Regulator of G protein signaling protein suppression of Galphao protein-mediated alpha2A adrenergic receptor inhibition of mouse hippocampal CA3 epileptiform activity.
Activation of G protein-coupled alpha(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 alpha(2)ARs and G proteins (Galpha(o) or Galpha(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 alpha(2)AR subtype involved, equilibrium dissociation constants (pK(b)) were determined for the selective alphaAR 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 pK(b) values correlated best with affinities determined previously for the mouse alpha(2A)AR subtype (r = 0.98, slope = 1.07). Furthermore, the inhibitory effects of EPI were lost in hippocampal slices from alpha(2A)AR-but not alpha(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 Galpha subunits to enhance signaling by that G protein, the EPI-mediated inhibition of bursts was significantly more potent in slices from RGS-insensitive Galpha(o)(G184S) heterozygous (Galpha(o)+/GS) mice compared with either Galpha(i2)(G184S) heterozygous (Galpha(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 alpha(2A)AR/Galpha(o) protein-mediated pathway under strong inhibitory control by RGS proteins. This suggests a possible role for RGS inhibitors or selective alpha(2A)AR agonists as a novel antiepileptic drug therapy.
Goldenstein
Brianna L
BL
Department of Pharmacology, Physiology and Therapeutics, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND 58202-9037, USA.
Nelson
Brian W
BW
Xu
Ke
K
Luger
Elizabeth J
EJ
Pribula
Jacquline A
JA
Wald
Jenna M
JM
O'Shea
Lorraine A
LA
Weinshenker
David
D
Charbeneau
Raelene A
RA
Huang
Xinyan
X
Neubig
Richard R
RR
Doze
Van A
VA
D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009638:Norepinephrine / Q000494:pharmacology; D010109:Oxymetazoline / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D020710:RGS Proteins / Q000502:physiology*; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*
C547769:Adra2a protein, mouse; D058669:Adrenergic alpha-2 Receptor Antagonists; D007093:Imidazoles; D020710:RGS Proteins; D018341:Receptors, Adrenergic, alpha-2; C050701:atipamezole; D010109:Oxymetazoline; D037342:Pertussis Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D009638:Norepinephrine; D004837:Epinephrine