Do enkephalins directly affect calcium-spikes in hippocampal pyramidal cells?

Although bath application of 10(-6) g/ml tetrodotoxin abolished the fast action potentials of pyramidal cells in hippocampal slices of rats, action potentials of lower amplitude and longer duration could still be evoked by intracellular current injection. FK 33-824 (an enkephalin analogue) had no effect on the threshold or shape of these presumed calcium-spikes. These data suggest that enkephalins, which induce bursting discharges in pyramidal cells, do not exert this action by a direct effect on inward calcium movement through the pyramidal cell membrane.