The modulation of cocaine-induced conditioned place preferences by alcohol: effects of cocaine dose

Ethanol inhibits dopamine uptake via organic cation transporter 3: Implications for ethanol and cocaine co-abuse

Concurrent cocaine and alcohol use is among the most frequent drug combination, and among the most dangerous in terms of deleterious outcomes. Cocaine increases extracellular monoamines by blocking dopamine (DA), norepinephrine (NE) and serotonin (5-HT) transporters (DAT, NET and SERT, respectively). Likewise, ethanol also increases extracellular monoamines, however evidence suggests that ethanol does so independently of DAT, NET and SERT. Organic cation transporter 3 (OCT3) is an emergent key player in the regulation of monoamine signaling. Using a battery of in vitro, in vivo electrochemical, and behavioral approaches, as well as wild-type and constitutive OCT3 knockout mice, we show that ethanol's actions to inhibit monoamine uptake are dependent on OCT3. These findings provide a novel mechanistic basis whereby ethanol enhances the neurochemical and behavioral effects of cocaine and encourage further research into OCT3 as a target for therapeutic intervention in the treatment of ethanol and ethanol/cocaine use disorders.

Ethanol pre-exposure differentially impacts the rewarding and aversive effects of α-pyrrolidinopentiophenone (α-PVP): Implications for drug use and abuse

RATIONALE

Exposure to a drug can subsequently impact its own reactivity as well as that of other drugs. Given that users of synthetic cathinones, i.e., "bath salts", typically have extensive and varied drug histories, an understanding of the effects of drug history on the behavioral and physiological consequences of synthetic cathiones may be important to their abuse liability.

OBJECTIVES

The goal of the current work was to assess the effects of an ethanol pre-exposure on the rewarding and aversive effects of α-PVP.

METHODS

Adult male Sprague Dawley rats were exposed to ethanol prior to combined conditioned taste avoidance/conditioned place preference training in which rats were injected with 1.5, 3 or 5 mg/kg of racemic α-PVP or vehicle. Following a 7-day washout period, rats were then tested for thermoregulatory effects of α-PVP using subcutaneous probes to measure body temperature changes over the course of 8 h. This was followed 10 days later by assessments for α-PVP-induced locomotor activity and stereotypies over a 1-h session.

RESULTS

α-PVP induced significant dose- and trial-dependent taste avoidance that was significantly attenuated by ethanol history and dose- and time-dependent increases in locomotor activity that were significantly increased by ethanol. α-PVP also induced place preferences and dose- and time-dependent increases in body temperature, but these measures were unaffected by ethanol history.

CONCLUSIONS

α-PVP's aversive effects (as measured by taste avoidance) were attenuated, while its rewarding effects (as indexed by place preference conditioning) were unaffected, by ethanol pre-exposure. Such a pattern may indicate increased α-PVP abuse liability, as changes in the balance of aversion and reward may impact overall drug effects and likelihood of drug intake. Future self-administration studies will be necessary to explore this possibility.

Effect of Modulation of the Astrocytic Glutamate Transporters' Expression on Cocaine-Induced Reinstatement in Male P Rats Exposed to Ethanol

AIM

Reinforcing properties of ethanol and cocaine are mediated in part through the glutamatergic system. Extracellular glutamate concentration is strictly maintained through several glutamate transporters, such as glutamate transporter 1 (GLT-1), cystine/glutamate transporter (xCT) and glutamate aspartate transporter (GLAST). Previous findings revealed that cocaine and ethanol exposure downregulated GLT-1 and xCT, and that β-lactam antibiotics restored their expression.

METHODS

In this study, we investigated the effect of ampicillin/sulbactam (AMP/SUL) (200 mg/kg, i.p.), a β-lactam antibiotic, on cocaine-induced reinstatement and locomotor activity in male alcohol preferring (P) rats using free choice ethanol (15 and 30%, v/v) and water. We also investigated the effect of co-exposure to ethanol and cocaine (20 mg/kg, i.p.) on GLT-1, xCT and GLAST expression in the nucleus accumbens (NAc) core, NAc shell and dorsomedial prefrontal cortex (dmPFC).

