Alterations of the functional properties of the parallel fibers in the cerebellum of the "scrapie mouse".

Alterations of the functional properties of the cerebellar parallel fibers have been investigated in scrapie mice by recording the compound action potential elicited by the superficial stimulation of the cerebellum. As soon as the 12th week following intracerebral inoculation, i.e. during the silent incubation period, there is a clear decrease of the response amplitude and of the recruiting properties. Depth profiles of the response indicate the progressive disappearance of the most superficial fibers. With respect to the remaining parallel fibers, the conduction velocity becomes progressively reduced, the duration of the refractory periods increases and the hyperexcitability and increased velocity characterizing the supernormal period are greatly reduced. Most of these electrophysiological alterations can be related to changes of the membrane properties and/or modifications of the metabolic processes ensuring the active ionic transport across the membrane.