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

Abstract

In vitro, the respiratory activity in rodents is characterized by: (i) the rapidly peaking, slowly decrementing pattern of spontaneous and rhythmic active phases recorded from the motor rootlets, and (ii) the specific location of their rhythmic generator in the ventrolateral medulla. The aim of the present study was to assess whether the trigeminal and facial motor rootlets still exhibit respiratory activity in the absence of peripheral and higher 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 regular and synchronized bilaterally and ipsilaterally with the hypoglossal or cervical C1-C6 rootlets. Brainstem transection experiments demonstrated that for both the trigeminal and facial rootlets, the spontaneous rhythmic activity originates from the medulla, in a region consistent with the pre-Bötzinger complex and the rostral ventrolateral medulla. The pattern of the respiratory motor activity recorded from the trigeminal and facial rootlets was identical to the pattern recorded from the hypoglossal and cervical C1-C6 rootlets with rapidly peaking, slowly decrementing characteristics. The duration 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 delayed compared with that of the trigeminal, facial and hypoglossal rootlets. However, no difference in the onsets of the active phases of the cranial rootlets could be observed. Removal of the rostral pons suppressed the delay in onset of the active phases of the phrenic rootlets. Our findings show that: (i) rhythmic activities of the trigeminal and facial rootlets are preserved in absence of control by peripheral or high cerebral structures; (ii) the pattern and the location of the rhythmic generator for these activities are of the respiratory type; and (iii) the rostral pons is responsible for a delay in the onset of the active phases of the phrenic rootlets compared with that of the trigeminal, facial and hypoglossal rootlets.