Effects of dihydropyridine calcium channel antagonists in ethanol withdrawal; doses required, stereospecificity and actions of Bay K 8644

L-Type Calcium Channel Blockers: A Potential Novel Therapeutic Approach to Drug Dependence

This review describes interactions between compounds, primarily dihydropyridines, that block L-type calcium channels and drugs that cause dependence, and the potential importance of these interactions. The main dependence-inducing drugs covered are alcohol, psychostimulants, opioids, and nicotine. In preclinical studies, L-type calcium channel blockers prevent or reduce important components of dependence on these drugs, particularly their reinforcing actions and the withdrawal syndromes. The channel blockers also reduce the development of tolerance and/or sensitization, and they have no intrinsic dependence liability. In some instances, their effects include reversal of brain changes established during drug dependence. Prolonged treatment with alcohol, opioids, psychostimulant drugs, or nicotine causes upregulation of dihydropyridine binding sites. Few clinical studies have been carried out so far, and reports are conflicting, although there is some evidence of effectiveness of L-channel blockers in opioid withdrawal. However, the doses of L-type channel blockers used clinically so far have necessarily been limited by potential cardiovascular problems and may not have provided sufficient central levels of the drugs to affect neuronal dihydropyridine binding sites. New L-type calcium channel blocking compounds are being developed with more selective actions on subtypes of L-channel. The preclinical evidence suggests that L-type calcium channels may play a crucial role in the development of dependence to different types of drugs. Mechanisms for this are proposed, including changes in the activity of mesolimbic dopamine neurons, genomic effects, and alterations in synaptic plasticity. Newly developed, more selective L-type calcium channel blockers could be of considerable value in the treatment of drug dependence. SIGNIFICANCE STATEMENT: Dependence on drugs is a very serious health problem with little effective treatment. Preclinical evidence shows drugs that block particular calcium channels, the L-type, reduce dependence-related effects of alcohol, opioids, psychostimulants, and nicotine. Clinical studies have been restricted by potential cardiovascular side effects, but new, more selective L-channel blockers are becoming available. L-channel blockers have no intrinsic dependence liability, and laboratory evidence suggests they reverse previously developed effects of dependence-inducing drugs. They could provide a novel approach to addiction treatment.

From Gene to Behavior: L-Type Calcium Channel Mechanisms Underlying Neuropsychiatric Symptoms

The L-type calcium channels (LTCCs) Cav1.2 and Cav1.3, encoded by the CACNA1C and CACNA1D genes, respectively, are important regulators of calcium influx into cells and are critical for normal brain development and plasticity. In humans, CACNA1C has emerged as one of the most widely reproduced and prominent candidate risk genes for a range of neuropsychiatric disorders, including bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder, autism spectrum disorder, and attention deficit hyperactivity disorder. Separately, CACNA1D has been found to be associated with BD and autism spectrum disorder, as well as cocaine dependence, a comorbid feature associated with psychiatric disorders. Despite growing evidence of a significant link between CACNA1C and CACNA1D and psychiatric disorders, our understanding of the biological mechanisms by which these LTCCs mediate neuropsychiatric-associated endophenotypes, many of which are shared across the different disorders, remains rudimentary. Clinical studies with LTCC blockers testing their efficacy to alleviate symptoms associated with BD, SCZ, and drug dependence have provided mixed results, underscoring the importance of further exploring the neurobiological consequences of dysregulated Cav1.2 and Cav1.3. Here, we provide a review of clinical studies that have evaluated LTCC blockers for BD, SCZ, and drug dependence-associated symptoms, as well as rodent studies that have identified Cav1.2- and Cav1.3-specific molecular and cellular cascades that underlie mood (anxiety, depression), social behavior, cognition, and addiction.

Differential Roles for L-Type Calcium Channel Subtypes in Alcohol Dependence

It has previously been shown that the inhibition of L-type calcium channels (LTCCs) decreases alcohol consumption, although the contribution of the central LTCC subtypes Cav1.2 and Cav1.3 remains unknown. Here, we determined changes in Cav1.2 (Cacna1c) and Cav1.3 (Cacna1d) mRNA and protein expression in alcohol-dependent rats during protracted abstinence and naive controls using in situ hybridization and western blot analysis. Functional validation was obtained by electrophysiological recordings of calcium currents in dissociated hippocampal pyramidal neurons. We then measured alcohol self-administration and cue-induced reinstatement of alcohol seeking in dependent and nondependent rats after intracerebroventricular (i.c.v.) injection of the LTCC antagonist verapamil, as well as in mice with an inducible knockout (KO) of Cav1.2 in Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα)-expressing neurons. Our results show that Cacna1c mRNA concentration was increased in the amygdala and hippocampus of alcohol-dependent rats after 21 days of abstinence, with no changes in Cacna1d mRNA. This was associated with increased Cav1.2 protein concentration and L-type calcium current amplitudes. Further analysis of Cacna1c mRNA in the CA1, basolateral amygdala (BLA), and central amygdala (CeA) revealed a dynamic regulation over time during the development of alcohol dependence. The inhibition of central LTCCs via i.c.v. administration of verapamil prevented cue-induced reinstatement of alcohol seeking in alcohol-dependent rats. Further studies in conditional Cav1.2-KO mice showed a lack of dependence-induced increase of alcohol-seeking behavior. Together, our data indicate that central Cav1.2 channels, rather than Cav1.3, mediate alcohol-seeking behavior. This finding may be of interest for the development of new antirelapse medications.

Are Alcohol Anti-relapsing and Alcohol Withdrawal Drugs Useful in Cannabinoid Users?

Cannabinoids are still classified as illegal psychoactive drugs despite their broad and increasingly acknowledged therapeutic potential. These substances are most famous for their wide recreational use, particularly among young adults to either alter the state of consciousness, intensify pleasure induced by other psychoactive substances or as an alternative to the previously abused drugs. It is important to emphasize that cannabinoids are often taken together with a variety of medications intended for the treatment of alcohol use disorder (AUD) or alcohol withdrawal syndrome (AWS). These medications include disulfiram, acamprosate, and naltrexone. In this paper, we summarize recent advances in the knowledge of possible beneficial effects and interactions between cannabinoids and drugs commonly used for treatment of AUD and AWS either comorbid or existing as a separate disorder.

Functional effects of alcohol withdrawal syndrome on peripheral sympathetic neurotransmission in vas deferens of adult rats

AIMS

Alcohol withdrawal syndrome (AWS) is characterized by a set of physiological modifications triggered by abrupt withdrawal and/or decreasing consumption of ethanol (EtOH), which may manifest 16-48 h after ceasing consumption. The relationship between the effects of AWS and central and peripheral sympathetic neurotransmission is unknown. This study investigates the possible mechanisms on the sympathetic system during periods of AWS.

