Kim JongBun, Yao Aubrey, Atherley Richard, Carstens Earl, Jinks Steven L, Antognini Joseph F
Department of Anesthesiology, University of California, Davis, California 95616, USA.
Anesth Analg. 2007 Oct;105(4):1020-6, table of contents. doi: 10.1213/01.ane.0000280483.17854.56.
Volatile anesthetics act primarily in the spinal cord to produce immobility but their exact site of action is unclear. Between 0.8 and 1.2 minimum alveolar anesthetic concentration (MAC), isoflurane does not depress neurons in the dorsal horn, suggesting that it acts at a more ventral site within the spinal cord such as in premotor interneurons and motoneurons. We hypothesized that isoflurane, halothane, and propofol would exert a greater depressant effect on nociceptive responses of ventral horn neurons when compared with dorsal horn neurons.
Rats were anesthetized with isoflurane or halothane and responses of dorsal (<1200 microm deep) and ventral (>1200 microm) lumbar neurons to noxious mechanical stimulation of the hindpaw were determined at 0.8 and 1.2 MAC. In a third group anesthetized with isoflurane at 0.8 MAC, we administered 5 mg/kg propofol while recording responses from dorsal horn or ventral horn neurons.
Dorsal horn neuronal responses were not significantly affected when either isoflurane or halothane was increased from 0.8 to 1.2 MAC; propofol also had no significant effect. On the other hand, with increased isoflurane or halothane concentration, responses of ventral horn neurons were depressed by 60% and 45%, respectively. Propofol profoundly depressed (>90%) ventral horn neurons.
These data suggest that, in the peri-MAC range, isoflurane, halothane, and propofol have little or no effect on neuronal responses to noxious mechanical stimulation in the spinal dorsal horn but depress such responses in the ventral horn. Immobility produced in the 0.8-1.2 MAC range by these anesthetics appears to result from a depressant action in the ventral horn.
挥发性麻醉剂主要作用于脊髓以产生制动效果，但其确切作用部位尚不清楚。在0.8至1.2倍最低肺泡有效浓度（MAC）之间，异氟烷不抑制背角神经元，这表明它作用于脊髓内更靠腹侧的部位，如运动前中间神经元和运动神经元。我们假设，与背角神经元相比，异氟烷、氟烷和丙泊酚对腹角神经元的伤害性反应具有更大的抑制作用。
用异氟烷或氟烷麻醉大鼠，并在0.8和1.2 MAC下测定腰段背侧（<1200微米深）和腹侧（>1200微米）神经元对后爪有害机械刺激的反应。在第三组以0.8 MAC的异氟烷麻醉的大鼠中，我们静脉注射5 mg/kg丙泊酚，同时记录背角或腹角神经元的反应。
当异氟烷或氟烷从0.8 MAC增加到1.2 MAC时，背角神经元反应无显著影响；丙泊酚也无显著作用。另一方面，随着异氟烷或氟烷浓度增加，腹角神经元反应分别被抑制60%和45%。丙泊酚使腹角神经元反应显著抑制（>90%）。
这些数据表明，在MAC周围范围内，异氟烷、氟烷和丙泊酚对脊髓背角神经元对有害机械刺激的反应几乎没有影响，但会抑制腹角的此类反应。这些麻醉剂在0.8 - 1.2 MAC范围内产生的制动效果似乎是由于对腹角的抑制作用。
