Rostral ventral medulla (RVM) cells have been classified as on, off, neutral, and serotonergic. RVM contains both serotonergic and non-serotonergic cell types. In addition to the obvious neurochemical difference between these two cell types, there are anatomical, physiological, and functional differences.
Serotonergic cells comprise about 15 % of the cells in RVM. They have relatively few (3–5) mediolaterally oriented dendrites, which typically extend for less than 750 μm (Gao and Mason 1997). Most serotonergic RVM cells send unmyelinated axons through the dorsolateral funiculus into the spinal cord. The axons travel through and collateralize heavily in the ventrolateral medulla, a region that contains neurons involved in cardiovascular and respiratory control. Serotonergic cells are heterogeneous in neurochemistry, anatomy, and physiology. Most serotonergic cells contain at least one, and often several, co-...