Behavioral and neurochemical changes caused by repeated ethanol and cocaine administration

Liquiritigenin decreases selective molecular and behavioral effects of cocaine in rodents

Cocaine, as an indirect dopamine agonist, induces selective behavioral and physiological events such as hyperlocomotion and dopamine release. These changes are considered as consequences of cocaine-induced molecular adaptation such as CREB and c-Fos. Recently, methanolic extracts from licorice was reported to decrease cocaine-induced dopamine release and c-Fos expression in the nucleus accumbens. In the present study, we investigated the effects of liquiritigenin (LQ), a main compound of licorice, on acute cocaine-induced behavioral and molecular changes in rats. LQ attenuated acute cocaine-induced hyperlocomotion in dose-dependent manner. In addition, LQ inhibited CREB phosphorylation and c-Fos expression in the striatum and the nucleus accumbens induced by acute cocaine. Results provide strong evidence that LQ effectively attenuates the acute behavioral effects of cocaine exposure and prevents the induction of selective neuroadaptive changes in dopaminergic signaling pathways. Further investigation of LQ from licorice extract might provide a novel therapeutic strategy for the treatment of cocaine addiction.

Behavioral characteristics and neurobiological substrates shared by Pavlovian sign-tracking and drug abuse

Drug abuse researchers have noted striking similarities between behaviors elicited by Pavlovian sign-tracking procedures and prominent symptoms of drug abuse. In Pavlovian sign-tracking procedures, repeated paired presentations of a small object (conditioned stimulus, CS) with a reward (unconditioned stimulus, US) elicits a conditioned response (CR) that typically consists of approaching the CS, contacting the CS, and expressing consummatory responses at the CS. Sign-tracking CR performance is poorly controlled and exhibits spontaneous recovery and long-term retention, effects that resemble relapse. Sign-tracking resembles psychomotor activation, a syndrome of behavioral responses evoked by addictive drugs, and the effects of sign-tracking on corticosterone levels and activation of dopamine pathways resemble the neurobiological effects of abused drugs. Finally, the neurobiological profile of individuals susceptible to sign-tracking resembles the pathophysiological profile of vulnerability to drug abuse, and vulnerability to sign-tracking predicts vulnerability to impulsive responding and alcohol self-administration. Implications of sign-tracking for models of drug addiction are considered.

Inhibitory Effects of Coptidis rhizoma and Berberine on Cocaine-induced Sensitization

Substantial evidence suggests that the behavioral and reinforcing effects of cocaine can be mediated by the central dopaminergic systems. Repeated injections of cocaine produce an increase in locomotor activity and the expression of tyrosine hydroxylase (TH) in the main dopaminergic areas. Protoberberine alkaloids affect neuronal functions. Coptidis rhizoma (CR) and its main compound, berberine (BER) reduced the dopamine content in the central nervous system. In order to investigate the effects of CR or BER on the repeated cocaine-induced neuronal and behavioral alterations, we examined the influence of CR or BER on the repeated cocaine-induced locomotor activity and the expression of TH in the brain by using immunohistochemistry. Male SD rats were given repeated injections of saline or cocaine hydrochloride (15 mg/kg, i.p. for 10 consecutive days) followed by one challenge injection on the 4th day after the last daily injection. Cocaine challenge (15 mg/kg, i.p) produced a larger increase in locomotor activity and expression of TH in the central dopaminergic areas. Pretreatment with CR (50, 100, 200 and 400 mg/kg, p.o.) and BER (200 mg/kg, p.o.) 30 min before the daily injections of cocaine significantly inhibited the cocaine-induced locomotor activity as well as TH expression in the central dopaminergic areas. Our data demonstrate that the inhibitory effects of CR and BER on the repeated cocaine-induced locomotor activity were closely associated with the reduction of dopamine biosynthesis and post-synaptic neuronal activity. These results suggest that CR and BER may be effective for inhibiting the behavioral effects of cocaine by possibly modulating the central dopaminergic system.

