Figure 4.

GABAergic input blocks the Ca²⁺ component of the dendritic response above the critical frequency. (A) Reconstruction of a biocytin-filled L5 pyramidal neuron and an interneuron located at the top of layer 4 that innervated the pyramidal neuron. The rat was 49 days old. A dendritic whole-cell recording pipette was located 700 μm distal to the soma, and another pipette was located at the soma. (B) Dendritic potential in response to a supracritical train of APs (100 Hz) elicited at the soma of the pyramidal neuron. The two bottom traces represent schematically the time course of the current injected at the somata of both neurons. (C) The regenerative potential in the dendrite was blocked in a manner similar to the block due to extracellular Cd²⁺ (50 μM), when a compound IPSP, generated by eight APs elicited in the presynaptic neuron (200 Hz), preceded the pyramidal cell stimulation.