Accelerated loss of motor neurons in the brachial lateral motor column in muscular dystrophic chicks.

We have examined the development of the brachial lateral motor column in White Leghorn chickens that are homozygous for muscular dystrophy. We found an accelerated loss of motor neurons between days 6 and 11 in ovo in the dystrophic embryos such that at the end of this time they had only 80% of the population in age-matched controls. After day 11 in ovo the rate of motor neuron loss was the same in both normal and dystrophic birds. To determine whether the accelerated motor neuron loss was due to expression of the dystrophic gene within the spinal cord itself or whether it was secondary to abnormalities in some other tissue, we exchanged the brachial region of the spinal cord between normal and dystrophic embryos at 2 days in ovo, allowed the resulting chimeras to develop until 11 days in ovo and estimated the motor neuron population in the transplanted segment of cord. We found that spinal cords transplanted into normal hosts had significantly higher populations of motor neurons than spinal cords transplanted into dystrophic hosts. We concluded that the accelerated motor neuron loss seen in dystrophic birds is not intrinsic to the cord but is influenced by other tissues in the embryo.