Fig. 4. Effect of halothane on activity of spinal dorsal horn neurons. ( A ) Examples of responses of a spinal dorsal horn neuron to nonnoxious and noxious stimuli before and 30 min and 2 h after the incision. ( B ) Examples of low-threshold and high-threshold receptive fields (RFs) of a spinal neuron. The data in ( A ) and ( B ) were obtained from the same neuron in which administration of 2.2% halothane was started 20 min before the incision and continued for up to 30 min after the incision and then discontinued ( fig. 1C ). BR, brush stimulation; VF, 4-g von Frey hair stimulation; PP, pinprick stimulation; PI, pinch stimulation. ( C ) Mean changes in responses to nonnoxious and noxious stimuli and RF sizes in the control group, the 1.1% halothane (Hal) group (n = 6), the 2.2% halothane (Hal) group (n = 7), and the 2.2% halothane (Hal) (30 min) group (n = 8). When ad-ministration of 2.2% halothane was continued for up to 30 min after the incision in the 2.2% Hal (30 min) group, low-threshold RF and responses to brush and pinch stimuli at 30 min after the incision were abolished ( arrow ). There are no significant differences in the increased responses to brushing and pinching stimuli and increased RF sizes among the groups before administration of anesthetics and at 1 and 2 h after the incision had been made.