Neurotransmitters, receptors and synaptic transmission

Ladislav Vyklický

Institute of Physiology Academy of Sciences CR, Prague http://www.biomed.cas.cz/d331/index.html

Neurotransmitters, receptors and synaptic transmission

2nd grade – Medical faculty LF UK

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2

Brain

Colonies of yeast

…communicate using the released ammonia – this is a sign of „… this is my place, go away"

Jan E. Purkyně 1787-1869

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Ramon y Cajal 1852-1934

Human brain consists of ~ 50, 000, 000, 000 neurons

http://upload.wikimedia.org/wikipedia/commons/1/15/PurkinjeCell.jpg

http://upload.wikimedia.org/wikipedia/commons/c/c6/Cajal-mi.jpg

1921 Otto Loewi (1873-1961) (in 936 awarded by NP)

1st heart 2nd heart

Vagus stimulation

Extracellular fluid

↓ Reduction in the heart rate

Reduction in the heart rate

Acetylcholine

Chemical synapse

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The designation "synapse" comes from Charles Scott Sherrington (1857-1952; in 1932, he was awarded the Nobel Prize)

The neurons of adult humans form 1 01 4 to 5 × 1 01 4 (1 00- 500 trillion) of the synaptic contacts

Chemical signalisation

For multicellular organisms there is a need to coordinate the activity of individual cells and tissues- this happens by means of chemical signaling.

Signals e.g. external (odorants), internal (hormonas, growth factors, ionts, neurotransmitters); serve as a chemical signal molecules linking adjacent or remote cells

Even external signals, which are not chemical, e.g. light or heat are in converted to chemical signal

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Receptor- ion channels

G protein coupled receptors

Receptors heaving direct enzymatic activity

Intracellular receptors

The substance could be considered a neurotransmitter if it meets the following criteria (Paton 1958) :

1. Presynaptic neuron must contain expected substance and be able to release it

2. The substance must be released after stimulation of the

presynaptic axon 3. The application of the substance on the postsynaptic neuron gives

rise to the same effect as the natural neurotransmitter 4. The effect of substances on the postsynaptic neuron must be

pharmacologically affected similarly to the the action natural neurotransmitter

5. In the vicinity of synapses must be present "enzyme", which uptakes or decomposes the neurotransmitter

Definition of the neurotransmitter

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Ionotropic receptors Metabotropic receptors

Receptors for neurotransmitters

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Enzyme / ion channel

Ionotropic receptor Metabotropic receptor

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Transmitters – aminoacids and their metabolites

Group Neurotransmitter Metabotropic R Ionotropic RAminoacid Glutamate mGlu NMDA R, AMPA R, Kainate RAminoacid Gamma amino butiric acid GABAB R GABAA RAminoacid Glycine - Glycine R

Monoamine (Phe/Tyr) Dopamine Dopamine R -Monoamine (Phe/Tyr) Norepinephrine (noradrenaline) Adrenergic R -Monoamine (Phe/Tyr) Epinephrine (adrenalin) Adrenergic R -

Monoamine (Trp) Serotonin (5-hydroxytryptamin) Serotonine R 5-HT3Monoamine (Trp) Melatonine Melatoninine R -Monoamine (His) Histamine Histamine R -

Other Anandamide Canabinoid R -Other Adenosine triphosphate P2Y12 R P2X ROther Acetylcholine Muscarinic R Nicotinic RGas Nitric oxice Guanylyl cyclase -Gas carbon monooxiode - K+ channels

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Transmitters - peptides

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…activate only metabotropic receptors Group Neurotransmitter Metabotropic R Function

Hypophyseal Vasopressin Vasopresin R Aggression, depressionHypophyseal Oxytocin Oxytocin R Stress, anxiety, maternal behavior, aggression, faith, confidence, love

Opioid Corticotropin Corticotropine R CNSOpioid Dynorphin delta OP1 Analgesia, antidepressive effects, drug addiction, cocaine dependenceOpioid Endorphin kapa OP2 Analgesia, sedative effects, miosa, the main receptor for morphineOpioid Enkephalin mu OP3 Analgesia, physical dependence, respiratory depression, euphoria

