Central circuits regulating the sympathetic outflow to lumbar muscles in spinally transected mice by retrograde transsynaptic transport.

Xiang HB, Liu C, Liu TT, Xiong J. Int J Clin Exp Pathol. 2014 May 15;7(6):2987-97. I gave this paper a look because I’d been thinking about differential control of nerves and how the RVLM plays in to this in some species. In this paper, they injected the lumbar epaxial muscles (near L5 vertebrae) of mice with a pseudorabies virus (PRV) with a red fluorescent protein reporter in order to map which regions of the CNS control lumbar sympathetic nerve activity. The mice were also given spinal transections at L2, caudal to where the sympathetic nerve exits so that they could “cut out” any PRV transport through motor neurons. They tracked expression time in different regions and found IML labeling by day 3, and that some animals began to show labeling in RVLM and PVN by day 3 as well, with one animal showing labeling in the raphe pallidus (RPa). By day 4 labeling in those areas was much more widespread, covering those areas as well as the medullary and pontine reticular regions, the A5, the locus coeruleus and the ventromedial hypothalamus. By day 5 and 6, labeling began to show up all over, e.g. in the dorsal brainstem, midbrain, cortex, etc. They also did a count of cells that were labeled with PRV and also expressed TH and TPH. I’m somewhat surprised that they DIDN’T see the most TH-positive neurons in the RVLM (they saw the most in the A5, which makes sense), but they DID see a lot of TPH-positive neurons in the RVLM. So LSNA is controlled by serotonergic presympathetic neurons? I think that for their next trick they should label different nerves with PRV that will report different colors and see what colocalizes – that would be a messy study that would be hard to interpret, but the presence or lack of coexpression would still suggest a lot one way or the other. -DH