Qualitative aspects on motility changes in mice induced by low doses of apomorphine and clonidine.

Single mice were treated with apomorphine (0.05, 0.2 or 0.8 mg/kg) or clonidine (0.025 or 0.05 mg/kg), and were placed in a new kind of motility meter, allowing classification of movements in terms of size, and also charting the motility with the help of an X/Y pen recorder. All treatments induced reduction of motility in this model. Apomorphine, 0.8 mg/kg, considerably changed the motility type, whereas the lower doses did not. This finding is consistent with earlier studies on gross lobomotor activity and suggests that the higher dose alone evokes a significant direct net stimulation of postsynaptic dopamine receptors, whereas the lower doses merely reduce the physiological stimulation of these receptors by inhibiting dopamine neurotransmission. Clonidine, 0.025 mg/kg, depressed motility at least as much as did 0.05 mg/kg, in agreement with previous behavioural studies.