LUMBAR CATHETERIZATION OF THE SPINAL SUBARACHNOID SPACE IN THE RAT

The method commonly used for catheterization of the lumbar subarachnoi d space in the rat implies inserting the catheter through the atlanto- occipital (A-O) membrane and moving the catheter caudally along the sp inal cord. The method is associated with a considerable morbidity. A m ethod for direct catheterization of the lumbar subarachnoid space was therefore developed. Major surgery was avoided by using a catheter-thr ough-needle technique. Of 32 rats, none died. There were no signs of n eurological disturbances, and all animals gained weight as normal the first week after implantation. Data from rats catheterized by the A-O method were used for comparison. Of 40 animals, 2 died, 11 showed sign s of neurological disturbances, and the mean weight was reduced during the first week after catheterization. The two groups of animals showe d different behavioural responses to intrathecal injection of N-methyl -D-aspartate (NMDA, 0.1-1.6 mM, 15 mu l) which is thought to stimulate afferent pathways mediating nociception. Animals with a lumbar cathet er showed licking, biting and scratching behaviour in a dose-related m anner for concentrations up to 1.6 mM. The animals with A-O catheters showed a maximum level of this behaviour already at 0.4 mM, while 0.5 mM induced convulsions. A possible explanation of this difference in r esponse to NMDA could be a long-lasting pain state in the A-O group, c aused by catheter-induced changes in the spinal cord and by the extens ive surgery. It is concluded that the direct lumbar catheterization ha s several advantages compared to the A-O method, decreasing the suffer ing of the animals, the neurological disturbances and the interference with nociceptive functions of the spinal cord.