The effects of dopamine D-2 receptor ligands on novelty-induced behavior in the rat open field test

To determine the potential role of dopamine D-2 receptor in mechanisms of a nxiety, the effects of the preferential dopamine D-2 receptor agonist, quin pirole, and antagonists, haloperidol and (-) sulpiride, were examined, in c omparison to the action of the preferential dopamine Dg receptor agonist, ( +/-)7-OH-DPAT and d-amphetamine, in the rat open field test. The effects of dopamine D-2 receptor ligands in active doses were additionally verified i n the Vogel conflict procedure. Quinpirole at the lower dose of 1.0 mg/kg p roduced a selective anti-thigmotactic effect, and increased the number of e ntries into the central part of the open field, without any influence on an imals motility. At this dose the drug also increased punished but not free drinking. Both haloperidol and (-) sulpiride reduced the number of entries into the central sector of the open field without changing rat motor activi ty. (-) Sulpiride in a dose-dependent manner decreased also the time spent in the central part of the open field. No effect of the antipsychotics was observed in the Vogel conflict test. (+/-)7-OH-DPAT failed to exert any act ion in the open field test, except the general inhibitory effect at the hig hest dose examined. d-Amphetamine increased rats ambulation without any eff ect on exploratory behavior. The data are discussed in relation to the role of changes in dopaminergic activity in modulation of anxiety, and relative importance of dopamine D-2 receptor mechanisms.