Article Figures & Data
Figures
- Fig. 1.
NiCl2 reduces the amplitude of composite EPSCs. A, Average of EPSCs evoked in a CA3 neuron by stimulation of mossy fibers in control conditions (40 traces;left) and in the presence of NiCl2 (24 traces; middle). On the right, EPSCs (to the first stimulus) recorded in control conditions and in the presence of NiCl2 have been averaged, normalized, and superimposed.B, Plot of EPSC1 (filled symbols) and EPSC2 (open symbols) amplitude versus time before, during (horizontal bar), and after application of NiCl2. C, Mean peak amplitude of the first EPSC before (white column) and during (black column) superfusion of NiCl2 (n= 5). D, Mean paired-pulse facilitation ratio in control conditions and during NiCl2 application (n = 4). In this and the following figures, error bars refer to SEM. *p < 0.05; **p < 0.005.
- Fig. 2.
Pressure application of NiCl2reversibly reduces the peak amplitude of composite EPSCs evoked in a CA1 pyramidal neuron by stimulation of the Schaffer collateral.A, Average of 10 EPSCs recorded in control conditions, in the presence of NiCl2, and during washout. NiCl2 reduced the amplitude of the first EPSC from 77.7 to 42.5 pA. B, The amplitudes of EPSC1 (filled symbols) and EPSC2 (open symbols) are plotted against time before, during (horizontal bar), and after application of NiCl2. The concentration of NiCl2 in the pressure pipette was 300 μm. C, Mean peak amplitude of EPSC1 evoked in CA3 neurons by stimulation of mossy fibers in control conditions (white column) and during (black column) superfusion of NiCl2(n = 10). D, Mean paired-pulse facilitation ratio of mossy fiber EPSCs in control conditions and during NiCl2 application (n = 10). **p < 0.001.
- Fig. 3.
Pressure application of the toxin SNX 482 close to mossy fiber terminals reduces the peak amplitude of mossy but not associative–commissural fiber EPSCs. A, Average of composite EPSCs evoked in a CA3 neuron by stimulation of the mossy fibers before (left) and during (right) SNX 482 application. C, Plot of the peak amplitude of EPSC1 (filled symbols) and EPSC2 (open symbols) before and during application of SNX 482 (horizontal bar; concentration of SNX 482 into the pressure pipette, 1 μm). B,D, Similar presentation for EPSCs evoked in the same CA3 neuron by stimulation of associative–commissural fibers. Note that SNX 482 reduced the amplitude of mossy fiber EPSCs but did not affect associative–commissural EPSCs (mean peak amplitude values before and during SNX 482 were 76.7 and 26.5 pA for mossy fiber EPSCs and 59.0 and 58.8 pA for associative–commissural fiber EPSCs). Mean PPF ratio of mossy fiber EPSCs recorded in seven CA3 pyramidal cells before and during toxin application. F, Plot of the ratio of CV−2 (toxin over control) versus relative EPSC amplitudes (expressed as the ratio of the amplitude during SNX 482 application to the baseline amplitude). The regression line has been fitted through the data (least-square approximation; regression coefficient is 0.43; p < 0.05). Eachsymbol represents one cell (n = 21).
- Fig. 4.
Occlusion between the effects of SNX 482 and NiCl2 indicates a common site of action. A, Examples of composite EPSC (average of 10 traces) evoked in a CA3 pyramidal neuron by stimulation of mossy fibers before (left) and during (middle) pressure application of SNX 482 (concentration in the pipette, 0.3 μm). Nine minutes after toxin application, superfusion of NiCl2 (30 μm) did not affect the amplitude or shape of the EPSC (right). EPSC peak amplitude values were 94.5, 58.0, and 55.0 pA in control, in SNX 482 and in NiCl2, respectively. B, Summary data from five cells. Differences in percentage block between SNX 482 and NiCl2 are not statistically significant (p > 0.1). C, Composite EPSCs (average of 10 responses) evoked in a CA3 pyramidal neuron by stimulation of mossy fibers before (left) and during (middle) pressure application of ω-CTx-MVIIC (concentration in the pipette, 10 μm). Ten minutes after the toxin, bath application of NiCl2 (30 μm) produced an additional reduction of EPSC amplitude (right). EPSCs peak amplitude values were 103.4, 33.8, and 12.0 pA in control, in ω-CTx-MVIIC, and in NiCl2, respectively. D, Summary data from five cells. Differences in percentage block between ω-CTx-MVIIC and NiCl2 were statistically significant (p < 0.001).
- Fig. 5.
NiCl2 reduces the peak amplitude of EPSPs evoked in a CA3 pyramidal neuron by minimal stimulation of the associative–commissural fibers. A, Ten individual traces obtained by paired stimuli (50 msec interval) delivered to associative–commissural fibers at 0.05 Hz from −60 mV in control conditions, during NiCl2 perfusion, and 13 min after wash. Note the increased number of response failures during NiCl2application. B, Averages of responses obtained before (n = 87), during (n = 60), and 13 min after wash (n = 40). C, Plot of EPSP amplitudes evoked by the first (EPSP1;filled symbols) and second (EPSP2;open symbols) pulse in the paired-pulse paradigm before, during (horizontal bar), and after application of NiCl2. D, Mean peak amplitude of the first EPSP before (white column) and during (black column) superfusion of NiCl2 (n= 13). E, Mean failure rates before (white column) and during (black column) application of NiCl2 (n = 13). F, Mean paired-pulse facilitation ratio in control conditions and during NiCl2 application (n = 12). *p < 0.05; **p < 0.001.
- Fig. 6.
NiCl2 reduces the peak amplitude of EPSCs evoked in CA3 pyramidal neurons by minimal stimulation of the mossy fibers. A, Ten individual traces of EPSCs recorded from a holding potential of −60 mV, in control conditions and in the presence of NiCl2. Note decreased EPSC amplitudes during NiCl2 application and increased number of response failures after the first pulse. In this experiment, failure rate increased from 18.7 to 58.7%. B, Average EPSCs from the same experiment (n = 56 in control andn = 32 during application of NiCl2). C, Plot of EPSC1 (filled symbols) and EPSC2 (open symbols) amplitude versus time before, during (horizontal bar), and after application of NiCl2. D–F, Mean values of the EPSC1 amplitude (D), failure rate (E), and paired-pulse facilitation ratio (F) before (white columns) and during (black columns) NiCl2 application (n = 5). *p < 0.05.
