NSC 4352 - EXAM 3 - lect 11-12 & Lect 13

Monomeric G-proteins or "small G-proteins"

"Small" G proteins belong to the Ras superfamily of small GTPases (>100 proteins). These proteins are homologous to the alpha (α) subunit found in heterotrimers. However, a small GTPase can function independently as a hydrolase enzyme to bind to and hydrolyze GTP to form GDP. Involved in signal transduction of surface signals to vesicle apparatus and cytoskeleton.

Based upon the distribution of endocannabinoid receptors in the brain, it can be surmised that these compounds have a likely influence on

(all) neocortex hippocampus basal ganglia hypothalamus

Catecholamines - dopamine

• movement/motor disorders (Parkinson) • reward/motivation • addiction • schizophrenia

Cys-loop receptors

• nicotinic acetylcholine receptor (nAChR • 5-HT3 receptor • GABA receptor • Glycine receptor

Metabotropic GABA receptors (GABAB )

• stimulate opening of potassium (K+) channels. Opening of K+ channels inhibits/hyperpolarizes the cell by bringing the membrane potential closer to EK+ • inhibit Ca2+ channels --> also leads to hyperpolarization Calcium 7 transmembrane domains •Two major subtypes BR1 and BR2-probably assemble as homodimers or heterodimers •Each have splice variants

Internal calcium regulates

• the gating and kinetics of voltage-gated channels • the gating and kinetics of ligand-gated channels • Gene expression • Second messenger activation

Signaling at cerebellar parallel fiber synapses during long-term synaptic depression

1) parallel fibers activate AMPA and mGluR 2) LTD results from fewer AMPA receptors (long-term depression) 3) climbing fiber depolarizes membrane potential to open Ca2+ channels

which of the following is the correct sequence of enzyme actions in the synthesis of epinephrine?

1. Dopamine beta-hydroxylase 2. Tyrosine hydroxylase 3. Phenylethanolamine-N-methyl transferase 4. DOPA decarboxylase. 2 - 4 - 1 - 3

Binding of acetylcholine to the two alpha subunits results in the

15 ° rotation of all M2 helices. The cytoplasm side of the nAChR (nicotinic acetylcholine receptors) receptor has rings of high negative charge that determine the cation specificity of the receptor and remove the hydration shell of the passing ions.

One typically finds _______ subunits in the nicotinic acetylcholine receptors.

5

Which statement describes a possible outcome for a neurotransmitter after release into the synaptic cleft? A- Activation of G-protein-coupled receptor on postsynaptic cell B- Uptake into postsynaptic cell via endocytosis C- Modulation by an enzyme, increasing its efficiency D- Reuptake into postsynaptic terminal via transporter proteins

A- Activation of G-protein-coupled receptor on postsynaptic cell Explanation:-After the synaptic vessicles fuse to the presynaptic membrane, it allows neurotransmitter to release into the synaptic cleft and after the neurotransmitter is released into the synaptic cleft, it binds to receptors on the postsynaptic cell membrane and activate G-protein-coupled receptor on it.

rate-limiting step for acetylcholine

CAT

2 types of cannabinoid receptors (G-protein coupled receptors

CB1 and CB2 Highest density of any G protein-coupled receptor

Cyclic nucleotide(s) - cAMP

Cyclic adenosine monophosphate (cAMP, cyclic AMP) cAMP is synthesized from ATP by adenylyl cyclase An increase in cAMP leads (among other things) to activation of Protein kinase A (PKA). PKA is also known as cAMP dependent protein kinase. PKA then phosphorylates other effector proteins

Two types of Receptors

Ionotropic = ligand-gated channels receptor IS channel Metabotropic = G-protein-coupled receptors receptor modulates channel, or other intracellular effects

Catecholamines

Of the ~80 billion neurons in the human brain only ~500,000 (0.00062%) use catecholamines as neurotransmitters, but each of these connects to thousands of other neurons

Dopamine pathways

PKA and PKC pathway Two families of Dopamine receptors (D1-type and D2 type) modulate a large number of ion channels and synaptic currents. Their actions are typically antagonistic, but can be synergistic, too.

Opioids

Peptides that bind to the same postsynaptic receptors as opium Plant alkaloids, especially morphine, are the active ingredients in the sap, or the seeds of opium poppies Morphine is processed (acetylated) to produce heroin. Morphine, heroin, and synthetic opiates such as methadone and fentanyl are potent analgesics.

removal mechanism

acetylcholine: Achease glutamate: transporters GABA: transporters glycine: transporters Catecholamines: transporters (MAO, COMT) serotonin: transporters (MAO) histamine: transporters ATP: hydrolysis to AMP and adenosine neuropeptides: proteases endocannabinoids: hydrolysis by FAAH nitric oxide: spontaneous oxidation

NE - Norepinephrine - increases what

alertness and vigilance Locus coeruleus

which toxin blocks neuromuscular transmission by irreversibly binding to nicotinic acetylcholine receptors, thus preventing acetylcholine from opening postsynaptic ion channels?

alpha-bungarotoxin

precursor for neuropeptides

amino acids

Myasthenia gravis is characterized by

an autoimmune attack on acetylcholine receptors.

