Neural Basis for Regulation of Vasopressin Secretion by Presystemic Anticipated Disturbances in Osmolality, and by Hypoglycemia The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Kim, Angela. 2020. Neural Basis for Regulation of Vasopressin Secretion by Presystemic Anticipated Disturbances in Osmolality, and by Hypoglycemia. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences. Citable link https://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37365939 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA Neural Basis for Regulation of Vasopressin Secretion by Presystemic Anticipated Disturbances in Osmolality, and by Hypoglycemia A dissertation presented by Angela Kim to The Division of Medical Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Neuroscience Harvard University Cambridge, Massachusetts April 2020 © 2020 Angela Kim All rights reserved. Dissertation Advisor: Bradford B. Lowell Angela Kim Neural Basis for Regulation of Vasopressin Secretion by Presystemic Anticipated Disturbances in Osmolality, and by Hypoglycemia Abstract Vasopressin (AVP), released by magnocellular AVP neurons of the hypothalamus, is a multifaceted hormone. AVP regulates many physiological processes including blood osmolality, blood glucose, and blood pressure. In this dissertation, I present two independent studies investigating the neural mechanism for role of AVP in fluid and glucose homeostasis. In regards to regulating water excretion and hence blood osmolality, magnocellular AVP neurons are regulated by two temporally distinct signals: 1) slow systemic signals that convey systemic osmolality information, and 2) rapid ‘presystemic’ signals that anticipate future osmotic challenges. Magnocellular AVP neurons show bidirectional presystemic responses to feeding and drinking. In our first study, we identified and characterized the neural circuits mediating presystemic regulation of AVP release. Using in vivo calcium imaging and opto- and chemo- genetic approaches, we demonstrated that presystemic regulation of magnocellular AVP neurons is mediated by two functionally-distinct neural circuits that transmit information related ingestion of either water or food, which decrease or increase osmolality, respectively. We also validated a brainstem circuit mediating blood pressure information to magnocellular AVP neurons that is completely separate from water- and food-related presystemic circuits. iii Next, we focused on the glucoregulatory function of AVP. We adopted a wide range of in vitro and in vivo techniques in mice and human to provide a comprehensive analysis of central and peripheral pathways mediating AVP’s glucoregulatory effect. We performed the very first in vivo simultaneous real-time monitoring of blood glucose and magnocellular AVP neuron activity in mice to demonstrate robust activation of magnocellular AVP neurons by hypoglycemia. We further demonstrated that A1/C1 neurons in the brainstem mediate this activation. We showed that AVP acts on V1b subtype of AVP receptors specifically expressed on pancreatic alpha cells to stimulate glucagon release, which then stimulates hepatic glucose production. Taken together, our data shows that activity of magnocellular AVP neurons is tightly regulated by multiple functionally-distinct neural circuits. We propose that proper regulation of AVP release is crucial for homeostasis of multiple physiological processes, and dysregulation of AVP release might underlie certain diseases with impaired water and glucose balance. iv Table of Contents Title Page………………………………………………………………………………………….i Copyright Page……………………………………………………….…………………………..ii Abstract……………………………………………................................................................….iii Table of Contents………………………………............................................................……..….v List of Figures………………………………………………………………….........................viii Acknowledgement……………………………………………………………..............................x Chapter 1. Introduction 1.1 Introduction to Vasopressin..................................................................................................2 1.2 Systemic regulation of vasopressin release……………………...........................................4 1.3 New insight into hypothalamic function…...................................................................…....6 1.4 Presystemic regulation of Vasopressin neurons............................................................……8 1.5 Osmotic homeostasis and significance of presystemic regulation......................................12 References….............................................................................................................................16 Chapter 2. Regulation of Vasopressin Secretion by Presystemic Anticipated Disturbances in Osmolality 2.1 Introduction….....................................................................................................................22 2.2 Results 2.2.1 Vasopressin neurons receive inhibitory and excitatory inputs from the LT...............24 2.2.2 Water-related presystemic regulation of vasopressin neurons is mediated by the LT...........................................................................................................................……27 2.2.3 Presystemic signals enter the LT at the level of MnPO..............................................31 2.2.4 SON-projecting LT neurons show presystemic response to water-predicting cues and drinking................................................................................................................................34 2.2.5 The LT does not mediate food-related presystemic regulation of vasopressin Neurons................................................................................................................................37 2.2.6 Vasopressin neurons receive excitatory inputs from A1/C1 neurons in the VLM…..40 v 2.2.7 A1/C1 neurons in the VLM mediate hypotension-induced, but not feeding-induced, activation of vasopressin neurons.........................................................................................43 2.2.8 Perinuclear zone GABAergic neurons do not mediate food-related presystemic regulation of vasopressin neurons........................................................................................45 2.2.9 AgRP and POMC neurons do not mediate food-related presystemic regulation of vasopressin neurons..............................................................................................................48 2.2.10 Food-related presystemic regulation of vasopressin neurons is mediated by unknown neurons in the ARC..............................................................................................51 2.3 Discussion….......................................................................................................................54 2.4 Methods...............................................................................................................................55 References.................................................................................................................................62 Chapter 3. Regulation of Vasopressin Secretion by Hypoglycemia 3.1 Introduction.........................................................................................................................66 3.2 Results 3.2.1 Glucagon secretion in response to an insulin tolerance test is driven by Vasopressin…......................................................................................................................68 3.2.2 Vasopressin evokes hyperglycemia and hyperglucagonemia.....................................75 3.2.3 Hypoglycemia evokes Vasopressin secretion via activation of A1/C1 neurons.........79 3.2.4 Vasopressin -induced glucagon secretion maintains glucose homeostasis during dehydration….......................................................................................................................83 3.2.5 Insulin-induced Vasopressin secretion may underlie counter-regulatory glucagon secretion in human, and is diminished in subjects with Type 1 Diabetes............................85 3.3 Discussion...........................................................................................................................88 3.4 Methods...............................................................................................................................90 References...............................................................................................................................109 Chapter 4. Conclusion 4.1 Summary of findings.........................................................................................................116 4.2 Function of presystemic regulation in Vasopressin neurons.............................................118 4.3 Significance of functionally distinct circuits in regulation of Vasopressin release..........120 4.4 Neural mechanism for stress-induced Vasopressin release..............................................122 vi 4.5 Lack of food-predicting cue response in magnocellular Vasopressin neurons.................123 4.6 Technical consideration: rabies retrograde tracing...........................................................125