Fig. 1.

Excitatory responses are mediated by both AMPA and NMDA receptors in barrelette and interbarrelette cells. (A) Barrelette cells are characterized by a transient K⁺ conductance (I_A) that delays the generation of Na⁺ spikes upon membrane depolarization. (B) Interbarrelette cells are distinguished by a low threshold T-type Ca²⁺ conductance (I_T) that results in a triangular depolarization. (C, D) EPSCs contain an early fast declining and late slowly declining components. With the presence of Mg²⁺ (2 mM ) in ACSF and GABAergic antagonist, the late component of the EPSC at −70 mV is much smaller in amplitude than that at +60 mV, suggesting the EPSCs are mediated by both AMPA and NMDA receptors. Each record is an average of 10 traces in this and subsequent figures.

(E, F) Both in barrelette and interbarrelette cells, the early component of EPSCs is blocked by 10 μM NBQX, an antagonist of AMPA receptors (1 vs. 2 traces). Note that even in the presence of 2 mM Mg²⁺, a considerable amount of NMDA-EPSC remained at −70 mV (interbarrelette cell trace 2). (G, H) The late component of EPSCs is blocked by 100 μM D-APV, an NMDAR antagonist (1 vs. 2 traces). (I, J) Superimposed D-APV-sensitive NMDA-EPSCs and pharmacologically isolated AMPA-EPSCs indicate that the peaks of AMPA-EPSC and NMDA-EPSC separate from each other (insets show expanded traces with very little overlap of the peaks of EPSCs).