Download GABA A receptor

Neurotransmitter
Su Bo
Institute of neurobiology
0531-88382329; [email protected]
1
Outline

Neurotransmitter categories

Neurotransmitter chemistry

Some important neurotransmitters
2
Discovery of Neurotransmitter


1904, Renton Elliott, hypothesis neurotransmitter;
1914, Henry Dale discovered acetylcholine;



stimulation of the parasympathetic nervous system;
1920, Otto Loewi (奥托 洛维) ;
1929 Dale purified acetylcholine from mammalian
organs
1936 Nobel prize winner
3
Basic Concepts of NT

Neurotransmitter递质
Endogenous signaling molecules that alter the
behaviour of neurons or effector cells.

Neuromodulator调质
Endogenous signaling molecules that regulate the
behaviour of neurons or effector cells.
4
Criteria for neurotransmitter

The molecule must be synthesized
and stored in the presynaptic neuron.

The molecule must be released by
the presynaptic axon terminal upon
stimulation.

The molecule ,when experimentally
applied, must produce a response in
the postsynaptic cell that mimics the
response produced by the release of
neurotransmitter from the presynaptic
neuron.
5
Categories of neurotransmitters
Classical Transmitters
(small-molecule transmitters)
Large-molecule
neurotransmitters
others
Cholines
Amines
Amino acids
Neuropeptides
Acetylcholine
(Ach)
Dopamine (DA)
Glutamate
CCK
NO
Epinephrine（E）
Aspartate
Dynorphin
CO
Norepinephrine(NE)
GABA
Enkephalins
ATP
Serotonin (5-HT)
Glycine
VIP
Histamine(HIS)
Neuropeptide Y
Substance P
6
7
Neuropeptides
8
Outline

Neurotransmitter categories

Neurotransmitter chemistry

Some important neurotransmitters
9
Elements of Neurotransmitter System
10
Synthesis
Small-molecule neurotransmitter
Neuropeptide
11
Vesicular transporter

ATP-dependent H+ accumulation

Reverse transport

Vesicular ACh transporter (VAChT)

Vesicular monoamine transporter (VMAT)

Vesicular Glu transporter (VGLUT)

Vesicular inhibitory amino acid transporter (VIAAT)
12
Storage
small clear-core vesicles
large dense-core vesicles
40-60nm
90-250nm
Ach, Amino acids
Neuropeptides, Amines
13
囊泡储存是递质储存的主要方式
 递质合成后储存在囊泡内，囊泡内可以有数千个递质分
子。待释放的活动囊泡聚集在突触前膜活动区，为递质
的胞裂外排作好准备
– 小分子递质如乙酰胆碱、氨基酸类递质储存在直径
40~60 nm的小囊泡中，在电镜下囊泡中央清亮，为
小的清亮囊泡
– 神经肽储存在直径约90~250nm的大囊泡中，电镜下，
囊泡中央电子密度较高，为大的致密核心囊泡
– 单胺类递质储存的囊泡既有小的致密核心囊泡，也有
大的（直径60~120 nm）不规则形状的致密囊泡
Neurotransmitter Co-existence

Dale’s principle: A neuron has only one neurotransmitter.

Both a classical neurotransmitter (ACh or catecholamine)
and a polypeptide neurotransmitter exist in the terminal
of one neurons.

They are contained in different synaptic vesicles that can
be distinguished using the electron microscope.

The neuron can thus release either the classical
neurotransmitter or the polypeptide neurotransmitter
under different conditions.
15
Cotransmission

Cotransmission is the release of several
types of neurotransmitters from a single
nerve terminal.

Some neurons can release at least two neurotransmitters at the
same time, the other being a cotransmitter, in order to provide
the stabilizing negative feedback required for meaningful
encoding, in the absence of inhibitory interneurons.

GABA–glycine co-release.

Dopamine–glutamate co-release.

Acetylcholine–glutamate co-release.

Glutamate–dynorphin co-release
16
Release
fast 300us
slow 50ms
17
Ca2+ dependent Release
18
Ca2+ dependent release
Fura-2 staining
19
Tetanus
20
Lambert-Eaton myasthenic syndrome(LEMS)
21
Transmitter Termination

Diffusion

Reuptake

Enzymatic degradation: neuropeptides

Autoreceptor

Combination of above
22
Reuptake
Transporter exist in the
presynaptic membrane or the
membrane of glia surrounding
the synapse
Na+/K+-dependent transporter：
Glutamate
Na+/Cl--dependent transporter:
GABA, Amines
23
Two Families of Postsynaptic Receptors

