WDR response profiles of spinal dorsal horn neurons may be unmasked by barbiturate anesthesia

The number of WDR (convergent, multireceptive) neurons encountered in the spinal dorsal horn of physiologically intact, awake, drug-free cats has been much smaller than expected (9% in intact, drug-free animals). Control studies in barbiturate-anesthetized or spinal cord transected animals indicate that the dearth of WDR neurons was not just an artifact of the chronic recording technique. In those preparations WDR neurons represented 34% and 61% of the sample, respectively. Initial studies in which the effects of light barbiturate anesthesia on spinal dorsal horn neurons (n = 12) have been examined revealed that a 20 mg/kg dose of pentobarbital can, in some neurons (n = 4), unmask thermally evoked activity that was not present in the intact, drug-free animal. Responses to noxious mechanical stimuli were also enhanced following barbiturate administration. These changes resulted in a reclassification of neural type from low threshold in the intact, awake, drug-free animal to WDR in the anesthetized animal.