MAIN METHODS

Male Wistar rats were treated with EtOH (6-10 g/kg/day/v.o. 5 days). Subsequently, 1h, 24h, 48 h and 120 h after administration of the last dose of EtOH, the animals were sacrificed, and their vas deferens (VD) were removed to perform the following evaluations: (a) concentration-effect curves of sympathetic agonist; (b) activity of α2-adrenoreceptor; (c) function of voltage-dependent calcium channels (Cav); and (d) release of endogenous catecholamines measured in real time coupled to HPLC.

KEY FINDINGS

The results showed that the maximum effects of contraction were increased by agonists tested in at 24h and 48 h EtOH withdrawal. The inhibitory affinity (pIC50) of guanfacine was decreased 24h EtOH withdrawal. The function of Cav was also decreased as pIC50 values dropped 24h and 48 h EtOH withdrawal. The release of catecholamines increased 48 h after EtOH withdrawal. It is suggested that AWS triggers hyperactivity in peripheral sympathetic neurotransmission.

SIGNIFICANCE

The mechanisms underlying hyperactivity are possibly explained by a failure of autoregulation from catecholamines released by α2-adrenoreceptors and/or an increase of Cav function, which may be potential targets to attenuate the symptoms of AWS at the peripheral level.

Ethanol tolerance and withdrawal severity in high drinking in the dark selectively bred mice

BACKGROUND

Mouse lines are being selectively bred in replicate for high blood ethanol concentrations (BECs) achieved after limited access of ethanol (EtOH) drinking early in the circadian dark phase. High Drinking in the Dark-1 (HDID-1) mice are in selected generation S21, and the replicate HDID-2 line in generation S14. Tolerance and withdrawal symptoms are 2 of the 7 diagnostic criteria for alcohol dependence. Withdrawal severity has been found in mouse studies to be negatively genetically correlated with EtOH preference drinking.

METHODS

To determine other traits genetically correlated with high DID, we compared naïve animals from both lines with the unselected, segregating progenitor stock, HS/Npt. Differences between HDID-1 and HS would imply commonality of genetic influences on DID and these traits.

RESULTS

Female HDID-1 and HDID-2 mice tended to develop less tolerance than HS to EtOH hypothermia after their third daily injection. A trend toward greater tolerance was seen in the HDID males. HDID-1, HDID-2, and control HS lines did not differ in the severity of acute or chronic withdrawal from EtOH as indexed by the handling-induced convulsion (HIC). Both HDID-1 and HDID-2 mice tended to have greater HIC scores than HS regardless of drug treatment.

CONCLUSIONS

These results show that tolerance to EtOH's hypothermic effects may share some common genetic control with reaching high BECs after DID, a finding consistent with other data regarding genetic contributions to EtOH responses. Withdrawal severity was not negatively genetically correlated with DID, unlike its correlation with preference drinking, underscoring the genetic differences between preference drinking and DID. HDID lines showed greater basal HIC scores than HS, suggestive of greater central nervous system excitability.

L-type calcium channels and psychiatric disorders: A brief review

Emerging evidence from genome-wide association studies (GWAS) support the association of polymorphisms in the alpha 1C subunit of the L-type voltage-gated calcium channel gene (CACNA1C) with bipolar disorder. These studies extend a rich prior literature implicating dysfunction of L-type calcium channels (LTCCs) in the pathophysiology of neuropsychiatric disorders. Moreover, calcium channel blockers reduce Ca(2+) flux by binding to the α1 subunit of the LTCC and are used extensively for treating hypertension, preventing angina, cardiac arrhythmias and stroke. Calcium channel blockers have also been studied clinically in psychiatric conditions such as mood disorders and substance abuse/dependence, yielding conflicting results. In this review, we begin with a summary of LTCC pharmacology. For each category of disorder, this article then provides a review of animal and human data. In particular, we extensively focus on animal models of depression and clinical trials in mood disorders and substance abuse/dependence. Through examining rationale and study design of published clinical trials, we provide some of the possible reasons why we still do not have definitive evidence of efficacy of calcium-channel antagonists for mood disorders. Refinement of genetic results and target phenotypes, enrollment of adequate sample sizes in clinical trials and progress in physiologic and pharmacologic studies to synthesize tissue and isoform specific calcium channel antagonists, are all future challenges of research in this promising field. © 2010 Wiley-Liss, Inc.

Participation of L-type calcium channels in ethanol-induced behavioral stimulation and motor incoordination: effects of diltiazem and verapamil

Calcium flux through voltage gate calcium channels (VGCC) is involved in many neuronal processes such as membrane depolarization, gene expression, hormone secretion, and neurotransmitter release. Several studies have shown that either acute or chronic exposure to ethanol modifies calcium influx through high voltage activated channels. Of special relevance is the L-type VGCC. Pharmacological manipulation of L-type calcium channels affects ethanol intake, ethanol discrimination and manifestations of withdrawal syndrome. The present study investigates the role of L-type channels on the psychomotor effects (stimulation and sedation/ataxia) of ethanol by testing the effects of different L-type calcium channel blockers (CCB) on such behaviors. Mice were pretreated intraperitoneally with the CCB, diltiazem (0-40 mg/kg) or verapamil (0-30 mg/kg) 30 min before ethanol (0-3.5 g/kg). Locomotion was measured in an open field chamber for 20 min immediately after ethanol. The two CCB tested prevented locomotor stimulation, but not locomotor suppression produced by ethanol. Doses of the two CCB which reduced ethanol stimulation, did not alter spontaneous locomotion. The ataxic effects of ethanol (1.25 g/kg), measured with an accelerating rotarod task, were not affected by diltiazem (20mg/kg) or verapamil (15 mg/kg). In addition, our results indicated that ethanol is more sensitive to the antagonism of L-type calcium channels than other drugs with stimulant properties; doses of the two CCB that reduced ethanol stimulation did not reduce the psychomotor effects of amphetamine, caffeine or cocaine. In conclusion, these data provide further evidence of the important involvement of L-type calcium channels in the behavioral effects produced by ethanol.

Alcohol withdrawal-induced hippocampal neurotoxicity in vitro and seizures in vivo are both reduced by memantine

BACKGROUND

The ethanol withdrawal (EWD) syndrome is typically treated using benzodiazepines such as diazepam. However there is concern that benzodiazepines may not prevent neurotoxicity associated with EWD. Antagonists of glutamate/N-Methyl-D-Aspartate receptors (NMDARs) such as MK801 have been shown to be effective against both EWD-induced neurotoxicity in vitro and seizures in vivo. However, most of these agents have adverse side effects. An exception is the moderate affinity NMDAR channel blocker memantine, used in Alzheimer's dementia. The present studies examined the ability of memantine to protect against EWD-related toxicity in vitro and seizures in vivo.

