6-羟基多巴胺诱导的帕金森病大鼠眼内褪黑素受体的变化

Changes of melatonin receptors in both eyes of 6-hydroxydopamineinduced hemiparkinsonium rats

目的:观察6-羟基多巴胺(6-OHDA)诱导的偏侧帕金森病(PD)模型大鼠毁损同侧及对侧眼褪黑素受体MT1和MT2的变化及其与视网膜酪氨酸羟化酶(TH)的关系。方法:将6-OHDA注射至大鼠右侧黑质致密部和前脑内侧束两点,制备偏侧PD模型。大鼠分为溶剂对照和PD模型组,于建模后6周取双侧眼球。采用RTPCR和Western-Blot检测大鼠两侧眼组织褪黑素受体MT1和MT2的表达水平,采用免疫荧光组织化学检测MT1和MT2受体,以及TH在大鼠视网膜内的分布及表达情况。结果:与对照相比,PD大鼠毁损对侧眼组织MT1和MT2的mRNA水平分别降低了84.06%和81.66%(P<0.01),蛋白水平分别降低了59.06%和41.06%(P<0.01),而PD大鼠毁损同侧眼组织MT1和MT2的mRNA、蛋白水平无显著变化(P>0.05)。MT1和MT2受体在视网膜全层均有分布,且主要分布在感光细胞层内段、内丛状层、外丛状层和神经节细胞层,TH分布于内核层与内丛状层之间;与对照组相比,PD大鼠毁损对侧视网膜MT1和MT2以及TH荧光强度分别减少了61.6%、51.2%和43.0%(P<0.01),TH和MT1或TH和MT2存在共定位,且毁损对侧视网膜共定位细胞数减少52.3%,而PD大鼠毁损同侧视网膜无显著变化(P>0.05)。结论:6-OHDA诱导的偏侧PD大鼠毁损对侧眼褪黑素受体表达下调可能与PD有关。

Objective： To investigate the changes of MT1 and MT＇2 melatonin receptors and their relationship with tyro- sine hydroxylase （TH） in eyes both ipsilateral and contralateral to the lesion of 6-hydroxydopamine （6-OHDA）-induced hemiparkinsonium rats. Methods： Parkinson＇s disease （PD） model rats were established by a unilateral intracerebral in- jection of 6-OHDA into the right substantia nigra pars compacta and medial forebrain bundle. Rats were divided into the 6-OHDA-lesioned group and the vehicle-treated group, and sacrificed at six weeks post-lesion to remove eyeballs. The mRNA and protein expressions of MT1 and MT2 receptors were determined by RT-PCR and Western-Blot in both eyes of rats from both groups. Meanwhile, the distributions and contents of MT1 and MT2 receptors as well as TH were also as- sayed by immunohistochemistry in both retinas of rats. Results： In comparison to the vehicle, the mRNA levels of MT1 and MT2 receptors in the eye contralateral to the lesioned side were dramatically decreased by 84.06% and 81.66%, re- spectively （P 〈 0.01 ）, while the protein levels of MT1 and MT2 receptors distinctly declined by 59.06% and 41.06%, respectively （P 〈0.01 ）. No significant of MT1/MT2 mRNA and protein level was observed in the eyes ipsilateral to the lesioned side of PD rats （P 〉 0.05）. MT1 and MT2 receptors were found in all layers of retina, especially in the inner segments of photoreceptors （IS） , outer plexiform layer （ OPL）, inner plexiform layer （IPL） and ganglion cell layer （GCL）. TH positive neurons were seen at the border between IPL and the inner nuclear layer （INL）. In addition, mean immunofluorescence intensities of MT1, MT2 and TH in the contralateral retina of 6-OHDA-lesioned rats were reduced by approximate 61.6%, 51.2% and 43.0%, respectively （P 〈 0.01 ）, compared with the vehicle. Colocalization of TH/ MT1 or TI-I/MT2 was identified in ceils lining the inner boundary of the INL, and the numbers of co-localized cells showed a 52.3% reduction in the contralateral retina of hemiparkinsonium rats in comparison to the ipsilateral side. Less change of these molecules was observed in the ipsilateral retina to the lesion of PD rats （ P 〉 0.05 ）. Conclusion： These findings suggest that down-regulation of MT1 and MT2 melatonin receptors in the contralateral retina following 6-OHDA insult is possibly involved in the development of PD.