Ethanol Ataxia Research Articles

The PDE4 inhibitor apremilast modulates ethanol responses in Gabrb1-S409A knock-in mice via PKA-dependent and independent mechanisms

We previously showed that the PDE4 inhibitor apremilast reduces ethanol consumption in mice by protein kinase A (PKA) and GABAergic mechanisms. Preventing PKA phosphorylation of GABAA β3 subunits partially blocked apremilast-mediated decreases in drinking. Here, we produced Gabrb1-S409A mice to render GABAA β1 subunits resistant to PKA-mediated phosphorylation. Mass spectrometry confirmed the presence of the S409A mutation and lack of changes in β1 subunit expression or phosphorylation at other residues. β1-S409A male and female mice did not differ from wild-type C57BL/6J mice in expression of Gabrb1, Gabrb2, or Gabrb3 subunits or in behavioral characteristics. Apremilast prolonged recovery from ethanol ataxia to a greater extent in Gabrb1-S409A mice but prolonged recovery from zolpidem and propofol to a similar extent in both genotypes. Apremilast shortened recovery from diazepam ataxia in wild-type but prolonged recovery in Gabrb1-S409A mice. In wild-type mice, the PKA inhibitor H89 prevented apremilast modulation of ataxia by ethanol and diazepam, but not by zolpidem. In Gabrb1-S409A mice, inhibiting PKA or EPAC2 (exchange protein directly activated by cAMP) partially reversed apremilast potentiation of ethanol, diazepam, and zolpidem ataxia. Apremilast prevented acute tolerance to ethanol ataxia in both genotypes, but there were no genotype differences in ethanol consumption before or after apremilast. In contrast to results in Gabrb3-S408A/S409A mice, PKA phosphorylation of β1-containing GABAA receptors is not required for apremilast's effects on acute tolerance or on ethanol consumption but is required for its ability to decrease diazepam intoxication. Besides PKA we identified EPAC2 as an additional cAMP-dependent mechanism by which apremilast regulates responses to GABAergic drugs.

Functional interaction and cross-tolerance between ethanol and Δ9-THC: Possible modulation by mouse cerebellar adenosinergic A1/GABAergic-A receptors

We have previously shown a functional motor interaction between ethanol and Δ9-tetrahydrocannabinol (Δ9-THC) that involved cerebellar adenosinergic A1 and GABAergic A receptor modulation. We now report the development of cross-tolerance between intracerebellar Δ9-THC and intraperitoneal ethanol using ataxia as the test response in male CD-1 mice. The drugs [Δ9-THC (20μg), N6-cyclohexyladenosine, CHA (12ng), muscimol (20ng)] used in the study were directly microinfused stereotaxically via guide cannulas into the cerebellum except ethanol. Δ9-THC, infused once daily for 5 days followed 16h after the last infusion by acute ethanol (2g/kg) and Rotorod evaluation, virtually abolished ethanol ataxia indicating development of cross-tolerance. The cross-tolerance was also observed when the order of ethanol and Δ9-THC treatment was reversed, i.e., ethanol injected once daily for 5 days followed 16h after the last ethanol injection by Δ9-THC infusion. The cross-tolerance appeared within 24–48h, lasted over 72h and was maximal in 5-day ethanol/Δ9-THC-treated animals. Finally, tolerance in chronic ethanol/Δ9-THC/-treated animals developed not only to ethanol/Δ9-THC-induced ataxia, respectively, but also to the ataxia potentiating effect of CHA and muscimol, indicating modulation by cerebellar adenosinergic A1 and GABAA receptors. A practical implication of these results could be that marijuana smokers may experience little or no negative effects such as ataxia following alcohol consumption. Clinically, such antagonism of ethanol-induced ataxia can be observed in marijuana users thereby encouraging more alcohol consumption and thus may represent a risk factor for the development of alcoholism in this segment of population.

