Potentiation of ethanol toxicity by cyanamide in relation to acetaldehyde accumulation

The possibility that acetaldehyde accumulation potentiates the acute toxicity of ethanol was studied by pretreating rats with cyanamide, an aldehyde dehydrogenase inhibitor. At 30 min after administration of ethanol (7 to 9 g/kg, po), the levels of acetaldehyde in femoral venous blood of cyanamide-treated rats were increased from 10 to 20 to 600 mumol/liter and at death the concentrations of acetaldehyde in heart blood and cerebrospinal fluid were still 7 to 9 and 4 to 9 times higher, respectively, than in rats given ethanol only. The cyanamide pretreatment (25 mg/kg) significantly increased the mortality of rats given 6.5 to 7.0 g/kg ethanol and decreased the LD50 of ethanol from 7.3 to 5.9 g/kg. Cyanamide increased the late mortality, possibly because of sustained acetaldehyde accumulation. Although administration of the alcohol dehydrogenase inhibitor, 4-methylpyrazole (4-MP, 10 mg/kg), prevented the accumulation of acetaldehyde, it only partly counteracted the effect of cyanamide on mortality. After coadministration of cyanamide and 4-MP, the LD50 of ethanol was 6.5 g/kg, and after 4-MP alone, 6.7 g/kg. 4-MP by itself seemed to increase the early mortality of rats to ethanol poisoning. The results suggest that the potentiating effect of cyanamide on ethanol toxicity can partly be explained by acetaldehyde accumulation and that 4-MP can be used to inhibit this accumulation providing its central depressant effect is taken into account.     

Time course of the locomotor stimulant and depressant effects of a single low dose of ethanol in mice

The acute effects of alcohol on spontaneous locomotor activity in male Swiss mice were studied at various times after an IP injection of 2 g/kg ethanol. Subjects were placed alone in a novel arena and videotape recordings were made of behaviour: trials were of 500-s duration and commenced at either 30, 60, 120, or 180 min after alcohol administration. Measures of behaviour included various indices of ambulation and immobility, together with a more detailed ethological analysis of the frequencies of all other acts and postures shown by test animals. Ambulation showed a biphasic response to alcohol treatment, consisting of an initial stimulation followed by a suppression after 3 h. Immobility was also increased by alcohol, and showed peak stimulation in trials commencing 30 min after administration: thereafter there was a progressive return to baseline levels. Many behavioural elements were suppressed including rearing, digging, shaking, and abbreviated grooming. Ethanol thus appeared to produce two distinct types of depression, in terms of increased immobility (and suppression of other behaviour) and in terms of decreased ambulation, the latter occurring when immobility had returned to baseline levels.     

Differential effects of GABAA and GABAB agonists on sensitization to the locomotor stimulant effects of ethanol in DBA/2 J mice

 Contemporary theories of drug abuse suggest that behavioral sensitization plays an important role in addiction. However, few studies have examined the mechanisms underlying behavioral sensitization to ethanol. The present study examined the ability of THIP (2, 4, or 8 mg/kg) and baclofen (5.0, 6.25, or 7.5 mg/kg), GABA_A and GABA_B agonists, respectively, to prevent development of sensitization to the locomotor stimulant effects of ethanol (2 g/kg) in DBA/2 J mice. Ethanol was administered immediately before four 5-min activity trials conducted at 48-h intervals. Administration of ethanol on each of the four trials resulted in behavioral sensitization in control groups. While having few effects on activity when given alone, both GABA agonists completely blocked the acute stimulant response to ethanol on the first trial. Administration of THIP prior to ethanol on each trial failed to prevent development of sensitization. In contrast, all doses of baclofen blocked sensitization. Assessment of blood ethanol levels 15, 50 and 100 min after administration of ethanol indicated that baclofen did not change the pharmacokinetics of ethanol. These results indicate an important role for GABA_B receptors, but not GABA_A receptors, in development of sensitization to the locomotor stimulant effects of ethanol. Received: 11 April 1998 / Final version: 24 June 1998     

