Purpose: Fibromyalgia (FM) is characterized by chronic widespread pain with mechanical allodynia and hyperalgesia. However, the neural mechanisms of nociception/pain are poorly understood. The aim of this study was to examine the responsiveness of superficial dorsal horn (SDH) neurons using a rat model of FM.
Methods: Reserpine, a depleter of biogenic amines in the nervous system, was subcutaneously injected to make the mode. Extracellular recording of the SDH neurons in vivo was performed at the spinal segments L4/L5 under urethane anesthesia. Mechanical stimulation with a series of calibrated von Frey filaments was applied for 10 seconds to an identified receptive field of the SDH neurons.
Results: The SDH neurons showed mechanical stimulus intensity-dependent increases in the discharge rate both in the control and the reserpine-injected group. However, the magnitude of the mechanical response was significantly greater in the reserpine-injected group. Some SDH neurons in the reserpinized rats exhibited background discharges of low frequencies, although those in the control rats did not.
Conclusion: These results suggest that facilitated mechanical sensitivity of the SDH neurons is involved in mechanical allodynia and hyperalgesia in a rat model of reserpine-induced pain. Similar spinal mechanisms may underlie in FM patients.