Abstract
In the unanesthetized spinal cat i.v. injection of apomorphine depressed transmission of the monosynaptic reflex from extensor, flexor and dorsal root afferent sources. Polysynaptic discharges evoked from cutaneous afferents and from high threshold muscle afferents were effectively reduced as was the dorsal root reflex. Spontaneous and reflex activation of flexor efferents were initially depressed, then excited at higher concentrations of the drug. The effect of apomorphine is direct and not associated with the release of endogenous catecholamines since pretreatment with reserpine and a-methyl-p-tyrosine did not prevent its action. Haloperidol blocked the depressant effect of apomorphine whereas phenoxybenzamine, chlorpromazine and propranolol did not. It is concluded that apomorphine—claimed to act on central dopamine receptors—exerts distinct effects on spinal cord activity which are only in part similar to those of dopamine.
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