Mediation of acute ethanol-induced motor disturbances by cerebellar adenosine in rats

Ethanol-Induced Cerebellar Ataxia: Cellular and Molecular Mechanisms

The cerebellum is an important target of ethanol toxicity given that cerebellar ataxia is the most consistent physical manifestation of acute ethanol consumption. Despite the significance of the cerebellum in ethanol-induced cerebellar ataxia (EICA), the cellular and molecular mechanisms underlying EICA are incompletely understood. However, two important findings have shed greater light on this phenomenon. First, ethanol-induced blockade of cerebellar adenosine uptake in rodent models points to a role for adenosinergic A1 modulation of EICA. Second, the consistent observation that intracerebellar administration of nicotine in mice leads to antagonism of EICA provides evidence for a critical role of cerebellar nitric oxide (NO) in EICA reversal. Based on these two important findings, this review discusses the potential molecular events at two key synaptic sites (mossy fiber-granule cell-Golgi cell (MGG synaptic site) and granule cell parallel fiber-Purkinje cell (GPP synaptic site) that lead to EICA. Specifically, ethanol-induced neuronal NOS inhibition at the MGG synaptic site acts as a critical trigger for Golgi cell activation which leads to granule cell deafferentation. Concurrently, ethanol-induced inhibition of adenosine uptake at the GPP synaptic site produces adenosine accumulation which decreases glutamate release and leads to the profound activation of Purkinje cells (PCs). These molecular events at the MGG and GPP synaptic sites are mutually reinforcing and lead to cerebellar dysfunction, decreased excitatory output of deep cerebellar nuclei, and EICA. The critical importance of PCs as the sole output of the cerebellar cortex suggests normalization of PC function could have important therapeutic implications.

Chronic sleep restriction disrupts sleep homeostasis and behavioral sensitivity to alcohol by reducing the extracellular accumulation of adenosine

Sleep impairments are comorbid with a variety of neurological and psychiatric disorders including depression, epilepsy, and alcohol abuse. Despite the prevalence of these disorders, the cellular mechanisms underlying the interaction between sleep disruption and behavior remain poorly understood. In this study, the impact of chronic sleep loss on sleep homeostasis was examined in C57BL/6J mice following 3 d of sleep restriction. The electroencephalographic power of slow-wave activity (SWA; 0.5-4 Hz) in nonrapid eye movement (NREM) sleep and adenosine tone were measured during and after sleep restriction, and following subsequent acute sleep deprivation. During the first day of sleep restriction, SWA and adenosine tone increased, indicating a homeostatic response to sleep loss. On subsequent days, SWA declined, and this was accompanied by a corresponding reduction in adenosine tone caused by a loss of one source of extracellular adenosine. Furthermore, the response to acute sleep deprivation (6 h) was significantly attenuated in sleep-restricted mice. These effects were long-lasting with reduced SWA and adenosine tone persisting for at least 2 weeks. To investigate the behavioral consequences of chronic sleep restriction, sensitivity to the motor-impairing effects of alcohol was also examined. Sleep-restricted mice were significantly less sensitive to alcohol when tested 24 h after sleep restriction, an effect that persisted for 4 weeks. Intracerebroventricular infusion of an adenosine A1 receptor antagonist produced a similar decrease in sensitivity to alcohol. These results suggest that chronic sleep restriction induces a sustained impairment in adenosine-regulated sleep homeostasis and consequentially impacts the response to alcohol.

Acetate as an active metabolite of ethanol: studies of locomotion, loss of righting reflex, and anxiety in rodents

It has been postulated that a number of the central effects of ethanol are mediated via ethanol metabolites: acetaldehyde and acetate. Ethanol is known to produce a large variety of behavioral actions such anxiolysis, narcosis, and modulation of locomotion. Acetaldehyde contributes to some of those effects although the contribution of acetate is less known. In the present studies, rats and mice were used to assess the acute and chronic effects of acetate after central or peripheral administration. Male Sprague-Dawley rats were used for the comparison between central (intraventricular, ICV) and peripheral (intraperitoneal, IP) administration of acute doses of acetate on locomotion. CD1 male mice were used to study acute IP effects of acetate on locomotion, and also the effects of chronic oral consumption of acetate (0, 500, or 1000 mg/l, during 7, 15, 30, or 60 days) on ethanol- (1.0, 2.0, 4.0, or 4.5 g/kg, IP) induced locomotion, anxiolysis, and loss of righting reflex (LORR). In rats, ICV acetate (0.7–2.8 μmoles) reduced spontaneous locomotion at doses that, in the case of ethanol and acetaldehyde, had previously been shown to stimulate locomotion. Peripheral acute administration of acetate also suppressed locomotion in rats (25–100 mg/kg), but not in mice. In addition, although chronic administration of acetate during 15 days did not have an effect on spontaneous locomotion in an open field, it blocked ethanol-induced locomotion. However, ethanol-induced anxiolysis was not affected by chronic administration of acetate. Chronic consumption of acetate (up to 60 days) did not have an effect on latency to, or duration of LORR induced by ethanol, but significantly increased the number of mice that did not achieve LORR. The present work provides new evidence supporting the hypothesis that acetate should be considered a centrally-active metabolite of ethanol that contributes to some behavioral effects of this alcohol, such as motor suppression.

Adenosine A2A receptors and their role in drug addiction

The specific events between initial presumably manageable drug intake and the development of a drug- addicted state are not yet known. Drugs of abuse have varying mechanisms of action that create a complex pattern of behaviour related to drug consumption, drug-seeking, withdrawal and relapse. The neuromodulator adenosine has been shown to play a role in reward-related behaviour, both as an independent mediator and via interactions of adenosine receptors with other receptors. Adenosine levels are elevated upon exposure to drugs of abuse and adenosine A2A receptors are enriched in brain nuclei known for their involvement in the processing of drug-related reinforcement processing. A2A receptors are found in receptor clusters with dopamine and glutamate receptors. A2A receptors are thus ideally situated to influence the signalling of neurotransmitters relevant in the neuronal responses and plasticity that underlie the development of drug taking and drug-seeking behaviour. In this review, we present evidence for the role of adenosine and A2A receptors in drug addiction, thereby providing support for current efforts aimed at developing drug therapies to combat substance abuse that target adenosine signalling via A2A receptors.

Acute functional tolerance to ethanol mediated by protein kinase Cepsilon

A low level of response to ethanol is associated with increased risk of alcoholism. A major determinant of the level of response is the capacity to develop acute functional tolerance (AFT) to ethanol during a single drinking session. Mice lacking protein kinase C epsilon (PKCepsilon) show increased signs of ethanol intoxication and reduced ethanol self-administration. Here, we report that AFT to the motor-impairing effects of ethanol is reduced in PKCepsilon (-/-) mice when compared with wild-type littermates. In wild-type mice, in vivo ethanol exposure produced AFT that was accompanied by increased phosphorylation of PKCepsilon and resistance of GABA(A) receptors to ethanol. In contrast, in PKCepsilon (-/-) mice, GABA(A) receptor sensitivity to ethanol was unaltered by acute in vivo ethanol exposure. Both PKCepsilon (-/-) and PKCepsilon (+/+) mice developed robust chronic tolerance to ethanol, but the presence of chronic tolerance did not change ethanol preference drinking. These findings suggest that ethanol activates a PKCepsilon signaling pathway that contributes to GABA(A) receptor resistance to ethanol and to AFT. AFT can be genetically dissociated from chronic tolerance, which is not regulated by PKCepsilon and does not alter PKCepsilon modulation of ethanol preference.

