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Neuropharmacology > Inhibitory Amino Acids > Flashcards

Inhibitory Amino Acids Flashcards

1
Q

What is the most predominant inhibitory neurotransmitter in the brain?

A

GABA

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2
Q

What is the second, and less major, inhibitory neurotransmitter?

A

glycine

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3
Q

What does GABA stand for?

A

gamma-amino-butryic-acid

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4
Q

Why does almost every neuron in the the CNS have GABA synapses?

A

Because GABA is the primary braking system of the brain; it keeps the firing rate of neurons in check

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5
Q

What are the two types of GABAergic neurons?

A
  1. Projection neurons

2. interneurons

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6
Q

What are projection neurons?

A

Neurons whose cell bodies reside in one nucleus, and whose terminals end in another nucleus

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7
Q

What are interneurons?

A

Neurons who exist within a singular nucleus

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8
Q

When was GABA first discovered as a neurotransmitter?

A

In the 1950’s

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9
Q

What is GABA synthesized from? Which enzyme is primarily responsible for its synthesis?

A

from glutamate; glutamic acid decarboxylase (aka GAD)

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10
Q

What are the two kinds of enzymes that synthesize GABA from glutamate?

A
  1. GAD65
  2. GAD67
    - both of these are named after their weight
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11
Q

What does GAD need to synthesize GABA?

A

It needs a cofactor, vitamin B6

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12
Q

What does GAD’s cofactor allow it to help with?

A

Increasing the affinity of glutamate

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13
Q

How, and by what mechanism, is GABA taken into the vesicle?

A

GABA is taken up into the vesicle via an active transporter, vesicular GABA transporter (GAT)

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14
Q

Which force allows GABA to enter the vesicle?

A

Through both electrostatic and diffusional forces (the active transporter depends on an ion gradient, helped by an antiporter)

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15
Q

How is GABA released from the vesicle?

A

Through exocytosis

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16
Q

How is GABA’s signal primarily terminated?

A

Through reuptake via the GABA transporter (GAT but NOT vesicular GAT) either on the presynaptic neuron, or nearby glial cells

17
Q

What is another method of GABA signal termination?

A

Termination via the enzyme GABA-transaminase (GABA-T)

- is a synthetic metabolic enzyme

18
Q

What are the two families of GABA receptors?

A
  1. GABAa

2. GABAb

19
Q

What type of receptor are GABAa receptors?

A

They are ligand-gated ion chanels (their response is almost immediate)

20
Q

What kind of receptors are GABAb receptors?

A

G-Protein Coupled Receptors (because their responses take hundreds of milliseconds)

21
Q

Describe GABAa receptors?

A
  • GABAa receptors are the primary focus of the inhibitory system because they are the most prevalent and are THE major inhibitor of the brain
  • they contain 5 subunits
  • they are permeable to Cl- ions (through diffusional forces only)
  • net effect is inhibitory, because cell membrane is hyperpolarized
22
Q

Describe the various binding sites of the GABAa receptor?

A

It has a GABA binding site, a barbiturate binding site, a benzodiazepine binding site, a steroid binding site, and, within the channel, a picarotoxin binding site

23
Q

What is the effect of a picarotoxin?

A

It causes the body to seize and convulse, because the toxin is a GABAa channel blocker, so the inhibitory signal cannot be carried out (therefore, the body loses control and begins to convulse)

24
Q

Which GABA receptor does alcohol have an effect on (as we know that alcohol does not have its own binding site)?

A

GABAa

25
Q

How do benzodiazepines affect the GABAa receptor?

A

They facilitate the effects of bound GABA by causing the channel to become open wider, for a longer duration, allowing more than usual Cl- flow (and enhancing the inhibition signal)

26
Q

How do barbiturates affect the GABAa receptors?

A

The binding of barbiturates also opens the channel wider for a longer duration, but it doesn’t need GABA to be bound to the active site in order to accomplish this
- this leads to danger because now the brain has lost its ability to inhibit the signal being carried out by other neurons, and it has lost its feedback mechanism

27
Q

Why is it so dangerous to mix alcohol with barbiturates?

A

Because barbiturates don’t need GABA bound in order to have an effect on the channel and because alcohol does not have its own binding site (and therefore also does not need for GABA to be bound to have an effect), as well as the fact that it disrupts the excitability of the neuron, over-inhibition follows, and the individual goes into a coma or dies as a result

28
Q

What are the three subunits of the GABAa receptors?

A

alpha, beta and gamma

29
Q

What effect do steroids have on GABAa receptors?

A

they open up the GABAa receptor more, allowing more Cl- flow into the membrane and causing a higher inhibitory effect

30
Q

What is the main difference between how benzodiazepines work on GABAa receptors, and how barbiturates act on GABAa receptors (exam question)?

A

The main difference is that benzodiazepines NEED GABA bound to the receptor in order to take effect, while barbiturates DO NOT NEED GABA to be bound to the receptor in order to have an effect

31
Q

Through what two processes do GABAa receptors adapt to an increased influx of inhibitory signals?

A

Through sensitization and downregulation

32
Q

What are some known ways that alcohol acts on the inhibitory system?

A
  1. alcohol potentiates the GABAa currents (increasing Cl- flow)
  2. alcohol inhibits NDMA response (decreasing Ca2+ flow)
33
Q

What is the classification for benzodiazepines acting on the GABAa receptors?

A

They are positive allosteric modulators that fall into three categories:

  1. full allosteric modulators (FAM) (have a similar effect to agonists)
  2. selective allosteric modulators (SAM)
  3. partial allosteric modulators (PAM)
34
Q

Describe full allosteric modulators (FAM)? What are some medications that act in this way?

A

all of them act with high potency and high efficacy at a large number of GABA receptor types (therefore, they are not very highly selective) - these are the most dangerous, and the most addictive
- example of FAMs is alprazolam (brand name xanax)

35
Q

Describe selective allosteric modulators (SAM)? What are some medications that act in this way?

A

all of them have a high potency and high efficacy, but act only on selective GABAa receptors
- example of SAMs is diazepam (brand name valium)

36
Q

Describe partial allosteric modulators (PAM)? What are some medications that act in this way?

A

all of them have a high potency, but low efficacy (meaning fewer Cl- ions flowing in) and they only act on selective GABAa receptors
- an example of PAMs is ambien or lunesta

37
Q

What is the main problem with FAMs and barbiturates?

A

They are memory eroding (because they inhibit LTP)

Neuropharmacology (18 decks)

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