Melatonin Attenuates RVLM Neuro-inflammation and Sympathetic Activation in Stress-induced Hypertension Rats

Shutian Zhang

doi:10.20944/preprints202002.0448.v1

Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Version 1 : Received: 23 February 2020 / Approved: 28 February 2020 / Online: 28 February 2020 (16:30:19 CET)

Background: Hypertension is a cardiovascular syndrome with the highest morbidity and mortality worldwide. Hypertension caused by various stress factors is called stress-induced hypertension (SIH). The rostral ventrolateral medulla (RVLM) "neuroinflammatory-sympathetic overactivation" is involved in SIH formation. Melatonin has anti-inflammatory, anti-oxidant and blood pressure lowering effects. The present study is to explore the antihypertensive effects and mechanism of central melatonin which based on microglia derived neuroinflammation. Methods: Stress-induced hypertension (SIH) was induced by electric foot-shock stressors with noise interventions in rats. Melatonin (0.01，0.1，1 mmol/L) was administered to RVLM and then blood pressure (BP) and serum norepinephrine (NE) were monitored to reflect sympathetic vasomotor activity in SIH rats. Excitatory neurotransmitter (Glutamate) and inhibitory neurotransmitter [γ-aminobutyric acid (GABA)] were measured using ELISA kits. Markers of microglia M1 polarization (CD86) and pro-inflammatory cytokines (PICs (IL-1β, TNF-α)) expression in the RVLM were measured by RT-qPCR. Results: (1) Stress-induced increase in blood pressure and serum NE concentration; RVLM microinjection melatonin attenuated the elevation of blood pressure and increase of plasma NE in SIH rats in a dose-dependent manner. (2) The expression of CD86, PICs (IL-1β, TNF-α) and c-fos were increased in SIH rats; RVLM injection melatonin attenuated RVLM neuroinflammation and its effect is concentration-dependent. (3). Stress-induced increase in glutamate concentration in RVLM; RVLM injection melatonin reduced glutamate level and increased GABA level in SIH rats in a concentration-dependent manner. Conclusion: RVLM injection of melatonin inhibits M1 polarization and has anti-hypertensive effects. Melatonin reduces M1 polarization in microglia might be a novel target and a new strategy for anti-stress induced-hypertension.

Stress; Hypertension; Microglia; Neuroinflammation; Sympathetic overactivation

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Melatonin Attenuates RVLM Neuro-inflammation and Sympathetic Activation in Stress-induced Hypertension Rats

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