Adenosine A1 receptors modulate the anxiolytic-like effect of ethanol in the elevated plus-maze in mice

The anxiolytic property of ethanol is generally accepted to be an important motivational factor for its consumption and the development of alcohol dependence. Recent studies suggest that adenosine receptors mediate important actions of ethanol, such as motor incoordination and hypnotic effects. In addition, several lines of evidence support the involvement of adenosine in anxiety. The aim of the present study was to evaluate the role of adenosine receptors in the anxiolytic-like effect of ethanol in mice. The effects of acute administration of the adenosine receptor antagonists caffeine (nonselective), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, adenosine A1 receptor antagonist) and 4-(2-[7-amino-2-[2-furyl][1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol (ZM241385, adenosine A(2A) receptor antagonist), together with the adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA), and their interaction with ethanol in the elevated plus-maze test in mice were studied. The highest doses of caffeine (30.0 mg/kg, i.p.) and DPCPX (6.0 mg/kg, i.p.) produced an anxiogenic-like effect, while CCPA administration (0.25 mg/kg, i.p.) showed an anxiolytic-like activity. The prior administration of "non-anxiogenic" doses of caffeine (10.0 mg/kg, i.p.) and DPCPX (3.0 mg/kg, i.p.), but not ZM241385 (1.0 mg/kg, i.p.), significantly reduced the anxiolytic-like effect of ethanol (1.2 g/kg, i.p.). Moreover, anxiolytic-like response was observed by the co-administration of "non-anxiolytic" doses of CCPA (0.125 mg/kg) and ethanol (0.6 g/kg). These results reinforce the involvement of adenosine in anxiety and suggest that the activation of adenosine A1 receptors, but not adenosine A(2A) receptors, mediate the anxiolytic-like effect induced by ethanol in mice.

Acute ethanol-induced adenosine diphosphate ribosylation regulates the functional activity of rat striatal pertussis toxin-sensitive g proteins

BACKGROUND

We demonstrated previously that striatal adenosine modulates ethanol-induced motor incoordination (EIMI) via adenosine A1 receptors coupled to pertussis toxin (PT)-sensitive G protein and adenylyl cyclase-cyclic adenosine monophosphate (cAMP). Additionally, intrastriatal (IST) PT antagonizes EIMI and its potentiation by the adenosine A1 agonist N-cyclohexyladenosine; it also inhibits cAMP concentration.

METHODS

Guide cannulas were stereotaxically implanted for IST pretreatment with PT followed 5 days later by IST of N-cyclohexyladenosine and intraperitoneal ethanol. The adenosine diphosphate (ADP) ribosylation reaction involved PT-catalyzed [P]nicotinamide adenine dinucleotide (NAD) labeling of rat striatal membranes. Antagonism of EIMI (Rotorod method) after IST microinfusion of PT was investigated to determine whether it was due to a decrease in the functional activity of G proteins due to ADP ribosylation of the Gialpha subunit caused it.

RESULTS

Striatal membranes from IST PT (0.5 microg)-treated animals exhibited significantly attenuated (up to 90%) in vitro ADP ribosylation with [P]NAD. Striatal membranes from animals injected with ethanol (1.5 g/kg intraperitoneally) exhibited statistically significant increase (11%) in in vitro ADP ribosylation. Similarly, ethanol (50 mM) added to striatal membranes from untreated animals produced significant stimulation of in vitro ADP ribosylation. The decrease in the functional activity of G proteins due to ADP ribosylation of the Gialpha subunit after IST PT was functionally correlated with marked attenuation in EIMI, as observed previously. This finding suggests a blockade of functional activity of PT-sensitive striatal Gi/Go proteins (i.e., fewer available sites for labeled NAD incorporation). The in vivo ethanol results indicate that it must have caused an increase in the ribosylation capacity of Gialpha in vivo (i.e., increased Gi activity). Increased ADP ribosylation by in vitro ethanol increases Gi/Go activity, consistent with EIMI, as previously reported.

CONCLUSIONS

The results provide biochemical evidence of an ethanol-induced increase in ADP ribosylation of Gialpha causing a decrease in the functional activity of G proteins coupled via Gi/Go to adenylyl cyclase-cAMP. These results confirm the previously observed antagonism of EIMI by PT (IST).

Adenosine A1 Receptor Blockade Mimics Caffeine's Attenuation of Ethanol-Induced Motor Incoordination

The effects of co-administration of caffeine and ethanol were assessed on the motor coordination of rats on the accelerating rotarod (accelerod). Ethanol (2.5 g/kg, orally) decreased motor performance on the accelerod. Co-administration of caffeine (5 and 20 mg/kg, orally) dose-dependently attenuated this ethanol-induced deficit. Caffeine (20 mg/kg, orally) alone did not affect motor performance in the test. As caffeine is a non-selective adenosine receptor antagonist the ability of adenosine A(1) and A(2A) receptor blockade to attenuate ethanol-induced motor incoordination was determined. Pre-treatment with the adenosine A(1) receptor antagonist DPCPX (5 mg/kg, intraperitoneally) attenuated ethanol (2.5 g/kg, orally)-induced motor incoordination. By contrast, prior administration of the adenosine A(2A) selective antagonist SCH 58261 (10 mg/kg intraperitoneally) had no effect on the ethanol-induced motor deficit. These data demonstrate that adenosine A(1) receptor blockade mimics the inhibitory action of caffeine on ethanol-induced motor incorordination, and may contribute to the ability of caffeine to offset the acute intoxicating actions of ethanol.

The effects of adenosine ligands R-PIA and CPT on ethanol withdrawal

The potential anxiogenic or anxiolytic effects of R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA), an adenosine agonist, and 8-cyclopentyl-1,3,dimethylxanthine (CPT), an adenosine antagonist, were tested during chronic exposure to ethanol and to ethanol-induced withdrawal in rats. Effects on anxiety were measured by the elevated plus maze and dark-light box. Ethanol consumption and preference was tested in an additional experiment. In testing of elevated plus maze performance during withdrawal from ethanol, R-PIA produced no change in the anxiety-related behaviors of total arm entries and percent open arm entries, but produced a significant decrease in percent open arm time. CPT produced at least partial recovery from the anxiogenic effects of ethanol withdrawal on all three measures of elevated plus maze performance, although peak effects were seen at the intermediate dose of CPT (0.08 mg/kg) for total arm entries and percent open arm time. CPT also showed anxiolytic effects at low to intermediate doses (0.04, 0.08 mg/kg) in the dark-light box. CPT did not reduce the preference for ethanol over water or the total consumption of ethanol over a range of ethanol doses. In summary, the adenosine agonist, R-PIA, exacerbated the effects of ethanol withdrawal, whereas the adenosine antagonist, CPT, at least partially blocked the anxiogenic effects produced by ethanol withdrawal. These results suggest that adenosine antagonists, at least at some doses, may be useful for ameliorating the anxiogenic effects produced by ethanol withdrawal, although it does not appear useful for reducing consumption.

