A new digitized method of the compulsive gnawing test revealed dopaminergic activity of salvinorin A in vivo.
The compulsive gnawing (CG) test has been used for numerous years as an assay to determine the dopaminergic activity of various compounds. We developed a new method of quantification via a digitization step which allowed a more precise measurement of the gnawing activity. It was the aim of the present study to explore possible dopaminergic effects of salvinorin A (SA), the major active compound of Salvia divinorum, using the new digitized CG test. A group of experiments using male C57BL6 mice were performed to validate the new method of quantification showing only significant increases of gnawing when the dopamine reuptake inhibitors buproprion (20 mgkg, p.0.) and nomifensine (10 mgkg, i.p.) were given concomitantly with apomorphine (10 mgkg, i.p.). Different concentrations of the SA (1.0, 2.5, 5, and 10 mgkg, i.p.) were tested with positive dopaminergic activity when administered with apomorphine which differed from the semisynthetic counterpart U-69593. Furthermore, the activity observed with SA was unsuccessfully antagonized by the κ-opioid receptor antagonist norbinaltorphimine (NorBNI 10 and 20 mgkg, i.p.), while the dopamine antagonist haloperidol did successfully block (0.06 mgkg, i.p.) the gnawing activity seen with SA. Our data further strengthen the argument that salvinorin A is not a selective κ-opioid receptor agonist and is the first in vivo study that veers from salvinorin A acting solely like its synthetic counterparts. Furthermore, the digitized CG test system used in this study provides a new computational method to accurately detect behavior associated with dopaminergic neurotransmission.