Acute hyperosmotic stimulus of the Organum Vasculosum of the Lamina Terminalis leads to increase in the blood pressure dependent on release of ATP into the Paraventricular Nucleus of the Hypothalamus of rats

Abstract

The neural network involved in hyperosmolality-induced hypertension includes the activation of the organum vasculosum of the lamina terminalis (OVLT) with monosynaptic connections to the paraventricular nucleus of the hypothalamus (PVN) that expresses an abundance of purinergic receptors including P2 receptors. Previously, we have shown that hyperosmotic-induced sympathoexcitation at the level of the PVN depends on the P2 receptors. More recently, we have shown that hyperosmotic stimulus induces the release of ATP in the PVN, at least in part, from astrocytes. Here we hypothesize that the increase in the blood pressure (BP) induced by acute hyperosmotic stimulus in the OVLT involves the release of ATP within the PVN neurons, acting on P2 receptors. Thus, we sought to determine (1) whether P2X7-expressing OVLT and PVN neurons are activated by hyperosmotic challenge, and (2) what effects P2 receptor antagonism on changes in the BP mediated by an acute hyperosmotic stimulus in the OVLT. Adult Wistar rats (10-12 weeks old; CEUA ICB/USP: #4895140819 and #1521230221) were used in two protocols: 1) Double-labeling immunofluorescence of P2X7 (anti-P2X7 receptor, 1:500) expressing neurons with FOS (anti-cfos, 1:3000) animals received i.v administration of hypertonic (NaCl, 3M, n=4) or isotonic saline (NaCl, 0.154M, n=4), followed by evaluation of immunostaining to FOS and P2X7 receptors in the OVLT and PVN; 2) OVLT-PVN microinjections and BP monitoring: under anesthesia rats (n=5), received catheters in the femoral vein and artery for the administration of urethane (1g/kg) and BP recording signals, respectively. Microinjections of 3M NaCl (50nL) were administered into the OVLT, before and after bilateral antagonism of P2 purinergic receptors (PPADS, 10uM-100nL on each side) in the PVN with simultaneous BP recording. Data were expressed as the mean ± SD, and statistical significance level of p<0.05 by Student’s T-test. Immunoreactive neurons for the P2X7 receptor subunit were observed in all compartments of the OVLT and PVN. Hyperosmotic stimulus significantly increased the number of Fos+ neurons in both the OVLT and PVN. While a small number of P2X7 receptors expressing OVLT and PVN neurons was observed in rats treated with isotonic saline, significantly more P2X7-expressing neurons expressed Fos+ in the OVLT with hypertonic saline. The stimulus of the OVLT with 3M NaCl elicited a significant increase in the BP. This effect was attenuated after bilateral injection of PPADS in the PVN (ΔMAP: NaCl OVLT:+10±1mmHg vs. NaCl OVLT post-PPADS PVN: +2.4±1.3mmHg, p<0.0001). Collectively, our findings indicate that hyperosmotic stimulation activates a subset of P2X7 expressing OVLT and PVN neurons and that the elevation in the BP induced by hyperosmotic stimulus in the OVLT involves the endogenous release of ATP within the PVN, likely as part of the neural control of circulation during osmotic challenges. Financial Support: FAPESP #2019/19894-8, CAPES #88887.364432/2019-00. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.