Abstract
α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPArs), which mediate fast excitatory glutamatergic transmission, are tetramers made from four subunits (GluR1–4 or GluRA–D). Although synaptic AMPArs are not normally detected by immunocytochemistry in perfusion-fixed tissue, they can be revealed by using antigen retrieval with pepsin. All AMPAr-positive synapses in spinal cord are thought to contain GluR2, while the other subunits have specific laminar distributions. GluR4 can be alternatively spliced such that it has a long or short cytoplasmic tail. We have reported that <10% of AMPAr-containing synapses in lamina II have the long form of GluR4, and that these are often arranged in dorsoventrally orientated clusters. In this study, we test the hypothesis that GluR4-containing receptors are associated with dorsal dendrites of projection neurons in laminae III and IV that express the neurokinin 1 receptor (NK1r). Immunostaining for NK1r was carried out before antigen retrieval, and sections were then reacted to reveal GluR2 and either GluR4 (long form), GluR3 or GluR1. All NK1r-positive lamina III/IV neurons had numerous GluR2-immunoreactive puncta in their dendritic plasma membranes, and virtually all (97%) of the puncta tested were labelled (usually strongly) with the GluR4 antibody. Sizes of puncta varied, but many were elongated and they were significantly larger than nearby puncta that were not associated with the NK1r cells. None of the GluR2 puncta on these cells was positive for GluR1, while 85% were GluR3-immunoreactive. These results show that synaptic AMPArs on the dendrites of the lamina III/IV NK1r projection neurons contain GluR2, GluR3 and GluR4, but not GluR1 subunits.
Highlights
The spinal dorsal horn can be divided into six laminae based on cytoarchitectonic criteria (Rexed, 1952)
The main finding of this study is that dendrites belonging to the large neurokinin 1 receptor (NK1r)-expressing projection neurons with cell bodies in laminae III and IV have a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAr) puncta that are strongly immunoreactive with a GluR4 antibody, and contain GluR2 and GluR3, but not GluR1
There are several lines of evidence to support the suggestion that the punctate staining seen with antibodies against AMPAr subunits after antigen retrieval with pepsin represents receptors located at the postsynaptic aspect of glutamatergic synapses (Watanabe et al, 1998)
Summary
The spinal dorsal horn can be divided into six laminae based on cytoarchitectonic criteria (Rexed, 1952). Most dorsal horn neurons have axons that remain within the spinal cord (interneurons), there are discrete groups of cells with axons that project to the brain (projection neurons). One population of projection neurons consists of large cells with somata in lamina III–IV that express the neurokinin 1 receptor (NK1r, the main receptor for substance P) and have dorsal dendrites that enter lamina I The main excitatory neurotransmitter in the spinal cord, is used by primary afferents, excitatory interneurons and projection neurons (Broman et al, 1993; Todd et al, 2003; Maxwell et al, 2007). AMPArs are tetramers made from four subunits (GluR1–4 ⁄ GluRA–D), and subunit composition affects receptor properties, for example receptors lacking GluR2 are Ca2+-permeable (Burnashev et al, 1992)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
