Przemyslaw Bienkowski

Ethanol-reinforced behaviour in the rat: effects of naltrexone

It has been repeatedly reported that endogenous opioid pathways play an important role in ethanol drinking behaviour. In line with these findings, a non-selective opioid receptor antagonist, naltrexone, seems to reduce relapse rates in detoxified alcoholics. The aim of the present study was to evaluate the effects of naltrexone on (i) ethanol self-administration; (ii) extinction of responding for ethanol; (iii) reinstatement of ethanol-seeking induced by non-contingent presentations of ethanol-associated stimuli. Male Wistar rats were trained to lever-press for 8% ethanol in an operant procedure where ethanol was introduced in the presence of sucrose. The selectivity of naltrexones actions was assessed by studying its effects on water-reinforced behaviour in separate control experiments. Acute injections of naltrexone (1 or 3 mg/kg) did not alter ethanol self-administration. Repeated treatment with naltrexone (3 mg/kg, before three consecutive self-administration sessions) progressively reduced ethanol intake. In the extinction procedure, acute administration of 3 mg/kg naltrexone suppressed responding previously reinforced with ethanol. Similarly, naltrexone (1-3 mg/kg) potently and dose-dependently inhibited reinstatement of ethanol-seeking produced by non-contingent deliveries of the liquid dipper filled with 8% ethanol. In the control experiments, lower doses of naltrexone (1-3 mg/kg) did not exert any effect on either reinforced or non-reinforced (extinction) lever-pressing for water. These results indicate that: (i) subchronic treatment with naltrexone leads to progressive reduction of ethanol self-administration; (ii) single doses of naltrexone may increase extinction and attenuate cue-induced reinstatement of ethanol-reinforced behaviour.

Bitter and sweet components of ethanol taste in humans

This study examined taste descriptions elicited by ethanol and by other tastants in humans. All subjects described 10% ethanol as bitter and approximately 30% of the subjects described it as sweet and/or sour. Highly significant correlations were found between sweetness of some sucrose solutions (0.6-1%) and intensity of the taste of ethanol. In another experiment, quinine (bitter) solutions were rated as similar to 10% ethanol taste and this effect was potentiated by the addition of sucrose. In contrast, citric acid (sour) tended to decrease similarity ratings when added to the quinine solutions. Taken together, these findings suggest that: (1) in humans ethanol tastes both bitter and sweet; and (2) the relationship between sucrose and ethanol intakes previously found in animals and humans may result, at least partially, from similar taste responses elicited by sucrose and ethanol.

Time-dependent changes in alcohol-seeking behaviour during abstinence

Exposure of alcohol addicts to alcohol-related environmental cues may elicit alcohol-seeking behaviour even after protracted abstinence. The purpose of the present study was to assess time-dependent changes in alcohol-seeking behaviour in rats trained to respond for alcohol. The rats were re-exposed to alcohol-associated stimuli after 1, 28 or 56 days of withdrawal. During the re-exposure session, the rats were first allowed to respond in extinction. Then, reinstatement of alcohol-seeking behaviour was evoked by a complex of discrete alcohol-associated cues (auditory and light cues combined with taste and smell of alcohol). Extinction behaviour depended on abstinence duration with maximal responding after 28-day abstinence. Reinstatement of alcohol-seeking behaviour evoked by the discrete cues was highest after 56-day abstinence. No correlations were found between individual alcohol intakes, extinction behaviour and cue-induced reinstatement. These results suggest that: (i) alcohol-seeking behaviour may become more intense after long-term imposed abstinence; (ii) alcohol self-administration, extinction behaviour, and reinstatement of alcohol-seeking behaviour may be regulated by separate neural mechanisms.

GABAB receptors as a therapeutic strategy in substance use disorders: Focus on positive allosteric modulators

γ-Aminobutyric acid B (GABAB) receptors and their ligands are postulated as potential therapeutic targets for the treatment of several brain disorders, including drug dependence. Over the past fifteen years positive allosteric modulators (PAMs) have emerged that enhance the effects of GABA at GABAB receptors and which may have therapeutic effects similar to those of agonists but with superior side-effect profiles. This review summarizes current preclinical evidence supporting a role of GABAB receptor PAMs in drug addiction in several paradigms with relevance to reward processes and drug abuse liability. Extensive behavioral research in recent years has indicated that PAMs of GABAB receptors may have a therapeutic efficacy in cocaine, nicotine, amphetamine and alcohol dependence. The magnitude of the effects observed are similar to that of the clinically approved drug baclofen, an agonist at GABAB receptors. Moreover, given that anxiolytic effects are also reported with such ligands they may also benefit in mitigating the withdrawal from drugs of abuse. In summary, a wealth of data now supports the benefits of GABAB receptor PAMs and clinical validation is now warranted.

