Group I and II mGluRs have opposite effects on holding current. A: group I drugs. Ai: agonist (S)-3,5-dihydroxyphenylglycine (DHPG, 100 μM, n = 5) shifts holding current in the negative direction. Aii: antagonist AIDA (1 mM, n = 5) shifts holding current in the positive direction. B: group II drugs. Bi: agonist DCG IV (1 μM, n = 7) shifts holding current in the positive direction. Bii: antagonist LY341495 (2 μM, n = 8) shifts holding current in the negative direction. All holding current measurements in A and B were made relative to pre-drug holding current.