RESULTS

Cocaine exposure decreased ethanol intake and preference. Cocaine and ethanol co-exposure acquired place preference and increased locomotor activity compared to ethanol-exposed rats. GLT-1 and xCT expression were downregulated after cocaine and ethanol co-exposure in the NAc core and shell, but not in dmPFC. AMP/SUL attenuated reinstatement to cocaine as well attenuated the decrease in locomotor activity and ethanol intake and preference. These effects were associated with upregulation of GLT-1 and xCT expression in the NAc core/shell and dmPFC. GLAST expression was not affected after ethanol and cocaine co-exposure or AMP/SUL treatment.

CONCLUSION

Our findings demonstrate that astrocytic glutamate transporters within the mesocorticolimbic area are critical targets in modulating cocaine-seeking behavior while being consuming ethanol.

Alcohol inhibits morphine/cocaine reward memory acquisition and reconsolidation in rats

RATIONALE AND OBJECTIVE

Alcohol is a recreational substance that is generally socially acceptable and legal in most areas worldwide. An alcohol overdose will produce an inhibitory effect on the brain and impair cognition and memory. In this study, we examined the effect of alcohol on the acquisition, consolidation, and reconsolidation of drug reward memory induced by morphine and cocaine in rats.

METHODS

Rats were trained to acquire morphine sulfate (10 mg/kg, s.c.) and cocaine (10 mg/kg, i.p.) conditioned place preference (CPP) via an unbiased CPP paradigm. Vehicle or alcohol (0.25, 0.75, 1.5 g/kg, i.p.) was administered at various time-points, including 30 min before each CPP conditioning session (acquisition), immediately after each CPP conditioning session (consolidation), immediately after the reactivation of CPP (reconsolidation with re-exposure), or without reactivation to the drug-paired context (reconsolidation without re-exposure). Conditioning scores were recorded before or after each conditioning session or memory reactivation.

RESULTS

Alcohol at a dose of 1.5 g/kg but not 0.25 g/kg or 0.75 g/kg significantly inhibited the acquisition and reconsolidation of morphine- and cocaine-associated memory. In contrast, alcohol had no effect on the consolidation of morphine- or cocaine-induced CPP.

CONCLUSIONS

The results suggested that pre-exposure alcohol dose-dependently attenuated morphine- or cocaine-induced place preference and prevented drug reinstatement in rats by disrupting memory reconsolidation, which may be explained by the inhibitory effect of alcohol on dopaminergic and glutamatergic neurotransmission.

Alcohol Interaction with Cocaine, Methamphetamine, Opioids, Nicotine, Cannabis, and γ-Hydroxybutyric Acid

Millions of people around the world drink alcoholic beverages to cope with the stress of modern lifestyle. Although moderate alcohol drinking may have some relaxing and euphoric effects, uncontrolled drinking exacerbates the problems associated with alcohol abuse that are exploding in quantity and intensity in the United States and around the world. Recently, mixing of alcohol with other drugs of abuse (such as opioids, cocaine, methamphetamine, nicotine, cannabis, and γ-hydroxybutyric acid) and medications has become an emerging trend, exacerbating the public health concerns. Mixing of alcohol with other drugs may additively or synergistically augment the seriousness of the adverse effects such as the withdrawal symptoms, cardiovascular disorders, liver damage, reproductive abnormalities, and behavioral abnormalities. Despite the seriousness of the situation, possible mechanisms underlying the interactions is not yet understood. This has been one of the key hindrances in developing effective treatments. Therefore, the aim of this article is to review the consequences of alcohol's interaction with other drugs and decipher the underlying mechanisms.

