Projectome-based characterization of hypothalamic peptidergic neurons in male mice.

The hypothalamus coordinately regulates physiological homeostasis and innate behaviors, yet the detailed arrangement of hypothalamic axons remains unclear. Here we mapped the whole-brain projections of over 7,000 hypothalamic neurons expressing distinct neuropeptides in male mice, identifying 2 main classes and 31 types using single-neuron projectome analysis. These classes/types exhibited regionally biased soma distribution and specific neuropeptide enrichment. Notably, many projectome types extended long-range axon collaterals to distinct brain regions, allowing single axons to co-regulate multiple targets. We uncovered topographic organization of certain peptidergic axons at specific targets, along with diverse single-neuron projectome patterns in Orexin, Agrp and Pomc populations. Furthermore, hypothalamic peptidergic neurons showed correlated innervation of subdomains in the periaqueductal gray and organized into modular subnetworks within the hypothalamus, providing a structural basis for coordinated outputs. This dataset highlights the complexity of hypothalamic axonal projections and lays a foundation for future investigation of the circuit mechanisms underlying hypothalamic functions.