Norepinephrine

[Page 2299]Norepinepherine (NE) is a small-molecule neurotransmitter that was originally identified as an important component of the peripheral nervous system, where it functions within the sympathetic branch of the autonomic nervous system. Later work demonstrated that NE-containing fibers are widely distributed across the central nervous system (CNS) as well. These fibers stem from two clusters of NE neurons in the brainstem. Specifically, NE neurons of the locus coeruleus send widespread axon projections to regions of the cerebral cortex, thalamus, hypothalamus, cerebellum, brainstem, and spinal cord, whereas NE neurons of the lateral tegmental nuclei send more discrete projections to the limbic nuclei. The extensive distribution of NE within the CNS suggests that this neurotransmitter plays an appreciable role in the regulation of CNS output and behavior, ...