Tachykinin Neurokinin A NK 2 PNSTachykinin Neurokinin B NK 3 Brain developmentTachykinin Substance P NK 1 Vomiting, nociception

Bombesin Neuromedine R CNSGastrin releasing peptide - Stress, circadian rythm, PNS

N-Acetylaspartylglutamate mGluR3 NociceptionNeuropeptide Y Neuropeptide Y Appetite, circadian rhythms, anxietyCholecystokinin Cholecystokinin R Regulation of nociception, anxiety, memory and apetite

Vasoactive intestinal peptide VIP R Circadian rythmSomatostatin Somatostatin R GIT

Acetylcholine Catecholamine family Dopamine Noradrenaline Serotonine Histamine Aminoacids

Glutamate GABA Glycine

Peptides Purines Gasses NO

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Ionotropic receptors

Metabotropic receptors

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Chemical synapse

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Postsynaptic density

Synaptic vesicles

Synaptic cleft

Postsynaptic neuron

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3-D reconstruction of a molecule of ACh receptor

Ion channels are trensmembrane proteins forming a pore, that alows ion flux acros the cytoplasmatic membrane

Selective filter

Sensor

Gate

Structure of ion channels

Membrane

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Neurotransmitter activated ion channels are usually oligomeric complexes composed of several subunits

Trimer Tetramer Hexamer Pentamer

Conexonone channels

Glutamate receptors

Cis – loop receptors ATP – IK GABA Glycine Acetylcholine Serotonine

Basic principles of neurotransmitter activation of ion channels

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17 17

Presynaptic site Postsynaptic

site

A + Rclosed A + ARclosed AARclosed AARopen

AARdesensitized

Neurotransmitters at synapse – What determines the time course of postsynaptic currents

Receptor properties

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AARdesensitized


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Bound transmitter Unbound transmitter


AARdesensitized


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AARdesensitized





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Excitatory

Excitatory

Inhibitory -70 mV

-50 mV

Hyperpolarization (Cl- flow to the interior of the cell)

Depolarization (Na+ flow to the interior of the cell)

-80 mV

EPSC decrement in dendrites

Time

EPSC EPSC

EPSC EPSC

Relativní vzdálenost

Cable properties

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1000 – 10 000 synaptic contacts on a neuron

Passive

Active


Time

EPSC EPSC

EPSC EPSC


Cable properties

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Passive

Active


Time

EPSC EPSC

EPSC EPSC


Cable properties

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Passive

Active

Summation of postsynaptic currents

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Receptor (R) consists of seven membrane spanning regions

Extracellulr space

Cytosol G protein

Ligan binding and receptor activation

Receptor interacts with the G protein to promote conformational change and the change of GDP for GTP

G protein dissociates from the receptor α-GTP and βγ

subunits dissociate

Both α-GTP and βγ can now interact with their appropriate effectors

Members of the RGS family of G-protein regulators stimulate GTP hydrolysis

α-catalyzed hydrolysis of GTP to GDP inactivates α and promotes reassembly of the trimer

Metebotropic receptors

1

6 5

4 3

2

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Extracellular space

Intracellular space Adenylyl cyclase

αs

αs

γ β β

β

β γ

αi γ

γ αi

ATP cAMP

Protein kinase A

↑ cAMP production ↓ cAMP production

AC

AC +

-

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GPCR - αs and αi (metabotropic receptors affecting cAMP concentration)

cAMP

Adenosine

αs - stimulation

αi - inhibition

cAMP and phosphorylation/dephosphorylation

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Stimulation of metabotropic receptors leads to 5-fold increase in the intracellular concentration of cAMP for ~5 seconds. This increase is only temporary – cAMP is enzymatically broken down into AMP by cAMP phosphodiesterase.

cAMP- dependent protein kinase A (PKA)

protein … serine … protein protein … threonine … protein

P

intracellular proteins – ion channels, receptors, enzymes

PKA Kinase A ancoring protein

(A kinase anchoring protein - AKAP)

serine/threonine phsphoprotein phosphatase (PP) typ 1, 2a, 2b a 2c.