Expression of behavioral sensitization to the cocaine-like fungicide triadimefon is blocked by pretreatment with AMPA, NMDA and DA D1 receptor antagonists

Triadimefon (TDF) is a triazole fungicide that blocks the reuptake of dopamine (DA), much like cocaine. A recent study in our laboratory found that intermittent injections of TDF led to robust locomotor sensitization in response to challenge TDF after a 2-week withdrawal period. The current study sought to determine whether the expression of TDF behavioral sensitization could be prevented by the DA D1-like receptor antagonist SCH 23390 (SCH), the DA D2-like receptor antagonist remoxipride (Rem), the competitive NMDA antagonist CPP, or the AMPA antagonist NBQX. Adult male C57/BL6 mice were injected with vehicle or 75 mg/kg TDF twice a week for 7 weeks, with locomotor activity measured periodically across the 14 doses. After a 2-week withdrawal period, mice were pretreated with SCH (0.015 mg/kg), Rem (0.3 mg/kg), CPP (2.5 mg/kg) or NBQX (10.0 mg/kg) followed 30 min later by vehicle or 75 mg/kg TDF and tested for the expression of TDF sensitization. Intermittent administration of TDF led to the development and robust expression of behavioral sensitization in terms of vertical activity. Pretreatment with SCH, NBQX and CPP successfully blocked the expression of vertical sensitization to TDF, while Rem pretreatment did not. All four antagonists, however, attenuated the neurochemical changes normally associated with TDF sensitization as measured 8 h after the 2-week TDF challenge. This paper reveals that NMDA, AMPA and DA D1-like receptors are necessary for the behavioral expression of sensitization to the fungicide triadimefon.

Protective efficacy of neuroactive steroids against cocaine kindled-seizures in mice

Neuroactive steroids demonstrate pharmacological actions that have relevance for a host of neurological and psychiatric disorders. They offer protection against seizures in a range of models and seem to inhibit certain stages of drug dependence in preclinical assessments. The present study was designed to evaluate two endogenous and one synthetic neuroactive steroid that positively modulate the gamma-aminobutyric acid (GABA(A)) receptor against the increase in sensitivity to the convulsant effects of cocaine engendered by repeated cocaine administration (seizure kindling). Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one) and ganaxolone (a synthetic derivative of allopregnanolone 3alpha-hydroxy-3beta-methyl-5alpha-pregnan-20-one) were tested for their ability to suppress the expression (anticonvulsant effect) and development (antiepileptogenic effect) of cocaine-kindled seizures in male, Swiss-Webster mice. Kindled seizures were induced by daily administration of 60 mg/kg cocaine for 5 days. All of these positive GABA(A) modulators suppressed the expression of kindled seizures, whereas only allopregnanolone and ganaxolone inhibited the development of kindling. Allopregnanolone and pregnanolone, but not ganaxolone, also reduced cumulative lethality associated with kindling. These findings demonstrate that some neuroactive steroids attenuate convulsant and sensitizing properties of cocaine and add to a growing literature on their potential use in the modulation of effects of drugs of abuse.

Gamma-vinyl GABA, an irreversible inhibitor of GABA transaminase, alters the acquisition and expression of cocaine-induced sensitization in male rats

We examined the effect of (+/-)-gamma-vinyl GABA (GVG, Vigabatrin), an irreversible inhibitor of the enzyme GABA transaminase, on the acquisition and expression of cocaine-induced sensitization in albino male Sprague-Dawley rats. Animals received a single injection of 1 ml/kg i.p. of 0.9% saline or 15 mg/kg i.p. of (-)-cocaine and locomotor activity was assessed using automated locomotor cages and stereotyped behaviors were scored using a 4-point rating scale (Day 1). Subsequently, animals were given 15 mg/kg i.p. of cocaine every 48 h in their home cage for 1 week (Days 3, 5, and 7) and then given no treatment for 1 week. A challenge injection of 15 mg/kg i.p. of cocaine, but not vehicle, produced a significant increase in locomotor activity and stereotyped behaviors on Day 15 compared to animals that received cocaine on Day 1. Administration of 75 mg/kg i.p. of GVG 2.5 h before the cocaine injections did not significantly alter the acquisition of cocaine-induced locomotor sensitization. However, 150 mg/kg i.p. of GVG significantly attenuated the acquisition of cocaine-induced locomotor sensitization. Administration of 150 mg/kg i.p. of GVG 2.5 h before the cocaine challenge injection on Day 15 significantly attenuated the expression of cocaine-induced locomotor sensitization. Acquisition and expression of cocaine-induced sensitization of stereotypy was also significantly attenuated by 150 mg/kg i.p. of GVG. Since sensitization may be one of the factors involved in relapse to drug use, the present results, in combination with previous findings that GVG blocks the rewarding and incentive motivating effects of cocaine, suggest that GVG might prove useful in the treatment of cocaine addiction.

