The priming effect of rewarding brain stimulation in rats depends on both the cost and strength of reward but survives blockade of D2-like dopamine receptors.

Receipt of an intense reward boosts motivation to work for more of that reward. This phenomenon is called the priming effect of rewards. Using a novel measurement method, we show that the priming effect of rewarding electrical brain stimulation depends on the cost, as well as on the strength, of the anticipated reward. Previous research on the priming effect of electrical brain stimulation utilized a runway paradigm in which running speed serves as the measure of motivation. In the present study, the measure of motivation was the vigour with which rats executed a two-lever response chain, in a standard operant-conditioning chamber, to earn rewarding electrical stimulation of the lateral hypothalamus. In a second experiment, we introduced a modification that entails self-administered priming stimulation and alternating blocks of primed and unprimed trials. Reliable, consistent priming effects of substantial magnitude were obtained in the modified paradigm, which is closely analogous to the runway paradigm. In a third experiment, the modified paradigm served to assess the dependence of the priming effect on dopamine D2-like receptors. The priming effect proved resilient to the effect of eticlopride, a selective D2-like receptor antagonist. These results are discussed within the framework of a new model of brain reward circuitry in which non-dopaminergic medial forebrain bundle fibers and dopamine axons provide parallel inputs to the final common paths for reward and incentive motivation.

The priming effect of food persists following blockade of dopamine receptors.

The priming effect of rewards is a boost in the vigor of reward seeking resulting from the previous receipt of a reward. Extensive work has been carried out on the priming effect of electrical brain stimulation, but much less research exists on the priming effect of natural rewards, such as food. While both reinforcement and motivation are linked with dopamine transmission in the brain, the priming effect of rewards does not appear to be dopamine-dependent. In the present study, an operant method was developed to measure the priming effect of food and then applied to investigate whether it is affected by dopamine receptor antagonism. Long-Evans rats were administered saline or one of the three doses (0.01, 0.05, 0.075 mg/kg) of the dopamine D1 receptor family antagonist, SCH23390, or the dopamine D2 receptor family antagonist, eticlopride. Although dopamine receptor antagonism affected pursuit of food, it did not eliminate the priming effect. These data suggest that despite the involvement of dopamine transmission in reinforcement and motivation, the priming effect of food does not depend on dopamine transmission.