Basic NeuroscienceA novel slice preparation to study medullary oromotor and autonomic circuits in vitro

- We have developed a new way of sectioning the medulla for in vitro studies.
- The slice encapsulates sensory, integrative, and motor nuclei for oromotor control.
- Axonal connections were validated with both tract tracing and live-cell imaging.
- Neurons in integrative and motor nuclei were activated by sensory area stimulation.
- The slice serves as an in vitro model to study oromotor and autonomic pathways.

BackgroundThe medulla is capable of controlling and modulating ingestive behavior and gastrointestinal function. These two functions, which are critical to maintaining homeostasis, are governed by an interconnected group of nuclei dispersed throughout the medulla. As such, in vitro experiments to study the neurophysiologic details of these connections have been limited by spatial constraints of conventional slice preparations.New methodThis study demonstrates a novel method of sectioning the medulla so that sensory, integrative, and motor nuclei that innervate the gastrointestinal tract and the oral cavity remain intact.ResultsImmunohistochemical staining against choline-acetyl-transferase and dopamine-β-hydroxylase demonstrated that within a 450 μm block of tissue we are able to capture sensory, integrative and motor nuclei that are critical to oromotor and gastrointestinal function. Within slice tracing shows that axonal projections from the NST to the reticular formation and from the reticular formation to the hypoglossal motor nucleus (mXII) persist. Live-cell calcium imaging of the slice demonstrates that stimulation of either the rostral or caudal NST activates neurons throughout the NST, as well as the reticular formation and mXII.Comparison with existing methodsThis new method of sectioning captures a majority of the nuclei that are active when ingesting a meal. Tradition planes of section, i.e. coronal, horizontal or sagittal, contain only a limited portion of the substrate.ConclusionsOur results demonstrate that both anatomical and physiologic connections of oral and visceral sensory nuclei that project to integrative and motor nuclei remain intact with this new plane of section.