Dissociation between the locomotor and anxiolytic effects of acetaldehyde in the elevated plus-maze: Evidence that acetaldehyde is not involved in the anxiolytic effects of ethanol in mice

Acetaldehyde, the first product of ethanol metabolism, has been suggested to play a major role in many behavioral effects of ethanol. However, very few studies have directly tested the behavioral effects of the acute administration of acetaldehyde. In particular, the role of this metabolite in ethanol-induced anxiolytic effects has never been extensively tested. The aim of the present study was to characterize the anxiolytic effects of acetaldehyde in two strains of mice, C57BL/6J and CD1 mice with the elevated plus-maze procedure. The results show that acute injections of ethanol (1–2 g/kg) induced significant dose-dependent anxiolytic effects in both strains of mice. In contrast, acetaldehyde failed to produce any anxiolytic effect, although it induced a significant hypolocomotor effect at the highest doses. In an independent experiment, cyanamide, an aldehyde dehydrogenase inhibitor, prevented the locomotor stimulant effects of ethanol, although it failed to alter its anxiolytic effects. Together, the results of the present study indicate that acetaldehyde is not involved in ethanol-induced anxiolytic effects, although it may be involved in its sedative/hypolocomotor effects.     

GABAB receptor stimulation accentuates the locomotor effects of morphine in mice bred for extreme sensitivity to the stimulant effects of ethanol

Mice selectively bred for divergent sensitivity to the locomotor stimulant effects of ethanol (FAST and SLOW) also differ in their locomotor response to morphine. The GABA(B) receptor has been implicated in the mediation of locomotor stimulation to both ethanol and morphine, and a reduction in ethanol-induced stimulation has been found with the GABA(B) receptor agonist baclofen in FAST mice. We hypothesized that GABA(B) receptor activation would also attenuate the locomotor stimulant responses to morphine in these mice. In order to test this hypothesis, baclofen was administered to FAST-1 and FAST-2 mice 15 min prior to morphine, and activity was recorded for 30 min. Baclofen attenuated stimulation to 32 mg/kg morphine in FAST-1 mice, but only at a dose that also reduced saline activity. There was no stimulant response to 32 mg/kg morphine in FAST-2 mice, or to 16 mg/kg or 48 mg/kg morphine in FAST-1 mice, but the combination of baclofen with these morphine doses accentuated locomotor activity. Therefore, it appears that GABA(B) receptor activation is not a common mechanism for the locomotor stimulant responses to ethanol and morphine in FAST mice; however, these data suggest that GABA(B) receptor activation may instead enhance some of the behavioral effects of morphine.     

Endogenous acetaldehyde in rats. Effects of exogenous ethanol, pyrazole, cyanamide and disulfiram

Male Long-Evans rats consumed the alcohol and aldehyde dehydrogenase inhibitors pyrazole, cyanamide or disulfiram, for 6 days. No endogenous blood acetaldehyde could be detected in controls and pyrazole treated rats, endogenous blood concentrations up to 2-5 nmoles/ml were, however, measured in the cyanamide and disulfiram-treated animals. Other rats received daily ethanol gastric intubations in addition to the consumption of the inhibitors. Little or no acetaldehyde was detected in the controls and pyrazole treated animals during acute ethanol intoxication or on the subsequent days. High blood levels (200-500 nmoles/ml) were observed in the rats consuming cyanamide and disulfiram, and concentrations up to 10-12 nmoles/ml were still found on the following day after all the ethanol had been eliminated. This acetaldehyde and the endogenous acetaldehyde could only be observed with the hemolyzation method in which blood hemolyzates were directly heated prior to headspace GC analysis; none was detected if blood proteins were first precipitated and removed with perchloric acid. It is suggested that aldehyde dehydrogenase inhibitors elevate endogenous concentrations of bound acetaldehyde and that exogenous ethanol increases this form of acetaldehyde.     

