title: Immunohistochemical localization of mu opioid receptor in the marginal division with comparison to patches in the neostriatum of the rat brain.
abstract: BACKGROUND
  Mu opioid receptor (MOR), which plays key roles in analgesia and also has effects on learning and memory, was reported to distribute abundantly in the patches of the neostriatum. The marginal division (MrD) of the neostriatum, which located at the caudomedial border of the neostriatum, was found to stain for enkephalin and substance P immunoreactivities and this region was found to be involved in learning and memory in our previous study. However, whether MOR also exists in the MrD has not yet been determined.
  
  
  METHODS
  In this study, we used western blot analysis and immunoperoxidase histochemical methods with glucose oxidase-DAB-nickel staining to investigate the expression of MOR in the MrD by comparison to the patches in the neostriatum.
  
  
  RESULTS
  The results from western blot analyses revealed that the antibody to MOR detected a 53 kDa protein band, which corresponded directly to the molecular weight of MOR. Immunohistochemical results showed that punctate MOR-immunoreacted fibers were observed in the "patch" areas in the rostrodorsal part of the neostriatum but these previous studies showed neither labelled neuronal cell bodies, nor were they shown in the caudal part of the neostriatum. Dorsoventrally oriented dark MOR-immunoreactive nerve fibers with individual labelled fusiform cell bodies were firstly observed in the band at the caudomedial border, the MrD, of the neostriatum. The location of the MOR-immunoreactivity was in the caudomedial border of the neostriatum. The morphology of the labelled fusiform neuronal somatas and the dorsoventrally oriented MOR-immunoreacted fibers in the MrD was distinct from the punctate MOR-immunoreactive diffuse mosaic-patterned patches in the neostriatum.
  
  
  CONCLUSIONS
  The results indicated that MOR was expressed in the MrD as well as in patches in the neostriatum of the rat brain, but with different morphological characteristics. The punctate MOR-immunoreactive and diffuse mosaic-patterned patches were located in the rostrodorsal part of the neostriatum. By contrast, in the MrD, the dorsoventrally parallel oriented MOR-immunoreactive fibers with individual labelled fusiform neuronal somatas were densely packed in the caudomedial border of the neostriatum. The morphological difference in MOR immunoreactivity between the MrD and the patches indicated potential functional differences between them. The MOR most likely plays a role in learning and memory associated functions of the MrD.
authors.affiliation: College of Biophotonics, South China Normal University, Guangzhou, GD 510631, China.
authors.forename: Chuanxing
authors.initials: C
authors.lastname: Wang
authors.forename: Si Yun
authors.initials: SY
authors.lastname: Shu
authors.forename: Zhouyi
authors.initials: Z
authors.lastname: Guo
authors.forename: Ye Feng
authors.initials: YF
authors.lastname: Cai
authors.forename: Xinmin
authors.initials: X
authors.lastname: Bao
authors.forename: Changchun
authors.initials: C
authors.lastname: Zeng
authors.forename: Bingyi
authors.initials: B
authors.lastname: Wu
authors.forename: Ziyou
authors.initials: Z
authors.lastname: Hu
authors.forename: Xuemei
authors.initials: X
authors.lastname: Liu
mesh_terms: D000818:Animals; D015153:Blotting, Western; D007124:Immunoenzyme Techniques; D007858:Learning; D008297:Male; D008568:Memory; D017072:Neostriatum / Q000033:anatomy & histology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000378:metabolism* / Q000502:physiology
chemical_list: D017450:Receptors, Opioid, mu