Sustained antagonism of acute ethanol-induced ataxia following microinfusion of cyclic AMP and cpt-cAMP in the mouse cerebellum

Ataxia is a conspicuous physical manifestation of alcohol consumption in humans and laboratory animals. Previously we reported possible involvement of cAMP in ethanol-induced ataxia. We now report a sustained antagonism of ataxia due to multiple ethanol injections following intracerebellar (ICB) cAMP or cpt-cAMP microinfusion. Adenylyl cyclase drugs cAMP, cpt-cAMP, Sp-cAMP, Rp-cAMP, adenosine A1 agonist, N6-cyclohexyladenosine (CHA) and GABAA agonist muscimol were directly microinfused into the cerebellum of CD-1 male mice to evaluate their effect on ethanol (2g/kg; i.p.) ataxia. Drug microinfusions were made via stereotaxically implanted stainless steel guide cannulas. Rotorod was used to evaluate the ethanol's ataxic response. Intracerebellar cAMP (0.1, 1, 10fmol) or cpt-cAMP (0.5, 1, 2fmol) 60min before ethanol treatment, dose-dependently attenuated ethanol-induced ataxia in general agreement with previous observations. Intracerebellar microinfusion of cAMP (100fmol) or cpt-cAMP (2fmol) produced a sustained attenuation of ataxia following ethanol administration at 1, 4, 7 and 25h or 31h post-cAMP/cpt-cAMP microinfusion. At 31h post-cAMP, the ataxic response of ethanol reappeared. Additionally, marked antagonism to the accentuation of ethanol-induced ataxia by adenosine A1 and GABAA agonists, CHA (34pmol) and muscimol (88pmol), respectively, was noted 24h after cAMP and cpt-cAMP treatment. This indicated possible participation of AC/cAMP/PKA signaling in the co-modulation of ethanol-induced ataxia by A1 adenosinergic and GABAergic systems. No change in normal motor coordination was noted when cAMP or cpt-cAMP microinfusion was followed by saline. Finally, Rp-cAMP (PKA inhibitor, 22pmol) accentuated ethanol-induced ataxia and antagonized its attenuation by cAMP whereas Sp-cAMP (PKA activator, 22pmol) produced just the opposite effects, further indicating participation of cAMP-dependent PKA downstream. Overall, the results support a role of AC/cAMP/PKA signaling in the expression of ethanol-induced ataxia and its co-modulation by adenosine A1 and GABAA receptors.

The Role of Nicotinic Acetylcholine Receptor (nAChR) α7 Subtype in the Functional Interaction Between Nicotine and Ethanol in Mouse Cerebellum

Many epidemiological studies report that alcoholics overwhelmingly smoke tobacco and vice versa, which suggests a possible functional interaction between ethanol and nicotine. Although nicotine-ethanol interaction is well documented within the central nervous system, the mechanism is not well understood. Therefore, it is important from a public health standpoint to understand the mechanisms involved in nicotine and ethanol functional interaction. The intracerebellar (ICB) administration of nicotine significantly attenuates ethanol ataxia through nicotinic acetylcholine receptor (nAChR) α(4)β(2) subtype. This study, an extension of earlier work, was intended to investigate the possible role of nAChR subtype α(7) in mitigating ethanol ataxia. The effect of ICB injection of PNU-282987 (α(7) agonist; 25 ng to 2.5 μg) and the antagonist methyllycaconitine was evaluated on ethanol (2 g/kg; i.p.)-induced ataxia with a Rotorod. Cerebellar nitric oxide was determined fluorometrically in the presence of ethanol and/or PNU-282987. Attenuation of ethanol-induced ataxia following PNU-282987 microinfusion was dose-dependent suggesting the participation of α(7) subtype in nicotine and ethanol interaction. Intracerebellar pretreatment with methyllycaconitine (α(7) -selective antagonist; 6 ng) virtually abolished the attenuating effect of PNU-282987 as well as the effect of nicotine, but not of RJR-2403 (α(4)β(2) -selective agonist; 125 ng) on ethanol-induced ataxia. Finally, ethanol administration significantly decreased cerebellar NO(x), whereas ICB PNU-282987 significantly increased and/or opposed ethanol-induced decrease in NO(x). These results were functionally in agreement with our Rotorod data. These observations confirmed the following: (i) α(7) participation in nicotine-ethanol interaction and (ii) α(7) selectivity of methyllycaconitine. Overall, the results demonstrate the role of cerebellar nAChR α(7) subtype in nicotine-induced attenuation of ethanol-induced ataxia in cerebellar NO(x)-sensitive manner.

