Blocking D1R and D2R with selective antagonists impairs object discrimination.

<p>Guinea pigs from the saline group (A) spent a significantly greater proportion of time exploring novel objects within the initial 30 seconds time interval but this tapered down over the 3-minute test window. By contrast, guinea pigs from both the SCH23390 group (B), or the sulpiride group (C), did not exhibit this characteristic feature during the initial 30 second time interval or any other interval over the 3-minute observation period. Note that the object exploration time does not evolve with time in the SCH23390 animal group which reflects the failure of habituation response during the test. Only guinea pigs in the saline group spent significantly more cumulative time with the novel object versus the familiar object (D), whereas there were insignificant differences in time spent between the novel and familiar objects in the SCH23390 group (E) or the sulpiride group (F). Group data (G) for calculated discrimination index revealed significant preferences for novel objects relative to familiar objects in guinea pigs injected with saline, but not SCH23390 or sulpiride [F(2, 32) = 8.791; p = 0.0008; within subject 1-way ANOVA with Tukeys post-hoc tests]. Only guinea pigs that exhibited the same preferences for FAM1 and FAM2 objects during the familiarization phase were used here. Asterisks indicate statistical differences and further discussed in text.