Experimental scrapie in rats: first electrophysiological observations.

Scrapie was transmitted (1st passage) to various strains of rats through intracerebral (IC) inoculation of sheep-scrapie, mouse-scrapie and hamster-scrapie brains. For the 2nd passage, Wistar rats were chosen and inoculated IC with rat-scrapie brain from the 1st passage. Three groups of 12 rats were considered (S for sheep, M for mouse, H for hamster). Electrodes were chronically implanted for EEG recording. From 100 to 110 days after inoculation, EEG abnormalities were observed, consisting of spindle-shaped bursts of diphasic spikes sporadically occurring during quiet wakefulness. Between 130 and 230 days, EEG signs diversified and became more pronounced. Simultaneously, changes occurred in the sleep-wakefulness cycle: active wakefulness decreased and was replaced by quiet wakefulness (rats were motionless , as if prostrate ). Slow wave sleep diminished, giving way to an unstable low voltage sleep. EEG disturbances clearly preceded the onset of the clinical signs (the latter appearing at about the 8th month). The disease was fairly similar in the S, M and H groups. The interest of the experimental scrapie rat model is discussed in the framework of current research on the neurophysiology of the subacute spongiform encephalopathies.