Cocaine-Induced Sensitization is Linked to Distal Chromosome 6 Region in Congenic Mouse Model

Genetic association of nucleus accumbens 5-hydroxyindoleacetic acid level and alcohol preference drinking in a quasi-congenic male mice: Potential modulation by Grm7 gene polymorphism

OBJECTIVE

To test the hypothesis that predisposition to high alcohol drinking behavior is genetically associated with hypoactive serotonergic function in the Nucleus Accumbens (NAc).

METHOD

Alcohol avoiding C5A3 and alcohol preferring I5B25A mice of the Quasi-congenic Recombinant QTL Introgression (RQI) mouse strains were subjected to in vivo microdialysis in the NAc. Neurotransmitter and metabolite contents were analyzed by HPLC and samples were collected in three phases: Baseline, Control, and Alcohol. Samples were collected with 20 min intervals.

RESULTS

Between-strain differences restricted to small chromosome segments significantly affected both alcohol preference drinking and NAc 5-HIAA levels [F_{1, 13} = 5.569 p=.035 (General Linear Model Repeated Measures ANOVA and Tests of Between-Subjects Effects)]. Whole genome biallelic DNA marker genotyping allowed the identification of 16 differential microsatellite markers associated with low 5-HIAA levels and excessive alcohol drinking. Chromosome 6 markers were linked to Grm7 (51.19 centimorgan), a reported candidate gene for modulation of addiction. The results are consistent with earlier reports of association of low 5-HIAA and high alcohol consumption in rats and primates, including Homo sapiens.

CONCLUSION

Low NAc 5-HIAA and high alcohol consumption are genetically associated in a quasi-congenic mouse model carrying variants of the Grm7 gene. We propose that constitutional polymorphism in Grm7 may modulate CRF neuron activity via altered mGluR7 expression thus targeting CRF pathways to substance use circuits. This raises the possibility of modulation of DRN 5-HT neurons leading to hypo- or hyper-serotonergic condition in NAc and higher or lower alcohol preference drinking.