Interhemispheric connections between olfactory bulbs improve odor detection
Fig 6
Contralateral olfactory inputs preserve reproductive pheromone detection in food odor background.
(A) Illustration of the experimental setup depicting an adult zebrafish brain explant expressing GCaMP6s in excitatory neurons, and the tube for odor delivery to the intact nose. Three odors were used: pgf2α, food odor extract (food), and an odor mixture of pgf2α and food odor extract. Food odor was delivered at different concentrations (control [−]: 0 μg/mL; low [+]: 25 μg/mL; medium [++]: 100 μg/mL; high [+++]: 400 μg/mL). The dashed square indicates the imaged olfactory bulb. (B) Ventral fish brain dissection with the contralateral olfactory nerve sectioned, preventing contralateral inputs to modulate the odor responses measured. (C) Odor response time course of three representative pgf2α-selective MCs in the presence of contralateral olfactory inputs. Black arrowheads indicate odor onset. (D) Odor response time course of three representative pgf2α-selective MCs without contralateral olfactory inputs. (E) Odor response maps to pgf2α, food odor, and the odor mixture in the olfactory bulb receiving contralateral inputs. Black asterisks indicate pgf2α-selective glomeruli. (F) Odor response maps for the same fish and imaging plane than in (E), without contralateral inputs. (G) Relative response of pgf2α-selective cells to the odor mixture in all conditions. Each circle represents a pgf2α-selective MC with (black) or without (red) contralateral inputs. The response amplitude of each pgf2α-selective MC to the odor mixture is normalized to its response to pgf2α alone. Values close and superior to 1 represent conserved or enhanced responses to pgf2α in presence of food odor, respectively. Values close to 0 indicate suppression of the pgf2α response in the presence of food odor (**p < 0.01, Mann–Whitney U test). The number of pgf2α-selective MCs is as follows (with contralateral inputs): control (−), 57 MCs in seven fish; low (+), 61 MCs in six fish; medium (++), 83 MCs in eight fish; and high (+++), 25 MCs in five fish. The number of pgf2α-selective MCs is as follows (without contralateral input): control (−), 72 MCs in five fish; low (+), 53 MCs in six fish; medium (++), 77 MCs in six fish; and high (+++), 56 MCs in five fish. The response of the cell placed in a dashed square is out of range (3.3). (H) Correlation between MCs’ odor responses to pgf2α and odor mixtures for all conditions (**p < 0.01, Student t test). High and low pattern correlation values indicate high and low similarities with the pgf2α response pattern, respectively. Each circle represents correlation within a single fish, with contralateral input (in black) or without contralateral input (in red). (I) Correlation between MCs’ odor responses to food odor and odor mixtures for all conditions (**p < 0.01, Student t test). High and low pattern correlation values indicate high and low similarities with the food odor response pattern, respectively. Numerical data used to generate this figure can be found in S1 Data. GCaMP6, genetically encoded calcium sensor, circular permutated green florescent protein-Calmodulin-M13 peptide 6; MC, mitral cell; pgf2α, prostaglandin 2α.