Chapter 6: Neurotransmitters and their receptors

Question 1

how big are neuropeptides?

Answer 1

3 to 36 amino acids (large neurotransmitters)

Question 2

small-molecule peptides (individual amino acids or transmitters) include…

Answer 2

glutamate, GABA, acetylcholine, serotonin, and histamine

Question 3

give examples of biogenic amines (sub category of small-molecule peptides grouped due to their similar chemical properties and postsynaptic actions)

Answer 3

dopamine, norepinephrine, epinephrine, serotonin, and histamine

Question 4

what is the role of ACh?

Answer 4

it is the neurotransmitter at skeletal
neuromuscular junctions, as well as at the neuromuscular synapse between the vagus nerve and cardiac muscle fibres.

ACh also serves as a transmitter at synapses in the ganglia of the visceral motor system and at a variety of sites in the CNS

Question 5

what is acetylcholinesterase (AChE)?

Answer 5

a powerful hydrolytic enzyme that reuptakes ACh from cholinergic synapses (particularly the NMJ).

Question 6

the nerve gas sarin is an example of what?

Answer 6

an organophosphate (a drug that interacts with cholinergic enzymes)

Question 7

how are organophosphates lethal?

Answer 7

• They inhibit AChE, allowing ACh to accumulate at cholinergic synapses.
• This build-up of ACh depolarizes the
  postsynaptic muscle cell and renders it refractory to subsequent ACh release, causing neuromuscular paralysis and
  other effects

Question 8

Many of the postsynaptic actions of ACh are mediated by which receptor?

Answer 8

the nicotinic ACh receptor (nAChR) (ionotropic ligand-gated ion channel)

Question 9

what are muscarinic ACh receptors (mAChR)?

Answer 9

mAChRs are metabotropic and mediate most of the effects of ACh in the brain

Question 10

name all the types of metabotropic neurotransmitter receptors (8)

Answer 10

1. muscarinic
2. glutamatergic
3. GABAb
4. dopamine
5. adrenergic
6. histamine
7. serotonin
8. purine

Question 11

mAChR blockers that are therapeutically useful include atropine, scopolamine and ipratropium. what do they do?

Answer 11

atropine (used to dilate the
pupil)
scopolamine (effective in preventing motion sickness)
ipratropium (useful in the treatment of asthma

Question 12

what is involved in the glutamate–glutamine cycle? (3)

Answer 12

• Glutamate synthesized in the presynaptic cytoplasm is packaged into synaptic vesicles
  by vesicular glutamate transporters (VGLUTs).
• Once released, glutamate is removed from the synaptic cleft by the excitatory amino acid transporters (EAATs).
• Glutamine is then transported out of the glial cells by a different transporter, the system N transporter 1 (SN1), and transported into nerve terminals via SAT2.

Question 13

which type of glutamatergic receptor are the primary mediators of excitatory transmission in the brain?

Answer 13

AMPARs

Question 14

what is a difference between excitatory ionotropic glutamate receptors and metabotropic glutamate receptors?

Answer 14

mGluRs cause slower postsynaptic responses that can either excite or inhibit postsynaptic cells.

Question 15

how is the structure of mGluRs unique?

Answer 15

they are dimers of two identical subunits

Question 16

why did lack of vitamin B6 in infant formula cause a series of infant deaths?

Answer 16

• GAD catalyzes the conversion of glutamate to GABA
• GAD requires a co-factor, pyridoxal phosphate, for activity.
• Because pyridoxal phosphate is derived from vitamin B6, a deficiency of this vitamin can lead to diminished GABA synthesis.
• the subsequent loss of synaptic inhibition caused seizures that in some cases were fatal

Question 17

biogenic amines are implicated in which behaviours?

Answer 17

ranging from central homeostatic functions to cognitive phenomena such as attention

Question 18

what are the five well-established biogenic amine neurotransmitters?

Answer 18

the three catecholamines dopamine,
norepinephrine (noradrenaline), and epinephrine (adrenaline),
and histamine and serotonin

Question 19

how does cocaine exert its psychotropic effects?

Answer 19

by inhibiting DAT, thereby increasing dopamine concentrations in the synaptic cleft