Localization of muscarinic acetylcholine receptor dependent rhythm generating modules in the Drosophila larval locomotor network

Mechanisms of rhythm generation have been extensively studied in motor systems that control locomotion over terrain in limbed animals; however, much less is known about rhythm generation in soft-bodied terrestrial animals. Here we explored how muscarinic acetylcholine receptor (mAChR) dependent rhythm generating networks are distributed in the central nervous system (CNS) of soft-bodied Drosophila larvae. We measured fictive motor patterns in isolated CNS preparations using a combination of Ca2+ imaging and electrophysiology while manipulating mAChR signalling pharmacologically. Bath application of the mAChR agonist oxotremorine potentiated rhythm generation in distal regions of the isolated CNS, whereas application of the mAChR antagonist scopolamine suppressed rhythm generation in these regions. Oxotremorine raised baseline Ca2+ levels and potentiated rhythmic activity in isolated posterior abdominal CNS segments as well as isolated anterior brain and thoracic regions, but did not induce rhythmic activity in isolated anterior abdominal segments. Bath application of scopolamine to reduced preparations lowered baseline Ca2+ levels and abolished rhythmic activity. These results suggest the presence of a bimodal gradient of rhythmogenicity in the larval CNS, with mAChR dependent rhythm generating networks in distal regions separated by medial segments with severely reduced rhythmogenic abilities. This work furthers our understanding of motor control in soft-bodied locomotion and provides a foundation for study of rhythm generating networks in an emerging genetically tractable locomotor system.

Relative Contribution of Proprioceptive and Vestibular Sensory Systems to Locomotion: Opportunities for Discovery in the Age of Molecular Science

Locomotion is a fundamental animal behavior required for survival and has been the subject of neuroscience research for centuries. In terrestrial mammals, the rhythmic and coordinated leg movements during locomotion are controlled by a combination of interconnected neurons in the spinal cord, referred as to the central pattern generator, and sensory feedback from the segmental somatosensory system and supraspinal centers such as the vestibular system. How segmental somatosensory and the vestibular systems work in parallel to enable terrestrial mammals to locomote in a natural environment is still relatively obscure. In this review, we first briefly describe what is known about how the two sensory systems control locomotion and use this information to formulate a hypothesis that the weight of the role of segmental feedback is less important at slower speeds but increases at higher speeds, whereas the weight of the role of vestibular system has the opposite relation. The new avenues presented by the latest developments in molecular sciences using the mouse as the model system allow the direct testing of the hypothesis.

Retinal optic flow during natural locomotion

We examine structure of visual motion on the retina during natural locomotion in real world environments. We demonstrate that eye-movement-free/head-centered optic flow is highly unstable due to the complex, phasic head movements that occur throughout the gait cycle. In contrast, VOR-mediated retinal optic flow has stable, reliable features that may be valuable for the control of locomotion. In particular, the sign and magnitude of the curl of retinal flow at the fovea specifies the degree to which a walker will pass to the left or right of their fixation point. In addition, the peak in the divergence of the retinal flow field specifies the walker's overground velocity/momentum vector in retinotopic coordinates. If we assume a walker can reliably determine the body-relative position of their fixation, this retinotopic cue for their body's momentum could be an essential aspect of the visual control locomotion over complex terrain.Clickable Video Links (Click here for a playlist of all videos)https://www.youtube.com/playlist?list=PLWxH2Ov17q5HRHVngfuMgMZn8qfOivMafVideo 1. Gaze Laser Skeleton – Video (Full Speed) – Free Walking – Raw (See Figure 1)Video 2. Gaze Laser Skeleton – Video (1/4 Speed) – Free Walking – Optic Flow VectorsVideo 3. Gaze Laser Skeleton – Video (1/4 Speed) – Free Walking – Optic Flow StreamlinesVideo 4. Sim. Eye Trajectory – Sim. Retinal Flow – Fixation Aligned with PathVideo 5. Sim. Eye Trajectory – Sim. Retinal Flow – Fixation to Left of PathVideo 6. Sim. Eye Trajectory – Sim. Retinal Flow – Fixation to Right of PathVideo 7. Sim. Eye Trajectory – Sim. Retinal Flow – Vertical Sin WaveVideo 8. Sim. Eye Trajectory – Sim. Retinal Flow – Horizontal Sin WaveVideo 9. Sim. Eye Trajectory – Sim. Retinal Flow – CorckscrewVideo 10. Gaze Laser Skeleton – Sim. Retinal Flow – Ground LookingVideo 11. Gaze Laser Skeleton – Video (Full Speed) – Rocky Terrain – RawVideo 12. Gaze Laser Skeleton – Video (1/4 Speed) – Rocky Terrain – Optic Flow StreamlinesVideo 13. Gaze Laser Skeleton – Sim. Retinal Flow – Rocky TerrainVideo 14. Quadcopter Gimbal – Video (Full Speed) – Optic Flow Streamlines

