FIGURE 1.

Tonic and phasic firing activity in toad olfactory receptor neurons. (A) An olfactory neuron responded with a sustained increase in action potential firing (left) and another ORN gave a brief train of action potentials (right) to an identical 5-μM stimuli of geraniol, under cell-attached conditions. (B) Prolonged depolarizations induced a sustained (left) and transient (right) firing activity in two other ORNs. Depolarizations were induced by +20 mV steps in the pipette potential in the absence of odorants; cell-attached V-clamp condition. (C) Sustained firing increase from an ORN to a 2-μM geraniol stimulus (left, top), under whole cell conditions. A similar response was triggered by a current step in the same cell (left, bottom). Another ORN responded to a 20-μM geraniol stimulus with a transient firing followed by a plateau (right, top), and with a comparable response when depolarized by a current step (right, bottom). Whole cell I-clamp conditions, I_h = 0 pA.