The combination of MDPV and ethanol results in decreased cathinone and increased alcohol levels. Study of such pharmacological interaction

Methylenedioxypyrovalerone (MDPV) is a new psychostimulant cathinone acting as a selective dopamine transporter blocker. Due to the concomitant consumption of ethanol (EtOH) and new psychoactive substances, it is of interest to explore a possible pharmacological interaction between MDPV and EtOH. In locomotor activity assays, EtOH (1g/kg i.p.) elicited a reduction in the stimulant effect induced by low doses of MDPV (0.1-0.3mg/kg, s.c.) in rats, jointly with a decrease in blood and brain MDPV concentrations. Experiments in rat liver microsomes showed different effects depending on the [MDPV]/[EtOH] relationship, evidencing, at certain concentrations, the enhancing effect of EtOH on MDPV metabolism. These suggest that EtOH interacts with MDPV at microsomal level, increasing its metabolic rate. The interaction between both substances was also supported by results in plasma EtOH concentration, which were significantly increased by MDPV, in such a manner that EtOH elimination rate was significantly reduced. The possible toxicological impact of this phenomenon deserves further investigation. In contrast, the rewarding properties of MDPV were unaltered by EtOH. Microdialysis experiments verified that, in the NAcc, both substances could also act synergistically, in such a manner that extracellular dopamine concentrations are maintained. Finally, if the psychostimulant effect induced by MDPV decreased with EtOH, it could favor the boosting and re-dosing in search of the desired effects. However, as the rewarding effect of each dose of the substance would not decrease, the addictive liability could increase considerably. Moreover, we must warn about the increase in EtOH concentrations when consumed concomitantly with MDPV.

Alcohol Interactions with Psychostimulants: An Overview of Animal and Human Studies

Alcohol consumption with psychostimulants is very common among drug addicts. There is little known about the possible pharmacological interactions between alcohol and psychostimulants. Among most commonly co-abused psychostimulants with alcohol are methamphetamine, cocaine, 3,4-methylenedioxymethamphetaminen, and nicotine. Co-abuse of alcohol with psychostimulants can lead to several neurophysiological dysfunctions such as decrease in brain antioxidant enzymes, disruption of learning and memory processes, cerebral hypo-perfusion, neurotransmitters depletion as well as potentiation of drug seeking behaviour. Moreover, co-abuse of alcohol and psychostimulants can lead to increase in heart rate, blood pressure, myocardial oxygen consumption and cellular stress, and the risk of developing different types of cancer. Co-abuse of alcohol with psychostimulants during pregnancy can lead to fetal brain abnormalities. Further studies are needed to investigate the pharmacokinetics, pharmacodynamics, and neurochemical changes on co-abuse of alcohol and psychostimulants.

Ethanol and cocaine: environmental place conditioning, stereotypy, and synergism in planarians

More than 90% of individuals who use cocaine also report concurrent ethanol use, but only a few studies, all conducted with vertebrates, have investigated pharmacodynamic interactions between ethanol and cocaine. Planaria, a type of flatworm often considered to have the simplest 'brain,' is an invertebrate species especially amenable to the quantification of drug-induced behavioral responses and identification of conserved responses. Here, we investigated stereotypical and environmental place conditioning (EPC) effects of ethanol administered alone and in combination with cocaine. Planarians displayed concentration-related increases in C-shaped movements following exposure to ethanol (0.01-1%) (maximal effect: 9.9±1.1 C-shapes/5 min at 0.5%) or cocaine (0.1-5 mM) (maximal effect: 42.8±4.1 C-shapes/5 min at 5 mM). For combined administration, cocaine (0.1-5 mM) was tested with submaximal ethanol concentrations (0.01, 0.1%); the observed effect for the combination was enhanced compared to its predicted effect, indicating synergism for the interaction. The synergy with ethanol was specific for cocaine, as related experiments revealed that combinations of ethanol and nicotine did not result in synergy. For EPC experiments, ethanol (0.0001-1%) concentration-dependently increased EPC, with significant environmental shifts detected at 0.01 and 1%. Cocaine (0.001-1 μM) produced an inverted U-shaped concentration-effect curve, with a significant environmental shift observed at 0.01 μM. For combined exposure, variable cocaine concentrations (0.001-1 μM) were administered with a statistically ineffective concentration of ethanol (0.0001%). For each concentration of cocaine, the environmental shift was enhanced by ethanol, with significance detected at 1 μM. Cocaethylene, a metabolite of cocaine and ethanol, also produced C-shapes and EPC. Lidocaine (0.001-10 μM), an anesthetic and analog of cocaine, did not produce EPC or C-shaped movements. Evidence from planarians that ethanol produces place-conditioning effects and motor dysfunction, and interacts synergistically with cocaine, suggests that aspects of ethanol neuropharmacology are conserved across species.

