SUMMARY AND CONCLUSIONS

1. To quantify the variability in the characteristics of inhibitory glycinergic and GABAergic currents at single synaptic connections between cultured rat embryonic spinal cord or medullary neurons, we have used patch clamp techniques to record miniature inhibitory postsynaptic currents in cell- attached patches. Experiments were performed with the patch pipette containing either a low calcium internal saline to allow comparison with subsequent whole-cell recordings or external saline with tetrodotoxin, DL-2-amino-5- phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione, a solution which is more appropriate for bathing a nerve terminal. 2. The mIPSCs recorded from the synapses restricted to the cell-attached patches were characterized by their times to peak, amplitudes, and time constants of decay. The degree of variability in these characteristics was quantified using the following model- independent parameters: the coefficient of variation, skewness, and kurtosis. The distribution of time to peak values has a mean value of 5.6 +/- 0.5 ms, the lowest coefficient of variation (0.33 +/- 0.01), is fairly symmetrical, and has a Gaussian shape with respect to peakedness. On the other hand, both the amplitude and decay time constant distributions are highly skewed and more peaked than Gaussian distributions. The mean amplitude is -6.6 +/- 0.6 pA with a coefficient of variation of 0.60 +/- 0.05, while the mean decay time constant is 22.8 +/- 1.0 ms with a coefficient of variation of 0.81 +/- 0.03. 3. The amplitude distributions for spontaneous inhibitory currents recorded from cell-attached patches are best fitted by the sum of multiple Gaussians. The coefficient of variation for the first Gaussian peak fitted to the amplitude distributions is 0.290 +/- 0.028. 4. Decay time distributions were consistently best fitted by the sum of four Gaussians with decay constants of: D1 = 5.7 +/- 0.2 (n=12), D2 = 11.2 +/- 0.7 (n=11), D3 = 20.6 +/- 0.8 (n=12), and D4 = 43.8 +/- 2.3 (n=16) ms. These mean values are essentially identical to those reported in the preceding paper for mIPSCs recorded in the whole-cell configuration. 5. In eight neurons we were able to record mIPSCs both in cell- attached patches and in subsequent whole-cell configurations. The properties of mIPSCs recorded from single synapses (i.e. times to peak, amplitude, and time constants of decay) show as much variability as those of mIPSCs recorded subsequently in the whole-cell mode; that is, there are no statistically significant differences in the coefficients of variation, skewness or kurtosis for the three different distributions.

Received 14 November 1995; accepted in final form 22 January 1996. APS Manuscript Number J720-4. Article publication pending J. Neurophysiol. ISSN 1080-4757 Copyright 1996 The American Physiological Society. Published in APStracts on 8 February 96