Participation of GABAB Receptors of Parafacial Respiratory Group in the Regulation of Respiration in Rats.

The respiratory effects of microinjections of baclofen and 2-hydroxysaclofen into the parafacial respiratory group were studied in experiments on rats. It was shown that activation of GABAB receptors of the parafacial respiratory group suppressed external respiration due to a decrease in the tidal volume and inspiratory flow rate. In parallel, we observed a decrease in the amplitude and an increase in the duration of inspiratory bursts of the diaphragm. Injection of GABAB receptor blocker into the parafacial respiratory group increased pulmonary ventilation due to an increase in volumetric parameters of the inspiratory phase. This effect was accompanied by prolongation of expiration and lengthening of the intervals between the inspiratory bursts of the diaphragm. These results suggest that GABAB receptors of the parafacial respiratory group are an important element of the central mechanisms regulating the volumetric respiratory parameters and are involved in the regulation of the phases of the respiratory cycle.

Role of GABAA Receptors of Parafacial Respiratory Group in Control of Respiration in Rats.

The role of GABAergic inhibition in the regulation of activity of the parafacial respiratory group was studied on narcotized mature rats. Microinjections of GABAA agonist muscimol into the parafacial respiratory group inhibited external respiration and bioelectrical activity of the diaphragmatic muscle resulting in diminished tidal volume and decreased respiration rate accompanied by prolonged inspiration, expiration, and intervals between the inspiratory bursts in the phrenic electromyogram. In contrast, microinjections of GABAA antagonist bicuculline into this group stimulated respiration and markedly increased its volumetric parameters. In addition, blockade of GABAA receptors affected the expiratory phase and interburst intervals in the phrenic electromyogram, but produced no effect on respiration rate. These findings attested to contribution of GABAA-mediated inhibition into the performance of parafacial respiratory group. The study revealed different roles of GABAA receptors in modulation of the mechanisms of respiration rate control in mature rats and formation of inspiratory motor outputs originating from the parafacial respiratory group.

[THE INFLUENCE OF INFORMATION LOAD ON THE TIMECOURSE OF SPECTRAL PARAMETERS OF HEART RATE VARIABILITY IN STUDENTS WITH DIFFERENT CHRONOTYPES].

In the study, distinctions in daily timecourse of spectral parameters of the heart rate variability (HRV) at rest wakefulness and at information load in students with different chronotypes are revealed. The most pronounced changes in the general spectral power of HRV due to fluctuations of all parameters, but especially the VLF, LF, HF waves and the LF/HF index were found in students with a daily chronotype at rest and after implementation of load tests during the different periods of the school day. In persons with an evening chronotype in conditions of rest, the greatest variability was found in a spectral HF component of HRV, and responses to information load were found during the day in different combinations of changes of LF and HF components and the LF/HF index. In students with a morning chronotype during rest wakefulness, considerable fluctuations of a proportion of LF waves were observed, whereas in response to information load during certain periods of the day, representation of LF and HF components of the spectrum was changed. The wide variability of HRV spectral parameters in students with daily activity, compared to students with early and late activities, reflects the advantages of persons with a daily chronotype in terms of adaptation to different operation modes and irregular stress information in the course of the day.

Respiratory response to microinjections of GABA and penicillin into various parts of the ventral respiratory group.

Experiments on rats showed that local injection of GABA (10(-4) M) into the rostral and caudal compartments of the ventral respiratory groups decreased the respiratory rhythm, but increased lung ventilation (especially injection into the rostral part). Penicillin (10(-7) M) injected into the rostral division increased the tidal volume and practically did not change the respiratory rate, but its injection into the caudal part reduced the tidal volume and increased respiratory rate. These results indicate that GABAergic mechanisms including GABA(A) sites play an ambiguous role in the regulation of respiration at the level of the rostral and caudal parts of the ventral respiratory group.

Respiratory effects of stimulation of the limbic cortex in rats and their modulation with serotonin.

Acute experiments on rats showed that the anterior cingulate gyrus contains 2 efferent regions of the functional respiratory system (inhibitory supragenual and excitatory infragenual areas). Stimulation of these cortical areas produced a respiratory effect, which depended on activity of serotoninergic mechanisms in the solitary tract nucleus.