Figure 6. α-DTX potentiates responses of Purkinje cells to dendritic photolytic release of glutamate.

Glutamate was locally released by photolysis on the dendrite of a Purkinje cell and the response of the cell monitored. A, average firing rate of a Purkinje cell in the presence and absence of 142 nm α-DTX. The transient increases in the firing rate correspond to photolytic pulses of glutamate. α-DTX increased the amplitude of responses. B, raw data showing the response of the Purkinje cell shown in A to photolytic release of glutamate in the presence and absence of α-DTX. C, scatter plots of the response of 11 Purkinje cells to dendritic photolytic release of glutamate in the presence and absence of α-DTX. The right-hand plot shows the average of individually normalized responses (mean ± s.e.m., n = 11). **P < 0.01, one-way ANOVA. D, the intensity of the UV light required for photolysis was adjusted to release different concentrations of glutamate on the dendrites of a Purkinje cell to produce EPSPs of varying amplitude. The traces of raw data show these EPSPs under control conditions and in the presence of 142 nm α-DTX. Application of α-DTX increased both the peak amplitude and duration of responses. The dotted lines mark −60 mV. E, the scatter plots show EPSP peak amplitude and area in four different experiments before and after application of α-DTX. Filled circles show EPSPs that triggered a calcium spike. The inset in each graph shows the ratio of the peak amplitude or EPSP area before and after application of α-DTX.