Local cobalt injection: a method to discriminate presynaptic axonal from postsynaptic neuronal activity.

The local application of cobalt reversibly blocks the calcium channel conductance and therefore synaptic transmission. The blockage of synaptic transmission is a useful tool to discriminate between the origins of a response recorded with extracellular metal electrodes from central nervous system substructures. Incoming presynaptic fiber activity is not affected while activity from postsynaptic elements as intrinsic neurons and cell processes are blocked. In addition, local cobalt application does not change the stimulation conditions under which the system is tested.