Epileptogenesis up-regulates metabotropic glutamate receptor activation of sodium-calcium exchange current in the amygdala.
Postsynaptic metabotropic glutamate (mGlu) receptor-activated inward current mediated by Na(+)-Ca(2+) exchange was compared in basolateral amygdala (BLA) neurons from brain slices of control (naïve and sham-operated) and amygdala-kindled rats. In control neurons, the mGlu agonist, quisqualate (QUIS; 1-100 microM), evoked an inward current not associated with a significant change in membrane slope conductance, measured from current-voltage relationships between -110 and -60 mV, consistent with activation of the Na(+)-Ca(2+) exchanger. Application of the group I selective mGlu receptor agonist (S)-3,5-dihydroxyphenylglycine [(S)-DHPG; 10-1000 microM] or the endogenous agonist, glutamate (10-1000 microM), elicited the exchange current. QUIS was more potent than either (S)-DHPG or glutamate (apparent EC(50) = 19 microM, 57 microM, and 0.6 mM, respectively) in activating the Na(+)-Ca(2+) exchange current. The selective mGlu5 agonist, (R, S)-2-chloro-5-hydroxyphenylglycine [(R,S)-CHPG; apparent EC(50) = 2. 6 mM] also induced the exchange current. The maximum response to (R, S)-DHPG was about half of that of the other agonists suggesting partial agonist action. Concentration-response relationships of agonist-evoked inward currents were compared in control neurons and in neurons from kindled animals. The maximum value for the concentration-response relationship of the partial agonist (S)-DHPG- (but not the full agonist- [QUIS or (R,S)-CHPG]) induced inward current was shifted upward suggesting enhanced efficacy of this agonist in kindled neurons. Altogether, these data are consistent with a kindling-induced up-regulation of a group I mGlu-, possibly mGlu5-, mediated responses coupled to Na(+)-Ca(2+) exchange in BLA neurons.
Keele
N B
NB
Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas 77555-1031, USA.
Zinebi
F
F
Neugebauer
V
V
Shinnick-Gallagher
P
P
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000679:Amygdala / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004827:Epilepsy / Q000503:physiopathology*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D007696:Kindling, Neurologic / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives / Q000494:pharmacology; D010648:Phenylacetates / Q000494:pharmacology; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D012640:Seizures / Q000503:physiopathology; D012964:Sodium / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D015854:Up-Regulation / Q000502:physiology*
C107349:2-chloro-5-hydroxyphenylglycine; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D010648:Phenylacetates; D018094:Receptors, Metabotropic Glutamate; D018698:Glutamic Acid; D013779:Tetrodotoxin; D008734:Methoxyhydroxyphenylglycol; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D016318:Quisqualic Acid; D012964:Sodium; D002118:Calcium; D005998:Glycine; C010117:3,4-dihydroxyphenylglycol