Effect of some beta-carbolines on phenylethylamine and apomorphine stereotypies in rats

Tetrahydro-beta-carbolines (THBC:s) have recently been shown to occur in the human body and their role in mental diseases has been discussed. The effect of THBC:s and some other beta-carbolines (25 mg/kg IP) were studied on the stereotypies caused by apomorphine (APO, 2 mg/kg IP) and phenylethylamine (PEA, 50 mg/kg IP) in rats. These effects of dopaminergic drugs like apomorphine as well as of phenylethylamine have sometimes been used as animal models of paranoid schizophrenia. Dose effect relationships were studied from ther most potent substances. All beta-carbolines studied significantly inhibited APO stereotypy. 6-Methoxyharmalan was most effective followed by beta-carboline (BC), tetrahydro-beta-carboline (THBC), 1-methyl-THBC, 6-methoxy-THBC and 6-hydroxy-THBC. 6-Methoxyharmalan, 6-hydroxy-THBC and BC inhibited also PEA stereotypy. Other substances studied were ineffective. beta-Carbolines did not inhibit PEA and APO stereotypies in the same way. Thus the mode of PEA and APO stereotypies seems to differ, and beta-carbolines seem influence these stereotypies by more than one mechanism. If dopamine hypothesis is valid, the beta-carbolines formed in human body may protect rather than worsen in paranoid psychoses.