cAMP

Adenosine

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Transmitters and hormons acting through activation of Gαs (cAMP increase) adenosine, epinephrine, norepinephrine, dopamine, histamine, prostaglandins, serotonine, ACTH, antidiuretic hormone = vasopresin, calcitonin, CRH, FSH, glucagone, oxytocine, secretine, VIP, Thyreotropin–releasing hormone (TRH),TSH Transmitters and hormons acting through activation of Gαi (cAMP decrease) Acetylcholine, adenosine, epinephrine, norepinephrine, dopamine, GABA, glutamate, neuropeptide Y, opioids, serotonine, Angiotensine, melatonine, Growth hormone inhibitory hormone (somatostatine)

GPCR - αs and αi (metabotropic receptors affecting concentration of cAMP)

αi

αs

GPCR - αq (metabotropic receptors … activation PKC)

Intracellullar space

Fosfolipase C

αq γ

β

ER

Komplex of the metabotropic receptor and G- proteins

IP3 stimulates release of Ca2+ from ER

αq PLC

PIP2

PLC

DAG

PLC

IP3

IP3 receptor

Protein kinase C

PKC

PKC

Inositol trisphosphate (IP3)

Ca2+ Calmodulin dependent protein kinase (CAMP)

PLC

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Inositol trisfosphate (IP3)

Diacylglycerol (DAG)



Fosfolipase C

αq γ

β

ER



αq PLC

PIP2

PLC

DAG

PLC

IP3

IP3 receptor

Protein kinase C

PKC

PKC



Fosfatidylinositol-4,5-bisfosfát

PLC

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http://upload.wikimedia.org/wikipedia/en/6/61/Phosphatidylinositol-4,5-bisphosphate.jpg



Fosfolipase C

αq γ

β

ER



αq PLC

PIP2

PLC

DAG

PLC

IP3

IP3 receptor

Protein kinase C

PKC

PKC



Fosfatidylinositol-4,5-bisfosfát

PLC

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Calmodulin

• Ca2+ - Calmodulin dependent protein kinase

• Phosphatase (Calcineurin)

• Protease (Calpain)

• Endonuclease

Ca2+


http://upload.wikimedia.org/wikipedia/en/6/61/Phosphatidylinositol-4,5-bisphosphate.jpg

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Transmitters and hormons that activate IP3 a DAG acetylcholine, epinephrine, norepinephrine, bradykinine, endotheline, glutamate, histamine, leukotriens, prostaglandins, serotonine, tachykinine, thromboxane A2. antidiuretic hormone = vasopresin, cholecystokinin, gastrine, neurotensine, oxytocine, Thyreotropin–releasing hormone (TRH), TSH


αq




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Cholin

CH3 - COOH Acetate

Cholin acetyltransferase

Acetylcholine (ACh) was discovered by Henry H. Dale (in 1914) … its role of neurotransmitter was described by Otto Loewi … in 1936 both were awarded by NP

Acetylcholinesterase

Acetyl-CoA

Acetylcholine „Vagusstoff“ 35

8 nm

2,5 nm

Nicotinic ACh receptor

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8 nm

2,5 nm

17 nACh subunits

(α1)2β1δε (α1)2β1δγ

(α3)2(β4)3 Ganglia

(α4)2(β2)3 CNS (α3)2(β4)3 (α7)5

Nicotinic ACh receptor

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1.5-4.0 x 107 Ach receptors

60 vesicles is released during EPSC – Each contain 104 molecules of ACh

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Botulinum toxin is a protein produced by the bacterium Clostridium botulinum, and is considered the most powerful neurotoxin ever discovered - 100 g would be sufficient to kill all people. BT – prevents fusion of vesicles with the presynaptic membrane

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Bungarus fasciatus

Alfa-Bungarotoxine

Tubocurarine

Strychnos Toxifera

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Sarin (Organophosphate)

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Myasthenia gravis

Ptosis

Normal

Ach E

MG

Ach R

Physostigmine

Physostigma venenosum

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http://upload.wikimedia.org/wikipedia/commons/b/b9/Koeh-237.jpg

Myasthenia gravis

Ptosis

Normal

Ach E

MG

Ach R

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Typ G-protein FunkceM1 Gq EPSP v autonomních ganglích

(Gi) sekrece sliných žláz a žaludku(Gs): v CNS (paměť?)Slow EPSP.

