Brainstem regions involved in the expiration reflex. A c-fos study in anesthetized cats

Abstract

Expression of the immediate-early gene c-fos, a marker of neuronal activation, was employed to localize brainstem neuronal populations functionally related to the expiration reflex (ER). Twelve spontaneously breathing, non-decerebrate, pentobarbital anesthetized cats were used. The level of Fos-like immunoreactivity (FLI) in 6 animals with repetitive ERs mechanically induced from the glottis (296+/-9 ERs) was compared to FLI in 6 control non-stimulated cats. Respiratory rate, arterial blood pressure, and end tidal CO(2) concentration remained stable during the experiment. In the medulla, increased FLI was found in the region of nucleus tractus solitarii (p<0.001), in the ventrolateral medulla along with the lateral tegmental field (p<0.01), and in the vestibular nuclei (p<0.01). In the pons, increased FLI was detected in the caudal extensions of the lateral parabrachial and Kölliker-Fuse nuclei (p<0.05). Within the rostral mesencephalon, FLI was enhanced in the midline area (p<0.05). A lower level of ER-related FLI compared to control animals was detected in the pontine raphe region (p<0.05) and the lateral division of mesencephalic periaqueductal gray (p<0.05). The results suggest that the ER is coordinated by a complex long loop of medullary-pontine-mesencephalic neuronal circuits, some of which may differ from those of other respiratory reflexes. The FLI related to the expulsive behavior ER differs from that induced by laryngeal stimulation and laryngeal adductor responses, particularly in ventrolateral medulla and mesencephalon.

Figure 1

An original record of blood pressure (BP), airflow (AF; expiration up) and tidal volume (V_T; expiratory volume up) during expiration reflexes induced by mechanical stimulation (stim) of the glottis.

Figure 2

Diagrammatic reconstructions of transverse medullary (+1 and +5), pontine (+10), and mesencephalic (+13 and +17) hemisections with the map of some brainstem structures (SCHEME), control levels of FLI in non-stimulated cats (CONTROL), and the ER-related immunoreactivity in animals with expiration reflex (ER). +1, +5, +10, +13, and +17 represent the positions of the transections (in mm) rostral to the obex. 3, oculomotor ncl; 5SP, parvocellular division of the alaminar spinal trigeminal ncl; VII, facial ncl; AQ, aqueduct; COE, ncl coeruleus; CS, superior central ncl; FTC, central tegmental field; FTG, gigantocellular tegmental field; FTL, medullary and pontine lateral tegmental fields; FTP, paralemniscal tegmental field; ICC, central ncl of the inferior colliculus; IF, interfascicular ncl; KF, Kölliker-Fuse ncl; LC, central linear ncl; LRN, lateral reticular ncl; MLB, medial longitudinal bundle; NA, ambigual ncl; NPBL, lateral parabrachial ncl; NTS, solitary tract ncl; P, pyramidal tract; PAG, periaqueductal grey; RFN, retrofacial ncl; RN, raphe nuclei; RR, retrorubral ncl; SCI, superior colliculus, intermediate layer; SOM, medial ncl of the superior olive; TB, trapezoid body; TX, tegmental decussations; VN, vestibular nuclei.

Figure 3

Examples of Fos immunoreactive neurons (dark dots) in cats with expiration reflexes (ER) compared to the control FLI in animals without ER (CONTROL). The level of immunoreactivity decreased in the lateral division of the caudal mesencephalic PAG (right top), but it was enhanced at the rostral ventrolateral medulla (right middle), in the midline area of the rostral mesencephalon (left top), and in the NTS (right bottom). The inset high power photograph of mNTS (left bottom) shows the dark brown staining in Fos positive neurons (arrows). A few weakly stained neurons appear in the high power inset, but these neurons were not clearly visible at low power and as such did not pass our criteria for counting. 3, oculomotor ncl; AQ, aqueduct; DMNV, dorsal motor nucleus of vagus; FTL, lateral tegmental field; LC, central linear ncl; mNTS, medial subnucleus of the solitary tract nucleus; PAG, periaqueductal grey; RFN, retrofacial ncl; S, solitary tract; TX, tegmental decussations..