The programmable CPG model based on Matsuoka oscillator and its application to robot locomotion

The central pattern generator (CPG) is an important functional unit in the spinal cord which can produce rhythmic signals to control locomotion. Recently, there has been a growing interest in programmable central pattern generators (PCPG). In this paper, a new PCPG oscillator and a generic PCPG model based on the Matsuoka oscillator are presented. The perturbation method is used to determine the convergence of the generic PCPG model. The sine signal, the mix signal and chaotic signals are provided as inputs to the model, and the simulation results show that the generic PCPG can learn arbitrary periodic signals. In this paper, the generic PCPGs are allocated at each joint of the compass-like and the three-link robots and their outputs are chosen as joint position commands. The simulations show that the generic PCPG can be used to control robot locomotion effectively. The contributions of this paper are as follows: (1) A new PCPG oscillator based on the Matsuoka oscillator is presented as a beneficial enhancement to the PCPG oscillators. (2) A generic PCPG model is built comprising three PCPG oscillators. It can learn any periodic input signal. These findings are a significant contribution to generic PCPG research.

A quantitative model of conserved macroscopic dynamics predicts future motor commands

In simple organisms such as Caenorhabditis elegans, whole brain imaging has been performed. Here, we use such recordings to model the nervous system. Our model uses neuronal activity to predict expected time of future motor commands up to 30 s prior to the event. These motor commands control locomotion. Predictions are valid for individuals not used in model construction. The model predicts dwell time statistics, sequences of motor commands and individual neuron activation. To develop this model, we extracted loops spanned by neuronal activity in phase space using novel methodology. The model uses only two variables: the identity of the loop and the phase along it. Current values of these macroscopic variables predict future neuronal activity. Remarkably, our model based on macroscopic variables succeeds despite consistent inter-individual differences in neuronal activation. Thus, our analytical framework reconciles consistent individual differences in neuronal activation with macroscopic dynamics that operate universally across individuals.

Flow interactions between uncoordinated flapping swimmers give rise to group cohesion

Many species of fish and birds travel in groups, yet the role of fluid-mediated interactions in schools and flocks is not fully understood. Previous fluid-dynamical models of these collective behaviors assume that all individuals flap identically, whereas animal groups involve variations across members as well as active modifications of wing or fin motions. To study the roles of flapping kinematics and flow interactions, we design a minimal robotic “school” of two hydrofoils swimming in tandem. The flapping kinematics of each foil are independently prescribed and systematically varied, while the forward swimming motions are free and result from the fluid forces. Surprisingly, a pair of uncoordinated foils with dissimilar kinematics can swim together cohesively—without separating or colliding—due to the interaction of the follower with the wake left by the leader. For equal flapping frequencies, the follower experiences stable positions in the leader’s wake, with locations that can be controlled by flapping amplitude and phase. Further, a follower with lower flapping speed can defy expectation and keep up with the leader, whereas a faster-flapping follower can be buffered from collision and oscillate in the leader’s wake. We formulate a reduced-order model which produces remarkable agreement with all experimentally observed modes by relating the follower’s thrust to its flapping speed relative to the wake flow. These results show how flapping kinematics can be used to control locomotion within wakes, and that flow interactions provide a mechanism which promotes group cohesion.

Adult spinal motoneurons change their neurotransmitter phenotype to control locomotion

A particularly essential determinant of a neuron’s functionality is its neurotransmitter phenotype. While the prevailing view is that neurotransmitter phenotypes are fixed and determined early during development, a growing body of evidence suggests that neurons retain the ability to switch between different neurotransmitters. However, such changes are considered unlikely in motoneurons due to their crucial functional role in animals’ behavior. Here we describe the expression and dynamics of glutamatergic neurotransmission in the adult zebrafish spinal motoneuron circuit assembly. We demonstrate that part of the fast motoneurons retain the ability to switch their neurotransmitter phenotype under physiological (exercise/training) and pathophysiological (spinal cord injury) conditions to corelease glutamate in the neuromuscular junctions to enhance animals’ motor output. Our findings suggest that motoneuron neurotransmitter switching is an important plasticity-bestowing mechanism in the reconfiguration of spinal circuits that control movements.