St-John W M
Department of Physiology, Dartmouth-Hitchcock Medical Center, Dartmouth Medical School, Lebanon, NH 03756, USA.
Prog Neurobiol. 1998 Oct;56(1):97-117. doi: 10.1016/s0301-0082(98)00031-8.
Normal respiration, termed eupnea, is characterized by periodic filling and emptying of the lungs. Eupnea can occur 'automatically' without conscious effort. Such automatic ventilation is controlled by the brainstem respiratory centers of pons and medulla. Following removal of the pons, eupnea is replaced by gasping, marked by brief but maximal inspiratory efforts. The mechanisms by which the respiratory rhythms are generated have been examined intensively. Evidence is discussed that ventilatory activity can be generated in multiple regions of pons and medulla. Eupnea and gasping represent fundamentally different ventilatory patterns. Only for gasping has a critical region for neurogenesis been identified, in the rostral medulla. Gasping may be generated by the discharge of 'pacemaker' neurons. In eupnea, this pacemaker activity is suppressed and incorporated into the pontile and medullary neuronal circuit responsible for the neurogenesis of eupnea. Evidence for ventilatory neurogenesis which has been obtained from a number of in vitro preparations is discussed. A much-used preparation is that of a 'superfused' brainstem of the neonatal rat. However, activities of this preparation differ greatly from those of eupnea, as recorded in vitro or in arterially perfused in vitro preparations. Activities of this 'superfused' preparation are identical with gasping and, hence, results must be reinterpreted accordingly. The possibility is present that mechanisms responsible for generating respiratory rhythms may differ from those responsible for shaping respiratory-modulated discharge patterns of cranial and spinal nerves. The importance of pontile mechanisms in the neurogenesis and control of eupnea is reemphasized.
正常呼吸，即平静呼吸，其特征是肺部周期性地充盈和排空。平静呼吸可以在无意识的情况下“自动”发生。这种自动通气由脑桥和延髓的脑干呼吸中枢控制。切除脑桥后，平静呼吸被喘息所取代，喘息的特点是短暂但最大程度的吸气努力。人们对呼吸节律产生的机制进行了深入研究。有证据表明，通气活动可以在脑桥和延髓的多个区域产生。平静呼吸和喘息代表了根本不同的通气模式。仅在延髓头端确定了喘息的神经发生关键区域。喘息可能由“起搏器”神经元的放电产生。在平静呼吸中，这种起搏器活动受到抑制，并整合到负责平静呼吸神经发生的脑桥和延髓神经元回路中。讨论了从多种体外制备物中获得的通气神经发生的证据。一种常用的制备物是新生大鼠的“灌流”脑干。然而，这种制备物的活动与平静呼吸在体外或动脉灌流体外制备物中记录的活动有很大不同。这种“灌流”制备物的活动与喘息相同，因此，结果必须相应地重新解释。产生呼吸节律的机制可能与塑造颅神经和脊神经呼吸调制放电模式的机制不同。脑桥机制在平静呼吸的神经发生和控制中的重要性再次得到强调。
