Fig. 6.

DHPG increases the frequency of GABAergic inhibitory postsynaptic currents (IPSCs) in mitral cells. Voltage-clamp recordings from mouse mitral cells were made with pipettes with a high chloride concentration (see methods). Ionotropic glutamate receptors were blocked with CNQX (10 μM) and APV (50 μM). Under these conditions, chloride-mediated IPSCs are reversed in polarity and appear as downward deflections (inward currents). A, top: application of DHPG (50 μM) evoked a prominent slow inward current in mitral cells recorded in slices from wild-type mice. Time points 1–3 are shown at faster time scale in the 3 lower traces, respectively. Note the increase in frequency of fast IPSCs (trace 2), which are completely blocked by the GABA_A receptor antagonist gabazine (5 μM, trace 3). B: in a mitral cell from an mGluR1^–/– mouse, the DHPG-evoked slow inward current was absent, but DHPG substantially increased the frequency of IPSCs. Recording conditions and labeling as in A. C: bar graph summarizing the effects of DHPG on the frequency of spontaneous IPSCs in mitral cells from wild-type (WT, n = 8) and mGluR1^–/– (mGluR1 KO, n = 6) mice. *, significantly different from respective control group, P < 0.05, paired t-test).