Regulator of G Protein Signaling Protein Suppression of Gαo Protein-Mediated α2A Adrenergic Receptor Inhibition of Mouse Hippocampal CA3 Epileptiform Activity

• Published in: Molecular pharmacology 2009-05, Vol.75 (5), p.1222
• Main Authors: Brianna L. Goldenstein, Brian W. Nelson, Ke Xu, Elizabeth J. Luger, Jacquline A. Pribula, Jenna M. Wald, Lorraine A. O'Shea, David Weinshenker, Raelene A. Charbeneau, Xinyan Huang, Richard R. Neubig, Van A. Doze
• Format: Article
• Language: English
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.108.054296

Activation of G protein-coupled α 2 adrenergic receptors (ARs) inhibits epileptiform activity in the hippocampal CA3 region. The specific mechanism underlying this action is unclear. This study investigated which subtype(s) of α 2 ARs and G proteins (Gα o or Gα i ) are involved in this response using recordings of mouse hippocampal CA3 epileptiform bursts. Application of epinephrine (EPI) or norepinephrine (NE) reduced the frequency of bursts in a concentration-dependent manner: (-)EPI > (-)NE >>> (+)NE. To identify the α 2 AR subtype involved, equilibrium dissociation constants (p K b ) were determined for the selective αAR antagonists atipamezole (8.79), rauwolscine (7.75), 2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride (WB-4101; 6.87), and prazosin (5.71). Calculated p K b values correlated best with affinities determined previously for the mouse α 2A AR subtype ( r = 0.98, slope = 1.07). Furthermore, the inhibitory effects of EPI were lost in hippocampal slices from α 2A AR-but not α 2C AR-knockout mice. Pretreatment with pertussis toxin also reduced the EPI-mediated inhibition of epileptiform bursts. Finally, using knock-in mice with point mutations that disrupt regulator of G protein signaling (RGS) binding to Gα subunits to enhance signaling by that G protein, the EPI-mediated inhibition of bursts was significantly more potent in slices from RGS-insensitive Gα o G184S heterozygous (Gα o +/GS) mice compared with either Gα i2 G184S heterozygous (Gα i2 +/GS) or control mice (EC 50 = 2.5 versus 19 and 23 nM, respectively). Together, these findings indicate that the inhibitory effect of EPI on hippocampal CA3 epileptiform activity uses an α 2A AR/Gα o protein-mediated pathway under strong inhibitory control by RGS proteins. This suggests a possible role for RGS inhibitors or selective α 2A AR agonists as a novel antiepileptic drug therapy.