Exp Neurobiol 8:99-105, 1999

Differential Effects of Intraganglionic Capsaicin and Vehicle on Substance P- and CGRP-immunoreactive Neurons in the Rat Dorsal Root Ganglia.

Won Taek Lee, Ho Yoon, Eun Jung Lee, Sung Ho Lee, Kyung Ah Park, Jong Eun Lee

Department of Anatomy, Yonsei University College of Medicine, Seoul, Korea.


To investigate the morphological effect of direct ganglionic injection of capsaicin, changes of number and size distribution of neurofilament-, substance P- and CGRP-immunoreactive neurons were investigated by immunohistochemical methods.
Twenty adult Sprague-Dawley rats were used for this study. 25 l of capsaicin in 5 l vehicle (Tween 80, ethanol, saline mixture) were injected to L5 ganglion and 5 l vehicle were injected to the contralateral L5 ganglion. For experimental control, 5 l vehicle were injected to L5 ganglion and sham operation procedures were done at the contralateral side. After immunohistochemical staining, count and measure the area of the neurofilament-, substance P- and CGRP-immunoreactive cell bodies of dorsal root ganglion have been done by image analyzer. Statistical analysis of the data has been done. Number and size distribution of neurofilament immunoreactive large neurons were not changed statistically. Number of substance P and CGRP immunoreactive neurons of direct capsaicin treated rats were decreased compared to vehicle treated and control rats. Small substance P and CGRP immunoreactive DRG neurons were more decreased in direct capsaicin treated rats. Vehicle of capsaicin also slightly decreased the number of substance P and CGRP immunoreactive neurons, but cell size distribution was not changed. Degenerative figures were found in dorsal root ganglion after both capsaicin and vehicle injection.
In conclusion, direct ganglionic injection of capsaicin decreases substance P and CGRP immunoreactive neurons, especially small sized neuron. Vehicle (Tween 80, ethanol, saline mixture) also decreases substance P and CGRP immunoreactive neurons, but non specific manner. Capsaicin degeneration is limited to selective population of dorsal root ganglion neuron even after intraganglionic capsaicin injection.

Key Words: dorsal root ganglion, capsaicin, neurofilament, substance P, CGRP