Evidence for conditioned place preference to a moderate dose of ethanol in adult male Sprague-Dawley rats

The present series of experiments examined affective properties of a moderate dose of ethanol using the conditioned place preference (CPP) paradigm in ethanol-naïve, adult male Sprague-Dawley rats. The apparatus and the procedure used were both unbiased. In Experiment 1, rats were given four 30 min conditioning sessions with 1.5 g/kg ethanol (i.p.) or an equivalent volume of saline on the paired side. Animals were found to demonstrate CPP to the ethanol-paired side, an unexpected finding at this relatively high dose in rats. To replicate this finding, and to examine the possibility of non-associative conditioning, an unpaired control group was included in Experiment 2. Once again, rats showed a CPP to the side paired with ethanol relative to either control group. Given that testing in an unfamiliar environment typically results in elevated levels of anxiety and that animals in Experiments 1 and 2 were not exposed to the apparatus prior to conditioning, Experiment 3 was conducted to examine the potential role of context unfamiliarity for induction of ethanol CPP in this test situation by varying whether animals were exposed to the apparatus prior to conditioning. In this study, pre-exposure to the CPP apparatus was found to eliminate the CPP to ethanol observed in rats who were not familiarized with the apparatus. Collectively, these studies demonstrate that ethanol-naïve rats can find ethanol reinforcing as indexed by the CPP test, and provide some evidence for the conditions under which this uncommon finding is observed.

Previous ethanol experience enhances synaptic plasticity of NMDA receptors in the ventral tegmental area

Alcohol addiction (alcoholism) is one of the most prevalent substance abuse disorders worldwide. Addiction is thought to arise, in part, from a maladaptive learning process in which enduring memories of drug experiences are formed. However, alcohol (ethanol) generally interferes with synaptic plasticity mechanisms in the CNS and thus impairs various types of learning and memory. Therefore, it is unclear how powerful memories associated with alcohol experience are formed during the development of alcoholism. Here, using brain slice electrophysiology in mice, we show that repeated in vivo ethanol exposure (2 g/kg, i.p., three times daily for 7 d) causes increased susceptibility to the induction of long-term potentiation (LTP) of NMDA receptor (NMDAR)-mediated transmission in mesolimbic dopamine neurons, a form of synaptic plasticity that may drive the learning of stimuli associated with rewards, including drugs of abuse. Enhancement of NMDAR plasticity results from an increase in the potency of inositol 1,4,5-trisphosphate (IP(3)) in producing facilitation of action potential-evoked Ca(2+) signals, which is critical for LTP induction. This increase in IP(3) effect, which lasts for a week but not a month after ethanol withdrawal, occurs through a protein kinase A (PKA)-dependent mechanism. Corticotropin-releasing factor, a stress-related neuropeptide implicated in alcoholism and other addictions, further amplifies the PKA-mediated increase in IP(3) effect in ethanol-treated mice. Finally, we found that ethanol-treated mice display enhanced place conditioning induced by the psychostimulant cocaine. These data suggest that repeated ethanol experience may promote the formation of drug-associated memories by enhancing synaptic plasticity of NMDARs in dopamine neurons.

Teratogenic effects of maternal antidepressant exposure on neural substrates of drug-seeking behavior in offspring

If neurotransmitter balance is upset in the developing nervous system by exposure to antidepressant drugs, structural and functional hedonic phenotypes of offspring may be affected. In order to test this hypothesis, two groups of pregnant Wistar dams were exposed to vehicle or fluoxetine by implantation on gestational day 14 of osmotic minipumps delivering 0 or 10 mg/kg/day fluoxetine for 14 days. The consequences of perinatal fluoxetine exposure on offspring conflict-exploratory behavior were quantified using the elevated plus-maze on postnatal day (PND) 30. Beginning on PND 60, the reinforcing properties of acutely administered cocaine were examined using a place conditioning procedure. Beginning on PND 90, a subset of rats were implanted with jugular catheters and allowed to acquire self-administration of cocaine in an operant environment. In support of the hedonic modulation hypothesis, perinatal fluoxetine produced a significant decline in both nucleus accumbens cell count (-9%) and serotonin transporter-like immunoreactivity in the raphe nucleus (-35%) on PND 120. In the elevated plus-maze, perinatal fluoxetine exposure decreased (-21%) overall activity. In the place conditioning trial, only the fluoxetine-treated group exhibited a significant place preference for the compartment paired previously with cocaine. In a cocaine self-administration extinction trial, there was a statistically significant increase (350%) in extinction response rate among fluoxetine-exposed offspring. These findings suggest that perinatal exposure to fluoxetine perturbs adult serotonergic neurotransmission and produces a positive hedonic shift for conditioned reinforcing effects of cocaine.

