Modulation of neuronal excitability is a prominent way of shaping the activity of neuronal networks. Recent studies highlight the role of calcium-activated chloride currents in this context, as they can both increase or decrease excitability. The calcium-activated chloride channel Anoctamin 2 (ANO2 alias TMEM16B) has been described in several regions of the mouse brain, including the olivo-cerebellar system. In inferior olivary neurons, ANO2 was proposed to increase excitability by facilitating the generation of high-threshold calcium spikes. An expression of ANO2 in cerebellar Purkinje cells was suggested, but its role in these neurons remains unclear. In the present study, we confirmed the expression of Ano2 mRNA in Purkinje cells and performed electrophysiological recordings to examine the influence of ANO2-chloride channels on the excitability of Purkinje cells by comparing wildtype mice to mice lacking ANO2. Recordings were performed in acute cerebellar slices of adult mice, which provided the possibility to study the role of ANO2 within the cerebellar cortex. Purkinje cells were uncoupled from climbing fiber input to assess specifically the effect of ANO2 channels on Purkinje cell activity. We identified an attenuating effect of ANO2-mediated chloride currents on the instantaneous simple spike activity both during strong current injections and during current injections close to the simple spike threshold. Moreover, we report a reduction of inhibitory currents from GABAergic interneurons upon depolarization, lasting for several seconds. Together with the role of ANO2-chloride channels in inferior olivary neurons, our data extend the evidence for a role of chloride-dependent modulation in the olivo-cerebellar system that might be important for proper cerebellum-dependent motor coordination and learning.

Cerebellar ataxias are characterized by a disturbance of motor coordination and learning. To understand the molecular mechanisms underlying especially hereditary cerebellar ataxias, many mouse models, often with altered Purkinje cell firing, have been studied in the past decades. Of particular interest were mouse lines with mutations in ion channels or their ligands. In this context, a recently described ANO2 -/mouse line has been reported to show a variety of ataxic symptoms, ranging from gait abnormalities and problems in motor coordination to severely impaired motor learning. These mice lack the calcium-gated chloride channel Anoctamin 2 (ANO2). First studies, focusing on the molecular mechanisms underlying the ataxic phenotype of ANO2 -/mice, indicate an involvement of ANO2 in two different processes in the neuronal network of the cerebellar cortex. Both mechanisms are thought to modulate the firing pattern of cerebellar Purkinje cells and could, therefore, explain the ataxic phenotype of ANO2 -/mice. This review summarizes the so far obtained data regarding the role of ANO2 in the coordination and learning of movements.