Effects of apomorphine and (+/-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine, injected into the striatum, on the caudate spindle in the rat.

The caudate spindle in rats was observed following bilateral application of apomorphine (1.5-50 micrograms) and (+/-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP, 0.3-3 micrograms) into the striatum. The smallest dose (1.5 micrograms) of apomorphine enhanced the spindle whereas with a larger dose (50 micrograms), suppression occurred. The preferential dopamine (DA) autoreceptor (inhibitory-receptor) agonist, (+/-)-3-PPP, enhanced the spindle, in a dose-dependent manner. The enhancing effect of apomorphine (1.5 micrograms) and (+/-)-3-PPP (3 micrograms) was prevented by neuroleptics, such as haloperidol (20 micrograms/kg, i.v.) and sulpiride (2 mg/kg, i.v.) at doses which, per se, did not affect the spindle. Small doses of neuroleptics are thought to block DA autoreceptors, suggesting that the enhancing effects of the DA agonists are mediated by autoreceptors. These results lend further support to the assumption that the development of the caudate spindle involves activation or DA receptors. Enhancement of the spindle, induced by injections of apomorphine into the striatum (small dose) and (+/-)-3-PPP, may be mediated by DA autoreceptors (inhibitory-receptors) located at presynaptic elements of the nigro-striatal DA system, while suppression may be due to stimulation of the postsynaptic DA receptors.