Modulation of cocaine-induced place preferences by alcohol

Behavioral and physiological evidence suggests that alcohol modulates the effects produced by cocaine. To assess whether such modulation is evident with cocaine's affective properties, the present studies examined the effects of alcohol on cocaine-induced conditioned place preferences (CPP). In Experiment 1, male Sprague-Dawley rats were assigned to one of three groups based on whether they were conditioned with 20 mg/kg cocaine (Group C), 0.5 g/kg alcohol (Group A), or the combination (Group C/A). On the first conditioning trial, animals were injected with the drug(s) or vehicle and placed on one side of a place preference apparatus. On the next day, animals initially injected with drug received vehicle (and vice versa) and placed on the other side of the chamber. This cycle was repeated four times. Animals were then tested for their compartment preference. In Experiment 2, subjects were treated identically except that 1.5 g/kg alcohol was administered. In both experiments, Group C displayed a significant preference for the drug-paired compartment. Group A (in both experiments) showed no conditioned effect. In Experiment 1, Group C/A failed to display a significant preference, spending an amount of time in each compartment that was the numerical average of Groups C and A. In Experiment 2, the cocaine-induced preference was completely abated by 1.5 g/kg alcohol. These results indicate that alcohol produces a dose-dependent modulation of the affective properties of cocaine.

Cocaine self-administration alters the locomotor response to microinjection of bicuculline into the ventral tegmental area of rats

Several studies indicate that repeated administration of cocaine can alter GABA(A) receptor function, particularly in the mesolimbic pathway. The purpose of the present study was to assess the effect of cocaine self-administration on GABA(A) receptor activity in the ventral tegmental area (VTA), measured by bicuculline-induced rotational behavior. In order to test whether the hypothesized alteration in GABA(A) receptor function persisted during withdrawal, rats were tested when drug-nai;ve and at two time points after cocaine self-administration. Eighteen rats were implanted with intrajugular catheters and unilateral guide shafts aimed at the VTA. Microinjection of the GABA(A) receptor antagonist bicuculline (10, 25 and 50 ng) produced a dose-dependent turning behavior in a direction ipsilateral to the side of the injection. A subset of six rats was given up to 2 weeks exposure to intravenous cocaine by self-administration and was tested for bicuculline-induced rotations early in withdrawal (24 h) and again at a late withdrawal time point (between 11 and 14 days after the last cocaine session). Cocaine self-administration reduced sensitivity to bicuculline-induced rotations at the early but not at the late withdrawal point, when compared to sensitivity in drug-naive animals. A separate control study that was conducted in seven rats determined that repeated injections of bicuculline in the cocaine self-administration animals was not the cause of the decrease in behavioral response to bicuculline at the early withdrawal time point. These results suggest that exposure to cocaine via self-administration reduces the function of GABA(A) receptors in the ventral midbrain, but this reduction in receptor sensitivity did not persist beyond 10 days of withdrawal from cocaine.

Lack of allosteric modulation of striatal GABA(A) receptor binding and function after cocaine sensitization

GABA(A) receptor binding after repeated cocaine has been shown to be either increased as indicated by benzodiazepine binding or decreased as indicated by convulsant-site binding. We measured the GABA binding site with [3H]-muscimol binding to GABA(A) receptors and found no differences between saline- and cocaine-sensitized rats. Allosteric modulation of [3H]-muscimol binding with flunitrazepam was also unchanged after cocaine sensitization. In addition, [3H]-flunitrazepam binding and allosteric modulation of [3H]-flunitrazepam binding with GABA was unchanged after 1 day withdrawal from repeated cocaine. GABA(A) receptor function and allosteric modulation of GABA(A) receptor function measured by GABA-stimulated Cl(-) uptake was also unchanged after withdrawal from repeated cocaine. Finally, in vitro cocaine reduced GABA(A) receptor function in striatal microsacs of saline- and cocaine-treated rats. In conclusion, repeated cocaine did not change the coupling of the GABA(A) receptor between the GABA and benzodiazepine (BZD) binding site after 1 day withdrawal.

