Dizocilpine prevents the development of tolerance to ethanol-induced error on a circular maze test

Promising strategies for the prevention of alcohol-related brain damage through optimised management of acute alcohol withdrawal: A focussed literature review

There is an increasing awareness of the link between chronic alcohol consumption and the development of cognitive, behavioural and functional deficits. Currently, preventative strategies are limited and require engagement in dedicated long-term rehabilitation and sobriety services, the availability of which is low. The acute alcohol withdrawal syndrome is an episode of neurochemical imbalance leading to autonomic dysregulation, increased seizure risk and cognitive disorientation. In addition to harm from symptoms of alcohol withdrawal (e.g. seizures), the underpinning neurochemical changes may also lead to cytotoxicity through various cellular mechanisms, which long-term, may translate to some of the cognitive impairments observed in Alcohol-Related Brain Damage (ARBD). Here we review some of the pharmacological and neurochemical mechanisms underpinning alcohol withdrawal. We discuss the cellular and pharmacological basis of various potential neuroprotective strategies that warrant further exploration in clinical populations with a view to preventing the development of ARBD. Such strategies, when integrated into the clinical management of acute alcohol withdrawal, may impact large populations of individuals, who currently face limited dedicated service delivery and healthcare resource.

Correlated changes in NMDA receptor phosphorylation, functional activity, and sedation by chronic ethanol consumption

Alcohol abuse leads to tolerance, dependence, and memory impairments that involve excitatory glutamatergic NMDA synaptic transmission. The NMDA receptor (NMDAR) is known to undergo activity-dependent adaptive functional changes. Since we observed that acute ethanol inhibition of the NMDAR was regulated by protein tyrosine phosphorylation, we investigated the role of protein tyrosine kinases and phosphatases on the NMDAR functions by chronic ethanol treatment. We carried out whole-cell recording, western blotting, and behavioral righting reflex measurements to assess the impact of chronic ethanol treatment on NMDAR function. Our results indicated that these receptors became resistant to the acute ethanol inhibition following chronic ethanol consumption. This resistance occurred without an increase in the NMDAR subunit expression but was associated with decreases in the levels of phospho-Y-1472 NR2B, increases in the levels of STEP33, increases in phospho-p38 mitogen-activated protein kinase (pp38 MAPK), and acquisition of tolerance to the sedative effects of ethanol. These data suggested that altered protein tyrosine phosphorylation of the NMDAR subunits significantly contributes to functional changes of this receptor by chronic ethanol ingestion. Therefore, preservation of the integrity of tyrosine phosphorylation mechanisms of the NMDAR may be important in controlling the progression of alcohol tolerance and dependence.

Altered NMDA glutamate receptor antagonist response in recovering ethanol-dependent patients

Ethanol is an antagonist of the N-methyl-D-aspartate (NMDA) glutamate receptor. Ethanol dependence upregulates NMDA receptors and contributes to crosstolerance with selective NMDA receptor antagonists in animals. This study evaluated whether recovering ethanol-dependent patients show evidence of a reduced level of response to the effects of the NMDA receptor antagonist, ketamine. In this double-blind study, 34 recently detoxified alcohol-dependent patients and 26 healthy comparison subjects completed 3 test days involving a 40-min infusion of saline, ketamine 0.1 mg/kg, or ketamine 0.5 mg/kg in a randomized order. Recovering ethanol-dependent patients showed reduced perceptual alterations, dysphoric mood, and impairments in executive cognitive functions during ketamine infusion relative to the healthy comparison group. No attenuation of ketamine-induced amnestic effects, euphoria, or activation was observed. The alterations in NMDA receptor function observed in recovering ethanol-dependent patients may have important implications for ethanol tolerance, ethanol dependence, and the treatment of alcoholism.

N-methyl-D-aspartate glutamate receptors and alcoholism: reward, dependence, treatment, and vulnerability

This review takes a translational neuroscience perspective on the role of glutamate systems in human ethanol abuse and dependence. Ethanol is a simple molecule with profound effects on many chemical systems in the brain. Glutamate is the primary excitatory neurotransmitter in the brain. Glutamatergic systems are targets for the actions of ethanol via its antagonism of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor and other mechanisms. The modulation of glutamatergic function by ethanol contributes to both euphoric and dysphoric consequences of ethanol intoxication. Adaptations within glutamatergic systems appear to contribute to ethanol tolerance and dependence and to both acute and protracted features of ethanol withdrawal. Perhaps because of the important glutamatergic mediation of the behavioral effects of ethanol, glutamatergic systems appear to contribute to the vulnerability to alcoholism, and novel glutamatergic agents may play a role in the treatment of ethanol abuse and dependence.