Rat striatal adenosinergic modulation of ethanol-induced motor impairment: possible role of striatal cyclic AMP

We have previously reported the involvement of the striatum in acute ethanol-induced motor incoordination and the striatal adenosinergic modulation of ethanol-induced motor incoordination through A1 receptor-mediated mechanism(s). The present study, a continuation of our previous work, was carried out to investigate the possible functional correlation between striatal cyclic AMP and ethanol-induced motor incoordination, and its modulation by striatal adenosine in Sprague-Dawley rats. Forskolin (0.1, 0.5 and 1.0 pmol), a known activator of adenylate cyclase, significantly attenuated ethanol-induced motor incoordination in a dose-dependent manner following its direct intrastriatal microinfusion. Forskolin also antagonized the accentuating effect of intrastriatal N6-cyclohexyladenosine on ethanol-induced motor incoordination. These results suggested that ethanol-induced motor incoordination might be functionally correlated to a decrease in the striatal cyclic AMP levels and that the striatal adenosine A1 receptors might modulate ethanol-induced motor incoordination through cyclic AMP signaling mechanism(s). Further support to this hypothesis was obtained by the actual measurement of the striatal cyclic AMP levels in the same experimental conditions as in motor coordination studies using high-performance liquid chromatography with fluoroscence detection. Regardless of the method (focused microwave irradiation, cervical dislocation or decapitation into a dry ice-ethanol mixture) used to kill the animals, a significant decrease in the striatal cyclic AMP levels was observed due to ethanol. Intrastriatal adenosine A1-selective agonist, N6-cyclohexyladenosine (24 ng), caused a further significant decrease in the striatal cyclic AMP levels in the ethanol- but not in the vehicle-treated animals. The further enhancement in the ethanol-induced decrease in the striatal cyclic AMP levels by intrastriatal N6-cyclohexyladenosine, therefore, functionally correlated with the observed potentiating effect of intrastriatal N6-cyclohexyladenosine on ethanol-induced motor incoordination. The effects of intrastriatal N6-cyclohexyladenosine+ethanol and of ethanol alone on the striatal cyclic AMP levels were blocked by intrastriatal pertussis toxin (500 ng) pretreatment, indicating the involvement of pertussis toxin-sensitive G-proteins (Gi, Go) and possibly of the adenosine A1 receptor coupled to the G-proteins in the striatum. Furthermore, ethanol alone significantly decreased the basal as well as the cyclic AMP-stimulated catalytic activities of the striatal cyclic AMP protein kinase, which were further reduced by intrastriatal N6-cyclohexyladenosine. The results of the present study therefore support an involvement of a cyclic AMP signaling pathway in the striatal adenosinergic modulation of ethanol-induced motor incoordination at the post-adenosine A1 receptor level.

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.

Adenosinergic modulation of ethanol-induced motor incoordination in the rat motor cortex

1. On going work in our laboratory has shown that adenosine modulates ethanol-induced motor incoordination (EIMI) when given systemically as well as directly into the cerebral ventricles, cerebellum and corpus striatum of the rat and/or mouse. 2. The objective of this study was to determine what effect adenosine agonists and antagonists would have within the rat motor cortex on EIMI. 3. The participation of the motor cortex in EIMI was suggested when microinfusion of the anti-ethanol compound, Ro15-4513, an inverse agonist of the benzodiazepine binding site, directly into the motor cortex significantly attenuated EIMI. Further, the adenosine agonists N6-cyclohexyladenosine (CHA) and 2-p-(2-carboxyethyl)-phenethylamino-5'-N-carboxaminoadenosine++ + hydrochloride (CGS-21680) significantly accentuated EIMI in a dose-related manner. The adenosine A1 receptor-selective agonist, CHA, appeared most potent in this modulatory effect when compared to the A2-selective agonist, CGS-21680. 4. The extent of diffusion of the adenosine drugs within the cortical tissue after their microinfusion was also checked by measuring the dispersion of microinfused [3H]CHA. The [3H]CHA dispersion study indirectly confirmed that the results of the present investigation were based on the effect of adenosine drugs within the motor cortex only. 5. Accentuation by the A1- and A2-selective adenosine agonists was significantly attenuated by the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) but not by the A2 receptor-selective antagonist 8-(3-chlorostyryl)caffeine (CSC) further suggesting modulation mainly by the A1-subtype. 6. Pretreatment of the motor cortex with pertussis toxin (PT) significantly reduced the capacity of both A1- and A2-selective adenosine agonists to accentuate EIMI suggesting the involvement of a PT-sensitive Gi/Go protein. 7. These data support earlier work which showed that adenosine modulates EIMI within the central nervous system (CNS), most likely via the A1 receptor, and moreover, extend that work by including the motor cortex as a brain area participating in the adenosinergic modulation of ethanol-induced motor impairment.

The striatal adenosinergic modulation of ethanol-induced motor incoordination in rats: possible role of chloride flux

Previous studies from our laboratory have provided strong evidence that brain adenosine modulates acute ethanol (i.p.)-induced motor incoordination (MI) through receptor mediated mechanism(s). Recently, we have reported the involvement of the striatum in ethanol-induced MI as well as the striatal adenosinergic modulation of the ethanol-induced motor deficit. The present study was thus designed to further characterize the modulatory effect of striatal adenosine on ethanol-induced MI and to look for its functional correlation with chloride flux within the rat striatum. Intrastriatal microinfusion of adenosine A1 receptor agonist N6-cyclohexyladenosine (CHA) and antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), significantly accentuated and attenuated, respectively, the motor incoordinating effect of ethanol while having no effect on the normal motor coordination in saline-treated control animals. These data confirmed the role of striatal adenosine in ethanol-induced MI. The selectivity of interactions between adenosine A1 agonist and antagonist and ethanol was further confirmed by the study in which neither intrastriatal CHA nor DPCPX significantly altered the MI induced by sodium pentobarbital. Previously, we have shown that intrastriatal Ro15-4513 not only significantly attenuated ethanol-induced MI but also blocked its accentuation by intrastriatal CHA. It is well known that Ro15-4513 antagonizes many, but not all, CNS effects of ethanol by blocking the ethanol potentiation of GABA-stimulated uptake of chloride. Therefore, experiments using striatal microsac preparations were carried out to investigate the possible modulation of chloride conductance by CHA and its relationship to ethanol. High concentrations of CHA (10 and 100 nM) increased the total chloride uptake by the striatal microsacs. Corresponding to the ethanol-adenosine interaction observed behaviorally, a much lower concentration (1 nM) of CHA, being ineffective itself, significantly enhanced the stimulatory action of ethanol on chloride uptake. This effect was blocked by either Ro15-4513 (100 nM) or DPCPX (10 nM). The modulatory effect of GABA and/or ethanol on chloride influx was also evaluated, and the results supported the appropriateness to use striatal microsac preparations in the present study. Overall, the data suggested a functional interaction between ethanol and striatal adenosine and further supported the hypothesis that striatal adenosine might, in part, modulate ethanol-induced MI through its effect on chloride conductance through chloride channels coupled to GABA-benzodiazepine receptor complex.

