The Small G Protein H-Ras in the Mesolimbic System Is a Molecular Gateway to Alcohol-Seeking and Excessive Drinking Behaviors

Abstract

Uncontrolled consumption of alcohol is a hallmark of alcohol abuse disorders, however, the central molecular mechanisms underlying excessive alcohol consumption are still unclear. Here, we report that the GTP binding protein, H-Ras in the nucleus accumbens (NAc) plays a key role in neuroadaptations that underlie excessive alcohol-drinking behaviors. Specifically, acute (15 min) systemic administration of alcohol (2.5 g/kg) leads to the activation of H-Ras in the NAc of mice, which is observed even 24 hrs later. Similarly, rat operant self-administration of alcohol (20%) also results in the activation of H-Ras in the NAc. Using the same procedures, we provide evidence suggesting that the exchange factor GRF1 is upstream of H-Ras activation by alcohol. Importantly, we show that infection of mice NAc with lentivirus expressing a short hairpin RNA (siRNA) that targets the H-Ras gene produce a significant reduction of voluntary consumption of 20% alcohol. In contrast, knockdown of H-Ras in the NAc of mice did not alter water, quinine and saccharine intake. Furthermore, using 2-bottle choice and operant self-administration proceduers, we show that inhibiting H-Ras activity by intra-NAc infusion of the farnesyltransferase inhibitor, FTI-276, produced a robust decrease of rats’ alcohol drinking, however, sucrose consumption was unaltered. Finally, intra-NAc infusion of FTI-276 also resulted in an attenuation of seeking for alcohol. Together, these results position H-Ras as a central molecular mediator of alcohol’s actions within the mesolimbic system and put forward the potential value of the enzyme as a novel target to treat alcohol use disorders.

Promising Pharmacogenetic Targets for Treating Alcohol Use Disorder: Evidence from Preclinical Models

“…basolateral amygdala of alcoholics [111]. Importantly, data from Ron and colleagues showing that pharmaco logical inhibition of H and KRas signaling with the farnesyltransferase, FTI276, in the nucleus accum bens reduces voluntary alcohol drinking and alco hol selfadministration in rats [124] validates the RAS superfamily as pharmacogenetic targets for treatment of AUD. The high rate of KRas mutations in multi ple forms of cancer has led to the development of anti cancer drugs that target the RAS signaling system that are now under clinical trials [125].…”

Prosapip1-Dependent Synaptic Adaptations in the Nucleus Accumbens Drive Alcohol Intake, Seeking, and Reward

“…Intra-NAc infusion of lentivirus was conducted as described in (Ben Hamida et al, 2012). Mice were anesthetized using isoflurane.…”

“…Immunohistochemistry was conducted as described previously (Ben Hamida et al, 2012). Specifically, mice were euthanized by CO 2 and transcardially perfused with 0.01M PBS followed by 4% paraformaldehyde (PFA) in phosphate buffer, pH 7.4.…”

From Signaling Pathways to Behavior

“…In the CNS, the major activators of H-Ras are GRF1 and GRF2, whereas the enzymes that stop H-Ras activity are SynGAP and neurofibromatosis type 1 (NF1) (Fernandez-Medarde & Santos, 2011;Ye & Carew, 2010). We recently found that rat-operant selfadministration of 20% alcohol results in the activation of H-Ras in the nucleus accumbens (NAc; Hamida et al, 2012). Importantly, shRNA-mediated knockdown of H-Ras in the NAc of mice or pharmacological inhibition of H-Ras activity in rats reduced excessive intake of alcohol without affecting consumption of water, quinine, saccharin, or sucrose .…”