RESPIRATORY RHYTHM GENERATION IN MAMMALS - SYNAPTIC AND MEMBRANE-PROPERTIES

Respiratory rhythm generation depends on a complex interaction between synaptic and membrane properties of functionally defined neurons. To gain a better understanding of how inhibitory and excitatory synaptic inputs lead to the generation of the respiratory rhythm we analyzed th e depolarization pattern of respiratory neurons that were recorded in the transverse slice preparation of mice (P8-22) and the in vivo adult cat. Using voltage-clamp recordings from respiratory neurons and spec ific antagonists for inhibitory synaptic transmission we demonstrate u nder in vitro conditions, that inspiratory (n = 7) and post-inspirator y neurons (n = 13) received concurrent glycinergic and glutamatergic s ynaptic input during inspiration. A similar conclusion was gained with chloride injections into in vivo respiratory neurons. The inhibitory input was essential not only for generating the characteristic depolar ization pattern of respiratory neurons, but also for switching the res piratory rhythm between inspiration and post-inspiration. The generati on of the depolarization pattern depends also on intrinsic membrane pr operties. Negative current injections reveal that excitatory synaptic input was amplified by intrinsic bursting properties in some inspirato ry neurons (n = 4) recorded in vitro. Although such properties have no t been described,under in vivo conditions our findings suggest that wi th respect to inspiratory, post-inspiratory and late-inspiratory neuro ns, the principle network organization is similar under both in vitro and in vivo conditions. (C) 1997 Elsevier Science B.V.