Role of mouse cerebellar nicotinic acetylcholine receptor (nAChR) α4β2- and α7 subtypes in the behavioral cross-tolerance between nicotine and ethanol-induced ataxia

We have demonstrated that nicotine attenuated ethanol-induced ataxia via nicotinic-acetylcholine-receptor (nAChR) subtypes α4β2 and α7. In the present study, ethanol (2g/kg; i.p.)-induced ataxia was assessed by Rotorod performance following repeated intracerebellar infusion of α4β2- and α7-selective agonists. Localization of α4β2 and α7 nAChRs was confirmed immunohistochemically. Cerebellar NOx (nitrite+nitrate) was determined flurometrically. Repeated intracerebellar microinfusion of the α4β2-selective agonist, RJR-2403 (for 1, 2, 3, 5 or 7 days) or the α7-selective agonist, PNU-282987 (1, 2, 3 or 5 days), dose-dependently attenuated ethanol-induced ataxia. These results suggest the development of cross-tolerance between ethanol-induced ataxia and α4β2 and α7 nAChR agonists. With RJR-2403, the cross-tolerance was maximal after a 5-day treatment and lasted 48h. Cross-tolerance was maximal after a 1-day treatment with PNU-282987 and lasted 72h. Pretreatment with α4β2- and α7-selective antagonists, dihydro-β-erythroidine and methyllycaconitine, respectively, prevented the development of cross-tolerance confirming α4β2 and α7 involvement. Repeated agonist infusions elevated cerebellar NOx 16h after the last treatment while acute ethanol exposure decreased it. Pretreatment with repeated RJR-2403 or PNU-282987 reversed ethanol-induced decrease in NOx. The NOx data suggests the involvement of the nitric oxide (NO)–cGMP signaling pathway in the cross-tolerance that develops between α4β2- and α7-selective agonists and ethanol ataxia. Both α4β2 and α7 subtypes exhibited high immunoreactivity in Purkinje but sparse expression in molecular and granular cell layers. Our results support a role for α4β2 and α7 nAChR subtypes in the development of cross-tolerance between nicotine and ethanol with the NO signaling pathway as a potential mechanism.

Attenuation of ethanol-induced ataxia by α 4β 2 nicotinic acetylcholine receptor subtype in mouse cerebellum: A functional interaction

