. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. -5 mV - 25 mV N -5mV -30 mV f\ -20mV -55 mV -80mV -105mV K-80 mV . -85mV -75 mV' > " '55mV -90 mV. -130 mV r -155 mV FIGURE 38. Voltage-clamp recordings during and after light steps; up = inward current. Values at left are absolute holding potentials. Dash lines indicate steady-state current in dark- ness for each holding potential. Voltage traces at top were recorded simultaneously with current (flowing from reference element in the bath) recordings. Lowest trace in each set indicates duration of light step. A susta
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. -5 mV - 25 mV N -5mV -30 mV f\ -20mV -55 mV -80mV -105mV K-80 mV . -85mV -75 mV' > " '55mV -90 mV. -130 mV r -155 mV FIGURE 38. Voltage-clamp recordings during and after light steps; up = inward current. Values at left are absolute holding potentials. Dash lines indicate steady-state current in dark- ness for each holding potential. Voltage traces at top were recorded simultaneously with current (flowing from reference element in the bath) recordings. Lowest trace in each set indicates duration of light step. A sustained inward current (Ca2*) is induced by light at holding potentials > RP in Na*-free ASW. The early outward current (K+) is marked at higher light intensity (middle column). Light intensity: in middle and left column: X 10" erg-cm"2-sec"1 (unfiltered) ; in right column: X 10" erg-cm"2-sec"1 (unfiltered). Paper re- cording amplifier saturates for some records in ASW (Alkon, 1979). Thus, a kind of regenerative or positive feedback mechanism is suggested as a neurophysiologic basis for the associative learning of Hermissenda. Light-induced depolarization enhances synaptic depolarization, which in turn enhances the light- induced depolarization, and so forth. With each successive trial, residual depolari- zation could potentiate and add to depolarization following the next stimulus pair. How does cumulative depolarization (Farley and Alkon, 1980; Alkon, in press) of the Type B membrane, in turn, cause a very long-lasting change which could account for the animals' decreased positive phototactic behavior ? A causal sequence which is consistent with the currently available data is as follows. Cumulative depolariza- tion, specific to stimulus pairing, causes inactivation of dark voltage-dependent K+ conductances (cf. Shoukimas and Alkon, 1980). Inactivation of voltage-dependent K+ conductance(s) causes increased total membrane resistance of th
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
