Ablation of TrkB from Enkephalinergic Precursor-Derived Cerebellar Granule Cells Generates Ataxia

In ataxia disorders, motor incoordination (ataxia) is primarily linked to the dysfunction and degeneration of cerebellar Purkinje cells (PCs). In spinocerebellar ataxia 6 (SCA6), for example, decreased BDNF-TrkB signalling appears to contribute to PC dysfunction and ataxia. However, abnormal BDNF-TrkB signalling in granule cells (GCs) may contribute to PC dysfunction and incoordination in ataxia disorders, as TrkB receptors are also present in GCs that provide extensive input to PCs. This study investigated whether dysfunctional BDNF-TrkB signalling restricted to a specific subset of cerebellar GCs can generate ataxia in mice. To address this question, our research focused on Trkb mice, in which the TrkB receptor was removed from enkephalinergic precursor-derived cerebellar GCs. We found that deleting Ntrk2, encoding the TrkB receptor, eventually interfered with PC function, leading to ataxia symptoms in the Trkb mice without affecting their cerebellar morphology or levels of selected synaptic markers. These findings suggest that dysfunctional BDNF-TrkB signalling in a subset of cerebellar GCs alone is sufficient to trigger ataxia symptoms and may contribute to motor incoordination in disorders like SCA6.