Serotonin reuptake blockers such as fluoxetine (Prozac) are used clinically

as antidepressants.

Muscarinic antagonists include

atropine (from deadly nightshade - belladonna) and scopolamine

Myasthenia Gravis is the result of an

autoimmune response Autoimmune disorder, caused by circulating antibodies that block AChRs (Nicotinic acetylcholine receptors) at the post-synaptic neuromuscular junction ACh has difficulty binding due to IgG (immunoglobulin G) blockade of the binding site. ACh rarely binds and ACh-esterase breaks it down

Noradrenaline (and Adrenaline)

packed into vesicles by VMAT = vesicular monoamine transporter reuptake via NET (NorEpinephrine Transporter) Degraded by MAO = monoamine oxidase, enzyme that degrades all Monoamines (sits on the membrane of mitochondria) act postsynaptically on 2 types of G-protein coupled receptors: α- and βadrenergic receptors known effects include both activation and inhibition of different types of K+ channels reserpine = inhibits VMAT and depletes norepinephrine stores NRI and SNRI = antidepressants inhibit the norepinephrine transporter Tropolone = inhibits COMT Prazosin = in an alpha1 antagonist AMPT = inhibits tyrosine hydroxylase and norepinephrine synthesis MAOI = antidepressants inhibit MAOA Yohimbine = is an alpha 2 antagonist clonidine = is an alpha 2 agonist propranolol is a beta antagonist

rate limiting step for glycine

phosphoserine

GABAB receptors are G-protein couples receptors that are coupled by the shortcut pathway to

potassium channels

Chewing betel nuts releases arecoline, a nicotinic agonist

produces euphoria

ATP-gated channels

purines

Synaptic inhibition

reduces the probability of firing an action potential. • GABAA or glycine receptors open chloride channels, which results in inward flow of negatively charged Clions --> hyperpolarization (B). • A synaptic potential can be depolarizing and yet be inhibitory. Depolarizing synaptic potentials can inhibit neurons as long as the ECl- is more hyperpolarized (negative) than the action potential threshold (C). chloride

Tolerance

refers to the diminished effect of a drug after repeated administration at the same dose, or the need to increase the dose to produce the same effect

precursor for glycine

serine

calcium as a messenger

intracellular targets: calmodulin protein kinases protein phosphatases ion channels synaptotagmin removal mechanisms: plasma membrane Na+/Ca2+ exchanger Ca2+ pump endoplasmic reticulum - Ca2+ pump mitochondria sources: plasma membrane - Voltage gated Ca2+ channels & various ligand gated channels endoplasmic reticulum - IP3 receptors and ryanodine receptors

Glutamate Receptors

ionotropic receptors: • NMDA = non-selective cation channels --> Na+, K+ , and Ca2+ (NMDA-R) • AMPA • kainate

Calmodulin, or CaM (an abbreviation for CALcium-MODULated proteIN)

is a calcium-binding protein expressed in all eukaryotic cells.

Dependence

is an adaptive state that develops in response to repeated drug administration; upon cessation of drug use this adaptive state may lead to withdrawal symptoms.

acetylcholine receptor (AChR) has two neurotransmitter binding sites

located in the extracellular domain, at αδ and either αε alpha gamma

precursor for endocannabinoids

membrane lipids

G-protein coupled receptors(GPCRS)

metabotropic receptors Proteins consisting of 7 transmembrane domains. Domains II, III, VI, and VII make up the neurotansmitter binding region G-proteins bind to both the loop between domains V and VI and the C-terminus

rate limiting step for ATP

mitochondrial oxidative phosphorylation; glycolysis;

Glutamate

most prevalent excitatory transmitter (>half of all synapses) Precursor: glutamine, released by glia cells Enzyme glutaminase catalyzes glutamate from glutamine VGLUT = vesicular glutamate transporter found only in cells that use glutamate as a neurotransmitter. 3 types, VGLUT 1, VGLUT 2, VGLUT 3. EAAT = excitatory amino acid transporter 5 different types - some on presynaptic terminals, others on glia cells. Plasma membrane transporters

ACh

muscarinic

Both excitatory and inhibitory neurotransmitters

neuropeptides, nitric oxide

rate limiting step of nitric oxide

nitric oxide synthase

nAChR (nicotinic acetylcholine receptors) is___ _____ cation channel

non-selective Higher driving force for Na+ (sodium) typically results in an inward current and an EPSP

Rat working for food pellet --> Light signals reward, which leads to dopamine release in the

nucleus accumbens (P.E.M Phillips)

rate limiting step for neuropeptides

synthesis and transport

Peptide neurotransmitters are often released

together with nonpeptide transmitters.

