Effects of cysteamine on flexion reflex facilitation by C-primary afferents in cats

Brief (20 s) conditioning stimuli at C-fiber intensity applied to the sural or gastrocnemius nerve evoked a facilitation of the flexor alpha-motoneurone discharges from small filaments of the posterior biceps semitendinosus nerve produced by subcutaneous stimulation of the plantar region in anesthetized spinal cats. Such C afferent-induced facilitation was blocked reversibly by cysteamine (50 mg.kg-1), a somatostatin depletor, without affecting the basic mechanisms of flexor reflexes, suggesting an important role played by somatostatin in transmission and/or modulation of nociceptive information in the spinal cord.