Apomorphine increases ethanol discrimination

Effects of N-methyl-D-aspartate agonists and antagonists in rats discriminating amphetamine

The present study assessed the interactions between N-methyl-D-aspartate (NMDA) agonists or antagonists and the discriminative stimulus effects of amphetamine. Adult male Sprague-Dawley rats were trained to discriminate 0.5 mg/kg (i.p.) of amphetamine from saline under a two-lever fixed-ratio schedule of food reinforcement. During test sessions, i.p. injections of the glycine site agonist D-cycloserine, the ion-channel blocker dizocilpine and the competitive antagonist CGP 43487 were coadministered with i.p. saline or with a full range of doses of amphetamine. D-Cycloserine did not substitute for amphetamine and attenuated the cueing effects of the drug. Both dizocilpine and CGP 43487 engendered intermediate levels of amphetamine-appropriate responses and potentiated the stimulus properties of amphetamine; however, the effects of CGP 43487 were very small and not dose-dependent. In an ancillary experiment, the training dose of amphetamine was reduced to 0.25mg/kg; under these conditions dizocilpine, but not CGP 43487, produced full substitution for the discriminative stimulus effects of amphetamine. These results show that drugs affecting NMDA receptor-based neurotransmission can modulate the discriminative stimulus effects of amphetamine.

Discriminative stimulus effects of ethanol: neuropharmacological characterization

Generally, compounds discriminated by animals possess psychotropic effects in animals and humans. As with many other drugs of abuse, strength of the ethanol discriminative stimulus is dose related. The majority of studies show that doses close to 1.0 g/kg are close to the minimum at which the discrimination can be learned easily. Substitution studies suggest that anxiolytic, sedative, atactic, and myorelaxant effects of ethanol all play an important role in the formation of its intercoeptive stimulus. Low doses of ethanol produce more excitatory cues, similar to amphetamine-like subjective stimuli, whereas higher doses produce rather sedative/hypnotic stimuli similar to those elicited by barbiturates. Substitution studies have shown that the complete substitution for ethanol may be exerted by certain GABA-mimetic drugs acting through different sites within the GABA(A)-benzodiazepine receptor complex (e.g., diazepam, pentobarbital, certain neurosteroids), gamma-hydroxybutyrate, and antagonists of the glutamate NMDA receptor. Among the NMDA receptor antagonists both noncompetitive (e.g., dizocilpine) and competitive antagonists (e.g., CGP 40116) are capable of substituting for ethanol. Further, some antagonists of strychnine-insensitive glycine modulatory sites among the NMDA receptor complex (e.g., L-701,324) dose-dependently substitute for the ethanol discriminative stimulus. On the other hand, neither GABA-benzodiazepine antagonists nor NMDA receptor agonists produce contradictory effects (i.e., reduce the ethanol discriminative stimulus). There is influence of a particular training dose of ethanol on the substitution pattern of different compounds. For example, 5-HT(1B/2C) agonists substitute for intermediate (1.0 g/kg) but not higher (2.0 g/kg) ethanol training doses. Discrimination studies with ethanol and drugs acting on NMDA and GABA receptors consistently indicate asymmetrical generalization. For example, ethanol is able to generalize to barbiturates and benzodiazepines, but neither the benzodiazepine nor barbiturate response generalizes to ethanol. Only a few drugs are able to antagonize, at least to some extent, the discriminative stimulus of ethanol (e.g., partial inverse GABA-benzodiazepine receptor antagonist Ro 15-4513 and the opioid antagonist naloxone). The ethanol stimulus effect may be increased (i.e., stronger recognition) by N-cholinergic drugs (nicotine), dopaminergic drugs (apomorphine), and 5-HT3 receptor agonists (m-chlorophenylbiguanide). Thus, the ethanol stimulus is composed of the several components, with the NMDA receptor and GABA(A) receptor complex being of particular importance. This suggests that a drug mixture may be more capable of substituting for ethanol (or block its stimulus) than a single compound. The ability of drugs to substitute for the ethanol discriminative stimulus is frequently, although not preclusively, associated with the reduction of voluntary ethanol consumption. The examples of positive correlation are gamma-hydroxybutyrate, possibly memantine and certain serotonergic drugs such as fluoxetine. However, it remains uncertain to what extent the discriminative stimulus of ethanol can be seen as relevant in the understanding of the complex mechanisms of dependence.

Predicting new effective treatments of alcohol addiction on the basis of their properties of inhibition of noradrenergic activity and/or thromboxane or on the activation of the dopamine reward system and/or beta-endorphin

On the basis of their properties of noradrenergic and/or thromboxane inhibition, or on their activation of the dopaminergic reward system and/or beta-endorphin, the following substances or treatments are predicted to be effective in treating alcohol or drug addiction: ginger; carbon dioxide; dietary sulfur; methionine; calcium; LHRH; high intensity light; interferon; negative ions; serotonin antagonists such as methysergide and cyproheptadine; guanabenz and guenfacine; antihistamines; head-out water immersion; X-irradiation; and forced unilateral left nostril breathing.

Etiology of alcoholism: relevance of prenatal hormonal influences on the brain, anomalous dominance, and neurochemical and pharmacological brain asymmetry

Because of possible prenatal hormonal influences on the brain, leading to anomalous dominance, pharmacological and neurochemical asymmetry, and consequent antisocial personality and phobic anxiety, the subject ingests ethanol for its tension-reducing properties via endorphinergic activation and the dopaminergic reward system. Due to presence of stress, and effects of anomalous dominance on ethanol metabolizing enzymes, ethanol-oxidizing systems are activated leading to high rates of ethanol elimination from the blood, and thus the decreased intensity of reaction to ethanol, leading to tolerance. Since stress can cause a decrease in the number of opiate receptors, a vicious cycle of ingesting more and more ethanol may be instituted.

The role of dopamine and serotonin receptors in the mediation of the ethanol interoceptive cue

The drug discrimination paradigm was used to evaluate the contribution of dopamine or serotonin receptors in the mediation of the stimulus properties of ethanol. Briefly, rats were trained to discriminate between ethanol (600 mg/kg, IP) and water vehicle. Dose-response relationships were observed for ethanol and rats were tested with various dopamine and serotonin receptor agonists and antagonists. The specific dopamine receptor agonists SKF 38393 (DA1) and LY 171555 (DA2) failed to produce appreciable ethanol-like stimulus effects. Furthermore, the dopamine receptor antagonists SCH 23390 (DA1) and haloperidol (DA2) did not affect ethanol-appropriate responding when administered in combination with the training dose of ethanol. A number of specific serotonergic receptor ligands were also tested. Quipazine, 5-MeODMT, buspirone, 8-OH-DPAT elicited intermediate ethanol-like stimulus properties in rats. The serotonin receptor blockers pizotifen, pirenperone and (-)propranolol were ineffective in blocking the interoceptive cue produced by 600 mg/kg ethanol. However, TFMPP produced strong ethanol-like discriminative properties and completely substituted for the training dose of ethanol. These results indicate that the stimulus properties of TFMPP are similar to those of a low dose of ethanol.

Nicotine-induced potentiation of ethanol discrimination

Rats were trained in a 2-lever, food-motivated operant task to discriminate intraperitoneal administration of ethanol (600 mg/kg) from vehicle. Dose-response curves for the ethanol cue were analyzed before and after pre-treatment of rats with intraperitoneal doses of 0.4 mg/kg or 0.2 mg/kg nicotine. Results demonstrate that nicotine potentiates ethanol-appropriate responding in test sessions. The results are discussed in light of the recognized correlation between smoking and alcohol intake.