Behavioral effects of alpha 2 adrenoceptor antagonists and their interactions with ethanol in tests of locomotion, exploration and anxiety in mice

Central norepinephrine transmission is required for stress-induced repetitive behavior in two rodent models of obsessive-compulsive disorder

RATIONALE

Obsessive-compulsive disorder (OCD) is characterized by repetitive behaviors exacerbated by stress. Many OCD patients do not respond to available pharmacotherapies, but neurosurgical ablation of the anterior cingulate cortex (ACC) can provide symptomatic relief. Although the ACC receives noradrenergic innervation and expresses adrenergic receptors (ARs), the involvement of norepinephrine (NE) in OCD has not been investigated.

OBJECTIVE

To determine the effects of genetic or pharmacological disruption of NE neurotransmission on marble burying (MB) and nestlet shredding (NS), two animal models of OCD.

METHODS

We assessed NE-deficient (Dbh -/-) mice and NE-competent (Dbh +/-) controls in MB and NS tasks. We also measured the effects of anti-adrenergic drugs on NS and MB in control mice and the effects of pharmacological restoration of central NE in Dbh -/- mice. Finally, we compared c-fos induction in the locus coeruleus (LC) and ACC of Dbh -/- and control mice following both tasks.

RESULTS

Dbh -/- mice virtually lacked MB and NS behaviors seen in control mice but did not differ in the elevated zero maze (EZM) model of general anxiety-like behavior. Pharmacological restoration of central NE synthesis in Dbh -/- mice completely rescued NS behavior, while NS and MB were suppressed in control mice by anti-adrenergic drugs. Expression of c-fos in the ACC was attenuated in Dbh -/- mice after MB and NS.

CONCLUSION

These findings support a role for NE transmission to the ACC in the expression of stress-induced compulsive behaviors and suggest further evaluation of anti-adrenergic drugs for OCD is warranted.

Noradrenergic targets for the treatment of alcohol use disorder

The role of norepinephrine (NE) in the development of alcohol use disorder (AUD) has been studied over the past several decades. However, the NE system has been largely ignored for many years as a potential target for medication development for AUD. More recently, preclinical and clinical studies have demonstrated the potential value of targeting NE signaling for developing new pharmacological treatments for AUD. This review contributes to a special issue of Psychopharmacology focused on promising targets for alcohol addiction. Specifically, this review coalesces preclinical and clinical neuroscience that re-evaluate the noradrenergic system, and in particular the alpha-1 receptor, as a potential target for AUD.

Effects of idazoxan on alcohol pharmacokinetics and intoxication: a preliminary human laboratory study

BACKGROUND

Preliminary basic and human studies suggest that the α2 -adrenergic antagonist idazoxan may represent a novel medication for alcohol dependence. The goal of this study was to evaluate the safety and tolerability of the co-administration of idazoxan with alcohol and explore whether pharmacokinetics (PK) and biobehavioral mechanisms of idazoxan may alter alcohol's effects.

METHODS

This was a preliminary double-blind, single-dose, placebo-controlled, crossover, randomized human laboratory study. Ten social drinkers were dosed, in 2 different alcohol challenge studies (ACS), with a single oral dose of idazoxan (40 mg) or placebo, followed by a fixed alcohol dose 60 minutes later. Participants returned after a 1-week washout, and they were crossed over to the opposite medication condition.

RESULTS

There were no significant differences in adverse events between idazoxan and placebo. Moreover, during the ACS paradigm, 40 mg idazoxan was well tolerated with no significant autonomic effects compared to placebo; idazoxan reduced the peak blood alcohol level (p < 0.01) and time to peak (p < 0.05) compared to placebo. A PK/pharmacodynamic model aligned the biobehavioral effects, demonstrating that the co-administration of 40 mg idazoxan with alcohol decreased alcohol-related stimulation (p < 0.05) and increased alcohol-related sedation (p < 0.05).

CONCLUSIONS

This study supports the safety and tolerability of 40 mg idazoxan when co-administered with alcohol. Additionally, this study suggests that idazoxan may alter the biphasic effects of alcohol by decreasing stimulation and increasing sedation. These findings have implications for further investigation of using idazoxan as a probe to develop potential novel medications to treat alcoholic patients.

