Alterations in central latency, motoneurone number and blood volume of spinal cord of the aging rat

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Abstract
Measurements were made of the central delay of the flexor reflex, the number of motoneurones in the ventral horn of the lumbar region of the cord, and the tissue blood volume of the lumbar region of the cord. There is a 50% decrease in tissue blood volume between the ages 450 and 550 days. A loss in the number of motoneurones of the cord of about 30% also occurs between the same ages. Central latency increases about 60% from a value of 3.51 msec. to 5.82 msec. between the ages 550 and 750 days. This rise in central latency takes place after the blood volume decrease and the loss in number of cells. It is suggested that the primary event in the aging of the nervous system of the white rat is a restriction of the vascular bed; with changes in latency secondary to the loss in neurones. These results are also taken as evidence that local, intrasegmental changes in the cord as well as alterations of suprasegmental downflow play an important role in aging of the spinal cord.