METHODS

Organotypic hippocampal slice cultures from neonatal rat pups were treated starting at 15 days in vitro with 100 mM ethanol for 10 days followed by a 24-hour EWD period. During the 24-hour EWD period cultures were treated with memantine (15 or 30 microM). MK801 (10 microM) was utilized as a positive control. For the in vivo studies, the ability of memantine (2, 5, 10, and 15 mg/kg) to reduce convulsions was analyzed in Swiss-Webster mice using the handling induced convulsion test paradigm.

RESULTS

In vitro studies demonstrated that memantine is effective at blocking EWD-induced neurotoxicity. In vivo experiments showed that memantine also significantly reduced convulsions induced by EWD in mice.

CONCLUSIONS

Memantine may be of therapeutic value during alcohol detoxification by virtue of its having neuroprotective effects in addition to anti-seizure activity. The potential role of memantine in treatment of alcoholism is deserving of further study.

Effects of the glucocorticoid antagonist, mifepristone, on the consequences of withdrawal from long term alcohol consumption

BACKGROUND

Studies were carried out to test the hypothesis that administration of a glucocorticoid Type II receptor antagonist, mifepristone (RU38486), just prior to withdrawal from chronic alcohol treatment, would prevent the consequences of the alcohol consumption and withdrawal in mice.

MATERIALS AND METHODS

The effects of administration of a single intraperitoneal dose of mifepristone were examined on alcohol withdrawal hyperexcitability. Memory deficits during the abstinence phase were measured using repeat exposure to the elevated plus maze, the object recognition test, and the odor habituation/discrimination test. Neurotoxicity in the hippocampus and prefrontal cortex was examined using NeuN staining.

RESULTS

Mifepristone reduced, though did not prevent, the behavioral hyperexcitability seen in TO strain mice during the acute phase of alcohol withdrawal (4 hours to 8 hours after cessation of alcohol consumption) following chronic alcohol treatment via liquid diet. There were no alterations in anxiety-related behavior in these mice at 1 week into withdrawal, as measured using the elevated plus maze. However, changes in behavior during a second exposure to the elevated plus maze 1 week later were significantly reduced by the administration of mifepristone prior to withdrawal, indicating a reduction in the memory deficits caused by the chronic alcohol treatment and withdrawal. The object recognition test and the odor habituation and discrimination test were then used to measure memory deficits in more detail, at between 1 and 2 weeks after alcohol withdrawal in C57/BL10 strain mice given alcohol chronically via the drinking fluid. A single dose of mifepristone given at the time of alcohol withdrawal significantly reduced the memory deficits in both tests. NeuN staining showed no evidence of neuronal loss in either prefrontal cortex or hippocampus after withdrawal from chronic alcohol treatment.

CONCLUSIONS

The results suggest mifepristone may be of value in the treatment of alcoholics to reduce their cognitive deficits.

Tolerance to the antinociceptive effects of ethanol during ethanol withdrawal

Prior research has indicated that tolerance develops to the antinociceptive effects of ethanol and continues even during withdrawal. Three potential pharmacological mechanisms for this tolerance are examined, using nitrendipine (L-type calcium channel blocker), theophylline (adenosine A1/A2 antagonist) and flumazenil (benzodiazepine antagonist). Rats received 10 days of exposure to an ethanol-containing liquid diet (6.5% w/v). A radiant heat tail-flick assay was used to assess hyperalgesia at 12 h after removal of the liquid diet, as well as tolerance to the effects of cumulative doses of ethanol (0.5-2 g/kg). Co-administration of flumazenil (10 mg/kg, i.p., b.i.d.), nitrendipine (5 mg/kg, i.p., b.i.d.) or theophylline (1 mg/kg, i.p., b.i.d.) with chronic ethanol prevented development of the hyperalgesia produced by ethanol withdrawal, but only theophylline reduced tolerance to the antinociceptive effects of ethanol administered during ethanol withdrawal. In contrast, when administered during ethanol withdrawal, theophylline (1-10 mg/kg) blocked the anti-hyperalgesic effects of ethanol during ethanol withdrawal, whereas nitrendipine (5-25 mg/kg) enabled ethanol to produce levels of antinociception comparable to non-dependent rats. These findings indicate that L-type calcium channels and adenosine receptors play important, but differing roles in the development of hyperalgesia during withdrawal, and to tolerance to the antinociceptive effects of ethanol.

Pregabalin is effective against behavioral and electrographic seizures during alcohol withdrawal

AIMS

Pregabalin has been shown to possess anticonvulsant, analgesic, and anxiolytic properties in a variety of testing situations. This study was designed to evaluate the ability of pregabalin to exert its anticonvulsant effects against behavioral and electrographic measures of CNS hyperexcitability associated with alcohol withdrawal in a mouse model of ethanol dependence.

METHODS

Adult mice were chronically exposed to ethanol and, upon withdrawal, were tested for behavioral signs of seizure activity (handling-induced convulsions) or abnormalities in spontaneous EEG activity recorded from cortical and subcortical sites.

RESULTS

Pregabalin (50-200 mg/kg) administered 1 and 4 h into withdrawal dose dependently reduced severity of handling-induced convulsions in comparison to vehicle-treated mice. Similarly, pregabalin reduced the frequency in which EEG activity was interrupted by trains of high-voltage synchronous activity in a dose-related fashion. Finally, pregabalin treatment of repeated withdrawals was effective in blocking the development of withdrawal sensitization observed in vehicle-treated mice.

CONCLUSIONS

Collectively, these results suggest that pregabalin may be an effective therapeutic agent for medical management of alcohol detoxification.

Estrogen neuroprotection against the neurotoxic effects of ethanol withdrawal: potential mechanisms

Ethanol withdrawal (EW) produces substantial neurotoxic effects, whereas estrogen is neuroprotective. Given observations that both human and nonhuman female subjects often show less impairment following EW, it is reasonable to hypothesize that estrogens may protect females from the neurotoxic effects of ethanol. This article is based on the assumption that the behavioral deficits seen following EW are produced in part by neuronal death triggered by oxidative insults produced by EW. The EW leads to activation of protein kinase C, especially PKCepsilon, which subsequently triggers apoptotic downstream events such as phosphorylation of nuclear factor-kappaB (NFkappaB) complex. On phosphorylation, active NFkappaB translocates to the nucleus, binds to DNA, and activates caspases, which trigger DNA fragmentation and apoptosis. In contrast, estrogens are antioxidant, inhibit overexpression of PKCepsilon, and suppress expression of NFkappaB and caspases. Estrogen treatment reduces the behavioral deficits seen during EW and attenuates molecular signals of apoptosis. The effects of ethanol and estrogen on each step in the signaling cascade from ethanol exposure to apoptosis are reviewed, and potential mechanisms by which estrogen could produce neuronal protection against the neurotoxicity produced by EW are identified. These studies serve as a guide for continuing research into the mechanisms of the neuroprotective effects of estrogen during EW and for the development of potential estrogen-based treatments for male and female alcoholics.

