1. The neurotransmitter serotonin is derived from which precursor amino acid?
2. The major inhibitory neurotransmitter in the mammalian CNS is
(D) 7-Aminobutyric acid
(E) Glutamic acid
3. The location of the blood-brain barrier is considered to be
(A) At the level of the brain capillaries
(B) At the level of glia
(C) At the level of neurons
(D) At the level of dendrites
4. Identify the major excitatory neurotransmitter system in the mammalian CNS.
(A) 7-Aminobutyric acid
(B) Histamine (c) Substance P
5. Agents that potentiate the actions of GABA in the brain will likely have which of the following effects?
(A) Elevate blood pressure
(B) Provide sedation
(C) Cause seizures
(D) Relieve pain
6. What is the number of neurotransmitters in the mammalian CNS?
(D) more than 20 ANSWERS
1. C. Dopamine is a precursor for norepinephrine and a neurotransmitter. Tyrosine is a precursor of dopamine and norepinephrine. Dopa (dihydroxy-phenylalanine) is a precursor of dopamine and subsequently also of norepinephrine. Glutamine can be converted to the neurotransmitter glutamic acid.
2. D. Acetylcholine and norepinephrine are important neurotransmitters in the peripheral autonomic nervous system but are not nearly as prominent in the CNS. Glycine is a major inhibitory neurotrans-
mitter in the spinal cord but not the rest of the CNS. Glutamic acid is a major excitatory neuro-transmitter in the mammalian CNS.
3. A. The site of the blood-brain barrier was hotly debated for many years until electron micrographs clearly showed that endothelial cells lining brain capillaries are so closely joined to each other that passages of substances cannot readily occur through the intercellular clefts located between adjacent cells and that this constitutes a barrier to the passage of many substances from the blood to the parenchyma of the brain.
4. D. GABA is the major inhibitory neurotransmitter in the mammalian CNS. Histamine is a CNS neuro-transmitter, but has limited distribution. This is also true for serotonin. Substance P is an excitatory neu-rotransmitter in the spinal cord.
5. B. Since GABA is an inhibitory neurotransmitter, agents that potentiate its action are likely to be CNS depressants with sedative activity. GABA has no significant effect on blood pressure and will decrease the incidence of seizures. It has no direct ability to relieve pain.
6. D. The exact number of agents identified as neuro-transmitters in the mammalian CNS is not established, but it is certainly more than 20. More and more compounds are being established as neurotrans-mitters as scientists who concentrate on this area.
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