Auditory and vestibular pathology of seizure-prone chicks.

The mutant sex-linked lethal recessive px (paroxysmal) gene, expressed in White Leghorn chicks (Gallus domesticus) causes seizures beginning on approximately day 8 post-hatching. Seizures are spontaneous and inducible by auditory but not by photic stimulation. Prior to seizure onset px chicks are indistinguishable from non-px siblings. With seizure onset is a decrease in food intake which causes deterioration and death by 4-10 weeks of age. In a preliminary histological study conducted on 22-day-old seizure-prone chicks, brains were perfused and sections treated according to a modified cupric-silver staining technique. Nuclei and fiber tracts of px auditory and vestibular systems were extensively degenerated; control brains showed essentially no degeneration. A second experiment was conducted with preseizure chicks to determine whether and to what extent degeneration occurs prior to seizure onset. Deep nuclei of px cerebellum appeared to be the first seriously affected (5 days of age). Extent of degeneration progressed steadily over time through 20 days of age, by which time all components of the two sensory systems were maximally affected. Ambient noise did not affect onset or extent of degeneration, nor did it affect onset of seizures.