A proteomics approach identifies Drosophila Syd-1 as a Bruchpilot binding partner that controls maturation on both sides of the neuromuscular junction.

Insect flight is one of the fastest, most intense and most energy-demanding motor behaviors. It is modulated on multiple levels by the biogenic amine octopamine. Within the CNS, octopamine acts directly on the flight central pattern generator, and it affects motivational states. In the periphery, octopamine sensitizes sensory receptors, alters muscle contraction kinetics, and enhances flight muscle glycolysis. This study addresses the roles for octopamine and its precursor tyramine in flight behavior by genetic and pharmacological manipulation in Drosophila. Octopamine is not the natural signal for flight initiation because flies lacking octopamine [tyramine-␤-hydroxylase (T␤H) null mutants] can fly. However, they show profound differences with respect to flight initiation and flight maintenance compared with wild-type controls. The morphology, kinematics, and development of the flight machinery are not impaired in T␤H mutants because wing-beat frequencies and amplitudes, flight muscle structure, and overall dendritic structure of flight motoneurons are unaffected in T␤H mutants. Accordingly, the flight behavior phenotypes can be rescued acutely in adult flies. Flight deficits are rescued by substituting octopamine but also by blocking the receptors for tyramine, which is enriched in T␤H mutants. Conversely, ablating all neurons containing octopamine or tyramine phenocopies T␤H mutants. Therefore, both octopamine and tyramine systems are simultaneously involved in regulating flight initiation and maintenance. Different sets of rescue experiments indicate different sites of action for both amines. These findings are consistent with a complex system of multiple amines orchestrating the control of motor behaviors on multiple levels rather than single amines eliciting single behaviors.

How does the sensory environment shape circuit organization in higher brain centers? Here we have addressed the dependence on activity of a defined circuit within the mushroom body of adult Drosophila. This is a brain region receiving olfactory information and involved in long-term associative memory formation. The main mushroom body input region, named the calyx, undergoes volumetric changes correlated with alterations of experience. However, the underlying modifications at the cellular level remained unclear. Within the calyx, the clawed dendritic endings of mushroom body Kenyon cells form microglomeruli, distinct synaptic complexes with the presynaptic boutons of olfactory projection neurons. We developed tools for high-resolution imaging of pre- and postsynaptic compartments of defined calycal microglomeruli. Here we show that preventing firing of action potentials or synaptic transmission in a small, identified fraction of projection neurons causes alterations in the size, number, and active zone density of the microglomeruli formed by these neurons. These data provide clear evidence for activity-dependent organization of a circuit within the adult brain of the fly.

Plastic changes at the presynaptic sites of the mushroom body (MB) principal neurons called Kenyon cells (KCs) are considered to represent a neuronal substrate underlying olfactory learning and memory. It is generally believed that presynaptic and postsynaptic sites of KCs are spatially segregated. In the MB calyx, KCs receive olfactory input from projection neurons (PNs) on their dendrites. Their presynaptic sites, however, are thought to be restricted to the axonal projections within the MB lobes. Here, we show that KCs also form presynapses along their calycal dendrites, by using novel transgenic tools for visualizing presynaptic active zones and postsynaptic densities. At these presynapses, vesicle release following stimulation could be observed. They reside at a distance from the PN input into the KC dendrites, suggesting that regions of presynaptic and postsynaptic differentiation are segregated along individual KC dendrites. KC presynapses are present in ␥-type KCs that support short-and long-term memory in adult flies and larvae. They can also be observed in ␣/␤-type KCs, which are involved in memory retrieval, but not in ␣Ј/␤Ј-type KCs, which are implicated in memory acquisition and consolidation. We hypothesize that, as in mammals, recurrent activity loops might operate for memory retrieval in the fly olfactory system. The newly identified KC-derived presynapses in the calyx are, inter alia, candidate sites for the formation of memory traces during olfactory learning.