M2 Gi zpomaluje srdeční činnost↑ K+ vodivost snižuje kontraktilní sílu srdce

↓ Ca2+ vodivost v CNSM3 Gq kontrakce hladkého svalstva

zvyšuje sekreci žláz - slinných a žaludku v CNS akomodace oka vasodilatace zvracení

M4 Gi zvýšená lokomoce↑ K+ vodivost v CNS↓ Ca2+ vodivost

M5 Gq v CNS

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EPSP in autonomic ganglia Secretion from salivary glands and stomach In CNS (memory?)

Slow heart rate (reduce contractile forces of atrium; reduce conduction velocity of AV node) In CNS

conductance

Smooth muscle contraction Increased endocrine and exocrine gland secretions, e.g. salivary glands and stomach In CNS Eye accommodation; Vasodilation

causes decreased locomotion In CNS

In CNS

conductance

conductance conductance

Function Type G- protein

Muscarinic Ach receptors

Gαs Gαi Gαq

Gαi

Gαq

Gαi

Gαq

Typ G-protein FunkceM1 Gq EPSP v autonomních ganglích

(Gi) sekrece sliných žláz a žaludku(Gs): v CNS (paměť?)Slow EPSP.

M2 Gi zpomaluje srdeční činnost↑ K+ vodivost snižuje kontraktilní sílu srdce

↓ Ca2+ vodivost v CNSM3 Gq kontrakce hladkého svalstva

zvyšuje sekreci žláz - slinných a žaludku v CNS akomodace oka vasodilatace zvracení

M4 Gi zvýšená lokomoce↑ K+ vodivost v CNS↓ Ca2+ vodivost

M5 Gq v CNS

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EPSP in autonomic ganglia Secretion from salivary glands and stomach In CNS (memory?)

Slow heart rate (reduce contractile forces of atrium; reduce conduction velocity of AV node) In CNS

conductance

Smooth muscle contraction Increased endocrine and exocrine gland secretions, e.g. salivary glands and stomach In CNS Eye accommodation; Vasodilation

causes decreased locomotion In CNS

In CNS

conductance

conductance conductance

Function Type G- protein

Atropa belladonna (Rulík zlomocný)

Atropin (antagonist)

Muscarinic Ach receptors

Gαs Gαi Gαq

Gαi

Gαq

Gαi

Gαq

Amanita muscaria

Muscarine (agonist)

CNS

Autonomic nervous system

Nervs and proximal ganglia Organs (muscle, heart, glands)

Preganglion fibre

Ganglion

ACh

N2 nicotinic ACh R

ACh

Muscarinic ACh R

Ganglion

ACh

N2 nicotinic ACh R

NA

α or β adrenergic receptors

Postganglion fibre

Synapse „en passant“

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Parasympathetic nervous system

Sympathetic nervous system

Parasympathicus - Acetylcholine is a neurotransmitter at preganglion and postgan neurons. The nerves which liberate acetylcholine are cholinergic. (Rest and digest)

Parasympathetic NS Sympathetic NS

Preganglion neurons Brainstem and spinal cord (S2-S4)

Postganglion neurons Usually in the vicinity of the target organ

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Acetylcholine

Neuronal plasticity - memory Arousal Attention Alzheimer disease (inhibitors of cholinesterase)

Cholinergic transmission in the CNS

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Phenylalanine

Phenylalanine hydroxylase (livr)

Adrenaline

CNS

Sympathetic NS

50 Adrenal gland

http://en.wikipedia.org/wiki/File:Catecholamines_biosynthesis.svg

Phenylalanine

Phenylalanine hydroxylase (livr)

Adrenaline

CNS

Sympathetic NS

Phenylpyruvate oligophernia (Phenylketonuria) Is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase • Mental retardation • Brain damage • Oligophrenia • Seizures

51 Adrenal gland

http://en.wikipedia.org/wiki/File:Catecholamines_biosynthesis.svg

Dopamine transporter DAT1

Reuptake

Dopaminergic neuron

Brain, striatum, bazal ganglia

MAO

Norepinephrinephrine transporter NET

Reuptake

Dopaminergic neuron COMT

Prefrontal cortex

D1 Gαs

D2 Gαi

D3 Gαi

D4 Gαi

D5 Gαs

Postsynaptic site Postsynaptic site

Dopaminergic system - CNS

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Dopamine degradation

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Parkinson disease – Schizophrenia – Drug ubusus