Alcohol Relapse Induced by Discrete Cues Activates Components of AP-1 Transcription Factor and ERK Pathway in the Rat Basolateral and Central Amygdala

Alcohol-related cues may induce relapse to heavy alcohol drinking and promote molecular adaptations in discrete brain regions. An exact nature of these molecular alterations is still unknown. In the present study, rats trained to self-administer ethanol were tested for cue-induced reinstatement of ethanol seeking after 30 days of abstinence. Next, a detailed immunocytochemical analysis of c-Fos activation was performed within seven nuclei of the amygdala. In the second experiment, c-Fos activation after reinstatement of ethanol seeking induced by discrete cues was compared with the activation pattern of its putative partner (c-Jun) and regulators (extracellular signal-regulated kinases and c-Jun N-terminal kinases). Reexposure to ethanol-associated context cues (an extinction session) potentiated c-Fos expression within the basolateral and central amygdala. Repeated presentation of ethanol-associated discrete cues in an extinction/reinstatement session led to even stronger c-Fos activation in the latter nuclei. In the second experiment, reexposure to the ethanol-associated context and discrete cues activated both c-Jun and extracellular signal-regulated kinases (ERK1/2) in the basolateral amygdala. Our observations suggest that the basolateral and central amygdala may be specifically involved in alcohol-seeking behavior induced by discrete cues.

Ethanol-reinforced behaviour in the rat: effects of uncompetitive NMDA receptor antagonist, memantine

Ethanol has been reported to alter NMDA receptor-mediated biochemical and electrophysiological responses in vitro. The aim of the present study was to evaluate the effects of an uncompetitive NMDA receptor antagonist memantine, in animal models of alcoholism. Male Wistar rats were trained to drink 8% ethanol in a free-choice, limited access procedure. A separate group of animals was trained to lever press for 8% ethanol in an operant procedure where ethanol was introduced in the presence of sucrose. The selectivity of memantines actions was assessed by studying its effects on food or water consumption in separate control experiments. Memantine (4.5-24 mg/kg) significantly, but not dose dependently, affected ethanol drinking in the limited access procedure. However, only 6 mg/kg memantine selectively decreased ethanol drinking. Memantine did not alter ethanol intake in rats trained to lever press for ethanol in the operant procedure. Only 9 mg/kg memantine reduced operant responding in the extinction procedure in the rats trained to lever press for ethanol. The same dose of memantine significantly reduced the operant behaviour of rats trained to respond for water. These results indicate that: (i) single doses of memantine only moderately and not dose dependently reduce alcohol drinking in the limited access procedure; (ii) memantine produces non-selective effects on operant behaviour in rats trained to lever press for ethanol in an oral self-administration procedure.

Effects of a novel uncompetitive NMDA receptor antagonist, MRZ 2/579 on ethanol self-administration and ethanol withdrawal seizures in the rat

It has been repeatedly reported that NMDA receptors may contribute to ethanol-induced discriminative stimulus effects and withdrawal syndrome. However, the role of NMDA receptors in the reinforcing properties of ethanol remains unclear. The aim of the present study was to evaluate effects of the novel low-affinity, uncompetitive NMDA receptor antagonist, 1-amino-1,3,3,5,5-pentamethyl-cyclohexane hydrochloride (MRZ 2/579), on ethanol self-administration and ethanol withdrawal-associated seizures in rats. Both an operant (lever pressing for ethanol) and non-operant two-bottle choice setups were employed to initiate ethanol self-administration. In another procedure, forced treatment with high doses (9--15 g/kg/day) was used to induce physical dependence on ethanol. MRZ 2/579 delivered chronically by osmotic minipumps (9.6 mg/day, s.c.) did not alter either operant or non-operant ethanol drinking behaviour in a maintenance phase of ethanol self-administration. In contrast, repeated daily injections of the drug (5 mg/kg, i.p.) led to a progressive decrease in operant responding for ethanol. MRZ 2/579 (0.5--7.5 mg/kg, i.p.) and another low-affinity NMDA receptor antagonist, memantine (1--10 mg/kg, i.p.) dose-dependently suppressed ethanol withdrawal seizures with efficacies comparable with that of a standard benzodiazepine derivative, diazepam. The results of the present study indicate that: (i) intermittent administration of MRZ 2/579 may lead to a gradual decrease of operant responding for ethanol; and (ii) the group of low-affinity uncompetitive NMDA receptor antagonists may be an interesting alternative to benzodiazepines in the treatment of alcohol withdrawal.

