Chronic stress is a factor in many psychiatric illnesses that share dysregulation of the prefrontal cortex (PFC), and impaired executive function mediated in the PFC. Current therapies are inadequate, and residual cognitive symptoms often persist. This may be because multiple PFC circuits are dysregulated, disrupting multiple cognitive processes. If different mechanisms are affected in different PFC circuits, treatments that are beneficial to one may be ineffective or even detrimental to another. Over the years, we have studied chronic stress-induced cognitive impairment in the medial PFC and the orbitofrontal cortex (OFC) using different stress paradigms, but we have never compared these sub-regions directly. We have, however, observed differences in signaling mechanisms and functional plasticity suggesting that they may respond differently to chronic stress. We have also seen that chronic unpredictable stress (CUS) induces cognitive deficits in both regions. Thus, we will now utilize CUS in this proposal for competing renewal to directly compare and contrast the circuit-level dysregulation underlying cognitive impairment induced by CUS in the mPFC and OFC. In four specific aims, we will investigate the generality of effects by assessing changes in different behaviors mediated in these regions relevant to stress- related psychiatric disorders. We will study differential changes in afferent-evoked responses in mPFC and OFC, then use optogenetics to manipulate functional plasticity in those pathways to determine if changes seen after stress are sufficient to account for stress-induced cognitive deficits, and if opposing them is therapeutic. We will study differences in signal transduction and structural anatomical plasticity that may underlie differential changes in functional response induced by CUS.
In Aim 1, we will assess differences in functional plasticity in mPFC (comparing IL and PL sub-regions) and OFC after CUS by measuring stress-induced changes in electrical responses elicited by stimulation of afferent input from the mediodorsal thalamus and ventral hippocampus to the mPFC, and from mediodorsal thalamus and basolateral amygdala to the OFC.
In Aim 2, we will use opto- genetics to test the effects of directly potentiating or attenuating afferent-evoked responses in these same circuits on behaviors mediated in the mPFC and OFC. We predict that attenuating responses in the mPFC and potentiating responses in the OFC will mimic the effects of stress, whereas eliciting the opposite effect in each region will be beneficial in rescuing CUS-induced cognitive deficits in stressed animals.
In Aim 3, we will assess changes in dendritic complexity and spine density on PFC pyramidal cells after stress, and test the role of new spine formation in the effects of optogenetically-induced plasticity.
In Aim 4, we will test the differential roles of plasticity-related signaling pathways in the mPFC and OFC. We predict that CUS will attenuate PI3K-Akt signaling in mPFC and attenuate JAK signaling in OFC. And we predict these deficits will be restored by opto- genetically-induced plasticity that rescues PFC-mediated cognition. By revealing how stress dysregulates PFC circuits mediating executive function, these results may inform new, targeted strategies to improve treatment.
Stress is a predisposing factor for many psychiatric illnesses that share changes in behavior and cognition related to dysregulation of the prefrontal cortex. This project addresses differential neurobiological mechanisms in the medial prefrontal and orbitofrontal cortex underlying the detrimental cognitive effects of chronic stress. Specifically, we will investigate different maladaptive changes in plasticity, circuit function, cellular morphology and signal transduction in these regions that nonetheless lead to similar behavioral changes in both. The results will add to our understanding of the mechanisms of stress-related neuropsychiatric pathology, and may reveal novel entry points for more selective, more effective, or complementary therapeutic strategies.
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