NMDAR1 and primary afferent terminals in the superficial spinal cord.

We previously demonstrated a predominance of contacts by one type of glomerular ending (presumably from unmyelinated fibers) upon postsynaptic sites expressing the GluR1 subunit of the AMPA receptor, and of contacts by another type of glomerular ending (presumably from small myelinated fibers) upon postsynaptic sites expressing GLuR2. We here investigate whether any one of three types of primary afferent terminals, two glomerular and one non-glomerular, have direct contacts with postsynaptic sites containing the NMDAR1 subunit. Counts of gold particles revealed that contacts by primary afferents with NMDAR1-positive sites were less frequent than in material processed for AMPA receptor subunits, but that all three types of terminals contact NMDAR1-immunopositive postsynaptic sites in about equal proportions.