Abstract
Stimulation of the right pleurovisceral connective at frequencies greater than 0.2 Hz produces a steady-state facilitation of the Input 1 excitatory postsynaptic potential (EPSP) in neuron R15 of Aplysia. The magnitude of facilitation is reduced by increases in the concentration of extracellular calcium. Unfacilitated EPSPs (EPSP 1) exhibited a power function dependence on the concentration of extracellular calcium with an exponent (X EPSP 1 ) of approximately 3. The exponent for facilitated released (X EPSP SS ) was examined by comparing steady-state EPSP amplitudes obtained in different static concentrations of calcium (Method A), or by changing the calcium concentration during continuous stimulation and determining changes in steady state EPSP amplitudes (Method B). Method A failed to reveal any dependence of X EPSP SS on stimulation frequency, while Method B revealed frequency-dependent changes in X EPSP SS consistent with the hypothesis that presynaptic calcium accumulation is at least partly responsible for steady-state facilitation. At a stimulation frequency of 0.5 Hz, the X EPSP SS value was significantly reduced to 2/3 of the X EPSP 1 value.
Published Version
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