Prefrontal-hypothalamic circuitry mediates chronic stress-induced cardiovascular susceptibility - Summary Cardiovascular disease is the leading cause of death worldwide and psychosocial stress is a significant predictor of disease incidence and severity. However, the specific neurobiological mechanisms that mediate the cardiovascular consequences of stress are largely unknown. Therefore, the current proposal will determine how the cortical circuits responsible for cognitive appraisal of stress regulate physiological stress responses. Recent studies in rats identified a population of cells in the infralimbic (IL) region of the medial prefrontal cortex that integrate endocrine and autonomic responses to stress in a sexually-divergent manner. Further, stimulation of IL glutamate neurons and chronic stress interact sex-specifically to affect cardiac structure and function. While the activity of excitatory IL projection neurons is critical for regulating the deleterious effects of chronic stress, the pathways used by these cells to modulate reactivity of autonomic and endocrine systems remain to be determined. Preliminary data indicate that IL projections to the posterior hypothalamus (PH) reduce male stress responses but enhance female stress responses. These excitatory IL projections target both inhibitory GABAergic and excitatory glutamatergic neurons in the male and female PH. Further, chronic variable stress upregulates PH gene expression related to glutamate and GABA signaling in males but not females. Altogether, these findings led to the hypothesis that sex-specific IL glutamatergic signaling to the PH differentially engages glutamatergic and GABAergic cells to regulate cardiovascular and endocrine stress reactivity, as well as the consequences of chronic stress on vascular stiffness and cardiac hypertrophy. This hypothesis will be tested in 3 aims. First, circuit signaling will be examined with patch-clamp slice electrophysiology in male and female rats. Specific experiments will determine how IL glutamate signaling targets genetically-defined postsynaptic PH GABAergic and glutamatergic cells as well as chronic stress- induced circuit plasticity. Second, in vivo optogenetic activation of IL synapses in the PH following chronic variable stress will interface with measures of heart rate, blood pressure, and neuroendocrine stress responses. This approach will isolate circuit effects to normalize or exacerbate stress reactivity. Third, a combinatorial viral approach will be used to retrogradely inhibit IL projections to the PH with Cre-dependent tetanus toxin. In addition to cardiovascular telemetry and hypothalamic-pituitary-adrenal hormones, cardiac hypertrophy and microvascular function will be assessed in chronically-stressed male and female rats to determine circuit regulation of stress-induced cardiac and vascular dysfunction. Collectively, these experiments will determine specific circuit and cellular pathways linking cognitive appraisal with physiological stress responses. Further, this investigation is poised to not only increase understanding of brain-body interactions and sex-based health disparities, but also identify potential targets to mitigate cardiovascular risk.
