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 microg/kg, IP) influences rat spatial learning, water-maze performance was examined in the place (hidden platform)--and cue (visible platform)--versions of the Morris water maze. In addition, other unlearned behaviors were examined, namely, vocalization and wall hugging during the place task, and motor abilities during a motor test battery. The results obtained show that HU 210 at 50 or 100 microg/kg (once daily for 4 days, 60 min before a daily session) impaired 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 session. Motor activity was compromised by the same treatment schedule. When the drug was discontinued, the effects produced by HU 210 at 50 microg/kg reversed in 3 days, while disruption of acquisition and vocalization caused by HU 210 at 100 microg/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 impairment of spatial learning.