<Li> In the stomach and intestines, a reduction in digestive activity . This results from a generally inhibitory effect of norepinephrine on the enteric nervous system, causing decreases in gastrointestinal mobility, blood flow, and secretion of digestive substances . </Li> <P> The noradrenergic neurons in the brain form a neurotransmitter system, that, when activated, exerts effects on large areas of the brain . The effects are manifested in alertness, arousal, and readiness for action . </P> <P> Noradrenergic neurons (i.e., neurons whose primary neurotransmitter is norepinephrine) are comparatively few in number, and their cell bodies are confined to a few relatively small brain areas, but they send projections to many other brain areas and exert powerful effects on their targets . These noradrenergic cell groups were first mapped in 1964 by Annica Dahlström and Kjell Fuxe, who assigned them labels starting with the letter "A" (for "aminergic"). In their scheme, areas A1 through A7 contain the neurotransmitter norepinephrine (A8 through A14 contain dopamine). Noradrenergic cell group A1 is located in the caudal ventrolateral part of the medulla, and plays a role in the control of body fluid metabolism . Noradrenergic cell group A2 is located in a brainstem area called the solitary nucleus; these cells have been implicated in a variety of responses, including control of food intake and responses to stress . Cell groups A5 and A7 project mainly to the spinal cord . </P> <P> The most important source of norepinephrine in the brain is the locus coeruleus, which contains noradrenergic cell group A6 and adjoins cell group A4 . The locus coeruleus is quite small in absolute terms--in primates it is estimated to contain around 15,000 neurons, less than one millionth of the neurons in the brain--but it sends projections to every major part of the brain and also to the spinal cord . </P>

Neurons that release norepinephrine as a neurotransmitter are called