STIMULATION OF THE NIGROSTRIATAL DOPAMINE SYSTEM PRODUCES HYPERTENSION AND TACHYCARDIA IN RATS

To test for the ability of the nigrostriatal dopamine (DA) system to influence cardiovascular function, experiments were carried out to assess the effects of electrical or chemical stimulation of the nigrostriatal DA system on arterial blood pressure, heart rate, and striatal DA release in anesthetized rats. Electrical stimulation of the substantia nigra pars compacta (SNC), in addition to enhancing the DA release in the corpus striatum (CS), elicited proportional hypertension and tachycardia. This could be mimicked by microinjection of two excitatory amino acids, kainic acid and glutamate, into the SNC area of rat brain. The SNC stimulation-induced hypertension, tachycardia, and increased striatal DA release were attenuated by prior destruction of the nigrostriatal DA system produced by intramedial forebrain bundle injection of 6-hydroxydopamine and by prior blockade of postsynaptic DA receptors produced by intra-CS injection of DA receptor antagonists, haloperidol or pimozide. The SNC stimulation-induced hypertension was attenuated by spinal transection, whereas the SNC stimulation-induced tachycardia was attenuated by bilateral vagotomy. The data suggest that stimulation of the nigrostriatal DA system produces both hypertension and tachycardia in rats.