Behavioural measures of depression and anxiety in rats with spinal nerve ligation-induced neuropathy

The behaviour of rats with spinal nerve ligation-induced neuropathic pain w as studied using tests developed to measure depression and anxiety. Adult m ale Sprague-Dawley rats were tested with the open held test, elevated plus maze, two compartment test and forced swimming test. Spontaneous motility w as measured in a photocell observation box. Mechanical sensitivity was test ed with von Frey hairs and cold sensitivity with the acetone drop test. The L5-6 spinal nerves were ligated or a sham operation was performed and the rats were followed for 2 weeks before the same set of tests were repeated. Most of the neuropathy operated rats had mechanical and cold allodynia. Wit h post-injury there was a significant decrease in the activity in the open field test and motility box tests, when compared with the pre injury result s. In the elevated plus maze test there was a significant reduction in the motility, but there was no change in the time spent in the closed wings. In the two compartment test there were no significant differences between the pre- and post-injury results. There were no differences between the rats w ith spinal nerve ligation injury and the sham operated rats in any of the t ests. The results were also comparable when rats that developed a high degr ee of neuropathy were compared with the rats with low degree of neuropathy and the sham operated group. In conclusion, spinal nerve ligation injury of the spinal nerves L5-6 induces mechanical and cold allodynia, but it does not seem to produce general suffering or measurable anxiety to the animals. Furthermore, tests for anxiety and depression were not able to predict whi ch animals were vulnerable to express symptoms of neuropathic pain after ne rve injury. (C) 1999 International Association for the Study of Pain, Publi shed by Elsevier Science B.V.