Activity of Different Populations of Neurons of the Bulbar Respiratory Center of Rats in the Dynamics of Hypobaric Hypoxia

We examined the involvement of different groups of inspiratory and expiratory neurons, INs and ENs, respectively, of the bulbar respiratory center, RC, in the control of respiration under conditions of hypobaric hypoxia. Such conditions were created in a laboratory altitude chamber and corresponded to a “lift” up to 8000 m altitude. At the beginning of such a “lift,” at a pressure corresponding to an altitude of 4000–5000 m, a decrease in the pO 2 in the inspired air to 98–85 mm Hg induced increases in the frequency of spiking of the examined neurons. Within a phase of extreme hypoxia, at an “altitude” of 7500 to 8000 m (pO 2 = 64–58 mm Hg), we observed considerable suppression of the activity of bulbar respiratory neurons. Impulse activity of INs and ENs within different stages of hypoxia demonstrated considerable specificity; INs were characterized by relatively higher resistivity with respect to the action of this factor. Among subgroups of these units, “early” and “full” INs were found to be more resistive with respect to the oxygen insufficiency. After “descent” of the animals and recovery of the normal atmospheric pressure, characteristics of spiking of most bulbar respiratory neurons gradually returned to the initial values.