Analysis of the Role of GABAergic Mechanisms in Regulation of the Respiratory Activity of Parafacial Structures of the Brainstem in Rats

Acute experiments on anesthetized adult rats breathing atmospheric air of constant gas composition were performed in order to assess changes in the parameters of the spirogram and the bioelectric activity of the diaphragm in response to microinjections of GABA_A -agonist muscimol into the retrotrapezoid nucleus/ parafacial respiratory group (RTN/pFRG) region. Microinjections of muscimol into RTN had an inhibitory effect on respiration, which developed sufficiently quickly. The rats demonstrated a decrease in the respiratory minute volume and the inspiratory flow rate, which occurred primarily due to a change in the temporal parameters of respiration, including its reduced frequency. The reactions of external respiration corresponded to а significant increase in the duration of inspiratory bursts and a less pronounced decrease in the amplitude of oscillations on the electromyogram (EMG) of the diaphragm. Microinjections of muscimol into pFRG also caused respiratory depression; however, a decrease in the lung ventilation and inspiratory flow rate was associated predominantly with a decrease in the tidal volume and a slight prolongation of inspiration and expiration. In this case, the diaphragm EMG showed a pronounced decrease in the oscillation amplitude in combination with a slight increase in the duration of inspiratory bursts and interburst intervals. The obtained experimental data indicate that GABA_A -receptors contribute to the activity of the RTN/pFRG region and constitute an important link in the central mechanisms of respiratory control in mammals breathing atmospheric air of unchanged gas composition. Thus, GABA_A -receptors of RTN make a significant contribution to regulation of the phase structure of the respiratory cycle and the frequency of diaphragmatic inspiratory bursts, while GABA_A -receptors of pFRG are more involved in the inhibitory modulation of the volumetric parameters of external respiration and the amplitude of diaphragmatic activity oscillations.

parafacial respiratory group, retrotrapezoid nucleus, GABA_A-receptors, external respiration, electromyogram of the diaphragm

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