The present invention relates to a therapeutic agent for neuropathic pain containing, as an active ingredient, a compound represented by general formula (I) or a pharmacologically acceptable acid addition salt thereof: (wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, A, and B have the same definitions as those described in the specification), and an animal model produced by administering (+)-4a-(3-hydroxyphenyl)-2-methyl-1,2,3,4,4a,5,12,12a-octohydro-trans-qui- nolino[2,3-g]isoquinoline. The present invention makes it possible to perform drug treatment for neuropathic pain. The therapeutic effect of a compound against neuropathic pain can also be evaluated.