Schedule-induced polydipsia alters cocaine- but not ethanol-induced suppression of saccharin consumption

Under traditional water-deprived conditions, both LiCl and morphine produce comparable suppression of saccharin consumption after repeated pairings. However, under conditions of spaced food deliveries (i.e., schedule-induced polydipsia; SIP), morphine produces a significantly weaker suppression than LiCl. The differential responses have been attributed to an increase in the rewarding effects of drugs of abuse (such as morphine) that masked the expression of the aversive effects, a masking not evident with LiCl which has no reported rewarding effects. The present study extended this characterization to two additional drugs of abuse; cocaine and ethanol. Following schedule-induced saccharin consumption, female Sprague-Dawley rats were given injections of LiCl, cocaine, ethanol (at doses comparably effective in conditioning taste aversions under water deprivation) or distilled water vehicle. Although cocaine and ethanol both suppressed SIP, only cocaine produced a significantly delayed suppression relative to LiCl. The differential effects of cocaine (and morphine), but not ethanol, may be a function of the different reward profiles of these drugs. Given the differential ability of drugs of abuse to suppress consumption under conditions of spaced feedings, the SIP procedure may be a useful baseline to assess the rewarding effects of such drugs. Further, given the differential results with cocaine and ethanol, the relative rewarding effects of drugs may be differentially indexed in this preparation, as well.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Hallucinatory and rewarding effect of salvinorin A in zebrafish: kappa-opioid and CB1-cannabinoid receptor involvement

RATIONALE

The hallucinatory effect and potential abuse of salvinorin A, the major ingredient of Salvia divinorum, has not been documented in animals.

OBJECTIVE

The effects of salvinorin A on the zebrafish (Danio rerio) model, through its swimming behavior and conditioned place preference (CPP) task, was studied.

MATERIALS AND METHODS

Swimming activity was determined in a squared observational chamber after an i.m. treatment of salvinorin A (0.1-10 microg/kg). For the CPP test, zebrafish were given salvinorin A (0.2 and 1 microg/kg) or vehicle and evaluated in a two-compartment chamber.

RESULTS

Salvinorin A (0.1 and 0.2 microg/kg) induced accelerated swimming behavior in comparison with vehicle, whereas a "trance-like" effect, at doses as 5 and 10 microg/kg, was obtained. Pretreatment with the kappa-opioid antagonist, nor-binaltorphimine (nor-BNI; 10 mg/kg) and the cannabinoid type 1 (CB(1)) antagonist, rimonabant (1 mg/kg), blocked salvinorin A-induced both stimulating and depressive effects obtained at a dose of 0.2 and 10 microg/kg, respectively. In the CPP test, salvinorin A (0.2 and 0.5 microg/kg) produced an increase in the time spent in the drug-associated compartment. A dose of 1 microg/kg produced no effect, whereas a dose of 80 microg/kg induced aversion. Pretreatment with nor-BNI or rimonabant fully reversed the reinforcing properties of salvinorin A (0.5 microg/kg).

CONCLUSIONS

Taken together, these results indicate that salvinorin A, as is sometimes reported in humans, exhibits rewarding effects, independently from its motor activity, suggesting the usefulness of the zebrafish model to study addictive behavior. These effects appear mediated by activation of both kappa-opioid and cannabinoid CB(1) receptors.

