Figure 4.

Temporal contrast enhancement in OSN presynaptic terminals is mediated by GABA_A and GABA_B receptors. A, Pharmacological inhibition of GABA_B receptors with CGP54626 has no effect on presynaptic electrical responses of OR22a-expressing OSNs in DM2 to a 1 s pulse of 1:5 Eb. Mean ± SEM; n = 5. B, Pharmacological inhibition of GABA_A receptors with PTX appears to slightly increase magnitude and prolong presynaptic electrical responses in DM2 to 1 s pulses of 1:5 Eb. Mean ± SEM; n = 5. C–F, Simultaneous pharmacological inhibition of GABA_A and GABA_B receptors increases magnitude and prolongs presynaptic electrical responses in DM2 to 1 s pulses of 1:5 (C) and 1:3 (E) Eb. Simultaneously recorded PID signals are identical before and after drug application (D, F). Mean ± SEM; n = 9. G, Maximum presynaptic voltage responses indicate that only simultaneous pharmacological inhibition of GABA_A and GABA_B receptors significantly increases the magnitude of voltage responses. Mean ± SEM; n = 5 for CGP54626, n = 5 for PTX, and n = 9 for CGP54626+PTX. Statistical analysis: two-way repeated-measures ANOVA with Bonferroni post hoc test, ***p < 0.001. H, Sharpness coefficient indicates that only simultaneous inhibition of GABA_A and GABA_B receptors significantly reduces the temporal contrast enhancement of presynaptic voltage responses. The sharpness of responses to 1:3 Eb is reduced significantly more than that to 1:5 Eb, which is consistent with the larger sustained peripheral response to 1:3 Eb (Fig. 2F). Mean ± SEM; n = 5 for CGP54626, n = 5 for PTX and n = 9 for CGP54626+PTX. Statistical analysis: two-way repeated-measures ANOVA with Bonferroni post hoc test, **p < 0.01; ***p < 0.001. I, Removal of the antennae reduces lateral inhibition of the maxillary palp glomerulus VM7 (Olsen and Wilson, 2008). In response to 1:5 Eb, removal of the antennae increases presynaptic voltage responses and reduces sharpness. Mean ± SEM; n = 7. Statistical analysis: paired t test, *p < 0.05.