The role of noradrenergic neurons in morphine analgesia

The role of noradrenergic neurons in morphine analgesia has been studied in tail-flick test of rats with pharmacologic manipulations of the monoamine system. Pretreatment with alpha-methyl-DOPA, the precursor of the false noradrenergic transmitter alpha-methyl-noradrenaline, abolished the reserpine antagonism to morphine analgesia. The morphine analgesia manifested in this condition could be blocked by bilateral dorsolateral fuiculus lesion at T2 spinal level, while it remained intact after dorsal columnlesion at the same level, indicating that the analgesia was mediated by descending inhibition via dorsolateral funiculus. Since alpha-methyl-noradrenaline is resistant to reserpine depletion as demonstrated by our fluorescence histochemical study, we favour a major role of noradrenergic neurons in morphine analgesia.