| Abstract: | Experiments were conducted on brain isolated from the frogRana ridibunda using a current chop technique of transmembrane polarization and discrete measurement of membrane potential by a single microelectrode during intervals between waves of current. It was found that the current-voltage relationship of the motorneuron is non-linear; i.e., membrane resistance decreases considerably in step with increased depolarizing current. After the initial reduction, membrane resistance began to climb back when a more protracted current lasting 1–2 min was applied; consequently membrane potential level shifted towards more positive values of +50 mV and above at current levels of 40–60 nA. It then became possible to bring about complete reversal of monosynaptic EPSP produced in the lumbar motoneurons by stimulation of the brainstem reticular formation or by microelectrode stimulation of the ventrolateral tract descending fibers and to measure reversal potential of these EPSP directly, without resorting to computing or extrapolation. Measurements varied mainly between 0 and –10 mV.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 534–542, July–August, 1986. |
