Structural and Molecular Properties of Insect Type II Motor Axon Terminals

A comparison between the axon terminals of octopaminergic efferent dorsal or ventral unpaired median neurons in either desert locusts (Schistocerca gregaria) or fruit flies (Drosophila melanogaster) across skeletal muscles reveals many similarities. In both species the octopaminergic axon forms beaded fibers where the boutons or varicosities form type II terminals in contrast to the neuromuscular junction (NMJ) or type I terminals. These type II terminals are immunopositive for both tyramine and octopamine and, in contrast to the type I terminals, which possess clear synaptic vesicles, only contain dense core vesicles. These dense core vesicles contain octopamine as shown by immunogold methods. With respect to the cytomatrix and active zone peptides the type II terminals exhibit active zone-like accumulations of the scaffold protein Bruchpilot (BRP) only sparsely in contrast to the many accumulations of BRP identifying active zones of NMJ type I terminals. In the fruit fly larva marked dynamic changes of octopaminergic fibers have been reported after short starvation which not only affects the formation of new branches (“synaptopods”) but also affects the type I terminals or NMJs via octopamine-signaling (Koon et al., 2011). Our starvation experiments of Drosophila-larvae revealed a time-dependency of the formation of additional branches. Whereas after 2 h of starvation we find a decrease in “synaptopods”, the increase is significant after 6 h of starvation. In addition, we provide evidence that the release of octopamine from dendritic and/or axonal type II terminals uses a similar synaptic machinery to glutamate release from type I terminals of excitatory motor neurons. Indeed, blocking this canonical synaptic release machinery via RNAi induced downregulation of BRP in neurons with type II terminals leads to flight performance deficits similar to those observed for octopamine mutants or flies lacking this class of neurons (Brembs et al., 2007)

One hundred years of phase polymorphism research in locusts

One hundred years ago in 1921, Sir Boris Uvarov recognized that two locust species are one species but appearing in two different phases, a solitarious and a gregarious phase. As locust swarms are still a big problem affecting millions of people, basic research has tried to understand the causes for the transition between phases. This phenomenon of phase polymorphism, now called polyphenism, is a very complex multifactorial process and this short review will draw attention to this important aspect of insect research

A revision of brain composition in Onychophora (velvet worms) suggests that the tritocerebrum evolved in arthropods

<p>Abstract</p> <p>Background</p> <p>The composition of the arthropod head is one of the most contentious issues in animal evolution. In particular, controversy surrounds the homology and innervation of segmental cephalic appendages by the brain. Onychophora (velvet worms) play a crucial role in understanding the evolution of the arthropod brain, because they are close relatives of arthropods and have apparently changed little since the Early Cambrian. However, the segmental origins of their brain neuropils and the number of cephalic appendages innervated by the brain - key issues in clarifying brain composition in the last common ancestor of Onychophora and Arthropoda - remain unclear.</p> <p>Results</p> <p>Using immunolabelling and neuronal tracing techniques in the developing and adult onychophoran brain, we found that the major brain neuropils arise from only the anterior-most body segment, and that two pairs of segmental appendages are innervated by the brain. The region of the central nervous system corresponding to the arthropod tritocerebrum is not differentiated as part of the onychophoran brain but instead belongs to the ventral nerve cords.</p> <p>Conclusions</p> <p>Our results contradict the assumptions of a tripartite (three-segmented) brain in Onychophora and instead confirm the hypothesis of bipartite (two-segmented) brain composition. They suggest that the last common ancestor of Onychophora and Arthropoda possessed a brain consisting of protocerebrum and deutocerebrum whereas the tritocerebrum evolved in arthropods.</p

De fabrica systematis nervosi evertebratorum

Hermann von Helmholtz, der Namensgeber der Helmholtz-Gemeinschaft, ist den meisten als Physiker bekannt und wurde auch als der "Reichskanzler der Physik" bezeichnet. In Vergessenheit geraten ist die Tatsache, dass er Medizin studiert hat und als Mediziner seine wissenschaftliche Laufbahn begann. 1842 schrieb er als 21-Jähriger seine Promotion über ein neurowissenschaftliches Thema. In dieser Zeit publizierte Christian Ehrenberg, Professor an der Berliner Universität, das erste Bild einer Nervenzelle. Gleichzeitig wurde auch die Zelltheorie von Jacob Henle und Matthias Schleiden in Berlin formuliert. Sie besagt, dass alle Gewebe einschließlich des Gehirns aus Zellen bestehen. Hermann Helmholtz stellte sich in seiner Doktorarbeit die Frage, wie das Nervensystem von wirbellosen Tieren aufgebaut ist. Sind die Prinzipien ähnlich oder ganz anders als bei Wirbeltieren und dem Menschen? Betreut von dem bekanntesten Physiologen und Anatomen dieser Zeit, Johannes Müller, untersuchte er das Nervensystem von Blutegel, Hausspinne, Schmetterling, Regenwurm, Flusskrebs oder Teichmuschel. Er kam zu der Erkenntnis, dass sich die Nervensysteme dieser Wirbellosen, oder auch Invertebraten genannt, nicht grundsätzlich von den Nervensystemen der Wirbeltiere inklusive des Menschen unterscheiden. Alle Grundelemente wie Zellen und Fortsätze sind identisch, so dass der Aufbau von Nervensystemen nach einem in der Tierwelt einheitlichen Plan erfolgt. Diese neurowissenschaftlichen Erkenntnisse von Helmholtz sind in der "Neuroscience Community" in Vergessenheit geraten, denn er schrieb seine Doktorarbeit in Latein. Sie wurde bisher nie in eine andere Sprache übersetzt. Helmut Kettenmann, Neurowissenschaftler am Max-Delbrück Centrum für Molekulare Medizin in der Helmholtz-Gemeinschaft, hat nun zusammen mit der Altphilologin Julia Heideklang von der Humboldt-Universität und Joachim Pflüger, Invertebraten-Neurobiologe an der Freien Universität, diese Dissertation sowohl ins Englische als auch ins Deutsche übersetzt. Die Doktorarbeit wird ausführlich eingeführt und kommentiert und zeigt , dass Hermann Helmholtz schon als 21-Jähriger noch heute gültige Erkenntnisse auf neurowissenschaftlichem Gebiet formulierte, die seine herausragenden, teils visionären Fähigkeiten schon früh unter Beweis stellten

Developmental and activity-dependent plasticity of filiform hair receptors in the locust

A group of wind sensitive filiform hair receptors on the locust thorax and head makes contact onto a pair of identified interneuron, A4I1. The hair receptors’ central nervous projections exhibit pronounced structural dynamics during nymphal development, for example, by gradually eliminating their ipsilateral dendritic field while maintaining the contralateral one. These changes are dependent not only on hormones controlling development but on neuronal activity as well. The hair-to-interneuron system has remarkably high gain (close to 1) and makes contact to flight steering muscles. During stationary flight in front of a wind tunnel, interneuron A4I1 is active in the wing beat rhythm, and in addition it responds strongly to stimulation of sensory hairs in its receptive field. A role of the hair-to-interneuron in flight steering is thus suggested. This system appears suitable for further study of developmental and activity-dependent plasticity in a sensorimotor context with known connectivity patterns