Effect of Melatonin on Parkinson-Like Syndrome Induced by I-Methyl-4-Phenyl Tetrahydropyridine in Mice

This work was carried out on 144 adult male albino mice; 72 adult mice were divided into 3 groups (MPTP or Parkinsonian model, prophylactic, and treated). Each group consisted of 24 adult male mice.Parkinson’s model group was injected daily S.C. with 30 mg MPTP / kg for 3 successive days Prophylactic group was injected with low dose of melatonin (0.5 mg / mice / day) I.P. for 2 weeks prior to MPTP injection.The treated group was injected firstly with MPTP and then treated with therapeutic dose of melatonin (1.0 mg / mice / day). The other 72 mice were considered as control groupsThe effects of MPTP in inducing Parkinsonian like syndrome and the protective effect of melatonin were studied in each group by clinical tests, histopathological study, immunohistochemical techniques, molecular examination and biochemical analysis. The clinical studies included, observation for the appearance of muscle tremors in the experimental animals, recording of number of movement /minute by activity cage apparatus, recording griping time on rotating rod (seconds) by Rota rod apparatus and recording descending time (seconds) on vertical pole by pole test.Blood sample was taken from each animal immediately before scarification to be used for estimation of plasma levels of free radicals (nitric oxide & lipid peroxidation products) and antioxidant enzymes (glutathione peroxidase & superoxide dismutase) by using spectrophotometer. Brain from each mouse of all studied groups was dissected and preserved for histopathological examination and immunohistochemical studies. Anatomically localized substantia nigra was freshly used for molecular studies that included detection of DNA fragmentation and Tunnel Technique. In Parkinsonian model group, as a result of MPTP administration, obvious resting tremors and significant decrease in the frequency of movement/ minute, loss of ability to coordinate the limb movement, seen as significant decrease in griping time on rotating rod and prolonged the descending time of pole test. It is concluded that MPTP administration led to significant reduction motor activity of the mice.Histopathological and immunohistochemical studies of Parkinsonian model showed severe degenerative changes in most dopaminergic neurons. In spite of the marked degeneration and necrosis of dopaminergic neurons, apoptotic cells could not be detected by molecular studies in all Parkinson’s model subgroups. Hence apoptosis had undetectable role in the pathogenesis of neuronal death in MPTP neurotoxicity. Biochemical analysis of blood samples of Parkinsonian model group revealed significant progressive increase in plasma levels of free radicals: nitric oxide (NO) and lipid peroxidation products (LP). Meanwhile, plasma levels of antioxidant enzymes, glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) decreased significantly in all subgroups when compared with that of its control values. All Parkinson’s model subgroups had typical clinical features of Parkinsonian like syndrome, which were positively correlated with the measured plasma oxidant indices and antioxidant enzymes. While in prophylactic group of mice, administration of melatonin significantly decreased parkinsonian symptoms when compared with that of Parkinson’s model group. Histopathological and immunohistochemical studies, of slides representing the prophylactic group of mice, revealed an obvious increase in the number of dopaminergic neurons and the THpositive neurons of substantia nigra and red nuclei. Also, the majority of dopaminergic neurons of SN and red nuclei preserved their normal histological architecture. Also, melatonin administration to this group of mice decreased significantly the plasma levels of free radicals and increased significantly the antioxidant enzymes in comparable to that of Parkinson’s model group. Melatonin performed its neuroprotective role through its ability to inhibit the formation of free radicals or scavenge them. Hence, application of melatonin in low protective dose succeeded in protecting the vulnerable dopaminergic neurons against the administered MPTP and restoring their neurotransmitter with consequent reestablishing the normal motor activity. Application of melatonin in high therapeutic dose to treated group succeeded to decrease parkinsonian symptoms significantly in comparable to that of Parkinson’s Egypt J. Neurol. Psychiat. Neurosurg. Vol. 44 (1) – Jan 2006 364 model group. However, the improvement in clinical test was more obvious in prophylactic than treated group. Histopathological and immunohistochemical examinations showed that, application of melatonin as a therapeutic agent failed to regenerate the MPTP lesioned neurons as shown by histopathological and immunohistochemical studies. In spite of this, melatonin may allow sprouting of dopamine terminals with subsequently restoring the released neurotransmitters from sbstantia nigra and improving the detectable clinical signs of MPTP induced Parkinsonism. Biochemical analysis of blood samples of this group revealed significant decrease of plasma free radicals (LP& NO) and significant increase antioxidant enzymes (GSH-Px and SOD). Hence administration of melatonin as a therapeutic agent was able to inhibit the production of oxidant indices and to enhance the antioxidant enzymes. In spite of this, the increased antioxidant enzymes may not be sufficient to treat the lesioned neurons after MPTP toxicity. In conclusions: MPTP succeed to induce typical Parkinson’s model. Melatonin has antioxidant protective role, so its application in low prophylactic dose is beneficial in protecting the neurons against the injected neurotoxin MPTP. However, application of melatonin as therapeutic agent after MPTP neurotoxicity failed to regenerate the MPTP damaged neurons, in spite of this it may allow sprouting of dopamine terminals with subsequent restoring the released neurotransmitters from SN and improving the detectable clinical signs of MPTP induced Parkinsonism. (Egypt J. Neurol. Psychiat. Neurosurg. , 2007,