Analysis of unitary spikes recorded extracellularly from frog olfactory receptor cells and axons.

1. Differences in unitary spike conformation were systematically investigated with extracellular recordings at different depths in the frog's olfactory epithelium. Platinum-black metal-filled micro-electrodes were used in the unit recordings. Their properties were carefully investigated and compared with those of micropipettes.2. Three basic types of spikes were recorded: a diphasic spike with a positive-negative voltage sequence, a diphasic spike with a negative-positive voltage sequence and a triphasic spike with a positive-negative-positive voltage sequence.3. The triphasic spike was correlated with the action potential in the axon. The initially negative diphasic spike was correlated with the action potential initiated in the cell body region. The initially positive diphasic spike was correlated with the spread of the impulse into the receptor cell dendrite.4. A model is discussed which accounts for the differences in spike conformations and provides a basis for analysing impulse activity in spontaneously active and stimulus-driven olfactory receptor cells.