Characteristic response of striatal astrocytes to dopamine depletion

Astrocytes and astrocyte-related proteins play important roles in maintaining normal brain function,and also regulate pathological processes in brain diseases and injury.However,the role of astrocytes in the dopamine-depleted striatum remains unclear.A rat model of Parkinson’s disease was therefore established by injecting 10μL 6-hydroxydopamine(2.5μg/μL)into the right medial forebrain bundle.Immunohistochemical staining was used to detect the immunoreactivity of glial fibrillary acidic protein(GFAP),calcium-binding protein B(S100B),and signal transducer and activator of transcription 3(STAT3)in the striatum,and to investigate the co-expression of GFAP with S100B and STAT3.Western blot assay was used to measure the protein expression of GFAP,S100B,and STAT3 in the striatum.Results demonstrated that striatal GFAP-immunoreactive cells had an astrocytic appearance under normal conditions,but that dopamine depletion induced a reactive phenotype with obvious morphological changes.The normal striatum also contained S100B and STAT3 expression.S100B-immunoreactive cells were uniform in the striatum,with round bodies and sparse,thin processes.STAT3-immunoreactive cells presented round cell bodies with sparse processes,or were darkly stained with a large cell body.Dopamine deprivation induced by 6-hydroxydopamine significantly enhanced the immunohistochemical positive reaction of S100B and STAT3.Normal striatal astrocytes expressed both S100B and STAT3.Striatal dopamine deprivation increased the number of GFAP/S100B and GFAP/STAT3 double-labeled cells,and increased the protein levels of GFAP,S100B,and STAT3.The present results suggest that morphological changes in astrocytes and changes in expression levels of astrocyte-related proteins are involved in the pathological process of striatal dopamine depletion.The study was approved by Animal Care and Use Committee of Sun Yat-sen University,China(Zhongshan Medical Ethics 2014 No.23)on September 22,2014.

Cortical regulation of striatal projection neurons and interneurons in a Parkinson's disease rat model

Striatal neurons can be either projection neurons or interneurons, with each type exhibiting distinct susceptibility to various types of brain damage. In this study, 6-hydroxydopamine was injected into the right medial forebrain bundle to induce dopamine depletion, and/or ibotenic acid was injected into the M1 cortex to induce motor cortex lesions. Immunohistochemistry and western blot assay showed that dopaminergic depletion results in significant loss of striatal projection neurons marked by dopamine- and cyclic adenosine monophosphate-regulated phosphoprotein, molecular weight 32 k Da, calbindin, and μ-opioid receptor, while cortical lesions reversed these pathological changes. After dopaminergic deletion, the number of neuropeptide Y-positive striatal interneurons markedly increased, which was also inhibited by cortical lesioning. No noticeable change in the number of parvalbumin-positive interneurons was found in 6-hydroxydopamine-treated rats. Striatal projection neurons and interneurons show different susceptibility to dopaminergic depletion. Further, cortical lesions inhibit striatal dysfunction and damage induced by 6-hydroxydopamine, which provides a new possibility for clinical treatment of Parkinson＇s disease.