Immobilizing Doses of Halothane, Isoflurane or Propofol, Do Not Preferentially Depress Noxious Heat-Evoked Responses of Rat Lumbar Dorsal Horn Neurons with Ascending Projections

BACKGROUND: The spinal cord is an important site where volatile anesthetics decrease sensation and produce immobility. Beyond this knowledge, our under-standing of a site of anesthetic action is limited. Previous evidence suggests that dorsal horn neurons with ascending projections may be more susceptible to depression by general anesthetics than local spinal interneurons. In this study we evaluated the effects of volatile and injectable general anesthetics on lumbar dorsal horn neurons with and without ascending projections. METHODS: Thirty-seven adult male rats underwent laminectomies at C1, for place-ment of a stimulating electrode, and T13/L1, for extracellular recording from the spinal cord dorsal horn. Neuronal responses to heat were evaluated under two doses of halothane, isoflurane, or propofol anesthesia. RESULTS: Under both halothane and isoflurane anesthesia, increasing the dose from 0.8 to 1.2 minimum alveolar concentration (MAC) had no significant effect on heat-evoked responses in neurons that had ascending projections identified via antidromic stimulation (AD) or those without ascending projections (nAD). Hea