GABAB receptor stimulation accentuates the locomotor effects of morphine in mice bred for extreme sensitivity to the stimulant effects of ethanol

Mice selectively bred for divergent sensitivity to the locomotor stimulant effects of ethanol (FAST and SLOW) also differ in their locomotor response to morphine. The GABA_B receptor has been implicated in the mediation of locomotor stimulation to both ethanol and morphine, and a reduction in ethanol-induced stimulation has been found with the GABA_B receptor agonist baclofen in FAST mice. We hypothesized that GABA_B receptor activation would also attenuate the locomotor stimulant responses to morphine in these mice. In order to test this hypothesis, baclofen was administered to FAST-1 and FAST-2 mice 15 min prior to morphine, and activity was recorded for 30 min. Baclofen attenuated stimulation to 32 mg/kg morphine in FAST-1 mice, but only at a dose that also reduced saline activity. There was no stimulant response to 32 mg/kg morphine in FAST-2 mice, or to 16 mg/kg or 48 mg/kg morphine in FAST-1 mice, but the combination of baclofen with these morphine doses accentuated locomotor activity. Therefore, it appears that GABA_B receptor activation is not a common mechanism for the locomotor stimulant responses to ethanol and morphine in FAST mice; however, these data suggest that GABA_B receptor activation may instead enhance some of the behavioral effects of morphine.     

Ontogeny of the stimulant and sedative effects of ethanol in male and female Swiss mice: gradual changes from weaning to adulthood

Rationale  

The adolescent period is characterized by a specific sensitivity to the effects of alcohol, which is believed to contribute to the enhanced risks of alcohol dependence when drinking is initiated early during adolescence. In adolescent rodents, while the reduced sensitivity to the sedative effects of ethanol has been well characterized, its stimulant effects have not yet been extensively studied.     

The interactive effects of methylphenidate and ethanol on ethanol consumption and locomotor activity in mice

The concomitant use of alcohol (EtOH) and the psychotherapeutic agent dl-methylphenidate (MPH) has risen as a consequence of an increase in ADHD diagnoses within the drinking age population. It was recently found that the combination of MPH and EtOH increases the self-report of pleasurable feelings relative to MPH alone. This finding raises concerns regarding the combined abuse liability for these two widely used drugs. The present behavioral study reports on the development of an adult male C57BL/6J (B6) mouse model to further characterize this MPH-EtOH interaction. We examined the effects of MPH on EtOH consumption in a limited access paradigm and EtOH stimulation of locomotor activity. B6 mice consumed about 2 g/kg EtOH daily and MPH dose-dependently reduced drinking. The most effective dose of MPH was 1.25 mg/kg, which produced a 41% decrease in drinking and had no effect on locomotor activity. However, when the 1.25 mg/kg dose of MPH was combined with a stimulatory dose of ethanol (1.75 g/kg) by intraperitoneal injection, there was a significantly enhanced stimulation of locomotor activity. The drug combination increased activity compared to the vehicle or MPH injections by 45% and increased the activity relative to EtOH alone by an additional 25%. The results of the EtOH and MPH interactions observed with the mouse model appear to be behaviorally relevant and suggest several converging mechanisms that may underlie MPH-EtOH interactions.     

Escalation of food-maintained responding and sensitivity to the locomotor stimulant effects of cocaine in mice

Escalation of drug self-administration is a consequence of extended drug access and is thought to be specifically related to addiction, but few studies have investigated whether intake of non-drug reinforcers may also escalate with extended-access. The goal of these studies was to determine the effects of limited and extended-access to food reinforcers on behavioral and pharmacological endpoints in mice. In distinct groups, responding on a lever was maintained by liquid reinforcement, or nose-poke responses were maintained by sucrose pellets or liquid food in sessions lasting 1 h (limited-access) or 10 h (extended-access). The reinforcing strength of each food, as well as reinforcer-associated cues, was tested before and after extended-access using a progressive ratio (PR) schedule, and locomotor activity in response to novelty and increasing doses of cocaine was assessed in an open field setting in all animals after access to food reinforcers. Escalation of lever-pressing behavior reinforced by liquid food, but not nose-poke behavior reinforced by liquid food or sucrose pellets, was observed across successive extended-access sessions. A concomitant increase in the reinforcing strength of liquid food and its associated cues was apparent in mice that escalated their responding, but not in mice that did not escalate. Finally, extended reinforcer access leading to behavioral escalation was accompanied by an increased sensitivity to the psychostimulant effects of cocaine compared to limited-access. These findings indicate that behavioral escalation can develop as a consequence of extended-access to a non-drug reinforcer, although both the nature of the reinforcer (liquid versus solid food) and the topography of the operant response (lever versus nose-poke) modulate its development. These data also suggest that some of the behavioral and pharmacological corrolaries of behavioral escalation observed following extended-access to drug self-administration may not be due to drug exposure, but rather, may result from basic behavioral processes which underlie operant responding maintained by appetitive stimuli.     

