Cellular and Circuit Mechanisms Responsible for Dynorphin Actions in mPFC

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Project Summary: Pharmacological activation of kappa opioid receptors (KOR) in humans elicits reports of dysphoria and cognitive disruption. KOR activation in rodents by agonists or by stress-evoked dynorphin release has been shown to produce aversion, increase anxiety-like behaviors, increase the rewarding effects of drugs of abuse (e.g. cocaine, amphetamine, heroin, ethanol & nicotine), increase addictive drug self-administration, and reinstate extinguished drug-seeking behaviors. The cellular and molecular mechanisms responsible for these dynorphin-dependent, pro-addictive behaviors are not fully understood, and a better understanding may suggest new therapeutic approaches to the treatment of stress-related diseases including relapse to drug use. Prior studies supported by this award demonstrated that KOR activation in the dorsal raphe, ventral tegmentum and ventral striatum by stress-induced release of dynorphin or pharmacological KOR agonist administration produces aversion in mice and potentiates cocaine conditioned place preference by activating p38 MAPK in serotonergic and dopaminergic neurons to regulate excitability and serotonin transport. Recent studies supported by this award continued to define the molecular and cellular sites of dynorphin action in the medial prefrontal cortex (mPFC) and mechanisms of KOR regulation of neuronal circuit function at each of these sites in brain. Studies proposed in the present application will continue to build on this strong foundation by characterizing cellular and molecular mechanisms responsible for dynorphin / KOR induced cognitive disruption in the mPFC. We propose to address three questions: What are the individual contributions of pre- and postsynaptic KORs in the mPFC in controlling behavior in an operant delayed alternation task? What are the behavioral stimuli required to evoke dynorphin release in mPFC? What are the effects of dynorphin release and KOR activation on excitability of mPFC neurons? Our background studies establish that pharmacological KOR activation disrupts performance in the delayed alternation operant task, and this effect can be blocked by local KOR inactivation by a KOR antagonist (norBNI) or by virally-mediated genetic excision of PFC KORs (AAV-Cre in the PFC of floxed KOR male mice). The effects of KOR activation on delayed alternation performance in females are not yet known. Stress-induced release of endogenous dynorphins in PFC also disrupt performance in the delayed alternation task, but the efficacy of different forms of behavioral stress have not yet been established. KOR is expressed on both pre- and postsynaptic components of the PFC circuit, but the respective contributions to controlling delayed alternation performance are not yet understood. Preliminary results demonstrate that naloxone precipitated withdrawal in morphine dependent male mice evokes dynorphin release in mPFC, and this suggests that dynorphin-mediated disruption of cognition may be a component of the opioid abstinent state. The proposed studies would further advance our understanding of the therapeutic potential of kappa selective ligands in the treatment of chronic pain and drug addiction.