The significance of intrathecal catheter location in rats

Although chronic intrathecal catheterization is a widely used method in rats, few calibration experiments have been performed. In this study, we investigated the correlation between the side position of the catheter tip and the side differences observed in the motor and sensory disturbances after intrathecal administration of lidocaine to a large number of rats. The existence of a sensory block was determined by the paw withdrawal test. The motor impairment was assessed by observing the complete clubbing of the hindpaw and measuring the hindpaw grip strength. After experimental use, we established the position of the catheter tip. The catheter tips were variously located in all directions of the transverse plane in the rat spinal subarachnoid space. Lidocaine administration (100 or 500 microg/5 microL; n = 264 and 112, respectively) led to dose-dependent motor and sensory disturbances. The effect of 100 microg of lidocaine exhibited side differences; i.e., the extents of both motor (r = 0.77) and sensory (r = 0.60 and r = 0.67 for the right and the left side, respectively) disturbances correlated significantly with the location of the catheter tip. Our data have shown that detection of the paralytic and/or antinociceptive effect of small-dose lidocaine before planned experiments is a simple and reliable method for prediction of the location of the catheter tip. We suggest that the position of the catheter might cause side differences in the drug effect, especially if small doses of drugs are administered and their effects are investigated on both sides.