Effects of ethanol on nicotine-induced conditioned place preference in C57BL/6J mice

It has been shown that small doses of ethanol (<or= 1.0 g/kg) may antagonize the discriminative stimulus properties of nicotine. The aim of the present study was to evaluate whether ethanol could antagonize nicotine's rewarding effects in the conditioned place preference procedure. For comparison, effects of ethanol on nicotine-induced seizures were assessed. Male C57BL/6J mice were used in all experiments. Lower doses of nicotine (0.3 and 0.6 mg/kg, s.c.) induced significant conditioned place preference, while higher doses (0.9 and 1.2 mg/kg) induced neither conditioned place preference nor conditioned place aversion. In the following experiments, ethanol (0.5 or 1.0 g/kg, i.p.) was administered 5 min before 0.3 mg/kg nicotine. Ethanol did not antagonize nicotine-induced conditioned place preference. Contrary to our hypothesis, a non-significant (p = 0.07) enhancement of nicotine-induced place preference conditioning was observed in mice pre-treated with 1.0 g/kg ethanol. Both doses of ethanol (0.5 and 1.0 g/kg) suppressed seizures elicited by a high dose of nicotine (6.0 mg/kg). Ethanol totally eliminated clonic-tonic component of nicotine-induced seizures. Maximal blood ethanol levels after i.p. administration of 0.5 or 1.0 g/kg ethanol exceeded 60 and 115 mg%, respectively. The present results may indicate that the rewarding and seizure-inducing effects of nicotine are differentially modulated by clinically relevant concentrations of ethanol in mice.

Concurrent use and order of use of cocaine and alcohol: behavioural differences between users of crack cocaine and cocaine powder

AIMS

The study investigates patterns of cocaine use and alcohol use when these substances were taken on their own, the order of administration of alcohol and of cocaine when the two substances were taken together, and changes in the doses of alcohol and of cocaine when the two substances were taken together. The study further investigates differences in the combined use of the two substances by users of cocaine powder and crack cocaine.

DESIGN

Entry criteria for the study were current (previous 30 days) use of both alcohol and cocaine. Study participants (n = 102) were recruited from clinical and non-clinical settings. Data were collected by face-to-face structured interviews.

FINDINGS

Different patterns of combined cocaine and alcohol use were reported by cocaine powder and crack cocaine users. Cocaine powder users tended to take increased doses of both cocaine and alcohol when these were used in combination. During high-dose crack using episodes, crack users tended to drink lower amounts of alcohol than usual. Cocaine powder users tended to use cocaine and alcohol concurrently. Crack users tended to use alcohol at the end of crack-using sessions.

CONCLUSIONS

The observed differences are not understood clearly but may be influenced by differential effects of route of administration upon absorption, bioavailability and the balance of euphoric/dysphoric effects. Research studies of the combined use of cocaine and alcohol should distinguish explicitly between the use of cocaine by different routes of administration, and this should be specified in the description of subject samples.

The effects of cocaine, alcohol and cocaine/alcohol combinations in conditioned taste aversion learning

We have recently reported that alcohol attenuates cocaine place preferences. Although the basis for this effect is unknown, alcohol may attenuate cocaine reward by potentiating its aversive effects. To examine this possibility, these experiments assessed the effects of alcohol on cocaine-induced taste aversions under conditions similar to those that resulted in attenuated place preferences. Specifically, Experiments 1 and 2 assessed the effects of alcohol (0.5 g/kg) on taste aversions induced by 20, 30 and 40 mg/kg cocaine. Experiment 3 examined the role of intertrial interval in the effects of alcohol (0.5 g/kg) on cocaine (30 mg/kg) taste aversions. In Experiments 1 and 2, cocaine was effective at conditioning aversions. Alcohol produced no measurable effect. Combining cocaine and alcohol produced no greater aversion than cocaine alone (and, in fact, weakened aversions at the lowest dose of cocaine). In Experiment 3, varying the intertrial interval from 3 days (as in the case of Experiments 1 and 2) to 1 day (a procedure identical to that in which alcohol attenuated cocaine place preferences) resulted in significant alcohol- and cocaine-induced taste aversions. Nonetheless, alcohol remained ineffective in potentiating cocaine aversions. Thus, under these conditions alcohol does not potentiate cocaine's aversiveness. These results were discussed in terms of their implication for the effects of alcohol on cocaine-induced place preferences. Further, the effects of alcohol on place preferences conditioned by cocaine were discussed in relation to other assessments of the effects of alcohol on the affective properties of cocaine and the implications of these interactions for alcohol and cocaine co-use.

