Understanding how repeated administration of addictive psychostimulant drugs, like cocaine, impairs prefrontal cortical activity is fundamental to understanding drug addiction. Drugs of abuse enhance dopamine receptor signaling in the brain and can lead to long-lasting addiction-associated changes in neuronal excitability. This proposal seeks to identify the mechanism underlying these changes in excitability. Previously, metabotropic glutamate 5 receptors (mGluRS) have been shown to be necessary for the rewarding and locomotor activating effects of cocaine. We have identified a burst-triggered mGluR5- induced slow after-depolarization (sADP) in the prefrontal cortex that is mediated by a non-selective cation current which we believe to be a TRPC5 channel current.
In specific aim 1 we plan to characterize activation of the sADP and establish a role for TRPC5 channels. We will use current and voltage patch- clamp recording combined with pharmacology in wild-type and TRPC5 floxed knock-out mice to determine the role of the TRPC5 channel in the sADP. We will determine the distribution of the TRPC5 channels using real-time PCR, in situ hybridization, and immunoblots.
In specific aim 2 we plan to examine the mechanism by which repeated cocaine exposure decreases the sADP. My preliminary data indicates that dopamine modulates the sADP through a D1R/protein kinase A pathway. Interestingly, D1R modulation is absent after withdrawal from repeated cocaine exposure. Patch-clamp electrophysiology will be used to examine the pathway through which D1Rs modulate the sADP and how cocaine alters this modulation.
In specific aim 3 we plan to establish a role for TRPC5 channels in cocaine-reward. We propose that the loss of the mGluR5/TRPC5-mediated sADP in the PFC is partially responsible for the reported lack of response to cocaine in mGluRS knock-out mice. We will use both a local knockout of prefrontal cortical TRPC5 channels using an adeno associated viral bicistronic vector containing Cre and green fluorescent protein (AAV-Cre-GFP) and a global knockout strategy using CAMKII-Cre expressing mice crossed with floxed TRPC5 mice. We will test the floxed TRPC5 knockout mice for cocaine-induced locomotor activity and conditioned place-preference to establish a role for the TRPC5 channel in mediating the psychomotor activating and rewarding effects of cocaine. The prefrontal cortex is a brain area susceptible to addiction-associated changes induced by exposure to drugs of abuse. The goal of this proposal is to implicate the newly described TRPC5 ion channels in prefrontal cortical information processing, response to dopamine and cocaine-induced behaviors. ? ? ?