Agmatine, an endogenous imidazoline receptor ligand modulates ethanol anxiolysis and withdrawal anxiety in rats

Present study investigated the role of agmatine in ethanol-induced anxiolysis and withdrawal anxiety using elevated plus maze (EPM) test in rats. The anxiolytic-like effect of ethanol was potentiated by pretreatment with imidazoline I(1)/I(2) receptor agonist agmatine (10-20 mg/kg, i.p.), imidazoline I(1) receptor agonists, moxonidine (0.25 mg/kg, i.p.) and clonidine (0.015 mg/kg, i.p.), imidazoline I(2) receptor agonist, 2-BFI (5 mg/kg, i.p.) as well as by the drugs known to increase endogenous agmatine levels in brain viz., L-arginine, an agmatine biosynthetic precursor (100 microg/rat, i.c.v.), ornithine decarboxylase inhibitor, DFMO (125 microg/rat, i.c.v.), diamine oxidase inhibitor, aminoguanidine (65 microg/rat, i.c.v.) and agmatinase inhibitor, arcaine (50 microg/rat, i.c.v.). Conversely, prior administration of I(1) receptor antagonist, efaroxan (1 mg/kg, i.p.), I(2) receptor antagonist, idazoxan (0.25mg/kg, i.p.) and arginine decarboxylase inhibitor, D-arginine (100 microg/rat, i.c.v.) blocked the anxiolytic-like effect of ethanol. Moreover, ethanol withdrawal anxiety was markedly attenuated by agmatine (10-20 mg/kg, i.p.), moxonidine (0.25 mg/kg, i.p.), clonidine (0.015 mg/kg, i.p.), 2-BFI (5 mg/kg, i.p.), L-arginine (100 microg/rat, i.c.v.), DFMO (125 microg/rat, i.c.v.), aminoguanidine (65 microg/rat, i.c.v.) and arcaine (50 microg/rat, i.c.v.). The anti-anxiety effect of agmatine in ethanol-withdrawn rats was completely blocked by efaroxan (1 mg/kg, i.p.) and idazoxan (0.25 mg/kg, i.p.). These results suggest that agmatine and imidazoline receptor system may be implicated in ethanol-induced anxiolysis and withdrawal anxiety and strongly support further investigation of agmatine in ethanol dependence mechanism. The data also project agmatine as a potential therapeutic target in overcoming alcohol withdrawal symptoms such as anxiety.

Pharmacological properties, central nervous system effects, and potential therapeutic applications of atipamezole, a selective alpha2-adrenoceptor antagonist

Atipamezole is an alpha2-adrenoceptor antagonist with an imidazole structure. Receptor binding studies indicate that its affinity for alpha2-adrenoceptors and its alpha2/alpha1 selectivity ratio are considerably higher than those of yohimbine, the prototype alpha2-adrenoceptor antagonist. Atipamezole is not selective for subtypes of alpha2-adrenoceptors. Unlike many other alpha2-adrenoceptor antagonists, it has negligible affinity for 5-HT1A and I2 binding sites. Atipamezole is rapidly absorbed and distributed from the periphery to the central nervous system. In humans, atipamezole at doses up to 30 mg/subject produced no cardiovascular or subjective side effects, while at a high dose (100 mg/subject) it produced subjective symptoms, such as motor restlessness, and an increase in blood pressure. Atipamezole rapidly reverses sedation/anesthesia induced by alpha2-adrenoceptor agonists. Due to this property, atipamezole is commonly used by veterinarians to awaken animals from sedation/anesthesia induced by alpha2-adrenoceptor agonists alone or in combination with various anesthetics. Atipamezole increased sexual activity in rats and monkeys. In animals with sustained nociception, atipamezole increased pain-related responses by blocking the noradrenergic feedback inhibition of pain. In tests assessing cognitive functions, atipamezole at low doses has beneficial effects on alertness, selective attention, planning, learning, and recall in experimental animals, but not necessarily on short-term working memory. At higher doses atipamezole impaired performance in tests of cognitive functions, probably due to noradrenergic overactivity. Recent experimental animal studies suggest that atipamezole might have beneficial effects in the recovery from brain damage and might potentiate the anti-Parkinsonian effects of dopaminergic drugs. In phase I studies atipamezole has been well tolerated by human subjects.

