Fig. 1. ( A ) Schematic drawing of location of a typical receptive field (RF) responding to nonnoxious (low-threshold, dotted line ) and noxious stimuli (high-threshold, solid line ). A 1-cm-long incision was made in the center of the RF through the skin, fascia, and muscle, and the skin was apposed with two sutures. Nonnoxious and noxious mechanical stimuli were applied on the injured site (1–2 mm from the incision site). ( B, ,C, D ) Schematic illustration of the experimental protocols. In the 1.1% halothane (Hal), 2.2% halothane (Hal), 1.4% isoflurane (Iso), and 2.8% isoflurane (Iso) groups, administration of the anesthetics was started and continued for 20 min, and the incision was then made; administration of the anesthetics was discontinued just after suturing ( B ). In the 2.2% halothane (Hal) (30 min) and 2.8% isoflurane (Iso) (30 min) groups, administration of the anesthetics was started and continued for 20 min, and the incision was then made; administration of the anesthetics was continued for the next 30 min and then discontinued ( C ). In some neurons (n = 5), administration of 1.1% halothane was started at 20 min before the incision and continued during the experiment. The timings of assessment of neuronal activity are shown in ( B, C, D ). SP, spontaneous activity; RF, receptive field; Response, evoked responses to nonnoxious and noxious stimuli.