The effect of progesterone on expression and development of neuropathic pain in a rat model of peripheral neuropathy.

Neuropathic pain results from lesions or diseases affecting the somatosensory system. The management of patients with chronic neuropathic pain remains a challenge. Several studies support the crucial role of neuroactive steroids in the modulation of pain. The present study was designed to investigate the effect of systemic administration of progesterone on expression and development of hyperalgesia and allodynia scores in chronic constriction injury model of neuropathic pain in rat. Progesterone at doses of 5, 10 and 15 mg/kg and its vehicle were injected intraperitoneally on days 1-13 after the surgery to study the effect of progesterone on development of neuropathic pain and only on 14th day post-surgery in order to assess its effect on expression of neuropathic pain.The chronic administration of progesterone significantly reduced the behavioral scores of cold- and mechano-allodynia and heat hyperalgesia but single dose of progesterone did not have any effect on behavioral scores of neuropathic pain. Our data indicate that the early chronic administration of progesterone prevents the development of neuropathic pain but its acute injection does not change the expression of neuropathic pain. These results suggest that progesterone could be considered as a new approach for management of neuropathic pain.