Freely behaving mice can brake and turn during optogenetic stimulation of the Mesencephalic Locomotor Region

Abstract

AbstractBackgroundStimulation of the Mesencephalic Locomotor Region (MLR) is increasingly considered as a target to improve locomotor function in Parkinson’s disease, spinal cord injury and stroke. A key function of the MLR is to control the speed of forward symmetrical locomotor movements. However, the ability of freely moving mammals to integrate environmental cues to brake and turn during MLR stimulation is poorly documented.Objective/hypothesisWe investigated whether freely behaving mice could brake or turn based on environmental cues during MLR stimulation.MethodsWe stimulated the cuneiform nucleus in mice expressing channelrhodopsin in Vglut2-positive neurons in a Cre-dependent manner (Vglut2-ChR2-EYFP) using optogenetics. We detected locomotor movements using deep learning. We used patch-clamp recordings to validate the functional expression of channelrhodopsin and neuroanatomy to visualize the stimulation sites.ResultsOptogenetic stimulation of the MLR evoked locomotion and increasing laser power increased locomotor speed. Gait diagram and limb kinematics were similar during spontaneous and optogenetic-evoked locomotion. Mice could brake and make sharp turns (∼90⁰) when approaching a corner during MLR stimulation in an open-field arena. The speed during the turn was scaled with the speed before the turn, and with the turn angle. In a reporter mouse, many Vglut2-ZsGreen neurons were immunopositive for glutamate in the MLR. Patch-clamp recordings in Vglut2-ChR2-EYFP mice show that blue light evoked short latency spiking in MLR neurons.ConclusionMLR glutamatergic neurons are a relevant target to improve locomotor activity without impeding the ability to brake and turn when approaching an obstacle, thus ensuring smooth and adaptable navigation.Highlights-Mice brake and turn when approaching the arena’s corner during MLR-evoked locomotion-Speed decrease is scaled to speed before the turn during MLR-evoked locomotion-Turn angle is scaled to turn speed during MLR-evoked locomotion-Gait and limb kinematics are similar during spontaneous and MLR-evoked locomotion