Motor control in zebrafish : excitatory drive and developmental changes
Year: 2014
Type: dissertation
Abstract: An essential characteristic of human and animal life is the ability to move from one place to \nanother, in order to survive in a complex environment. All the different forms of locomotion, \nlike walking, swimming, crawling and flying, have one common feature: rhythmic and alternating movements of the body. These movements are generated by neuronal networks \nin the spinal cord. The overall aim of this thesis is to investigate the mechanisms underlying \nlocomotion in zebrafish, with particular focus on excitatory drive and developmental \nchanges. \n \n \n \nExcitatory interneurons are believed to represent the core components for the generation of \nthe locomotor rhythm, since they drive both inhibitory interneurons and motoneurons. By \nablating one specific group of interneurons, the V2a interneurons, we show that they \nrepresent an intrinsic source of excitation necessary for the normal expression of the \nlocomotor rhythm. Ablation of V2a interneurons results in an increase in the threshold to \ninduce swimming and a decrease in swimming frequency and episode duration. \n \n \n \nTo demonstrate that the excitatory drive from ipsilateral premotor V2a interneurons is also \nsufficient to drive swimming, we used optogenetics to activate the V2a interneurons \nspecifically. Upon illumination, V2a interneurons displayed rhythmic oscillations that \nresembled the typical beat-and-glide swimming. Peripheral nerve recordings confirmed that \nthe bursting activity in single neurons corresponds to swimming activity, which is \ncharacterized by left-right-alternation and rostrocaudal delay. This indicates that swimming \nactivity emerges from the activity of an underlying V2a interneuron network. \n \n \n \nThe third aim of this thesis is to reveal the developmental changes of the swimming pattern \nand the motoneuron properties. By systematically recording peripheral nerve activity and \nprimary motoneuron properties during different developmental stages, we were able to \ndefine the time frame of the switch in swimming behavior from larval episodic to adult \ncontinuous swimming to 4-5 weeks post fertilization. Primary motoneurons stop participating \nin swimming within the same time window and are from around 6 weeks onward only active \nduring escape behavior. \n \n \n \nIn conclusion, we show that the excitatory V2a interneurons in zebrafish are necessary and \nsufficient for the rhythm generating network to generate a coordinated swimming motor \npattern and that there is a major switch in the locomotor pattern and primary motoneuron \nrecruitment around 4-5 weeks of development.
Author: Sabine Görgens
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2124005455