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

Abstract

Recent studies showed that respiratory rhythm generation depends on oscillators located in the pre-Bötzinger complex (pre-BötC) 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-BötC. Blockade of glycinergic and gamma-aminobutyric acidic inhibition synchronized preBötC and RTN/pFRG activity and significantly increased preBötC 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-BötC arising from the RTN/pFRG, (2) excitatory drive from the RTN/pFRG that triggers the preBötC 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.

Active Expiration Induced by Excitation of Ventral Medulla in Adult Anesthetized Rats

“…In contrast to our results in vivo in adult rats, in neonatal rat brainstem en bloc preparations blockade of GABA and glycine receptors synchronizes preBötC and RTN/pFRG activity (Onimaru et al, 1990; Iizuka, 2003; Funke et al, 2008). Notwithstanding the differences between in vitro preparations and whole animals, the different postsynaptic effects of GABA and glycine receptor activation through development may be the result of perinatal changes in Cl − -mediated currents (Ren and Greer, 2006).…”

The Cellular Building Blocks of Breathing

“…Most of these studies confirm the importance of synaptic inhibition in the generation of various characteristics of the respiratory rhythm (3, 12, 462, 515), and they also demonstrate that inhibition is an important determinant for the interaction between different areas of the respiratory network. One of these studies shows, for example, inhibitory interactions between the parafacial respiratory group (pFRG) and the preBötC (166). The pFRG seems to be critical for the generation of active expiration, as shown in a series of elegant studies using modern in vivo approaches (142, 144).…”

Calcium imaging of neuronal activity in the most rostral parafacial respiratory group of the newborn rat

“…In the dye-incubation method, the number of neurons that indicated clear respiratory activity was less than expected. The Ca 2? imaging has been mainly used in in vitro slice preparations [5,6,11,12], while voltage-sensitive dye imaging has been previously used for en bloc brainstem-spinal cord or in situ perfused brainstem preparations [1,18]. The present study on brainstem-spinal cord preparations from neonatal rats showed that the use of targeted microinjection of the Ca 2?…”

“…Fluctuation of intracellular Ca 2? concentration corresponds to single-cell activity, and this method has been successfully used in rhythmic in vitro slice preparations [5,6,11,12]. Recently, Ca 2? imaging has been applied to analyze respiratory (motor-) neuron activity in en bloc brainstem-spinal cord preparations from newborn mice [13].…”