36-year-old man with schizophrenia was prescribed haloperidol 5 years ago and was responding very well. Recently, he developed involuntary facial movements that could only be alleviated by increasing his dose of the medication. This adverse reaction was likely due to which mechanism?

Question

A. 5-HT receptor sensitization.
B. DA receptor sensitization.
C. Decreased synthesis of 5-HT receptors.
D. Decreased synthesis of DA receptors.
E. Uncoupling DA receptors from their G-proteins.

Answer 1

The involuntary facial movements described in your scenario are characteristic of tardive dyskinesia, which can develop in patients taking antipsychotic medications like haloperidol over an extended period of time. Tardive dyskinesia is believed to be associated with changes in dopamine (DA) receptor sensitivity due to long-term blockade of these receptors by antipsychotic drugs.

The most likely mechanism involved in the development of tardive dyskinesia is "DA receptor sensitization," which occurs due to long-term dopaminergic blockade leading to upregulation or increased sensitivity of dopamine receptors. Consequently, increasing the dose of haloperidol might temporarily alleviate the symptoms, but it is not a sustainable or suitable solution.

Hence, the correct answer is:

B. DA receptor sensitization.