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Abstract:
Abstract: Cannabinoids, psychoactive ingredients in
marijuana, have been shown to produce a variety of alterations in
cognition. Neocortical regions important to higher cognitive
functions are rich in cannabinoid receptors. The application of
rodent models of higher cognitive processes to the study of the
actions of cannabinoids is an essential prerequisite to
understanding their influence on underlying neurobiological
mechanisms. To assess the role of endogenous cannabinoids in time
perception in the rat, we applied a standard operant fixed interval
(FI-30s) time-production paradigm. On some trials, the first
response after the completion of the FI-30s resulted in
reinforcement. On other probe trials, no reinforcer was delivered
following completion of the 30 sec interval. This produced a
bell-shaped distribution of responses as a function of time,
thought to represent the subject's perception of the duration of
the FI-30s. Cannabinoid receptor antagonist SR 141718A (0-2 mg/kg
i.p.) was used to reduce binding of endogenous cannabinoids. It
shifted the distribution in a manner suggesting that elapsed time
was underestimated. In contrast, cannabinoid receptor agonist WIN
55212-2 (0- 1 mg/kg i.p.) and THC (0-4 mg/kg i.p.) shifted the
distribution in a manner suggesting that elapsed time was
overestimated. These results suggest that cannabinoid receptors
play an important role in time perception.
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