The neuroanatomical basis of slow saccades in spinocerebellar ataxia type 2 (Wadia-subtype).

In a case of spinocerebellar ataxia type 2, Wadia-subtype (SCA2), with slow horizontal saccades, we used parvalbumin immunohistochemistry to identify the omnipause (OPNs) excitatory (EBNs), and inhibitory burst neurons (IBNs) of the saccade generator. Nissl sections was used to measure neuronal diameters, and synaptophysin staining to estimate of synaptic density on the cell somata. Morphometric and synaptic density measurements of the abducens motoneurons were identical in SCA2 and the control. A significant cell loss and reduced synaptic density on somata was found only in the EBN area. We conclude that degeneration of the EBNs is the most likely cause for the slowing of horizontal saccades.