Novel-object place conditioning: behavioral and dopaminergic processes in expression of novelty reward.

In a choice situation, rats given repeated access to novel objects in one of two distinct environments display an increase in preference for the novelty-paired environment. The experiments in this present report extend the generality of this effect to new procedures. Further, this shift in preference depends on object novelty; no systematic shift in preference was observed if the environment was paired with a familiar object. Experiments in the present report also provided evidence against non-associative accounts that rely on mechanisms that leave the paired environment more novel than the unpaired environment (e.g. object interaction interfering with environmental familiarization). Consistent with a conditioning account is the loss of place conditioning when access time with the novel objects was shortened from 10 min to 5 or 2.5 min. Interestingly, although a decrease in time with objects prevented place conditioning, these groups showed a novelty-conditioned increase in activity. Finally, treatment with the dopamine D(1) antagonist SCH-23390 (0.03 mg/kg) or the dopamine D(2)/D(3) antagonist eticlopride (0.1 mg/kg) before the post-conditioning preference test blocked expression of the novel-object place conditioning. Taken together, these experiments establish that the increased preference produced by object-environment pairings reflects a conditioned association between environmental cues and the appetitive effects of receiving access to novel stimuli.