HCRTR2 (Fig. 4c; Extended Data Fig. 8a), which is thought to regulate sleep-wakefulness and is highly expressed in mouse hypothalamus45. Conversely, Trh and Nxph4 show enriched expression in mouse but not human SP (Fig. 4d; Extended Data Fig. 8b). Interestingly, Trh is also not expressed in the rat SP18, suggesting this pattern is specific to mouse. These results indicate that the evolutionary elaboration of SP in primates is associated with altered gene expression.
