Light and electronmicroscopic study of area M, the chemosensitive area of the ventral medulla oblongata.

An electron and light microscopic study was performed to elucidate the structure of area M, an area on the ventral surface of the medulla oblongata which participates in the central respiratory control of the cat. We found no particular morphological barriers to fluid transport from the cerebrospinal fluid space towards the capillaries of this area. The astroglial contacts proved to be mostly gap junctions; furthermore, no tight junctions could be found here. Multipolar ganglion cells could be localized at a depth of 400-800 micron. These cells form numerous synaptic contacts with thin, unmyelinated axons running superficially, parallel to the pial surface in area M. Our findings support the contention that the ventral chemosensitive areas of the medulla oblongata are influenced by the chemical constitution of the cerebrospinal fluid.