[Diphasic action of apomorphine on motility of the rat. I. Dose-effect relationship in exploratory and basal motility].

The effect of 8 doses of apomorphine HCl (0 - 6.25 - 13.46 - 29.01 - 62.5 - 134.65 - 290.1 - 625.0 microgram/kg, s.c. 15 min before) upon rat 30-min locomotor activity was evaluated in naive animals and in rats habituated to the actometer for 90 min. The doses of 29.01 - 62.5 - 134.65 significantly inhibited the exploratory activity of naive rats and the higher doses did not significantly influence such elevated baseline motility. On the contrary, low baseline motility of habituated rats resulted unaffected by the lower doses of apomorphine, whereas it was greatly stimulated by the doses of 290.1 and 625.0. It was concluded that suitable baselines of rat motility are required for the appearance of apomorphine stimulating effects at pre- and post-synaptic dopamine receptor levels.