The effect of caffeine on the spinal reflexes in warm-blooded animals

Summary

The effect of the intravenous injection of caffeine upon flexor and extensor reflexes and reciprocal inhibition was studied on spinal cats. The change of the motor cell excitability was investigated by their direct stimulation with the aid of microelectrodes inserted into the gray matter of the spinal cord. Caffeine provokes biphasic changes in the reflex responses, i.e., the initial brief intensification of the reflexes is replaced by their more prolonged depression. Reciprocal inhibition decreases at the phase of reflex intensification, and increases during the depressive action of caffeine. Caffeine raises the motor cell excitability in the spinal cord, which increase remains manifest during the depression of the reflex responses. This leads to the conclusion that the reflex activity depression during the second phase of caffeine action is caused not be reduced excitability of the motor cells, but by the latered condition of the synaptic transmission of excitation, or by the functional changes developing in the intercalary neurons.