After ACh, epinephrine and norepinephrine are the neurotransmitters that have received most study. Again, they have two separate receptors:
- α-adrenergic receptor, blocked by phentolamine;
- β-adrenergic receptor, blocked by propranolol (see Fig. 38.2).
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| The latter drug used to be commonly used by cardiologists (many other β-blockers the mainstay of treatment in coronary heart disease), but neurologists also use it as part of the treatment of Parkinson's disease. This disease results from a deficiency of dopamine, the precursor of epinephrine and norepinephrine. Many adrenergic effects are promoted by cAMP, but other neurotransmitters have either excitatory or inhibitory effects (Fig. 39.3) (see Chapter 40).
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