Ichiji Tasaki

Bio: Ichiji Tasaki is an academic researcher from National Institutes of Health. The author has contributed to research in topics: Squid giant axon & Squid. The author has an hindex of 36, co-authored 122 publications receiving 5156 citations. Previous affiliations of Ichiji Tasaki include Marine Biological Laboratory & Keio University.

Fast axonal transport in squid giant axon

Abstract: Video-enhanced contrast-differential interference contrast microscopy has revealed new features of axonal transport in the giant axon of the squid, where no movement had been detected previously by conventional microscopy. The newly discovered dominant feature is vast numbers of "submicroscopic" particles, probably 30- to 50-nanometer vesicles and other tubulovesicular elements, moving parallel to linear elements, primarily in the orthograde direction but also in a retrograde direction, at a range of steady velocities up to +/- 5 micrometers per second. Medium (0.2 to 0.6 micrometer) and large (0.8 micrometer) particles move more slowly and more intermittently with a tendency at times to exhibit elastic recoil. The behavior of the smallest particles and the larger particles during actual translocation suggests that the fundamental processes in the mechanisms of organelle movement in axonal transport are not saltatory but continuous.

Demonstration of two stable potential states in the squid giant axon under tetraethylammonium chloride.

Abstract: 1. Intracellular injection of tetraethylammonium chloride (TEA) into a giant axon of the squid prolongs the duration of the action potential without changing the resting potential (Fig. 3). The prolongation is sometimes 100-fold or more. 2. The action potential of a giant axon treated with TEA has an initial peak followed by a plateau (Fig. 3). The membrane resistance during the plateau is practically normal (Fig. 4). Near the end of the action potential, there is an apparent increase in the membrane resistance (Fig. 5D and Fig. 6, right). 3. The phenomenon of abolition of action potentials was demonstrated in the squid giant axon treated with TEA (Fig. 7). Following an action potential abolished in its early phase, there is no refractoriness (Fig. 8). 4. By the method of voltage clamp, the voltage-current relation was investigated on normal squid axons as well as on axons treated with TEA (Figs. 9 and 10). 5. The presence of stable states of the membrane was demonstrated by clamping the membrane potential with two voltage steps (Fig. 11). Experimental evidence was presented showing that, in an "unstable" state, the membrane conductance is not uniquely determined by the membrane potential. 6. The effect of low sodium water was investigated in the axon treated with TEA (Fig. 12). 7. The similarity between the action potential of a squid axon under TEA and that of the vertebrate cardiac muscle was stressed. The experimental results were interpreted as supporting the view that there are two stable states in the membrane. Initiation and abolition of an action potential were explained as transitions between the two states.

Nerve impulses in individual auditory nerve fibers of guinea pig

Abstract: To UNDERSTAND how the cochlea analyzes and responds to complex sound stimuli, it is desirable to know what kind of message individual nerve fibers carry from the ear to the central nervous system. In 1942, Galambos and and Davis (9) recorded electric responses of single ganglion cells in the cochlear nucleus, which they once believed to be from single auditory nerve fibers. Those responses, recorded from the secondary neurons in the auditory system, indicate that each element responds to a tone of a particular frequency with a particularly high sensitivity. Galambos (8) also described an inhibitory interaction between the responses to two different sound stimuli in the cochlear nucleus. It is therefore possible that the selective response of each element at this level of the auditory system to a particular frequency could be largely due to some complicated interaction among nerve impulses arriving at the cochlear nucleus over a large number of primary auditory nerve fibers. Quite recently, it has been shown in this Institute (21,22) that the basal turn of the guinea pig cochlea responds to practically all frequencies in the audible range, while the upper parts of the cochlea respond only to sounds of low frequencies. By the method of differential recording of the microphonic response across the cochlear partition, it was shown that when the response of the upper part of the cochlea (to low-frequency sounds) had been eliminated by a local injection of an isotonic KC1 solution there were still good normal responses in the basal turn, both microphonics and nerve action potentials. These results exclude any sharp localization of vibratory motion in the cochlea. The “resonance curve” obtained by Bekesy (3), which correlates mechanical displacement of the cochlear partition of the dead human and animal ears with place in the cochlea at various frequencies, is not very sharp. Nevertheless, the large microphonic and nerve action potentials induced by low-frequency sound in the basal turn still seem difficult to reconcile with Bekesy’s curves, which show a fairly rapid decay in amplitude of vibration toward the basal turn. More direct information as to the nerve impulses in the primary auditory neurons seemed to offer a solution of this difficulty.