DIAZEPAM IMPAIRS PLACE LEARNING IN NAIVE BUT NOT IN MAZE-EXPERIENCED RATS IN THE MORRIS WATER MAZE

Anxiolytic benzodiazepines have been shown to impair place learning in the Morris water maze, However, a dear-cut demonstration of a direct and specific effect on mnemonic processes has not yet been offered. In the present study, the effects of diazepam on place navigation in the Morris water maze were studied in rats. Three conditions were examine d: learning, reversal learning and learning after familiarisation of a nimals with the maze. In view of the anxiolytic and sedative propertie s of diazepam, appropriate doses of the drug, i.e. those that produced an anxiolytic effect but no major motor impairment, were initially se lected in the water-lick conflict and rotarod tests, respectively. Dos es of 2.5 and 5 mg/kg PO increased punished drinking in the water-lick conflict test without significantly decreasing rotarod performance. T hese doses were then used to assess the effects of diazepam on spatial behaviour. Diazepam, at both doses, impaired place learning in behavi ourally naive rats. Such an effect appeared to be transient: diazepam- treated rats eventually reached control performance. Moreover, analysi s of the probe trial at the end of training revealed adoption of a spa tial strategy to locate the submerged platform. Neither reversal learn ing nor learning after familiarisation was affected. These results do not replicate previous findings in the Morris water maze and provide s ome evidence that the diazepam-induced place learning deficit may be p rimarily anxiolytic in nature.