Immunoreactivity for the NMDA NR1 subunit in bulbospinal catecholamine and serotonin neurons of rat ventral medulla.

Auton Neurosci. 2013 Oct;177(2):114-22. doi: 10.1016/j.autneu.2013.02.024. Epub 2013 Apr 4. Llewellyn-Smith IJ, Mueller PJ. In this paper, the two awesome authors tackled a pretty good question that had always been overlooked; we know that presympathetic RVLM neurons can be excited by glutamate and that they show expression of the NMDAR1/NR1 subunit... but do ALL of these neurons express it, and if not, what percentage do and don't? To figure this out, they started with CTB injections at T9-T10 to retrogradely label spinally projecting neurons, and then they looked at TH+ and TH- neurons in the RVLM. They also looked at spinally projecting serotonergic (TpH+) and non-serotonergic (TpH-) neurons in the raphe pallidus (RPa). Once they had CTB labeled cells, they used fluorescent-conjugated antibodies to label CTB in blue, NR1 in red, and TH or TpH in green. Then it was just an issue of counting single, double, and triple labeled cells. They found that pretty much all spinally projecting neurons in the RVLM had NR1, with 100% of C1 neurons and ~96% of non-C1 showing expression. The overall distribution of CTB labeled C1 and non-C1 was about 50/50, with a slightly higher proportion (60%) in the 120um rostral to FN0. The story was pretty much the same with TpH in the RPa, except that about 80% of the cells were TpH+ vs 20% TpH-. The conclusion here is that yes, basically 100% of these cells express the NR1 subunit, so probably 100% of these cells use NMDAR to control their release of neurotransmitter. In the case of the RVLM, as we suspect, NMDAR regulation may be altered in disease states. -DH