Figure 1.

Sensitization observed in the activity of Drosophila OSNs (A) and in Ca²⁺ level of cultured cells expressing odorant receptors (ORs) (B). The first weak odor stimulation did not enhance the spike frequency in OSNs expressing Or22a. However, the same stimulus repeated 20 s later elicited a robust increase in OSN activity (A). Similarly, a first stimulation of HEK293 cells expressing Or22a + Orco enhanced the intracellular Ca²⁺ concentration [Ca²⁺]_i only slightly whereas the second stimulus led to a strong rise (B). For experimental information see Getahun et al. (2013) (A) and Mukunda et al. (2016) (B).