WBR0610

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
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 the brain of a rat and measures the change in the local concentration of several neurotransmitters. Upon stimulation of the caudate, the researcher observes an increase in the release of a neurotransmitter known to inhibit the globus pallidus internus. Which of the following amino acids is the released 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 involved in the direct and indirect pathways of the fine tuning of 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. References: First Aid 2014 page 110]]
Approved	Approved::No
Keyword	WBRKeyword::Basal ganglia, [[WBRKeyword::GABA]], WBRKeyword::glycine
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::