The overall goal of this research proposal is to assess the physiological significance of the endocannabinoids (eCBs) in the rostral ventrolateral medulla (RVLM) circuits which regulate cardiovascular function. The central nervous system is directly involved in the regulation of arterial blood pressure (ABP), largely through actions of the sympathetic nervous system on renal function and vasculature. The RVLM is a critical component in the central neural pathway since presympathetic RVLM neurons receive inputs from multiple brain areas and from the spinal cord, and thus mediate many cardiovascular reflexes. Hypertension may result from an imbalance between sympathetic vasomotor neuron activity and those cells that inhibit it. An increase in sympathetic nervous system activity is often associated with disinhibition of RVLM neurons; however, the underlying mechanisms remain unidentified. eCBs are endogenous ligands with a broad range of cardiovascular effects which activate: (1) G protein-coupled cannabinoid type-1 receptor (CB1R), (2) transient receptor potential vanilloid type 1 (TRPV1), or (3) both, indicating a duality of function. Our preliminary data demonstrate that activation of TRPV1 decreases both the excitability of presympathetic RVLM neurons as well as ABP and renal sympathetic nerve activity (RSNA). In addition, TRPV1 expressing neurons were identified in the lateral hypothalamus (LH) and these neurons project to the RVLM. Our multi-disciplinary approaches will use in vivo renal nerve and ABP recordings in rats following eCBs administration into RVLM, optogenetics in combination with telemetry measurements of ABP, fluorescent immunostaining, and in vitro patch-clamp recordings of synaptic currents in identified presympathetic RVLM neurons of transgenic mice. We will test the hypothesis that presympathetic RVLM neurons receive TRPV1 and CB1R expressing inhibitory inputs which determine the excitability of RVLM neurons and thus control ABP. Delineating these mechanisms of brainstem eCBs is essential to predict their impact on the central control of cardiovascular function caused by the activation of TRPV1 and/or CB1R. We believe our results will have clinical significance by providing direct evidence about the regulation of ABP by cannabinoids and will allow the development of novel therapeutic strategies for the treatment of hypertension.
This study will reveal the site and effect of endocannabinoids on a brainstem area involved in blood pressure control. Endocannabinoid actions in the brainstem can have important clinical implications for the treatment of such medical conditions as hypertension.
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