Article Figures & Data
Figures
- Fig. 1.
Mossy fiber→CA3 excitatory synaptic transmission is inhibited by activation of kainate receptors containing the GluR6 subunit. A, Middle, A representative experiment shows that the amplitudes of evoked AMPA receptor-mediated mossy fiber EPSCs were reduced by application of 3 μmkainate to neurons in acute slices from wild-type mice.Top, Representative traces of EPSCs are shown. mGluR activation with 10 μm L-CCG-1 suppressed transmission, which served to identify the input as a mossy fiber. EPSCs were evoked at 0.1 Hz frequency by monopolar stimulation in the stratum lucidum. Bottom, A diagram illustrates the slice preparation and recording configuration for mossy fiber stimulation. B, Kainate application to CA3 neurons from GluR6−/− mice did not inhibit excitatory transmission, whereas mGluR-mediated suppression was intact at these synapses. C, A summary of the effect of application of kainate on mossy fiber→CA3 recordings from the mice used in this study is shown. Mossy fiber transmission was suppressed by −85.7 ± 4.8% (n = 9) in wild-type mice and −86.8 ± 5.6% (n = 7) in GluR5−/− mice with 3 μm kainate. No inhibition was seen in either GluR6−/− mice (+4.1 ± 7.1% change; n = 5) or GluR5−/−/GluR6−/−mice (−8.5 ± 4.8% change; n = 4). Activation of mGluRs with L-CCG-1 suppressed mossy fiber transmission in each of the mice tested. Calibration: A,x-axis, 30 msec; y-axis, 1500 pA;B, x-axis, 30 msec;y-axis, 66 pA. DG, Dentate gyrus.
- Fig. 2.
Depression of the mossy fiber EPSC is not caused by a reduction in the input resistance of the pyramidal neuron.A, Top, The increased holding current during a −10 mV step applied before the evoked EPSC demonstrates that the input resistance of the cell is reduced after application of kainate. Bottom, During kainate application, mossy fiber EPSCs failed or were greatly reduced in amplitude. B, The mean input resistance and normalized current plotted against the time of the recording show that both are reduced during kainate application. However, input resistance recovers fully by ∼7 min after kainate application, while the EPSC amplitude is still significantly depressed. Input resistances and EPSC amplitudes were normalized to the respective means of the control periods before application of kainate.C, The mean input resistance is not correlated with the mean normalized EPSC (data from 5 neurons). Calibration:A, top, x-axis, 15.5 msec;y-axis, 1.2 nA; inset,x-axis, 14 msec; y-axis, 0.3 nA;bottom; x-axis, 10 msec;y-axis, 300 pA.
- Fig. 3.
Associational-commissural synaptic transmission is suppressed by activation of kainate receptors containing the GluR6 subunit. A, Middle, Associational-commissural EPSC amplitudes from wild-type CA3 neurons were suppressed by kainate application (n = 9). Amplitudes of the EPSCs were normalized to the mean EPSC amplitude during the control period before application of kainate.Top, Representative EPSCs from one wild-type recording are shown. EPSCs were evoked at 0.1 Hz frequency by stimulation in the stratum radiatum. Bottom, A diagram illustrates the slice preparation and recording configuration for associational-commissural stimulation. The stimulating electrode is shown in the stratum radiatum; EPSCs were also evoked by stimulation in the stratum oriens. B, Bottom, Associational-commissural synaptic transmission is not inhibited by 3 μm kainate in CA3 pyramidal neurons from GluR6−/− mice (n = 7). Amplitudes of the EPSCs were normalized to the mean EPSC amplitude during the control period before application of kainate. Top, Representative EPSCs from one recording are shown. C, A summary of the effect of application of kainate on associational-commissural→CA3 recordings from the mice used in this study is shown. Collateral transmission was suppressed by −90.0 ± 4.0% (n = 12) in wild-type mice and −80.5 ± 11.9% (n = 5) in GluR5−/− mice with 3 μm kainate. No inhibition was seen in either GluR6−/− mice (−8.7 ± 2.8% change; n = 8) or GluR5−/−/GluR6−/−mice (−2.8 ± 4.8% change; n = 3). mGluR activation with L-CCG-1 did not suppress associational-commissural transmission in these recordings. Calibration: A,x-axis, 30 msec; y-axis; 200 pA;B, x-axis, 30 msec;y-axis, 75 pA.
- Fig. 4.
