Postnatal Development Differentially Affects Voltage-Activated Calcium Currents in Respiratory Rhythmic Versus Nonrhythmic Neurons of the Pre-Bötzinger Complex

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Abstract
The mammalian respiratory network reorganizes during early postnatal life. We characterized the postnatal developmental changes of calcium currents in neurons of the pre-Bötzinger complex (pBC), the presumed site for respiratory rhythm generation. The pBC contains not only respiratory rhythmic (R) but also nonrhythmic neurons (nR). Both types of neurons express low- and high-voltage-activated (LVA and HVA) calcium currents. This raises the interesting issue: do calcium currents of the two co-localized neuron types have similar developmental profiles? To address this issue, we used the whole cell patch-clamp technique to compare in transverse slices of mice LVA and HVA calcium current amplitudes of the two neuron populations (R and nR) during the first and second postnatal week (P0–P16). The amplitude of HVA currents did not significantly change in R pBC-neurons (P0–P16), but it significantly increased in nR pBC-neurons during P8–P16. The dehydropyridine (DHP)-sensitive current amplitudes did not significantly change during the early postnatal development, suggesting that the observed amplitude changes in nR pBC-neurons are caused by (DHP) insensitive calcium currents. The ratio between HVA calcium current amplitudes dramatically changed during early postnatal development: At P0–P3, current amplitudes were significantly larger in R pBC-neurons, whereas at P8–P16, current amplitudes were significantly larger in nR pBC-neurons. Our results suggest that calcium currents in pBC neurons are differentially altered during postnatal development and that R pBC-neurons have fully expressed calcium currents early during postnatal development. This may be critical for stable respiratory rhythm generation in the underlying rhythm generating network.