Effect of cyanamide on the metabolism of ethanol and acetaldehyde and on gluconeogenesis by isolated rat hepatocytes

Previous experiments demonstrated that acetaldehyde stimulated glucose production from pyruvate, whereas gluconeogenesis from glycerol, xylitol and sorbitol was inhibited [A.I. Cederbaum and E. Dicker, Archs Biochem. Biophys. 197, 415 (1979)]. To determine the mechanism whereby acetaldehyde affects glucose production from these precursors, and to evaluate the role of acetaldehyde in the actions of ethanol, experiments with cyanamide were carried out. The oxidation of acetaldehyde by isolated rat liver cells was inhibited by cyanamide after a brief incubation period. Associated with this inhibition of acetaldehyde oxidation was an inhibition of ethanol oxidation by cyanamide and an increase in the amount of acetaldehyde which arose during the oxidation of ethanol. Ethanol oxidation was decreased because of the ineffective removal of acetaldehyde in the presence of cyanamide. Cyanamide had no effect on hepatic oxygen uptake. The increase in the β-hydroxybutyrate/acetoacetate ratio produced by acetaldehyde was completely prevented by cyanamide, whereas the slight increase in the lactate/pyruvate ratio was not prevented by cyanamide. Cyanamide partially reversed the ethanol-induced increase in the lactate/pyruvate ratio, but it completely prevented the ethanol-induced increase in the β-hydroxybutyrate/acetoacetate ratio. The ethanol-induced change in the mitochondrial redox state may, therefore, be due primarily to the mitochondrial oxidation of the acetaldehyde which arises during the oxidation of ethanol. The inhibitory effects of acetaldehyde on gluconeogenesis from glycerol, xylitol and sorbitol, as well as the stimulation of acetaldehyde of glucose production from pyruvate, were completely prevented by cyanamide. These results indicate that the effects of acetaldehyde on gluconeogenesis represent metabolic effects, rather than direct effects of acetaldehyde. Changes in the cellular NADH/NAD^? ratio as a consequence of acetaldehyde metabolism are postulated to be responsible for these actions of acetaldehyde. Ethanol stimulated glucose production from pyruvate, while inhibiting gluconeogenesis from glycerol, xylitol and sorbitol. Cyanamide, which prevented the effects of acetaldehyde on gluconeogenesis, also prevented the effects of ethanol on gluconeogenesis. This prevention by cyanamide may be suggestive for a role for acetaldehyde in the actions of ethanol on gluconeogenesis. The possibility cannot be ruled out, however, that the prevention of the effects of ethanol by cyanamide may be due to the partial inhibition of ethanol oxidation by cyanamide. These results indicate that cyanamide is an effective inhibitor of acetaldehyde oxidation by isolated liver cells and therefore can be used to determine the mechanism whereby acetaldehyde affects metabolic function. Depending on the reaction under investigation, acetaldehyde can have direct or indirect effects on cellular metabolism.     

