View source for WBR0610

{{WBRQuestion
|QuestionAuthor={{Rim}} {{Alison}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|SubCategory=Neurology
|MainCategory=Biochemistry
|SubCategory=Neurology
|MainCategory=Biochemistry
|SubCategory=Neurology
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=Neurology
|MainCategory=Biochemistry
|SubCategory=Neurology
|MainCategory=Biochemistry
|SubCategory=Neurology
|MainCategory=Biochemistry
|SubCategory=Neurology
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=Neurology
|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?
|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 [[GABA|gamma-aminobutyric acid (GABA)]]. [[GABA]] is an inhibitory neurotransmitter derived from glutamate.  The synthesis of GABA requires [[vitamin B6]].
|AnswerA=Tryptophan
|AnswerAExp=[[Tryptophan]] is not a precursor for GABA.
|AnswerB=Glycine
|AnswerBExp=[[Glycine]] is not a precursor for GABA.
|AnswerC=Glutamate
|AnswerCExp=[[Glutamate]] is the precursor for GABA, the synthesis of which requires vitamin B6.
|AnswerD=Arginine
|AnswerDExp=[[Arginine]] is not a precursor for GABA.
|AnswerE=Lysine
|AnswerEExp=[[Lysine]] is not a precursor for GABA.
|EducationalObjectives=GABA is synthesized from glutamate using the enzyme L-glutamic acid decarboxylase and pyridoxal phosphate (vitamin B6) as a cofactor.
|References=Roberts E, Wein J, Simonsen DG. Gamma-Aminobutyric Acid (GABA), Vitamin B6, and Neuronal Function - a Speculative Synthesis. Vitam Horm. 1964;22:503-59.<br>
First Aid 2014 page 110
|RightAnswer=C
|WBRKeyword=Basal ganglia, GABA, Glycine, Vitamin B6, Pyridoxine
|Approved=Yes
}}