The effects of hallucinogenic drugs on maze exploration in the rat over a 24 hour period.

1. The variation with clock-hour in the behaviour of naive rats in a Y-maze has been recorded.2. The number of entries recorded was highest during the light period while the number of faecal boluses was highest during the dark period. Rearing showed a biphasic periodicity.3. The responses to LSD, mescaline and amphetamine also showed significant variation with clock-hour.4. In general, amphetamine, 1.25 mg/kg, increased the number of entries and the number of rears, the effect being greatest at the end of the light period. LSD, 100 mug/kg, and mescaline, 12.5 mg/kg, decreased the number of entries and the number of rears.5. All three drugs decreased the number of faecal boluses. The possible significance of these responses in terms of an effect on the emotional state of the animals is discussed.