In order to explore further the putative differential behavioral consequences of D1 dopamine and D2 dopamine receptor antagonism, SCH 23,390 (0.01-0.12 mg/kg) and raclopride (0.12-1.0 mg/kg) were administered to two separate groups of rats that had been trained in an eight-trial-per-day format to run down an alleyway, climb a vertical rope, and run across a horizontal board to access sweetened milk. Although both drugs dose-dependently reduced the speed of task completion, only raclopride produced vigorous, maldirected jumping behavior in the floor segment of the apparatus. The number of such jumps increased with dose. This raclopride-specific jumping phenomenon may provide a new behavioral arena for investigating the functional differences between D1 and D2 receptor antagonism.
Effects of haloperidol (0.04-0.32 mg/kg) were assessed in 10 hungry rats trained in a 10-trials-per-day format to run down an alleyway, climb a vertical rope, and run across a horizontal board to obtain sweetened milk. Rope lengths of 0.59 m and 1.32 m defined low- and high-effort requirements, respectively. Haloperidol produced substantial within-session decrements on Trials 2-10, but the drug did not affect rope-climbing speed more than horizontal running speed. Drug-induced within-session decrements were similar for both low- and high-effort requirements. After treatment with the 0.16-mg/kg dose, force-time waveforms of the climbing behavior documented instances of arrest of movement on the rope, but no bradykinesia of individual locomotor acts was discerned. Results suggest that haloperidol may produce associative deficits as well as disruptions of motor processes.
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