ABSTRACT
Noradrenergic (NE) neurons are confined to three groups in the pons and medulla oblongata: the well-defined locus coeruleus or A6 cell group, a more diffuse but continuous lateral and ventral group that arches through the pons and medulla, and a third dorsal medullary group known as A2 cell group, centered in the dorsal motor nucleus of the vagus. The different methodologies employed in numerous investigations of the neuroanatomical connections between NE cell groups have given rise to some disagreements. There is general agreement that the basic organization of the central catecholaminergic system consists of cell bodies located in caudal brain stem that give rise to ascending and descending fiber systems terminating in widespread areas of the brain. The nuclei of brain stem reticular formation (BSRF) all contain about the same amount of 5HT. Excitatory and oscillatory as well as inhibitory responses to raphe stimulation have been found in BSRF neurons.
