Interactive contributions of intracellular calcium and protein phosphatases to massed-trials learning deficits in Hermissenda.
Using Hermissenda as subjects, massed-trials training deficits were examined. Associative pairings of light and rotation induced a progressively greater conditioned foot contraction in response to light as the intertrial interval (ITI) was extended (up to 8 min). In contrast, a short ITI (30 s) produced no evidence of learning. In a corresponding in vitro conditioning experiment that mimicked training of the intact animal, facilitation of neuronal excitability in the animal's B photoreceptors paralleled the results obtained in vivo. Imaging of intracellular Ca2+ using Fura-2 indicated that Ca2+ levels remained elevated during short ITIs. This Ca2+ accumulation appears to induce activation of protein phosphatases because normal facilitation of the B photoreceptors was induced with a short ITI if training occurred in the presence of a phosphatase inhibitor. These results suggest that intracellular Ca2+ and protein phosphatases contribute interactively to the kinetics of memory formation and provide evidence that an accumulation of intracellular Ca2+ across training trials may impede memory formation.
Muzzio
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Department of Psychology, Rutgers, The State University of New Jersey, Piscataway 08903, USA.
Ramirez
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Talk
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Matzel
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D000818:Animals; D001245:Association Learning / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D003214:Conditioning, Classical / Q000502:physiology*; D007424:Intracellular Fluid / Q000502:physiology; D011939:Mental Recall / Q000502:physiology*; D008974:Mollusca; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology
D010749:Phosphoprotein Phosphatases; D002118:Calcium