THE EFFECT OF CHANGES IN THE CALCIUM CONTENT OF THE CEREBROSPINAL FLUID ON SPINAL REFLEX ACTIVITY IN THE DOG

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Abstract
The effect of changes in the Ca content of balanced salt solns. perfused through the lower spinal subarachnoid space at constant pressure and temp. was studied in barbitalized dogs with spinal cord sectioned at T10. Ca-free solns. produced an augmentation of the spinal flexion reflex, an increase in muscle tone, and spontaneous twitching of the muscles of the lower half of the body. The tetany produced by Ca-free perfusions was not due to spontaneous firing of the motoneurones nor of the dorsal or ventral rootlets. The twitching required the integrity of the spinal reflex arcs, for it disappeared when these arcs were broken. It was probably due to an increased responsiveness of the cord neurones to the normally incident afferent impulses from the periphery. Similar motor activity was seen with Na citrate perfusions, differing in that the twitching persisted, with diminution, when synaptic transmission was abolished. Citrate caused spontaneous firing of the motoneurones, or of the dorsal and ventral rootlets, or both. High Ca solns., up to 4 times normal concs., were without effect.

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