Multiunit activity patterns in the brachial spinal cord of dystrophic chick embryos

Impaired muscle-nerve interaction (motility) characterizes the brachial region of dystrophic embryos

During development ex ovo, the avian mutant with an hereditary form of muscular dystrophy demonstrates biochemical, histochemical, and physiological (functional) abnormalities which may result from impaired muscle-nerve interaction. To investigate if impaired functional activity also characterizes the dystrophic process during development in ovo, limb motility, an index of embryonic functional muscle-nerve interaction, was compared between normal and dystrophic embryos from day 6E through day 16E. A highly significant reduction in this parameter was exhibited by dystrophic wings from day 11E to day 14E inclusive. In contrast, genotypically dystrophic hind limbs demonstrated values equivalent to normal legs. Thus, in the dystrophic embryo, impaired muscle-nerve interaction characterized the brachial region exclusively during a specific period of embryogenesis.

Developmental neuron cell death in dystrophic and normal chickens

The numbers of motoneurons in the brachial lateral motor columns were determined from the 6th embryonic day through the 5th week posthatching in age-matched dystrophic and normal chickens. The overall magnitude of cell loss was not significantly different between the dystrophic and normal strains. However there was a trend toward more motoneurons in the brachial lateral motor columns of dystrophic embryos and posthatch chickens which was found to be statistically significant at the 8th and 9th days of embryonic life. These observations are taken to suggest that, in addition to strain differences unrelated to the dystrophic gene, there may exist a temporal delay in developmental neuron cell death in dystrophic chick embryos that may be secondary to the primary defect within the dystrophic muscle.

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.

Development and growth of extensor carpi radialis longus muscle in normal and dystrophic chickens

The development and growth of the skeletal muscles in normal and dystrophic chickens were studied to obtain a clue to the mechanism of dystrophic pathogenesis. A relatively small and isolated muscle--the extensor carpi radialis longus (ECRL) muscle--was utilized to analyze quantitatively the histologic and physiologic parameters. Both normal and dystrophic chickens attained qualitatively the same parameters, but there were some quantitative differences. The first disorder to appear in the dystrophic muscle was a substantial retardation of muscle cell proliferation in the early postnatal development, and the fiber loss was fully compensated by hypertrophy of the remaining cells. The succeeding abnormalities in the dystrophic muscle, e.g., reduction of efficiency in the tension output per unit area, were interpreted as compensating reactions. Therefore, it is likely that the dystrophic lesions in avian muscular dystrophy are caused by retardation of muscle cell proliferation in the early postnatal period. Possible mechanisms for the retardation are discussed in terms of the nerve--muscle trophic interactions which could be greatly intensified in the early postnatal period.

Chicken muscular dystrophy: an inherited disorder of flight

Dystrophic (University of California, Davis, line 413) and normal control (Davis, 1. 412) chicks (Gallus domesticus) between 7 and 49 days old were tested for flight-related pathology and righting ability. Drop-evoked lateral flight developed in control chicks between 7 and 13 days. Dystrophic chicks never developed lateral flight. Both dystrophic and control chicks showed drop-evoked wing-flapping on the day of hatching. Also, dystrophic chicks had a normal but slightly higher drop-evoked flapping rate than controls at 13 days. Thus, the neural circuits that initiated and generated the rate of drop-evoked wing-flapping, present in dystrophic chicks at birth, were intact at 13 days, when deficiencies in lateral flight and righting ability were already present. The righting behavior of control chicks was superior to that of dystrophic chicks at all ages from 7 to 49 days.

Creatine kinase isozyme transition in chicks with hereditary muscular dystrophy

In both normal chicks and chicks with hereditary muscular dystrophy the BB (brain) and MB (hybrid) isozymes were the predominant forms of creatine kinase (CK) activity in embryonic skeletal muscle. As myogenesis progressed, activity due to the MM (muscle) isozyme progressively increased, and by 1 week ex ovo, the MM isozyme accounted for approximately 97% of total muscle activity in both genotypes. During this time, the proportion of the MM isozyme was slightly but significantly lower in dystrophic muscles. After hatching the proportion of the MB isozyme and its total activity decreased in normal muscle, but increased in dystrophic pectoral muscle, and by 5 months ex ovo, the MB isozyme accounted for 10% of total CK activity. Prior to hatching there was no consistent difference in total CK activity between normal and dystrophic tissues, but by 1 week after hatching and thereafter, total CK activity was significantly lower in dystrophic pectoral muscle.