Nonlinear analysis of intracellular recording of rostral ventrolateral medulla neurons using whole-cell patch-clamp technique

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To determine mechanisms underlying blood pressure elevation, we compared electrophysiological characteristics of neurons in the rostral ventrolateral medulla (RVLM) of neonatal Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Using the whole-cell patch-clamp technique, we examined the properties of RVLM neurons in brainstem-spinal cord preparations with a preserved sympathetic neuronal network. The baseline membrane potential of RVLM neurons was shallower (-49±1 mV vs.-53±2 mV) and the firing rate was faster (5.1±0.3 Hz vs.4.1±0.5 Hz) in SHR (n=56) than in WKY (n=33). Superfusion with angiotensin II (6 micromol/L) depolarized the RVLM neurons in SHR (8.9±1.9 mV) to a greater extent than in WKY (1.8±0.8 mV). Angiotensin II type 1 (AT_1) receptor antagonist, candesartan (0.12 micromol/L), induced significant membrane hyperpolarization (4.9±1.1 mV) and a decrease in the firing rate in RVLM neurons of SHR but not in those of WKY.After superfusion with the AT_2 receptor antagon … More ist, PD123319 (60 micromol/L), the hyperpolarization was abolished, suggesting angiotensin II action through AT_2 receptors to be involved in this hyperpolarization. Electrophysiological properties of RVLM neurons and their response to angiotensin II differ between WKY and SHR.The significant hyperpolarization and decreased firing rate caused by candesartan suggest that endogenously generated angiotensin II actually binds to AT_1 receptors on RVLM neurons, thus tonically contributing to a higher membrane potential and a faster firing rate in hypertensive rats. These differences in RVLM neurons suggest a mechanism possibly leading to elevation in blood pressure.Additionally, by recording blood pressure (BP), heart rate, renal sympathetic nerve activity (RSNA), and ipsilateral renal blood flow (RBF) in conscious WKY and SHR, we found coherence peaks of the transfer function between RSNA and BP and between RSNA and RBF at 0.05 and 0.80 Hz, below the respiratory-and cardiac-related fluctuations. The coherence was significantly higher and gain smaller in SHR than in WKY.Mutual information values showed strong linear and nonlinear relationships between RSNA and both BP and RBF at 0-0.1 Hz, and the relationships were similar in the two strains. The higher coherence implies that BP and RBF were more linearly correlated with RSNA in hypertensive rats, whereas the nonlinear correlation was greater in normotensive rats. Time delay values demonstrated that RSNA preceded BP and RBF under closed-loop conditions. Distinct low-frequency RSNA oscillations arising from the central nervous system generated hemodynamic fluctuations in conscious rats, independently of the baroreflex. Less