STRIATAL EXCITATORY AND METABOTROPIC PKA REGULATION IN STRESS AND RESILIENCE Project Summary Mental disorders such as anxiety and depression are major health concerns that contribute unabated to a large portion of all morbidity and mortality. These complex disorders may be viewed as mal- adaptations that arise in brain circuitry. Normally, motivated behaviors and executive functions require processing of sensory-triggered excitatory neurotransmission and assignment of emotional context. One place this occurs is in the ventral striatum, or nucleus accumbens (NAc), where cortical glutamatergic and midbrain dopaminergic inputs converge to mediate brain functions such as reward and stress responses. NAc dysfunction is broadly implicated in the etiology of many mental illnesses. For example, stress-induced alterations in NAc activity are linked to the pathophysiology of depression. Insight into the mechanisms by which glutamate and dopamine neurotransmission are integrated within the NAc may shed light on some causes of mental illness, or implicate new drug targets and treatment strategies. Here, we introduce a new signaling mechanism which we hypothesize is controlled by striatal glutamatergic and dopaminergic signaling to allow concerted regulation of PKA activity. Specifically, our preliminary data indicates that glutamate controls constitutive phosphorylation of the RII-beta (RIIb) regulatory subunit by Cdk5, which then directly affects PKA activation by D1-type dopamine receptors via a second PKA-dependent RIIb auto-phosphorylation mechanism. We hypothesize that this unique mechanism mediates striatal plasticity and behavioral responses to stress and that chronic stress can cause mal-adaptations in this mechanism so that glutamate and dopamine signaling are uncoupled and PKA signaling is dysregulated. We further hypothesize that this mechanism may be targeted to improve striatal plasticity and behavioral resilience. To pursue this novel premise, we propose to 1) study the regulation of RIIb/PKA and explore downstream effectors in vitro and in vivo; 2) study the role of RIIb/PKA phosphorylation in ventral striatal neuronal excitability and synaptic plasticity and 3) study the regulation of this mechanism by acute and chronic stress, and determine how it contributes to behavioral responses to stress. These studies will yield important information on the mechanisms that integrate brain circuitry and how they are affected by stress. Thus, we will better understand some of the basis by which stress may contribute to complex mental disorders such as anxiety and depression and how they may be more effectively treated.
Mental illnesses such as anxiety and depression extract enormous costs in the U.S., while available treatments often address the symptoms rather that the molecular causes. Greater understanding of the neurobiological basis of neuropsychiatric disorders is the first step toward more effective treatments. The goal of this research is to understand a new fundamental mechanism by which the brain integrates environmental experiences with emotional context, how this mechanism mediates synaptic plasticity and behavioral responses to stressful conditions, how this mechanism may become dysregulated, and how it may be targeted to improve behavioral responses to stress.
