Muscarinic receptors antipsychotic drug blockade

Of the drugs used for treating parkinsonism, the anticholinergics are the only class that can provide benefit in the treatment of the drug-induced parkinsonism seen with antipsychotic therapy. This is because the blockade of dopamine receptors by the antipsychotics leads to increased activity of the striatal neurons. Blockade of the muscarinic receptors reduces this excitatory activity. 

The first phenothiazine antipsychotic drugs, with chlorpromazine as the prototype, proved to have a wide variety of central nervous system, autonomic, and endocrine effects. Although efficacy of these drugs is primarily driven by D2-receptor blockade, their adverse actions were traced to blocking effects at a wide range of receptors including a adrenoceptors and muscarinic, Hi histaminic, and 5-HT2 receptors. 

FIGURE 11—7. This figure represents an icon of a conventional antipsychotic drug. Such drugs generally have at least four actions blockade of dopamine 2 receptors (D2) blockade of muscarinic-cholinergic receptors (Ml) blockade of alpha 1 adrenergic receptors (alpha 1) and blockade of histamine receptors (antihistaminic actions [HI ). 

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