1996 Volume 27 Issue 1 Pages 63-75
It has been known that intracerebroventricular (i. c. v.) administration of 6-hydroxydopamine (6-OHDA) induces severe symptoms such as akinesia, adipsia, and aphagia in adult rats. However, in immature rats to which 6-OHDA was administered at the neonatal period (2 and 4 days old), hyperactivity in locomotion, rearing, and grooming was observed, and the brain dopamine turnover ratio was also increased. The present study was made to investigate the mechanisms for abnormal behaviors and brain mono-amine turnover ratios in neonatally 6-OHDA-treated immature rats. The administration of 6R-5, 6, 7, 8-tetrahydro-L-biopterin (6R-BH4, i. c. v.), an agent for raising dopamine and serotonin turnover on the 24th day, suppressed the abnormal behaviors to the intact level and increased brain serotonin turnover ratio, with dopamine turnover ratio unaffected. The administration of naloxone (NX, s. c.), an opioid peptide receptor antagonist on the 24th day, resulted in quit same effects. These data suggest that activated abnormal behaviors were caused by the increase in dopamine turnover ratio due to the compesatory mechanism for 6-OHDA-induced dopamine neuron injury, and that 6R-BH4 and naoxone-induced increase in serotonin turnover ratio had a suppressive effect on abnormal hyperactivity.
