Botulinum Toxin Type A Attenuates Activation of Glial Cells in Rat Medullary Dorsal Horn with CFA-induced Inflammatory Pain

ABSTRACT

The activation of glial cells in the spinal cord has been contribute to the initiation and maintenance of pain facilitation induced by peripheral inflammation and nerve injury. The present study investigated effects of botulinum toxin type A (BoNT-A), injected subcutaneously or intracisternally, on the expression of microglia and astrocytes in rats. Complete Freund's Adjuvant (CFA)-induced inflammation was employed as an orofacial chronic inflammatory pain model. A subcutaneous injection of 40 microL CFA into the vibrissa pad was performed under 3% isoflurane anesthesia in SD rats. Immunohistochemical analysis for changes in Iba1 (a microglia marker) and GFAP (an astrocyte marker), were performed 5 days after CFA injection. Subcutaneous injection of CFA produced increases in Iba1 and GFAP expression, in the ipsilateral superficial lamia I and II in the medullary dorsal horn of rats. Subcutaneous treatment with BoNT-A attenuated the up-regulation of Iba1 and GFAP expressions induced by CFA injection. Moreover intracisternal injection of BoNT-A also attenuated the up-regulated Iba1 and GFAP expressions. These results suggest that the anti-nociceptive action of BoNT-A is mediated by modulation activation of glial cells, including microglia and astrocyte.