Expression of the immediate-early gene c-fos, a marker of neuronal activation was employed in adult anesthetized non-decerebrate cats, in order to localize the brainstem neuronal populations functionally related to sniff-like (gasp-like) aspiration reflex (AR). Tissues were immunoprocessed using an antibody raised against amino acids of Fos and the avidin-biotin peroxidase complex method. The level of Fos-like immunoreactivity (FLI) was identified and counted in particular brainstem sections under light microscopy using PC software evaluations in control, unstimulated cats and in cats where the AR was elicited by repeated mechanical stimulation of the nasopharyngeal region. Fourteen brainstem regions with FLI labeling, including thirty-seven nuclei were compared for the number of labeled cells. Compared to the control, a significantly enhanced FLI was determined bilaterally in animals with the AR, at various medullary levels. The areas included the nuclei of the solitary tract (especially the dorsal, interstitial and ventrolateral subnuclei), the ventromedial part of the parvocellular tegmental field (FTL - lateral nuclei of reticular formation), the lateral reticular nucleus, the ambigual and para-ambigual regions, and the retrofacial nucleus. FLI was also observed in the gigantocellular tegmental field (FTG - medial nuclei of reticular formation), the spinal trigeminal nucleus, in the medullar raphe nuclei (ncl. raphealis magnus and parvus), and in the medial and lateral vestibular nuclei. Within the pons, a significant FLI was observed bilaterally in the parabrachial nucleus (especially in its lateral subnucleus), the Kölliker-Fuse nucleus, the nucleus coeruleus, within the medial region of brachium conjunctivum, in the ventrolateral part of the pontine FTG and the FTL. Within the mesencephalon a significantly enhanced FLI was found at the central tegmental field (area ventralis tegmenti Tsai), bilaterally. Positive FLI found in columns extending from the caudal medulla oblongata, through the pons up to the mid-mesencephalon suggests that the aspiration reflex is thus co-ordinated by a long loop of medullary-pontine-mesencephalic control circuit rather than by a unique “center“.
Experiments were carried out to determine whether there are separate drives from the selected neuronal networks of the brainstem affecting the discharge patterns of laryngeal and respiratory pump muscles during cough. Twenty-four non-decerebrate spontaneously breathing cats anesthetized with sodium pentobarbitone were used. Microinjections of kainic acid into the lateral tegmental field of the medulla, medullary midline or pontine respiratory group eliminated the cough evoked by mechanical stimulation of the tracheobronchial and laryngopharyngeal mucosa. These stimuli, in most cases, provoked irregular bursts of discharges in the posterior cricoarytenoid and thyroarytenoid laryngeal muscles (or they had no effect on them). No pattern of laryngeal muscle activities following lesions resembled the laryngeal cough response. Lesions of the target regions did not result in any apparent changes in the eupnoeic pattern of laryngeal activity. Neurons of the medullary lateral tegmental field, raphe nuclei and the pontine respiratory group seem to be indispensable for the configuration of the central cough motor pattern. However, these neurons do not appear to be essential for the discharge patterns of laryngeal motoneurons during eupnoea. The residual laryngeal „cough“ responses are probably mediated by an additional motor drive.
The importance of neurons in the pontine respiratory group for the generation of cough, expiration, and aspiration reflexes was studied on non-decerebrate spontaneously breathing cats under pentobarbitone anesthesia. The dysfunction of neurons in the pontine respiratory group produced by bilateral microinjection of kainic acid (neurotoxin) regularly abolished the cough reflexes evoked by mechanical stimulation of both the tracheobronchial and the laryngopharyngeal mucous membranes and the expiration reflex mechanically induced from the glottis. The aspiration reflex elicited by similar stimulation of the nasopharyngeal region persisted in 73 % of tests, however, with a reduced intensity compared to the pre-lesion conditions. The pontine respiratory group seems to be an important source of the facilitatory inputs to the brainstem circuitries that mediate cough, expiration, and aspiration reflexes. Our results indicate the significant role of pons in the multilevel organization of brainstem networks in central integration of the aforementioned reflexes.
The involvement of rapheal and medial parts of the medullary reticular formation in both generation of airway reflexes and changes in breathing were studied in 18 chloralose or pentobarbitone anaesthetized, non-paralyzed cats. Chemical lesions to the medullary midline region (0—4 mm rostral to the obex) produced by localized injections of the neurotoxin kainic acid regularly abolished the cough reflexes evoked from the tracheobronchial and laryngopharyngeal regions and in most cases also the expiration reflex induced from the glottal area. The aspiration reflex elicited from the nasopharynx was spared, but was less intense. However, the signs of cough and expiration reflexes were preserved in the neurogram of the recurrent laryngeal nerve. The experiments have shown the importance of raphe nuclei and other medullary midline structures for the occurrence of cough and expiration reflexes. One possible explanation for the elimination of these expulsive processes is the removal of an important source of facilitatory input to the spinal respiratory motoneurons or to the brainstem circuitries that mediate cough and expiration reflexes . The role of the medullary midline in modulation of eupnoeic breathing and blood pressure is also discussed.
The involvement of the intermediate area and Botzinger complex (BOT) of the rostral ventral respiratory group (r-VRG) in laryngeal control and generation of the expiration reflex were studied in anaesthetized non-paralyzed cats. Focal cooling (to 20 °C) of the nucleus paraambigualis (NPA) caused changes in the frequency and timing of breathing with the concomitant rise in laryngeal resistance. Cooling of the nucleus ambiguus resulted in a consistent drop in laryngeal resistance. Alterations in timing and intensity of breathing but no changes in laryngeal patency were found during cooling of the BOT. The expiration reflex was inhibited by cooling of either the NPA or BOT. The role of these medullary regions in the control of laryngeal patency and central integration of the expiration reflex is discussed.