Reuptake

Postsynaptic site

Dopaminergic neuron

Treatment of schizophrenia D4 is 4-fold increased

Haloperidol (inhibitor of D receptors

Dihydroxyphenylalanine DOPA

Treatment of Parkinson disease

Cocaine (inhibitor of dopamine and

norepinephrine transporter)

Erythroxylum coca 54

Parkinson disease – Schizophrenia – Drug ubusus

Reuptake

Postsynaptic site

Dopaminergic neuron

Treatment of schizophrenia D4 is 4-fold increased

Haloperidol (inhibitor of D receptors

Dihydroxyphenylalanine DOPA

Treatment of Parkinson disease

Cocaine (inhibitor of dopamine and

norepinephrine transporter)

Erythroxylum coca

PET

Substancia nigra

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http://upload.wikimedia.org/wikipedia/commons/d/d7/Sir_William_Richard_Gowers_Parkinson_Disease_sketch_1886.jpg

http://upload.wikimedia.org/wikipedia/commons/9/94/DA-loops_in_PD.jpg

Dopamine receptors • Control of movement • Memory, attention, motivation • Sleep • Control of vomiting and nausea • A system of pleasure, aggression, addiction • The behavior of "the search for reward„ • Anhedonia – the inability to feel pleasure • Schizophrenia • Bipolar disorder • Alcohol dependency • Control of food intake • Sexual behavior • Social phobia • Pain • ADHD Attention-deficit hyperactivity disorder • Parkinson disease

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CNS

Autonomic nervous system

Nerve and proximal ganglia

Organs (muscle and glands)

Preganglion fibre

Ganglion

ACh

N2 nicotinic ACh R

ACh

Muscarinic ACh R

Ganglion

ACh

N2 nicotinic ACh R

NA

α or β adrenergic receptors

Postganglion fibre

Synapse „en passant“

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Sympathetic nervous system

Sympathetic nervous system Acetylcholine is the neurotransmitter on the preganglionic neurons. On the postganglionic neurons it is the norepinephrine (noradrenaline). The nerves which liberate noradrenaline are called adrenergic. (Hunting and defence)

Parasymphatetic NS Sympathetic NS

Preganglion neurons Intermediolateral part of the spinal cord (T1-L3)

Prevertebral and paravertebral ganglia

PNS – Sympathetic nervous system - Norepinephrine

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Uptake

Norepinephrine neuron

MAO

Postsynaptic site

COMT

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PNS – Sympathetic nervous system - Norepinephrine

Receptor GPCR Effect α1 Gq ↑ Vasoconstriction; ↓ intestine mobility; α2 Gi ↓ Insulin release; ↓ Transmitter release;

Sfincter contraction β1 Gs ↑ Heart rate;

↑ Lipolysis β2 Gs Relaxation of smooth muscle β3 Gs ↑ Lipolysis

Serotonine and norepinephrine

transporter

Uptake

CNS MAO

Postsynaptic site

Norepinephrine neuron

Depression, mood disorders, anxiety, Attention Deficit Hyperactivity Disorder (ADHD)

Noradrenaline - CNS

Antidepressants (Serotonin–norepinephrine reuptake inhibitors - SNRIs) Inhibit reuptake of norepinephrine (NE activate postsynaptic receptor for longer)

Noradrenaline

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Biosynthesis and metabolism of serotonin

MAO

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Biosynthesis and metabolism of serotonin

MAO Ecstasy (MDMA - 3,4-methylendioxymetamfetamin) It is the most typical representative of the so called “recreation drug“ (originally developed as a to lose weight on the basis of the suppression of appetite)

… it releases serotonin from the synaptic vesicles

Serotonin transporter (SERT) - polymorphism of this gene may play a role in: sudden death of newborns, aggressive, degenerative diseases (AD), posttraumatic stress, sensitivity to the depression.

Selective serotonin reuptake inhibitors (SSRI 's) are used for psychiatric illness and in particular for obsessive compulse disorder.

