Intrathecal noradrenaline has a dose-dependent inhibitory or facilitatory effect on the flexion reflex in the rat.

The effect of intrathecal noradrenaline (NA) on the hamstring flexion reflex to subcutaneous electrical shocks was examined in unanaesthetized, decerebrate, spinalized rats. Low doses of NA (200 ng and 2 micrograms) depressed and high doses (20 micrograms and 200 micrograms) facilitated the reflex. It is suggested that the primary effect of NA in the dorsal horn is inhibitory and in the ventral horn excitatory. Furthermore, the neurons mediating these effects are more sensitive to NA in the dorsal horn than in the ventral horn.