SPINAL MUSCULAR-ATROPHY IN HOLSTEIN-FRIESIAN CALVES

The clinical and neuropathological findings of spinal muscular atrophy (SMA) in Holstein-Friesian calves are described in four females and o ne male from a dairy farm composed of 150 cows and 2 breeding bulls. L ocomotion difficulties started at the age of 15 days, and progressed t o paraparesis and tetraparesis in 2 weeks. Signs consistent with dener vation were revealed with electromyography. The neuropathological exam ination showed degeneration and loss of motor neurons in the spinal co rd, together with astrocytosis. Among the remaining motor neurons were ghost cells and neurons filled with accumulations of straight filamen ts measuring 10-12 nm in diameter, which were strongly immunoreactive with antibodies produced against phosphorylated neurofilaments. Degene rating cells in SMA did not stain with the method of in situ labelling of nuclear DNA fragmentation and did not show c-Jun immunoreactivity. This feature contrasts with the in situ labelling of DNA breaks of ap optotic cells and with the strong c-Jun immunoreactivity restricted to dying cells during the whole process of naturally occurring cell deat h in the developing central nervous system. These features suggest tha t cell death in SMA differs from programmed cell death during normal d evelopment, and that pathological cell death in SMA should not be cons idered as a mere persistence or reactivation of normally occurring dev elopmental cell death.