic indices of alcohol withdrawal sensitization

Repeated cycles of chronic ethanol exposure and withdrawal result in sensitization of withdrawal-related CNS hyperexcitability that generally reflects an imbalance in activity of GABA and glutamate systems. Many pharmacological treatments for ethanol withdrawal target neuroadaptive changes in GABA and glutamate neurotransmission. The present study utilized a mouse model of repeated withdrawals to evaluate the ability of lorazepam and MK-801 treatments to antagonize behavioral and electroencephalographic (EEG) measures of sensitized withdrawal seizure activity. Adult male C3H/He mice received chronic intermittent ethanol vapor exposure in inhalation chambers (16 h/day) and during each withdrawal cycle, separate groups of mice were evaluated for handling-induced convulsions (HIC) or abnormal EEG (high-voltage “brief spindle episodes” (BSE)) activity. Lorazepam (0.5–1.0 mg/kg) or MK-801 (0.1–0.3 mg/kg) treatment at 1 h into each of three withdrawal cycles reduced behavioral (HIC) and electrographic (BSE) signs of seizure activity in a dose-related fashion compared to vehicle-treated mice. During a subsequent untreated withdrawal, mice previously treated with lorazepam or MK-801 for earlier withdrawals exhibited reduced HIC activity during the acute phase but exacerbated HIC activity during the protracted phase of this final (fourth) withdrawal cycle. Both lorazepam and MK-801 treatment conditions resulted in enhanced BSE activity during the entire fourth (untreated) withdrawal episode. Collectively, these results suggest that while treatment of repeated ethanol withdrawals with a benzodiazepine (lorazepam) or an NMDA receptor antagonist (MK-801) may have some initial benefits in ameliorating the development of sensitized withdrawal excitability, such treatment may also render subjects more vulnerable to seizure activity at later time points.

Effect of pattern and number of chronic ethanol exposures on subsequent voluntary ethanol intake in C57BL/6J mice

We previously demonstrated that chronic ethanol exposure and withdrawal experience significantly increased subsequent voluntary ethanol intake in C57BL/6J mice. This study was conducted to examine chronic ethanol conditions that optimize this enhanced ethanol-drinking behavior. The purpose of this study was to examine whether the pattern and/or number of chronic ethanol exposures influence subsequent ethanol intake. C57BL/6J mice were trained to drink ethanol (15% v/v) in a limited access situation (2 h/day) until stable intake was achieved. In experiment 1, mice received two cycles of chronic ethanol exposure delivered either in an intermittent [multiple withdrawal (MW)] or continuous [continuous exposure (CE)] pattern. One week of daily drinking sessions followed each exposure. In experiment 2, mice received either two or four cycles of chronic intermittent ethanol exposure (MW), each followed by a week of testing sessions. Three additional weeks of ethanol intake testing followed the last ethanol (or air) exposure. Experiment 1: Only the MW group evidenced a significant increase in ethanol intake compared to controls after the first chronic ethanol exposure. Both MW and CE groups consumed more ethanol than controls after the second ethanol-exposure period. Experiment 2: Ethanol intake in MW mice compared to controls significantly increased after two or four cycles of chronic ethanol exposure/withdrawal, and this heightened ethanol intake lasted longer in mice that received four cycles of chronic intermittent ethanol exposure. Increased voluntary ethanol intake after chronic ethanol exposure and withdrawal experience may be accelerated by intermittent (as opposed to continuous) ethanol exposure, and the effect may last longer with increased number of such experiences.

Increased Ethanol Drinking After Repeated Chronic Ethanol Exposure and Withdrawal Experience in C57BL/6 Mice