Many epidemiological studies support the notion that people who drink alcohol also smoke cigarettes and vice versa thereby suggesting a possible functional interaction between these two most widely used psychoactive substances. We have earlier demonstrated that direct intracerebellar (ICB) microinfusion of nicotine dose-dependently antagonizes ethanol-induced ataxia and further that this antagonism occurs in a glutamate-nitric oxide-cyclic guanylyl monophosphate (cGMP) sensitive manner. The present study was designed to determine the possible involvement of specific nicotinic acetylcholine receptor (nAChR) subtype α 4β 2 in nicotine-induced attenuation of ethanol ataxia. Using the Rotorod test and direct ICB microinfusion technique in stereotaxically cannulated CD-1 male mice, we performed the Rotorod test following ICB administration of the α 4β 2-selective agonist, (E)- N-methyl-4-(3-pyridinyl)-3-buten-1-amine (RJR-2403; 31.25, 62.5, 125 ng) on ethanol (2 g/kg; i.p.) ataxia at 15, 30, 45, 60 min post-ethanol injection. RJR-2403 dose-dependently attenuated ethanol ataxia suggesting a role of α 4β 2 subtype in ameliorating ethanol-induced ataxia. Pretreatment with ICB dihydro-β-erythroidine (DHβE: 125, 250, 500, 750 ng), a potent α 4β 2-selective antagonist, significantly reduced RJR-2403's effect further supporting the α 4β 2 involvement. DHβE (ICB) also antagonized ICB nicotine-induced attenuation of ethanol ataxia again reinforcing the role of α 4β 2 subtype. Additional evidence for the role of α 4β 2 subtype was provided when ICB α 4β 2 antisense oligodeoxynucleotide treatment markedly antagonized RJR 2403–induced attenuation of ethanol ataxia compared with missense-treated animals. This was confirmed with an associated decrease in the expression of α 4β 2 subtypes indicated by immunoblot experiments. In conclusion, the results of the present investigation support an important role of α 4β 2 nAChR subtype in the expression of nicotine-induced attenuation of ethanol ataxia.

Nicotine‐Ethanol Interaction: Regulation by two distinct nicotinic acetylcholine receptor (nAChR) subtypes in mouse cerebellum

We previously reported cross tolerance between nicotine and ethanol and attenuation of ethanol ataxia by intracerebellar (ICB) nicotine. Using rotorod and direct ICB infusion in cannulated mice, we studied the role of nAChR subtypes á4â2 and á7. RJR‐2403 [32.25, 62.5, 125 ng] a á4â2 agonist, markedly attenuated ethanol (2g/kg; i.p) ataxia dose dependently. Dihydro‐â‐erythroidine, DHâE, á4â2 antagonist, (500ng) significantly attenuated RJR's and nicotine‐induced attenuation of ethanol ataxia reinforcing the role of á4â2 subtype in nicotine‐ethanol functional interaction. Also, ICB infusion of PNU 282987 (250ng–2.5ug), a novel á7 subtype selective agonist reduced ethanol ataxia thus indicating the probable role of á7 nAChR subtype in this context. Moreover, pretreatment with methyllylcaconitine (MLA; 3–12ng; ICB), a á7‐subtype selective antagonist, effectively prevented PNU and nicotine attenuation of ethanol ataxia confirming the contribution of á7 subtype in ethanol's ataxia. Both DHâE and MLA per se had no effect on ethanol's ataxia precluding any tonic role of nAChR subtypes. Taken together, our results support a comparable role of nAChR á4â2 and á7 subtype in nicotine‐induced attenuation of ethanol ataxia. Future treatment strategies for ethanol ataxia might require manipulation of these nAChR subtypes to lessen alcohol related motor impairment.

Co-modulation of acute ethanol-induced motor impairment by mouse cerebellar adenosinergic A 1 and GABA A receptor systems

We have previously demonstrated that cerebellar adenosine modulates ethanol ataxia. Using Rotorod method, we investigated the role of cerebellar GABA A receptors in the adenosinergic modulation of ethanol ataxia in mice. Direct cerebellar microinfusion of GABA A agonist, muscimol (2.5, 5 and 10 ng) and antagonist, bicuculline (50, 100 and 200 ng), via permanently implanted guide cannulas, produced a marked and dose-dependent accentuation and attenuation, respectively, of ethanol (2 g/kg; IP) ataxia. The accentuation of ethanol ataxia by intracerebellar muscimol was through GABA A receptor because intracerebellar pretreatment with bicuculline virtually abolished muscimol effect. Intracerebellar microinfusion of adenosine A 1 agonist, N 6-cyclohexyladenosine (CHA: 4 ng), and antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX: 100 ng) markedly accentuated and attenuated, respectively, ethanol ataxia consistent with our previously published data. Intracerebellar microinfusion of CHA (4 ng) or DPCPX (100 ng) markedly enhanced and reduced, respectively, muscimol (10 ng)-induced accentuation of ethanol ataxia suggesting co-modulation of ethanol ataxia by cerebellar adenosinergic A 1 and GABA A receptors. Similarly, intracerebellar bicuculline (200 ng) pretreatment not only prevented CHA-induced accentuation of ethanol ataxia, but caused further decrease in ethanol ataxia. No change in the normal coordination was observed when microinfusion of the highest dose of muscimol, bicuculline, DPCPX or CHA alone or in combination was followed by saline injection instead of ethanol. The results of the present study suggest a functional similarity between GABA A and adenosine A 1 receptors even though both receptor types are known to couple to different signaling system and their location is on the opposite ends of the cerebellar granule cells, axons and axonal terminals (i.e., GABA A at the granule cells and adenosine A 1 on axons and axonal terminals of the granule cells) and act as co-modulators of ethanol ataxia.

