WBR0610
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| Author | [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::Neurology |
| Prompt | [[Prompt::A researcher, investigating the regulatory neurotransmitters in the basal ganglia, sends high frequency electrical impulses into specific areas of a rat brain. He then measures changes in the local concentration of neurotransmitters. Upon stimulation of the caudate, the researcher observes increased release of a neurotransmitter known to inhibit the globus pallidus internus. Which of the following amino acids is this neurotransmitter derived from?]] |
| Answer A | AnswerA::Tryptophan |
| Answer A Explanation | [[AnswerAExp::Tryptophan is not a precursor for GABA.]] |
| Answer B | AnswerB::Glycine |
| Answer B Explanation | [[AnswerBExp::Glycine is not a precursor for GABA.]] |
| Answer C | AnswerC::Glutamate |
| Answer C Explanation | [[AnswerCExp::Glutamate is the precursor for GABA, the synthesis of which requires vitamin B6.]] |
| Answer D | AnswerD::Arginine |
| Answer D Explanation | [[AnswerDExp::Arginine is not a precursor for GABA.]] |
| Answer E | AnswerE::Lysine |
| Answer E Explanation | [[AnswerEExp::Lysine is not a precursor for GABA.]] |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The caudate nucleus is one of three structures that compose the basal ganglia along with the putamen and globus pallidus. The caudate nucleus is involved in the direct and indirect pathways of coordinating voluntary motor activity. The caudate nucleus is physiologically stimulated by glutamate released from the motor cortex. Stimulation of the caudate nucleus, physiologically or experimentally, will likely lead to the release of gamma-aminobutyric acid (GABA). GABA is an inhibitory neurotransmitter derived from glutamate. The synthesis of GABA requires vitamin B6. Educational Objective: GABA is synthesized from glutamate using the enzyme L-glutamic acid decarboxylase and pyridoxal phosphate (vitamin B6) as a cofactor. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Basal ganglia, WBRKeyword::GABA, WBRKeyword::Glycine, WBRKeyword::Vitamin B6, WBRKeyword::Pyridoxine |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |