Repeated cycles of chronic ethanol exposure and withdrawal lead to an escalation in voluntary ethanol consumption. Chronic intermittent ethanol (CIE) exposure also has been shown to produce increased basal extracellular glutamate levels in the nucleus accumbens, a brain region intimately related to reward processes and the regulation of ethanol consumption. This effect has been shown to persist well beyond acute withdrawal and accompany excessive levels of drinking. Accordingly, it is hypothesized that elevated glutamatergic tone in the nucleus accumbens resulting from CIE exposure plays a role in promoting/driving excessive drinking associated with dependence. While there is some evidence to support this contention, the mechanism underlying elevated accumbal glutamate levels following CIE exposure is not known. The present proposal will address this issue. Specifically, studies proposed in this application will examine functional activity and expression levels of glutamate transporters in the nucleus accumbens and whether altering glutamatergic tone via manipulation of glutamate transporter activity influences drinking in the CIE model of dependence and relapse drinking.
In Aim 1, an in vitro glutamate uptake assay will be used to examine Na[+]-dependent and Na[+]- independent [[3]H]glutamate uptake in nucleus accumbens tissue in CIE-exposed and control mice. Additionally, since the main transporter responsible for extracellular removal of glutamate in the accumbens is Excitatory Amino Acid Transporter 2 (EAAT2), while the main contributor to extracellular glutamate in this region is the cystine-glutamate exchanger (system x{c}), Western blot analyses will be performed to evaluate surface expression of EAAT2, and total levels of the system x{c} in ethanol dependent and non-dependent mice.
Aim 2 will involve examining the effects of administering the beta-lactam antibiotic, Ceftriaxone, which decreases brain glutamate levels via up-regulation of EAAT2 expression, on ethanol drinking in dependent compared to non-dependent mice in the CIE model. Collectively, results from Aims 1 and 2 will provide valuable insight into mechanisms regulating glutamate homeostasis in the nucleus accumbens, especially as such activity plays a role in excessive drinking associated with dependence. The training portion of this NRSA proposal is designed to expand the candidate's research capabilities through acquiring new knowledge and skills that will enable her to apply additional experimental strategies and approaches in addressing her research interests. The overall goal of this NRSA proposal is to provide training and research opportunities that enhance the candidate's career development and foster her academic and research growth as she aspires to establish an independent research career in the alcohol field.
Increased concentrations of the neurotransmitter glutamate are thought to promote excessive alcohol consumption in dependent individuals. Studies in this proposal aim to examine the cause of these elevated glutamate levels in dependent subjects, and ascertain if reducing glutamate levels in the brain reduces alcohol drinking in dependent subjects.
| Griffin, William C; Ramachandra, Vorani S; Knackstedt, Lori A et al. (2015) Repeated cycles of chronic intermittent ethanol exposure increases basal glutamate in the nucleus accumbens of mice without affecting glutamate transport. Front Pharmacol 6:27 |
