The impact of chronic chemogenetic activation of AT1aR neurons in the PVN on energy balance and fluid intake

The renin-angiotensin system is classically known for its involvement in cardiovascular function and electrolytic balance and has more recently also been implicated in energy homeostasis. Angiotensin type-1a receptors (AT1aR) are robustly expressed throughout neural circuits that govern metabolism including the paraventricular nucleus of the hypothalamus (PVN), and the particular AT1aR(s) that are localized to the PVN have previously been implicated in energy balance. Here, we used designer receptor exclusively activated by designer drugs (DREADDs) technology to evaluate the impact of chronic chemogenetic excitation of AT1aR neurons within the PVN (referred to as PVN AT1aR ) on energy balance and fluid intake. Cre-inducible AAVs expressing excitatory DREADDs (hM3Dq; Gq-DREADDs) and/or mCherry were bilaterally injected into the PVNs of Agtr1a-Cre mice. Using this approach, the hM3Dq (present in Gq-DREADDS, but not control mice) can be activated pharmacologically via i.p. injection of Clozapine-N-Oxide (CNO), leading to approximately 8 hours of burst firing of PVN AT1aR neurons. After three weeks of recovery, the mice were placed in a TSE Phenomaster for habituation and for continuous evaluation of food intake, water intake, and energy expenditure throughout the experiment. Subsequently, CNO was administered to control and Gq-DREADDs mice by way of i.p. injections (3.0 mg/kg) performed at the onset of the dark-phase every other day for 12 days. In mice administered the Gq-DREADDs, chemogenetic excitation of PVN AT1aR consistently increased water intake and oxygen consumption. On the other hand, no clear differences in food intake, body weight or respiratory exchange ratio were noted in Gq-DREADDs mice upon CNO administration. Furthermore, in control mice, no significant differences were observed in any of the parameters evaluated. Neuroanatomical studies from our group already demonstrated that PVN AT1aR are neurosecretory and synthesize corticotropin-releasing hormone (CRH) mRNA. Thus, at the end of the study, mice were given CNO and blood samples were collected 90 min later to evaluate hypothalamic-pituitary-adrenal axis activity during chemogenetic activation of PVN AT1aR . Plasma corticosterone levels were significantly elevated in Gq-DREADDs mice relative to controls, findings that corroborate the activation of PVN AT1aR in these mice. Although our studies are still ongoing, these preliminary results suggest that the chemogenetic activation of PVN AT1aR may be suffcient to increase fluid intake and energy expenditure. The implication is that these neurons play a role in orchestrating behavioral and metabolic responses. FAPESP 2019/22767-8, 2022/00977-3 to JSA. AHA 23POST1020034 to KE. NHLBI R01HL136595, R35HL150750, R01HL145028 and NCCIH R65AT012142 to ADK & EGK. 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.