Reinstatement of ethanol seeking in rats: behavioral analysis.

The reinstatement model has been repeatedly used to study relapse to heroin- or cocaine-seeking behaviour in rats. The aim of the present study was to evaluate basic behavioral parameters of cue-induced reinstatement of ethanol seeking in a within-session paradigm. Rats were trained to respond for ethanol in an oral self-administration procedure where each lever press resulted in presentation of 0.1 ml of 8% ethanol from a liquid dipper. In the reinstatement paradigm operant behaviour was first extinguished for 20 or 60 min by switching the dipper off. Then, ethanol-associated stimuli were noncontingently delivered and reinstatement of responding was assessed. Deliveries of the empty dipper, i.e., visual/auditory cues only, did not result in any reinstatement. In contrast, 15 random presentations of the dipper containing either ethanol (4-8%; v/v) or water significantly reinstated ethanol seeking. In a control self-administration experiment responding dropped to nonsignificant levels when water was substituted for ethanol. The magnitude of reinstatement did not depend on the duration of the extinction phase. These results seem to indicate that in the present paradigm reinstatement of ethanol seeking is driven by a compound stimulus including the visual/auditory cues and some nonspecific sensory properties of liquid available in the dipper.

Functional polymorphism of matrix metalloproteinase-9 (MMP-9) gene in alcohol dependence: Family and case control study

AIM Matrix metalloproteinases (MMP) are extracellularly acting endopeptidases, whose substrates are extracellular matrix and adhesion proteins. In the gene polymorphism studies MMP-9 has been suggested to be involved in the pathogenesis of heart disease, cancer, bipolar disorder, and schizophrenia. In animal models MMP-9 has been shown to play a key role in a variety of neuronal plasticity phenomena, including learning and memory as well as drug addiction. METHOD We studied 139 families, Caucasians, with no history of psychiatric disorder of ICD-10 other than alcohol or nicotine dependence. The control subjects were 136 unrelated individuals, matched for ethnicity and gender, with no mental disorder. Alcohol and family history of alcoholism were assessed by means of a structured interview, based on the Polish version of SSAGA (Semi-Structured Assessment on Genetics in Alcoholism). RESULTS We found a statistically significant preferential transmission of the T allele (known to produce higher gene transcriptional activity) from parents to alcoholics (59%, p=0.046). In a case-control study genotype TT and T alleles were significantly more frequent in the alcoholics than in the controls (OR=2.6). CONCLUSION Our results suggest that the MMP-9 gene may play a role in the pathogenesis of alcohol dependence.

Depressive symptoms and taste reactivity in humans.

Animal studies suggest that induction of depression-like states may alter preference for sweet tastants. A major goal of the present study was to search for correlations between depressive symptoms measured by the Beck Depression Inventory (BDI) and taste responses to sweet and bitter substances. Thirty-three nonclinical volunteers rated intensity and pleasantness of chocolate and vanilla milk as well as of sucrose- and quinine-soaked filter paper disks. Reactivity to citric acid (sour) and sodium chloride (salty) was also tested with the paper disk methodology. Taste detection thresholds were assessed by means of electrogustometry. A weak inverse relationship was found between the BDI scores (range: 3-33) and rated intensity of paper disks soaked in 60% sucrose. No correlations were found between depressive symptoms and intensity, pleasantness or identification of the other samples. Similarly, there was no relationship between the BDI scores and responses to chocolate and vanilla milk. BDI scores were not associated with electrogustometric thresholds. These data suggest that depressive symptoms may not influence taste reactivity in nonclinical population.