Millhorn D E
J Physiol. 1986 Jan;370:217-31. doi: 10.1113/jphysiol.1986.sp015931.
The effects on respiratory and sympathetic neural activity, measured as integrated phrenic and cervical nerve activities respectively, during changing input from the central chemoreceptors was studied in anaesthetized, paralysed cats whose carotid sinus nerves and vagus nerves had been cut. Central respiratory drive was altered either by graded cold block of the intermediate areas, located bilaterally near the ventral surface of the medulla oblongata, or by step increases in end-tidal PCO2. Cervical nerve activity showed both a tonic (or mean) level of activity and a prominent cyclic discharge that was in phase with phrenic nerve activity. Graded focal cooling of the intermediate areas to 20 degrees C when end-tidal PCO2 was kept constant caused progressive decreases in phrenic activity, the amplitude of the inspiratory related discharge and mean arterial pressure, but only a small decrease in mean cervical nerve activity. Cooling the intermediate areas in the absence of the inspiratory related discharge (i.e. when phrenic activity was below the apnoeic threshold) led to a much smaller decrease in arterial pressure. Step increases of end-tidal PCO2 caused progressive increases of both cervical and phrenic nerve activities. The increase in cervical activity was due primarily, if not wholly, to a progressive increase in the amplitude of the inspiratory related discharge. These findings show that the predominant effect on sympathetic activity during stimulation of the central chemoreceptor and graded cold block of the intermediate areas is a change in the amplitude of the inspiratory related discharge and suggest that the change in arterial pressure that accompanies central chemoreceptor stimulation and graded cold block of the intermediate areas is mediated by the inspiratory related discharge rather than by an increase in the mean level of sympathetic activity. When phrenic activity was lowered to below apnoeic threshold by cooling the intermediate areas, step increases in end-tidal PCO2 caused inhibition rather than stimulation of cervical nerve activity. This finding indicates that sympathetic neurones are not activated by central chemoreceptor input directly, but rather indirectly via intracranial connexions with neuronal networks involved in regulation of respiration.
在切断了颈动脉窦神经和迷走神经的麻醉、麻痹猫中，研究了在中枢化学感受器输入变化期间，分别以膈神经和颈神经活动积分来衡量的对呼吸和交感神经活动的影响。通过对位于延髓腹侧面双侧的中间区域进行分级冷阻滞，或通过呼气末PCO₂的逐步升高来改变中枢呼吸驱动。颈神经活动既表现出一种紧张性（或平均）活动水平，又表现出与膈神经活动同步的显著周期性放电。当呼气末PCO₂保持恒定时，将中间区域分级局部冷却至20℃会导致膈神经活动、吸气相关放电幅度和平均动脉压逐渐降低，但平均颈神经活动仅略有下降。在没有吸气相关放电的情况下（即当膈神经活动低于呼吸暂停阈值时）冷却中间区域，导致动脉压下降幅度小得多。呼气末PCO₂的逐步升高导致颈神经和膈神经活动逐渐增加。颈神经活动的增加主要（如果不是完全）归因于吸气相关放电幅度的逐渐增加。这些发现表明，在刺激中枢化学感受器和对中间区域进行分级冷阻滞期间，对交感神经活动的主要影响是吸气相关放电幅度的变化，并表明伴随中枢化学感受器刺激和中间区域分级冷阻滞的动脉压变化是由吸气相关放电介导的，而不是由交感神经活动平均水平的增加介导的。当通过冷却中间区域使膈神经活动降低到呼吸暂停阈值以下时，呼气末PCO₂的逐步升高会抑制而不是刺激颈神经活动。这一发现表明，交感神经元不是直接由中枢化学感受器输入激活，而是通过与参与呼吸调节的神经网络的颅内连接间接激活。