Effect of NMDA antagonists, an NMDA agonist, and serotonin depletion on acute tolerance to ethanol

The effect of N-methyl-D-aspartate (NMDA) antagonists [dizocilpine, (+)MK-801, and ketamine], an NMDA agonist (D-cycloserine) and of brain serotonin (5-HT) depletion with p-chlorophenylalanine (p-CPA) on acute tolerance to ethanol was examined, using the tolerance model proposed by Radlow [Psychopharmacology 114 (1994) 1-8] and Martin and Moss [Alcohol Clin Exp Res 17 (1993) 211-216]. This model is based on the concept of a linear increase of acute tolerance with time; the rate of acute tolerance development is the slope of the output function that relates blood alcohol concentrations (BACs) and intoxication. Pretreatment with NMDA antagonists inhibited the development of acute tolerance to ethanol, whereas pretreatment with D-cycloserine enhanced it. Depletion of 5-HT by p-CPA also blocked acute tolerance to ethanol. These results on acute tolerance are similar to those previously found on rapid and chronic tolerance to ethanol.

In search of a new pharmacological treatment for drug and alcohol addiction: N-methyl-D-aspartate (NMDA) antagonists

The most challenging aspect of treating alcohol and drug addiction is the relapsing course of these disorders. Although substitution therapies for nicotine and opioid dependence have proven to be relatively effective, there is a need for new pharmacotherapies designed to decrease the frequency and severity of relapse. The aim of this paper is to provide an overview of the potential utility of N-methyl-D-aspartate (NMDA) receptor antagonists as treatments for substance abuse as shown in preclinical models and preliminary clinical trials. It is hypothesized that NMDA receptors mediate the common adaptive processes that are involved the development, maintenance, and expression of drug and alcohol addiction. Modulation of glutamatergic neurotransmission with NMDA receptor antagonists offers a novel treatment approach. It is proposed that NMDA antagonists may have multiple functions in treating addictions, including an attenuation of withdrawal effects, normalization of the affective changes following initiation of abstinence which arise from neurochemical changes resulting from chronic addiction, and an attenuation of conditioned responses arising from drug-related stimuli.

NMDA-receptor antagonists block the development of rapid tolerance to ethanol in mice

Several studies have emphasized the role of learning in the development of rapid and chronic tolerances. Recently, it was shown that the NMDA antagonists MK-801(dizocilpine) and ketamine block the development of tolerance to ethanol in rats submitted to tilt-plane apparatus. The present study examines the generality of this inhibition using mice submitted to the rota-rod test. Mice were tested in the rota-rod apparatus at 5, 10 and 15 minutes after intraperitoneal ethanol injections. The first experiment evaluated the time course of acute effects of different doses of ethanol (1.0-2.25 g/kg) in the rota-rod test. In the second experiment, the most effective dose of ethanol to produce rapid tolerance (RT) was determined. Mice were injected on day 1 with ethanol or saline and tested on the rota-rod. After 24 hours, all groups were injected with the same doses of ethanol and tested. The third experiment investigated whether ketamine (1.0-5.0 mg/kg) injected before ethanol on day 1 influenced the development of RT to ethanol. The last experiment compared the actions of the (+) and (-)MK-801 isomers (0.015-0.060 mg/kg) on RT to ethanol. Maximum motor impairment was obtained 5 minutes after ethanol injections. Pretreatment of animals with ketamine (2.5 and 5 mg/kg) or with (+)MK-801 (0.030 and 0.060 mg/kg) significantly blocked the development of RT. The (-)MK-801 isomer did not affect RT, suggesting that the blockade by MK-801 is stereospecific. These results confirm and extend previous studies showing that NMDA receptor antagonists block RT to the motor impairment produced by ethanol in other animals tested in different models.

Effect of NMDA antagonists on development of rapid tolerance to various barbiturates

We recently reported that the noncompetitive antagonists, (+)-MK-801 and ketamine, block the development of rapid tolerance to ethanol. We now show that pretreatment with these NMDA antagonists also blocks rapid tolerance to the various barbiturates (pentobarbital, barbital, and phenobarbital) examined. Tolerance to pentobarbital occurred under three difference conditions: (a) in groups of rats that were tested at repeated times on day 1 (intoxicated practice or testing group), (b) in groups of rats that were not tested on the apparatus but handled at the same times on day 1 (dummy testing or associative learning group), and (c) in groups of rats that were not subjected to testing at all on day 1 (nontesting). However, NMDA antagonists blocked intoxicated practice and associative tolerance, but not tolerance produced in the nontesting group. In the last experiment NMDA antagonist failed to block tolerance (unlearned) when animals were treated in the animal quarters and tested in a different room (i.e., in the laboratory). These findings suggest that NMDA antagonists affect barbiturate tolerance in a manner similar to their effect on ethanol tolerance.