Halothane depresses C-fiber-evoked windup of deep dorsal horn neurons in mice.

A progressive increase in the response of a nociceptive spinal neuron to repeated electrical C-fiber stimulation reflects a phenomenon called windup. Second order neurons in the dorsal horn, as well as motoneurons, can develop windup. Inhaled anesthetics act primarily in spinal cord to suppress movement induced by noxious stimulation. We hypothesized that halothane would depress neuronal windup in mice at concentrations that also prevented movement. We measured windup in deep dorsal horn neurons in lumbar spinal cord at 0.75 MAC (the minimum alveolar concentration of anesthetic that prevents movement in 50% of subjects in response to noxious stimulation), 0.9 MAC, and 1.1 MAC. The change from 0.75 to 0.9 MAC did not significantly decrease windup (-11+/-22%), but the change from 0.9 to 1.1 MAC decreased windup (-35+/-7%, P<0.01). We conclude that halothane depresses neuronal windup in the range that prevents movement, and that the effect on windup might play a role in halothane's immobilizing action.