Effects of cocaine administration on receptor binding and subunits mRNA of GABA(A)-benzodiazepine receptor complexes

The effects of intermittent intraperitoneal (i.p.) administration of cocaine (20 mg/kg) on GABA(A)-benzodiazepine (BZD) receptors labeled by t-[(35)S]butylbicyclophosphorothionate (TBPS), and on several types of mRNA subunits were investigated in rat brain by in vitro quantitative receptor autoradiography and in situ hybridization. Phosphor screen imaging with high sensitivity and a wide linear range of response was utilized for imaging analysis. There was a significant decrease in the level of alpha 1, alpha 6, beta 2, beta 3, and gamma 2 subunits mRNA, with no alteration of [(35)S]TBPS binding in any regions in the brain of rats at 1 h following a single injection of cocaine. In chronically treated animals, the mean scores of stereotyped behavior were increased with the number of injections. The level of beta 3 subunit mRNA was decreased in the cortices and caudate putamen, at 24 h after a final injection of chronic administrations for 14 days. In the withdrawal from cocaine, the frontal cortex and hippocampal complexes showed a significant increase in [(35)S]TBPS binding and alpha1 and beta 3 subunit mRNA in the rats 1 week after a cessation of chronic administration of cocaine. These findings suggest that the disruption of GABA(A)-BZD receptor formation is closely involved in the development of cocaine-related behavioral disturbances. Further studies on the physiological functions on GABA(A)-BZD receptor complex will be necessary for an explanation of the precise mechanisms underlying the acute effects, development of hypersensitization, and withdrawal state of cocaine.

Time-course effects of a single administration of cocaine on receptor binding and subunit mRNAs of GABA(A) receptors

We investigated the time-course effects of a single administration of cocaine (20 mg/kg) on GABA(A) receptor binding labeled by t-[(35)S]butylbicyclophophorothionate (TBPS) and on several types of GABA(A) receptor subunit mRNAs in the rat brain by in vitro quantitative receptor autoradiography and in situ hybridization. The levels of alpha 1, beta 2, and beta 3 subunit mRNAs in several brain regions such as the cortex, cerebellum, and striatum were significantly decreased within 1 h, while beta 3 subunit mRNA was increased in the dentate gyrus. All of these changes were transient, occurring within 1 h after the injection of cocaine. In the cortex and cerebellum, the reduction in alpha1 subunit mRNA was followed by a significant decrease in [(35)S]TBPS receptor binding, which occurred 4 h after cocaine injection. These findings suggest that acute cocaine administration discretely regulates GABA(A) receptor subunit mRNA levels in several brain regions through a change in transcription or turnover rates of subunit mRNAs, which may be closely related to cocaine-induced behavioral abnormalities.

Cocaine and alcohol interactions in the rat: effect of cocaine and alcohol pretreatments on cocaine pharmacokinetics and pharmacodynamics

