Universität zu Köln

Rosenbaum, Philipp (2013). Motor flexibility: neuronal control of walking direction and walking speed in an insect. PhD thesis, Universität zu Köln.

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Abstract

The neuronal basis of locomotion is largely investigated in many different vertebrate and invertebrate species. Especially studying the neuronal control of adaptive locomotor behaviors is important to reveal general insights into nervous system function. In this thesis, the stick insects Carausius morosus and Cuniculina impigra were used to investigate how important parts of the locomotor network generate different walking directions and walking speeds. In order to study which parameters have to be changed to generate the different behaviors, leg muscle, motoneuron, and premotor nonspiking interneuron activity was recorded. In the first part, leg muscle activity during forward, backward, and curve walking was studied in a slippery surface setup, in which the animal is stationary about a slippery substrate and all legs can freely move. Muscle activity and timing was compared during different walking directions. The main change was observed in protractor and retractor muscles which move the leg in anterior and posterior direction. These muscles almost completely reverse their phase of activity with the change of walking direction, and intermediate changes occur in the inside leg during curve walking, depending on the steepness of the curve. In the second and third part, leg motoneuron and interneuron activity was recorded intracellularly in the single-leg preparation, in which only one leg is able to move in the vertical plane on a treadwheel. Fictive forward and backward walking can be reliably elicited in this preparation. It is known that leg motoneurons receive tonic depolarizing synaptic inputs from higher centers throughout walking, and additional phasic excitatory and inhibitory inputs from leg sense organs, as well as phasic inhibitory inputs from the rhythm generating network. It could be shown that similar inputs shape the motoneuron modulation pattern also during backward walking. The phase of the step cycle in which the phasic inputs to protractor and retractor MNs occur reverses during backward walking. It was shown previously that stepping velocity in the single-leg preparation is correlated to flexor MN activity (stance) but not extensor MN (swing) activity. These findings are confirmed in this thesis and also held for backward walking. No such influences could be shown for other stance phase motoneurons. Furthermore, premotor nonspiking interneurons were recorded to investigate their contribution to the generation of different walking directions and walking speeds. These neurons are known to integrate signals from descending, central, and sensory sources and thus contribute to the control of timing and magnitude of the motor output. Previously identified (E3, E4, E5, E7, I1, I2), as well as newly described nonspiking interneurons providing synaptic drive to motoneurons of all leg joints were recorded during forward and backward stepping. Interestingly, neurons could be identified which contribute to the change in protractor and retractor muscle activity. Furthermore it could be shown that all recorded nonspiking interneurons contribute to the motor output during walking in both directions, suggesting that the same premotor network is responsible for the generation of both behaviors. NSI activity also underlies tonic and phasic synaptic inputs. Additionally, the contribution of NSIs to the generation of different stepping velocities was investigated.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Rosenbaum, Philipp philipp.rosenbaum@uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-52507
Date:	1 August 2013
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Zoologisches Institut
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language Motor control, insect, CPG, muscle activity, motorneuron, nonspiking interneuron UNSPECIFIED
Date of oral exam:	5 July 2013
Referee:	Name Academic Title Büschges, Ansgar Prof. Dr. Kloppenburg, Peter Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/5250