Effects of Glucocorticoids on C-Fos Express in a Subpopulation of Spinal Cord Neuronsof Rats Following Formalin-Induced Inflammation

Objective To supply morphological data for the actions of GCS on neurons.Methods Animal behavior observation,immunohistochemical neurons staining and norphometry were used in this study.Results The Sprague-Dawley rats were injected with 20 microliters of 2.5% formalin subcutaneously into the right hindpaw to induce acute continuous inflammation near the area of injection.After one hour the total number of Fos-like immunoreactive (Fos-LI) neurones in the ipsilateral lumbar spinal cord (segments L 4～L 5 )was significantly increased,which were predominantly located in the dorsal horn superficial layers( laminaeⅠ～Ⅱ).Fos-LI was sparse in the contralateral spinal cord.Pre-administered dexamethasone (0.05,1.00 and 5.00 mg/kg i.p.) dose-dependently reduced the total number of Fos-LI neurons more significantly in the dorsal horn superficial layers than in other areas.The total number of c-Fos-LI neurones in the ipsilateral lumbar spinal cord were positively correlated with the peripheral oedema and pain.The effects of GCS can be partly reversed by glucocorticoid receptor blocking agent RU 486.Conclusion ①The expression of c-fos in the dorsal horn of the spinal cord is in relation to peripheral noxious stimuli.②GCS had different effect of excitability on subpopulations of spinal neurons