Role of KCNQ (Ã¢â‚¬Å“M-typeÃ¢â‚¬Â) K+ channels of dopaminergic neurons as key regulators of cocaine addiction
Dopamine neurons in the ventral tegmental area (VTA) fire bursts of action potentials in response to the presentation of rewarding stimuli, producing a learning signal that is thought to play a central role in the development of pathological conditions such as addiction to psychostimulants, such as cocaine. The ease by which cocaine and other psychostimulants cause hyper-excitability of VTA neurons and the excessive presence of dopamine depend on a variety of intrinsic ionic conductances and signaling pathways in the VTA, of which most are still unclear. Hence, the study of ionic conductances that modulate VTA excitability has the potential to illuminate the cellular bases of addiction, as well as posing novel approaches for its
prevention or reversal. It has been shown that dopamine neurons of the VTA express Ã¢â‚¬Å“M-typeÃ¢â‚¬Â K+ ion channels, which play dominant roles in control of excitability, action-potential firing and neurotransmitter release throughout the nervous system. Composed of KCNQ2-5 subunits as distinct gene products, M currents are regulated by a variety of Gq/11-coupled metabotropic receptors as a means of controlling function in brain and nerve, and novel M-channel Ã¢â‚¬Å“openersÃ¢â‚¬Â are being developed to counter epilepsy, brain damage from stroke and traumatic brain injury and chronic pain. In VTA neurons, the neurophysiological role of M channels VTA is still little understood, nor is it known how manipulating the activity or expression of these channels could affect drug-related behaviors, such as psychostimulant self-administration. Indeed, development from cocaine or methamphetamine use to addiction is always associated with an increase in dopamine neuron firing, suggesting that we could counter this phenomenon by pharmacological intervention. Here we seek pilot funds to initiate a collaborative line of inquiry that combines Dr. Shapiro's expertise in studying the physiology and regulation of M-current using patch-clamp and imaging approaches with Dr. WanatÃ¢â‚¬â„¢s experience with the study of cocaine addiction and dopamine neuron function using in vivo and in vitro electrical recordings, in vivo neurochemical measurements, transgenic animals and cutting-edge behavioral assays, all in combination or in parallel. We hypothesize that up-regulation of M current activity in VTA could oppose the reinforcing properties of psychostimulants by countering increased dopamine neuron firing, a finding that could have far-reaching implications for drug abuse treatment. We will physiologically characterize the precise KCNQ gene products underlying M current in acutely isolated brain slices under voltage- and current-clamp, both in wild type mice and transgenic Cre-lox mice that lack KCNQ2 or KCNQ3 subunits specifically in dopaminergic neurons. We will then seek to determine the relationship between M current activity and levels of dopamine in the VTA associated with cocaine self-administration, in response to precise pharmacological and genetic manipulation of KCNQ/M channel expression, function or properties. Our study could implicate KCNQ/M channel Ã¢â‚¬Å“openersÃ¢â‚¬Â as potentially novel therapeutic agents to treat or prevent drug addiction. We believe that this pilot grant could provide preliminary data for major national funding, representing a seminal set of discoveries for the field. These findings could elucidate important neuro-adaptive mechanisms associated with psychostimulant use and point toward novel therapeutic targets to alleviate the devastating effects of chronic psychostimulant addiction.