The effects of dopamine D2 receptor ligands on novelty‐induced behavior in the rat open field test

Abstract

To determine the potential role of dopamine D2 receptor in mechanisms of anxiety, the effects of the preferential dopamine D2 receptor agonist, quinpirole, and antagonists, haloperidol and (–) sulpiride, were examined, in comparison to the action of the preferential dopamine D3 receptor agonist, (±)7-OH-DPAT and d-amphetamine, in the rat open field test. The effects of dopamine D2 receptor ligands in active doses were additionally verified in the Vogel conflict procedure. Quinpirole at the lower dose of 1.0 mg/kg produced a selective anti-thigmotactic effect, and increased the number of entries into the central part of the open field, without any influence on animals 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 activity. (–) 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 action in the open field test, except the general inhibitory effect at the highest dose examined. d-Amphetamine increased rats ambulation without any effect 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 D2 receptor mechanisms.