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Typ Iono/Metabotropní Mechanismus Účinek

5-HT1 Gi/Go Snižuje hladinu cAMP Inhibitory

5-HT2 Gq/G11 Zvyšuje IP3 and DAG. Excitační

5-HT3 Ligand-gated Na+ and K+ kanál. Depolarizace Excitační

5-HT4 Gs Zvyšuje hladinu cAMP Excitační

5-HT5 Gi/Go Snižuje hladinu cAMP Inhibiční



Type Inono/metabotropis Action 5-HT receptors

Serotoninové receptory modulují uvolňování řady neuropřenašeču glutamátu, GABA, dopaninu, noradrenalinu, acetylcholinu….

Serotonine (5HT) receptors

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Inhibitory Excitatory Excitatory Excitatory Inhibitory Excitatory Excitatory

In Ligand-gated Na+ channel

5-HT3 are ionotropic receptors – are excitatory CNS – anxiety PNS – nociception

Direct

Indirect

Indirect

Subtypes of serotonine receptors

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Subtypes of serotonine receptors

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Ergot (fungi)

Agonist of 5-HT1A, 1B, 1D, rec. Migrene, to stop haemorrhage

Ergotamine

Antagonists of 5HT6 5HT7 Antipsychotics (schizophrenia) and antidepresants (depressioin).

http://upload.wikimedia.org/wikipedia/commons/c/ca/Claviceps_purpurea.JPG

http://en.wikipedia.org/wiki/File:Ergotamine3.png

Matabotropní serotoninové receptory

Aphrodisiac Yohimbine is found naturally in an African tree Yohimbine – (Pausinystalia yohimbe). The main effect is to increase blood flow in the region of pelvis – promot blood circulation in penis.

Yohimbine – antagonist of 5-HT1B, 5-HT1D, 5-HT2A, 5-HT2B and agonist of 5-HT1A.

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http://en.wikipedia.org/wiki/File:Yohimbine_structure.svg

http://upload.wikimedia.org/wikipedia/commons/0/02/NAMA_Aphrodite_Syracuse.jpg

Matabotropic serotonine receptors

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LSD (Lysergic acid diethylamide)

Albert Hofmann 1938

Mescaline

Lophophora williamsii

AGONIST

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Albert Hofmann 1938

Mescaline


AGONIST

Stanislav Grof *1931 Prague

Studied the effect of LSD on behaviour … to understand pre- and perinathal psychology. He found that it is possible to induce similar mind states (after LSD) by holotropic breathing

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http://upload.wikimedia.org/wikipedia/commons/a/a3/Stanislav_grof01.jpg



Albert Hofmann 1938

Mescaline


AGONIST

Stanislav Grof *1931 Prague

Studied the effect of LSD on behaviour … to understand pre- and perinathal psychology. He found that it is possible to induce similar mind states (after LSD) by holotropic breathing

Salvador Dalí

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http://upload.wikimedia.org/wikipedia/commons/a/a3/Stanislav_grof01.jpg

http://upload.wikimedia.org/wikipedia/en/d/dd/The_Persistence_of_Memory.jpg

http://upload.wikimedia.org/wikipedia/commons/2/27/Salvador_Dali_NYWTS.jpg




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Mast cells are capable to release heparin and histamine - importance for allergic reactions.

Histidine Histamine

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http://en.wikipedia.org/wiki/File:SMCpolyhydroxysmall.jpg

Histamine receptors

Receptor Mechanism Function

H1 Gq

• Contraction of ileum • Affects the cirkadální rhythm • System vasodilatation • Bronchoconstriction (astma)

H2 Gs

• Increase heart rate • Increase HCl secretion in stomach • Relaxation of smooth muscle • Inhibition of synthesis of antibodies and prolipheration of T-

cells

H3 Gi • Neurotransmitter in the CNS • Presynaptic autoreceptors

H4 Gi • Chemotaxis of mast cells

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GABAergic Glycinergic

Purinergic (ATP) Cholinergic Serotonergic

Glutamatergic

Relative representation of synapses in the CNS

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Glutamát vázající domena

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Glutamic acid

AMPA (α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate)

NMDA N-methyl-D-aspartate

Kainate

Ionotropic glutamate receptors

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Receptor SubunitAMPA GluR1

GluR2GluR3GluR4

Kainate GluR5GluR6GluR7KA-1KA-2

NMDA NR1NR2ANR2BNR2CNR2DNR3ANR3B

Glutamate receptors are thought to be responsible for the reception and transduction of umami taste stimuli.

