Figure 2.

DPM Neurons Do Not Respond to the Appetitive Unconditioned Stimulus.

(A) Calcium influx into the DPM neuron processes that innervate the vertical lobes of the MB’s. Electric shock pulses of 90 V and 1.25 sec duration (red trace) were delivered every 5 sec. The upper trace represents the average %ΔF/F_o across the region of interest, which included the distal end of the vertical lobes. An obvious calcium response was observed with each shock pulse riding on the top of a decaying background due to bleaching over a 70 sec scanning period.

(B) Calcium influx into the DPM neuron processes that innervate the horizontal lobes of the MB’s. Electric shock pulses of 90 V and 1.25 sec duration (red trace) were delivered every 5 sec. The upper trace represent the average %ΔF/F_o across the region of interest, which included the area occupied by the horizontal lobes. An obvious calcium response was observed, with each shock pulse riding on the top of a decaying background due to bleaching over a 70 sec scanning period.

(C) Summary of DPM and taste neuron responses to sucrose, water, and odor stimuli. Flies were stimulated with water or a 2 M sucrose solution to the gustatory sensilla of the proboscis and the response of the neurons calculated as a ΔF/F_o. The responses of the DPM neurons (c316-gal4) to sucrose and water were not significantly different from zero (Wilcoxon signed rank test p=0≥0.0547 respectively). However, the DPM neurons tested in the same flies previously stimulated with sucrose exhibited a robust response to odor (Oct), providing assurance that the flies had the capability of responding. The response to odor was significantly different from the responses to water or sucrose (Kruskal-Wallis statistic of 13.37, p=0.0013; Mann-Whitney pairwise comparison, p=0.0006). As a positive control, the response of taste neurons (Gr5a-gal4) to sucrose stimulation was recorded. Flies were prepared as shown in panel D and stimulated with water or a saturated solution of sucrose. The Gr5a-gal4 neurons exhibited a significant increase in calcium influx in response to sucrose compared to the lack of response to water (Mann-Whitney pairwise comparison, p=0.0007). Error bars indicate the standard error of the mean. Asterisks indicate statistically significant differences. n=7–10 for all groups.

(D) Schematic illustration of a fly head showing the area of cuticle that was removed to image the Gr5a-gal4 neurons in the subesophageal ganglion. Removal of antennae and surrounding cuticle allowed visual access to this area of the brain. Gr5a-gal4 taste neurons were visualized in vivo using the G-CaMP reporter to monitor the change in calcium influx in response to sucrose. The green trace represents the region of interest selected for scanning.