Effects on the caudate spindle in rats of dopamine microinjected into the caudate nucleus

We examined the caudate spindle in control and pargyline-pretreated rats following bilateral application of 3 doses (15, 50 and 150 micrograms/site) of dopamine (DA) into the caudate nucleus. The highest dose of DA (150 micrograms) suppressed the spindle, whereas lower doses (15, 50 micrograms) enhanced the spindle in control rats. Haloperidol given into the bilateral caudate nucleus increased the spindle in control rats. In pargyline-pretreated rats, 50 and 150 micrograms DA caused marked suppression, but 15 micrograms DA caused enhancement. These findings indicate that the DA system may mediate the development of the caudate spindle. Suppression of the caudate spindle induced by intracaudate DA injection may be due to stimulation of postsynaptic DA receptors and enhancement mediated by DA autoreceptors on the DA nerve terminals in the caudate nucleus with a subsequent inhibition of DA neurotransmission.