Transmitter-gated ion
channels

G-protein-coupled
receptors

second messenger
systems

directly controls

controls channel
channel

fast
receptor indirectly

slow
24
Transmitter-gated ion channels
25
The general architecture of ligand-gated receptors
(A)One of the subunits of a complete receptor
(B)Assembly of either four or five subunits into a complete receptor
26
27
A diversity of subunits come together to
form functional ionotropic receptors
28
The basic structure of GPCR
29
Structure of GPCRs
30
Structure of GPCRs
These receptor proteins contain
seven transmembrane domains.
Portions of domains II, III, VI, and
VII make up the neurotransmitterbinding region.
G-proteins bind to both the loop
between domains V and VI and to
portions of the C-terminal region.
31
G-protein-coupled receptors
32
The basic mode of operation of G-proteins
33
The basic mode of operation of G-proteins
34
35
Gs/Gi－AC－cAMP
36
细胞膜
Gs
AC
ATP
C
C
R
R
cAMP
C
C
R
2cAMP
R
2cAMP
+
核 膜
37
Ｃ
Pi
DNA
Ｃ
Ｒ
Ｅ
Ｂ
Ｃ
Pi
Ｃ
Ｒ
Ｅ
Ｂ
Ｃ
Ｒ
Ｅ
Ｂ
Pi
ＣＲＥ
生理效应
Ｃ
Ｒ
Ｅ Pi
Ｂ
细
胞
核
结构基因
蛋白质
38
QIAGEN
Gq-PLC-IP3/DAG
40
Varieties of metabotropic neurotransmitter receptors
41
42
Agonist and Antagonist

Each neurotransmitter exerts its postsynaptic
effects by binding to specific receptors.

Neuropharmacological analysis: studying
different receptor subtypes using agonist and
antagonist.
43
Agonist

A substance that mimics a specific neurotransmitter, is
able to attach to that neurotransmitter's receptor and
thereby produces the same action that the
neurotransmitter usually produces.

Drugs are often designed as receptor agonists to treat a
variety of diseases and disorders when the original
chemical substance is missing or depleted.
44
Antagonist

Drugs that bind to but do not activate neuroreceptors,
thereby blocking the actions of neurotransmitters or the
neuroreceptor agonists.
45
Neuropharmacology of Receptor Subtypes
Neurotransmitter
Receptor subtype
Agonist
Antagonist
Acetylcholine(ACh) Nicotinic receptor
Nicotine
Curare
Muscarinic receptor Muscarine
Norepinephrine(NE) α receptor
Glutamate(Glu)
GABA
Atropine
Phenylephrine Phenixybenzamine
β receptor
Isoproterenol
Propranolol
AMPA
AMPA
CNQX
NMDA
NMDA
AP5
GABAA
Muscimol
Bicuculline
GABAB
Baclofen
Phaclofen
46
Neurotransmitter chemistry
47
Outline

Neurotransmitter categories

Neurotransmitter chemistry

Some important neurotransmitters
48
Acetylcholine (ACh)
49
ACh system

Arising from the basal forebrain
(基底前脑) and brain stem (脑干)

The medial septal nuclei (隔内
侧核) and basal nucleus of
Meynert project widely upon the
cerebral cortex (hippocampus)

The pontomesencephalotegmental complex (脑桥-中脑被盖复合体)projects to the
thalamus and parts of the
forebrain
50
51
Choline acetyltransferase (ChAT)

Be manufactured in the soma and transported to the
axon terminal

Only cholinergic neurons contain ChAT: a marker of
chonlinergic neurons

Transport of choline into neuron is the rate-limiting step
52
Acetylcholinesterase (AChE)

Can be manufactured by cholinergic neurons or
noncholinergic neurons

Specific for ACh degradation and has fast catalytic rates

Target of pharmacology
53
Ach Receptors

ACh is both an excitatory and inhibitory

Nicotinic ACh receptors (Ligand-gated ion channels)

N1(nicotinic neruronal, NN) : all autonomic ganglia
and hormone producing cells of adrenal medulla

N2(nicotinic muscle, NM): neuromuscular junction
55
Nicotinic ACh receptor

Permeable for Na+,
K+ and little Ca2+

Depolarization:
EPSP
56
Muscarinic ACh receptors (GPCR)

Muscarinic ACh receptors (M1-M5)
 Found
in the plasma membrane of
smooth and cardiac muscle cells, and in
cells of particular glands
57
Muscarinic ACh receptors (GPCR)

M1-R: ganglion

M2-R: heart

M3-R: exocrine glands, smooth muscle, endothelium
(produce NO)
58
Agonist and Antagonist
59
60
Monoamine
Catecholamines (CAT)
Dopamine (DA)
Norepinephrine (NE)
Epinephrine
Serotonin (5-HT)
Histamine
61
The biosynthetic pathway
for the catecholamines

