Protein kinase M ζ (PKMζ) is a constitutively active form of atypical PKC that is exclusively expressed in the brain and implicated in the maintenance of long-term memory1–9. Most studies that support a role for PKMζ in memory maintenance have used pharmacological PKMζ inhibitors such as the myristoylated zeta inhibitory peptide (ZIP) or chelerythrine. Here, we used a genetic approach and targeted exon 9 of the Prkcz gene to generate mice that lack both protein kinase C ζ (PKCζ) and PKMζ (Prkcz−/− mice). Prkcz−/− mice showed normal behavior in a cage environment and in baseline tests of motor function and sensory perception, but displayed reduced anxiety-like behavior. Surprisingly, they did not show deficits in learning or memory in tests of cued fear conditioning, novel object recognition, object location recognition, conditioned place preference (CPP) for cocaine, or motor learning, when compared with wild-type littermates. ZIP injection into the nucleus accumbens (NAc) reduced expression of cocaine CPP in Prkcz−/− mice. In vitro, ZIP and scrambled ZIP inhibited PKMζ, PKCι and PKCζ with similar Ki values. Chelerythrine was a weak inhibitor of PKMζ (Ki = 76 µM). Our findings show that absence of PKMζ does not impair learning and memory in mice, and that ZIP can erase reward memory even when PKMζ is not present.

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Cytochrome P450 (CYP) 2D6, an enzyme found in the liver and the brain, is involved in the metabolism of numerous centrally acting drugs (e.g. antidepressants, neuroleptics, opiates), endogenous neurochemicals (e.g. catecholamines) and in the inactivation of neurotoxins (e.g. pesticides, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)). Although CYP2D6 is essentially an uninducible enzyme in the liver, we show that smokers have higher CYP2D6 in the brain, especially in the basal ganglia. In order to determine whether nicotine, a component of cigarette smoke, could increase brain CYP2D, African Green monkeys were treated chronically with nicotine (0.05 mg/kg for 2 days, then 0.15 mg/kg for 2 days followed by 0.3 mg/kg for 18 days s.c., b.i.d.). Monkeys treated with nicotine showed significant induction of CYP2D in brain when compared to saline-treated animals as detected by western blotting and immunocytochemistry. No changes in liver CYP2D were observed in nicotine-treated monkeys. Induction was observed in various brain regions including those affected in Parkinson's disease (PD) such as substantia nigra (3-fold, p = 0.01), putamen (2.1-fold, p = 0.001) and brainstem (2.4-fold, p = 0.001), with the caudate nucleus approaching significance (1.6-fold, p = 0.07).Immunocytochemistry revealed that the expression of CYP2D in both saline-and nicotine-treated monkeys is cell-specific particularly in the cerebellum, frontal cortex and hippocampus. These results suggest that monkey brain expresses CYP2D, which is induced in specific cells and brain regions upon chronic nicotine treatment. Smokers, or those using nicotine treatment, may have higher levels of brain CYP2D6 that may result in altered localized CNS drug metabolism and inactivation of neurotoxins.

Although drugs of abuse have different chemical structures and interact with different protein targets, all appear to usurp common neuronal systems that regulate reward and motivation. Addiction is a complex disease that is thought to involve drug-induced changes in synaptic plasticity due to alterations in cell signaling, gene transcription, and protein synthesis. Recent evidence suggests that drugs of abuse interact with and change a common network of signaling pathways that include a subset of specific protein kinases. The best studied of these kinases are reviewed here and include extracellular signal-regulated kinase, cAMP-dependent protein kinase, cyclin-dependent protein kinase 5, protein kinase C, calcium/calmodulin-dependent protein kinase II, and Fyn tyrosine kinase. These kinases have been implicated in various aspects of drug addiction including acute drug effects, drug self-administration, withdrawal, reinforcement, sensitization, and tolerance. Identifying protein kinase substrates and signaling pathways that contribute to the addicted state may provide novel approaches for new pharma-cotherapies to treat drug addiction.