Adenosine A1 receptor antisense infused in striatum of rats: actions on alcohol-induced locomotor impairment, blood alcohol, and body temperature

Previous pharmacological studies show that adenosine receptors in the corpus striatum may be involved in locomotor coordination. The purpose of this investigation was to determine whether the adenosine A1 receptor subtype would alter the locomotor response due to incapacitating doses of alcohol. In these experiments, an antisense oligodeoxynucleotide (ODN) targeted to the adenosine A1 receptor was used to elucidate its possible role in locomotor function. After bilateral cannulation of the caudate nuclei of two strains of adult male rats, the animals were trained to remain on a rotorod for an entire 3-min interval. Then, a standard dose of 2.0 micrograms per 2.0 microliters of the A1 adenosine antisense (A1AS), dissolved in a pyrogen-free artificial cerebrospinal fluid (aCSF), was microinjected four times bilaterally into the caudate nuclei of the rats at successive 12-h intervals over 2 days. Three sets of controls were utilized: intragastric gavage with tap water alone: intragastric gavage of 3.5-4.0 g/kg 20% alcohol alone; and the aCSF vehicle alone microinjected identically in the caudate nuclei. The results showed that the intragastric administration of 20% alcohol in a dose of 3.5-4.0 g/kg caused a complete incapacitation of locomotor performance. Moreover, the A1AS injected in the striatum failed to alter significantly the action of alcohol in its impairment of the rats' ability to negotiate the rotorod. Concurrent measures of blood alcohol and body temperature taken to validate the efficacy of alcohol administration correlated precisely with the blockade of locomotor behavior of the animals. These findings thus suggest that because of the specificity of the A1AS probe, the A1 receptor in the striatum is not involved in the alcohol-induced incapacitation of locomotor activity.

Effect of ethanol on human placental transport and metabolism of adenosine

It has been suggested that adenosine is involved in the acute effects of ethanol in a number of tissues. The present study was undertaken to evaluate the role of adenosine on the vascular responses of perfused isolated human placental cotyledons after the acute administration of ethanol. The possibility that ethanol may effect the uptake and metabolism adenosine was also investigated. Uptake of adenosine was studied using the single-circulation paired-tracer dilution technique. Both adenosine and ethanol caused a dose-related increase in perfusion pressure of placental lobules. Pharmacologically relevant concentrations of ethanol (10-65 mM) significantly inhibited the uptake of [3H]adenosine between 25 and 50 per cent. Thin-layer chromatographic analysis of the perfusate after the administration of ethanol showed in a 17.9 +/- 0.6 per cent reduction of [3H]adenosine metabolism. These findings support the working hypothesis that placental adenosine, at least partially, mediates the placental disturbance elicited by the administration of acute ethanol, which may contribute to the pathogenesis of fetal alcohol syndrome.

Mouse cerebellar adenosinergic modulation of ethanol-induced motor incoordination: possible involvement of cAMP

As an extension of our previous work pertaining to brain adenosinergic modulation of ethanol-induced motor incoordination, the effect of direct intracerebellar administration of the A1-selective adenosine agonist, N6-cyclohexyladenosine (CHA) on ethanol-induced motor incoordination was evaluated. Marked accentuation of ethanol-induced motor impairment by CHA was observed. No change in the normal motor coordination was noted when CHA administration was followed by saline instead of ethanol. Intracerebellar cAMP or its analog, 8-(4-chlorophenylthio)-cAMP, significantly inhibited ethanol's motor impairment in a dose-related manner as well as abolished CHA's accentuating effect on ethanol-induced motor incoordination. These observations suggested a possible involvement of cAMP in the adenosinergic modulation and in the expression of ethanol-induced motor incoordination. Further support was provided by the observation of a marked accentuation and attenuation in a dose-related manner of ethanol-induced motor impairment as well as CHA's accentuation of ethanol's motor impairment by intracerebellar miconazole and forskolin, respectively. However, equimolar intracerebellar doses of miconazole and forskolin (inhibitor and stimulator of adenylyl cyclase, respectively) failed to significantly alter ethanol-induced motor incoordination probably due to their mutual functional antagonism. The expression of adenosinergic modulation and that of ethanol-induced motor impairment most likely involved Gi protein-coupled receptor(s) (such as adenosine receptors). The involvement of receptors linked to pertussis toxin-sensitive G-proteins was suggested because intracerebellar pertussis toxin pretreatment markedly inhibited ethanol-induced motor incoordination as well as CHA's accentuation of ethanol's motor impairment. Finally, cAMP, unlike its antagonism to CHA's accentuation, failed to antagonize the accentuation of ethanol-induced motor impairment by intracerebellar GABA(A) agonist (+)-muscimol. This indicated selectivity of cAMP participation in G protein coupled receptor (such as adenosine)-mediated response and not in ionic channel coupled receptor (such as GABA(A))-mediated mechanism. Overall, the data suggested a possible involvement of cerebellar adenylyl cyclase-cAMP signalling pathway in the adenosinergic modulation of ethanol's ataxia.

Effects of ethanol and acetate on adenosine production in rat hippocampal slices

Since adenosine has been shown to mediate some actions of ethanol we have examined the effect of ethanol (20 and 80 mM) or its metabolite acetate (5 and 20 mM) on the formation and release of adenosine by rat hippocampal slices. The ATP pool of the slices was radioactively labelled by preincubation with [3H]-adenine. The efflux of radioactivity under basal conditions and following ATP breakdown induced by combined hypoxia/hypoglycaemia was examined. Ethanol or acetate did not increase the total efflux of [3H]-purines, but changed the composition to a larger proportion of [3H]-adenosine. The release of endogenous adenosine was also increased. This type of effect exactly mirrors that previously reported for purine nucleoside transport inhibitors. The present results thus show that ethanol (20 mM) can increase adenosine release from a brain slice by a mechanism that probably involves transport inhibition.

