Effects of a piperazine derivative, piribedil, on exploration, locomotor activity and social behaviour in the rat

• 1.

  1. The piperazine derivative, piribedil (ET495), in doses ranging from 10 to 100 mg/kg reduced locomotor activity and exploration in rats naive to the holeboard, but had less effect on exploration and was without effect on locomotor activity in rats familiar with the apparatus.

• 2.

  2. Doses of 5–100 mg/kg disrupted the usual between-day decrement in exploration and locomotor activity, but did not change the increase in head-dipping when novel objects were introduced on the second day.

• 3.

  3. ET495 and amphetamine counteracted each other's effects on locomotor activity, but had similar and additive effects on exploration.

• 4.

  4. Haloperidol did not antagonise the effects of ET495.

• 5.

  5. ET495 (0.5 & 1 mg/kg) increased social interaction between male rats when they were tested in an unfamiliar arena, but was without effect in a familiar one.

• 6.

  6. The effects of ET495 are dependent on the animal's familiarity with the test arena, but over the dose-range tested (0.5 to 100 mg/kg) there was no evidence of low doses acting on presynaptic receptors to produce stimulation of locomotor activity or exploration. The enhanced social interaction found after low doses might reflect a presynaptic action.