Nicotine addiction and alcohol use disorders are very widespread and often occur together. Currently, there is no single drug approved for the simultaneous treatment of both conditions. Although these conditions share common genetic factors, the molecular mechanisms underlying their comorbidity are unknown. We have previously shown that mice lacking protein kinase C epsilon (PKCε) show decreased ethanol self-administration and reward as well as increased aversion to ethanol. Here we find that Prkce −/− mice self-administer less nicotine and show decreased conditioned place preference for nicotine compared with wild-type mice. In Prkce −/− mice, these behaviors are associated with reduced levels of α 6 and β 3 nicotinic receptor subunit mRNA in the ventral midbrain and striatum as well as a functional deficit in cholinergic modulation of dopamine release in nucleus accumbens. Our results indicate that PKCε regulates reward signaling through α 6 -containing nicotinic receptors and suggest that PKCε could be a target for the treatment of comorbid nicotine and alcohol addictions.T obacco addiction remains the leading cause of premature mortality in the world, and half of all tobacco users will die of tobacco-related disease (1). Nicotine is the primary, if not the only, compound that maintains addiction to tobacco (2), and smokers will adjust their level of cigarette smoking to maintain constant levels of plasma nicotine (3). Current approved pharmacotherapies for smoking cessation all target nicotinic acetylcholine receptors (nAChRs) and include nicotine-replacement therapy, bupropion (a nicotinic antagonist) (4), and varenicline (a partial nicotinic agonist) (5). Although this approach is effective in the short term, long-term abstinence rates are low, underscoring the need for the discovery of new drug targets and development of new treatments.It is striking that, among all drug addictions, alcohol and tobacco addictions are highly comorbid with more than 60% of smokers in the US reporting concurrent binge drinking or heavy use of alcohol (6). Likewise, the prevalence of smoking among those with alcohol use disorders has been reported to be as high as 88-96% (7, 8). In humans, a single exposure to alcohol can increase the urge to smoke and increase cigarette consumption (9, 10). Conversely, in rats, s.c. injections of nicotine can increase ethanol self-administration (11) and promote reinstatement for ethanol responding after extinction (11,12). In rats that selfadminister i.v. nicotine and oral alcohol, the extinction of alcohol responding is prolonged if nicotine remains available (13), suggesting that combined use of both substances may make it more difficult to successfully quit the use of nicotine or alcohol alone. Nicotine and alcohol addictions appear to share common genetic factors (14-16), but the molecular mechanisms underlying their comorbidity are unknown. Currently, no pharmaceutical agent has been approved to treat comorbid nicotine and alcohol addictions.The protein kinase C (PKC) family of serine/...

Alcohol and nicotine are often used together, and there is a high rate of co-occurrence between alcohol and nicotine addiction. Most animal models studying alcohol and nicotine interactions have utilized passive drug administration, which may not be relevant to human co-addiction. In addition, the interactions between alcohol and nicotine in female animals have been understudied, as most studies have used male animals. To address these issues, we developed models of alcohol and nicotine co-consumption in male and female mice that utilized voluntary, oral consumption of unsweetened alcohol, nicotine and water. We first examined drug consumption and preference in single-drug, sequential alcohol and nicotine consumption tests in male and female C57BL/6 and DBA/2J mice. We then tested chronic continuous and intermittent access alcohol and nicotine co-consumption procedures. We found that male and female C57BL/6 mice readily co-consumed unsweetened alcohol and nicotine. In our continuous co-consumption procedures, we found that varying the available nicotine concentration during an alcohol abstinence period affected compensatory nicotine consumption during alcohol abstinence, and affected rebound alcohol consumption when alcohol was re-introduced. Consumption of alcohol and nicotine in an intermittent co-consumption procedure produced higher alcohol consumption levels, but not nicotine consumption levels, compared with the continuous co-consumption procedures. Finally, we found that intermittent alcohol and nicotine co-consumption resulted in physical dependence. Our data show that these voluntary co-consumption procedures can be easily performed in mice and can be used to study behavioral interactions between alcohol and nicotine consumption, which may better model human alcohol and nicotine co-addiction.

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