Evaluation of Formalin-Induced Pain Behavior and Glutamate Release in the Spinal Dorsal Horn Using In Vivo Microdialysis in Conscious Rats

Abstract

Measurement of neurotransmitters in the spinal dorsal horn in conscious animals remains a technical challenge. Here we applied concentric microdialysis to measure formalin-induced glutamate (Glu) release in the ipsilateral dorsal horn in conscious, freely-moving rats. Hind paw formalin injection induced flinching nociceptive behaviors accompanied by increased Glu in the dorsal horn (maximum = 294%). Both flinching and Glu increase were prevented by morphine (3 mg/kg, s.c.). Accordingly, concentric microdialysis is a sensitive technique for studying neurochemical modulation induced by pain and analgesics in the spinal dorsal horn of awake rats. Measurement of Glu provides information on modulation of excitatory signals.