Hideomi Fukuda

The chloride-dependent depression by GABA in the frog spinal cord☆

Spontaneous activities from ventral and dorsal roots of the isolated perfused spinal cord of the bullfrog were inhibited by GABA. beta-Alanine showed a strong and glycine a weaker inhibitory effect. The inhibitory effect of GABA was markedly reduced in a chloride-free medium, whereas glycine and beta-alanine still showed an inhibitory effect similar to that seen in normal medium. Employing the sucrose-gap method, a marked depolarization in the dorsal root and a small but obvious hyperpolarization in the ventral root were found by the application of GABA. These results support the view that GABA is one of the transmitters involved in pre- and postsynaptic inhibition of the spinal cord. The postsynaptic hyperpolarizing effect of GABA on motoneurones would be caused directly through increased permeability of the membrane to chloride ion. The depolarizing effect of GABA on primary afferent terminals is discussed in connection with chloride dependency.

Excitation of rat muscle spindle afferents by lyoniol-A

Abstract The effect of lyoniol-A, a diterpenoid from an Ericaceous plant, on the de-efferented muscle spindle was studied to elucidate the mechanism responsible for abnormal behaviours in mammals resulting from administration of the agent. Increase in the frequency of afferent discharges in response to lyoniol-A (200–300 Hz) was much greater than that obtained on stretching the muscle or after suxamethonium. The result showed that lyoniol-A did not affect the extrafusal fibres nor intrafusal fibres and that adaptation, one of the characteristics of a muscle spindle, did not appear after an administration of the agent. In conclusion, lyoniol-A is a potent muscle spindle excitant that is likely to be a pharmacologically useful tool, and this action may largely responsible for the abnormal behaviours resulting from an administration of lyoniol-A. The experiment also dealt with lyoniol-B (deacetyl-lyoniol-A), grayanotoxin-I and veratridine.

Depression by strychnine of afferent discharges from the muscle spindle of the bullfrog in vitro

Abstract Strychnine (1.25 × 10−5 − 1 × 10−4M) caused a reduction in the rate of afferent discharge from the muscle spindle of the isolated M. extensor longus dig. IV from the bullfrog subjected to stretch. The possible site of action of the drug is discussed.

Decrease in the extracellular potassium activity of the frog spinal cord during the application of aliphatic anions

Ionic mechanisms of physiological and pharmacological phenomena have been investigated by substituting the extracellular ions with the other inactive foreign ionsl,2,s,10,1L In these studies selected ions were expected to have little or no pharmacological effects by themselves. Thus, the resultant alterations in the physiological functions were analyzed as the consequences of lack of removed ions. We reported that the potential in dorsal and ventral roots of isolated frog spinal cord measured by a sucrose-gap method was markedly hyperpolarized during the perfusion with Ringer solution in which chloride ion was substituted by propionate s. On the other hand, Barker and Nicoll 1, who employed isethionate as a main anion, reported that the perfusion of hemisected frog spinal cord with chloride-free medium caused a depolarization in root potentials. This discrepancy may be attributable to the undesired actions of employed foreign anions on the neuronal membrane. In the present study, the alterations ofextracellular potassium activity during the application of popular monovalent anions, which have frequently been employed as main anions in replacing extracellular chloride ion, were examined. Experiments were carried out on the isolated perfused spinal cord 9 of the bullfrog (Rana catesbeiana) weighing 80-150 g. Procedures for preparing isolated perfused spinal cord, drug application, and a sucrose-gap method were the same as described elsewhere 6-s. Potassium-sensitive microelectrodes were prepared according to the technique described by Walked 4 and Vysko~il and K[i~ ~3. The potassium-sensitive microelectrode was filled with 0.5 M KC1, with about 500/zm column of Corning ion exchanger resin (477317) in its tip, and a reference electrode was filled with solution of 0.15 M NaCI. Tips of these electrodes were assembled under microscopic observation