Mechanisms of the development of sensitizations in the snail: the participation of calcium and calmodulin.

A single sensitizing exposure led to brief (up to 1 h) and prolonged (several hours) changes in the defense reactions of snails, in the activity of command neurons, as well as in the content of bound calcium in these neurons. The application of the specific calmodulin blocker, W7, or the removal of Ca2+ from the medium bathing the snail's CNS before the sensitizing exposure, exerted a suppressant influence on the development of both the brief and the prolonged behavioral and neuronal effects of sensitization. At the same time, the application of W7 or the removal of Ca2+ following the application of the sensitizing influence did not suppress the development of the prolonged changes in the command neurons. The data obtained make it possible to assume that calmodulin directly participates in the regulation of the membrane and synaptic events leading to the development of the brief effects of sensitization. In addition, it is probably involved in the initiation of the metabolic reactions leading to the occurrence of the prolonged effects; however, it does not take part directly in their manifestation.