Anatomical mapping of 'angiotensin sensitive' hypothalamic circuits: implications for the neural control of energy balance
Authors: De Sa Jessica , Elsaafien Khalid , Scott Karen , Colombari Debora , Krause Eric , de Kloet Annette 
Published: May 2023

The rising incidence of obesity is largely attributed to increased food intake and/or decreased energy expenditure. Increased intake of high-fat diet (HFD) stimulates the renin-angiotensin system and elevates levels of angiotensin II (Ang II). Ang II exerts physiological effects by activating angiotensin type-1 receptors (AT1aR) expressed in a variety of tissues, including the brain. In particular, AT1aR are robustly expressed in the paraventricular nucleus of the hypothalamus (PVN) and prior studies found that the deletion of AT1aR from PVN neurons promotes hyperphagia that exacerbates HFD-induced obesity. Here, we conduct neuroanatomical studies to probe potential mechanism(s) by which neurons within the PVN that express AT1aR (referred to as PVNAT1aR) impact food intake and energy expenditure. The PVNs of mice with expression of Cre-recombinase directed to the AT1aR gene yellow fluorescent protein (eYFP) were injected with a Cre-inducible adeno-associated virus (AAV) synthesizing eYFP. Using this approach, PVNAT1aR can be visualized with the presence of eYFP. Three-weeks later, brains were collected and processed for immunohistochemistry and/or in situ hybridization. Confocal microscopy revealed that PVNAT1aR synthesize corticotropin-releasing hormone (CRH) mRNA and send axonal projections to the median eminence. Intriguingly, we also observed that PVNAT1aR send axon collaterals to the arcuate nucleus of the hypothalamus (ARC), where they form appositions onto neurons that produce proopiomelanocortin (POMC). The firing of POMC neurons is coupled to decreased food intake and we’ve initiated in vivo studies to evaluate whether activation of PVNAT1aR affects feeding behavior and energy expenditure. Cre-inducible AAVs synthesizing the light sensitive opsin, ChR2, and/or eYFP were delivered into the PVN of AT1aR-Cre mice. Subsequently, mice were implanted with a chronic dwelling fiber-optic terminating in the PVN. After recovery, mice were fed either HFD (60%) or standard CHOW for 5 weeks. On the day of the experiment, mice were food deprived during the light phase and food was reintroduced at the onset of the dark phase. Using a randomized within-subject design, PVNAT1aR were optogenetically excited at the onset of the dark phase for 30 min or tethered to a fiber optic cable without light stimulation. Food intake and energy expenditure were measured using a TSE Phenomaster. While our functional studies are ongoing, our anatomical data suggest that PVNAT1aR may comprise a hypothalamic neurocircuit that promotes satiety, and therefore, may be a future therapeutic target for obesity. FAPESP (2019/22767-8, 2022/00977-3): NIH (HL-145028, HL-150750 and HL136595) This is the full abstract presented at the American Physiology Summit 2023 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.