tokens: In contrast to the protection provided by the putative antagonists , the well - characterized sigma receptor agonist di - o - tolylguanidine ( DTG ) and the novel sigma receptor agonist BD1031 ( 3R - 1 - [ 2 - ( 3 , 4 - dichlorophenyl ) ethyl ] - 1 , 4 - diazabicyclo [ 4 . 3 . 0 ] nonane ) each worsened the behavioral toxicity of cocaine .