Fig. 7.

Pinning the siphon increases the excitability of LE cell somata in the abdominal ganglion. A, Examples of different LE cells from the same cluster tested for excitability before and ∼15 min after pinning the siphon. Excitability was tested by injecting into the soma a 1 sec depolarizing pulse at 2.5 times the threshold current for initiating a spike with a 20 msec pulse. Note that the cell tested after pinning showed an immediate discharge of 13 spikes and an afterdischarge of 4 spikes. B, Mean number of spikes evoked in different subsets of LE cells before and 5–45 min after pinning (p < 0.01). C, Hyperexcitability relative to baseline observed 1 hr after pinning is blocked by perfusing the siphon with a 1:1 solution of isotonic and ASW during pinning. Left, Hyperexcitability at least 1 hr (60–90 min) after pinning with ASW perfusion of the siphon (p < 0.01). Right, Lack of significant hyperexcitability at least 1 hr after pinning with MgCl₂ perfusion. Values are means of the average difference in spike number (postpinning–prepinning) in each preparation.