Brain-wide mapping of efferent projections of glutamatergic (Onecut3(+)) neurons in the lateral mouse hypothalamus

AimThis study mapped the spatiotemporal positions and connectivity of Onecut3(+) neuronal populations in the developing and adult mouse brain. MethodsWe generated fluorescent reporter mice to chart Onecut3(+) neurons for brain-wide analysis. Moreover, we crossed Onecut3-iCre and Mapt-mGFP (Tau-mGFP) mice to visualize axonal projections. A dual Cre/Flp-dependent AAV construct in Onecut3-iCre cross-bred with Slc17a6-FLPo mice was used in an intersectional strategy to map the connectivity of glutamatergic lateral hypothalamic neurons in the adult mouse. ResultsWe first found that Onecut3 marks a hitherto undescribed Slc17a6(+)/Vglut2(+) neuronal cohort in the lateral hypothalamus, with the majority expressing thyrotropin-releasing hormone. In the adult, Onecut3(+)/Vglut2(+) neurons of the lateral hypothalamus had both intra- and extrahypothalamic efferents, particularly to the septal complex and habenula, where they targeted other cohorts of Onecut3(+) neurons and additionally to the neocortex and hippocampus. This arrangement suggests that intrinsic reinforcement loops could exist for Onecut3(+) neurons to coordinate their activity along the brain's midline axis. ConclusionWe present both a toolbox to manipulate novel subtypes of hypothalamic neurons and an anatomical arrangement by which extrahypothalamic targets can be simultaneously entrained.