Calcium channel antagonists attenuate cross-sensitization to the rewarding and/or locomotor effects of nicotine, morphine and MK-801

The present study focused on the evaluation of behavioural cross-sensitization, particularly in locomotor activities and conditioned rewarding effects, between nicotine and morphine, cocaine, amphetamine or MK-801. Nicotine (0.5 mg kg(-1))-experienced mice manifested an enhanced locomotor response to morphine (5 mg kg(-1)) or MK-801 (0.3 mg kg(-1)). No cross-sensitization was observed between nicotine and amphetamine (2 mg kg(-1)) or cocaine (15 mg kg(-1)). Additionally, the L-type voltage-dependent calcium-channel antagonists, nimodipine and verapamil, but not diltiazem, at a dose of 20 mg kg(-1) injected before morphine or MK-801 challenge, blocked the expression of this cross-sensitization. In the second test, an enhancement of morphine place conditioning in rats pre-exposed to nicotine (0.5 mg kg(-1), injected daily for 5 days) was demonstrated. After two conditioning sessions, morphine (5 mg kg(-1)) induced a clear place preference only in animals that had previously received nicotine injections. The administration of nimodipine (10 and 20 mg kg(-1)), verapamil (10 and 20 mg kg(-1)) and diltiazem (10 and 20 mg kg(-1)) prior to nicotine dose-dependently prevented this sensitization to the rewarding effect of morphine produced by prior injections of nicotine. These findings support the hypothesis that similar neural calcium-dependent mechanisms are involved in the appetitive effects of nicotine and morphine and in the sensitized locomotor stimulant effects of nicotine and morphine or MK-801.

Mechanisms of cardiovascular dysregulation during alcohol withdrawal

Alcohol withdrawal (AW) is often accompanied by functional cardiovascular abnormalities which return to normal in few days. However, in some patients, they can predict future alterations in the cardiovascular system, even if they remain in abstinence. These changes are mediated by several central and peripheral mechanisms closely related to AW. The level of activation in the sympathetic nervous system is an important factor regulating the functioning of the cardiovascular system in AW directly and/or indirectly with L-type calcium channels and nitric oxide (NO). Other factors may contribute to cardiovascular alterations in AW including the renin-angiotensin-aldosterone system, vasopressin, cortisol and sodium sensitivity. Monitoring of the cardiovascular system is needed in patients undergoing treatment for AW. The patients with elevated systolic blood pressure (SBP) and diastolic blood pressure (DBP) after resolution of AW may require a fuller work-up of their cardiovascular system.

Opposing effects of ethanol and nicotine on hippocampal calbindin-D28k expression

Long-term ethanol exposure produces multiple neuroadaptations that likely contribute to dysregulation of Ca(2+) balance and neurotoxicity during ethanol withdrawal. Conversely, nicotine exposure may reduce the neurotoxic consequences of Ca(2+) dysregulation, putatively through up-regulation of the Ca(2+)-buffering protein calbindin-D(28k). The current studies were designed to examine the extent to which 10-day ethanol exposure and withdrawal altered calbindin-D(28k) expression in rat hippocampus. Further, in these studies, we examined the ability of nicotine, through action at alpha(7)(*)-bearing nicotinic acetylcholine receptors (nAChRs), to antagonize the effects of ethanol exposure on calbindin-D(28k) expression. Organotypic cultures of rat hippocampus were exposed to ethanol (50-100 mM) for 10 days. Additional cultures were exposed to 500 nM (-)-nicotine with or without the addition of 50 mM ethanol, 100 nM methyllycaconitine (an alpha(7)*-bearing nAChR antagonist), or both. Prolonged exposure to ethanol (>/=50 mM) produced significant reductions of calbindin-D(28k) immunolabeling in all regions of the hippocampal formation, even at nontoxic concentrations of ethanol. Calbindin-D(28k) expression levels returned to near-control levels after 72 h of withdrawal from 10-day ethanol exposure. Extended (-)-nicotine exposure produced significant elevations in calbindin-D(28k) expression levels that were prevented by methyllycaconitine co-exposure. Co-exposure of cultures to (-)-nicotine with ethanol resulted in an attenuation of ethanol-induced reductions in calbindin-D(28k) expression levels. These findings support the suggestion that long-term ethanol exposure reduces the neuronal capacity to buffer accumulated Ca(2+) in a reversible manner, an effect that likely contributes to withdrawal-induced neurotoxicity. Further, long-term exposure to (-)-nicotine enhances calbindin-D(28k) expression in an alpha(7)* nAChR-dependent manner and antagonizes the effects of ethanol on calbindin-D(28k) expression.

Selectivity of the protective effects of dihydropyridine calcium channel antagonists against the ethanol withdrawal syndrome

Four dihydropyridine calcium channel antagonists were compared for their ability to protect against the hyperexcitability produced in mice by withdrawal from chronic ethanol treatment and to protect against seizures due to bicuculline or pentylenetetrazol. Comparison was also made of their effects on locomotor activity, body temperature and motor co-ordination, and with the corresponding effects of the benzodiazepine, diazepam. Nitrendipine, nimodipine, nicardipine (at 50 and 10 mg/kg) and isradipine (at 10 and 4 mg/kg) decreased the withdrawal hyperexcitability, but showed no anticonvulsant action against either bicuculline or pentylenetetrazol. Diazepam (1.5 and 4 mg/kg) both protected against the withdrawal signs and decreased seizure incidence after bicuculline and pentylenetetrazol, although the latter effects were of shorter duration than those on the withdrawal signs. The four dihydropyridines decreased spontaneous locomotor activity, an effect which lasted up to 6 h. Only isradipine and diazepam had any ataxic actions at the doses tested. All the dihydropyridines had hypothermic actions, considerably shorter in duration than effects on withdrawal hyperexcitability, with little evidence of dose dependence, except for nicardipine, which had a larger, dose-related, hypothermic action. Of the four compounds, isradipine was more potent in terms of dose, but not any more selective for effectiveness against the withdrawal signs, than the other three dihydropyridines, and nicardipine was slightly less effective in protecting against the withdrawal signs. The results indicate that the anticonvulsant effects of the dihydropyridines were selective for ethanol withdrawal hyperexcitability, whereas diazepam showed no such selectivity.

Nimodipine prevents the effects of ethanol in tests of memory

The effects of acute administration of the dihydropyridine calcium channel antagonist, nimodipine, were studied on the actions of ethanol in the radial arm maze and the object recognition test. In the former test, the effects of the drugs were examined on the performance in finding the four baited arms, after previous training in this task. Ethanol, at 1 g/kg, increased both the number of re-entries into baited arms (counted as errors of working memory) and the total number of arm choices required to complete the task. Administration of nimodipine, 10 mg/kg, with the ethanol, completely prevented the deleterious effects on memory in this task, but had no effects on the performance when given in the absence of ethanol. In the object recognition task, ethanol, 1 g/kg, significantly decreased the differences in the time spent exploring novel and familiar objects. Nimodipine, 10 mg/kg, given with the ethanol, completely prevented this effect, but nimodipine alone had no effects. The lack of changes in total exploration times indicated that the effects of ethanol in these tests were not due to loss of motor co-ordination or of alertness. The results are discussed in the light of the known actions of the drugs on brain function.