Chronic ethanol intoxication enhances [3H]CCPA binding and does not reduce A1 adenosine receptor function in rat cerebellum

The effects of acute and chronic treatment with ethanol on the function of A1 adenosine receptor in the rat cerebellar cortex were investigated. Acute administration of ethanol (0.5-5 g/kg) had no effect on the binding of the A1-receptor agonist [3H]2-chloro-N6-cyclopentyladenosine ([3H]CCPA) or that the antagonist [3H]8-cyclopentyl-1-3-dipropylxanthine ([3H]DPCPX) in rat cerebellar cortical membranes. Rats were rendered ethanol dependent by repeated forced oral administration of ethanol (12-18 g/kg per day) for 6 days. [3H]CCPA binding was increased by 23% in cerebellar cortical membranes prepared from rats killed 3 h after ethanol withdrawal compared with saline-treated animals. The increase in [3H]CCPA binding was still apparent 12-24 h after the last ethanol administration, but was no longer detectable 3-6 days after ethanol withdrawal. In contrast, the binding of [3H]DPCPX was not modified in the cerebellar cortex of rats killed at various times after ethanol withdrawal. The acute administration of CCPA [0.25-1 mg/kg, intraperitoneally (IP)] suppressed the tremors and audiogenic seizures apparent 24 h after ethanol withdrawal. Moreover, repeated coadministration of CCPA (0.5 mg/kg, IP, four times daily) and ethanol did not prevent the generation of audiogenic seizures during withdrawal but completely prevented mortality. Finally, CCPA antagonized with similar potencies and efficacies the isoniazid-induced convulsions observed in control and ethanol-withdrawn rats. These results indicate that long-term treatment with intoxicating doses of ethanol enhances [3H]CCPA binding but does not reduce the anticonvulsant efficacy of CCPA or the function of A1 adenosine receptors.

Possible role of striatal adenosine in the modulation of acute ethanol-induced motor incoordination in rats

Several reports from our laboratory have suggested the involvement of the brain adenosinergic system in ethanol-induced motor incoordination (EIMI). This study is an extension of the previous work and pertains to the evaluation of the role of the striatal adenosine in EIMI in male Sprague-Dawley rats. Using the motor incoordination induced by 1.5 g/kg of ethanol (ip) as a test response, the possible behavioral interactions between ethanol and adenosine agonists and antagonists in the striatum were investigated. Intrastriatal (IST) administration of adenosine A1-, A1 = A2-, and As-selective agonists, R(-)N6-(2-phenylisopropyl)adenosine (R-PIA), 5'-N-ethylcarboxamido-adenosine (NECA), and 5'-(N-cyclopropyl)-carboxamidoadenosine, respectively, significantly and dose-dependently accentuated EIMI when evaluated by rotorod test, suggesting the striatal adenosinergic modulation of EIMI. No significant change in normal motor coordination was noted, even when the highest IST doses of adenosine agonists were followed by saline instead of ethanol, suggesting that the observed behavioral interactions of these drugs were selective to ethanol. Hippocampus, which is known not to be involved in the normal motor functions, was selected as a control brain area because of the presence of high density of adenosine receptors, as well as the high levels of adenosine. Intrahippocampal NECA failed to alter EIMI, indicating the specific role of striatal and not hippocampal adenosinergic system in the modulation of EIMI. The potentiating effects of adenosine agonists N6-cyclohexyladenosine (CHA) and CGS-21680 on EIMI were blocked by adenosine A1- and A2-selective antagonists, 8-cyclopentyl-1,3-dipropylxanthine and 3,7-dimethyl-1-propargylxanthine, respectively, suggesting the participation of specific adenosine receptors in this functional interaction. A role for the adenosine A1 receptor in the striatal adenosinergic modulation of EIMI was favored based on the rank-order potency of adenosine agonists. IST pretreatment with pertussis toxin (PT), but not with PT beta-oligomer, nearly completely eliminated the accentuation of EIMI by CHA, further supporting the favored role of adenosine A1 receptors in EIMI. Histological and IST [3H]R-PIA distribution data confirmed that the observed behavioral effects were caused by exclusive striatal distribution of intrastriatally microinjected drugs. Data obtained suggested modulation of acute EIMI by striatal adenosine receptor-mediated mechanism(s) and the coupling of these adenosine receptor to the PT-sensitive Gi protein.

Possible central adenosinergic modulation of ethanol-induced alterations in [14C]glucose utilization in mice

The possible role of brain adenosine in acute ethanol-induced alteration in glucose utilization in the whole brain, as well as in the specific brain areas (cerebellum and brain stem), was investigated. Mice were killed 20-min postethanol, and the fresh tissue slices (300 microns) of brain and/or specific brain areas were incubated for 100 min in a 5.5 mM glucose medium in Warburg flasks using [6-(14)C]glucose as a tracer. Trapped 14CO2 was counted to estimate glucose utilization. Ethanol (2 g/kg, i.p.) markedly increased the glucose utilization in whole brain and in both motor areas of brain. Theophylline (50 mg/kg, i.p.), an adenosine antagonist, significantly reduced ethanol-induced increase in glucose utilization in whole brain, as well as in brain areas. However, adenosine agonist N6-cyclohexyladenosine (CHA; 0.1 mg/kg, i.p.) on the contrary, significantly accentuated ethanol-induced increase in glucose utilization in these tissues that was nearly completely blocked by theophylline pretreatment. Theophylline alone did not produce any significant change in glucose utilization, whereas CHA alone (in vivo and in vitro) significantly increased glucose utilization, as well as ethanol-induced increase in glucose utilization in an additive manner. Relevant supportive data were obtained by experiments in which adenosine deaminase (ADA), p-sulfophenyltheophylline (8-SPT), and CHA were administered in vitro to the slice preparations. Both ADA and 8-SPT were effective in almost completely blocking the ethanol-induced increase in glucose utilization, whereas CHA further enhanced the ethanol-induced increase in glucose utilization in an additive manner.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Intracerebellar nicotinic-cholinergic participation in the cerebellar adenosinergic modulation of ethanol-induced motor incoordination in mice

Many epidemiological studies have suggested a high correlation between the use of tobacco and ethanol, the two most frequently abused psychoactive drugs. Recently, we reported behavioral interactions between (-)-nicotine, (-)-cotinine and ethanol within the CNS. The present report is a confirmation and an extension of that study. Using a 2 g/kg ethanol-induced motor incoordination (EIMI) as the test response, possible behavioral interactions between (-)-nicotine, (-)-cotinine and ethanol and between (-)-nicotine, (-)-cotinine and adenosine agonist + ethanol in the cerebellum were investigated. (-)-Nicotine, 0.625, 1.25 and 5 ng intracerebellarly (ICB) significantly attenuated EIMI in a dose-related manner. Likewise, ICB injection of 1.25, 2.5, and 5 ng (-)-cotinine, a major metabolite of nicotine, significantly attenuated EIMI after the same i.p. dose of ethanol as in case of (-)-nicotine but less markedly compared to (-)-nicotine. No change in normal motor coordination was observed when the highest dose of (-)-nicotine or (-)-cotinine was injected ICB followed by saline control, suggesting selectivity of their behavioral interactions with ethanol. The attenuation of EIMI by (-)-nicotine and (-)-cotinine was blocked by ICB hexamethonium (1 microgram) and trimethaphan (100 ng), the purported nicotinic-cholinergic antagonists. Finally, the ICB injection of adenosine agonists, N6-cyclohexyladenosine (CHA) or 5'-N-ethylcarboxamidoadenosine (NECA), produced marked accentuation of EIMI which was significantly antagonized by ICB (-)-nicotine and (-)-cotinine. The data obtained in the present study suggested, for the first time, a cerebellar adenosinergic-nicotinic cholinergic interaction and modulation of EIMI. The data also suggested participation of cerebellar nicotinic-cholinergic receptors in EIMI.

