Tuesday, October 15, 2024 10/15/2024

Mechanisms of Synaptic Homeostasis Governing Pre-Sympathetic Neurons in the Hypothalamic Paraventricular Nucleus

Award Number: R01NS115072
ORGANIZATION: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
OPDIV: NIH
AWARD CLASS: DISCRETIONARY
AWARD ACTIVITY TYPE: SCIENTIFIC/HEALTH RESEARCH (INCLUDES SURVEYS)

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Project Summary Pre-sympathetic neurons (PSNs) of the hypothalamic paraventricular nucleus (PVN) are essential drivers of physiological and pathological increases of sympathetic nerve activity (SNA). Perhaps their most robust property is their resting state of discharge quiescence. Early studies linked quiescence to the dominance of synaptic inhibition, but mechanisms that establish and defend GABAergic inhibitory tonus in the PVN are understood only on a rudimentary level. This is an important knowledge gap because pathogenic factors that increase PVN-driven SNA must ultimately subvert or overwhelm mechanisms that regulate the quiescent resting state of PSNs. In preliminary studies, we uncovered a presynaptic mechanism that is novel to the PVN, referred to as “Glutamate-GABA strengthening (GGS)”, that increases GABAergic inhibition in pace with synaptic glutamate (Glu) spillover. To do so, GGS regulates the amplitude of GABA-A receptor-mediated inhibitory postsynaptic currents (IPSCs) through uptake of synaptically released Glu, ostensibly into local GABA terminals, by the neuronal excitatory amino acid transporter 3 (EAAT3). Once internalized, Glu is converted to GABA and GABA molecules are packaged into synaptic vesicles at greater than normal density. Stressors that acutely increase PVN-driven SNA are hypothesized to increase synaptic Glu release without changing extrinsic GABAergic input. As a result, “over-filled” GABA vesicles are released that dampen excitation and aid restoration of PSN quiescence. During chronic sympathoexcitation challenges accompanied by reduced GABA input, GGS is subverted (due to low GABA release) and can therefore provide little opposition to synaptic excitation. Proposed studies will use state-of-the-art transgenic mouse models, optogenetics and virus-mediated gene over-expression and CRISPR-Cas9 knockdown to assess mechanisms and functional outcomes of GGS. Kinetics, sensitivity and efficacy of GGS will be established at the single PSN level using a novel horizontal brain slice preparation that preserves Glu input from the forebrain median preoptic nucleus (MnPO) as well as GABA input from the PVN peri-nuclear zone (PNZ). Retrogradely transported AAV will be injected into the PVN of vGlut2-Cre mice to express channelrhodopsin (ChR2) in glutamatergic MnPO-PVN neurons. Optogenetic activation will determine the capacity of MnPO inputs to drive GGS amongst RVLM-projecting PVN PSNs. Using vGlut2fl/fl mice, we will determine functional effects of GGS on GABA-A receptor inhibitory tone and SNA responses to forebrain angiotensin II (AngII) and hyperosmolality when glutamatergic MnPO neurons have normal (vGlut2 intact) or diminished (vGlut2 knockdown) capacity to release Glu from PVN synapses. To further illuminate in vivo mechanisms and efficacy of GGS, EAAT3 on PNZ GABA inputs to the PVN will be increased and decreased to grade PVN GABAergic tonus and the magnitude of PVN-driven SNA responses to (1) acute forebrain AngII and hyperosmolality as well as (2) sub-acute water deprivation and high salt intake. Proposed studies will provide unprecedented mechanistic insight into the physiological role GGS plays in generating and defending PVN PSN quiescence, and are essential for advancing the goal of preventing and reversing disease-promoting sympathoexcitation.


Issue Date FY	Funding FY	Legal Entity Name	Legal Entity Address	Legal Entity City	Legal Entity State	Legal Entity Zip Code	Legal Entity COUNTY	Legal Entity COUNTRY	Assistance Listing	Award Code	Budget Year	Action Date	Action Type	Action Amount

Issue Date FY: 2024 ( Subtotal = $466,775 )
2024	2024	TEXAS A & M UNIVERSITY SYSTEM HEALTH SCIENCE CENTER	6003 TAMU	COLLEGE STATION	TX	77843	BRAZOS	USA	Extramural Research Programs in the Neurosciences and Neurological Disorders	001	5	8/8/2024	CHANGE OF GRANTEE / TRAINING INSTITUTION / AWARDING INSTITUTION	$466,775
2024	2023	THE UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER AT SAN ANTONIO	7703 FLOYD CURL DR	SAN ANTONIO	TX	78229	BEXAR	USA	Extramural Research Programs in the Neurosciences and Neurological Disorders	000	4	8/8/2024	NON-COMPETING CONTINUATION	$0
														Subtotal = $466,775

Issue Date FY: 2023 ( Subtotal = $487,008 )
2023	2023	UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER OF SAN ANTONIO	7703 FLOYD CURL DR	SAN ANTONIO	TX	78229	BEXAR	USA	Extramural Research Programs in the Neurosciences and Neurological Disorders	000	4	5/12/2023	NON-COMPETING CONTINUATION	$487,008
														Subtotal = $487,008

Issue Date FY: 2022 ( Subtotal = $487,008 )
2022	2022	UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER OF SAN ANTONIO	7703 FLOYD CURL DR	SAN ANTONIO	TX	78229	BEXAR	USA	Extramural Research Programs in the Neurosciences and Neurological Disorders	000	3	5/6/2022	NON-COMPETING CONTINUATION	$487,008
														Subtotal = $487,008

Issue Date FY: 2021 ( Subtotal = $486,489 )
2021	2021	UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER OF SAN ANTONIO	7703 FLOYD CURL DR	SAN ANTONIO	TX	78229	BEXAR	USA	Extramural Research Programs in the Neurosciences and Neurological Disorders	000	2	5/3/2021	NON-COMPETING CONTINUATION	$486,489
														Subtotal = $486,489

Issue Date FY: 2020 ( Subtotal = $483,891 )
2020	2020	UNIVERSITY OF TEXAS HEALTH SCIENCE CENTER OF SAN ANTONIO	7703 FLOYD CURL DR	SAN ANTONIO	TX	78229	BEXAR	USA	Extramural Research Programs in the Neurosciences and Neurological Disorders	000	1	6/29/2020	NEW	$483,891
														Subtotal = $483,891

Grand Total All Awards = $2,411,171

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Mechanisms of Synaptic Homeostasis Governing Pre-Sympathetic Neurons in the Hypothalamic Paraventricular Nucleus

Award Number: R01NS115072

ORGANIZATION: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE

OPDIV: NIH

AWARD CLASS: DISCRETIONARY

AWARD ACTIVITY TYPE: SCIENTIFIC/HEALTH RESEARCH (INCLUDES SURVEYS)

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