Data from: Mapping and analysis of the connectome of sympathetic premotor neurons in the rostral ventrolateral medulla of the rat using a volumetric brain atlas

Spinally projecting neurons in the rostral ventrolateral medulla (RVLM)
play a critical role in the generation of vasomotor sympathetic tone and
are thought to receive convergent input from neurons at every level of the
neuraxis; the factors that determine their ongoing activity remain
unresolved. In this study we use a genetically restricted viral tracing
strategy to definitively map their spatially diffuse connectome. We
infected bulbospinal RVLM neurons with recombinant rabies variant that
drives reporter expression in monosynaptically connected input neurons and
mapped their distribution using a MRI-based volumetric atlas and a novel
image alignment and visualization tool that efficiently translates the
positions of neurons captured in conventional photomicrographs to
Cartesian coordinates. We identified prominent inputs from
well-established neurohumoral and viscero-sympathetic sensory actuators,
medullary autonomic and respiratory subnuclei, and supramedullary
autonomic nuclei. The majority of inputs lay within the brainstem (88 –
94%), and included putative respiratory neurons in the pre-Bötzinger
Complex and post-inspiratory complex that are therefore likely to underlie
respiratory-sympathetic coupling. We also discovered a substantial and
previously unrecognized input from the region immediately ventral to
nucleus prepositus hypoglossi. In contrast, RVLM sympathetic premotor
neurons were only sparsely innervated by suprapontine structures including
the paraventricular nucleus, lateral hypothalamus, periaqueductal grey and
superior colliculus, and we found almost no evidence of direct inputs from
the cortex or amygdala. Our approach can be used to quantify, standardize
and share complete neuroanatomical datasets, and therefore provides
researchers with a platform for presentation, analysis and independent
analysis of connectomic data.