This experiment was designed to investigate the effect of pretreatment with cocaine and alcohol on cocaine pharmacokinetics and pharmacodynamics. Four groups of rats (n = 8 per group) received one of the following pretreatments for two weeks: none, alcohol (10% v/v in drinking water), cocaine (15 mg/kg/day ip), and alcohol+cocaine (10% v/v in drinking water + 15 mg/kg/day ip). On the day of the experiment, cocaine was administered (30 mg/kg, ip) to each rat, either alone or in combination with alcohol (5 g/kg, po), in a balanced crossover experimental design. Plasma and brain ECF concentrations of cocaine and its three metabolites: benzoylecgonine, norcocaine, and cocaethylene were assayed by HPLC-UV. The percent change in brain dopamine concentration, mean arterial blood pressure, and heart rate were determined simultaneously. A sigmoid-E(max) model was used to describe the brain cocaine concentration-neurochemical effect (dopamine) relationship, and an indirect pharmacodynamic response model was used to describe the plasma cocaine concentration-cardiovascular effect relationships. Alcohol pretreatment led to significant increase in cocaine AUC(p), alpha(t1/2), and beta(t1/2). Cocaine pretreatment significantly increased cocaine bioavailability, absorption rate constant, TBC, and the formation clearance of cocaethylene. Acute alcohol coadministration with cocaine increased cocaine AUC(p) and bioavailability, reduced the fraction of cocaine dose converted to benzoylecgonine, and increased the formation of norcocaine. These results indicate that the pharmacokinetics of cocaine, either administered alone or in combination with alcohol, is significantly altered due to prior cocaine and/or alcohol use. Both cocaine and alcohol pretreatments increased the E(max) for dopamine, with no effect on the EC(50). Acute alcohol coadministration with cocaine significantly increased the E(max) for dopamine and reduced the EC(50). Cocaine pretreatment significantly decreased the I(max) for blood pressure, IC(50), and R(max). For the heart rate response, both alcohol and cocaine pretreatments significantly increased the IC(50), with no effect on I(max). These results indicate that both cocaine and alcohol pretreatments as well as acute alcohol coadministration lead to significant alterations in cocaine pharmacodynamics that are due, at least in part, to the changes in cocaine pharmacokinetics. If similar effects occur in humans, chronic cocaine and alcohol abusers may respond differently to cocaine administration compared to naïve users and may be at higher risks of cocaine central nervous system toxicity.

Endogenous GABA release is reduced in the striatum of cocaine-sensitized rats

The magnitude of behavioral sensitization to cocaine is correlated with decreased striatal GABA(A) receptor function. We examined whether GABA release from striatal slices is also altered in cocaine-treated rats. Behavioral sensitization was measured in rats receiving either saline or cocaine (15 mg kg(-1)) daily for 14 days. Cocaine-treated rats showed a significant increase in locomotion and stereotypy over days. Potassium-stimulated endogenous GABA release was measured from superfused striatal slices of these rats. GABA release was significantly decreased in cocaine-treated rats. However, striatal slices preloaded with [(3)H]GABA exhibited a slight but significant increase in release after cocaine sensitization. Similar treatment with a nonsensitizing dose of cocaine (7.5 mg kg(-1)) did not change endogenous GABA release. Saline- and cocaine-treated rats showed no differences in striatal glutamic acid decarboxylase activity at either a saturating or K(m) concentration of glutamate. Therefore, the decrease in endogenous GABA release is not due to a decrease in GABA synthesis, but may reflect changes in GABA storage pools. These data are consistent with an overall decrease in GABA transmission, both pre- and postsynaptically, in the striatum of sensitized rats, which could contribute to enhanced striatal output and behavioral sensitization.

Increased acute cocaine sensitivity and decreased cocaine sensitization in GABA(A) receptor beta3 subunit knockout mice

The role of the GABA(A) receptor beta3 subunit in determining acute cocaine sensitivity and behavioral sensitization to repeated cocaine was measured in mice missing both (-/-), one (+/-), or neither (+/+) allele of the beta3 gene. Locomotor stimulation induced by one cocaine injection (20 mg/kg, i.p.) was found to be greater in -/- mice compared with +/+ mice, whereas cocaine-induced behaviors were intermediate in +/- mice. Amphetamine did not cause greater locomotor responses in -/- mice, suggesting that the increased sensitivity of -/- mice to cocaine does not generalize to other psychomotor stimulants. GABA-stimulated chloride uptake was 51% lower in striatum of -/- mice compared with +/+ mice, but only 27% lower in cortex. After 14 daily cocaine injections, the behavioral response to cocaine was increased in +/+ and +/- mice, but was not increased further in -/- mice. Additionally, repeated cocaine exposure decreased striatal GABA(A) receptor function in +/+ and +/- mice. In -/- mice, GABA(A) receptor function was not decreased any further by repeated cocaine injections. Thus, alterations in the beta3 subunit may be responsible for determining the behavioral responses induced by acute and repeated cocaine treatment, as well as mediating the neurochemical adaptation that occurs during sensitization to repeated cocaine.

