Functionally different neurons are organized topographically in the rostral ventrolateral medulla of rabbits.

Ootsuka Y, Terui N. J Auton Nerv Syst. 1997 Dec 3;67(1-2):67-78.

One of the things we suspect in our lab is that the rat RVLM has a sort of viscerotopic organization that allows for differential activation of sympathetic nerves.  We believe this not only because our lab has published on it already and seen it in some of our unpublished work, but also because it has been seen in other mammals.  This paper was one in which they showed this organization exists in rabbit RVLM
In this paper, the authors examine RVLM activity in rabbits using different methods than we use.  They used a pulsed doppler flowmeter in order to measure vascular conductance.  They measured arterial pressure and conductance in the kidney, fore- and hindlimb muscles, ear skin. They also measured the heart rate via ecg. They then gave GABA microinjections in a grid-pattern within the RVLM in order to inhibit vasomotor tone and constructed contour maps demonstrating where GABA injections resulted in the greatest vascular conductance.
Their results suggest that there is a relationship between target organ and location in the RVLM, but that these regions seem to overlap.  They mention that activation of multiple regions with one injection may be partially due to their spatial resolution, which they estimate to be about 0.5mm due to the dye spots they used as markers.  This fits pretty well with the accepted formula for finding microinjection sizes, as well as our own data, and it's why I am trying to increase the resolution with my project.
One final thing I appreciated about this paper was their use of straight GABA to do their experiments.  I initially found it counterintuitive for studing RVLM activity, but their discussion pointed out that other groups using glutamate found multiple injections often resulted in to unrepeatable results, presumably due to glutamate excitotoxicity.  They chose GABA because it showed a much shorter effect than other inhibitory compounds (eg glycine and muscimol). This meant that by waiting 5 minutes in between injections, they could get repeatable results in the same animal that would not be possible using other drugs.  This brought on decreases intersubject variability and increases the data yield per animal used.

-dh