Effect of different doses of estrogen on the nigrostriatal dopaminergic system in two 6-hydroxydopamine-induced lesion models of Parkinson's disease.

Parkinson's disease results from a degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNpc) and it is more prevalent in men than in women. Estrogen has neuroprotective action of the nigrostriatal dopaminergic (NSDA) neurons. It was investigated whether differences in plasma 17β-estradiol (E2) levels alter the degree of neuroprotection in NSDA neurons. Ovariectomized rats, implanted with subcutaneous capsules containing 400, 800 or 1,600 μg of E2 or corn oil, were injected with 1 μg of 6-OHDA in the SNpc or the medial forebrain bundle (MFB). Striatal dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and plasma E2 levels were measured. Only at 400 μg, E2 protected striatal DA against lesion of the MFB. In the SNpc, E2 failed to prevent DA depletion, but increased DOPAC/DA ratio in the striatum. In an NSDA moderate lesion, E2 has a neuroprotective action. In a severe lesion, E2 could stimulate DA activity in remaining neurons.