Central behavioral interactions between ethanol, (-)-nicotine, and (-)-cotinine in mice

A high correlation between alcohol use and smoking has long been suggested by epidemiological data. We examined the potential behavioral interactions between ethanol and nicotine using ethanol-induced motor incoordination as the test response in mice. Effect of pretreatment of various doses of (-)-nicotine, (-)-cotinine, a major metabolite of nicotine, and (+)-nicotine administered ICV on ethanol (IP)-induced motor incoordination was investigated. (-)-Nicotine (0.19, 0.38, 0.77 and, 1.54 nmoles ICV) produced significant attenuation of motor incoordination due to ethanol (2 g/kg IP) in a nearly dose-related manner which was blocked by ICV hexamethonium and trimethaphan, both purported nicotinic antagonists. (-)-Cotinine (0.35, 0.70, 1.41 nmole ICV) produced similar attenuation but was les potent than (-)-nicotine. Attenuation by (+)-nicotine (0.19, 0.38, and 0.77 nmoles ICV) was also significant but only at 0.77 nmole dose level. (+)-Nicotine-induced attenuation of motor incoordination by ethanol was antagonized by nicotinic antagonists. Data obtained suggest a central behavioral interaction between ethanol and nicotine at least through the participation of cholinergic nicotinic receptors.

Tolerance to adenosine's accentuation of ethanol-induced motor incoordination in ethanol-tolerant mice

Our previously published reports have provided data that have supported a functional correlation between ethanol-induced changes in the characteristics of adenosine receptor, adenosine uptake and release in the brain, and ethanol-induced motor incoordination. The present data demonstrated a cross-tolerance between ethanol and adenosine further supporting the hypothesis that brain adenosine modulates the motor impairing effects of ethanol. Mice that received (-)-N6-cyclohexyladenosine (CHA) [0.25 mg/kg/day, intraperitoneally (ip)] for 10 days exhibited marked attenuation (cross-tolerance) to acute ethanol-induced motor incoordination compared with chronic saline (ip) controls. The attenuation of acute ethanol-induced motor incoordination was essentially same in animals that received CHA (25 ng/5 microliters/day for 10 days) by the intracerebroventricular (icv) route as opposed to the controls that chronically received artificial cerebral spinal fluid by the same route. Similarly, tolerance was exhibited to acute CHA (0.125 mg/kg ip and 12.5 ng/5 microliters icv) by animals fed liquid ethanol (19.5 g/kg/24 hr) for 10 days compared with none in the pair-fed sucrose controls. Scatchard plots using cerebellar tissue homogenates from animals given chronic CHA or chronic ethanol indicated no change in Bmax and/or Kd values for CHA binding when compared with CHA binding in tissues from their respective controls. However, a lack of any change in the binding characteristics cannot rule out the involvement of adenosine receptors in the observed cross-tolerance between ethanol and CHA. The results may suggest desensitization of adenosine A1 receptors due to chronic CHA and ethanol as an alternate possible explanation in the development of cross-tolerance between adenosine (CHA) and ethanol.

Actions of ethanol and acetate on rat cortical neurons: ethanol/adenosine interactions

Recent studies have suggested that ethanol may exert some of its central depressant actions by increasing the extracellular levels of adenosine in the brain. Ethanol can inhibit the cellular uptake of adenosine, thus increasing its extracellular concentration. After ethanol metabolism by the liver, blood acetate levels are elevated and acetate metabolism in the brain could also lead to the production of adenosine. Rat cerebral cortical cup release experiments failed to reveal any elevation in the extracellular levels of either adenosine or inosine following the intraperitoneal (IP) administration of ethanol (1.5 g/kg) or acetate (2 g/kg). IP-administered ethanol (0.5 and 1.0 g/kg) enhanced the magnitude and duration of the inhibition by iontophoretically applied adenosine of the spontaneous firing of rat cerebrocortical neurons; an action which would be consistent with the block of adenosine uptake. Acetate, applied iontophoretically, depressed the spontaneous firing of 63% of the cerebrocortical neurons tested. 8-p-Sulphophenyltheophylline, an adenosine antagonist, was ineffective at blocking these inhibitions, indicating that adenosine generation is unlikely to have played a major role in the acetate-evoked depression of cerebral cortical neurons.

Electrophysiological actions of acetate, a metabolite of ethanol, on hippocampal dentate granule neurons: interactions with adenosine

Acetate is the primary breakdown product of ethanol metabolism in the liver and has been found in the brain following ethanol ingestion in rats. Systemically administered acetate has been shown to cause motor impairment, an effect which is blocked by the adenosine receptor blocker, 8-phenyltheophylline (8-PT). The effects of sodium acetate were investigated in this study using intracellular recording techniques in rat hippocampal dentate granule cells, and were compared to the actions of ethanol and adenosine individually and in conjunction with 8-PT. Acetate hyperpolarized the membrane at 0.4-0.8 mM. The amplitude and duration of the postspike train afterhyperpolarization (AHP) were increased by acetate when the cell was repolarized to the control resting membrane potential. Comparable results were seen in voltage clamp. Acetate also decreased spike frequency adaptation. The effects of acetate were mimicked by adenosine (50 microM) and ethanol (20 mM). The ethanol effects occluded those produced by acetate. All of the effects of acetate, adenosine and ethanol could be inhibited with prior perfusion of 8-PT (1-10 microM). These data suggest that the actions of the major metabolite of ethanol, acetate, may be mediated by adenosine receptor activation.

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.

Physiological and pharmacological properties of adenosine: therapeutic implications

Adenosine is a nucleoside which has been shown to participate in the regulation of physiological activity in a variety of mammalian tissues, and has been recognized as a homeostatic neuromodulator. It exerts its actions via membrane-bound receptors which have been characterized using biochemical, electrophysiological and radioligand binding techniques. Adenosine has been implicated in the pharmacological actions of several classes of drugs. A number of studies strongly suggest that the nucleoside may regulate cellular activity in many pathological disorders and, in that respect, adenosine derivatives appear as promising candidates for the development of new therapeutic compounds, such as anticonvulsant, anti-ischemic, analgesic and neuroprotective agents.

Functional correlation between subclasses of brain adenosine receptor affinities and ethanol-induced motor incoordination in mice

To further investigate if the modulation of ethanol-induced motor incoordination is by brain adenosine A1 and/or A2 receptor, adenosine analogs with wide variability in their affinity for A1 and A2 subtypes were administered ICV and their effect on ethanol-induced (IP) motor incoordination was evaluated by rotorod. A dose-dependent marked accentuation of ethanol-induced motor incoordination by adenosine agonists (CHA, NECA, CPA, DCCA) tested, with nearly no effect on normal motor coordination in the absence of ethanol, was observed. There was a positive correlation between A2 affinity, A2/A1 affinity ratio but a negative correlation between A1 affinity and the potency (ED50) of adenosine agonists to accentuate ethanol-induced motor incoordination. However, with the high potency of CHA and NECA, both having significant affinity for A1 and A2 receptors, together with the well known membrane perturbation by ethanol, it seems difficult to rule out until more information becomes available the contribution of A1 receptor activation to adenosine modulation of ethanol-induced motor incoordination. The high density of high affinity A2 (A2a) in the striatum and of A1 in the cerebellum and several brain areas and the known importance of these two brain areas in the motor control, indirectly supports or at least provides a circumstantial evidence for a functional correlation between ethanol-induced motor incoordination and brain adenosine receptors.

