Abstract
Cellular and synaptic mechanisms operating in the brainstem respiratory network are not completely understood. Embedded in the respiratory network, the pre-Botzinger complex (pre-BötC) receives convergent inputs from numerous neuron populations. Hypoglossal motoneurons (XII MNs) are a major cranial motor output of the respiratory network and their activation during breathing, including by pre-BötC-driven circuits, is essential for maintaining upper airway patency. We applied sharp microelectrode intracellular recording techniques to characterize pre-BötC neuron and XII MN respiratory spiking patterns and input synaptic drives within in situ perfused brainstem-spinal cord preparations of mature rats, which allow analysis of patterning mechanisms during inspiratory and expiratory phases in an intact brainstem. A population of pre-BötC inspiratory neurons showed post-inspiratory hyperpolarization followed by ramping membrane potential and excitatory synaptic drive with characteristic pre-inspiratory spiking activity. In the XII motor nucleus we distinguished three groups of respiratory MNs by their spiking profile (including pre-inspiratory spiking) and membrane potential time course during the respiratory cycle. Our data suggest multiple pattern formation mechanisms and sources of synaptic drive shaping membrane potential trajectories of pre-BötC neurons and XII MNs in situ.
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