Reconfiguration of respiratory-related population activity in a rostrally tilted transversal slice preparation following blockade of inhibitory neurotransmission in neonatal rats

Recent studies showed that respiratory rhythm generation depends on oscillators located in the pre-Botzinger complex (pre-BotC) and the parafacial respiratory group (pFRG). To study inhibitory synaptic interactions between these two oscillators, we developed a rostrally tilted transversal slice preparation, which preserves these regions. The onset of rhythmic mass activity in the retrotrapezoid nucleus (RTN)/pFRG preceded that of the pre-BotC. Blockade of glycinergic and gamma-aminobutyric acidic inhibition synchronized preBotC and RTN/pFRG activity and significantly increased preBotC burst frequency, amplitude, and duration. Population imaging revealed recruitment of inspiratory-like neurones, while expiratory-like neurones lost their phasic activity. The reconfiguration after disinhibition reveals: (1) synaptic inhibition of the pre-BotC arising from the RTN/pFRG, (2) excitatory drive from the RTN/pFRG that triggers the pre-BotC burst. Our findings support the view that these synaptic interactions in vitro relate to the initiation of the inspiratory phase or to the steering of the expiratory-inspiratory phase transition in vivo.