Effects of calcium channel blockers on pentylenetetrazol drug discrimination in rats

The effects of the dihydropyridine L-type calcium channel blockers nitrendipine and nimodipine on the pentylenetetrazol (PTZ) drug discrimination, an operant model of anxiety, were investigated. Male Long-Evans rats were trained to discriminate PTZ (16 mg/kg, i.p.) from saline. Both nitrendipine (5.0-25 mg/kg, i.p.) and nimodipine (5.0-25 mg/kg, i.p.) partially substituted for the PTZ discriminative stimulus. However, pretreatment with nitrendipine (25 mg/kg, i.p.) or nimodipine (25 mg/kg, i.p.) produced no change in the PTZ dose-effect function. Rats were given a nutritionally balanced liquid diet containing 6.5% ethanol for 10 days. Rats selected the PTZ drug lever during withdrawal. Subchronic coadministration of nitrendipine (1.25-5.0 mg/kg, i.p., b.i.d.) with ethanol failed to dose-dependently reduce PTZ-lever responding, but it did reverse withdrawal signs. Acute administration of nitrendipine (5, 10, and 20 mg/kg, i.p.) produced marked suppression of lever responding, but it failed to significantly reduce levels of PTZ-lever responding. Although calcium channel blockers reduce signs of ethanol withdrawal, they also markedly reduce rates of behavior and produce no clear effects on anxiety-like behaviors induced by ethanol withdrawal.

Ethanol regulates calcium channel subunits by protein kinase C delta -dependent and -independent mechanisms

Chronic exposure to ethanol increases the number of functional L-type voltage-gated calcium channels in neural cells. In PC12 cells, this adaptive response is mediated by protein kinase C delta (PKCdelta), but the mechanisms by which this occurs are not known. Since expression of several different calcium channel subunits can increase the abundance of functional L-type channels, we sought to identify which subunits are regulated by ethanol. Incubation of PC12 cells with 120-150 mm ethanol for 6 days increased levels of alpha(1C), alpha(2), and beta(1b) subunit immunoreactivity in cell membranes and selectively increased the abundance of mRNA encoding the alpha(1C-1) splice variant of alpha(1C). In cells expressing a fragment of PKCdelta (deltaV1) that selectively inhibits PKCdelta, there was no increase in membrane-associated alpha(1C), alpha(2), and beta(1b) immunoreactivity following chronic ethanol exposure. However, ethanol still increased levels of alpha(1C-1) mRNA in these cells. These results indicate that ethanol increases the abundance of L-type channels by at least two mechanisms; one involves increases in mRNA encoding a splice variant of alpha(1C) and the other is post-transcriptional, rate-limiting, and requires PKCdelta.

Ethanol and amino acids in the central nervous system: assessment of the pharmacological actions of acamprosate

Ethanol induces alterations in the central nervous system by differentially interfering with a number of neurotransmitter systems, although the mechanisms by which such effects are executed are not well understood. The present review therefore, is designed to ascertain the effect of ethanol on both excitatory and inhibitory amino acid neurotransmitters, as well as the sulphonated amino acid taurine, assayed by the microdialysis technique within specific brain regions of rat during different types of alcohol intoxication, acute and chronic, as well as during the withdrawal period. Such an understanding of these pharmacological actions of ethanol on neurotransmitters is essential in order to provide the impetus for the development of appropriate therapeutic intervention to ameliorate the multitude of neurochemical disorders induced by ethanol. In addition the possible mode of action of a new therapeutic drug for the treatment of alcoholism, acamprosate will be discussed. The first part of this review will be limited to studies of the effect of ethanol on both amino acid neurotransmitters and the sulphonated amino acid taurine, a possible neuromodulator. While, the second part will seek to establish the possible mechanism of action of a new therapeutic drug, acamprosate, which is used to combat the effects of ethanol, particularly during the craving period, as well as maintaining abstinence in weaned alcoholics.

Taurine blocks the glutamate increase in the nucleus accumbens microdialysate of ethanol-dependent rats

During ethanol withdrawal, dramatic changes in the concentration of many neurotransmitters may be responsible for many of the adverse effects. In the present study, the technique of microdialysis was used to assay the changes in excitatory and inhibitory amino acids after withdrawal from chronic ethanol intoxication. Rats were made physically dependent on ethanol by vapor inhalation for 4 weeks. The basal concentrations of both arginine and GABA were significantly decreased in ethanol-dependent rats, although there were no significant changes in any of the other amino acid basal concentration assayed (i.e.. glutamate and taurine). During the first 12 h after withdrawal from ethanol, only glutamate increased significantly (p < 0.05) at 6 h, and for the duration of the study period of 12 h. To investigate whether either taurine and ethanol interact with amino acids during ethanol withdrawal, two other ethanol-dependent groups were injected with a single intraperitoneal injection of either taurine or ethanol 5 h after commencement of ethanol withdrawal. The IP injection of ethanol (2 g/kg) significantly increased taurine microdialysate content, and although this dose of ethanol was not able to block completely the increase of glutamate release after ethanol withdrawal, a delayed decrease in glutamate content was observed by the end of the period of the study (i.e., 11-12 h). However, IP injection of taurine (45 mg/kg) significantly blocked the increased glutamate release during ethanol withdrawal. This latter finding suggests that taurine may interact with glutamate, possibly by inducing a blockade of glutamate release during ethanol withdrawal.

Discriminative and affective stimulus effects of dihydropyridine calcium channel modulators: relationship to antialcohol effects

Voltage-operated calcium channels (VOCCs) have been implicated in alcoholism. Thus, dihydropyridine (DHP) VOCC antagonists, such as nimodipine, reduce ethanol (EtOH) intake and preference in a variety of animal models of alcoholism. Paradoxically, the DHP VOCC agonist BAY k 8644 also demonstrates antialcohol effects in such models. The antialcohol effects of BAY k 8644 are stereoselective [the "agonistic" (-)-enantiomer being more potent than the "antagonistic" (+)-enantiomer], and are not blocked by pretreatment with nimodipine. The present review summarizes studies on the effects of DHPs in drug discrimination (DD), conditioned taste aversion (CTA), and conditioned place preference (CPP) paradigms, and discusses the possibility that the apparent antialcohol effect of these compounds is related to their discriminative and/or affective stimulus effects. In rats trained to discriminate nimodipine from vehicle, (-)-BAY k 8644 completely generalizes to the nimodipine cue; whereas, in rats trained to discriminate (-)-BAY k 8644, nimodipine completely generalizes to, and is unable to block, the (-)-BAY k 8644 cue. The same stereoselectivity is obtained for BAY k 8644 in DD paradigms and models of alcoholism. The apparent similarity of these profiles of activity suggests that a common neurobiological mechanism underlies the discriminative stimulus and antialcohol effects of DHPs. It appears unlikely, however, that the antialcohol effects of DHPs are based on substitution for, or blockade of, the EtOH cue, as these compounds were not found to generalize to, or block, the EtOH cue. Comparison of the effects of DHPs in CTA and CPP paradigms suggests that the affective stimulus effects of these compounds are dissimilar, and that the mechanism underlying the latter effects is probably not related to the mechanism underlying the antialcohol effects of DHP VOCC modulators.

