Inhibition of Locomotor Activity of Rats by Low Doses of Different Dopamine (DA) Receptor Agonists
Apomorphine-HCl (APO) or the ergot derivative lisuride hydrogen maleate (LHM), both supposed to stimulate directly DA receptors, were injected subcutaneously to male Wistar rats (80–100 g). Immediately following the drug or vehicle application locomotor activity of individual rats was recorded during 10 min time inter vals for 30–240 min using circular photocell motility meters. APO or LHM had a biphasic action on locomotor activity; in low doses (0.006–0.1 mg/kg) they caused hypomotility, while doses > 0.1 mg/kg produced motor stimulation. The suppression of motor activity induced by 0.1 mg/kg of APO or by 0.025 mg/kg of LHM was followed by hyperactivity; LHM caused a more pronounced and more long-lasting stimulation.