Behavioral Interaction Between Nicotine and Ethanol: Possible Modulation by Mouse Cerebellar Glutamate

Epidemiological studies show that people who drink alcoholic beverages also smoke cigarettes and vice versa. Furthermore, animal studies provide circumstantial evidence for ethanol and nicotine interaction. Previously, we demonstrated that intracerebellar nicotine attenuates ethanol ataxia. This study investigated the possible role of glutamate in modulating the interaction of nicotine and ethanol. Glutamate drugs N-methyl-d-aspartate (NMDA) and (+)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrate (AMPA) as well as their antagonists were directly microinfused into the cerebellum of CD-1 male mice to evaluate their effect on ethanol (2 g/kg i.p.) ataxia. Drug microinfusions were made via stereotaxically implanted stainless-steel guide cannulas. Rotorod was used to evaluate the ataxic response of ethanol. Microinfusion of nicotine (0.3125, 1.25, 5 ng) significantly attenuated ethanol ataxia dose-dependently, confirming the functional interaction between nicotine and ethanol as reported earlier. Intracerebellar pretreatment with hexamethonium, a nicotinic receptor (nAChR) antagonist, significantly blocked nicotine-induced attenuation of ethanol ataxia suggesting participation of nAChRs. When ethanol was injected before nicotine microinfusion, nicotine failed to attenuate ethanol ataxia, indicating the critical importance of initial activation of nAChRs by nicotine. Intracerebellar microinfusion of NMDA (30, 60, 125 ng) and its antagonist, (+)-MK-801 (50, 100, 200 ng), significantly increased and decreased, respectively, the nicotine-induced attenuation of ethanol ataxia in a dose-related manner, suggesting participation of the NMDA receptor. Similarly, intracerebellar microinfusion of AMPA (7.5, 15, 30 ng) and its antagonist, nitro -2, 3-dioxobenzoquinoxaline-sulfonamide (NBQX; 25, 50, 100 ng), significantly increased and decreased, respectively, the nicotine-induced attenuation of ethanol ataxia in a dose-dependent manner. This suggests participation of the AMPA receptor and further supports involvement of the glutamate system in the ethanol-nicotine interaction. Intracerebellar nicotine failed to attenuate sodium-pentobarbital (25 mg/kg i.p.) ataxia, suggesting the relative specificity of the nicotine-ethanol interaction. The results suggested that glutamate modulates the functional interaction between nicotine and ethanol because NMDA and AMPA enhanced the nicotine-induced attenuation of ethanol ataxia, whereas (+)-MK-801 and NBQX reduced the attenuation.

