Showing papers in "Journal of Neurophysiology in 1959"

Active phase of frog's end-plate potential.

Abstract: IT HAS BEEN CONSIDERED that the end-plate potential (e.p.p.) is generated by the brief ionic flux across the end-plate membrane and the later slowly declining phase of the e.p.p. is due to the dissipation of the charge along and across the muscle membrane. This consideration was supported by some authors. Kuffler (21) observed with a single nerve-muscle preparation that the later slowly decaying part of the e.p.p. was destroyed by a propagated muscle impulse and obtained a duration of transmitter action (3-4 msec. at 20°C.) by observing the size of the e.p.p. that was built after the invasion of a propagated muscle impulse. Katz (18) demonstrated that the neuromuscular transmitter produced a brief phase of impedance loss at the end-plate region. Recently Fatt and Katz (10) observed by measuring the displacement of the total charge along and across the muscle membrane during the e.p.p. that the active depolarization process at the end-plate had ceased within 2 msec. On the other hand the time course of the actively depolarizing phase of the e.p.p. was estimated by an analysis of the time course of the e.p.p., it being assumed that the exponentially decaying phase was attributable to the passive repolarization of the muscle membrane (7,19). The purpose of the present experiment was to determine directly the time course of the active phase of the e.p.p. by using the voltage clamp method which was originally described by Hodgkin et al. (14) and was also applied to the squid giant synapse by Tasaki and Hagiwara (29). When the membrane potential is clamped at the resting membrane potential with negative feed-back during the neuromuscular transmission, the electrotonic spread of the charge along the muscle fibre membrane can be eliminated. The feed-back current which flows through the muscle membrane to hold the membrane potential at the resting value is due to the brief electric change at the end-plate, i.e., it will show the active phase of the e.p.p. To simplify the expression, the feed-back current during neuromuscular transmission will be called provisionally the “end-plate current.” A preliminary report of the present experiment appeared in 1958 (27).

Stria vascularis as source of endocochlear potential

Abstract: IT IS WELL KNOWN (1, 2, 12, 6) that, when a recording microelectrode is pushed into the endolympatic space of the cochlea of a guinea pig or a cat, the potential at the tip of the electrode rises 70-90 mV. above the potential level in the perilymphatic space. Although the ionic composition of the endolymph is unique among various body fluids because of its high potassium content (lo), the DC potential in the cochlear endolymph, which Dr. H. Davis proposed to designate as “endocochlear” potential, seems to be maintained by some oxidative process in the cochlea rather than by a difference in ions between the periand endolymph (5, 11, 9). The present investigation deals with the anatomical localization of the source of the endocochlear potential. In the first half of the present investigation the so-called “waltzing guinea pigs” were used. These were kindly supplied to us by Dr. Grant L. Rasmussen of this Institute. The animals of this special breed are completely devoid of the organ of Corti in their cochlea, and it was possible to demonstrate in these deaf animals that hair cells in the organ of Corti are not needed for the maintenance of the potential. The latter half of the present work was done on normal guinea pigs, using the method of direct measurement of the DC potential on the surface of the exposed endolympha tic space. The observations described in the present paper indicate that the endocochlear potential is generated by the cells in the stria vascularis on the wall of the endolymphatic space. Essentially the same conclusion was reached more-or-less simultaneously by Davis et al. (4) and by Misrahy (8) who used entirely different methods.

Distribution in time and space of prepyriform electrical activity.

Abstract: IN A PREVIOUS STUDY (9) evidence was found that a large proportion of the spontaneous electrical activity recorded from the basal forebrain of the anesthetized cat was generated bilaterally by the prepyriform cortex, not by the subcortical structures in which the recording electrodes were located. This finding raised the question of how the oscillating potentials of the brain are transmitted, i.e., to what extent the spread of EEG activity is due (i) to continuous spread of membrane depolarization along axonal or dendritic fibers; (ii) to the formation of intracellular?extracellular current loops such as occur on a shorter time scale in peripheral nerve, with instantaneous field distribution of the current through the brain; and (iii) to successive activation of contiguous cells. To approach this question a study was made of the nature of the various wave forms generated by the prepyriform cortex and of their rates, directions, and distances of spread in and around the cortex.