Perinatal protein malnutrition enhances rewarding cocaine properties in adult rats

The rewarding properties of cocaine were assessed in adult rats submitted to a protein malnutrition schedule from the 14th day of gestation up to 40 days of age (deprived rats), as compared with well-nourished animals (control rats) using the conditioned place preference paradigm. Dose-response curves to cocaine (3, 5, 10, 15, 30, 45 or 60 mg/kg i.p.) revealed in deprived rats a conditioning effect with doses of 5 and 10mg/kg; doses of 15 and 30 mg/kg did not show any conditioning place preference and doses of 45 and 60 mg/kg revealed a significant aversive effect. In control rats, cocaine elicited place preference with doses of 10, 15 and 30 mg/kg, whereas 45 and 60 mg/kg did not show either conditioning or aversive effects. Furthermore, sensitization to the conditioning effect of cocaine was obtained in deprived animals with a low dosage of cocaine, that was ineffective in controls (5 mg/kg/day for 10 days). Related to the higher rewarding effects, sensitized deprived rats showed a selective and significant increase in FosB expression in nucleus accumbens (core and shell) and basolateral amygdala, brain areas related to the rewarding neuronal circuits. These results suggest that a deficient nutritional status during early life may induce in adult subjects an increased responsiveness to behavioral effects of cocaine and/or enhanced its reinforcement properties.

Cocaine-induced conditioned taste avoidance over extended conditioned stimulus–unconditioned stimulus intervals

Although long-delay learning has been demonstrated numerous times in the conditioned taste avoidance procedure, the empirical evidence showing this is almost exclusively limited to studies using emetics. Given that compounds outside the emetic class (e.g. drugs of abuse) are also effective in inducing conditioned taste avoidances, the present study assessed the ability of cocaine, a non-emetic psychoactive compound, to support long-delay conditioning as the unconditioned stimulus in conditioned taste avoidance preparation. Using saccharin as the conditioned stimulus, two taste-drug pairings were followed by six extinction trials during which saccharin was presented without subsequent injections of cocaine. During the two conditioning trials, animals were injected subcutaneously with cocaine (32 mg/kg) at different conditioned stimulus-unconditioned stimulus intervals, that is, 10, 60, 120, 180, 240, 300, 420 and 540 min. A control group of animals was given an equi-volume injection of the drug vehicle at the 10-min conditioned stimulus-unconditioned stimulus interval. After two conditioning trials, all treatment groups consumed significantly less saccharin than controls, with the magnitude of the effect decreasing as the conditioned stimulus-unconditioned stimulus interval increased. After six extinction trials, animals injected with cocaine at 10, 60 and 120 min conditioned stimulus-unconditioned stimulus intervals still consumed significantly less than controls. These results with cocaine suggest that taste avoidance learning over long delays is not limited to classical emetic compounds and may, in fact, be characteristic of taste avoidance learning in general.

Cocaine, but not alcohol, reinstates cocaine-induced place preferences

Alcohol has been reported to modulate the reinforcing and aversive properties of cocaine. Given these effects, the present study examined whether this interaction could be extended to cocaine seeking using the conditioned place preference (CPP) procedure. Specifically, 31 drug-naive, male Sprague-Dawley rats were injected every other day (for 8 days) with either 20 mg/kg cocaine or vehicle in an alternating sequence prior to being restricted to a drug or vehicle side of a place preference chamber for 30 min. On Day 9, subjects were given 15-min access to the entire chamber to assess compartment preference. Animals then underwent extinction by pairing both compartments with vehicle for an additional 8 days. Extinction was assessed in the same manner as place conditioning. The animals were then given priming injections of vehicle, 15 mg/kg cocaine, 0.5 or 1.0 g/kg alcohol on the day following the extinction test. Pairing 20 mg/kg cocaine with a specific compartment resulted in a significant place preference. Breaking the relation between the compartment and the drug by pairing both compartments with vehicle extinguished this preference. Interestingly, only 15 mg/kg cocaine was able to reinstate the cocaine-induced place preference, suggesting that the ability to reinstate cocaine seeking may be drug specific.