Effects of nimodipine on extracellular dopamine levels in the rat nucleus accumbens in ethanol withdrawal

Withdrawal from chronic ethanol intoxication is associated with a reduction of dopamine neurotransmission. However, the mechanisms of dopamine depletion, a putative neurochemical correlate of the dysphoric symptomatology, are not yet understood. To assess the role of L-type calcium channels in the inhibition of the dopaminergic system in the withdrawal state, the effects of the dihydropyridine calcium channel antagonist nimodipine on the extracellular levels of dopamine were studied in the nucleus accumbens shell of awake rats 10 h after withdrawal from chronic ethanol intoxication. In control, chronic sucrose-withdrawn rats, nimodipine did not change extracellular dopamine levels. However, in ethanol-withdrawn rats nimodipine (5 or 10 mg/kg s.c.) increased extracellular dopamine to 136 +/- 16 and 305 +/- 19% of pre-administration values, respectively, the latter dose elevating levels above those of controls. The elevations of extracellular DA by nimodipine (10 mg/kg) were associated with a significant reduction (-17%) of the overall behavioural score of the withdrawal symptomatology, as evaluated for 11 behavioural items. Significant reductions of the score for convulsions (-47%) and, to a lesser extent, for catatonia (-30%) and tremors (-15%) contributed to the overall effect. It is suggested that overactivity of L-type calcium channels is involved in the mechanisms of dopamine depletion as well as in certain behavioural/neurological signs associated with ethanol withdrawal. By restoring depleted dopamine levels, dihydropyridines might ameliorate the dysphoric symptoms of ethanol abstinence.

Regulation of neuronal voltage-gated calcium channels by ethanol

Voltage-gated calcium channels are key regulators of neuronal excitability. Several studies indicate that intoxicating concentrations of ethanol inhibit L-type, N-type and possibly T-type channels. The effects of ethanol on other channel subtypes are not yet clear. Chronic exposure to ethanol is associated with increases in functional L-type channels and this may contribute to signs of ethanol withdrawal. Preclinical studies in animals suggest that L-type calcium channel antagonists decrease ethanol consumption and signs of alcohol withdrawal. Although L-type channel antagonists do not appear to alter the performance impairing or psychological effects of acute ethanol administration, clinical trials will be needed to determine if L-type channel antagonists reduce ethanol consumption in humans.

Ethanol exposure during the third trimester equivalent results in long-lasting decreased synaptic efficacy but not plasticity in the CA1 region of the rat hippocampus

Fetal alcohol syndrome is a major cause of mental retardation. We investigated possible long-lasting effects of alcohol on the hippocampus using a model for human third trimester brain development. Treatment of neonatal rats with an ethanol vapor atmosphere of 39.4+/-2.6 mg ethanol/liter of air for 3 h a day from postnatal day 4 through 9 produced daily blood ethanol levels of 351+/-14 mg/dL. Separation control animals were removed from their mothers in parallel with the ethanol vapor treatment, while suckle controls were left to develop normally. We prepared hippocampal slices from these animals between postnatal days 45 and 60 and recorded extracellular responses to Schaffer collateral stimulation. The maximum population spike in the CA1 pyramidal region and population excitatory postsynaptic potentials in the stratum radiatum did not differ significantly between groups. However, slices prepared from ethanol-treated rats as opposed to separation and suckle controls required larger stimulus currents to produce normal postsynaptic responses. In addition, the ratio of the population excitatory postsynaptic potential (pEPSP) slope to the presynaptic volley was significantly reduced in ethanol-treated rats. Ethanol vapor-treated rats and separation control rats did not exhibit any significant changes in long-term potentiation or paired-pulse potentiation compared with normal suckle controls. These results suggest that early postnatal ethanol treatment produces a long-lasting reduction in synaptic efficacy but not plasticity.

Differing acute interactions of ethanol with two structurally related dihydropyridines, nitrendipine and felodipine

Previous work showed that while several dihydropyridine calcium channel antagonists have protective effects against the ethanol withdrawal syndrome, felodipine differed in lacking this action. Dihydropyridine calcium channel antagonists have also been shown to potentiate the acute behavioral actions of ethanol. The present study compares the effects of felodipine on the acute effects of ethanol, with those of nitrendipine, a dihydropyridine previously shown to be effective against the ethanol withdrawal syndrome. Comparison was made at doses of the compounds that have previously been shown to produce similar displacement of dihydropyridine binding in central nervous system (CNS) tissue. Felodipine had a small potentiating effect on the general anesthetic effects of ethanol, but was considerably less effective in this respect than nitrendipine. Some potentiation of the ataxic effect of ethanol was seen after concurrent administration of felodipine, but this was less than that seen after nitrendipine. In the locomotor studies, both felodipine and nitrendipine significantly decreased the locomotor stimulation produced by ethanol; the effects of the two compounds were similar, but dose-dependency was not seen at the doses tested. Chronic administration of felodipine for 2 weeks did not produce tolerance to the sedative effect of felodipine or cross-tolerance to nitrendipine. After chronic administration of the felodipine, administration of an acute dose of ethanol resulted in an increase in locomotor activity, but this was not seen after chronic administration of nitrendipine or vehicle. The results, therefore, suggest that felodipine was considerably less effective in potentiating the acute effects of ethanol than nitrendipine at doses that were equi-effective in displacing central dihydropyridine binding. The interactions of these two calcium channel antagonists with ethanol, therefore, did not parallel their effects on central dihydropyridine binding.

Chronic ethanol administration alters activity in ventral tegmental area neurons after cessation of withdrawal hyperexcitability

The present study investigated the activity of neurons in the mesolimbic dopamine system after the end of the acute phase of the behavioural signs of ethanol withdrawal in mice. This was designed to provide a comparison with earlier behavioural studies, in which greater development of sensitisation to amphetamine and cocaine, but no change in the initial effects of these compounds, or in the behaviour in the absence of drug treatment, was seen when repeated injection of these psychostimulants were given after chronic ethanol consumption. In the present study, single unit recordings were made from dopamine-sensitive neurons in the ventral tegmental area in perfused midbrain slices prepared 24 h after cessation of chronic ethanol consumption. Profound decreases in firing of the ventral tegmental area (VTA) neurons were seen in slices prepared after the ethanol treatment. Firing rates increased after application of N-methyl-dl-aspartate, but still remained lower and more variable after the ethanol treatment. Application of dopamine or amphetamine, following stimulation of firing with a low concentration of N-methyl-dl-aspartate, also resulted in lower firing rates in slices from ethanol-treated mice. No changes were seen in release of tritiated dopamine, in response to applied KCl or amphetamine, from slices of striatum or cerebral cortex, prepared 24 h after cessation of the chronic ethanol consumption, compared with control values. The results demonstrate that very substantial decreases in firing rate, and in the number of active cells, occur in VTA neurons at a time when withdrawal hyperexcitability was no longer apparent and overt changes in behaviour were not seen.

