Abstract
Drosophila central neurons arise from neuroblasts that generate neurons in a pair-wise fashion, with the two daughters providing the basis for distinct A and B hemilineage groups. 33 postembryonically-born hemilineages contribute over 90% of the neurons in each thoracic hemisegment. We devised genetic approaches to define the anatomy of most of these hemilineages and to assessed their functional roles using the heat-sensitive channel dTRPA1. The simplest hemilineages contained local interneurons and their activation caused tonic or phasic leg movements lacking interlimb coordination. The next level was hemilineages of similar projection cells that drove intersegmentally coordinated behaviors such as walking. The highest level involved hemilineages whose activation elicited complex behaviors such as takeoff. These activation phenotypes indicate that the hemilineages vary in their behavioral roles with some contributing to local networks for sensorimotor processing and others having higher order functions of coordinating these local networks into complex behavior.
Highlights
A major obstacle to understanding how the central nervous system (CNS) translates sensory inputs into appropriate motor outputs is the CNS’s staggering cellular complexity
The complexity of the elicited behavior reflects the complexity of the hemilineage’s projection pattern and the neuropil region to which it projects. These findings suggest that the hemilineages provide a functional as well as an anatomical ground plan for the thoracic nervous system, and that thorax-mediated behaviors occur by combinations of simple movements elicited by relatively simple ventral hemilineages, which are orchestrated by a hierarchy of increasingly complex dorsal hemilineages
Our study focused on the anatomy and function of the hemilineage clusters of the thoracic CNS
Summary
A major obstacle to understanding how the central nervous system (CNS) translates sensory inputs into appropriate motor outputs is the CNS’s staggering cellular complexity. Even the small CNS of Drosophila has on the order of 100,000 neurons (Power, 1943; Chiang et al, 2011), each of which is capable of making connections with dozens of synaptic partners. To understand such a complex system, it is helpful to parse its elements into relevant units organized in a functional hierarchy. This approach can be seen in the analysis of the vertebrate brainstem and spinal cord, which are the major sites of sensorimotor processing for locomotor behaviors. The hindbrain of the zebra fish is structured from clusters of cell types that are recruited in predictable ways to assemble functional circuits (Koyama et al, 2011)
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