Tyrosine

Tyrosine hydroxylase:

Rate-limiting enzyme

a marker of
catecholaminergic
neurons
62
Termination


Reuptake: Na+/Cl--dependent transporter

Dopamine transporter (DAT）

Norepinepherine transporter (NET)

Target of different drugs: amphetamine and cocaine
Enzymatic degradation:

Monoamine oxidase (MAO):
MAOI: antidepressant – phenelzine (苯乙肼) and tranylcypromine (强
内心百乐明)

Catechol-O-methyl transferase (COMT)
Postsynapse, Synaptic cleft
63
Stimulant drug action on the
catecholamine axon terminal
64
Dopamine (DA)

Arising from the
substantia nigra and
the ventral tegmental
area（腹侧被盖区）

Project to the
striatum (caudate
nucleus and
putamen), limbic and
frontal cortical region
respectively.
65
DA receptors

D1-D5: all are GPCRs

D1-like receptors: D1 and D5

D2-like receptors:

D2: domperidone 多潘立酮

D3: autoreceptor

D4: psychotropic drugs (chlorpromazine 氯丙嗪)
66
Norepinephrine (NE) as NT


NE in both PNS and CNS
PNS:


Smooth muscles, cardiac muscle and glands.
 Increase in blood pressure, constriction of arteries
CNS:
Arising from the locus coeruleus
（蓝斑核）, project to vast area of
the CNS, including the spinal cord,
cerebellum, thalamus and cerebral
cortex
67
68
Adrenergic receptor
α1 : α1A 、α1B 、α1D
α2: α2A 、α2B、 α2C
β : β1 、β2、 β3
70
Adrenergic receptor
location
α1
α2
function
blood vessels of skin,
vasoconstriction, sphincter
mucosa, abdominal viscera, constriction
kidneys, salivary glands
inhibition of NE release
Membrane of adrenergic
(autoreceptor);promotes
axon terminals (pre-synaptic blood clotting, pancreas
receptors), platelets
decreased insulin secretion
β1
Mainly heart muscle cells
β2
Lungs, most other
sympathetic organs, blood
vessels serving the heart
(coronary vessels);
β3
Adipose tissue
increased heart rate and
strength
atagonist
Phentolamine (酚妥
拉明）Prazosin (哌
唑嗪)
Phentolamine (酚妥
拉明）Yohimbine (
育亨宾)
Propranolol (普萘洛
尔) Atenolol (阿替洛
尔)
dilation of bronchioles &
Propranolol (普萘洛
blood vessels (coronary
尔) Butoxamine
vessels), relaxation of smooth
muscle in uterus
stimulation of lipolysis
71
Serotonin (5-HT)

Arising from the raphe
nuclei（中缝核群）,
clustered along the
midline of the brain
stem

Project extensively to
all levels of the CNS
72
Serotonin (5-HT)

Tryptophan

TPH: rate-limiting enzyme

SSRI: serotonin reuptake
inhibitor
--antidepressant
Fluoxetine 氟西汀(百忧解)
73
Medications Available to Treat Depression

Tricyclic antidepressants (TCA): amitriptyline（阿米替林）

MAO inhibitors (MAOI): moclobemide（马氯贝胺）

NE reuptake inhibitors (NRI): maprotiline（马普替林）

Serotonin reuptake inhibitors (SSRI): fluoxetine（氟西汀）

Serotonin/NE reuptake inhibitors (SNRI): venlafaxine（文拉法新）

NaSSA: mirtazapine（米氮平）
74
5-HT receptors


GPCR:

5-HT1－Gi: cerebrovascular constriction (migraine)

5-HT2－Gq: vasoconstriction (hypertension)
Ligand-gated ion channel

5-HT3: permeable for Na+/K+
（ondansetron 昂丹司琼）
75
Amino acids
Excitatory amino acid, EAA
Inhibitory amino acid, IAA
76
Glutamate
Glutamine cycle
77
Glutamate receptors


Ligand-gated ion channels

NMDA receptor: N-methyl-D-aspartate (N-甲基-D-天
冬氨酸)

AMPA receptor:α-amino-3-hydroxyl-5-methyl-4isoxazole-propionate (α-氨基-3-羟基-5-甲基-4-异噁唑戊酸)

KA receptor: kainic acid (海人藻酸)
GPCRs

mGluRs: metabotropic glutamate receptor 1-7
78
NMDA receptor

Four subunits:
NR1 and NR2

Glycine binding site
(co-agonist)