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.

Protein kinase Cdelta mediates ethanol-induced up-regulation of L-type calcium channels

Brief ethanol exposure inhibits L-type, voltage-gated calcium channels in neural cells, whereas chronic exposure increases the number of functional channels. In PC12 cells, this adaptive response is mediated by protein kinase C (PKC), but the PKC isozyme responsible is unknown. Since chronic ethanol exposure increases expression of PKCdelta and PKCepsilon, we investigated the role these isozymes play in up-regulation of L-type channels by ethanol. Incubation with the PKC inhibitor GF 109203X or expression of a PKCdelta fragment that inhibits phorbol ester-induced PKCdelta translocation largely prevented ethanol-induced increases in dihydropyridine binding and K+-stimulated 45Ca2+ uptake. A corresponding PKCepsilon fragment had no effect on this response. These findings indicate that PKCdelta mediates up-regulation of L-type channels by ethanol. Remaining responses to ethanol in cells expressing the PKCdelta fragment were not inhibited by GF 109203X, indicating that PKCdelta-independent mechanisms also contribute. PKCdelta overexpression increased binding sites for dihydropyridine and L-channel antagonists, but did not increase K+-stimulated 45Ca2+ uptake, possibly because of homeostatic responses that maintain base-line levels of channel function. Since L-type channels modulate drinking behavior and contribute to neuronal hyperexcitability during alcohol withdrawal, these findings suggest an important role for PKCdelta in alcohol consumption and dependence.

Central effects of acamprosate: part 1. Acamprosate blocks the glutamate increase in the nucleus accumbens microdialysate in ethanol withdrawn rats

One of the known behavioral actions of acamprosate is to decrease hypermotility during alcohol withdrawal. However, the mechanism of this effect remains unclear. In this study, the concentrations of excitatory and inhibitory amino acids were assayed by the microdialysis technique with OPA/BME precolumn derivatization and electrochemical detection in the nucleus accumbens of male Wistar rats which were either alcoholized by ethanol inhalation or simultaneously alcoholized and treated orally by acamprosate (400 mg/kg/day) for 4 weeks. Without treatment, extracellular glutamate increased during the withdrawal phase, while other amino acids tested (aspartate, arginine, taurine, alanine and GABA) remained stable. In contrast, the alcoholized rats treated with acamprosate failed to present the increase in glutamate during ethanol withdrawal, while other amino acids tested also remained stable. The observed glutamate increase could be responsible for the hyperexcitability observed during episodes of ethanol withdrawal. These results suggest that acamprosate is able to reduce the ethanol withdrawal syndrome by reducing the concentration of glutamate in the nucleus accumbens.

Comparison of the effects of drugs on hyperexcitability induced in hippocampal slices by withdrawal from chronic ethanol consumption

1 The effects of drugs, previously demonstrated to have a range of effects on the behavioural signs of ethanol withdrawal hyperexcitability, were examined in area CA1 in isolated hippocampal slices prepared after withdrawal from chronic ethanol in vivo. 2 The decreases seen after the ethanol treatment in the thresholds for production of single and multiple population spikes were prevented when the dihydropyridine calcium channel antagonist, isradipine, was included in the perfusion medium at 4 microM. 3 Another dihydropyridine, felodipine, which had no activity against withdrawal signs in vivo, did not affect the changes in field potentials, at concentrations up to 10 microM. 4 Diltiazem, which increased withdrawal hyperexcitability in vivo, had no effect on the withdrawal changes in field potentials at 30 microM; higher concentrations affected the control slices. 5 The novel anticonvulsant, gabapentin, at 1 microM but not at 100 nM, significantly decreased the signs of withdrawal hyperexcitability in the hippocampal slices. When the CCKB antagonist, CI988, was added to the bathing medium, at 1 microM, there were small, but significant decreases in the withdrawal hyperexcitability. 6 The results showed that the actions of these drugs on the changes in the field potentials in isolated hippocampal slices were very similar to their previously demonstrated effects on the convulsive signs of ethanol withdrawal in vivo, but differences were seen in the corresponding comparison with anxiolytic actions in vivo.

Expression of c-Fos protein immunoreactivity in rat brain during ethanol withdrawal is prevented by nifedipine

Male rats were made physically dependent on ethanol by inhalation of the vapour for 10 days, and c-Fos protein-like immunoreactivity was visualised in the brain of these animals after various periods of ethanol withdrawal. Immunostaining for c-Fos appeared 2 h after ethanol withdrawal, the number of cells increased significantly at 8 h, but c-Fos had returned to basal level after 24 h. Immunoreactive cells were distributed throughout the brain but were concentrated in cerebral cortex, striatum, and hippocampus. Intraperitoneal injection of the calcium channel antagonist nifedipine (3 x 100 mg/kg) prior to, and during ethanol withdrawal totally prevented c-Fos protein-like expression. These results suggest that the superinduction of c-Fos protein in the brain of rats undergoing ethanol withdrawal is induced by calcium influx into neuronal cells, and may be related to previously reported increases in L-type voltage-operated calcium channels in the brain associated with ethanol dependence.

The novel anticonvulsant, gabapentin, protects against both convulsant and anxiogenic aspects of the ethanol withdrawal syndrome

The effects of the anticonvulsant, gabapentin, were investigated, in mice, on the withdrawal convulsive behaviour and anxiety-related behaviour that are produced by cessation of prolonged intake of ethanol. When given at 50 or 100 mg/kg, this compound decreased the rise in handling-induced hyperexcitability which occurs during the withdrawal period; the effects were most pronounced for the first 4 hr after administration. Gabapentin also decreased the convulsive response to an audiogenic stimulus during the withdrawal period. The elevated plus-maze, with both traditional and ethological indices of activity was used as a test of anxiety-related behaviour after cessation of chronic ethanol treatment. Gabapentin, at 50 and 100 mg/kg, was found to decrease some, although not all, of the signs of withdrawal-induced anxiety. At doses up to and including 200 mg/kg, gabapentin had no effect on motor co-ordination or spontaneous locomotor activity in control animals. The results demonstrated that gabapentin has a selective action in decreasing both convulsive and anxiety-related aspects of withdrawal behaviour after chronic ethanol treatment. It is possible that further studies with this compound may shed further light on the mechanisms involved in the withdrawal syndrome.

