Molecular and Neuronal Mechanisms for Amino Acid Taste Perception in the Drosophila Labellum

IR76b-expressing neurons in Drosophila melanogaster are necessary for associative reward learning of an amino acid mixture

“…There are two potential explanations for this result: either both the rewarding and punishing effects induced by activating IR76b+ neurons indeed relate to amino acids, and the IR76b+ neurons are sufficient and required for the rewarding effect, but not required for the punishing effect; or the IR76b+ neurons mediate a punishing sensation of some unknown stimulus. Notably, in adult flies, IR76b is involved in sensing of aversive high sodium taste [19] and is co-expressed with GR66a in some presumably bitter-sensing neurons [10,15]. Whether this is the case also in larvae is not known yet.…”

“…'push-pull' behavioural organization may help the animals to find an optimal concentration of amino acids.Little is known about the neuronal circuits underlying amino acid sensing and processing [9]. In adults, both sweet-sensing and bitter-sensing gustatory receptor neurons have been shown to respond to amino acids, dependent on different combinations of gustatory and ionotropic receptors [10]. Specifically, the ionotropic receptor [11] IR76b is broadly expressed in external and pharyngeal taste neurons in D. melanogaster (larvae [12][13][14], adults [15,16]), and is required for innate preference or avoidance of amino acids (larvae [2], adults [10,16]) as well as other appetitive and aversive tastants [17][18][19].…”

“…In adults, both sweet-sensing and bitter-sensing gustatory receptor neurons have been shown to respond to amino acids, dependent on different combinations of gustatory and ionotropic receptors [10]. Specifically, the ionotropic receptor [11] IR76b is broadly expressed in external and pharyngeal taste neurons in D. melanogaster (larvae [12][13][14], adults [15,16]), and is required for innate preference or avoidance of amino acids (larvae [2], adults [10,16]) as well as other appetitive and aversive tastants [17][18][19]. The IR76b+ neurons physiologically respond to several single amino acids (larvae [2], adults [10,16]) and yeast [20].However, it remains open whether IR76b, or the neurons expressing it, are also involved in learning about amino acids.…”

“…Specifically, the ionotropic receptor [11] IR76b is broadly expressed in external and pharyngeal taste neurons in D. melanogaster (larvae [12][13][14], adults [15,16]), and is required for innate preference or avoidance of amino acids (larvae [2], adults [10,16]) as well as other appetitive and aversive tastants [17][18][19]. The IR76b+ neurons physiologically respond to several single amino acids (larvae [2], adults [10,16]) and yeast [20].However, it remains open whether IR76b, or the neurons expressing it, are also involved in learning about amino acids. Previous studies demonstrated that this is not a trivial question: in the case of the bitter tastant quinine, for example, larval GR66a+ neurons were found to be required specifically for…”

“…Specifically, the ionotropic receptor [11] IR76b is broadly expressed in external and pharyngeal taste neurons in D. melanogaster (larvae [12][13][14], adults [15,16]), and is required for innate preference or avoidance of amino acids (larvae [2], adults [10,16]) as well as other appetitive and aversive tastants [17][18][19]. The IR76b+ neurons physiologically respond to several single amino acids (larvae [2], adults [10,16]) and yeast [20].…”