The Effects Of L-Dopa On Midbrain Microglia Of Rats

Parkinson,s disease (PD) is a common neurodegenerative disorder characterized bythe preferential loss of dopaminergic (DA) neurons in the substantia nigra (SN) parscompacta and the widespread presence of Lewy bodies (LB). The administration oflevodopa (L-DOPA) is a main method for the symptomatic treatment of PD. Now thequestion of whether L-DOPA-based therapy in PD is neurotoxic remains conflicting,whereas in vivo trials in animal models and human studies provided controversial results.Several studies have demonstrated that the intranigral administration of6-hydroxydopamine (6-OHDA）is an established model of the phase of human PD, awidespread microglial activation and increased level of inflammatory cytokines, tumornecrosis factor alpha (TNF-α) were noted in the SN along with the specific degenerationof DA neurons. At this point, a note of caution should be added. we evaluated the effectson microgial and DA neurons induced by L-Dopa (intranigral or intragastricadministration), using the6-OHDA model of PD as a standard of comparison. Thepurpose of the present study is to observe the potential toxicity of L-Dopa, which willprovide the experimental basis for safe and rational administration of L-Dopa.1, methods:(1)Sprague-Dawley (SD) rats were randomly divided into experimental and controlgroup seperataly.6-OHDA(5ug/uL),L-Dopa(50ug/uL,5ug/uL,1ug/uL)was injectedrespectively into the left striatum of brain in experimental groups, and normal salinewas injected into the same target areas of brain in control groups.(2) SD rats were randomly divided into experimental and control group seperataly.The rats of experimental groups were treated by intragastric administrationwith different doses of L-Dopa（200mg/kg.d、100mg/kg.d、10mg/kg.d）. The normalsaline was instead of L-Dopa in control group.(3)Four weeks after injection, the rats of all groups were observed theApomorphine-induced rotational behavior. (4)Four weeks after injection, the tyrosine hydroxylase positive neurons in thesubstantia nigra (SN) were observed with immunocytochemical method. The changeof IBA1positive microglias and the level of TNF-α was assayed byimmunofluorescence method, and the numbers of positive neurons were counted.2, Results:(1) Four weeks after injection, compared with control group, the numbers of IBAIand TNF-α positive cells in SN of6-OHDA group were significantly increased(P<0.001), the number of tyrosine hydroxylase positive neurons was decreasedsignificantly (P<0.001)．(2) Four weeks after injection, compared with control group, the numbers of IBAIand TNF-α positive cells in SN of high concentration L-Dopa (50ug/uL) group weresignificantly increased(P<0.05),the number of tyrosine hydroxylase positive neuronswas decreased significantly (P<0.05).(3) Four weeks after injection, compared with control group, the numbers of IBAIand TNF-α positive cells in SN of other L-Dopa groups (intragastric administrationand intranigral administration with low and middle doses) were not significantlyincreased (P>0.05)，the number of tyrosine hydroxylase positive neurons was notdecreased significantly (P>0.05).3,Conclusion:(1) Similar to the6-OHDA-induced lesion, high dose L-Dopa injected into striatumof normal rat is neurotoxic, which induced the microglial activation and the DAneurons lesion. The general dose of L-Dopa for oral administration is not neurotoxicin normal rats.(2)The possibility that the high dose L-Dopa via oral administration will beneurotoxic under the circumstance of brain severely pathologically impaired, is notexcluded.