Differential actions of RO 15-1788 and diazepam on poikilothermia, motor impairment and sleep produced by ethanol

In adult male Sprague-Dawley rats kept at an ambient temperature of 23-25 degrees C, ethanol was injected intraperitoneally in a dose of 4.0 g/kg to produce a clear-cut impairment of autonomic and motorial functions. Following the injection of ethanol, motor coordination, measured on a rotorod, behavioral sleep, righting reflex and colonic temperature were monitored at predetermined intervals for 5.0-7.0 hr. In the first experiment, either 1.0 mg/kg RO 15-1788 (flumazenil), a benzodiazepine (BZ), receptor antagonist, or 1.0-5.0 mg/kg diazepam, a classical benzodiazepine receptor agonist, were injected intraperitoneally either alone or concurrently with ethanol's administration. In the second study, either RO 15-1788 (1.0 or 2.0 mg/kg) or diazepam (1.0 or 5.0 mg/kg) was injected at the nadir of the fall of body temperature induced by ethanol. Although RO 15-1788 alone failed to affect the rats' temperature, it did not prevent the characteristic ethanol-induced hypothermia but rather potentiated it in a dose-dependent manner. Further, this BZ receptor antagonist exacerbated motor incoordination and other behavioral effects when given either simultaneously with ethanol or at the nadir in the animals' core temperature. Although diazepam evoked a dose-dependent hypothermia, it did not enhance ethanol-induced hypothermia when both drugs were administered simultaneously. However, diazepam augmented motor incoordination and other effects and served to delay their recovery. When given to the rats at the nadir of ethanol hypothermia, diazepam did not potentiate ethanol's thermolysis but retarded the recovery from hypothermia; it caused also a dose-dependent delay in the recovery of motor coordination and other responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism of the anti-conflict effects of phenobarbital, but not diazepam, by the A-1 adenosine agonist l-PIA

The present study examined the effects of the anxiolytics diazepam and phenobarbital, the A-1 adenosine agonist N6-R-phenylisopropyladenosine (l-PIA), and the A-2 adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) on conflict behavior. Water-restricted rats were trained to drink from a tube that was electrified (0.5 mA intensity) on a FI-29s schedule, electrification being signaled by a tone. After 3 weeks of daily 10-min sessions, the animals accepted a stable number of shocks (punished responding) and consumed a consistent volume of water (unpunished responding) per session. Different doses of l-PIA and NECA were then tested separately at weekly intervals. In addition, the effects of diazepam and phenobarbital were determined in animals pretreated with saline, l-PIA, or NECA. Neither l-PIA (15-250 nmole/kg) nor NECA (2.5-20 nmole/kg) produced a significant anti-conflict effect when administered alone. Diazepam (1.25-10 mg/kg) or phenobarbital (10-40 mg/kg) administration to saline-pretreated rats resulted in a dose-dependent increase in punished responding (shocks received) with minimal effects on unpunished responding (water intake). Neither l-PIA nor NECA pretreatment reliably altered the effects of diazepam on conflict behavior. Pretreatment with l-PIA, but not NECA, significantly reduced the anti-conflict effects of phenobarbital on conflict behavior. These data suggest that phenobarbital, but not diazepam, anti-conflict responses may involve interactions with A-1 adenosine receptors.

Alcohol-induced poikilothermia, sleep and motor impairment: actions on brain of EGTA and verapamil

In the early 1970's, calcium ions were implicated in the mechanism underlying the perturbation of the "set point" for body temperature produced by a thermolytic drug. Since Ca++ is thought to be involved in the incapacitating effects of ethanol on body temperature and motor coordination, this investigation sought to compare the differential central actions of a Ca++ chelating agent with those of a Ca++ channel antagonist on ethanol-induced poikilothermia and motor functions. A chronically indwelling cannula for intracerebroventricular (ICV) injection was implanted stereotaxically in each of 25 adult male Sprague-Dawley rats. Following postoperative recovery, each rat was given ethanol in a 20% v/v solution by the intraperitoneal route in a dose of 4.0 g/kg, which was selected to insure a clear-cut impairment of autonomic and motorial functions. Colonic temperature, behavioral sleep, righting reflex and degree of motor coordination on a rotorod were monitored at selected intervals for 5.0-7.0 hr after the injection of ethanol. Two experimental designs were used: First, either 12.5, 25 or 50 micrograms ethyleneglycol-bis-(beta-amino ethyl ether) N,N'-tetra-acetic acid (EGTA), or 25 or 50 micrograms verapamil, both dissolved in an artificial CSF vehicle, were infused ICV at the same time as ethanol's administration. In the second design, the compounds were infused at the nadir of the ethanol-induced temperature decline. EGTA infused ICV in the rat together with ethanol produced a dose-dependent inhibition of ethanol hypothermia and a more rapid recovery of the animal's righting reflex, arousal and motor coordination than that following ethanol alone. Although verapamil infused ICV in the 50 micrograms but not 25 micrograms dose minimized the poikilothermic response to ethanol, it was not as efficacious as that of EGTA. When infused ICV at the point of maximum fall in the rats' temperature. EGTA entirely reversed the hypothermia induced by ethanol and evoked a thermogenic response in the rat. In contrast, verapamil infused ICV in the same doses tended only to retard the further decline in the animal's body temperature. Similarly EGTA was far more effective than verapamil in ameliorating the other physiological actions of ethanol in terms of the reversal of areflexia, behavioral sleep and motor incoordination. These results suggest that the characteristic attributes of membrane Ca++ in terms of its binding and other neuronal properties play a significant functional role in the incapacitating action of ethanol on the diverse physiological processes mediated by the brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain adenosine modulation of behavioral interactions between ethanol and carbamazepine in mice

The effect of the anticonvulsive drug carbamazepine on ethanol-induced motor incoordination and loss-of-righting reflex was investigated in male CD-1 mice. The results of the investigation showed that carbamazepine significantly potentiated the motor incoordinating effect of ethanol in a dose-dependent fashion. Although carbamazepine did not alter the onset time, it significantly prolonged the duration of ethanol-induced loss-of-righting reflex. Pretreatment with theophylline significantly attenuated the carbamazepine-induced potentiation of ethanol-induced motor incoordination and loss-of-righting reflex. Results from a blood ethanol study indicated no effect of carbamazepine on the clearance of ethanol. The data suggest the involvement of nonadenosinergic mechanism in carbamazepine-ethanol behavioral interactions which is responsible for the accentuating effects of carbamazepine on ethanol-induced motor incoordination and duration of loss-of-righting reflex.

