Chronic stress-induced cardiovascular effects are decreased by a cortical-brainstem neural circuit

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Project Summary Chronic exposure to stress is a risk factor for the leading cause of global mortalities, cardiovascular disease. Although chronic stress alters our physiological stress response, the biological mechanisms responsible for cardiovascular disease development remain unclear. Therefore, this proposal addresses this substantial health problem by determining the neural basis of the cardiovascular stress response and investigating a prospective avenue to alleviate physiological insults caused by chronic stress. Human imaging studies have revealed the prefrontal cortex is a key site for processing stress-related information. Within the rat prefrontal cortex, the infralimbic area (IL) is critical for behavioral and physiological stress reactivity. Interestingly, brain stimulation studies targeting this shared cortical area in humans and rats see a vasodepressor effect. Further, stimulating IL neurons in male rats protects against cardiovascular deficits caused by chronic stress. To determine the biological pathways involved, we explored downstream IL pathways and identified IL inputs to the rostral ventrolateral medulla (RVLM). Because the RVLM initiates the sympatho-adrenomedullary stress response, an IL-to-RVLM circuit may underlie a crucial link between stress appraisal and sympathetic reactivity. Preliminary studies found that stimulating the IL-to-RVLM circuit during novel restraint stress blunts corticosterone release in male and female rats. Further, gene expression analysis revealed chronic stress exposure increases brainstem catecholamine-synthesis transcripts in both sexes. Because RVLM catecholamine neurons drive sympathetic outflow, we hypothesize that IL input may reduce sympathoexcitation by inhibiting RVLM catecholamine activity, thereby reducing the cardiovascular consequences of chronic stress. (Aim 1) To determine the role of the IL-to-RVLM circuit during chronic stress, intersectional genetics will be used to reduce IL-to-RVLM signaling and measure catecholamine synthesis enzyme expression after chronic stress, in males and females. By using fluorescent in situ hybridization coupled with immunolabeling, mRNA expression changes of catecholamine synthesis enzymes would clarify how chronic stress alters neurogenic-driven sympathetic activity in male and female rats and the necessity of the IL-to-RVLM circuit for chronic stress neural adaptations. (Aim 2) Next, we will determine if optogenetically stimulating the IL-to-RVLM circuit alleviates the cardiovascular sensitization caused by chronic stress. By measuring real-time hemodynamics and electrocardiography during acute stress, we can assess if stimulating IL-to-RVLM signaling reduces sympathoexcitation and cardiovascular hyperreactivity caused by chronic stress. Results from these experiments will examine neural pathways responsible for cardiovascular stress responding and identify chronic stress-induced changes that can contribute to pathologies and disease. Moreover, these experiments will determine if this circuit could represent a target to safeguard cardiovascular health against the deleterious consequences of chronic stress.