Effects of dopaminergic agonists on rotational behavior and striatal dopamine metabolism following unilateral electrical stimulation of the substantia nigra in the rat

Abstract

In order to clarify pharmacological properties of the rotational behavior produced by unilateral electrical stimulation of the substantia nigra, we have tested effects of dopamine (DA) agonists on the behavior and striatal DA metabolism in unanesthetized rats. Male Wister rats (260-300g) were chronically implanted with bipolar electrodes in the right substantia nigra. An intranigral injection oí 6-hydroxydopamine (8 μg/ 4 μl)markedly depressed the rotational behavior. The rotational behavior was significantly suppressed by apomorphine (0.5 and 1 mg/kg s.c.) and bromocriptine(10 mg/kg i.p.), and slightly accelerated by methamphetamine (0. 5 mg/kg s. c.)· Concentrations of DOPAC and HVA in the ipsilateral striatum increased after the unilateral electrical stimulation for 30 min in probenecid treated rats. Pretreatment with bromocriptine reduced an increase in concentrations of DOPAC and HVA. These results suggest that the rotational behavior produced by electrical stimulation results from the activation of unilateral nigro-striatal dopaminergic neurons. Inhibition of the rotational behavior with DA agonists may be due to the reduction in the DA release through the activation of presynaptic DA recepter.