UNILATERAL NEONATAL INTRACEREBROVENTRICULAR 6-HYDROXYDOPAMINE ADMINISTRATION IN RATS .2. EFFECTS ON EXTRACELLULAR MONOAMINE, ACETYLCHOLINE AND ADENOSINE LEVELS MONITORED WITH IN-VIVO MICRODIALYSIS

6-hydroxydopamine (6-OHDA, 100 mu g in 5 mu l) was injected into the r ight ventricle of 3-day-old Sprague Dawley rats in order to produce a unilateral dopamine (DA) lesion. At adult stage, the rats were implant ed with microdialysis probes into the left and right striata. On the i njected side, basal extracellular levels of DA were reduced by >65%, a s compared to the contralateral side or to the levels found in vehicle -injected rats. Extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) a nd homovanillic acid (HVA) were reduced by >95%, while acetylcholine ( ACh) was decreased by >50%. d-Amphetamine (2 mg/kg SC) produced a 10-f old increase in extracellular DA levels in the striatum contralateral to the 6-OHDA-injected side, while on the ipsilateral side, DA levels were not affected by d-amphetamine. d-Amphetamine produced an increase (>2 fold) in extracellular ACh levels, on both ipsilateral and con tr alateral sides. Choline and adenosine levels were unaffected by any of the experimental conditions. Thus, neonatal unilateral ICV administra tion of 6-OHDA produced an ipsilateral decrease in striataI extracellu lar DA, DOPAC and HVA levels, compared to the contralateral side. A re duction of extracellular ACh levels was also observed on the 6-OHDA-in jected side. The DA releasing effect of d-amphetamine was abolished on the 6-OHDA-injected side, but not that on ACh levels, indicating that striatal DA and ACh d-amphetamine-induced release are produced by ind ependent mechanisms in the neonatally unilateral 6-OHDA-treated animal s. As a whole the present study gives evidence showing that neonatal u nilateral ICV treatment with 6-OHDA produces a predominantly unilatera l lesion of the mesencephalic DA systems.