The Effects of Hyperventilation upon the Spinal Pain Modulating System

本研究旨在探讨过度换气对猫腰段脊髓背角宽动态范围(WDR)细胞的影响。猫在安氟醚麻醉下，行中脑去大脑和腰椎板切除。脊髓在T12-L1处横断。WDR细胞主要对伤害性外周刺激作出反应，用微电极从脊髓背部1500-2000微米处取样。分别测定大鼠自发活动和挤压后爪感受区的伤害性活动，并通过两系列实验研究过度换气的影响。第一组在PaCO_2控制在35-45 MHG后，调整呼吸频率和潮气量，使低碳酸血症水平降至25-30和20-25毫米汞柱。正常碳酸血症恢复后，细胞活性恢复正常。…的低碳酸血症对WdR细胞活性有较好的抑制作用增加PaCO_2 20~25 mm Hg、纳洛酮0.1 mg/kg或酚妥拉明0.5 mg/kg加生理盐水1.0ml静脉滴注。观察WDR细胞放电的变化。PaCO_2为25-30 mm Hg和20-25 mm Hg的低碳酸血症显著抑制WDR细胞的活性。在PaCO_2为25-30毫米汞柱时，自发活动抑制约20%，诱发活动抑制27%。Ar PaCO_2为25-30毫米汞柱时，自发活动受到抑制。约50%，诱发活性为33%。提示过度换气对WDR细胞的单位活动有抑制作用。纳洛酮和酚妥拉明均能明显拮抗过度换气对WDR细胞活性的抑制作用，提示过度换气对WDR细胞单位活动有抑制作用，其抑制机制不仅与内源性阿片类药物有关，还与肾上腺素能痛觉调制系统有关。较少

The purpose of this study is to investigate the effects of hyperventilation on the wide dynamic range (WDR) cell of the dorsal horn of the feline lumbar spinal cord.Under enflurane anesthesia, cats were prepared with midcollicular decerebration and lumbar laminectomy. The spinal cord was transected at T12-L1. WDR cells, responding primarily to noxious peripheral stimuli, were sampled with a microelectrode at the depth of 1500-2000 um from the cord dorsum. Spontaneous activity and noxiously evoked activity by pinching the receptive field on the hind paw were measured.Two series of experiments were carried out to characterize the effects of hyperventilation. In the first, following the control period with PaCO_2 of 35-45 mHg, respiratory rate and tidal volume were adjusted to make a level of hypocapnia as low as 25-30 and 20-25 mmHg. The recovery of cell activity was followed when normocapnia was restored. In the second, after activities of WDR cells were well suppressed by hypocapnia of … More PaCO_2 20-25mmHg, naloxone 0.1mg/kg or phentolamine 0.5mg/kg with normal saline 1.0 ml was given intravenously. Changes of firings of WDR cells were investigated. Retuening to normocapnia, recovery of firings was followed.Hypocapnia with PaCO_2 of 25-30 mmHg and 20-25 mmHg suppressed the activity of WDR cell significantly. At PaCO_2 of 25-30 mmHg, spontaneous activity was suppressed for about 20 % and evoked activity for 27 %. Ar PaCO_2 of 25-30 mmHg the spontaneous activity was suppressed for. about 50 % and evoked activity for 33 %. The results suggest that hyperventilation has suppressive effects on single-unit activity of WDR cell. Both naloxone and phentolamine significantly antagonized the suppressive effects of hyperventilation upon the activity of WDR cell.Our results suggest that hyperventilation has suppressive effects on single-unit activity of WDR cell and the mechanisms of those suppressive effects are related to not only endogeneous opiate but also adrenergic pain modulating system. Less