Cable Properties of Dendrites in Hippocampal Neurons of the Rat Mapped by a Voltage‐sensitive Dye

Abstract

Dendrites of pyramidal neurons from embryonic rat hippocampus are investigated in culture using a voltage-sensitive fluorescent dye. The electrical response to somatic stimulation is observed as a time-resolved map with a resolution of 0.9 microm at a time constant of 0.4 ms without signal averaging. The data are interpreted in terms of a tapering cable with Hodgkin-Huxley parametrization. The spread of short hyperpolarizing transients is damped by capacitive shunting. The invasion of an action potential is boosted by voltage-gated conductances of a low density. No irregularity is observed at a bifurcation. The passive cable parameters of internal resistance and membrane resistance at resting voltage are Ri = 300 omega cm and Rm = 40 (k)omega cm2 respectively, at a maximum sodium conductance of approximately 4.4 mS/cm2. The electrotonic length constant and the dynamic length constant at 1 kHz are 580 and 90 microm respectively. These results are compatible with electrophysiological data of dendrites in slices of adult hippocampus and with optical data of narrow processes of leech neurons in culture. The functional implications of boosting an action potential by voltage-gated channels of low density are considered.

A Strict Correlation between Dendritic and Somatic Plateau Depolarizations in the Rat Prefrontal Cortex Pyramidal Neurons

“…One is then tempted to conclude that by calibrating the optical signal in the cell body, with simultaneous whole-cell measurement, we could arrive at the exact amplitude of the electrical signal elsewhere on the dendritic tree. In fact, that would be possible if the voltage-sensitive dye was bound only to the excitable plasma membrane, as in experiments using extracellular staining of neurons (Ross and Krauthamer, 1984;Meyer et al, 1997;Bullen and Saggau, 1999). Unfortunately, when applied intracellularly, voltage-sensitive dyes indiscriminately bind to all lipid bilayers, those in the plasma membrane, as well as those that make intracellular organelles.…”

Genetic Targeting of Individual Cells with a Voltage‐Sensitive Dye through Enzymatic Activation of Membrane Binding

“…To achieve that goal, optical recording with fluorescent voltage-sensitive dyes bound to the neuronal plasma membrane is a most promising tool. [1][2][3] This method has been successfully used to record the activity of arborised neurons in dissociated cell culture, [4][5][6][7] and to map the average activity of many neurons in brain tissue. [3,8] Optical recording from individual neurons in a tissue, however, requires selective staining of cells with a voltage-sensitive dye to avoid perturbations caused by fluorescence of other neurons, glia cells and the extracellular matrix in the vicinity.…”

Optical Recording of Action Potentials with Second-Harmonic Generation Microscopy

“…The current capabilities demonstrated here are most immediately applicable to reproducibly stimulated systems, as are often used for current optical V m recording techniques (Zecevic, 1996). It should be feasible to investigate spike initiation zones (Zecevic, 1996) and AP propagation properties (Fromherz and Muller, 1994;Meyer et al, 1997) deep in intact ganglia, where one-photon methods are not appropriate. Repeated line scans at varying spatial positions over processes will allow for the generation of high-resolution time series movies of AP propagation, leading to the experimental analysis of electrical propagation properties at complex structures, such as axon bifurcations and varicosities.…”