Modulatory effects of GABA and gabazin on respiratory responses during electrostimulation of nucleus raphe magnus

Objective. Nucleus raphe magnus, preliminary consisting of serotonergic and GABAergic neurons, is involved in modulation of different respiratory responses. GABA, a neurotransmitter participating in res-piratory rhythmogenesis, is known to have inhibitory effects on respiratory parameters. Materials and Methods. The authors studied the responses of respiratory pattern and bioelectric activity of inspiratory muscles in rats to electrostimulation of the rostral nucleus raphe magnus before and during microinjections of GABA or gabazine. Experiments were conducted on adult rats anaesthetized with urethane. Results. A decrease both in inspiratory duration and in amplitude parameters during electrical stimulation of the nucleus raphe magnus was found. Gabazine microinjected into the same nucleus induced inhalation shortening, reduction in tidal volume, decrease in bioelectric activity of external intercostal muscles, and uptick in expiratory duration. Microinjections of GABA induced increase in bioelectric activity of external intercostal muscles and minute volume. During electric stimulation after microinjection of GABA, maximal amplitude of oscillations of inspiratory muscles also increased. Besides, breathing frequency reduction and amplitude increase were recorded. Electric stimulation after administration of gab-azine also caused increase of the tidal volume, minute volume, maximal amplitude of oscillations of bursting activity of the diaphragm and external intercostal muscles. Conclusion. The obtained data confirm the involvement of GABA via activation of GABAa receptors in modulation of respiration by neurons of nucleus raphe magnus.