Parietal Block Using Bupivacaine in the Rat: An Anatomical, Behavioral and Histological Study.

Purpose: Animal models of regional anaesthesia are useful for studying the effects of blocks and improve their efficacy. The aim of our experiments was to validate a multi-site paravertebral block in the rat. Material and methods: Dissection and indigo carmine dye injection were performed in five rats (3 rats were dissected and 2 were dye injected). In other groups (n=7rats/group), after inflammation inductive carrageenan injection in the abdominal wall, bupivacaine or saline was injected laterally to the spinal column at the T5, T10, L1, L4 and S1 level. The efficacy of the block on mechanical nociception was measured using von Frey hairs. In addition, we measured c-Fos immunoreactive nuclei in the cord. Results: The multi-site injection showed a perinervous distribution of the injected solution without intra-thoracic, intra-abdominal or epidural diffusion. Bilateral block with a relatively small volume of bupivacaine (0.5 mL) significantly increased the threshold to mechanical pain as compared to control (p=0.007) and significantly decreased the number of c-Fos immunoreactive nuclei in the posterior horn of the spinal cord (p<0.0001). Conclusion: This study shows that a parietal abdominal wall block is easy to perform in the rat. This block allows investigators to explore the mechanisms of action of abdominal parietal wall blocks.