Comparative characteristics of respiratory pattern responses to microinjection of kainic acid into different parts of the nucleus ambiguus.

Experiments on anesthetized rats were performed using local chemical exclusion of neurons with kainic acid to study the relative roles of the rostral, intermediate, and caudal parts of the nucleus ambiguus in the mechanisms controlling respiration. The characteristics of the respiratory rhythm and pattern responses to chemical exclusion of different parts of this nucleus were observed. In particular, sequential exclusion of the left and right rostral parts of the nucleus ambiguus reproducibly induced significant decreases in the respiration rate and respiratory volume in the first minutes; in 83% of experiments, there was also irreversible respiratory arrest. Exclusion of symmetrical intermediate parts of the nucleus ambiguus was followed by bradypnea and decreases in pulmonary ventilation, the greatest respiratory effects being noted only after injection of kainic acid into the second symmetrical area, irreversible respiratory arrest being seen in 50% of cases. Exclusion of symmetrical caudal areas of the nucleus ambiguus resulted only in small decreases in respiratory frequency without significant changes in respiratory volume and gave rise to the smallest incidence of respiratory arrest, i.e., 33%.

[Comparative characteristic of respiratory pattern responses to kainic acid microinjections in different parts of the nucleus ambiguous]. / Sravnitel'naia kharakteristika reaktsii patterna dykhaniia na mikroin''ektsii kainovoi kisloty v razlichnye otdely dvoinogo iadra.

In rats, local chemical isolation of neurones by the kainic acid helped to investigate into comparative role of different parts of the n. ambiguus in respiratory control mechanisms. We disclosed specific peculiarities of responses of rhythm and respiratory pattern to chemical isolation of different parts of the n. ambiguus. In particular, it was found that consecutive isolation of the left and right rostral parts of the n. ambiguus caused a significant decrease of the respiration rate and respiratory volume and also resulted in irreversible cessation of respiration in 83% of experiments. Isolation of symmetric medial parts of the n. ambiguus resulted in bradypnoe and a decrease of pulmonary ventilation; maximal respiratory effect was recorded after kainic acid injection in the symmetric part only, thus the irreversible cessation of respiration was recorded in 50% of experiments. After isolation of symmetric caudal parts of the n. ambiguus we observed an insignificant decrease of the respiration rate without significant changes of the respiratory volume, and number of the respiration cessation was minimal: 33%.