A, B. Examples of SHG opposing NMDA-induced excitation (20 nA) in WDR neurons under pentobarbital anesthesia. Responses are plotted in terms of the total number of action potentials (spikes) measured during the 5 seconds of NMDA application and 5-seoncds after. The trial number represents the order of the consecutive pulse applications, separated by 5-second intervals. The build-up of excitation is caused by the rapidly repeated applications. In A, recovery from suppression induced by 100 s of SHG application is illustrated; in B, a dose-response experiment with SHG is displayed. C: Effect of spermidine (Spdn, 0-40 nA) applied continuously at different doses on responses to 20 nA NMDA, including at the largest Spdn dose during continuously applied SHG (30 nA). Responses were averaged from the final 4 of 5 applications, parallel to those shown in Figures 4A and 4B. The response in the presence of SHG can be noted to be less than with NMDA alone in the absence of Spdn.