Metabotropic glutamate receptors

80

Metabotropic glutamate receptors are all named mGluR# and are further broken down into three groups: Group Receptor Effect 1 mGluR1 Increase in Ca2+ concentration in the cytoplasm. mGluR5 Release of K+ from the cell by activating K+ ionic channels 2 mGluR2 Inhibition of adenylyl cyclase causing shutdown of the cAMP-dependent pathway mGluR3 3 mGluR4 Activation of Ca2+ channels, allowing more Ca2+ to enter the cell mGluR6 mGluR7 mGluR8

↑ [Ca2+]i

Depolarisation

Glu Gly Glu Gly

Activation of NMDA R

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10 ms

1 pA (10-12 A)

Closed

Open

Long term potentiation LTP

82

Before glutamate 30 min after glutamate

A B

Excitotoxicity

80 s Glutamate 2 s

Time (s)

Ra

tio

100 M glutamateµ

Neurons

Glia

100 mM Glutamate

NMDA receptor and intracellular Ca2+

Ca2+

Cell death

Increase in the intracellular Ca2+ concentration – an important step in excitotoxicity induction

Endonuclease

DNA Fragmentation

Phospholipase

Arachidonic acid

Protease (Calpain)

Ca-binding prot. (Calmodulin)

Mitochondria damage

Free radicals

Cytoskeleton disruption

Nitric oxide synthase

↓ ATP

↓ pH

Glutamate NMDA receptor

Alzheimer dementia

Functional changes of glutamatergic neurons

Neurodegeneration In: hippocampus, nucleus basalis Meynerti, amygdala, cortex

Glutamate and Alzheimer dementia

? Pathology

Tonic increase in the extracellular glutamate concentration

Excesive activation of NMDA receptors

• Alzheimer’s disease • Consequences of head stroke • Traumatic lesion of the brain • Parkinson’s disease • Tardive dyskinezia • Huntington’s disease • Amyotrophic lateral sclerosis • Olivopontocerebellar degeneration • AIDS • Alergic encephalomyelitis

• Epilepsy • Anxiety • Depression • Schizophrenia • Chronic pain • Drug addiction

Prominent neurodegeneration Other

Pathology in the “glutamatergic“ system




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GABAA receptors – ionotropic receptors GABAB receptors – metabotropic receptors • GABAB1 • GABAB2

Reduce activity of adenylyl cyclase (reduce Ca2+ conductance and increase K+)

GABA receptors

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α (alfa) subunit (6) GABRA1, GABRA2, GABRA3, GABRA4, GABRA5, GABRA6 β (beta) subunit (3) GABRB1, GABRB2, GABRB3 γ (gama) subunit (3) GABRG1, GABRG2, GABRG3 δ (delta) subunit (3) GABRD ε (epsilon) subunit GABRE π (pi) subunit GABRP θ (theta) subunit GABRQ ρ (rho) subunit GABRR1, GABRR2, GABRR3

Ionotropic GABAA receptors

90

19 subunits

http://upload.wikimedia.org/wikipedia/commons/0/06/GABAA_receptor_schematic.png

… potentiate GABA EPSC: Barbiturates Diazepam (Valium) Ethanol Inhalation anesthetics (anxiolytic and hypnotic effect)

GABAA receptors are composed of five subunits (α2β2γ) are Cl- permeant and are inhibitory

Ionotropic GABAA receptors

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http://upload.wikimedia.org/wikipedia/commons/4/46/NAchR_2BG9.png

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Glycine activated ion channel contains five subunits α-subunit (α1-4) GLRA1, GLRA2, GLRA3, GLRA4 - (binds glycine) β-subunit (GLRB) Ion channels are Cl- permeant – therefore inhibitory

Is expresed only in the spinal cord There are pure glycinergic synapses as well as mixed where glycine is released together with GABA

Ionotropic glycine receptor

93

Strychnos nux-vomica L Strychnine

Pharmacology of glycine receptor

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-

+

- Renshaw cell

Motoneurone

Motoneurone

ACh

GLY

GLY

Mechanism of strychnin induced convulsions

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Neurotransmitters, receptors and synaptic transmission