The effect of intrastriatal injection of estrogen on pallidal field potential and rigidity in Parkinsonian -ovariectomized rats



The major pathological feature of Parkinson’s disease (PD) is a progressive loss of dopamine-producing neurons of the substantia nigra pars compacta (SNc), resulting in a reduction of dopamine (DA) content in the target field of these neurons, the striatum (STR). The present evidences suggest that female sex hormones may influence the onset and severity of PD symptoms. PD is more prevalent in men than in women by an approximate ratio of 3:2, suggesting a possibly protective influence of estrogen on predisposition to the disease. In this work, the effect of intrastriatal injection of 3 µg/3µl of estrogen on globus pallidus (GP) extracellular field potential and muscular stiffness before and after lesioning the SNc by 6-hydroxydopamine (6-OHDA) in 12 ovariectomized Wistar rats (180-220 g) has been tested. Results showed that decreased GP local EEG amplitude significantly improved after estrogen therapy in Parkinsonian-ovariectomized rats in both pre-and post- SNc lesioning (P<0.01). Meanwhile, the GP local EEG amplitude in pretreated-lesioned ovariectomized rats and then treated by estrogen was significantly (P<0.01) higher than post- lesion treated ones. These findings suggest that estrogen pretreatment in female rats suffering from PD has an important defense mechanism by which estrogen modulates DA function. Recent studies suggest that estrogen alter the function of both pre-synaptic SNc neurons and their post-synaptic targets in the STR, thereby exerting a potent modulatory influence over dopaminergic transmission within the basal ganglia. It seems that pretreatment by estrogen may prevent the reduction of GP local EEG amplitude and can attenuate muscular stiffness induced by 6-OHDA as a selective neurotoxin for dopaminergic system.