Astrocyte activation in the anterior cingulate cortex and altered glutamatergic gene expression during paclitaxel-induced neuropathic pain in mice
Spinal astrocyte activation contributes to the pathogenesis of paclitaxel-induced neuropathic pain (PINP) in animal models. We examined gene expression of glial fibrillary acidic protein (GFAP; an astrocyte marker), glutamate transporters and receptor subunits in the anterior cingulate cortex (ACC) by real time PCR at 7 days post first administration of paclitaxel, a time point when mice had developed thermal hyperalgesia. Changes in the ACC, an area in the brain involved in pain perception and modulation, might contribute to the pathophysiology of PINP. GFAP transcripts levels were elevated by more than fivefold in the ACC of paclitaxel-treated mice. The 6 glutamate transporters (GLAST, GLT-1 EAAC1, EAAT4, VGLUT-1 and VGLUT-2) quantified were not significantly altered by paclitaxel treatment. Of the 12 ionotropic glutamate receptor subunits transcripts analysed 6 (GLuA1, GLuA3, GLuK2, GLuK3, GLuK5 and GLuN1) were significantly up-regulated, whereas GLuA2, GLuK1, GLuK4, GLuN2A and GLuN2B were not significantly altered and GLuA4 was lowly expressed. Amongst the 8 metabotropic receptor subunits analysed only mGLuR 8 was significantly elevated. In conclusion, during PINP there is astrocyte activation, no change in glutamate transporter expression and differential up-regulation of glutamate receptor subunits in the ACC. Thus, targeting astrocyte activation and the glutamatergic system might be another therapeutic avenue for management of PINP.