l-Tetrahydropalmatine (l-THP) is a drug for assuaging dull pain and anxiety insomnia.

In this paper, a study on the catalepsy was made on rats. 1 . Given intraperitoneally 70~100 mg/kg in rats, l-THP caused not only a catalepsy, but also a significant rise of 5-HIAA in the brain, which is a valid index of serotoninergic neuronal activities. 2. If the activities of 5-HT neurons were depressed by PCA (20 mg/kg, ip) or PCPA ( 300 mg/kg, ip) 48 hours previously, l-THP produced in rats a marked augmentation of catalepsy associated with a significant decrease of 5-HT and 5-HIAA contents in brain. This augmentation lasted more than 7 hours. Cinanserin, a blocking anent of 5-HT receptor, also exhibited a similar but less augmentation. 3. If the activities of 5-HT neurons were strengthened by an injection of a load-dosage of l-tryptophan or probenecid, the catalepsy induced by l-THP was reduced. These results showed that the brain serotoninergic system was involved in l-THP-induced catalepsy, which bore an inverse relationship to the content of brain serotonin.