Instead, a gradual shift in the relative abundance of fast-gating GluR3/4 over slow-gating GluR1 may account for the speeding of decay kinetics at the calyx of Held-MNTB synapse. immunohistochemistry assays with subunit-specific antibodies, we exhibited that this glutamate receptor (GluR) 2 subunit is usually virtually absent at all developmental ages. Antibody staining patterns suggest a gradual shift in subunit composition from GluR1- to GluR3/4-dominant phenotypes. Kinetic analyses of deactivation, desensitization, and recovery from desensitization in outside-out patches in response to ultrafast application of glutamate lend supportive evidence that such a shift in the gating phenotype likely accounts for the accelerated time course throughout development. Finally, by pharmacologically manipulating AMPAR gating and using simulated EPSCs to evoke action potentials, we exhibited that quick decay kinetics of AMPAR EPSCs is essential for this synapse to accommodate high-frequency firing without compromising spike amplitude. Hence, developmental alterations in the subunit composition likely dictate changes in the time course of AMPAR EPSCs and play an indispensable role in the refinement of high-fidelity neurotransmission at the calyx of Held synapse. given in 100 and 200 Hz trains. Note that synaptic depressive disorder (Wang and Kaczmarek 1998; Joshi and Wang, 2002) was incorporated into simulated trains in which the EPSC amplitude declined along a single exponential curve with a time constant WP1066 of 70 msec from initial amplitude of 5 nA, and Mouse monoclonal to CD20 that the only variable altered was the decay time constant. Comparable observations were made in four other MNTB neurons. All recordings in this physique were made in the presence of MK-801. Open in a separate window Physique 5. Kinetic properties of AMPARs in outside-out patches of developing MNTB neurons. = 10) and P13-15 (= 8) neurons. The average values for each group of data are indicated by the cross sign in parallel with scattered data. = 4) and P13-15 (packed circles; = 4) neurons. The current amplitude in response to the second application is usually normalized to that of the first response in each sweep and plotted against the interpulse time. Solid lines are single exponential fits, and values are given. Holding potential was -60 mV for all of these experiments. and = 6) have much smaller values than P7 synapses (= 6) at any given voltage. and replotted, and linear regression of these two units of data gives comparable slopes. = 7) synapse at -60 and +60 mV in the presence of MK-801 (10 m) are shown. Right panel displays superimposed natural traces and averaged traces of individual events at +60 and -60 mV. = 6) and P14 synapses (= 7) at -60 and +60 mV, showing faster decay time course at -60 mV than at +60 mV. for evoked mEPSCs. = 6) and P14 synapses (= 6). Statistic difference ( 0.05; Student’s test) is usually indicated by asterisk in this and subsequent figures. When kinetic properties of spontaneous miniature EPSCs (mEPSCs) are compared at +60 mV and -60 mV in P7 and P14 synapses, we found that as with the evoked responses, values at +60 mV were always greater than that at -60 mV for either age group [P7, 0.73 0.04 msec (+60 mV), 0.58 0.02 msec (-60 mV) vs P14, 0.60 0.06 msec (+60 mV), 0.43 0.03 msec (-60 mV)] (Fig. 1shows common recordings from P7 and P14 synapses in Sr2+ (after MK-801 blockade of NMDARs), and in each case, delayed release events at +50 and -60 mV were collected and analyzed (Fig. 1depicts sample recordings of spontaneous mEPSCs in control answer at P8 and P15 synapses. Because of rare occurrences of spontaneous mEPSCs in young synapses, we just compared the number of release events in a time block of 2 min (Fig. 2and and are from WP1066 individual cells in each age group. curves and kainate whole-cell currents as in and curves for AMPA EPSCs in control and after HPP-SP blockade. Note that this block is not strongly voltage dependent. = 4) and presence (closed circles; = 4) of HPP-SP. The current amplitude of the EPSC at any given time was normalized to that at time WP1066 0. Note that high-frequency activation caused only a 27% rundown in current amplitude under control conditions, whereas there was an additional block of the current (43%) in the presence of HPP-SP. AMPARs devoid of GluR2 mediate synaptic transmission during development AMPARs that contain the GluR4 subunit may mediate fast synaptic transmission in rat and chick auditory synapses (Geiger et al., 1995; Otis et al., 1995; Zhou et al., 1995; Wang et al., 1998; Caicedo and Eybalin, 1999; Ravindranathan et al., 2000). We postulated that during development, the AMPAR complex might switch from subunits that are slow gating and Ca2+.