Triphenyl phosphite-induced neuropathy in the avian forebrain: a silver impregnation study of the visual and auditory systems of the Japanese quail.

Single subcutaneous injections of triphenyl phosphite (TPP) (62.5-500 mg/kg body weight) were made in the Japanese quail (Coturnix coturnix japonica). The extent and density of resultant central nervous system degeneration were mapped by using the Fink-Heimer silver impregnation method to selectively impregnate degenerating axons and terminals. In addition to resulting in degeneration in the medulla and cerebellum, exposure to TPP also resulted in axonal and terminal degeneration in specific midbrain and forebrain nuclei and tracts related to the auditory and visual systems. Auditory system nuclei containing axonal and terminal degeneration included the lateral mesencephalic nucleus, pars dorsalis, the nucleus ovoidalis, and area L of Rose in the caudal neostriatum. Anterograde degeneration was also noted in nuclei and tracts related to the visual tectofugal system-the brachium of the superior colliculus, nucleus rotundus, pretectal nuclei, and the ectostriatum. Additional degeneration was noted in the paleostriatum primitivum, dorso-intermediate posterior thalamic nucleus, lateral spiriform nucleus, and the pedunculopontine tegmental nucleus, all of which are related to visuomotor control. These results indicate that in the Japanese quail, exposure to TPP yields anterograde degeneration in nuclei and tracts involved with the transmission and processing of higher order visuomotor, visual sensory, and auditory sensory information.