![]() ![]() Intracellular recordings demonstrate that classical conditioning causes the following changes to type B photoreceptors: an increase in input resistance ( R N), an enhanced long-lasting depolarization (LLD) in response to light ( Crow and Alkon, 1980 Farley and Alkon, 1982 West et al., 1982 Frysztak and Crow, 1994), a reduction in the calcium-dependent, I KCa, and transient, I A, potassium currents ( Alkon et al., 1982, 1984, 1985), a reduction in the calcium current ( Collin et al., 1988), translocation of protein kinase C ( McPhie et al., 1993 Muzzio et al., 1997), and facilitation of the IPSP in type A photoreceptors by type B photoreceptor action potentials ( Frysztak and Crow, 1994, 1997 Schuman and Clark, 1994). Classical conditioning in Hermissenda uses light as the conditioned stimulus and turbulence as the unconditioned stimulus. Hermissenda crassicornisis a model system for studying classical conditioning because many of the behavioral and biophysical properties are similar to those in mammals ( Lederhendler and Alkon, 1989 Matzel et al., 1990). Characteristics of these currents suggest that I Klgt is responsible for the long-lasting depolarization seen after light termination, and thus plays a role in classical conditioning. An increase in light duration or intensity causes an increase in the time-to-peak and duration of I Klgt. Latency of I Nalgt is decreased by intensity, whereas rise time is increased by duration. An increase in light duration or intensity causes an increase in the peak conductance of both I Nalgt and I Klgt. The third current component is a prolonged reduction in potassium currents, I Klgt it is accompanied by an increase in input resistance, and it appears at potentials close to rest. Substitution of trimethylammonium chloride for sodium reduces both currents equally, suggesting that I plateau represents partial inactivation of I Nalgt. One current component is a transient sodium current, I Nalgt another is a plateau sodium current, I plateau, which persists for the duration of the light stimulus. ![]() ![]() Three distinct current components are distinguished by their temporal and voltage characteristics and sensitivity to pharmacological agents. Thus, the present study measures the effect of holding potential, duration, and intensity on the light-induced currents in discontinuous single-electrode voltage clamp mode. Furthermore, the contribution of voltage-dependent potassium currents to the long-lasting depolarization in type B photoreceptors depends on light-induced currents active at resting potentials. Light duration and intensity influence classical conditioning in Hermissenda through their effects on the light-induced currents. ![]()
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