RESUMO
OBJECTIVE Histamine is a conserved neuromodulator in mammalian brains and critically involved in many physiological functions.Understanding the precise structure of histaminergic network is the cor-nerstone in elucidating its function.METHODS Herein,using novel HDC-CreERT2 mice and genetic labeling strategies,we reconstructed a whole brain 3D structure of histaminergic neurons and their outputs at 0.32×0.32×2 μm3 pixel resolution with a cutting-edge fluorescence micro-optical sectioning tomography system(fMOST).And we dissect an appetite control circuit originating from the TMN to medial septal nucleus(MS)using fiber photometry,optogenetics,and chemogenetics interfer-ence.RESULTS We quantified the fluorescence density of all brain areas and found that histaminergic fiber density varied significantly among brain regions.The density of histaminergic fiber was positively correlated with the amount of histamine release induced by optogenetic stim-ulation or physiological aversive stimulation.Moreover,we reconstructed fine morphological structure of 60 hista-minergic neurons via sparse labeling,and uncovered the largely heterogeneous projection pattern of individual his-taminergic neuron.Lastly,we found that MS-projecting histaminergic circuit is functionally inhibited during food consumption,and bidirectionally modulates feeding behavior via downstream H2,but not H1,receptors on MS glutamatergic neurons.CONCLUSION Collectively,this study reveals an unprecedented whole-brain quanti-tative analysis of histaminergic projections at the meso-scopic level,providing a foundation for future functional histaminergic study.And we also demonstrate that this MS-projecting histaminergic circuit is critically involved in feeding,and H2Rs in MS glutamatergic neurons is a promising target for treating body weight problems.