Kimberly A. Scearce-Levie - US grants

DESCRIPTION: (Applicant's Abstract) Many abused drugs signal through the G protein pathway. All of the known opioid receptors are Gi coupled. The role of Gi in drug addiction will be explored using a novel system that provides direct control of Gi signaling in vivo, with temporal, spatial and pharmacological specificity. Genetically modified Gi-coupled kappa-opioid receptors can be activated only by the synthetic ligand spiradoline, and not by endogenous ligands. Inducible expression of this Receptor Activated Solely by Synthetic Ligand (RASSL) in selected brain regions of transgenic mice will be used to assess the functional consequences of Gi stimulation in those regions. Specific Aim 1: To gain control of Gi signaling in brain regions that contribute to the development of addiction. The kappa-opioid RASSL has been placed under the control of the tetracycline-controlled, inducible, tissue-specific expression system. This allows the RASSL to be expressed specifically in neural reward regions and activated by an exogenous drug, spiradoline, at precise times. Specific Aim 2: To characterize which specific behaviors associated with addiction, such as drug-seeking, drug taking, or withdrawal, are mediated by Gi signaling. Stimulation of the RASSL in neural reward regions should evoke some of the behaviors associated with addiction. Techniques to assess the behavioral response to RASSL stimulation will include drug, self-administration, conditioned place preference, and evaluation of withdrawal symptoms.

DESCRIPTION (provided by applicant): G protein coupled receptors (GPCRs) are essential for normal function of the central nervous system. Abnormalities in GPCR function may contribute to pathological states like schizophrenia, attention deficit disorder, bipolar disorder and drug addiction. This proposal aims to dissect the role of specific G protein signaling pathways in sensory perception, integration and gating. Engineered GPCRs developed by Dr. Bruce Conklin, the co-mentor on this proposal, fully activate Gi signaling in response to a synthetic ligand, but are insensitive to endogenous peptides and neurotransmitters. These RASSLs (receptors activated solely by synthetic ligands) have been expressed in specific brain regions of mice. RASSLs act as switches that activate the Gi signaling pathway in a specific neural circuit when triggered by drug administration. RASSLs will be used to activate Gi signaling in selected neural circuits of transgenic mice to reveal the contribution of this signaling pathway to olfactory behavior, and the abnormal sensory gating involved in psychoses and schizophrenia. Specific Aim 1 tests the hypothesis that RASSL activation can selectively disrupt olfactory behavior. Aim 2 tests the hypothesis that an imbalance of Gi signaling can induce disturbances in sensorimotor gating, attention or activity similar to those seen in schizophrenic patients. Aim 3 tests the hypothesis that the RASSL-mediated changes in behavior observed in Aims 1 and 2 correlate with markers of neural activity in specific circuits. The candidate, a Ph.D. neurobiologist, has leaned how to use RASSLs, both in vitro and in vivo, during 3.5 years of post-doctoral training with Dr. Conklin. Since this project requires sophisticated morphological, biochemical and behavioral analysis of transgenic mouse models, the candidate has joined the laboratory of Dr. Lennart Mucke, the primary sponsor of this project. Dr. Mucke's experience analyzing mouse models of human neuropsychiatric disease will contribute to the successful completion of this project. The mentoring and training received during this project will help the candidate achieve her career goal of an independent faculty research position.