Cocaine and alcohol interactions in the rat: effect on cocaine pharmacokinetics and pharmacodynamics

The effect of alcohol coadministration on cocaine pharmacokinetics and pharmacodynamics was investigated in awake, freely moving rats. Cocaine plasma and brain extracellular fluid (ECF) concentration-time profiles were characterized after intraperitoneal (ip) administration of 30 mg/kg cocaine to rats that were pretreated with either normal saline or alcohol at 5 g/kg in a balanced crossover experimental design. The neurochemical response to cocaine administration, measured as the change in dopamine concentration in the nucleus accumbens (N ACC) and the change in the mean arterial blood pressure were monitored simultaneously. Intragastric alcohol administration significantly increased cocaine systemic bioavailability after ip administration from 0.550 +/- 0.044 to 0. 754 +/- 0.071. Also, the absorption rate constant increased from 0. 199 +/- 0.045 to 0.276 +/- 0.059 min-1 due to alcohol coadministration; however, this increase was not significant. Alcohol inhibition of cocaine metabolism caused an increase in cocaine elimination half-life from 26.3 +/- 3.6 to 40.0 +/- 8.1 min. Also, cocaine tissue distribution was enhanced by alcohol, resulting in a significant increase in cocaine volume of distribution. Analysis of the brain cocaine concentration-neurochemical effect relationship by the sigmoid-Emax pharmacodynamic model showed that Emax increased from 850 +/- 200 to 1550 +/- 640% of baseline due to alcohol coadministration, whereas EC50 decreased from 3400 +/- 580 to 2000 +/- 650 ng/mL, indicating higher cocaine potency in the presence of alcohol. The estimates of the indirect inhibitory pharmacodynamic model used to examine the plasma cocaine concentration-change in blood pressure relationship were not significantly different after the two treatments. These results indicate that alcohol significantly alters cocaine absorption, distribution, and elimination, resulting in higher and prolonged cocaine plasma concentration. Alcohol coadministration also potentiates the neurochemical response to cocaine administration.

Beer consumption in rats: the influence of ethanol content, food deprivation, and cocaine

A series of experiments examined various aspects of beer consumption in male Wistar rats. In the first experiment, rats were given home cage access to either beer or ethanol solutions under free access conditions. It was found that rats consumed greater amounts of moderate strength beer (2.7% ethanol by volume) or regular strength beer (5.0% ethanol) than equivalent dilute ethanol solutions in water. Consumption of 2.7% beer was greater than 5.0% beer and access to either beer, but not dilute ethanol, solutions caused substantial increases in total fluid intake per day. In the second experiment, individual rats given daily 30-min drink sessions consumed more 2.7% beer than 3.85% beer and more 3.85% than 5.0% beer. A "hangover" effect was evident after the first day of consumption of 5.0% beer with subsequent intake of this beer suppressed after high intake on first exposure. Intake of the low-strength beer approached intake of isocaloric (8.6%) sucrose solution. In a third experiment, a lick-based progressive ratio paradigm was implemented where rats had to emit progressively greater number of licks for a fixed volume (0.1 ml) of 2.7% beer or 8.6% sucrose. Using this paradigm, it was shown that food deprivation increased the motivation to consume beer and sucrose as shown by elevated break points (the highest ratio reached). Food deprivation also increased locomotor activity in the drinking environment. In contrast, cocaine (20 but not 10 mg/kg) caused a decrease in the break point for sucrose and beer, an effect probably mediated by the anorexic properties of the drug. It is concluded that rats will avidly consume beer, particularly of moderate alcohol content, but that such consumption may be mediated more by the nutritive and palatable characteristics of the beer rather than by the psychoactive effects of the alcohol it contains.

