A 34-year-old man who is a heavy smoker started a medical assisted program to quit
smoking. Therapy included the administration of clonidine, an agonist at alpha-2
presynaptic receptors which is believed to act mainly on noradrenergic neurons in the
brain. Which of the following areas of the brain is the richest in noradrenergic neurons?
A. Median Raphe Nucleus B. Stria Terminalis C. Locus Ceruleus D. Substantia Nigra E. Thalamus
Locus ceruleus-answer: c
(katzung, pp 520, brunton, pp 452)
most noradrenergic neurons in the brain are found in the locus ceruleus, a bluish area on each
side of the median eminence of the brain stem. locus ceruleus sends a particularly large
number of projections to the amygdala and hippocampus, where norepinephrine release is
thought to mediate emotion and memory formation. another brain region which is rich in
noradrenergic neurons is the lateral tegmental area of the reticular formation.
clonidine activates presynaptic alpha-2 receptors located on noradrenergic terminals and this
decreases norepinephrine release from those terminals. it seems that this reduction of central
adrenergic activity is the basis of the therapeutic effect of the drug in case of withdrawal from
addicting drugs, including nicotine and opioids.