Dendritic Membrane Properties of Crayfish Nonspiking Interneurons

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Physiological properties of the dendritic membrane of LDS interneuron, an identified nonspiking interneuron in the terminal abdominal ganglion of the crayfish Procambarus clarkii Girard, have been studied using the single electrode voltage clamp (SEVC) technique. The site of electrode penetration into the dendrite was visualized under the dissecting microscope in situ during experiment by epiilluminating the Lucifer-filled cell and the microelectrode with blue light.The dendritic membrane showed outward rectification to intracellularly injected current both at the thick branch on the midline and at the peripheral branches. Accordingly, the membrane time constant was shorter during depolarization than during hyperpolarization. The time course of compound PSP evoked by direct stimulation of presynaptic sensory neurons became shorter as the cell was more depolarized from the resting potential and vice versa. In contrast to the rectifying membrane property which was observed at any site of … More dendrites, the input resistance and membrane time constant were dependent of electrode penetration sites. Thus, the input resistance was significantly lower at the thick bridge portion than at peripheral branches.A single intracellular microelectrode was placed at the bridge portion and the SEVC technique was applied to LDS dendrites. In response to hypepolarizing command voltage (10-50mV) applied to the cell held at the resting potential, a small inward leakage current was observed in proportion to the hyperpolarization. By contrast, the cell showed an additional outward current superimposed on the outward leakage current. The amount of additional current was dependent of the amount of depolarization. This current showed transient increase at the onset of depolarization and became steady in about 80-100msec. The finding that the steady outward current was reduced to 70-80% by perfusion of 10mM TEA indicates that it resembles the well known delayed rectifier K current. Characteristics of the transient early current are to be further studied. Less