Antisense inhibition of striatal GABAA receptor proteins decreases GABA-stimulated chloride uptake and increases cocaine sensitivity in rats

The functional status of striatal GABAA receptors appears to be inversely related to the magnitude of cocaine-induced behaviors. Exposure of striatum to antisense oligodeoxynucleotides (ASODNs) targeted to the mRNAs for the alpha 2 and the beta 3 subunits of the GABAA receptor should decrease expression of receptor proteins and therefore might be expected to increase cocaine sensitivity. ASODNs, scrambled ODNs or saline were injected into right lateral ventricle of rats and behavioral responses to cocaine were tested 18-20 h after treatment. Animals injected separately with alpha 2 or beta 3 ASODNs exhibited increased behavioral sensitivity to cocaine compared to rats injected with saline or scrambled ODNs including performing more 360 degrees turns to the left than to the right. There was significantly less GABA-stimulated Cl uptake in right striatum compared to left striatum of ASODN-treated rats with no significant difference between sides in control animals. Specific binding to benzodiazepine and convulsant sites on the GABAA receptor was not selectively altered by ASODN treatment. Combined alpha 2 beta 3 ASODN treatment did not affect either cocaine sensitivity or GABAA receptor function. There was no difference between the density of Nissl stained cells in the left and right edges of striatum in control or ASODN-treated rats indicating the absence of significant neurotoxic effects of the ASODN treatment. Injection of fluorescein-conjugated ASODNs indicated that ASODN is present in striatum at times during which behavioral and neurochemical indices of GABA receptor function are decreased. Thus, the functional status of GABAA receptors in striatum may be involved in determining cocaine sensitivity.

Ethanol modulates cocaine-induced behavioral change in inbred mice

We recently conducted a study of the behavioral effects of combined cocaine and ethanol in genetically defined mice. Male and female C57BL/6 (B6) and DBA/2 (D2) were tested in an automated activity monitor on 2 consecutive days. On day 1, all animals received an IP injection of sterile saline and were placed into the activity monitor for 30 min. Behaviors measured were total distance traveled, stereotypy, nosepokes, and wall-seeking. On day 2, all animals were tested again for 15 min following injection of one of the following: saline, 10% v/v ethanol at 2.0 g kg(-1) or 2.0 g kg(-1) ethanol plus 5, 15, or 30 mg kg(-1) cocaine. Cocaine alone at the same doses was injected into separate groups of animals. For the B6 strain, the overall effect of ethanol was to reduce cocaine-induced locomotor stimulation; no consistent effect of ethanol on cocaine-induced locomotion was observed in D2 mice. Cocaine-induced inhibition of nosepokes in both strains and sexes was partially reversed by ethanol. Ethanol also partially reversed cocaine-elevated stereotypy in both strains and both sexes. In B6 mice, cocaine-increased wall seeking tended to be reversed by coadministration of ethanol, whereas no consistent pattern was observed in the D2s. Results from this study suggest that the several measures affected by cocaine (locomotor activity, stereotypy, exploration, thigmotaxis) were, in turn, differentially affected by concurrent treatment with ethanol. Furthermore, our results point to genetic-based differences in ethanol's effects on cocaine-related behaviors. We address the implications for combined ethanol and cocaine use in humans.

Enhanced sensitivity to benzodiazepines in active cocaine-abusing subjects: a PET study

OBJECTIVE

Because cocaine enhances dopamine brain activity and dopamine signals are transferred through gamma-aminobutyric acid pathways, the authors hypothesized GABA-ergic disruption in cocaine-abusing subjects. This study tests this hypothesis.

METHOD

GABA brain function was assessed indirectly by measuring the brain metabolic responses to lorazepam, a drug that facilitates GABA neurotransmission. Thirteen current cocaine-abusing subjects and 14 comparison subjects were scanned twice with positron emission tomography and [18F]fluorodeoxyglucose; the first scan was obtained after placebo administration and the second after lorazepam administration (30 micrograms/kg).

RESULTS

Despite significantly higher plasma lorazepam concentrations in comparison subjects than in cocaine-abusing subjects, lorazepam-induced decrements in whole brain metabolism were significantly greater in cocaine-abusing (mean = 21%, SD = 13%) than in comparison (mean = 13%, SD = 7%) subjects. These differences were largest in striatum, thalamus, and parietal cortex. Lorazepam-induced sleepiness in cocaine-abusing subjects was intense and was significantly greater than in comparison subjects, and it was correlated with lorazepam-induced changes in thalamic metabolism. Whereas regional metabolic measures during placebo administration were significantly higher in cocaine-abusing subjects than in comparison subjects, the measures during lorazepam administration were equivalent for both groups.

