Pontine and medullary control of the respiratory activity in the trigeminal and facial nerves of the newborn mouse: an in vitro study

In vitro, the respiratory activity in rodents is characterized by: (i) the rapidly peaking, slowly decrementing pattern of spontaneous and rhythmic ac tive phases recorded from the motor rootlets, and (ii) the specific locatio n of their rhythmic generator in the ventrolateral medulla, The aim of the present study was to assess whether the trigeminal and facial motor rootlet s still exhibit respiratory activity in the absence of peripheral and highe r cerebral structures, and to compare the onset of their active phases with that of other respiratory rootlets, using the in vitro isolated brainstem- spinal cord preparation of the newborn mouse and rat. Spontaneous rhythmic activity was recorded from the trigeminal and facial rootlets. It was regul ar and synchronized bilaterally and ipsilaterally with the hypoglossal or c ervical C-1-C-6 rootlets. Brainstem transection experiments demonstrated th at for both the trigeminal and facial rootlets, the spontaneous rhythmic ac tivity originates from the medulla, in a region consistent with the pre-Bot zinger complex and the rostral ventrolateral medulla, The pattern of the re spiratory motor activity recorded from the trigeminal and facial rootlets w as identical to the pattern recorded from the hypoglossal and cervical C1-C 6 rootlets with rapidly peaking, slowly decrementing characteristics. The d uration of the ascending part and the total duration of their active phases were similar. The onset of the active phases of the phrenic rootlets was d elayed compared with that of the trigeminal, facial and hypoglossal rootlet s. However, no difference in the onsets of the active phases of the cranial rootlets could be observed, Removal of the rostral pens suppressed the del ay in onset of the active phases of the phrenic rootlets. Our findings show that: (i) rhythmic activities of the trigeminal and facial rootlets are pr eserved in absence of control by peripheral or high cerebral structures; (i i) the pattern and the location of the rhythmic generator for these activit ies are of the respiratory type; and (iii) the rostral pens is responsible for a delay in the onset of the active phases of the phrenic rootlets compa red with that of the trigeminal, facial and hypoglossal rootlets.