Pharmacological treatment of alcoholism

1. Pharmacological treatments are effective as part of a treatment plan that includes substantial education, psychological therapy and social support. This paper reviews recent literature on animal models of and treatment for alcohol abuse under seven categories: agents to block craving or reduce alcohol intake, agents to induce aversion to alcohol, agents to treat acute alcohol withdrawal, agents to treat protracted alcohol withdrawal, agents to diminish drinking by treating associated psychiatric pathology, agents to decrease drinking by treating associated drug abuse, and agents to induce sobriety in intoxicated individuals. 2. The benzodiazepines provide safe and effective treatment for detoxification, although current research focuses on finding drugs with a smaller likelihood of dependence. As yet, there are no drugs that effectively reverse the intoxicating effects of alcohol. 3. Currently, only two major groups of drugs that are relatively safe have shown any effect at reducing alcohol consumption: aversives such as disulfiram, and opioid antagonists such as naltrexone. 4. Finally, it is important to customize therapy for each patient rather than putting everyone through a standard treatment plan, especially in regards to the use of antidepressant or antipsychotic medications. Tailoring the program to the patient's needs dramatically improves the outcome of therapy and reduces the risk of adverse effects.

Comparative analysis of anxiety-like behavior in partition and plus-maze tests after agonistic interactions in mice

The behavior of C57BL/6J male mice with experience of repeated victories (winners) or defeats (losers) in daily agonistic interactions, was examined in the plus-maze and partition tests. The latter procedure assesses the reactivity of mice to another conspecific in the neighboring compartment of a common cage, communicative behavior or level of sociability. The behavior of mice after 10 days (T10) and 20 days (T20) of agonistic confrontations, as well as in controls (5 days of individual housing) was analyzed. Significant differences were found between T10 and T20 losers and controls in both tests. In the partition test, a decrease in the number of approaches and total and average time spent near the partition was found in T10 and, more pronounced, in T20 losers. In the plus-maze, losers showed fewer open and total entries than controls. Moreover, rarely did they pass from one enclosed arm to another, and also showed a decreased number of 'peepings' from enclosed arms. Percentage of open time did not differ significantly in losers compared to controls. It is suggested that the level of losers' sociability, estimated as low by the partition test, can include anxiety as a component, which is confirmed, at least partly, by some parameters of the plus-maze test. There were no differences in the partition or plus-maze tests between T10 winners and controls. However, all parameters of partition behavior were significantly different between T20 winners and controls. In the plus-maze, similar to losers, T20 winners displayed fewer open arm entries, number of "peepings,' and passages than controls. It was concluded that parameters of the partition and plus-maze tests correlate in mice with the alternative experience of agonistic confrontations, positive or negative. A combination of these two tests may be used for estimation of developing anxiety in mice.

Anxiolytic-like effects of yohimbine in the murine plus-maze: strain independence and evidence against alpha 2-adrenoceptor mediation

The influence of alpha 2-adrenoceptor antagonists in animal models of anxiety is quite inconsistent, with results spanning the full range of effect from anxiogenesis to anxiolysis. In the present study, an ethological technique was used to examine the effects of yohimbine (0.5-4.0 mg/kg) on plus-maze behaviour in DBA/2 mice. Results indicated significant anxiolytic-like effects on standard spatiotemporal measures at 2.0-4.0 mg/kg, and on risk assessment measures across the entire dose range. Full-scale follow-up studies with T1 and BALB/c strains confirmed that this action of yohimbine in the murine plus-maze is not peculiar to DBA/2 mice. The more selective alpha 2-adrenoceptor antagonist, idazoxan (0.63-5.0 mg/kg), exerted much weaker behavioural effects in the maze while the alpha 2-adrenoceptor agonist, clonidine (0.01-0.1 mg/kg), produced a profile consistent with non-specific behavioural disruption. Data are discussed in relation to the possible involvement of 5-HT1A receptor mechanisms in the observed anxiolytic-like effects of yohimbine in the murine plus-maze.

Noradrenergic response to acute ethanol administration in healthy subjects: comparison with intravenous yohimbine

The effects of oral administration of ethanol [1.1 ml/kg 95% ethanol administered as a 20% (by volume) solution] and intravenous administration of the alpha 2 adrenergic receptor antagonist yohimbine hydrochloride (0.4 mg/kg), alone and in combination, were compared using a double-blind, placebo-controlled design. Twelve healthy subjects completed 4 test days during which drug effects on subjective measures of intoxication and anxiety, plasma levels of the norepinephrine (NE) metabolite 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) and cortisol, and cardiovascular indices were assessed. Acutely administered oral ethanol significantly increased the subjective measures of intoxication and anxiety, plasma MHPG, and sitting systolic blood pressure compared with placebo. Intravenous yohimbine significantly increased subjective measures of intoxication and anxiety, plasma MHPG and cortisol, and blood pressure relative to placebo. The ethanol-induced increase in plasma MHPG was significantly greater than that following yohimbine, whereas yohimbine resulted in significantly greater increases in anxiety, plasma cortisol, and blood pressure measurements than ethanol. The combined administration of ethanol and yohimbine had a clear additive effect of increasing the severity of acute intoxication compared with ethanol or yohimbine alone, and resulted in a significantly greater plasma MHPG response compared with either drug given alone. Although the pharmacokinetic effects of ethanol administration on NE metabolism must be considered, these findings suggest that the intoxicating and anxiogenic effects of acute ethanol administration may be associated with increased NE turnover, as measured by plasma MHPG, in healthy human subjects. In addition, these results indicate that ethanol and yohimbine may act additively to increase ethanol intoxication and that they may increase NE turnover through different physiological mechanisms.

