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Direct Regulation of Diurnal Drd3 Expression and Cocaine Reward by NPAS2
Ozburn AR, Falcon E, Twaddle A, Nugent AL, Gillman AG, Spencer SM, Arey RN, Mukherjee S,  Lyons-Weiler J, Self DW, and McClung CA
Biological Psychiatry, In Press

Circadian gene disruptions are associated with the development of psychiatric disorders, including addiction. However, the mechanisms by which circadian genes regulate drug reward remain poorly understood.  

To increase our understanding of these mechanisms, investigators in the laboratory of Colleen McClung, PhD, conducted a study using mice with a mutation in Neuronal PAS domain protein 2 (NPAS2) and mice with a small hairpin RNA mediated knock-down of NPAS2 or circadian locomotor output cycles kaput (CLOCK) protein in the nucleus accumbens.   Under the mentorship of Dr. McClung and in collaboration with colleagues at the University of Texas Southwestern Medical Center, Dr. Angela Ozburn and her team performed conditioned place preference assays for cocaine, and utilized cell sorting techniques, qPCR and chromatin immunoprecipitation assays followed by deep sequencing.

The investigators found that NPAS2 mutants exhibit decreased sensitivity to cocaine reward which can be recapitulated with a knock-down of NPAS2 specifically in the nucleus accumbens, demonstrating thefunctional importance of NPAS2 in this region.   They also found that reducing CLOCK (a homologueof NPAS2) expression in the nucleus accumbens had no effect, which suggests an important distinction in NPAS2 and CLOCK function.   In addition, the researchers found that NPAS2 expression is restricted to Drd1 expressing neurons, (i.e. “direct” pathway circuitry) while CLOCK expression is ubiquitous, and that NPAS2 and CLOCK have distinct temporal patterns of DNA binding in the nucleus accumbens.  Novel and unique DNA binding sites were identified for each protein.  The team also identified the Drd3 dopamine receptor as a direct transcriptional target of NPAS2 and found that NPAS2 knock-down in the nucleus accumbens disrupts its diurnal rhythm in expression.   Chronic cocaine treatment likewise disrupts the normal rhythm in NPAS2 and Drd3 expression in the nucleus accumbens, which may underlie certain aspects of behavioral plasticity in response to cocaine. Collectively, these findings identify an important and novel role for the circadian protein, NPAS2, in the nucleus accumbens in the regulation of dopamine receptor expression and drug reward.  This study is important because it demonstrates a mechanistic link between the function of a specific circadian protein in the nucleus accumbens and the regulation of cocaine reward.

Contributors:
Angela R. Ozburn, PhD, Andrea G. Gillman, PhD, and Colleen A. McClung, PhD (Department of Psychiatry, University of Pittsburgh School of Medicine) 

Alan Twaddle and James Lyons-Weiler, PhD (Bioinformatics Analysis Core, Clinical and Translational Science Institute, University of Pittsburgh School of Medicine)

Edgardo Falcon, PhD, Alexandria L. Nugent, PhD, Sade M. Spencer, PhD, Rachel N. Arey, PhD, Shibani Mukherjee, PhD, and David W. Self, PhD (Department of Psychiatry, University of Texas Southwestern Medical Center)

This article appeared in a recent issue of Biological Psychiatry.  Click here to view the abstract.