Molecular pathogenesis of alcohol withdrawal seizures: the modified lipid-protein interaction mechanism

The phrase alcohol withdrawal seizures (AWS) refers to seizures that result from the withdrawal of alcohol after a period of chronic alcohol administration. A mechanism of AWS is postulated, namely the modified lipid-protein interaction (MLPI) mechanism. This hypothesis is based upon an evaluation of the mechanisms of membrane fluidity, calcium channels, gamma-aminobutyric acid (GABA) and glutamate in the molecular pathogenesis of AWS. The mechanism hypothesizes that acute ethanol treatment alters the neuronal membrane lipids which then perturbs protein events, such as affecting the GABAA receptors, NMDA receptors and voltage-dependent Ca2+ channels synergistically or in combination. Subsequent adaptations in these systems occur after prolonged administration of ethanol. A sudden withdrawal of ethanol then leads to hyperexcitability which results in AWS.

Effects of dihydropyridines on the components of the ethanol withdrawal syndrome: possible evidence for involvement of potassium, as well as calcium?

Comparison was made of the ability of two dihydropyridine calcium channel antagonists, nitrendipine and felodipine, to prevent a range of signs of ethanol withdrawal. The increases in handling-induced behavior seen in mice during withdrawal from chronic ethanol treatment were prevented by administration of nitrendipine, 50 mg/kg, but not by, felodipine, 10 mg/kg, a dose that caused a similar displacement of dihydropyridine binding in central nervous system tissue, in vivo and in vitro. A higher dose of felodipine, 20 mg/kg, also had no effects. Nitrendipine, but not felodipine, prevented audiogenic seizures during the withdrawal phase. Similarly, nitrendipine prevented both the decrease in thresholds for N-methyl-DL-aspartate seizures and the increase in thresholds for convulsions due to 4-aminopyridine, which were seen during the withdrawal period, while felodipine did not alter either of these changes. Withdrawal from the ethanol chronic treatment increased the thresholds to seizures produced by intravenous aminophylline; this change was also prevented by nitrendipine. The significance of this increase in thresholds was lost after felodipine administration. In naive mice (not treated with ethanol) the doses of nitrendipine and felodipine used in the withdrawal studies were tested against the effects of convulsant drugs. Both dihydropyridines increased, to similar extents, the thresholds for seizures produced by bicuculline, pentylenetetrazol, and by N-methyl-DL-aspartate. The thresholds for aminophylline were unaltered by either dihydropyridine. In contrast, the thresholds for seizures due to 4-aminopyridine in the naive animals were not changed by felodipine, but were increased by nitrendipine. The results suggest that changes in potassium, as well as calcium, may possibly be involved in some of the stages of the ethanol withdrawal syndrome.

Monosialoganglioside attenuates the excitatory and behavioural sensitization effects of ethanol

The effects of long-term monosialoganglioside GM1 treatment on the acute excitatory effects of ethanol and behavioural sensitization to this effect were studied, using locomotion frequency of mice observed in an open field as an experimental parameter. GM1 (30 mg/kg, once a day, for 21 days) did not modify mouse behaviour but decreased both the acute excitatory (1.8 g/kg) and the behavioural sensitization effects of ethanol (1.8 g/kg, once a day for 21 days, 30 min after GM1 injections). GM1 administered acutely 30 min or 24 h before ethanol did not modify the ethanol-induced increase in locomotion frequency. These results agree with previous reports in which ganglioside treatment modified both dopaminergic plasticity and other behavioural and biochemical effects of ethanol.

Effects of diltiazem, a Ca2+ channel blocker, on naloxone-precipitated changes in dopamine and its metabolites in the brains of opioid-dependent rats

The effects of diltiazem, an L-type Ca2+ channel blocker, on naloxone (an opioid receptor antagonist)-precipitated withdrawal signs and changes in extracellular levels of dopamine (DA) and its metabolites in various brain regions of morphine (a mu-opioid receptor agonist) or butorphanol (a mu/delta/kappa mixed opioid receptor agonist) dependent rats were investigated using high performance liquid chromatography fitted with an electrochemical detector (HPLC-ED). Rats were rendered opioid-dependent by continuous intracerebroventricular (i.c.v.) infusion with morphine (26 nmol/microliters per h) or butorphanol (26 nmol/microliters per h) for 3 days. The expression of physical dependence produced by these opioids, as evaluated by naloxone (5 mg/kg. i.p.)-precipitated withdrawal signs, was reduced by concomitant infusion of diltiazem (10 and 100 nmol/microliters per h). Under the same condition, naloxone decreased the levels of: DA in the cortex, striatum, and midbrain; 3,4-dihydroxyphenylacetic acid (DOPAC) in the cortex, striatum, limbic areas, and midbrain: and homovanilic acid (HVA) in the striatum, limbic areas, and midbrain regions. In animals rendered dependent on butorphanol, the results obtained were similar to those of morphine-dependent rats except for the changes in DOPAC levels. Furthermore, concomitant infusion of diltiazem and opioids blocked the decreases in levels of DA, DOPAC, and HVA in a dose-dependent manner. These results suggest that the augmentation of intracellular Ca2+ mediated through L-type Ca2+ channels during continuous opioid infusion results in a decrease in extracellular levels of DA and its metabolites in some specific regions, which are intimately involved in the expression of withdrawal syndrome precipitated by naloxone.

Glucocorticoid interactions with ethanol effects on depolarization-induced calcium influx in brain synaptosomes

Depolarization-induced Ca2+ influx in brain synaptosomes is known to be inhibited by ethanol and stimulated by glucocorticoids. The present study was undertaken to characterize the interactions of corticosterone (CORT) with ethanol effects on 45Ca2+ uptake in synaptosomes depolarized by high K+ (70 mM). CORT was shown to antagonize the inhibitory effects of ethanol on the fast-phase component of the K(+)-induced 45Ca2+ uptake (the initial 3 s following depolarization). Glucocorticoid antagonism of ethanol inhibition of the 45Ca2+ uptake exhibited a high degree of steroid specificity; steroids with glucocorticoid activity including cortisol, dexamethasone and triamcinolone were effective, whereas gonadal steroids and excitatory neuroactive steroid metabolites were ineffective. From the shift of concentration-response relationships when CORT and ethanol were present in combination, the interaction between steroid stimulation and ethanol inhibition of 45Ca2+ uptake occurred in an additive manner over the range of their effective concentrations. Parallel to 45Ca2+ uptake, the binding sites for [3H]PN 200-110 were reduced by ethanol and increased by CORT. These opposite effects on [3H]dihydropyridine labeled sites were found also to antagonize each other, and the antagonism again occurred in an additive relationship. These results demonstrate that glucocorticoids antagonized ethanol inhibition of voltage-dependent Ca2+ channel activity in brain synaptosomes, and support the notion that these steroids may be among the endogenous factors that modulate neuronal sensitivity to ethanol.