Postnatal changes in the termination pattern of recurrent axon collaterals of triceps surae alpha-motoneurons in the cat.
alpha-Motoneurons innervating the triceps surae and short plantar muscles were stained intracellularly with horseradish peroxidase (HRP) in 0-44-day-old kittens and adult cats. The terminal arborizations of the recurrent axon collaterals in the spinal cord were studied in the light microscope (LM). The short plantar motoneurons lacked axon collaterals in all age groups. With a few exceptions in the youngest kittens (0-1 days of age), the projection field of the axon collaterals of triceps surae motoneurons did not change during development. The exceptional motoneurons had axon collaterals projecting ventromedial to the adult termination areas in Rexed's laminae VII and IX. Within all parts of the projection field, there was a substantial postnatal reduction in the number of axon collateral swellings, interpreted as synaptic terminals, and a total elimination of short and thin axonal processes without swellings. The findings are discussed in relation to earlier demonstrated loss of synaptic terminals on the motoneurons and elimination of polyneuronal innervation of muscle fibers postnatally.
D000818:Animals; D001369:Axons / Q000502:physiology; D002415:Cats; D009046:Motor Neurons / Q000166:cytology* / Q000502:physiology; D024510:Muscle Development; D009132:Muscles / Q000294:innervation*; D009433:Neural Inhibition