Cocaine Gene Network · Molecular Analysis of Gene Regulatory Networks Underlying the Persistence of Drug Addiction

Molecular Analysis of Gene Regulatory Networks Underlying the Persistence of Drug Addiction

Drug addiction is caused by the long-lasting effects of drugs of abuse on neural circuits in the brain. Initial, acute exposure to drugs is followed by transition of some users to chronic use, a subset of which experience loss of control over drug consumption and develop addiction. Drugs alter the reward circuitry in the brain, effectively making drug-associated environmental stimuli more difficult to ignore and leading to intense craving and relapse to drug seeking. A major problem in addiction is that even long after being removed from the drug, and the physical symptoms of withdrawal have subsided, addicts show a high persistency to relapse when exposed to drug-associated cues. This suggests that drug exposure causes the formation of a pervasive memory in the brain of the addicts, which underlies the susceptibility to relapse. The nucleus accumbens (NAc), a central integrator of the brains’ reward circuitry, has been extensively associated with the development of addiction. Furthermore, it is known that gene expression induced by the experience of drugs of abuse within this brain structure, is necessary for the development of drug addiction. In this project, we aimed to define the organization and the logic of the gene expression networks that underlie the development of drug addiction using mice as an experimental model. Specifically, we aimed to understand how these gene expression networks are reorganized following chronic drug exposure, assuming that this knowledge will provide insight into mechanisms underlying the development of addiction. Furthermore, identifying the relevant genes is expected to provide targets for the development of therapeutic approaches In the period of MC-CIG grant support, we have successfully established a productive research lab, and equipped with all the necessary equipment for implementation of the research plan proposed in the grant application. The lab currently comprises of a PhD-level research associate and lab manager, a computational biologist (research scientist), a postdoctoral scholar, 8 graduate students (5 PhD and 3 MSc) and 4 undergraduate trainees. The essential experimental setups have been developed, including establishment of a dissociated neuronal culture system, and the necessary setups for viral vector cloning, virus production, stereotactic surgery, behavior (behavioral sensitization and conditioned-place preference), fluorescently-directed dissection of virally-infected brain structures, high-throughput analysis of transcription by microfluidic qPCR and RNAseq, and multi-colored single molecular in-situ hybridization. Using the experimental setups in the lab, we have developed a comprehensive characterization of the gene expression programs induced by cocaine experience in the brain. This work has led to two papers which have already been published and are influencing the field. We further developed the tools to investigate the function of specific genes in supporting the development of behavioral correlates of drug addiction in mice. These approaches have been implemented in-vivo for the investigation of the role of defined gene products within specific neuronal types in regions of the reward circuitry in supporting the development of addiction correlates in mice. This work is currently in development for publication and will likely result in at least 2 major publications. An unexpected and highly promising avenue of research has developed from this work, which promises to expand to a number of new avenues of research and potentially form the basis of a new field in neuroscience. Studying the gene expression programs induced by cocaine in naïve mice, or mice with different levels of prior exposure to the drug, we find induction of robust and highly reproducible gene expression programs. This suggested to us that defined experiences may be encoded by unique patterns of gene expression in relevant brain regions. We addressed this notion by careful development of 14 discrete experiences (such as development of a contingent sucrose habit, aversive experience of LiCl injections or gentle footshock), studying the gene expression programs induced in 8 different structures within the mouse brain. The result of this study is the observation of very low variation between individual mice in the transcriptional response to a given experience, whereas each experience had a very robust and reliable transcriptional signature associated with it, in relevant brain regions. The gene expression patterns we observed were clear enough to enable the decoding of the recent experience of each individual mouse with above 90% accuracy. Furthermore, a small subset of the gene expression response is sufficient for this decoding. We believe this new approach to the investigation of experience-dependent plasticity, which we coin “behavioral transcriptomics” is a widely applicable approach to investigating the encoding of experience in the brain, as well as the formation of habits and compulsions. This work has been recently published in the journal eLife, garnering significant attention from both the scientific community, as well as the general public. We believe this approach will form the basis for a new field of research in neuroscience. A follow-up project, in which we are addressing, with high resolution, the coherence of the genetic definition of neuronal ensembles encoding experience, is anticipated to be submitted for publication within a few weeks. This manuscript has garnered attention from the media, with multiple newspaper articles covering this work published in England, Israel, Spain and Indonesia, as well as radio and TV interviews in Israel (for some media coverage see: https://www.newscientist.com/article/2166029-we-can-read-memories-by-analysing-brain-gene-activity/ http://www.dailymail.co.uk/sciencetech/article-5603921/Your-memories-read-replayed-DIE.html https://www.metro.news/total-recall-gene-code-may-help-us-find-a-murderer/1012472/; https://www.express.co.uk/news/science/945396/science-news-death-memories-murder https://youtu.be/LBof9ws390M?t=15m49s; https://www.kan.org.il/Podcast/item.aspx?pid=10138 The final results of the project provide a deeper understanding of the mechanisms underlying the encoding of the long-term memory of cocaine experience in the brain, likely underlying the development of cocaine addiction. The project largely developed along the lines defined in the original plan, as well as leading to unexpected and important observations.

Data: CORDIS, © European Union