IONIC CURRENTS OF KENYON CELLS FROM THE MUSHROOM BODY OF THE HONEYBEE

The mushroom bodies have been suggested to be essentially involved in learning and memory in insects. In the honeybee Apis mellifera they ar e composed of about 340,000 intrinsic elements, called Kenyon cells, w hich can be easily separated from all other neurons of the brain. Here we describe a preparation in which we studied ionic currents in the i solated Kenyon cell somata, using tight-seal whole-cell recording. Sev eral outward and inward currents were identified and investigated by t he use of pharmacological agents and in ion substitution experiments: a rapidly inactivating A-type potassium current that is completely blo cked with 5 mM 4-aminopyridine; a calcium-activated potassium current that is blocked by 1-100 nM charybdotoxin; a delayed rectifier-type po tassium current that is only weakly sensitive to tetraethylammonium bu t is blocked by 100 mu M quinidine; a rapidly activating and inactivat ing, TTX-sensitive sodium current; a persistent sodium current that is both TTX and cadmium sensitive; and a calcium current that is complet ely blocked at 50 mu M cadmium and is affected by verapamil and nifedi pine only at high concentrations (100 mu M). The currents described he re are very similar to currents found in other insect neurons or muscl e cells. This preparation will not only facilitate studies concerning the action of transmitters and neuromodulators that are contained with in neurons converging onto the Kenyon cells, but will also allow a stu dy of the role of the adenylyl cyclase pathway, elements of which are expressed in Kenyon cells, and are known to be essential for learning in invertebrates.