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Jacopo Biomembranes > Lecture 10 > Flashcards

Lecture 10 Flashcards

1
Q

What does GABA-T stands for?

A

Gaba-transaminase

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2
Q

What does GAD stands for?

A

Glutamic acid decarboxylase

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3
Q

What does VGAT stands for?

A

Vescicular GABA amin acid transporter

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4
Q

Lis the drugs that enhances GABAaR function (Positive allosterisc modulators- PAMs):

A

Anxyolitic, anticonvulsant, analgesic, amnestitic

Sedative/hypnotic/ general anaesthetic

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5
Q

What are the three differences in the molecular mehcanisms by which either Barbiturates or benzodiazepines enhances GABAa receptor function?

A

1) Benzodiazepines increase the probability of the channel opening
2) Barbiturates promote open states of long duration
3) Barbiturates at higher concentrations directly activate the receptor

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6
Q

Describe modulation of α1β1 GABAaR:

A

It is activated by GABA
Blocked by picrotoxin and bicuculline
Enhanced by barbitures but no effect of benzodiazepines. This lack of effect lead to the search ofr additional subunits.

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7
Q

Why are GABA subtypes important?

A

Because they have distinct physiological and pharmacological properties, distinct CNS distribution and they mediate different behaviors.

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8
Q

What do α subunits contribute to the binding pocket of GABAa?

A

They contribute the negative (secondary) interface composed of Loops D, E and F.

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9
Q

What do β subunits contribute to the binding pocket of GABAa?

A

They contribute the positive (primary) interface composed of loops A, B and C

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10
Q

What does each interface of GABA-GABAaR binding pocket comprise?

A

Three discontinous loops that form the orthosteric binding pocket.

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11
Q

What are the three types of α subunits and how is their sensitivity to classical benzodiazepines??

A

WT α1: Sensitive to classical benzodiazepines
WT α6: Insensitive to classical benzodiazepines
α1/6 point (H to R) mutation: insensitive to classical benzodiazepines.

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12
Q

List the GABAaR isoforms and the respective effect of benzodiazepines and I.V anaesthetic behavior:

A 
α1: sedation
α2, α3: anxyolitic, analgesic
α5: cognition
β2: sedation, anaesthesia
β3: immobility, anaesthesia
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13
Q

Describe GABAbR structure:

A

A heterodimer with GABAb1 providing the GABA binding domain and GABAb2 the G-protein coupling to Gi and Go.

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14
Q

Describe the function of Gi α subunit in GABAbR:

A

It inhibits adenylate cyclase (AC) activity to decrease cAMP.

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15
Q

What is the result of POSTSYNAPTIC GABAbR activation?

A

It causes the Gi βγ complex to open a K+ channel causing hyperpolarization.

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16
Q

What is the result of PRESYNAPTIC GABAbR activation?

A

It causes the Go βγ complex to decrease the probability of voltage-gated Ca2+ channels opening, thereby increasing the quantal release of neurotransmitter.

17
Q

What is Baclofen?

A

A selective GABAbR agonist used clinically to treat spasticity.

18
Q

What are the two postsynaptic actions performed by GABA on GABAa and GABAb respectively?

A

GABA acts post-synaptically to activate chloride-conducting GABAaRs to produced IPSP.
Addiotanly GABA activates postsynaptic G-protein coupled GABAbR (via Gi) causing the opening of a potassium channel leading to further, but prologend hyperpolarization (ie-prolonged IPSP).

19
Q

What is the presynaptic action performed by GABA on GABAbR?

A

GABA also acts presynaptically to activate GABAbRs (via Go) to decrease the probability of Ca2+ channel opening and consequently decrease GABA release upon a second stimulus.

20
Q

Describe feed-forward inhibition:

A

Bi-synaptic inhibitory response (GABA) arrives 1-5 msec after the monosynaptic excitatory (Glutamate) input, thereby limiting the time window for the summation of excitatory inputs to generate an action potential.

21
Q

Describe feed-back inhibition:

A

The firing of a neuron A activates an inhibitory interneuron B that in turns inhibits the neuron A. Once inhibition decays the neuron A can fire again, initiating another cycle of inhibition. Such circuits generate neuronal oscillations.

22
Q

By what characteristics do the differen types of GABA neurons differ?

A

1) Firing rate
2) the part of the principal neuron they innervate
3) the subtype of synaptic GABAaRs they activate

23
Q

How do activation of activation of α1-GABAARs differs from α2-GABAARs.​

A

Activation of α1-GABAARs produces briefer IPSCs than those ​mediated by α2-GABAARs.​

24
Q

Describe cholecystokinin interneurons:

A

Asynchronous release of GABA

Express CB1 receptors.

25
Q

Describe parvalbumin fast spiking interneurons:

A

Synchronous GABA release

Express μ opioid receptors.

26
Q

Describe strychnine:

A

A potent competitive antagonist that enhances the perception of pain and causes convulsions.

27
Q

What are the strychnine-sensitive glycine receptors?

A

Anion-selective transmitter-gated ion channles

28
Q

What are some of the physiological functions of strychnine?

A

1) respiratory rhythm
2) motor control
3) muscle tone
4) sensory and pain processing.

29
Q

Explain how strychnine acts as a co-agonist:

A

It acts as a co-agonist (with glutamate) to activate the excitatory NMDA receptor.

30
Q

What does GlyT1 stands for?

A

Astrocytic glycine transporter

31
Q

What does GlyT2 stands for?

A

Neuronal glycine transporter

32
Q

What does VIAAT stands for?

A

Vesicle inhibitory amino acid transporter

33
Q

How is the expression of strychnine compared to that of GABAaRs?

A

More restricted in the CNS, it is found in spinal cord, brainstem, and a few selected brain regions such as the cerebellum and the raphe nuclei.

34
Q

How is synaptic GABA-ergic mIPSCs compare to glycine?

A

GABA-ergic mIPSC are prologend compare to glycine. Both fast (glycine) and slow (GABA) events occur in the same motor neuron.

35
Q

What do mutations in the glycine receptor cause?

A

Hyperekplexia (human startle disease).

36
Q

What is hyperekplexia?

A

Rare neurological disorder characterised by neonatal hypertonia (spasticity), exaggerated startle response to unexpected stimuli and variable incidence of apnoea, intellectual disability and delays in speech acquisition.
It disrupts the function of glycinergic synapses in the neuromotor pathways of spinal cord and brainstem.

37
Q

What is used to treat hyperekplexia?

A

Clonazepam, a benzodiazepine that is a GABAaR positive allosteric modulator (PAM).

38
Q

What mutations is thought to cause hyperekplexia?

A

R271L/Q is the most frequent mutation. It decreases both glycine sensitivity and the single channel conductance (γ).

39
Q

What do fainting goats express?

A

Strychnine-sensitive glycine receptor mutations.

Jacopo Biomembranes (16 decks)

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