Differential sensory and motor blockade after spinal cocaine in the rat and marmoset.

Various concentrations of local anaesthetic agents have been injected into the rat and marmoset via a chronically implanted cannula in the subarachnoid space. In the rat, cocaine at a concentration of 0.125% produced analgesia without motor blockade whereas higher concentrations produced motor blockade in some animals. No clear differentiation could be shown with any concentrations of lignocaine or bupivacaine. In the marmoset, 0.125% cocaine resulted in sensory block in four out of five marmosets without motor blockade, whereas 0.25% cocaine produced motor block in two out of four marmosets. It would appear that differential blockade of sensory function without motor loss can be achieved by cocaine. New local anaesthetics based on cocaine or similar chemical structures would seem potentially valuable.