Voltage signals of individual Purkinje cell dendrites in rat cerebellar slices

For investigating neuronal information processing at the cellular level, a technique which visualizes the voltage distribution within single neurons in situ would be extremely useful. Voltage-sensitive dyes are, in principle, capable of reporting membrane potential [Cohen, L.B. and Salzberg, B.M., Rev. Physiol. Bochem. Pharmacol., 83 (1978) 35-88 Grinvald, A., Lieke, E.E., Frostig, R.D. and Hildesheim, R., J. Neurosci., 14 (1994) 2545-2568; Kleinfeld, D., Delaney, K.R., Fee, M.S., Flores, J.A., Tank, D.W. and Gelperin, A., J. Neurophysiol., 72 (1994) 1402-1419]. However, their application to single cells internally is technically difficult [Antic, S. and Zecevic, D., J. Neurosci., 15 (1995) 1392-1405; Grinvald, A., Salzberg, B.M., Lev-Ram, V. and Hildesheim, R., Biophys. J., 51 (1987) 643-651; Kogan, A. Ross, W.N., Zecevic, D. and Lasser-Ross, N., Brain Res., 700 (1995) 235- 239; Zecevic, D., Nature, 381 (1996) 322-325]. An alternative strategy consists in applying the dye from the outside to all cells in the tissue while manipulating a single cell by current injection [Krauthamer, V. and Ross. W.N., J. Neurosci., 4 (1984) 673-682; Ross, W.N. and Kreuthamer, V., J. Neurosci., 4 (1984) 659-672]. Here, we modify this technique to further enhance spatial at the cost of temporal resolution [Borst, A. Z. Naturforsch., 50 (1995) 435-438]. Applied to rat cerebellar slices we demonstrate that the potential spread in individual Purkinje cells can be imaged up to even fine dendritic branches: The acquired optical signals suggest that steadily hyperpolarized Purkinje cells are electrically compact. When permanently depolarized, the somatic input res stance s significantly diminished, yet the spatial voltage drop along the dendrites remains unchanged. As demonstrated by compartmental modeling, this hints to a concentration of outward rectifying currents at the soma of the cells.