Recording of a 99 mV action potential and pharmacological experiments for validating subthreshold potentials at 10 DIV. (A) Spontaneous activity measured on channel 44 showing subthreshold oscillations that are illustrated in the insets of a 1 s time window at the beginning of the trace (lower inset) and just at the action potential generation (top inset). (B) Concurrent recording with A from a nearby channel 46 showing some potential oscillations and negative spikes that occur simultaneously with those in A. (C) Recording with a solution containing D-APV (50 μM), CNQX (10 μM), and PTX (1 mM) to block NMDA, AMPA, and GABA receptors, respectively, shows a single oscillation prior to the spike on the same channel as in A. (D) Same in C from channel 37 showing no oscillations prior to the large action potential.