Excitatory amino acids increase glycogen phosphorylase activity in the rat spinal cord.

Glycogen phosphorylase is present in nervous tissue in an active and inactive form. Using a histochemical technique, an investigation into which putative neurotransmitters have the capacity to modify the activity of the enzyme, has been performed on the rat spinal cord. Intrathecal injections of L-glutamate and L-aspartate elevate glycogen phosphorylase activity in the dorsal horn, while substance P has no effect and only high doses of adenosine triphosphate (ATP) increase the enzyme activity. In addition the N-methyl-D-aspartate receptor antagonist, 5-amino-phosphonovaleric acid was found to block the elevation of glycogen phosphorylase activity in the dorsal horn produced by the peripheral activation of chemo-sensitive primary afferents. Excitatory amino-acid neurotransmitters can therefore, acting via second messengers and protein kinases, modify glycogen metabolism in the spinal cord.