In previous studies we have reported that spinal nerve ligation (SNL), a model of neuropathic pain, results in the loss of over 20% of neurons in the rostral portion of the ventromedial medulla (RVM) in rats, 10 days after SNL. The RVM is involved in pain modulation and we have proposed that loss of pain inhibition from the RVM, including loss of RVM serotonin neurons, contributes to the increased hypersensitivity observed after SNL. In the present study we examined whether RVM neuronal loss occurs in two other models of neuropathic pain, chronic constriction injury (CCI) and spared nerve injury (SNI). We found no evidence for neuronal loss 10 days after either nerve injury, a time when robust tactile hypersensitivity is present in both CCI and SNI. We conclude that loss of RVM neurons appears not to be required for expression of tactile hypersensitivity in these models of neuropathic pain.
Bibliographical noteFunding Information:
The authors gratefully acknowledge financial support from USPHS Grant DA017758 to M.W., Grant T32 DA 007234 , the Minnesota Medical Foundation , the Office of the Vice President for Research , University of Minnesota , and the Department of Neuroscience , University of Minnesota .