Peripheral and brainstem auditory function in paroxysmal (px) White Leghorn chicks.

The paroxysmal (px) chick is a mutant White Leghorn (Gallus domesticus) which appears normal at hatching and during the subsequent week. By ca. 8 days posthatching, various symptoms develop, of which the most obvious are depressed food intake (anorexia) and audiogenic seizures. Histological evidence suggests that central auditory and vestibular nuclei and fiber tracts begin to degenerate prior to seizure onset. This degeneration, which affects central and peripheral components of both systems, becomes increasingly severe over time although auditory stimulation continues to elicit seizures. Characterization and analysis of peripheral and brainstem auditory response to auditory stimuli indicated that major response differences between px and normal chicks exist in peaks reflecting brainstem activity (P3A, P3B, P4A, P5A). In 5 of 8 px chicks, these later response peaks were either grossly abnormal in terms of amplitude and latency (including amplitude input/output functions) or often entirely absent. Early peaks (P1A and P2A), however, in px waveforms were normal in morphology and amplitude, indicating normal function of peripheral auditory structures. Although lower body temperature of px chicks may account for some of the longer latencies observed, other abnormalities (e.g. absence of peaks) could not be produced in normal birds by induced hypothermia.