Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC18
Altered GABAA and NMDA receptor expression in the hypothalamic paraventricular nucleus of hypertensive and pregnant rats
S. C. Cork1, P. L. Chazot1, S. Pyner1
1. School of Biological and Biomedical Sciences, University of Durham, Durham, United Kingdom.
The autonomic nervous system plays an essential role in regulation of the cardiovascular system, and over activation of the sympathetic branch has been shown to be characteristic of many cardiovascular diseases, including hypertension1. Interestingly however, sympathoexcitation is also required to maintain cardiovascular function vital for foetal development during pregnancy2. The paraventricular nucleus of the hypothalamus (PVN) is an important brain site for integration of cardiovascular inputs and a known site for autonomic regulation3. Studies have shown that GABA elicits inhibitory effects within the PVN through the GABAA receptor, whereas glutamate has an excitatory effect through the NMDA receptor3. Under normal physiological conditions, GABAergic inhibition suppresses autonomic outflow from this nuclei. However, electrophysiological evidence has shown that in hypertension, glutamatergic activity is increased and GABAergic inhibition is attenuated4. In this study, we aimed to investigate the composition of GABAA and NMDA receptors in the PVN in the hypertensive and pregnant rat to determine the contribution these receptors may make to altered sympathetic nerve activity. All experiments were performed in accordance with the Animals (Scientific Procedures) Act, 1986. Animals (female Wistar rat (n=4), female spontaneously hypertensive rat (SHR; 14wk, n=4) and pregnant Wistar rat (E19, n=4)) were euthanized with sodium pentobarbital (60mg/kg intracardial), brains were extracted and frozen in isopentane (-20○C). The PVN was located using neuroanatomical landmarks and two 600μm slices were taken. Bilateral punches were then taken and subjected to quantitative immunoblotting for the GluN1 and GluN2A subunits of the NMDA receptor and the α1 subunit of the GABAA receptor. Results were normalised against β-actin and analysed using ImageJ. Expression of the GluN1 and GluN2A subunit of the NMDA receptor and GABAAα1 subunit was found throughout the rostrocaudal extent of the PVN in all models. In the pregnant animal, a significant decrease (p<0.05) in expression of the GABAAα1 subunit was observed, but no significant changes were observed in expression of the NMDA receptor subunits. In the SHR, expression of the GluN2A subunit was significant increased (p<0.05), while, expression of the GABAAα1 subunit was significantly decreased (p<0.05). This is the first study to examine the subunit conformation of the GABAA and NMDA receptor in the PVN of hypertensive and pregnant animals. We have shown that these animals show differential changes in their inhibitory and/or excitatory receptor subunit conformations. These changes may contribute to the sympathoexcitation characteristic of these states.
Where applicable, experiments conform with Society ethical requirements