Every month we are giving you a sneak peek at our question content in our SmartBanks. These questions are handpicked and are statistically some of the toughest we have to offer. Be sure you come back often to check for more freebie questions. The following is our psychiatry question of the month.
Psychiatry Sample Question:
Which of the following mood stabilizers has been shown to inhibit inositol monophosphatase, possibly affecting neurotransmission via phosphatidyl inositol second messenger system?
A) Carbamazepine
B) Oxcarbazepine
C) Lamotrigine
D) Lithium
E) Valproate
Answer and Analysis
Correct answer: D
Lithium is a monovalent ion, a member of the group IA alkali metals on periodic table. Lithium has FDA approved indications for manic episodes of manic-depressive illness and maintenance treatment for manic-depressive patients with a history of mania. It has also been used in treating bipolar depression, vascular headache and neutropenia. Lithium does not bind to plasma proteins, is not metabolized and is excreted through the kidneys. Therapeutic actions of lithium are unknown and complex. It alters sodium transport across cell membranes in nerve and muscle cells. It alters metabolism of catecholamines and serotonin neurotransmitters. It has been shown to inhibit inositol monophosphatase, possibly affecting neurotransmission via phosphatidyl inositol second messenger system. It has been shown to reduce protein kinase C activity, possibly affecting genomic expression associated with neurotransmission. It also increases cytoprotective proteins and activates signaling cascades utilized by endogenous growth factors. Regular monitoring of serum lithium concentrations is important. Effective serum concentration for acute treatment should generally be between 1.0 and 1.5 mEq/L for acute treatment, 0.6 and 1.2 mEq/L for chronic treatment.
Answer A: Carbazepine acts as a blocker of voltage-sensitive sodium channels. It interacts with the open channel conformation of voltage-sensitive sodium channels, as well as at a specific site of the alpha pore-forming subunit of voltage-sensitive sodium channels. It may inhibit glutamate release. It has not been shown to inhibit inositol monophosphatase.
Answer B: Oxcarbazepine acts as a blocker of voltage-sensitive sodium channels. It interacts with the open channel conformation of voltage-sensitive sodium channels and a specific site of the alpha pore-forming subunit of voltage-sensitive sodium channels. It may inhibit glutamate release. It’s actions are similar to carbamazepine. It has not been shown to inhibit inositol monophosphatase.
Answer C: Lamotrigine blocks voltage-sensitive sodium channels and interacts with the open channel conformation of voltage-sensitive sodium channels. It interacts at a specific site of the alpha pore-forming subunit of voltage-sensitive sodium channels. It inhibits glutamate and aspartate release. It does not inhibit inositol monophosphatase.
Answer E: Valproate acts by blocking voltage-sensitive sodium channels by an unknown mechanism. It increases brain concentrations of gamma-aminobutyric acid (GABA) by an unknown mechanism. It does not inhibit inositol monophosphatase.
Bottom Line: The mood-stabilizing effects of lithium remain elusive. Some theories include: alterations of ion transport and effects on neurotransmitters and neuropeptides, as well as second messenger systems. It has been shown to inhibit inositol monophosphatase, possibly affecting neurotransmission via phosphatidyl inositol second messenger system.
For more information, see:
Sadock B., Sadock V., and Ruiz P. Psychopharmacological Treatment. In Kaplan and Sadock’s Synopsis of Psychiatry: behavioral sciences/clinical psychiatry. 11th ed. Philadelphia: Wolters Kluwer; 2015
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