Effects of dizocilpine in withdrawal seizure-prone (WSP) and withdrawal seizure-resistant (WSR) mice

mTOR activation is required for the anti-alcohol effect of ketamine, but not memantine, in alcohol-preferring rats

Glutamate NMDA receptors mediate many molecular and behavioral effects of alcohol, and they play a key role in the development of excessive drinking. Uncompetitive NMDA receptor antagonists may, therefore, have therapeutic potential for alcoholism. The first aim was to compare the effects of the NMDA antagonists memantine and ketamine on ethanol and saccharin drinking in alcohol-preferring rats. The second aim was to determine whether the effects of the two NMDA receptor antagonists were mediated by the mammalian target of rapamycin (mTOR). TSRI Sardinian alcohol-preferring rats were allowed to self-administer either 10% w/v ethanol or 0.08% w/v saccharin, and water. Operant responding and motor activity were assessed following administration of either memantine (0-10mg/kg) or ketamine (0-20mg/kg). Finally, ethanol self-administration was assessed in rats administered with either memantine or ketamine but pretreated with the mTOR inhibitor rapamycin (2.5mg/kg). The uncompetitive NMDA receptor antagonists memantine and ketamine dose-dependently reduced ethanol drinking in alcohol-preferring rats; while memantine had a preferential effect on alcohol over saccharin, ketamine reduced responding for both solutions. Neither antagonist induced malaise, as shown by the lack of effect on water intake and motor activity. The mTOR inhibitor rapamycin blocked the effects of ketamine, but not those of memantine. Memantine and ketamine both reduce alcohol drinking in alcohol-preferring rats, but only memantine is selective for alcohol. The effects of ketamine, but not memantine, are mediated by mTOR. The results support the therapeutic potential of uncompetitive NMDA receptor antagonists, especially memantine, in alcohol addiction.

Anxiety-like behaviors following chronic ethanol exposure

Rodent models of ethanol withdrawal-induced anxiety have been used to explore the neurobiology underlying withdrawal and to evaluate the utility of therapeutic agents aimed at reducing withdrawal severity. Of the many tests of anxiety-like behavior, the elevated plus maze, light/dark box, and open field are the most commonly used. In general, ethanol withdrawal decreases most or all of the individual behaviors recorded in these tasks, indicating the occurrence of an anxiogenic-like effect of withdrawal in rodents, although these effects of withdrawal have not always been found. Potential problems with interpreting the effects of withdrawal as being indicative of an anxiety-like state include the effects of withdrawal on motivation to explore an apparatus, non-specific effects of withdrawal on locomotion, and the use of test parameters that have not been pharmacologically validated. For example, most of the published studies interpreted as having shown increased anxiety-like behavior during ethanol withdrawal have also observed concurrent decreases in locomotion. At a minimum, a given test of anxiety-like behavior during withdrawal should be responsive to the dose and duration of ethanol exposure that was used to produce physical dependence, and should not non-specifically decrease locomotion. In addition, standard anxiolytic drugs should ameliorate the anxiogenic-like effects of withdrawal, preferably in multiple tests of anxiety-like behavior.

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.

Alcohol place preference conditioning in high- and low-alcohol preferring selected lines of mice

High- and low-alcohol preferring (HAP and LAP) selected lines of mice diverge greatly in free-choice alcohol consumption. This study investigated whether the lines differ in a measure of alcohol reward not dependent on drinking, specifically place conditioning. Mice were subjected to a differential conditioning procedure in which four alcohol-paired CS+ trials on one floor cue (0, 1.5, 3, or 4 g/kg; ns=20-24) alternated with four saline-paired CS- trials on a different floor cue. Testing was on a split floor, half CS+ and half CS-. HAP and LAP mice showed no preference at 0 g/kg, and equivalent, moderate preference at 1.5 and 3 g/kg alcohol. At 4 g/kg, LAP, but not HAP mice showed an increase in preference. The present findings imply greater efficacy of alcohol preference conditioning in LAP mice, but do not speak for line differences in sensitivity. Results do not support the hypothesis that selection for high drinking yields greater efficacy of alcohol as a reinforcer when reward is measured using a technique that does not rely on drinking. Low drinking in LAP mice may emerge from innate taste avoidance of alcohol as a result of selective breeding for low preference, which prevents them from encountering alcohol's rewarding, pharmacological effects.

Immunocytochemical analysis of glutamate and GABA in selectively bred mice

Withdrawal Seizure Prone (WSP) and Withdrawal Seizure Resistant (WSR) mice have been selectively bred for differential ethanol withdrawal handling-induced convulsions (HICs). In addition, it has been observed that WSP mice exhibit drug-naive HICs. This latter finding suggests that WSP and WSR mice differ in their susceptibility to HICs. Alterations in the glutamate and gamma-aminobutyric acid (GABA) systems have been implicated in convulsive activity and have been proposed to underlie the manifestation of ethanol withdrawal symptoms. It is therefore possible that WSP and WSR mice are genetically different with respect to their glutamatergic and/or GABAergic systems. To test this hypothesis, we have analyzed WSP and WSR mice that are both drug- and HIC-naive for differences in the density of nerve terminal glutamate and GABA immunoreactivity within the CA1 subfield of the hippocampus (CA1) and layer II of the somatosensory cortex (SSC). The major finding of this study is that drug- and HIC-naive WSP mice exhibit a significantly greater density of presynaptic glutamate immunoreactivity associated with asymmetric synapses within the CA1, but not the SSC, when compared to WSR mice. The density of GABA immunoreactivity within nerve terminals associated with symmetric synapses does not differ between the selected lines in either brain region. Since prior drug exposure and HICs cannot account for the observed differences in these naive mice, the results strongly suggest that the density of nerve terminal glutamate immunoreactivity within the CA1 is a reflection of inherent genetic differences between WSP and WSR mice. Furthermore, an elevated density of presynaptic glutamate immunoreactivity may be an underlying neurochemical correlate to increased susceptibility to drug-naive and ethanol withdrawal convulsions.

[3H]MK-801 binding in various brain regions of rat lines selected for differential alcohol sensitivity

N-Methyl-D-aspartate (NMDA) receptors are sensitive to ethanol at concentrations relevant to intoxication. To ascertain possible involvement of NMDA receptors in differential ethanol sensitivity between alcohol-sensitive ANT (alcohol-nontolerant) and alcohol-insensitive AT (alcohol-tolerant) rat lines, characterization of a noncompetitive NMDA antagonist [3H]MK-801 binding to brain membranes was carried out. Saturation analyses of [3H]MK-801 binding to cerebrocortical, hippocampal, and cerebellar synaptosomal membranes revealed no statistically significant differences in either the affinity constant (Kd) or binding site density (Bmax) between the rat lines. Autoradiographic analysis of [3H]MK-801 binding to ANT and AT brain sections revealed a regionally heterogenous distribution of binding, without any detectable differences between the AT and ANT sections whether these were prepared from the brains of acutely ethanol-treated or nontreated animals. Glutamate, glycine, or the two in combination greatly increased [3H]MK-801 binding to brain membranes. In extensively washed crude cerebrocortical membranes, the maximal effect (Emax), but not potency (EC50) of glycine to increase [3H]MK-801 was slightly greater (p < 0.01) in the ANT than AT rats. The effects of glutamate or glutamate in the presence of saturating concentration of glycine (30 microM) were not significantly different between the two lines. Association parameters (t1/2 and Beq values) of [3H]MK-801 to its cortical binding sites were also similar. These results do not indicate any clear qualitative difference in [3H]MK-801 binding to NMDA receptors or in its modulation by glutamate and glycine between the ANT and AT rat lines.