Horseradish peroxidase retrograde labeling of primary sensory axons in therat: a comparison between three different intraspinal injection methods

Study aim: In order to improve the results of intraspinal retrograde labeli ng of post-ganglionic primary sensory axons by horseradish peroxidase (HRP) , the authors compared three different intraspinal injection methods of thi s tracer into the inferior thoracic spinal cord in the rat. Material and method: 'Open field' method (group 1, N = 8); stereotactic inj ection, needle tip diameter = 0.72 mm (group 2, N = 8); stereotactic inject ion, needle tip diameter = 0.24 mm (group 3, N = 8). Histological features of the spinal injection site showed that tissue damages due to injection wa s more extensive and deeper than expected. HRP transported in retrograde fa shion from injection site to sensory body cells located in dorsal root gang lia (DRG) was revealed by the Mesulam histochemical technique. Results: The mean number of labeled neurons per DRG was 652 in group 3, 116 in group 2, and 77 in group 1. Differences were statistically significant, especially between groups 1 and 3 (P = 4.10(-16)) and groups 2 and 3 (P = 2.10(-17)). Conclusion: Retrograde labeling of primary sensory axons by HRP (or another axonal tracer) with fine needle stereotactic intraspinal injection may rep resent an alternative to anterograde labeling. This reliable and reproducib le method may be useful in studies dealing with regeneration of post-gangli onic primary sensory axone. (C) 2000 Editions scientifiques et medicales El sevier SAS.