Mg2+ binding site
79
NMDA and AMPA
receptor

AMPA receptors are
permeable to Na+ and K+,
not Ca2+

AMPA produce fast EPSC
NMDA receptors produce
slower EPSC
80
NMDA receptor

Transmitter-gated
and voltage
dependent

MK-801: openchannel blocker
81
Coexistence of NMDA and AMPA receptors
82
Agonist and Antagonist
CNQX: 6-氰基-7-硝基喹喔啉-2，3-二酮
AP5: D-2-氨基-5-磷酸基戊酸
83
NMDA and AMPA receptor

NMDA receptors are permeable to Na+/K+/Ca2+

Ca2+ is very important for cell function. It can trigger
neurotransmitter release, active many enzymes, regulate
the opening of a variety of channels, and affect gene
expression;

in excessive amounts, Ca2+ can even trigger the death of
cell (Excitotoxicity).

Activation of NMDA receptors can cause widespread and
lasting changes in the postsynaptic neuron, especially
long-term memory.
84
GABA (γ-aminobutyric acid)

GABAergic neurons are distributed widely
in the NS. They are the major source of
synaptic inhibition in the NS.
85
GABA (γ-aminobutyric acid)

GAD (glutamic acid
decarboxylase):

a good marker of
GABAergic neurons

Pyridoxal
phosphate: VB6
GABA tansaminase
GAD
lack of B6 --- GABA
content↓--- loss of
synaptic inhibition -- seizures
86
GABA receptors


Ligand-gated ion channels

GABAA and GABAC: Cl- channel ↑---IPSP

In CNS, GABAA is the major receptor.

GABAA is the target of sedative-hypnotics and
antiepileptic drugs
GPCR:

GABAB: Gi---AC↓/K+↑---IPSP
87
GABAA receptor

Five subunits: αβγare
absolutely necessary
(2α2βγ)

GABA: β subunit

Agonist: Muscimol （蝇
蕈醇）

Antagonist: Bicuculline
（荷包牡丹碱）
88
GABAA receptor

Benzodiazepine: α subunit

Sedative-hypnotics （镇静催眠药）

Agonist: diazepam （地西泮）安定

Inverse agonist: β-carboline （卡波
林）


Antagonist: flumazenil （氟马西尼）
Barbiturate: antiepileptic drugs （抗癫
痫药）and anaesthesia（麻醉）

Neurosteroids: as barbiturate

Picrotoxin: antagonist
89
Glycine
90
Glycine

Glycine is the major NT in interneurons at spinal cord
(Renshaw cell)

Serine hydroxymethyltransferase:
Mutations---hyperglycinemia (a devastating neonatal disease)---
lethargy（嗜睡）seizures（抽搐）and mental retardation（智力低下）

Co-agonist for NMDA receptor

Glycine receptor: Cl- channel 3α2β

Antagonist: strychinine （士的宁）---excited effect or
eclampsia
91
Neuropeptide

Pre-propeptide

Propeptide

Active peptide
92
Differentia between classical transmitters
and neuropeptides
neuropeptides
Molecular
classical
transmitters
small
Synthesis
axon terminal
propeptide cleave
Storage
small clear-core
large dense-core
Termination
reuptake
Effect
fast and accurate
enzymatic
degradation
slow and long
large
93
Neuropeptide
94
Opioid peptides
95
POMC:
Proopiomelanocortin
(阿黑皮原）
Proenkephalin
（脑啡肽原）
96
Opioid receptor

GPCR:

μ: β-EP (midbrain and thalamus)

κ: Dyn A and Dyn B

δ: L-ENK and β-EP

Agonist: Morphine(吗啡)
Codeine(可待因）

Antagonist: Naloxone (纳洛酮）
97
NO
Robert F. Furchgott
Louis J. Ignarro
Ferid Murad
1998: Nobel prize for Physiology or Medicine
98
Differentia between classical transmitters and NO
NO
Classical transmitters
Synthesis
enzymatic promotion
enzymatic promotion
Storage
no vesicle
vesicle
Release
diffuse
exocytosis
Termination
diffuse
enzymatic degradation
or reuptake
Receptor
effect enzyme
receptor
Effecting site
extensive
mainly at synapse
Direction
bidirectional
unidirectional
99
Synthesis, release, and termination of NO
100
NO

eNOS: Smooth muscle relaxation;

nNOS: Involved in 1) memory and learning;
2)regulation of neurotransmitter release.
101
Emphases

Neurotransmitter categories

Ach、NE

5-HT SSRI

NMDA receptor

GABAA receptor

Differentia between classical transmitters and
neuropeptides

NO signal pathway
102
103