Ir76b1 mutant flies do not show significant changes in the expected avoidance response to food laced with different acids (5% acetic acid, 5% glycolic acid, 10% citric acid, 20% lactic acid, 5% tartaric acid, 2% propionic acid, 2% butyric acid, or 10mM HCl), as compared to controls. GRNs enervating S6 and S10 sensilla do not show changes in the responses (frequency of spikes) to 1% acetic acid, 1% glycolic acid, 1% tartaric acid, 5% citric acid, 1% propionic acid, 1% butyric acid, 10mM HCl, and 20% lactic acid, as compared to controls.
Ir76b1 hetero- and homozygotes show the expected increased food consumption induced by dietary amino acids, as observed in controls.
Adults with homozygous Ir76b1 have proboscis extension rates that are significantly reduced in response to fatty acids and significantly increased in response to sucrose, compared to controls.
Ir76b1/Ir76b1 and Ir76b1/Ir76b2 adult females have significantly reduced preference for oviposition on acid-containing medium, compared to controls.
Ir76b1/Ir76b1 mutant females exhibit a significant reduction in feeding preference index for yeast extract, but no significant change in feeding preference index for sucrose, as compared to wild type.
Ir76b1 homozygous, but not heterozygous, larvae have significantly reduced attraction to appetitive concentrations of Asp, Glu and Phe, but not Cys, amino acids, compared to controls; food intake in the presence of high alanine concentrations, but not in the presence of caffeine, is significantly increased, compared to controls.
In olfactory preference assays for polyamines, Ir76b1/Ir76b1 (but not Ir76b1/+) flies show a significant decrease in their attraction to putrescine or cadaverine, as compared to wild type. Ir76b1/Ir76b1 mutants also show a significant decrease in neuronal activity of the IR41a-neuron-innervated glomerulus, and regions of the subesophageal zone, in response to putrescine odor, as compared to heterozygous controls. Ir76b1/Ir76b1 females display a loss of aversion to oviposit on polyamine-rich substrate (plain, sugar-free 1% agarose supplemented with either putrescine or cadaverine) versus non-supplemented substrate, in contrast to wild type flies, instead showing no preference for either substrate. Ir76b1/Ir76b1 mutants show a significant decrease in neuronal activity of the subesophageal zone in response to NaCl[] stimulation, as compared to controls.
Ir76b1 mutant adults show normal preference for less solid sucrose-agarose food than a harder one (higher agarose conc., same sucrose content) one in a two-way food choice assay.
L4 sensilla of mutant flies show a normal response to each of 50mM KCl, 50mM sucrose, water and to a number of butter tastants (0.1mM denatonium, 0.1mM berberine, 6mM caffeine, 0.1mM strychnine and 0.1mM quinine).
The firing of L6 sensilla in response to low salt (50mM NaCl) is impaired in mutant flies. The electrophysiological response of high salt gustatory receptor neurons in both the S4 and S8 sensilla in response to 500mM NaCl is normal.
Expression of Ir76bScer\UAS.cZa under the control of Scer\GAL4Gr5a.PUn in a Ir76b1 background results in the Gr5a gustatory receptor neurons in the L2 sensilla showing a robust electrophysiological response to NaCl.
Mutant flies show severe defects in attraction to low salt concentrations, while aversion to high salt concentrations is normal. There is a significant decrease in the frequency of action potentials elicited by 50mM NaCl in the L4 sensilla compared to wild type, while the electrophysiological response of the S6 sensilla to 50mM NaCl is normal. The firing frequency of gustatory receptor neurons in the L4 sensilla is reduced compared to wild type across all salt concentrations from 1 to 1000mM.
Expression of Ir76bScer\UAS.cZa under the control of Scer\GAL4Gr5a.PUn in a Ir76b1 background results in the Gr5a gustatory receptor neurons in the L2 sensilla showing a robust electrophysiological response to NaCl. These sensilla show no response to NMDGCl (indicating that the response to 50Mm NaCl is due to Na[+]). The response of these sensilla to 50mM sucrose is not significantly different from wild type.