Abstract

The purpose of this study was to examine the role of dopaminergic input to the nucleus accumbens in the reinforcing effects of natural rewards using the place preference paradigm. In experiment 1, 22 male albino rats were randomly assigned to three groups. One group had received 6-hydroxydopamine(6-OHDA) lesions of the nucleus accumbens. The other two groups were used as sham operated or no food control group, 6-OHDA lesion group did not show the conditioned place preference and it was similar to no food control group. However, there was no difference among the three groups in the amount of food intake and number of crossing. Experiment 2 was conducted to see whether dopaminergic receptors in the nucleus accumbens were involved in the food reinforcing process. Haloperidol(0.5㎕, 1.0㎕) was injected just before being placed in the non-preferred compartment with food, and saline was injected just before being placed in the preferred compartment with no food. Only saline was injected to two control groups, one group was received food in the non-preferred compartment and the other group was received no food in either compartment. Results revealed that haloperidol groups and no food control group did not show the conditioned place preference. And there was also no difference among the four groups in the amount of food intake and number of crossing. Experiment 3 was conducted to test state dependent explanation of the result of experiment 2, and also to examine whether tegmentostriatal dopamine influences to the response with conditioned reinforcer even when primary reinforcer is not presented. Thirty rats were randomly assigned to two groups. Either saline or haloperidol(0.5㎕) was injected with into the nucleus accumbens during the conditioning phase. Before the test phase, each group was sub-divided into two. Either saline or haloperidol(0.5㎕) was injected again to sub-groups just before being tested. Results revealed that only those rats that were injected with saline during conditioning and test phase significantly changed their preference to the compartment associated with food. None of the other three groups(saline+saline, haloperidol+haloperidol, haloperidol+saline treated) changed their preference. These results indicated that the deficit in haloperidol treated rats was not due to the state dependent learning, and that haloperidol blocked the response to the conditioned reinforcer. Taken together it may be concluded that tegmentostriatal dopamine takes part in the reinforcement process of natural reward.