呼吸リズムの発生機構

抄録

Is respiratory rhythm generated by pace-maker neurons or by network mechanisms? Although this longtime and important question has not been solved yet, recent studies provide evidence supporting pace-maker theory at least under some experimental conditions and clarified characteristics of respiratory pace-maker neurons. In respiratory rhythm generation, a term of pace-maker neurons indicates neurons that possess cellular property intrinsically producing rhythmic burst (but not tonic) activity. In pace-maker theory, it is hypothesized that intrinsic burst generating neurons are embedded in a network composed of neuronal population with same active phase and contribute to produce basic synchronized rhythm, whereas inhibitory synaptic connections are not necessary for the rhythm generation. At least two respiration-related rhythm generators have been suggested to exist in the medulla and to produce intrinsic periodic burst activity. One is an inspiratory (Insp) neuronal network (i.e., Insp rhythm generator), which is localized predominantly in the pre-Boetzinger complex of the ventrolateral medulla. Another is a pre-inspiratory (Pre-I) neuronal network (i.e., Pre-I rhythm generator), which generates activity prior to Insp bursts and is located in the more rostral ventrolateral medulla including the para-facial respiratory group (pFRG). We have shown that pFRG-Pre-I neurons serve as a primary rhythm generator, triggering inspiratory burst periodically in the brainstem-spinal cord preparation from newborn rat. In this presentation, we focus on mainly burst generating properties of Pre-I neurons and the ionic and synaptic mechanisms. [J Physiol Sci. 2006;56 Suppl:S54]