Inthisstudy,wesoughttoelucidatetheeffectsofmelatoninonlearningandmemoryaswellasapoptosisandexpressionoftheBaxorBcl-2proteinsinthesubgranularzoneofthedentategyrusinpinealectomizedrats.UsingtheMorriswatermazeandtheolfactorymemorytests,wefoundthattheaverageescapelatencyinpinealectomizedratswasclearlyincreasedcomparedwithsham-operatedrats.Moreover,theaverageescapelatencyinthemelatonin-treatedandpinealectomizedratswaslongerthanthatinthesham-operatedratsandshorterthanthatinthepinealectomizedanduntreatedrats.Immunohistochemistryandterminal-deoxynucleoitidyltransferasemediatednickendlabeling(TUNEL)showedthattherewerefewerBaximmunoreactivecellsandTUNEL-positive(apoptotic)cellsbutmoreBcl-2immunoreactivecellsinthemelatonin-treatedratscomparedwiththepinealectomizedrats.Thesham-operatedratsshowednumbersofthesecellssimilartothemelatonin-treatedrats.TheseexperimentalfindingsdemonstratethatmelatonintreatmentmayreduceabnormalapoptosisbypromotinggeneexpressionofBaxandsuppressinggeneexpressionofBcl-2inthesubgranularzoneofthedentategyrusinpinealectomizedrats.Theseeffectsappeartoresultintheinhibitionofcellularapoptosisandtheimprovementofspatiallearningandmemoryinpinealectomizedrats.