CONCLUSIONS

The enhanced sensitivity to lorazepam in cocaine-abusing subjects suggests disruption of GABA pathways that may reflect, in part, cocaine withdrawal. The intense sleepiness induced by lorazepam in some of the abusers, despite their significantly lower plasma concentrations, should alert clinicians of the potential toxicity from accentuated responses to sedative hypnotics in active cocaine-abusing subjects.

Cocaethylene toxicity

Concurrent use of cocaine and alcohol produces another psychoactive substance known as cocaethylene which has pharmacological properties similar to that of cocaine but which has a plasma half-life three to five times that of cocaine. This slow removal from the body makes it an attractive drug for abuse. However, cocaethylene has been associated with seizures, liver damage, and compromised functioning of the immune system. It also carries an 18- to 25-fold increase over cocaine alone in risk for immediate death.

Alcohol plus cocaine: the whole is more than the sum of its parts

Cocaethylene, an active metabolite that arises through hepatic transesterification of cocaine when cocaine and ethanol are used together, shares many neurochemical and pharmacological properties with cocaine. Cocaethylene is similar to cocaine in its properties as an indirect dopamine agonist, and human subjects cannot distinguish its effects from those of cocaine. Cocaethylene, and especially its isopropyl analog, are more selective indirect dopamine agonists than cocaine, with relatively weak potency at the serotonin transporter. Cocaethylene may contribute to the manifestations and consequences of combined cocaine and ethanol use, although its relative importance remains unclear.

Analysis of the biphasic locomotor response to ethanol in high and low responders to novelty: a study in Nijmegen Wistar rats

The aim of the study was to investigate the biphasic locomotor response to ethanol in rats. Based on the recent finding that high responders to novelty (HR) and low responders to novelty (LR), selected from an outbred Nijmegen Wistar rat population, show differences in ethanol intake and preference, it was initially investigated to what extent HR and LR differ in their locomotor response to ethanol. A dose-response curve (0.2-2.0 g/kg, i.p.) was established using standardized activity boxes. HR showed a significant increase at 0.5 g/kg, followed by a significant decrease at doses 1.0-2.0 g/kg; LR showed only a decrease at doses 1.0-2.0 g/kg. Secondly, it was investigated to what extent stress altered the ethanol-induced increase and decrease, respectively. For that purpose, the ethanol-induced locomotor effects (0.5 and 1.0 g/kg) were analyzed in habituated and non-habituated (stressed) HR and LR; habituation consisted of a 15-min adaptation period to the activity cages. Stress significantly enhanced the excitatory effects in HR, but had no effect on the sedative effects in HR and LR. Finally, the locomotor effects of sub-chronic treatment (7 days) with an excitatory (0.5 g/kg) or sedative (1.0 g/kg) dose were analyzed in HR and LR. The excitatory effect of 0.5 g/kg disappeared throughout the treatment in HR, whereas the sedative effects of 1.0 g/kg remained the same in HR and LR. It is concluded that the mechanism underlying the ethanol-induced motor excitation differs completely from that underlying the ethanol-induced sedation. Given the known differences in the make-up of the brain and endocrine system between HR and LR, these animals are suggested to be good models for studying the mechanisms underlying the biphasic locomotor response to ethanol in rats.

Chronic effects of ethanol on central adenosine function of mice

Chronic ingestion of 5% ethanol had no significant effect on open field locomotor of NIH Swiss strain male mice, nor were the depressant effects of a non-selective adenosine receptor agonist, NECA, or the stimulant effects of a non-selective antagonist, caffeine significantly altered. The density of cerebral cortical A1-adenosine receptors and of nitrendipine binding sites on calcium channels were significantly increased after chronic ethanol, while the density of striatal A2a-adenosine receptors were unchanged. The locomotor stimulant effects of ethanol (2.5 g/kg) were slightly decreased after chronic ethanol, but were markedly reduced in mice after chronic caffeine ingestion. The results suggest some involvement of adenosine systems in the effects of ethanol.