Antagonism of ethanol ataxia by intracerebellar nicotine: Possible modulation by mouse cerebellar nitric oxide and cGMP

We have reported previously that intracerebellar nicotine attenuates ethanol ataxia via nicotinic-cholinergic receptors. We report now that attenuation of ethanol ataxia by intracerebellar nicotine is modulated by cerebellar nitric oxide-guanylyl cyclase (GC) messenger system. Intracerebellar microinfusion of SNP (sodium nitroprusside, a nitric oxide donor; 15, 30, and 60 pg) and SMT ( S-methylisothiourea; 70, 140, and 280 fg; an inhibitor of inducible nitric oxide synthase), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related manner. Similarly, intracerebellar isoliquiritigenin (an activator of GC; 1, 2, and 4 pg) and ODQ (1 H [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, an inhibitor of GC; 375, 750, and 1500 fg), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related fashion. These results suggest that the functional interaction between nicotine and ethanol may involve modulation by cerebellar nitric oxide and cGMP. Intracerebellar microinfusion of isoliquiritigenin (4, 8, and 16 pg) in the absence of nicotine significantly attenuated ethanol ataxia dose-dependently indicating a tonic involvement of cGMP in ethanol ataxia. Finally, intracerebellar nicotine (5 ng) significantly increased and ethanol 2 g/kg i.p. decreased levels of total cerebellar nitrite + nitrate (NO x ) which were functionally correlated with ethanol ataxia and its attenuation by intracerebellar nicotine. The ethanol-induced decrease in NO x was significantly antagonized by intracerebellar nicotine. The NO x data further supported an involvement of nitric oxide in the behavioral interaction between nicotine and ethanol. Overall, the results of the present investigation demonstrate a functional correlation between cerebellar nitric oxide messenger system and the behavioral interaction between nicotine and ethanol.

Alcohol Ataxia Tolerance: Extinction Cues, Spontaneous Recovery, and Relapse

This article reviews ethanol ataxic tolerance experiments with rats that investigate spontaneous recovery after extinction and how extinction-related cues reduce this recovery. Tolerance to the effects of many drugs including ethanol is partly the result of Pavlovian conditioning. Tolerance to the ataxic (and other) effects of ethanol depends critically upon the circumstances in which the drug is administered. Tolerance shows other characteristics common in Pavlovian conditioning, e.g.,. it can be extinguished and is subject to spontaneous recovery. The analogy of spontaneous recovery to instances of relapse in humans potentially makes such spontaneous recovery relevant to both researchers and clinicians. Recently, "extinction cues" have been found to reduce spontaneous recovery and other relapse- like effects in the animal conditioning laboratory. These cues may work in part by activating an association formed during the extinction process, and thus they may serve as memory retrieval cues. Research assessing spontaneous recovery using an ethanol ataxia method, as well as other Pavlovian conditioning methods, has contributed to an understanding of the properties and utility of extinction cues. These topics are addressed and the potential implications of this research for treating substance abusers is considered.

An extinction cue reduces spontaneous recovery of ataxic ethanol tolerance in rats.

Ethanol ataxia experiments with rats investigated cue effects on conditioned tolerance. Spontaneous recovery (SR) was assessed 1 day and 18 days after extinction with conditioned stimuli (CSs) paired or unpaired with an ethanol unconditioned stimulus (US). Behavioral tolerance was assessed by not tilting the apparatus during conditioning. Non-associative processes were assessed post-conditioning with or without a buzzer cue. Bouton's (1993, Psychol Bull 114:80-99) memory theory was tested using an extinction cue and an associatively neutral cue presented during SR testing. Tolerance was conditioned to a room + strobelight CS by ethanol injections experienced on a tilting floor (standard conditioning). Controls received no ethanol or ethanol, either during the CS without the floor tilting or 11 h post-CS. SR testing occurred 1 day or 18 days after extinction (experiment 1). Conditioning was followed by tolerance and CR tests either with or without a 15-s buzzer cue (experiment 2). In extinction, the CS and cue occurred without ethanol; the cue occurred before 7% or none of the extinction trials. Testing occurred 18 days after extinction with or without that cue (experiment 3), or with an equally familiar ("neutral'') cue presented before conditioning (experiment 4). Tolerance developed without floor tilting. CS-US unpairings prevented tolerance. Tolerance SR occurred 18 days but not 1 day after extinction only after CS-US pairings (experiment 1). Post-conditioning tests showed no unconditioned effects of the cue (experiment 2). Testing with no cue 1 day after extinction with the cue resulted in no tolerance increase. The extinction cue reduced SR (experiments 3 and 4); the neutral cue did not (experiment 4). Cues correlated with extinction reduce SR. Non-associative and practice processes, Bouton's (1993, Psychol Bull 114:80-99) memory theory, alternative interpretations, and clinical implications are discussed.

