Mechanical ventilation

The rats were anesthetized initially with pentobarbital (45–50 mg/kg, i.p.). Then a tracheotomy was performed and mechanical ventilation (Kent Scientific Corporation, Litchfield, CT) was provided as described previously.^{27 (link)} In each experiment, we first determined the intensities of epidural SCS by recording the antidromic sciatic compound AP evoked by graded electrical stimulation (0.1–5.0 mA, 0.2 millisecond, biphasic) from epidural electrodes. A monopolar silver hook electrode was placed on the left sciatic nerve at mid-thigh level for recording compound APs. The reference electrode was placed in the nearby muscle. Both stimulating and compound AP recording areas were covered with mineral oil. We determined on-line the current thresholds that resulted in the first detectable Aα/β waveform (Aβ-threshold) and the peak Aα/β waveform (Aβ-plateau), without inducing an Aδor C-fiber waveform. Similar techniques have been used in previous studies.^{27 (link),51 (link),58 (link)}

Animals were placed under general anesthesia for nonsurvival neurophysiological studies. The rats were initially anesthetized with pentobarbital (45–50 mg/kg, i.p.). Then a tracheotomy was performed and mechanical ventilation (Kent Scientific Corporation, Litchfield, CT) at 50–70 cycles/min with inspiratory pressures of 10–14 cm H₂O was initiated. During the neurophysiological experiments, the anesthesia was maintained with 1.5% isoflurane, and animals were paralyzed with pancuronium bromide (1–2 mg/kg, i.p., Elkins-Sinn Inc., Cherry Hill, NJ) via intermittent injections given as needed (1 mg/kg/h, i.p.). Sufficient depth of anesthesia was judged from areflexia to sensory stimuli (e.g., no withdrawal reflexes, corneal reflex) when rats were in the unparalyzed state and by the absence of gross fluctuations of heart rate (300–350 beats per min) during paralysis. Core body temperature was kept in the normal range (36.0–37.0°C).

The rats were anesthetized initially with pentobarbital (45–50 mg/kg, i.p.). Then a tracheotomy was performed and mechanical ventilation (Kent Scientific Corporation, Litchfield, CT) was initiated at 50–70 cycles/minute with inspiratory pressures of 10–14 cm H₂O. During the neurophysiologic experiments, anesthesia was maintained with 1.5% isoflurane. To facilitate controlled ventilation during electrophysiology recording, we paralyzed animals with pancuronium bromide (1–2 mg/kg, i.p., Elkins-Sinn Inc., Cherry Hill, NJ). Sufficient depth of anesthesia was judged from areflexia to sensory stimuli (e.g., no withdrawal reflexes, corneal reflex) when rats were in the unparalyzed state and by the absence of gross fluctuations of heart rate (300–350 beats per minute) during paralysis. Core body temperature was kept in the normal range (36.0–37.0°C).