Ambiguous respiratory neurons are modulated by GABA(A) receptor-mediated inhibition

A group of respiratory neurons in the rostral nucleus ambiguus complex is known to generate the inspiratory and expiratory drives which enable spontaneous respiration to be sustained. Since previous studies indicated that mutual synaptic inhibition is required to produce oscillations between inspiratory and expiratory neurons, it may implicate GABAergic synaptic transmission between each group of neurons. In this study we tried to determine whether most ambiguous respiratory neurons are influenced by GABA(A) receptor-mediated inhibition. Eighty-eight respiratory interneurons showing rhythmic activity in synchrony with the spontaneous respiration were recorded in urethane-chloralose anesthetized Wistar rats. Multibarrel iontophoretic application of GABA(A) antagonist bicuculline produced a remarkable facilitation in maximum burst discharge rate, whereas the agonist muscimol reversed this effect completely. Simultaneous application of GABA and bicuculline increased the discharge rate more than in any single application or in the simultaneous application of GABA and muscimol. These results were statistically significant. These findings suggest strongly that GABA(A) receptors in the ambiguous respiratory neurons may have an inhibitory role in the synaptic transmission for maintaining the respiratory oscillation in the nucleus ambiguus.