Extinction and spontaneous recovery of ataxic tolerance to ethanol in rats.

Two experiments with rats using an ethanol ataxia method investigated extinction and spontaneous recovery of tolerance. Tolerance extinction has been shown with a variety of drugs and methods, but until now it has not been shown with ethanol ataxia. Extinction was investigated here because of its connection with cue exposure treatments, and also to allow an assessment of spontaneous recovery. Spontaneous recovery is the return of conditioned responses, such as those potentially contributing to tolerance, when time passes after extinction. In terms of response topography it resembles instances of relapse in humans. Its demonstration constitutes one technique for illustrating that the effects of extinction are often temporary. There are no published reports showing a recovery of tolerance to any drug due to the passage of time after extinction. A demonstration of spontaneous recovery contributes to an understanding of the effects and time course of tolerance extinction. It also raises the possibility that spontaneous recovery involving drug tolerance has mechanisms similar those involved in instances of spontaneous recovery studied more extensively with non-drug methods. In one experiment, ataxic tolerance was conditioned to a strobelight conditioned stimulus (CS) by exposing rats to the strobelight while experiencing the effects of an ethanol injection. Tolerance was extinguished in 17 or 24 once-daily trials by presenting the strobelight without ethanol (with saline). The effect of those numbers of trials was assessed on the day after extinction in the presence of the strobelight when ethanol was again injected. The effect was compared to the effect of the strobelight and ethanol in naive rats and in rats that had received only tolerance conditioning. In a second experiment, ataxic tolerance was conditioned and then extinguished over 17 trials, just as in the other experiment. Different groups were then tested 1, 12, 18, and 24 days after extinction in the presence of the strobelight when ethanol was again injected. Ataxic tolerance was fully extinguished after either 17 or 24 trials, as shown by comparisons with the naive and conditioning-only controls. Tolerance was greater (it recovered) when the strobelight CS was reintroduced 24, 18, and even 12 days after extinction, compared with testing 1 day after extinction. Conditioned ataxic tolerance can be extinguished, just as other conditioned tolerances can. More important, the return of tolerance over time after extinction represents spontaneous recovery of ethanol tolerance, and indicates that as in other conditioning preparations, extinction does not result in unlearning of the original conditioning association. The identification of spontaneous recovery of tolerance isolates a robust source of the potential for drug use relapse: the mere passage of time after extinction.

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 A 1-selective adenosine agonist, N 6-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 G i 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.

Disruption of tolerance to the ataxic effect of ethanol by an extraneous stimulus

According to a conditioning analysis, pharmacological conditional responses (CRs) contribute to tolerance. We previously reported (24) that, as expected on the basis of this model, tolerance to the hypothermic effect of ethanol is attenuated by “external inhibition,” for instance, by presentation of a novel stimulus (a strobe). However, results of more recent research (2,12,13) indicate that novel stimuli augment the hypothermic effect of ethanol in rats receiving the drug for the first time. It is possible, therefore, that a novel stimulus apparently attenuates ethanol tolerance because it augments ethanol-hypothermia, rather than because it functions as an external inhibitor. Two experiments were designed to evaluate external inhibition of tolerance to another effect of ethanol—ataxia. Although the initial ataxic effect of the drug (unlike the hypothermic effect) is not enhanced by a novel stimulus, the stimulus reinstated ethanol-induced ataxia in tolerant rats. The results demonstrate external inhibition of ethanol tolerance in a preparation not confounded by the effects of the novel stimulus on initial responding to ethanol.