HTR5A and insomnia: The results of the present animal experiments suggest that BX-YYR intervenes in hippocampal 5-HT and its receptor expression in PCPA insomnia model rats, possibly by elevating the hippocampal 5-HT content and 5-HT1A expression level and decreasing the 5-HT content and hippocampal 5-HT2A expression level, thus acting as a sleep-wake regulator.