NEURONS EXHIBITING ANTI-MOTOR ACTIVITY IN THE <EM>XENOPUS</EM> <EM>LAEVIS</EM> TADPOLE HINDBRAIN

Neural circuits function in a state-dependent manner. For example, motor outputs to the same sensory input can vary depending on the animal’s current behavioural state: sleep vs wakefulness, hunger vs satiety, movement vs rest. The mechanisms for locomotion initiation, maintenance and cessation have been studied extensively. In contrast, neurons active at rest and those involved in inducing and maintaining a state of immobility remain poorly understood. Previous whole-brain imaging experiments identified cell clusters in the Xenopus laevis tadpole hindbrain exhibiting anti-motor activity i.e., activity negatively correlated with fictive locomotion. To investigate this further, we employ calcium imaging, whole-cell patch-clamp electrophysiology and anatomical staining to study these cells’ activity, morphology and potential roles in motor/behavioural state control. Using epifluorescence GCaMP6s calcium imaging, we found cells in the ventral-rostral hindbrain with high baseline activity at rest. During fictive swimming, their activity decreased and slowly returned to baseline after locomotion termination. Guided by their calcium activity, whole-cell patch-clamp recordings were made to characterise these neurons’ firing patterns during swimming and resting states. Neurobiotin staining then revealed their morphology and axonal projection patterns. Our results elucidate the properties of a cell type potentially involved in setting the resting state in a simple vertebrate.