Fig. 4.

There are at least two sites for spike initiation in B21. A1, Spikes can be triggered by injecting current into the lateral process of B21 (bars under top traces). Left, In most preparations, spikes triggered in the lateral process were attenuated in the soma, suggesting that the soma was not making a major contribution to spike initiation. Right, To verify that the soma was not damaged, it was depolarized (bar under bottom trace), and current was injected into the lateral process. Full-size spikes were now observed in the soma. A2, Spikes can be triggered by injecting current into the soma of B21 (bars under bottom traces).Left, In 9 of 23 preparations, spikes triggered in this manner were attenuated in the lateral process, suggesting that the lateral process was not making a major contribution to spike initiation. Right, To verify that the lateral process was not damaged, it was depolarized (bar undertop trace), and current was injected again into the soma. B1–B4, Spikes can be initiated in both parts of B21 when the connection between the lateral process and soma is severed. B1, Preparation in which the data inB3 were obtained and viewed with epi-illumination alone (B1) or with both epifluorescence and epi-illumination (B2). B3, Spikes could be triggered in the isolated lateral process by injecting depolarizing current (bar). B4, Spikes could also be triggered by injecting current into the isolated soma/medial process (bar).