Perforant path synaptic transmission is augmented by activation of kainate receptors. A,Bottom, A representative recording from a wild-type CA3 neuron demonstrating that amplitudes of evoked perforant path EPSCs were increased and failures were decreased reversibly during kainate application. Top, Representative EPSCs. EPSCs were evoked at 0.1 Hz frequency by monopolar stimulation in the stratum lacunosum moleculare. B, A representative recording from a GluR6−/− CA3 neuron demonstrating that amplitudes of evoked perforant path EPSCs were decreased during kainate application. C, A recording from a GluR5−/− CA3 neuron that showed a reduction in EPSC amplitude during kainate application. Perforant path transmission in GluR5−/− neurons showed variable responses to 3 μm kainate; four of six synaptic responses were reduced, whereas EPSC amplitudes increased in the remaining two of six recordings. D, A representative recording from a GluR5−/−/GluR6−/−CA3 neuron demonstrating that amplitudes of evoked perforant path EPSCs were unchanged during kainate application. E,Left, A diagram illustrating the slice preparation and recording configuration for perforant path stimulation.Right, Summary of the effect of application of kainate on perforant path→CA3 EPSCs. PP transmission was enhanced by +170 ± 74% in wild-type mice. GluR5−/− neurons had variable responses to kainate—in four of six recordings kainate reduced EPSC amplitudes by −38.9 ± 3.9%, but in two neurons the amplitudes were increased by +44.9 and +113.3%. The mean for all six recordings, −5.2 ± 23.2%, is shown in the histogram. The mean change in GluR6−/− EPSC amplitudes was −38.1 ± 8.1%. Finally, GluR5−/−/GluR6−/−mice showed little change in amplitude during kainate application (+1.2 ± 6.6%). mGluRs activation with L-CCG-1 did not reduce associational-commissural transmission in these recordings. Calibration: A, x-axis, 32.5 msec;y-axis, 300 pA; B, x-axis, 32.5 msec; y-axis, 150 pA; C,x-axis, 32.5 msec; y-axis, 150 pA;D, x-axis, 32.5 msec;y-axis, 300 pA.
- Fig. 5.
mEPSC frequency is increased by application of kainate to CA3 pyramidal neurons from wild-type mice. A, Sample traces of mEPSC recordings from a CA3 pyramidal neuron in a hippocampal slice preparation from a wild-type mouse. Kainate was bath-applied at a concentration of 3 μm. The baseline noise is higher during kainate application because of the kainate receptor-mediated whole-cell current. B, Histogram from the same cell shown in A showing the mEPSC frequency in 30 sec bins. Kainate caused the mEPSC frequency to increase by ∼1.7-fold in this cell. The gap in thethird bin resulted from checking the series resistance of the recording. The cell was whole-cell patch clamped at −60 mV for the duration of the recording. C, D, Cumulative probability graphs of mEPSC interevent intervals (C) and amplitudes (D). Interevent intervals were significantly decreased in the presence of kainate, whereas amplitudes were unchanged. Calibration:A, x-axis, 400 msec;y-axis, 40 pA.
- Fig. 6.
GluR5 subunit-containing kainate receptors underlie the kainate-mediated increase in mEPSC frequency.A, Left, A mEPSC frequency histogram for a CA3 neuron from a GluR5−/−mouse shows a small decrease in frequency during kainate application.Middle, Right, No significant difference in the interevent interval (middle) or amplitude (right) cumulative distributions was detected.B, An mEPSC frequency histogram for a CA3 neuron from a GluR6−/− mouse shows an increase in frequency during kainate application similar to that observed in wild-type neurons. The cumulative probability histograms show that the interevent intervals are significantly briefer in the presence of kainate but that amplitudes are unchanged.C, The mEPSC frequency for a CA3 neuron from a GluR5−/−/GluR6−/−mouse does not change after application of kainate. No significant differences in the interevent interval or amplitude cumulative distributions were observed. D, A summary of all experiments for kainate-mediated changes in mEPSC frequency for recordings from wild-type and kainate receptor subunit knock-out mice is shown. mEPSCs from wild-type and GluR6−/− neurons increased after application of kainate. This increase in frequency is absent in GluR5 knock-out mice, and instead a small decrease was observed. mEPSC frequencies in recordings from GluR5−/−/GluR6−/−double knock-out mice show no change in mEPSC frequency in the presence of kainate. E, A summary of kainate-mediated changes in mEPSC frequency in wild-type and knock-out mice recorded in the presence of the nonselective Ca2+ channel blocker Cd2+ is shown. The mEPSC was depressed in wild-type and GluR5−/− mice, whereas no change in frequency was observed in GluR6−/− mice or the double knock-outs.
