The prefrontal cortex (PFC) undergoes protracted postnatal development such that its structure and behavioural function may be profoundly altered by environmental factors. Here we investigate the effect of lactational dietary manipulations on novel object recognition (NOR) learning and PFC monoamine neurotransmitter metabolism in early adolescent rats. To this end, Wistar rat dams were fed a high caloric cafeteria diet (CD) during lactation and resultant 24-26 day old offspring exposed to NOR testing and simultaneous PFC dopamine and serotonin metabolism measurement. In the second NOR choice trial where one familiar and one novel object were presented controls explored the novel preferentially to the familiar object both after a 5 min (P<0.001) or 30 min (P<0.05) inter-trial intervals (ITI). By contrast, offspring from dams fed on lactational CD failed to show any significant preference for the novel object at either time point. Compared with chow fed controls, their average exploration ratio of the novel object was lower after the 5 min ITI (P<0.05). Following a 60 minute ITI, neither CD nor control offspring showed a preference for the novel object. PFC dopamine metabolism was significantly reduced in the CD group (P<0.001), whereas serotonin metabolism was increased (P<0.001). These results suggest that an obesogenic lactational diet can have a detrimental impact on cognition in adolescent offspring associated with aberrant PFC serotonin and dopamine metabolism.