Voluntary ethanol drinking in C57BL/6J and DBA/2J mice before and after sensitization to the locomotor stimulant effects of ethanol

RATIONALE: Drug-induced sensitization has been associated with enhanced drug self-administration and may contribute to drug addiction. OBJECTIVES: We investigated the possible association between sensitization to the locomotor stimulant effects of ethanol (EtOH) and voluntary EtOH consumption. METHODS: Mice of the EtOH-avoiding DBA/2J (D2) and EtOH-preferring C57BL/6J (B6) inbred strains were offered the choice of an EtOH solution versus tap water (EtOH-experienced) or just water (Na), and voluntary consumption was measured. Mice from each condition then received repeated EtOH or saline injections, and locomotor responses were measured. Subsequently, all mice were offered the choice of EtOH versus water, and voluntary consumption was again measured. A subsequent study examined relative susceptibility of D2 and B6 mice to EtOH-induced locomotor sensitization. RESULTS: Voluntary EtOH consumption induced locomotor sensitization to an EtOH challenge in B6 mice. D2 mice consumed little EtOH, but developed sensitization with repeated EtOH treatments as expected. EtOH consumption was not altered in EtOH-sensitized D2 mice. Unexpectedly, B6 mice developed significant sensitization, and following sensitization, the EtOH-experienced EtOH-sensitized group consumed more EtOH than their EtOH-experienced salinetreated (non-sensitized) counterparts. In an independent study, B6 mice required between three and five EtOH injections to express sensitization, whereas for D2 mice, between one and three EtOH exposures were sufficient. CONCLUSIONS: Development of sensitization to the locomotor stimulant effects of EtOH may be associated with increased EtOH consumption in mice with high initial avidity for EtOH. In the same mice, voluntary EtOH consumption can also produce behavioral sensitization to the effects of EtOH.     

The effect of cyanamide and 4-methylpyrazole on the ethanol-induced locomotor activity in mice

To assess the role of cyanamide and 4-methylpyrazole (4-MP) in mediating ethanol-induced locomotor activity in mice, they were pretreated with cyanamide (12.5, 25, or 50 g/kg) prior to one ethanol injection (2.4 g/kg) and showed significantly depressed locomotor activity compared with control groups. Cyanamide (25 mg/kg) also cancelled out the biphasic action of ethanol (0, 0.8, 1.6, 2.4, 3.2, or 4 g/kg) on locomotor activity. The action of cyanamide and 4-MP in combined administration was also tested. Our data show that pretreatment with 4-MP alone does not change the spontaneous or ethanol-induced locomotor activity. Conversely, when mice were pretreated with cyanamide and 4-MP, the depressive effect of cyanamide on the locomotor activity induced by ethanol disappeared, and the locomotor activity rose to levels similar to those of the control group, recovering the biphasic ethanol effect. These effects cannot be attributed to peripheral elevated blood acetaldehyde levels, as pretreatment with 4-MP prevents accumulation of acetaldehyde. These data might suggest some influence of brain catalase and aldehyde dehydrogenase (ALDH) on the effects of ethanol.     

A comparison of the locomotor stimulant effects of D1-like receptor agonists in mice

Efficacy in stimulating adenylyl cyclase (AC) has traditionally been used to distinguish dopamine D1-like receptor agonists from dopamine D2-like receptor agonists. However, there is a limited association between the effects of D1-like agonists in behavioral assays and their effectiveness at stimulating AC. Other second messenger actions might contribute to the behavioral effects of D1-like agonists, as there is evidence for a link to the hydrolysis of phosphoinositide (PI). The present study compared the locomotor stimulant effects of five D1-like receptor agonists having different efficacies in assays of AC and PI activity. All D1-like agonists produced long-lasting biphasic effects on locomotor activity. SKF 38393, the prototypical partial agonist (based on AC activity), produced limited changes in locomotor activity, whereas the partial agonists SKF 75670 and SKF 77434 produced locomotor stimulant effects that were similar to or greater than those of the full efficacy agonists SKF 82958 and SKF 81297. However, there did not appear to be a relationship between maximal behavioral effects and AC stimulation or PI hydrolysis. The results suggest a complex relationship between the behavioral effects of D1-like agonists and their intrinsic efficacies as measured by AC and /or PI stimulation. Although a limited number of compounds were examined, neither second messenger system alone appears to account fully for these behavioral effects. The current classification of D1-like agonists according to their intrinsic efficacies as defined by AC stimulation needs further scrutiny.     

