Cardiovascular changes following DOCA/NaCl or conditioning in 6-hydroxydopamine-treated rats

Abstract

Two intracisternal injections of 200 μg 6-hydroxydopamine reduced brain catecholamine levels 90% and significantly lowered resting heart rate and blood pressure. In a classical aversive conditioning paradigm, 6-hydroxydopamine-treated rats displayed little or no conditioned heart rate response in anticipation of shock, but a potentiated unconditioned response to shock itself. The alteration in heart rate responses may have been due in part to alterations in general activity. Although 6-hydroxydopamine treatment did not abolish the hypertension caused by DOCA/NaCl treatment following uninephrectomy, the increase in blood pressure was significantly less than the blood pressure increase in control rats receiving this treatment. The 6-hydroxydopamine treatment, however, concomitantly reduced the amount of NaCl consumed after DOCA. Since peripheral tyrosine hydroxylase activity and amine levels were not significantly altered by 6-hydroxydopamine treatment, the alterations in cardiovascular responses following 6-hydroxydopamine must result from its central actions. Although 6-hydroxydopamine administration markedly altered the cardiovascular responses to conditioned stimuli, shock, and DOCA/NaCl treatment, it is difficult to ascribe these alterations to ablation of central catecholamine fibers participating directly in cardiovascular control. The link between destruction of catecholamine fibers and changes in cardiovascular responses may be secondary to changes in activity or ingestive behavior.