The effects of ethanol in combination with the alpha 2-adrenoceptor agonist dexmedetomidine and the alpha 2-adrenoceptor antagonist atipamezole on brain monoamine metabolites and motor performance of mice

The time course of the effects of ethanol alone and in combination with the selective alpha 2-adrenoceptor agonist dexmedetomidine and the alpha-adrenoceptor antagonist atipamezole was studied in NIH-Swiss mice. Core body temperature, rotarod performance, motility and changes in the noradrenaline, dopamine, and 5-hydroxytryptamine (5-HT) metabolite contents of different brain parts (limbic forebrain, striatum, lower brainstem, the rest of the forebrain + midbrain and hypothalamus) were measured. Atipamezole (3 mg/kg) attenuated the hypothermia induced by either ethanol (3 g/kg) alone or ethanol in combination with dexmedetomidine (0.3 mg/kg). Atipamezole shortened the duration of the ethanol-impaired and ethanol + dexmedetomidine-impaired rotarod performance. Further, atipamezole prevented the decreased motility due to the combined treatment with ethanol and dexmedetomidine. Ethanol increased 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) values. Dexmedetomidine alone decreased MHPG and 5-hydroxyindoleacetic acid (5-HIAA) concentrations and increased DOPAC and HVA values. Dexmedetomidine combined with ethanol resulted in a further increase in DOPAC and HVA values. Pharmacokinetic parameters did not contribute to this antagonism of ethanol's effects by atipamezole, nor did the antagonism observed in rotarod performance or hypothermia seem to correlate with the changes seen in the brain noradrenaline and dopamine or 5-HT metabolism. In conclusion, these findings suggest that several ethanol effects are not mediated via direct activation of alpha 2-adrenoceptors, even though some of ethanol's behavioral and physiological effects may be antagonized by coadministration of alpha 2-adrenoceptor antagonists.

Yohimbine can induce ethanol tolerance in an in vitro preparation of rat locus coeruleus

Noradrenergic neurons have been implicated in the development of ethanol dependence and tolerance. Moreover, the development of an hyposensitivity of alpha 2 adrenoceptors has been postulated during long-term exposition to ethanol. In order to test the putative role of alpha 2 receptors in ethanol intoxication, we have studied the interaction between ethanol and yohimbine, an alpha 2 antagonist, on the spontaneous firing rate of rat locus coeruleus (LC) in an in vitro slice model. The spikes from single neurons were recorded by glass microelectrodes. Ethanol at 100 mM, a concentration that parallels the behavioral effects in the human and in the animals, inhibits the firing activity of some LC cells. This inhibition was quickly reversed after stopping the ethanol perfusion and was observed for each further administration. However, if yohimbine (20 microM) was simultaneously perfused, the ethanol-induced inhibition was rapidly antagonized. This effect is reversible after long time washout of yohimbine. This suggests that alpha 2 adrenoceptors could be implicated in the inhibitory effect of ethanol on LC noradrenergic neurons and perhaps in the development of tolerance. However, other hypotheses are discussed, because yohimbine can also antagonize other types of receptors.

Effects of atipamezole, a novel alpha 2-adrenoceptor antagonist, in open-field, plus-maze, two compartment exploratory, and forced swimming tests in the rat

The behavioral effects of atipamezole (0.5-4.5 mg/kg), a new and highly selective alpha 2-adrenoceptor antagonist, were studied in four behavioral models: open-field, elevated plus-maze, two compartment exploratory test and forced swimming test. Atipamezole (1.5 and 4.5 mg/kg) produced a dose-dependent suppression of locomotor activity in the open field test. In the two compartment exploratory test, the same doses of atipamezole decreased locomotor activity in a 5 min test but not in a 10 min test. The numbers of transitions between the compartments were not significantly affected by atipamezole. Doses of 0.5-4.5 mg/kg did not significantly change the time spent in the open arms or the total number of arm entries in the plus-maze, and doses of 1.5 and 4.5 mg/kg decreased defecation marginally. Vocalization during the forced swimming test was increased by atipamezole (1.5 mg/kg) but the duration of immobility was not increased over the dose range (0.5-1.5 mg/kg) of atipamezole used. Our results suggest that, in the rat, atipamezole decreases motor activity in the early phase of the exploration of new surroundings. In the doses used, atipamezole may suppress defecation and increase vocalization in rats.

