Mother/offspring co-administration of the traditional herbal remedy yokukansan during the nursing period influences grooming and cerebellar serotonin levels in a rat model of neurodevelopmental disorders.

Neurodevelopmental impairment in the serotonergic system may be involved in autism spectrum disorder. Yokukansan is a traditional herbal remedy for restlessness and agitation in children, and mother-infant co-administration (MICA) to both the child and the nursing mother is one of the recommended treatment approaches. Recent studies have revealed the neuropharmacological properties of Yokukansan (YKS), including its 5-HT1A (serotonin) receptor agonistic effects. We investigated the influence of YKS treatment on behavior in a novel environment and on brain monoamine metabolism during the nursing period in an animal model of neurodevelopmental disorders, prenatally BrdU (5-bromo-2'-deoxyuridine)-treated rats (BrdU-rats). YKS treatment did not influence locomotor activity in BrdU-rats but reduced grooming in open-field tests. YKS treatment without MICA disrupted the correlation between locomotor behaviors and rearing and altered levels of serotonin and its metabolite in the cerebellum. These effects were not observed in the group receiving YKS treatment with MICA. These data indicate a direct pharmacological effect of YKS on the development of grooming behavior and profound effects on cerebellar serotonin metabolism, which is thought to be influenced by nursing conditions.