Octopamine indirectly affects proboscis extension response habituation in Drosophila melanogaster by controlling sucrose responsiveness.

Octopamine is an important neurotransmitter in insects with multiple functions. Here, we investigated the role of this amine in a simple form of learning (habituation) in the fruit fly Drosophila melanogaster. Specifically, we asked if octopamine is necessary for normal habituation of a proboscis extension response (PER) to different sucrose concentrations. In addition, we analyzed the relationship between responsiveness to sucrose solutions applied to the tarsus and habituation of the proboscis extension response in the same individual. The Tyramine-β-hydroxylase (Tβh) mutant lacks the enzyme catalyzing the final step of octopamine synthesis. This mutant was significantly less responsive to sucrose than controls. The reduced responsiveness directly led to faster habituation. Systemic application of octopamine or induction of octopamine synthesis by Tβh expression in a cluster of octopaminergic neurons within the suboesophageal ganglion restored sucrose responsiveness and habituation of octopamine mutants to control level. Further analyses imply that the reduced sucrose responsiveness of Tβh mutants is related to a lower sucrose preference, probably due to a changed carbohydrate metabolism, since Tβh mutants survived significantly longer under starved conditions. These findings suggest a pivotal role for octopamine in regulating sucrose responsiveness in fruit flies. Further, octopamine indirectly influences non-associative learning and possibly associative appetitive learning by regulating the evaluation of the sweet component of a sucrose reward.

Scheiner R ，Steinbach A ，Claßen G ，Strudthoff N ，Scholz H ... -  《-》

Activity of cGMP-dependent protein kinase (PKG) affects sucrose responsiveness and habituation in Drosophila melanogaster.

Scheiner R ，Sokolowski MB ，Erber J 《LEARNING & MEMORY》

Three Drosophila mutations that block associative learning also affect habituation and sensitization.

Duerr JS ，Quinn WG 《-》

Drosophila mutants lacking octopamine exhibit impairment in aversive olfactory associative learning.

Octopamine is a biogenic amine in invertebrates that is considered a functional homolog of vertebrate norepinephrine, acting as a neurotransmitter, neuromodulator and neurohormone. Octopamine regulates many physiological processes such as metabolism, reproduction and different types of behaviour including learning and memory. Previous studies in insects led to the notion that acquisition of an olfactory memory depends on the octopaminergic system during appetitive (reward-based) learning, but not in the case of aversive (punishment-based) learning. Here, we provide several lines of evidence demonstrating that aversive associative olfactory learning in Drosophila is also dependent on octopamine signalling. Specifically, we used Drosophila Tβh (tyramine-β-hydroxylase) mutants, which lack octopamine and are female sterile, to determine whether octopamine plays a role in aversive learning. We show that Tβh mutant flies exhibit a significant reduction in learning compared to control lines that is independent of either genetic background or the methods used to induce aversive olfactory memory. We also show that the learning deficits observed in Tβh mutants are not due to defects in sensorimotor behaviours. Finally, to unambiguously demonstrate that octopamine synthesis plays a role in aversive olfactory learning, we performed rescue experiments using the Gal4/UAS system. We show that expression of UAS-Tβh in octopamine/tyraminergic neurons using Tdc2-Gal4 in Tβh null mutant flies fully rescued both the aversive learning defects and female sterility observed in Tβh mutants.

Iliadi KG ，Iliadi N ，Boulianne GL 《-》

Responsiveness to sucrose and habituation of the proboscis extension response in honey bees.

Scheiner R 《JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY》