Neurotransmitters

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Neurochemistry/Neurotransmitters

Questions

86. A middle-aged man is brought to the hospital for a neurological examination after displaying uncontrollable movements of his upper limbs. He is diagnosed with a rare genetic disorder affecting dopamine synthesis in brainstem neurons. However, there is some controversy concerning the step in the biosynthesis of dopamine at which this failure takes place. If the failure lies in the immediate precursor stage in the biosynthesis of dopamine, which of the following is the precursor?

a. Tyrosine

b. Tyrosine hydroxylase

c. Tryptophan

d. L-Dihydroxyphenylalanine (L-DOPA)

e. Dopamine β-hydroxylase

87. If a patient is suffering from a genetic disorder affecting the rate-limiting step in the biosynthesis of dopamine, which of the following is the rate-limiting step?

a. Tryptophan hydroxylase

b. Tyrosine hydroxylase

c. Dopamine β-hydroxylase

d. Phenylethanolamine-N-methyltransferase

e. Choline acetyltransferase

88. A baby is born with an inherited autosomal recessive trait, causing a delay in development and resulting in the occurrence of seizures and mental retardation. The child is diagnosed with phenylketonuria (PKU). Which of the following is the most likely neurochemical locus of this genetic defect?

a. Tyrosine

b. Tryptophan

c. Tryptophan hydroxylase

d. Dopamine

e. Phenylalanine (Phe) hydroxylase

89. Your patient is suffering from a disorder of unknown etiology that blocks neural transmission at the neuromuscular junction. You recommend a drug whose specific action is believed to modulate the end-plate potential. Which of the following best describes a basic feature of the end-plate potential?

a. It is dependent upon the release of dopamine from the nerve ending.

b. The amplitude of this potential is much higher than that of central nervous system (CNS) postsynaptic potentials.

c. It is an all-or-none response.

d. It is unrelated to the concentration of transmitter released from the presynaptic terminals.

e. It is selectively associated with the opening of chloride channels.

90. Which one of the following is true concerning the channel at the neuromuscular junction associated with the end-plate potential?

a. Blocked by a noradrenergic β-receptor antagonist

b. Blocked by an N-methyl-D-aspartate-(NMDA-) receptor antagonist

c. Blocked by an α-amino-hydroxy-5-methyl-4-isoxazolepropionic acid-(AMPA-) receptor antagonist

d. Nicotinic gated

e. Muscarinic gated

91. A patient is admitted to the hospital because of a variable weakness of cranial nerves and limb muscles, which worsen significantly following exercise, but shows no clinical signs of denervation from tests, which includes electromyogram (EMG) recordings. This disorder is partially reversed by the administration of drugs that inhibit acetylcholinesterase. Which of the following is the most likely diagnosis?

a. Multiple sclerosis (MS)

b. Amyotrophic lateral sclerosis (ALS)

c. Myasthenia gravis

d. Lambert-Eaton syndrome

e. Muscular dystrophy (MD)

92. A 62-year-old man diagnosed with lung cancer displays weakness in his arms and legs. A battery of tests is administered to the patient, including those involving nerve conduction. The nerve conduction test reveals a reduction in the compound motor action potential of the muscles of the hand. However, the amplitude of this potential improves significantly following exercise involving the relevant muscles. Which of the following is the most likely diagnosis?

a. MS

b. ALS

c. Myasthenia gravis

d. Lambert-Eaton syndrome

e. MD

93. A patient receives a diagnosis of myasthenia gravis. Which of the following most likely constitutes the basis for this disorder?

a. The production of excessive quantities of acetylcholine (ACh)

b. The production of antibodies that act against nicotinic ACh receptors

c. A reduction in brain catecholamines

d. Reduction in presynaptic Ca²⁺ channels

e. Viral encephalitis

94. A patient complains of weakness in the proximal muscles of the limb as well as dryness of the mouth and constipation. On the basis of a neurological examination it is concluded that the patient is suffering from the Lambert-Eaton syndrome. Which of the following best characterizes the basic defect underlying this disorder?

a. The production of excessive quantities of ACh

b. The production of antibodies that act against nicotinic ACh receptors

c. A reduction in brain catecholamines

d. Reduction in presynaptic Ca²⁺ channels

e. Viral encephalitis

95. A 10-year-old boy accidentally swallows a toxic substance that contained a neurotoxin whose actions mimic those of curare. This results in neuromuscular blockade, partial respiratory failure, and paralysis. To which of the following receptors does this toxin bind?

a. γ-Aminobutyric acid-A (GABA_A) receptor

b. GABA_B receptor

c. Nicotinic receptor

d. NMDA receptor

e. Histamine receptor

96. It was discovered that a patient who was suffering from muscle weakness in his limbs had developed a deficiency in the availability of the enzyme required for the metabolism of the neurotransmitter present in the synapse at the neuromuscular junction. Which of the following enzymes was deficient in this patient?

a. Choline acetyltransferase

b. Glutaminase

c. Glutamine synthetase

d. Acetylcholinesterase

e. Serine hydroxymethyltransferase

97. A patient is admitted to the emergency room after taking a drug of abuse that destroys selective groups of neurons in the brainstem. After the patient became ambulatory, he was chronically depressed. Which of the following neuronal groups in the brainstem is most likely related, either directly or indirectly, to this patient’s condition?

a. Vestibular nuclei

b. Nucleus ambiguus

c. Trigeminal spinal nucleus

d. Dorsal column nuclei

e. Raphe nuclei

98. A study utilizing peripheral measures of a variety of neurotransmitters in patients suffering from chronic depression was conducted over a 4-month period. It was discovered that there was a significant decrease in one of these neurotransmitters. Which of the following neurotransmitters was most significantly reduced in these patients?

a. Enkephalin

b. Dopamine

c. Norepinephrine

d. Serotonin

e. Glycine

99. A patient is diagnosed with clinical depression and is administered a drug to treat this disorder. Which of the following properties best characterizes the drug given to the patient?

a. A selective serotonin reuptake inhibitor (SSRI)

b. A CNS depressant

c. A dopaminergic antagonist

d. A noradrenergic antagonist

e. An NMDA blocker

100. For management of a form of sleep disorder in which individuals tend to suffer from excessive sleep, a pharmaceutical company undertakes to develop a drug that selectively alleviates this problem by blocking the rate-limiting step in the biosynthesis of serotonin. Which of the following represents the rate-limiting step?

a. Tyrosine hydroxylase

b. Tryptophan hydroxylase

c. Phenylethanolamine-N-methyltransferase

d. Dopamine β-hydroxylase

e. Glutamic acid decarboxylase

101. An elderly man is brought to his physician by his family after increasing incidences of disorientation coupled with memory loss. The patient is diagnosed with Alzheimer disease. A few years later, after further physical and mental deterioration, the patient dies. An autopsy is taken of his brain and regional brain chemistry and neuropathology identified. Which of the following structures represents the most likely site where the neuropathology could be identified?

a. Cerebellar cortex

b. Substantia nigra

c. Vestibular nuclei

d. Basal nucleus of Meynert

e. Subthalamic nucleus

Questions 102 to 104

102. A patient was recently diagnosed with Alzheimer disease and is placed on a drug treatment program. Which of the following are the drugs of choice for this disorder?

a. Carbamazepine and gabapentin (Neurontin)

b. Haloperidol and clonidine

c. Memantine and donepezil (Aricept)

d. Paroxetine and sertraline

e. Levodopa and lithium

103. An analysis was undertaken of the histological, pathological, and neurochemical alterations in the brains of patients who died of Alzheimer disease. Following examination of the brain, which of the following would most likely be present in the affected regions?

a. A decrease in substance P in the hypothalamus and brainstem reticular formation

b. Marked degeneration of most myelinated pathways

c. Amyloid deposits and neurofibrillary tangles

d. Marked retrograde degeneration in sensory neurons of the brainstem

e. Glial loss associated with the medial lemniscus and spinothalamic pathways

104. A clinical study was conducted to develop a promising therapeutic strategy for treatment of Alzheimer disease. Which of the following strategies was utilized in this study?

a. Surgical removal of selective regions of the cerebral cortex

b. Administration of serotonergic agonists that act specifically on cerebral cortical neurons

c. Administration of cholinergic antagonists directed against nicotinic receptors in the cerebral cortex

d. Administration of noradrenergic agonists directed against α₂ receptors in the cerebral cortex

e. Administration of compounds that slow aggregation of amyloid-β peptide into its fibrillar form

105. Drug development aimed at blocking the biosynthesis or release of a certain neurotransmitter may result in the creation of a drug that can cause side effects by acting on neural systems unrelated to the neural systems the drug is designed to modulate. Which of the following neurotransmitters would appear to be the most difficult to control because of its ubiquity within the CNS and possible widespread side effects?

a. ACh

b. Glutamate

c. Norepinephrine

d. Dopamine

e. Substance P

106. A 73-year-old woman suffered an injury involving the left middle cerebral artery and affecting mainly the pre-and postcentral gyri. Characteristically, there were neurotoxic effects of cortical ischemia resulting from a stroke that were noted. Which of the following is a likely mechanism underlying the phenomenon of cortical neurotoxicity?

a. Entry of Ca²⁺ into the cell

b. Reduction of extracellular chloride

c. Delayed removal of norepinephrine from the synapse

d. Hypersensitivity of the postsynaptic membrane to GABA

e. Failure of degradation of ACh

107. A 47-year-old man who was suffering from repeated anxiety attacks was selected for a study for the treatment of this disorder. The study involved a determination of the efficacy of an experimental drug that specifically attempts to reduce anxiety levels. Which of the following is the most likely mechanism underlying the action of this drug?

a. Blockade of chloride channel permeability

b. Opioid receptor blockade

c. Binding of the drug to the GABA benzodiazepine site

d. Activation of muscarinic cholinergic receptor

e. Competitive binding of the GABA_A-receptor site

108. A 55-year-old woman is admitted to the hospital for treatment of hypertension. Prior to her admission to the hospital, her blood pressure had been slightly above normal, but her blood pressure had risen significantly over the past few weeks. A general medical and neurological examination indicates that she is otherwise in acceptable health, and no medical or neurological signs can be detected. Which of the following is the drug of choice to treat this patient?

a. Sumatriptan (Imitrex)

b. Clonidine

c. Topiramate

d. Valproic acid

e. Butorphanol

109. A 67-year-old man was on prazosin for the treatment of hypertension. The antihypertensive effect of prazosin is mediated by which one of the following receptors?

a. Cholinergic muscarinic receptors

b. Dopaminergic receptors

c. α₂-Adrenergic receptors

d. Serotonergic receptors

e. α₁-Adrenergic receptors

110. A 30-year-old man who develops chronic pain following a leg injury is treated with morphine. Subsequently, he develops an addiction to morphine. On which of the predominant receptor sites is this effect mediated?

a. Opioid nociceptin receptor

b. Opioid μ-receptor

c. Opioid δ-receptor

d. Opioid κ-receptor

e. Dopamine D₂-receptor

111

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