tokens: The effects of three SSRIs ( fluvoxamine , sertraline , paroxetine ) and three sigma - 1 receptor agonists ( SA4503 , 4 - phenyl - 1 - ( 4 - phenylbutyl ) piperidine ( PPBP ) , and dehydroepiandrostero ( DHEA ) - sulfate ) on NGF - induced neurite outgrowth in PC12 cells were examined .