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. 2019 Nov 13;8:e50566. doi: 10.7554/eLife.50566

Figure 6. AIA neurons are bistable and act as a nonlinear AND-gate.

(A) Representative example of membrane potential dynamics induced by current injection steps in current-clamped AIA neurons (n=45 AIA neurons recorded, all showing bimodal dynamics). Top, current injection protocol: a series of 5 s square pulses starting at −1 pA and increasing to 8 pA in 1 pA increments. Current injections between −1 and 2 pA had little effect on membrane potential (Vm), while the 3 pA step and all larger steps thereafter depolarized Vm from the resting Vm around −80 mV to a stable state of higher voltage around −20 mV. (B) Representative membrane potential dynamics (2 AIA neurons recorded) induced by current injection ramps at different slopes in AIA. Top, current injection protocol: two 15 s long ramping current injections from 0 pA to 5 pA (red) or 10 pA (blue) before returning to 0 pA, recorded from the same cell. AIA Vm is abruptly depolarized from around −80 mV to −20 mV when the current injection ramps reaches the same threshold around 2 pA. (C) Representative example of simultaneous membrane potential recording (upper traces) and calcium imaging in the AIA neurite (lower traces). Top, current injection protocol: a series of 5 s square pulses starting at −2 pA and increasing to 16 pA in 2 pA increments. Both membrane potential and GCaMP signals show bimodal all-or-none dynamics. (D) Summary of sensory neuron and AIA responses to various stimuli, and a model for how AIA uses AND-gate logic to integrate sensory information. In the absence of food odor, glutamatergic sensory neurons release glutamate and activate glutamate-gated chloride channels on AIA, preventing AWA from activating AIA. In the presence of food odor, AWA is activated, glutamatergic sensory neurons are inhibited, and AIA is disinhibited and more sensitive to AWA depolarization, resulting in reliable activation. Weak odor or optogenetic stimuli engage a subset of sensory neurons, resulting in a variable and delayed response in AIA. With respect to the delay, full conditions for the AIA AND-gate may be met when weak stimuli coincide with spontaneous sensory neuron activity (López-Cruz et al., 2019; Figure 5—figure supplement 2).

Figure 6—source data 1. Source data for Figure 6A–B and figure supplement.
Figure 6—source data 2. Source data for Figure 6C.

Figure 6.

Figure 6—figure supplement 1. Current-voltage relationship in AIA.

Figure 6—figure supplement 1.

(A) Representative example of whole-cell current traces induced by a series of voltage steps in voltage-clamped AIA neuron. Top, voltage step protocol: a series of 0.5 s square steps starting at −120 mV and increasing to 50 mV in 10 mV increments. The holding potential was set at −60 mV before and after applying each voltage step. (B) Current-voltage (I–V) relationship obtained from averaged voltage-clamp recordings in AIA. Black squares: peak currents measured by the absolute maximum amplitude of currents within the first 100 ms of each voltage step. Blue triangles: steady-state currents measured by the averaged current amplitudes of the final 50 ms of each voltage steps. N = 25 AIA neurons, error bars represent SEM.