The development of dependence may have significant motivational consequences regarding continued use and abuse of ethanol. We have developed a mouse model of ethanol dependence and repeated withdrawals that demonstrates sensitization of seizures and other symptoms of withdrawal. It is unclear whether such experience influences ethanol drinking behavior. The present series of experiments were designed to examine whether repeated cycles of chronic ethanol exposure and withdrawal has an impact on subsequent motivation to voluntarily self-administer ethanol. With the use of a modified sucrose-fading procedure, adult male C57BL/6J mice were trained to drink 15% (v/v) ethanol in a limited access procedure (2 hr/day). The animals were not food or water deprived at any time during the experiments. Once stable baseline intake was established, mice were exposed to four cycles of 16 hr of ethanol vapor (or air) in inhalation chambers separated by 8-hr periods of withdrawal. At 32 hr after the last cycle of ethanol exposure, all mice were tested for ethanol intake under limited access conditions for 5 consecutive days. The animals then received a second series of chronic ethanol exposure and withdrawal followed by another 5-day test period for ethanol drinking. Stable daily baseline intake was established in mice that drank 15% ethanol combined with 5% sucrose (experiment 1), 15% ethanol alone (experiment 2), 5% sucrose alone (experiment 3), or 15% ethanol when presented as a choice with water (experiment 4). After repeated cycles of chronic ethanol exposure and withdrawal experience, consumption of ethanol solutions increased over baseline levels and in comparison with control (air-exposed) groups. However, sucrose consumption did not change in mice that were trained to drink 5% sucrose. The increase in ethanol consumption after chronic ethanol exposure and withdrawal experience resulted in a significant increase in resultant blood ethanol levels. Once the positive reinforcing properties of ethanol were established, chronic ethanol exposure and withdrawal experience resulted in a significant increase in voluntary ethanol drinking that yielded a >2-fold increase in resultant blood ethanol levels. This increase in ethanol intake occurred whether ethanol was presented in combination with sucrose, alone (unadulterated), or as a choice with tap water. Furthermore, this effect seems to be selective for ethanol in that animals that were trained to drink a sucrose solution did not exhibit a change in their intake after similar chronic ethanol exposure. As such, this model may be useful in studying the mechanisms and conditions in which chronic ethanol treatment influences motivation to resume drinking after a period of abstinence (relapse).

Modulation of multiple ethanol withdrawal-induced anxiety-like behavior by CRF and CRF 1 receptors

Previous work demonstrated that rats subjected to multiple withdrawals from chronic ethanol exhibit a sensitization of anxiety-like behavior compared to animals withdrawn from treatment with an equal but continuous amount of ethanol. This study sought to examine whether corticotropin-releasing factor (CRF) could modulate this ethanol-withdrawal-induced anxiety-like behavior. Initially, rats were administered with CRF (1 μg) or vehicle intraventricularly on two occasions 5 days apart while on control diet (CD) followed by exposure to 7% ethanol diet (ED) for 5 days, with social interaction assessed 5 h into withdrawal. Social interaction was significantly reduced in the CRF-treated animals compared to vehicle-treated rats and vehicle- and CRF-treated rats maintained on CD, indicative that CRF given before ethanol exposure was capable of inducing an adaptive change that sensitized withdrawal-induced anxiety-like behavior. Next, the CRF 1 receptor antagonist CRA1000 (3 mg/kg, systemically), the CRF 2 receptor antagonist antisauvagine-30 (20 μg intraventricularly), or vehicle was injected 4 h after the ethanol was removed following the first and second cycles of chronic ethanol exposure and the effect on the multiple-withdrawal-induced anxiety-like behavior determined after the third withdrawal cycle. The CRF 1 receptor antagonist blocked the reduced social interaction behavior, whereas the CRF 2 receptor antagonist was without effect. Similar pretreatment with another CRF 1 receptor antagonist CP-154,526 (10 mg/kg systemically) during the first and second withdrawals also counteracted anxiety-like behavior. These findings indicate that the CRF system and CRF 1 receptors play key roles in the adaptive change responsible for the anxiety-like behavior induced by repeated withdrawals from chronic ethanol.

Repeated ethanol withdrawal produces site-dependent increases in EEG spiking.

Recent studies have suggested an important kindling-like exacerbation of ethanol withdrawal symptoms after repeated cycles of ethanol intoxication and withdrawal. Few studies, however, have evaluated the effect of multiple episodes of intoxication and withdrawal on spontaneous EEG activity after cessation of ethanol intake. In this study, electrographic activity in cortical and subcortical structures male Sprague-Dawley rats was examined after multiple cycles of ethanol intoxication and withdrawal. After surgical implantation of electrodes, animals received repeated cycles of chronic ethanol exposure in vapor inhalation chambers for 10 or 20 days, with 4-day withdrawal periods between each. Upon removal from the inhalation chamber, spontaneous EEG activity was recorded intermittently for 72 hr. These data were then examined for the presence of spikes and sharp waves. Results indicate that the levels of spike and sharp wave activity observed vary with both length of ethanol exposure and with the number of withdrawal cycles, and that these effects varied with neuronal site. Changes in spike and sharp wave activity were first observed within hippocampal areas, with other subcortical and cortical sites showing increased activity after additional ethanol exposure or additional cycles of intoxication and withdrawal. Hippocampal areas CA1 and CA3 differed significantly from one another in their response to chronic ethanol exposure, with area CA1 most affected by changes in amount of ethanol exposure and are CA3 most affected by number of withdrawal cycles. These results indicate an increased severity of the ethanol withdrawal syndrome after repeated ethanol withdrawal episodes and suggest differential, site-specific changes in neuronal excitability.