Characterization of the octopaminergic and tyraminergic neurons in the central brain of Drosophila larvae.

Drosophila larvae are able to evaluate sensory information based on prior experience, similarly to adult flies, other insect species, and vertebrates. Larvae and adult flies can be taught to associate odor stimuli with sugar reward, and prior work has implicated both the octopaminergic and the dopaminergic modulatory systems in reinforcement signaling. Here we use genetics to analyze the anatomy, up to the single-cell level, of the octopaminergic/tyraminergic system in the larval brain and subesophageal ganglion. Genetic ablation of subsets of these neurons allowed us to determine their necessity for appetitive olfactory learning. These experiments reveal that a small subset of about 39 largely morphologically distinguishable octopaminergic/tyraminergic neurons is involved in signaling reward in the Drosophila larval brain. In addition to prior work on larval locomotion, these data functionally separate the octopaminergic/tyraminergic system into two sets of about 40 neurons. Those situated in the thoracic/abdominal ganglion are involved in larval locomotion, whereas the others in the subesophageal ganglion and brain hemispheres mediate reward signaling.

Selcho M ，Pauls D ，Huser A ，Stocker RF ，Thum AS ... -  《-》

The role of octopamine and tyramine in Drosophila larval locomotion.

The characteristic crawling behavior of Drosophila larvae consists of a series of rhythmic waves of peristalsis and episodes of head swinging and turning. The two biogenic amines octopamine and tyramine have recently been shown to modulate various parameters of locomotion, such as muscle contraction, the time spent in pausing or forward locomotion, and the initiation and maintenance of rhythmic motor patterns. By using mutants having altered octopamine and tyramine levels and by genetic interference with both systems we confirm that signaling of these two amines is necessary for larval locomotion. We show that a small set of about 40 octopaminergic/tyraminergic neurons within the ventral nerve cord is sufficient to trigger proper larval locomotion. Using single-cell clones, we describe the morphology of these neurons individually. Given various potential roles of octopamine and tyramine in the larval brain, such as locomotion, learning and memory, stress-induced behaviors or the regulation of the energy state, functions that are often not easy to discriminate, we dissect here for the first time a subset of this complex circuit that modulates specifically larval locomotion. Thus, these data will help to understand-for a given neuronal modulator-how specific behavioral functions are executed within distinct subcircuits of a complex neuronal network.

Selcho M ，Pauls D ，El Jundi B ，Stocker RF ，Thum AS ... -  《-》

Tyramine as an independent transmitter and a precursor of octopamine in the locust central nervous system: an immunocytochemical study.

Octopamine and its precursor tyramine are biogenic amines that are found ubiquitously in insects, playing independent but opposite neuromodulatory roles in a wide spectrum of behaviors, ranging from locomotion and aggression to learning and memory. We used recently available antibodies to octopamine and tyramine to label the distribution of immunoreactive profiles in the brain and ventral nerve cord of the locust. In the brain and all ventral cord ganglia all known octopaminergic neurons were labeled with both the tyramine and octopamine antisera. In the brain the subesophageal ganglion and all fused abdominal ganglia we found somata that were only labeled by the tyramine antibody. Some prominent architectural features of the brain, like the protocerebral bridge, the central body, and associated neuropils, also contain intensely labeled tyramine-immunoreactive fibers. In addition, tyraminergic fibers occur in all ganglia of the ventral cord. For known octopaminergic neurons of the thoracic ganglia, octopamine-immunoreactivity was confined to the cell body and to the varicosities or boutons, whereas fiber processes always expressed tyramine-immunoreactivity. The distribution of the tyramine and octopamine content within these neurons turned out to be dependent on how the animal was handled before fixation for immunocytochemistry. We conclude that tyramine is an independent transmitter in locusts, and that in octopaminergic neurons the ratio between octopamine and its precursor tyramine is highly dynamic.

Kononenko NL ，Wolfenberg H ，Pflüger HJ 《-》

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 《-》

Light-induced activation of distinct modulatory neurons triggers appetitive or aversive learning in Drosophila larvae.

Schroll C ，Riemensperger T ，Bucher D ，Ehmer J ，Völler T ，Erbguth K ，Gerber B ，Hendel T ，Nagel G ，Buchner E ，Fiala A ... -  《CURRENT BIOLOGY》