Loss of the dentate nucleus neurons is associated with torpedo formation: a morphometric study in progressive supranuclear palsy and dentatorubro-pallidoluysian atrophy

Cerebellar torpedoes can be induced by direct damage to Purkinje cell axons. This raises the possibility that the loss of dentate nucleus neurons (DNNs) may also cause torpedo formation through synaptic detachment between DNNs and Purkinje cell axon terminals. To investigate this possibility, we conducted a morphometric study with an image analyzer in progressive supranuclear palsy (PSP) and dentatorubro-pallidoluysian atrophy (DRPLA). Using horizontal and sagittal sections of the cerebellar hemispheres containing the greatest proportion of the dentate nucleus, we determined the line densities of torpedoes, Purkinje cells, and DNNs. In PSP and DRPLA, the densities of DNNs were significantly lower, and the densities of torpedoes much greater than in controls, while those of Purkinje cells were normal in both diseases. In addition, the torpedo densities in PSP and DRPLA showed a strong negative correlation with the DNN densities. Thus, this study clearly demonstrated that torpedoes are formed in association with the loss of DNNs, suggesting that they may occur in consequence of synaptic disconnection of Purkinje cells from DNNs.