Learning impairment produced in rats by the cannabinoid agonist HU 210 in a water-maze task

To ascertain whether the cannabinoid agonist HU 210 (25, 50, or 100 mu g/kg , IP) influences rat spatial learning, water-maze performance was examined in the place (hidden platform)-and cue (visible platform)-versions of the M orris water maze. In addition, other unlearned behaviors were examined, nam ely, vocalization and wall hugging during the place task, and motor abiliti es during a motor test battery. The results obtained show that HU 210 at 50 or 100 mu g/kg (once daily for 4 days, 60 min before a daily session) impa ired learning in the place version but not in the cue one: wall hugging and enhanced vocalization were also displayed by the animals in the fourth ses sion. Motor activity was compromised by the same treatment schedule. When t he drug was discontinued, the effects produced by HU 210 at 50 mu g/kg reve rsed in 3 days, while disruption of acquisition and vocalization caused by HU 210 at 100 mu g/kg remained after 7 days' abstinence. Discussion centers on the possible specific cognitive mechanisms affected by the drug and on aspecific factors (i.e., anxiety-like state), which may contribute to the i mpairment of spatial learning. (C) 1999 Elsevier Science Inc.