Adaptive properties of olfactory receptors analysed with odour pulses of varying durations.

1. The adaptive properties of salamander of olfactory receptors have been analysed in extracellular unit recordings. Stimulation has been by step pulses of odour of varying durations for 1--10 sec. 2. The most common response was a prolonged impulse discharge that continued throughout the duration of the pulse and terminated abruptly within 1 sec of the end of the pulse. The interval for termination was relatively independent of the pulse duration. Pulses were frequently followed by a period of impulse inactivity lasting 1--3 sec, usually independent of previous pulse duration. 3. The impulse discharges were typically slowly adapting. Initially, during the first 1--2 sec, the frequency rose to 5--10 impulses/sec, at threshold concentration. In some cases, the initial level was maintained throughout the pulse, with little or no adaptation. More commonly, there was a distinct initial phasic peak, followed by decay to a lower level of 4--8 impulses/sec, which was maintained during the pulse. It was concluded that most olfactory receptors are slowly adapting, with variable phasic responsiveness dependent on odour concentration and other factors. 4. Reductions in impulse activity, compared with background, during a pulse were rarely seen. Methods for increasing the level of background activity and the use of very long duration pulses were necessary in order to bring out this type of response. Uniformly reduced activity throughout a pulse was seen clearly in only one case. A pattern consisting of a waning and then recovery of impulse frequency during a pulse was also observed in rare cases. 5. The results have shown that olfactory receptor discharges characteristically have a relatively precise relation to step pulses of odour of varying duration. The properties of the response have implications for the steps involved in the overall processes of activation and inactivation of receptor mechanisms at the olfactory mucosa.