Oxytocin attenuates tolerance not only to the hypothermic but also to the myorelaxant and akinesic effects of ethanol in mice

Inhibition of ethanol tolerance by oxytocin has been demonstrated previously using the hypothermic effect only. The purpose of the present experiment was to investigate the effect of oxytocin on the development of tolerance to ethanol-induced hypothermia, myorelaxation and akinesia in mice. Four groups of mice received daily intraperitoneal injections of saline or oxytocin (0.005 mg) plus saline or ethanol (2 g/kg). The peptide was administered 2 hours before ethanol. For five consecutive days, temperature measurements were performed 20 minutes before and after ethanol injection. Myorelaxation and akinesia were evaluated following the second temperature measure. Oxytocin pretreatment, which had no intrinsic effects, resulted in a robust selective attenuation of tolerance to ethanol-induced hypothermia, myorelaxation and akinesia. These results suggest that the mechanisms for peptide modulation are common to these three typical effects of ethanol.

Interactions of intracerebroventricular pertussis toxin treatment with the ataxic and hypothermic effects of ethanol

Pretreatment with pertussis toxin (0.5 and 1.0 microgram/animal, i.c.v., seven days prior to testing) reversed the reduction in locomotor activity in the holeboard test caused by administration of the alpha 2-adrenoceptor agonist, medetomidine (0.1 mg/kg, i.p.). Intrinsic behavioral effects of pertussis toxin treatment were also observed, these included a reduction in exploratory head-dipping and an increase in locomotor activity. These doses of pertussis toxin also reduced the ataxia induced by a 2.4 g/kg dose of ethanol. Pertussis toxin treated animals also exhibited a diminished hypothermic response to ethanol (2 g/kg), although the pertussis toxin treated animals had lower body temperatures prior to ethanol administration compared to sham treated animals. Neither the behavioral effect of pertussis holotoxin in the holeboard nor its effects on reversing medetomidine hypolocomotion or ethanol-induced ataxia were seen following administration of the binding oligomer of pertussis toxin which binds to the cell membrane but does not possess the enzymatically active subunit. These findings implicate mechanisms involving pertussis toxin sensitive G-proteins in modulating some behavioral and physiological effects of ethanol.

Differential effects of catecholamine antagonists on ethanol-induced excitation in mice

Catecholamine antagonists were assessed for their effects on ethanol-induced motor excitation. Motor excitation was measured in male Swiss-Webster mice using an open-field apparatus. Mice were treated with several doses of ethanol and at each dose, mice were pretreated with pimozide, a dopamine D2 antagonist, Schering 23390, a dopamine D1 antagonist, phenoxybenzamine, a noradrenergic alpha-1 antagonist, or yohimbine, a noradrenergic alpha-2 antagonist. Each mouse was subjected to only one dose regimen, and all injections were given IP. Ethanol produced an increase in locomotor activity. The degree to which pimozide attenuated ethanol excitation decreased with increasing ethanol dosage. At the highest dose of ethanol, pimozide increased ethanol excitation. Schering 23390 attenuated ethanol-induced excitation only at doses which affected motor activity per se. Phenoxybenzamine produced a dose-dependent reduction in ethanol excitation. Yohimbine had its greatest effects at the medium dose (4.0 mg/kg). These observations seem to indicate a role for both the dopamine D2 receptor and the noradrenergic alpha-1 receptor in ethanol-induced motor excitation.

Ethologically-based animal models of anxiety disorders

An overview of ethologically-based animal models suitable for investigating the pharmacological treatment of anxiety disorders is presented. The DSM-IIIR classification provides a framework for the discussion. The limitations of the models in current use are considered. It is suggested that there is a need for a greater emphasis on animal models of anxiety with an etiological basis.

