Role of Median Preoptic AT1a Receptors in Thirst Regulation

Undergraduate #121
Discipline: Biological Sciences
Subcategory: Physiology and Health

Robert Emeh - Alabama State University
Co-Author(s): Brent Shell, Joel Little, and Tom Cunningham, University of North Texas Health Science Center, Fort Worth, TX

The median preopotic nucleus (MnPO) is a hypothalamic nucleus that receives a complex set of afferent neural inputs from regions outside the blood brain barrier and is critical for body fluid regulation. Previous studies have shown that the MnPO is critical for behavioral and physiological responses to Angiotensin II (Ang II), a hormone and possible neurotransmitter that promotes thirst and vasopressin release. Lesions of the MnPO block thirst produced by peripheral Ang II. Also, Ang II applied directly to the MnPO promotes thirst. Thus the MnPO appears to contribute to both the peripheral and CNS actions of Ang II that maintain fluid homeostasis. This study’s aim is to discern the role of Ang II signaling at the MnPO in response to peripheral Ang II administration. In this study male Sprague Dawley rats were administered 2 mg/kg Ang II s.c. in 0.9% saline solution at days -7, and -3. Animals that responded to the peripheral Ang II received a 200-300 nl injection of virus containing AT1a shRNA as well as a GFP reporter into the MnPO. At days 14 and 18 post injection the animals were again administered subcutaneous Ang II and underwent a drinking test. At the end of the experiments, rats were perfused with 4% paraformaldehyde and the brains were used for c-Fos immunohistochemistry. We hypothesized that the injection of the AT1 knockdown virus into the MnPO will diminish angiotensin’s ability to promote thirst and therefore reduce Fos staining.

There were no significant differences in the drinking response to peripheral angiotensin between the AT1ashRNA hit (n=5) and miss (n=7) rats (P>.05). Immunohistochemical analysis of Fos, a marker for neuronal activity, revealed no differences in expression in the MnPO, SFO, and OVLT, and PVN between the AT1ashRNA hits and misses (P>.05). These results indicate that AT1a receptors in the MnPO are not necessary for water intake or Fos staining produced by peripherally injected Ang II. Other angiotensin receptors or neurotransmitter systems could contribute to these responses.

Funder Acknowledgement(s): 1. Department of Health and Human Services; 2. National Institute of Health; 3. National Heart, Lung and Blood Institute PO1 HL088052; 4. UNTHSC Summer Multicultural Advanced Research Training (SMART) Program; SMART grant 2R25HL007786-21 to Dr. Thomas Yorio, and R01HL119458 and P01HL08052 to T.C.

Faculty Advisor: Tom Cunningham,