Effect of acute ethanol on uptake of [3H]adenosine by rat cerebellar synaptosomes

Many classes of CNS-acting drugs have been suggested to act at least partially via inhibition of adenosine uptake. Synaptosomal uptake of [3H]adenosine and the effect of acute ethanol on it were studied in a rat brain area known to be involved in the coordination and modulation of normal motor activity, the cerebellum. Uptake of [3H]adenosine was found to be linear with time (about 40 sec) and increasing concentrations (up to 1.5 microM) of adenosine. The uptake of [3H]adenosine was inhibited by dilazep (IC50 = 2.5 x 10(-7) M) in a dose-dependent manner. Pharmacologically and/or toxicologically relevant concentrations of ethanol (2.5 to 100 mM) significantly inhibited the uptake of [3H]adenosine between 12 and 15%. Lineweaver-Burk plots indicated that both in vitro (25 mM) and in vivo (1.5 g/kg i.p.; 30 mM blood level) ethanol lowered Km as well as Vmax values for adenosine uptake to nearly the same extent. In the case of in vivo ethanol, no ethanol was present during the assay since synaptosome preparation would wash out residual ethanol. The results of the present study indicate possible membranal alterations by in vivo ethanol. It is concluded that the uptake of [3H]adenosine is inhibited by intoxicating concentrations of ethanol in vitro and by acute ethanol (1.5 g/kg) in vivo. This may partially explain the modulatory role of endogenous adenosine in ethanol-induced motor disturbances.

Effect of acute ethanol on release of endogenous adenosine from rat cerebellar synaptosomes

The effects of pharmacologically relevant concentrations of ethanol on the release of endogenous adenosine from rat cerebellar synaptosomes were investigated. Release was conducted for 5, 10, 30, or 60 s after which time the incubation medium (containing the released adenosine) was rapidly separated from the synaptosomal membranes by vacuum filtration. The adenosine content of the filtrate was measured by HPLC-fluorescence detection. Both basal and KCl-stimulated adenosine release consisted of an initial rapid phase, for the first 10 s, that was followed by a relatively slower phase. Basal endogenous adenosine release was estimated as 199 +/- 14 pmol/mg protein/5 s. Potassium (chloride) increased adenosine release from the basal level to 433 +/- 83 pmol/mg protein/5 s. Ethanol caused a dose-dependent increase of adenosine release. The interaction between dilazep and ethanol indicates that ethanol-stimulated release does not involve the dilazep-sensitive transport system. The results support previous findings that indicate that cerebellar adenosine is involved in the mediation of ethanol-induced motor disturbances in the rat.

Central nervous system effects and behavioral interactions with ethanol of centrally administered dilazep and its metabolites in mice

Dilazep (i.p.), a coronary vasodilator and an uptake inhibitor of adenosine, dose dependently potentiated acute ethanol-induced motor incoordination in mice. In view of peripheral cardiovascular depressive effects of dilazep, the effect of i.c.v. dilazep (25, 50 and 75 micrograms), and its metabolites, 1,4-bis(3-hydroxypropyl)perhydro-1,4-diazepine (BHPD) (15, 31 and 62 micrograms) and 1-[3-(3,4,5-trimethoxybenzoyloxy)propyl]perhydro-1,4-diazepine (TBPD) (62 and 125 micrograms) on ethanol-induced motor incoordination was studied. Dose-related potentiation of ethanol-induced motor incoordination was noted with dilazep and its metabolites. Whereas dilazep (i.p.) produced no apparent central nervous system (CNS) effects, by i.c.v. route, it caused CNS excitation including tonic-clonic seizures. Adenosine uptake inhibition, Ca2+ entry blockade or direct activation of adenosine receptors was ruled out as the possible mechanism of seizures because dipyridamole, verapamil or N6-(2-phenylisopropyl)-adenosine (R-PIA) administered i.c.v., while potentiating ethanol (i.p.)-induced motor incoordination did not produce seizures. The CNS excitation was minimal with BHPD and none with TBPD. Theophylline pretreatment partially blocked potentiation of ethanol-induced motor incoordination by dilazep and BHPD and not by TBPD. The data suggest dilazep-induced potentiation of ethanol-induced motor incoordination is partially due to central adenosine receptor mechanism and partly due to other yet unknown mechanism(s) and further supported our earlier reports about adenosine involvement in the CNS effects of ethanol. The data also suggest that dilazep (i.c.v.)-induced seizures are due to mechanism(s) other than adenosine uptake inhibition, Ca2+ entry blockade or direct adenosine receptor activation.

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.

Release of endogenous glutamate from rat cerebellar synaptosomes: interactions with adenosine and ethanol

The effects of ethanol and adenosine receptor agonist R-PIA and antagonist theophylline on release of endogenous glutamate were tested in rat cerebellar synaptosomal preparation. Release was carried out for 5 to 60 sec after which time the released glutamate was separated from the synaptosomal membranes by rapid filtration. The amount of released glutamate in the filtrate was measured by an enzyme-linked fluorometric assay. Basal endogenous glutamate release was estimated as 3.7 +/- 0.3 nmol/mg protein/5 sec and was stimulated by high K+. Glutamate release consisted of an initial rapid phase for the first 10 sec that was followed by a relatively slower phase. Both Ca2+-dependent and Ca2+-independent glutamate release were observed which suggested the involvement of both neuronal and glial constituents of the synaptosomal preparation, respectively. Pharmacologically relevant concentrations of ethanol (25-100 mM) caused a trend toward a dose-dependent inhibition of glutamate release. R-PIA and theophylline inhibited and stimulated, respectively, basal release of glutamate and R-PIA-inhibited release was blocked by theophylline. Ethanol (25 mM) blocked the stimulatory effect of theophylline and the results of experiments following the inclusion of adenosine deaminase suggested the involvement of adenosine in this effect of ethanol. The results support our previous findings that suggest an involvement of cerebellar adenosine in the motor disturbing effects of acute ethanol and extend those findings by indicating that ethanol inhibits glutamate release from granule cells of the cerebellar cortex through an adenosine-sensitive mechanism.

The effects of various methods of sacrifice and of ethanol on adenosine levels in selected areas of rat brain

The effect of acute ethanol on adenosine content in four motor areas of the male Sprague-Dawley rat brain was investigated using HPLC-fluorescence detection. Since basal adenosine levels are difficult to assess due to extremely rapid turnover of adenosine, four different methods of sacrifice were also evaluated for adenosine measurement. The rank order for best results in measuring adenosine content with the various methods of sacrifice was: focused microwave irradiation greater than decapitation into liquid nitrogen greater than immersion into liquid nitrogen greater than decapitation. These differences probably reflect differences in degree of hypoxia and postmortem anoxia, factors well known to elevate adenosine, associated with the sacrifice method. Focused microwave irradiation of appropriate duration was found to be the best method of sacrifice and the results probably most closely reflect true basal adenosine levels. No significant alteration in adenosine content in any brain region examined was observed due to ethanol administration.