Perivascular serotoninergic neurons: somatodendritic contacts and axonic innervation of blood vessels.

As shown by histofluorescence studies, a number of brain stem serotoninergic neurons have their cell bodies and dendrites in intimate contact with parenchymal blood vessels, including arterioles (perivascular serotoninergic neurons). Another, apparently distinct, phenomenon which was evidenced is the existence of a diffuse innervation by long serotoninergic axons of intrinsic blood vessels. These axons seem to be continuous with an adventitial nerve fiber network surrounding extrinsic blood vessels. A novel significant finding was that some of the perivascular neurons themselves can project an axonic process into the wall of the same vessel they embrace with their cell body and dendrites (a receptive as well as a vasomotor function?).