Effect of apamin, a selective blocker of Ca2+-activated K+-channel, on habituation and passive avoidance responses in rats.

The effects of apamin, a selective blocker of the small conductance K(Ca) channels were examined in both passive avoidance and habituation of exploratory activity in rats. In the two experiments, animals were subjected to two trials separated by a 24 h interval. Apamin was administered either before or after the first session (acquisition) or before the second session (restitution). In the passive avoidance test, apamin did not alter performance whenever the time of administration. In the habituation task, apamin (0.4 mg/kg) decreased activity (distance travelled, rearing) on the two sessions only when it was injected before acquisition but not when injection took place just after the acquisition session or before the restitution session. Taken together, these findings support the view that the blockade of apamin sensitive K(Ca) channels improved the acquisition in non-stressful task, but not in a stressful situation.