Locus Coeruleus

The locus coeruleus is a cluster of neurons in the brainstem which physiologically responds to stress and panic. The locus coeruleus is situated within the dorsal wall of the rostral pons in the lateral floor of the fourth ventricle. It is composed of medium-size neurons. The locus coeruleus gets inputs from other brain regions, primarily: medial prefrontal cortex; nucleus paragigantocellularis,integrates autonomic and environmental stimuli; nucleus prepositus hypoglossi; and lateral hypothalamus, which releases orexin, which is excitatory in the locus coeruleus.

The locus coeruleus is activated by stress, and will respond by increasing norepinephrine secretion, which in turn will increase cognitive function through the prefrontal cortex, increase motivation, activate the hypothalamic-pituitary-adrenal axis, and increase the sympathetic discharge/inhibit parasympathetic tone (through the brainstem).

The locus coeruleus gained prominence in the 1960s when new anatomical approaches revealed it to be the major source of norepinephrine (NE) in brain with projections throughout most central nervous system (CNS) regions, including the cerebral cortex, hippocampus, thalamus, midbrain, brainstem, cerebellum, and spinal cord. The locus coeruleus is densely innervated by fibers that contain opiates, glutamate, gamma-aminobutyric acid,serotonin, epinephrine, and the newly discovered peptide orexin/hypocretin. The sources of these various inputs have not been fully elucidated, though some major inputs have been identified.