A comparison of the effects of chronic administration of ethanol and acetaldehyde to mice: evidence for a role of acetaldehyde in ethanol dependence

After chronic exposure to ethanol or acetaldehyde vapour in concentrations which depress locomotor activity, mice show similar behavioural changes during withdrawal, and there is some degree of cross dependence. Mice exposed to acetaldehyde vapour had blood acetaldehyde concentrations similar to those of ethanol-treated mice, but brain acetaldehyde concentrations were apparently lower. There was no accumulation of acetaldehyde in blood or brain in either group during chronic administration. Chronic ethanol or acetaldehyde administration to mice is associated with an increase in the concentrations of the brain monoamines noradrenaline, dopamine and 5-HT. Withdrawal of ethanol or acetaldehyde is associated with a further, rapid, transient rise in the brain catecholamines, noradrenaline and dopamine. These results suggest that acetaldehyde may play a role in some of the biochemical and behavioural changes associated with ethanol dependence.     

Influence of hypoxia on the effects of ethanol and acetaldehyde

During experiments on male SHK mice it was established that a preliminary normobaric normocapnic hypoxic stimulation (30-minute inhalation of a gas mixture containing 10% of oxygen) increased the animal organism resistance to toxic effects of ethanol and its metabolite acetaldehyde.     

Non-amphetaminic mechanism of stimulant locomotor effect of modafinil in mice

Previously established dose-response curves indicated that modafinil 20–40 mg/kg i.p. elicited in mice an obvious stimulation of locomotor activity roughly similar to that induced by (+)amphetamine 2–4 mg/kg. The effects of various agents modifying dopamine transmission were compared on the locomotor response to both drugs. The preferential D2 dopamine receptor antagonist haloperidol 37.5–150 μg/kg i.p. suppressed the stimulant effect of (+)amphetamine in a dose dependent manner, but not that of modafinil. The D1 dopamine receptor antagonist SCH 23390 (7.5–30 μg/kg s.c.) reversed the (+)amphetamine but not the modafinil induced hyperactivity. The tyrosine hydroxylase inhibitor -methyl-para-tyrosine (200 mg/kg) suppressed the hyperactivity induced by 4 mg/kg dexamphetamine but not that induced by 20 mg/kg modafinil. Associating L-DOPA 150 mg/kg and benserazide 37.5 mg/kg with (+)amphetamine 2 mg/kg resulted in stereotyped climbing behavior, that was not observed with modafinil 10–80 mg/kg. The profound akinesia induced by reserpine (4 mg/kg s.c.; 5 h before testing) was reversed by (+)amphetamine 2 mg/kg but not by modafinil 40 mg/kg. Finally, on synaptosomes prepared from mouse striata preloaded with [³H]dopamine, modafinil 10⁻⁵ M did not increase the spontaneous [³H]dopamine release whereas (+)amphetamine, at the same concentration, doubled it. From all these differences between the two drugs, it is concluded that the mechanism underlying the modafinil induced stimulant locomotor effect differs completely from that of (+)amphetamine.     

Differential effects of past-year stimulant and sedative drug use on alcohol-related aggression

The goals of this study were to determine the effects of past-year stimulant and sedative drug use on alcohol-related aggression and to examine whether the relation between stimulant drug use and intoxicated aggression is better accounted for by behavioral disinhibition. Participants were 330 healthy social drinkers (164 men and 166 women) between 21 and 35 years of age. Past-year stimulant and sedative use and behavioral disinhibition were assessed via self-report questionnaires. Following the consumption of either an alcohol or a placebo beverage, participants were tested on a modified version of the Taylor Aggression Paradigm [Taylor, S. (1967). Aggressive behavior and physiological arousal as a function of provocation and the tendency to inhibit aggression. Journal of Personality, 35, 297-310] in which mild electric shocks were received from, and administered to, a fictitious opponent. Aggressive behavior was operationalized as the shock intensities administered to the fictitious opponent under conditions of low and high provocation. Results indicated that alcohol significantly strengthened the relation between stimulant drug use and aggression, but only among men. Behavioral disinhibition did not account for this effect. Regardless of past-year drug use, alcohol did not facilitate aggression among women. The present findings suggest that stimulant drug use may be a risk factor for intoxicated aggression for men. However, the underlying mechanisms accounting for this effect remain unclear.