Fig. 5.

Sodium substitution decreased the amplitude and duration of TTX-resistant plateau potentials. All the recordings were obtained in the presence of 1 μm TTX and 50 μm 1S,3R-ACPD.A, When most of the Na⁺ was replaced by NMDG in the perfusion medium, the amplitude of both the late depolarizing phase during the stimulation and the afterdepolarization were reduced (A2) compared with control conditions (A1). In neurons producing short plateaus (B1), the NMDG medium reduced the late phase of the regenerative depolarization (B2). The reduction was reversible (B3). C, Similar reversible effects were obtained when most of the Na⁺ was replaced by choline in the bath. In the choline medium, note the difference between a subthreshold (C2, first stimulation) and a suprathreshold response (second stimulation).