Clonidine reversal of increased norepinephrine metabolite levels during morphine withdrawal.

The production of the norepinephrine metabolite 3-methoxy-4-hydroxyphenethyleneglycol (MHPG) in brain regions innervated by the locus coeruleus was increased during naloxone-precipitated withdrawal from chronic morphine treatment. This MHPG increase was reversed by subcutaneous administration of clonidine. Changes in MHPG levels paralleled the elctrophysiological changes found by Aghajanian (1978) in locus coeruleus firing rate with similar treatments, demonstrating the usefulness of MHPG changes as an index of central noradrenergic function.