Respiratory network remains functional in a mature guinea pig brainstem isolated in vitro

We previously developed a perfused isolated brainstem preparation in the adult guinea pig (Morin-Surun and Denavit-Saubie 1989a) which permitted us to describe several types of rhythmic neuronal discharge. In the present study, we demonstrate that nearly all the periodic neuronal activity we recorded in the ventral respiratory areas were directly related to the respiratory-like periodic output of the hypoglossal nerve. This respiratory-like activity lasted several hours only when the brainstem was perfused by the basilar artery. This shows the necessity of the intraarterial perfusion to preserve a functional respiratory network. Analysis of the characteristics of hypoglossal respiratory-like activity shows that (1) two types of respiratory rhythms can be recorded; one with long respiratory phases (inspiratory and expiratory) and one with short respiratory phases. Depending on the preparation, either type occurs alone or intermingled with the other. (2) The shape of the inspiratory-like activity can change throughout the recording period while the periodicity remains stable. This preparation generates a respiratory rhythm and enables us to dissociate the different mechanisms involved in respiratory neurogenesis.