A chronically implanted delivery system of drugs to a nerve-end neuroma: effects on a behavioural chronic pain model

Autotomy has been suggested as an animal model of chronic pain. It starts about a week or two postoperatively and develops until 10 weeks after nerve section. This behaviour is thought to be triggered by activity of sensory fibres ending in a neuroma. Here we suggest to utilize it in combination with a novel drug delivery system which enables a direct and exclusive access of the drug to the neuroma. Alteration in the autotomy behaviour can then be related to the exclusive topical action on the sensory fibres within the neuroma. The sciatic nerve is transsected and its proximal end inserted into a PE tube sealed distally. A second, smaller tube originates in a wound exit in the back of the animal and subcutaneously leads into the large tube, where it is fixed by glue to the inner wall. Thus, the end of the smaller tube is juxtaposed to the nerve end. During the following weeks a neuroma develops within the tube. The resulting autotomy scores are then examined weekly. At various times after the operation, under light anaesthesia, drugs can be injected into the tube and the effect on the autotomy behaviour is monitored. An example is given, describing the autotomy suppressive effects of glycerol and alcohol, injected to different groups of rats immediately after the operation and compared to an injection 14 days postoperatively. This method is suggested as a pharmaco-behavioural assay for the assessment of the analgetic efficacy of drugs for chronic pain.