Behavioral effects of the inhibitors of phenylethanolamine-N-methyltransferase, LY 78335 and LY 134046, and their interactions with ethanol

The centrally active inhibitors of phenylethanolamine-N-methyltransferase (PNMT), LY 78335 and LY 134046, were investigated both alone and in combination with ethanol (2 g/kg) in a holeboard test of directed exploration and locomotor activity. Both PNMT inhibitors showed dose-related reductions in exploratory head-dipping but were without effect on locomotor activity. In combination with ethanol both PNMT inhibitors tended to attenuate the ethanol-induced reductions in exploratory head-dipping but did not effect ethanol's locomotor stimulant properties. LY 134046 showed neither an anxiolytic nor an anxiogenic profile in the plus-maze test of anxiety, nor did it alter the anxiolytic effects of either 1.2 g/kg or 2 g/kg ethanol. LY 134046 did, however, attenuate the ataxic effects of a 2.4 g/kg dose of ethanol. These results may suggest a role for adrenaline synthesis in some, but not all, of the behavioral effects of ethanol.

Idazoxan increases rough-and-tumble play, activity and exploration in juvenile rats

The effects of idazoxan, an alpha-2 noradrenergic antagonist, on play and open field behavior were assessed in juvenile rats. Play was assessed in two separate paradigms. Initially, juvenile rats were housed individually and given a daily 5 min opportunity to play with a responsive partner. Idazoxan (1-8 mg/kg) increased pinning, an indicator variable of play, but did not affect the frequency of dorsal contacts, an index of play solicitation. When rats were tested in a separate test for play solicitation using an unresponsive play partner, idazoxan increased all three measures of play solicitation. Idazoxan increased activity and exploration when rats were tested in an open field, suggesting that the effects of idazoxan on play may be due to an increase in behavioral arousal and/or attention. These data are consistent with a modulatory role for norepinephrine in the control of behavior.

Attenuation of hypothermic effects of ethanol by alpha 2-adrenoceptor blockers

Effects of selective alpha 2-adrenoceptor antagonists, atipamezole and idazoxan, on ethanol-induced hypothermia were investigated in mice. Ethanol significantly reduced (P less than 0.001) core temperature whilst both alpha 2-adrenoceptor antagonists were without effect when administered alone. However, both the 1 and 3 mg/kg doses of atipamezole significantly (P less than 0.05) attenuated the ethanol-induced reduction in body temperature 20 and 40 min after administration. The 3 mg/kg dose of idazoxan (but not the 1 mg/kg dose) also significantly (P less than 0.05) attenuated ethanol's hypothermic effect 20 min after administration but this effect was not statistically significant at 40 min. In a subsequent experiment using lower doses of atipamezole (0.03-1.0 mg/kg) the attenuation of ethanol-induced hypothermia caused by atipamezole was found to be dose-related. The effect of the benzodiazepine inverse agonist Ro 15-4513 on ethanol-induced hypothermia was also investigated. This compound possessed an intrinsic hypothermic action but neither attenuated nor enhanced the hypothermic effect of ethanol. These results suggest that alpha 2-adrenoceptor can, at least partially, modulate the hypothermic effects of ethanol.

Attenuation of the effects of ethanol on social behavior by alpha 2-adrenoceptor antagonists

In a social behavior test in mice ethanol (2 g/kg) significantly reduces the time spent in social interaction and increases locomotor activity. The relatively selective alpha 2-adrenoceptor antagonists atipamezole and idazoxan alone have no significant effect on either social interaction or locomotor activity in this test. However, when coadministered with 2 g/kg ethanol, atipamezole (0.3-3.0 mg/kg) significantly attenuated the ethanol-induced reduction in the time spent in social interaction without any effect on ethanol's locomotor stimulant action. Idazoxan (0.3-1.0 mg/kg) also showed a trend towards reversing the reduction in the time spent in social interaction although this was accompanied by a significant attenuation of the locomotor stimulant effect of ethanol. The results indicate that alpha 2-adrenoceptors may modulate ethanol's effects on social interaction in mice.

Antagonizing the behavioural effects of drugs: a discussion with specific reference to benzodiazepines and alcohol

It can be extremely difficult to interpret the results of experiments in which a treatment is found to antagonize the behavioural effects of a drug. This article discusses strategies that can be used to help identify the nature of the antagonism and examines what such experiments tell us about the mechanisms underlying the drug's behavioural effects. Examples are taken from research with both benzodiazepines and ethanol. It is suggested that behavioural studies using different strategies to reduce the effects of a drug will further enhance our understanding of the mechanisms mediating the drug's effects. Such studies will include comparisons between the effects of chronic drug exposure (tolerance studies), genetic manipulations, and pharmacological treatments.