Yokukansan, a traditional Japanese medicine, decreases head-twitch behaviors and serotonin 2A receptors in the prefrontal cortex of isolation-stressed mice.
Yokukansan, a traditional Japanese (Kampo) medicine, has recently been used to treat the behavioral and psychological symptoms of dementia (BPSD), including aggressiveness, excitability, and hallucination. The present study was designed to investigate the mechanisms underlying the ameliorative effects of yokukansan on BPSD using animals exhibiting hallucination-like behaviors. For this purpose, we initially examined whether chronic isolation stress increases the frequency of hallucination in response to a psychedelic drug. Using this animal model, we next examined the effects of yokukansan on drug-induced hallucination-like behaviors. Finally, we examined the density and mRNA levels of serotonin 2A (5-HT2A) receptors. Male mice were subjected to isolation stress for six weeks. Yokukansan was incorporated into food pellets, and administered to the mice for six weeks. In some experiments, yokukansan and each of seven constituent herbs were administered orally to the mice for the last two weeks during the six-week period of isolation stress. A 5-HT2A receptor agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI, 2.5mgkg), was injected into the mice, and head-twitch behaviors were quantified. The binding sites of 5-HT2A receptors on the plasma membrane of the prefrontal cortex (PFC) were assessed by a receptor-binding assay using tritium-labeled ketanserin, and the density and affinity were calculated from a Scatchard plot. The level of mRNAs was measured by PCR analyses. Isolation stress enhanced the frequency of the DOI-induced head-twitch response, and yokukansan treatment by feeding significantly reduced this enhancement. Isolation stress significantly increased the 5-HT2A receptor density in the PFC, and yokukansan treatment by feeding as well as administration significantly down-regulated this increase. Isolation stress and yokukansan did not affect the affinity. Among seven constituent herbs, Bupleurum Root, Uncaria Hook, Japanese Angelica Root, and Glycyrrhiza down-regulated the increase, but statistically not significant, in which their efficacies were over 50% relative to yokukansan. Neither isolation stress nor yokukansan affected mRNA levels of 5-HT2A receptors. Yokukansan attenuated drug-induced hallucination-like behaviors in isolated mice, which is suggested to be mediated by 5-HT2A receptor down-regulation in the PFC. This mechanism may underlie the ameliorative effects of yokukansan on hallucination.