Effects of locally applied dopamine to the nucleus accumbens on the motor activity of normal rats and following alpha-methyltyrosine or reserpine.

The motor activity of rats was investigated following bilateral application of various doses (0--80 micrograms) of dopamine to the nucleus accumbens. A high dose (80 micrograms) of dopamine increased the motor activity of normal as well as alpha-methyltyrosine- and reserpine-treated rats. It also increased the late motor activity (6--9 min) of normal rats, probably due to stimulation of postsynaptic dopamine receptors. Lower doses (10--40 micrograms) of dopamine suppressed initial (0--3 min) motor activity of normal rats, perhaps due to stimulation of dopamine autoreceptors on the dopamine nerve terminals in the nucleus accumbens with a subsequent inhibition of dopamine neurotransmission. An intermediate dose (40 micrograms) of dopamine was able to restore the motor activity of alpha-methyltyrosine-treated but not of reserpine-treated rats at all time intervals. This difference, indicating a restoration of the normal pattern of habituation by dopamine only in animals pretreated with alpha-methyltyrosine, suggests that normal behaviour is dependent on release of dopamine by nerve impulses.