Abstract Title

Role of Median Preoptic AT1a Receptors in Control of Thirst Regulation

RAD Assignment Number

302

Presenter Name

Brent Shell

Abstract

Purpose

Thirst is an essential mechanism for organisms to maintain osmotic and blood volume homeostasis and is therefore tightly regulated. Angiotensin II (Ang II) has long been known to stimulate thirst by both its action peripherally as a circulating hormone, and centrally acting as a peptide neurotransmitter. Peripherally circulating Ang II can elicit thirst by stimulating the Subfornical Organ (SFO), which in turn stimulates other hypothalamic nuclei regulating blood volume homeostasis such as the Median Preoptic Nucleus (MnPO) and Paraventricular Nucleus presumably through Ang II signaling. These hypothalamic nuclei then activate higher cognitive centers resulting in thirst. Central Ang II administered via intracerbroventricular (ICV) infusion also induces thirst by directly stimulating regions such as the MnPO through the Angiotensin Type 1 receptor and following a similar signaling pathway as peripheral Ang II only ignoring the circumventricular organs.

Methods

Male Sprague-Dawley rats are microinjected in the MnPO with either a virus to knockdown AT1aR expression (shAT1a) or a scramble virus (SCR) and instrumented with radio telemetry a week later. Our lab microinjected an adeno-associated virus with short hairpin RNA matched to the Angiotensin Type 1a receptor (At1aR) into the MnPO to test whether Ang II was necessary for thirst signaling in the MnPO. We hypothesized that Ang II was necessary for the thirst response to peripherally circulating Ang II as well as ICV injected central Ang II. Sprague Dawley rats were separated into subcutaneous (SC) and ICV Ang II administration groups. The SC group was pretested for their drinking response to 2mg/kg Ang II, and those animals that drank in response to the SC Ang II administration were utilized in the study. All animals were injected with the shAt1aR virus on Day 0, and were allowed to recover before drinking tests on day 14 and day 18. ICV animals were microinjected with the virus on Day 0 as well and instrumented with a chronic lateral ventricle cannula. These animals were administered 2ng Ang II in 1ul aCSF.

Results

Unexpectedly, we found that knockdown of AT1aR in the MnPO did not reduce drinking in the subcutaneous animals (p>.05), but did significantly reduce drinking in the ICV animals (P

Conclusions

Peripheral generation of thirst through Ang II may be predominantly mediated through glutamatergic neurotransmission from the SFO which only uses Ang II as a co-transmitter. Mechanistic understanding of thirst generation in the hypothalamus is critical for pharmacological manipulation with currently available pharmaceuticals as well as for development of future compounds.

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Role of Median Preoptic AT1a Receptors in Control of Thirst Regulation

Purpose

Thirst is an essential mechanism for organisms to maintain osmotic and blood volume homeostasis and is therefore tightly regulated. Angiotensin II (Ang II) has long been known to stimulate thirst by both its action peripherally as a circulating hormone, and centrally acting as a peptide neurotransmitter. Peripherally circulating Ang II can elicit thirst by stimulating the Subfornical Organ (SFO), which in turn stimulates other hypothalamic nuclei regulating blood volume homeostasis such as the Median Preoptic Nucleus (MnPO) and Paraventricular Nucleus presumably through Ang II signaling. These hypothalamic nuclei then activate higher cognitive centers resulting in thirst. Central Ang II administered via intracerbroventricular (ICV) infusion also induces thirst by directly stimulating regions such as the MnPO through the Angiotensin Type 1 receptor and following a similar signaling pathway as peripheral Ang II only ignoring the circumventricular organs.

Methods

Male Sprague-Dawley rats are microinjected in the MnPO with either a virus to knockdown AT1aR expression (shAT1a) or a scramble virus (SCR) and instrumented with radio telemetry a week later. Our lab microinjected an adeno-associated virus with short hairpin RNA matched to the Angiotensin Type 1a receptor (At1aR) into the MnPO to test whether Ang II was necessary for thirst signaling in the MnPO. We hypothesized that Ang II was necessary for the thirst response to peripherally circulating Ang II as well as ICV injected central Ang II. Sprague Dawley rats were separated into subcutaneous (SC) and ICV Ang II administration groups. The SC group was pretested for their drinking response to 2mg/kg Ang II, and those animals that drank in response to the SC Ang II administration were utilized in the study. All animals were injected with the shAt1aR virus on Day 0, and were allowed to recover before drinking tests on day 14 and day 18. ICV animals were microinjected with the virus on Day 0 as well and instrumented with a chronic lateral ventricle cannula. These animals were administered 2ng Ang II in 1ul aCSF.

Results

Unexpectedly, we found that knockdown of AT1aR in the MnPO did not reduce drinking in the subcutaneous animals (p>.05), but did significantly reduce drinking in the ICV animals (P

Conclusions

Peripheral generation of thirst through Ang II may be predominantly mediated through glutamatergic neurotransmission from the SFO which only uses Ang II as a co-transmitter. Mechanistic understanding of thirst generation in the hypothalamus is critical for pharmacological manipulation with currently available pharmaceuticals as well as for development of future compounds.