Katzung 12th ed - Chapter 21 - Introduction to CNS Drugs (1.5)

Question 1

What are metabotropic receptors?

Answer 1

This is one class of neurotransmitter receptors, which are G-protein coupled receptors, with a seven-transmembrane domain.

Question 2

What is a membrane-delimited pathway of ligand-receptor interactions? What is the alternative?

Answer 2

This is a type of metabotropic receptor mechanism. The signalling is entirely limited to the membrane, i.e. a very small area. For example, a ligand binds to a G-protein-linked receptor, which directly opens an ion channel, all within the plane of the cell membrane. This is as opposed to signalling pathways that make use of diffusible second messengers, such as when adenylyl cyclase generates cAMP which acts as a second messenger over considerable distances, to modulate an ion channel elsewhere.

Question 3

Apart from metabotropic receptors, what is the other class of neurotransmitter receptors?

Answer 3

Ionotropic receptors (also called ligand-gated ion channels)

Question 4

With regard to the resting membrane potential of the post-synaptic membrane, what is the effect of an **excitatory **signal? What is the effect of an inhibitory signal?

Answer 4

An excitatory signal will slightly depolarize the membrane, bringing the membrane potential closer to the threshold potential. An inhibitory signal will slightly hyperpolarize the membrane, making the membrane potential more negative, and less likely to have an action potential.

Question 5

GABA is sometimes referred to as an amino acid. What are the other two amino acids that act as neurotransmitters in the CNS?

Answer 5

Glycine and Glutamate.

Question 6

Why is GABA sometimes referred to as an amino acid? What is the basic chemical structure of GABA?

Answer 6

Gamma-aminobutyric acid is basically an amino acid without an R-group. It is a small hydrocarbon chain (only 4 carbon atoms) with an amine group at one end (NH2) and a carboxyl group at the other end (COOH).

Question 7

Is glutamate excitatory or inhibitory?

Answer 7

Excitatory.

Question 8

Does glutamate act on ionotropic or metabotropic receptors?

Answer 8

Both.

Question 9

Give a basic explanation of what happens to glutamate after it has exerted its effect on the post-synaptic membrane.

Answer 9

It is taken up into nearby glial cells and converted to glutamine by Glutamine synthetase. This glutamine can then go back into the pre-synaptic terminal to be converted back to glutamate (by Glutaminase).

Question 10

GABA and glycine: Are they inhibitory or excitatory neurotransmitters?

Answer 10

Inhibitory.

Question 11

GABA_A receptors are different from GABA_B receptors - which ones are ionotropic and which ones are metabotropic?

Answer 11

GABA_A are ionotropic. GABA_B are metabotropic.

Question 12

What are the two basic classes of receptors that Acetylcholine acts on?

Answer 12

Muscarinic and Nicotinic.

Question 13

Name the three monoamines in the CNS.

Answer 13

Dopamine, Noradrenaline, Serotonin (5-Hydroxytryptamine)

Question 14

Apart from one (very sparsely-distributed) serotonin receptor subtype, all monoamine receptors are: Metabotropic or Ionotropic?

Answer 14

Metabotropic.