Noradrenaline-mediated Differential Modulation of Cerebellar Module Activity during Locomotion

Abstract

The cerebellum is known for its role in maintaining coordinated motor movements. As the sole output of the cerebellum, the Purkinje cell (PC) is crucial for its role in gait, foot stride, limb trajectory, and balance. PCs were considered as homogeneous entities due to their cytoarchitecture, however, recent reports state that molecular identities and electrophysiological properties differ between zebrin II modules. Nonetheless, all cerebellar PCs have identical local synaptic circuits, as well as receiving noradrenergic inputs originating from the locus coeruleus (LC). The LC-noradrenaline (NA) circuit is active during motor behavior and give input to the cerebellum, but how NA contributes to cerebellar PC output and effect motor behavior remains unresolved. Here, we perform in vivo single-unit recordings of PCs from awake behaving mice along with pharmacological approaches and behavioral motion analysis to investigate how NA effects PCs across zebrin modules. Interestingly, we find that only PC modules expressing zebrin (Z+) have increased simple spike (SS) activity, while zebrin non-expressing (Z−) PCs have non-responsive ii SS activity during locomotion. This modulation of PC SS output in Z+ modules during locomotion was insubstantial by destroying the LC terminal or by local inhibition of adrenergic receptors (ARs) in the cerebellum. However, behavioral motion analysis show that blocking the noradrenergic neuromodulation of SS activity across zebrin positive PCs disrupt forelimb stride motion in DSP-4 injected mice but not in mice which were given acute local topical application of adrenergic receptor antagonist cocktail. To investigate the mechanism of SS enhancement of Z+ PCs, we examined the effect of α2-ARs on molecular layer interneurons (MLIs). Previous in vitro experiments have shown that MLIs contain α1 and α2-ARs which dual modulate MLI firing activity upon activation. In vivo MLI recordings from Z+ and Z− modules show that blockade of α2-ARs does not alter the firing frequency during locomotion in comparison to control. Next, we examined the effects of ARs on PCs. Blocking α2-ARs did not show any differences compared to control, but inhibition of β2-ARs located on PCs may modulate the SS of PC output in Z+ modules. Altogether, these findings show that NA acts as a neuromodulator in the cerebellum which modulates SS output of PCs in Z+ modules possibly via β2-ARs of PCs.