Retrograde tracing revealed a cluster of neurons projecting to the lateral hypothalamus (LH) surrounded by the olfactory cortex. (a) Coronal sections of the LH after injection of Alexa 555-conjugated cholera toxin B subunit (CTB, red) with DAPI staining (blue). Immunostaining for orexin (middle, green) or melanin-concentrating hormone (MCH) (right, green) was performed. Scale bars: 200 μm in left panel, 100 μm in middle and right panels. LH, lateral hypothalamus; DM, dorsomedial hypothalamus; VMH ventromedial hypothalamus, 3V, third ventricle; Me, medial amygdaloid nucleus; opt, optic tract. The structure boundaries were drawn using the Franklin and Paxinos mouse brain atlas31. (b) CTB-labelled cells in the frontal cortex and olfactory cortex. The inset in the left panel is magnified in the right panel. Scale bars: 500 μm in left panel, 100 μm in right panel. (c) The average number of CTB-labelled cells in each olfactory cortical area (average of three coronal sections) Data are shown as average ± SD with individual plots. ***p < 0.001. APC, anterior piriform cortex; AON, anterior olfactory nucleus; VTT, ventral tenia tecta; VON, ventral olfactory nucleus; OT, olfactory tubercle.