Abstract
The present experiment examined the effects of cocaine (0.0 and 15
mg/kg, i.p.) and ketamine (0.0, 10.0 and 15 mg/kg, i.p.) on timing
behavior using a 12-s differential reinforcement of low rates (DRL)
procedure and a 2- vs. 8-s bisection procedure in rats. DRL (time
production) and bisection (time perception) procedures are sensitive
to effects of dopaminergic drugs and provide an assessment of the
accuracy and precision of interval timing as well as the subject's
level of impulsivity. When administered to rats trained on either
the DRL or the bisection procedure, cocaine shifted the psychophysical
functions leftward relative to control conditions. In contrast, ketamine
produced no change in the temporal control of behavior on either
procedure. These differential effects of cocaine and ketamine are
consistent with previous reports suggesting that dopamine levels
in the dorsal striatum, but not in prefrontal cortex, ventral striatum
or hippocampal regions, are crucial for the regulation of the speed
of an internal clock.
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