Differential distribution in rat brain of mu opioid receptor carboxy terminal splice variants MOR-1C-like and MOR-1-like immunoreactivity: evidence for region-specific processing

J Comp Neurol. 2000 Apr 3;419(2):244-56. doi: 10.1002/(sici)1096-9861(20000403)419:2<244::aid-cne8>3.0.co;2-r.


The present study examined immunohistochemically the regional distribution of the mu opioid receptor splice variant MOR-1C by using a rabbit antisera generated against the C-terminal peptide sequences and compared it with MOR-1. Overall, the distribution of MOR-1C-like immunoreactivity (-LI) differed from MOR-1-LI. Both MOR-1C-LI and MOR-1-LI were prominent in a few central nervous system regions, including the lateral parabrachial nucleus, the periaqueductal gray, and laminae I-II of the spinal trigeminal nuclei and the spinal cord. In the striatum, hippocampal formation, presubiculum and parasubiculum, amygdaloid nuclei, thalamic nuclei, locus coeruleus, and nucleus ambiguous MOR-1-LI predominated, whereas MOR-1C-LI was absent or sparse. Conversely, MOR-1C-LI exceeded MOR-1-LI in the lateral septum, the deep laminae of the spinal cord, and most hypothalamic nuclei such as the median eminence, periventricular, suprachiasmatic, supraoptic, arcuate, paraventricular, ventromedial, and dorsomedial nuclei. Double-labeling studies showed colocalization of the two receptors in neurons of the lateral septum, but not in the median eminence or in the arcuate nucleus, even though both MOR-1 isoforms were expressed. Because both MOR-1 and MOR-1C are derived from the same gene, these differences in regional distribution represent region-specific mRNA processing. The regional distributions reported in this study involve the epitope seen by the combinations of exons 7, 8, and 9. However, if other MOR-1 variants containing exons 7, 8, and 9 exist, the antisera would not distinguish between them and MOR-1C.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alternative Splicing
  • Amino Acid Sequence / genetics
  • Animals
  • Brain / metabolism*
  • CHO Cells
  • Central Nervous System / metabolism
  • Cricetinae
  • DNA, Recombinant
  • Genetic Variation
  • Immunoblotting
  • Immunohistochemistry
  • Male
  • Molecular Sequence Data
  • Peptide Fragments / genetics
  • Protein Processing, Post-Translational
  • Rabbits
  • Rats / metabolism*
  • Receptors, Opioid, mu / chemistry
  • Receptors, Opioid, mu / genetics
  • Receptors, Opioid, mu / metabolism*
  • Tissue Distribution


  • DNA, Recombinant
  • Peptide Fragments
  • Receptors, Opioid, mu