rate limiting step for serotonin

tryptophan hydroxylase

rate limiting step for catecholamines

tyrosine hydroxylase

(Endo-) cannabinoids

Δ9-tetrahydrocannabinol (THC), the active component of marijuana Endocannabinoids: 2-AG anandamide delta9

Ionotropic GABA receptors (GABAA and GABAC)

• 5 subunits (heterodimeric) • Integral chloride (Cl- ) channel

Presynaptic actions of GABAB receptors

• Activation of presynaptic GABAB autoreceptors can inhibit release of GABA from the terminal. • Under some conditions spillover can also occur onto neighboring excitatory synapses. There, GABAB activation inhibits release of glutamate. • Finally, presynaptic GABAB receptors also inhibit release of dopamine, norepinephrine and serotonin.

Protein kinases General mechanisms of protein kinase activation

• catalytic subunits are responsible for transferring phosphate groups to target proteins • catalytic subunits are being kept inactive by regulatory subunits (autoinhibition) • Binding of the second messenger (cAMP; DAG; Ca2+) removes autoinhibition and allows catalytic domain to be activated

rate limiting step for GABA

GAD

precursor for histamine

Histidine

Shunting inhibition

If extracellular chloride is equal to Resting membrane potential, opening of Cl- channels does not hyperpolarize the cell, yet will act inhibitory on simultaneous EPSPs --> Opening of Cl- channels increases membrane conductance (i.e. reduces resistance). Based on Ohm's law (V=I*R), it takes more current (I) to change membrane potential (V) when resistance is lower.

Excitatory effects of GABA in the developing brain

In developing neurons the intracellular chloride concentration is controlled by the Na+/K+/Cl- cotransporter, yielding high intracellular levels of Cl- -->ECl- is often more positive than AP threshold (always depolarizing). In adult cells a K+/Cl- co-transporter pumps Cl- out of the cell, lowering the internal Cl- , making ECl- much more negative -->hyperpolarization

Molecular mechanisms underlying LTP

Induction and early phase: Rise in postsynaptic Ca2+ (through NMDARs) --> acts as second messenger At least 2 Ca2+-activated protein kinases: • Ca2+/calmodulin-dependent protein kinase II (CaMKII), and • Protein kinase C (PKC) Expression (maintenance) of LTP is typically due to insertion of AMPA-Rs into the postsynaptic membrane --> increased response to glutamate Late phase: Late LTP is induced by changes in gene expression and protein synthesis brought about by the persistent activation of protein kinases activated during early -LTP, such as MAPK ( Mitogen - Activated Protein Kinase). The extracellular signal -regulated kinase (ERK ) subfamily of MAPKs - may be the molecular link between early -LTP and late -LTP, since many signaling cascades involved in early -LTP, including CaMKII and PKC, can converge on ERK. Upon activation, ERK phosphorylates transcription factors such as CREB, leading to synthesis of new proteins

Heterotrimeric G-proteins activation

When a ligand binds to the receptor, a conformational change occurs in the receptor that allows the Gα subunit to exchange GDP for GTP. This exchange triggers the dissociation of the G α subunit from the Gβγ dimer and the receptor and it activates the subunit(s) --> The Gα-GTP monomer and the Gβγ dimer can now modulate the activity of other intracellular (effector) proteins. Gbetagamma

elimination of all beta subunits of the GABAA receptor would result in

a deficit in producing functional GABAA receptors

Listed below are the five steps in a nitric oxide (NO)-mediated signaling event. 1. Calcium binds to calmodulin 2. Activation of nitric oxide synthase 3. NO diffusion for tens of micrometers 4. Activation of guanylyl cyclase 5. Inactivation by reaction with oxygen. Which of the following is the correct sequence of these steps? a. 1; 2; 3; 4; 5 b. 5; 4; 3; 2; 1 c. 4; 2; 3; 1; 5 d. 2; 3; 4; 1; 5 e. 1; 5; 2; 3; 4

a. 1; 2; 3; 4; 5

Which of the following receptor types can be modulated by both barbiturates and benzodiazepines? a. GABAA b. GABAB c. GABAC d. Glycine e. Muscarinc ACh receptor

a. GABAA

Enhancement of endocannabinoid signaling produces anxiolytic and antidepressant-like effects

--> endocannabinoid system is involved in the regulation of emotional states. --> Mutant mice lacking CB1 receptors show anxiogenic and depressive-like behaviors.

General features of ionotropic receptors

1 subunit four transmembrane helices three transmembrane helices plus pore loop complete receptor (4 or 5 subunits)

Chemical signaling consists of

A molecular signal (neurotransmitter) A receptor molecule (transduces information provided by the signal) A target molecule (ion channel) that is altered to cause electrical response in the postsynaptic cell.

precursor for ATP

ADP

Ionotropic glutamates

AMPA NMDA Kainate

Glutamate receptors associate with 3 families of proteins

AMPA - GRIP and PICK NMDA - PSD-95 mGluR - Homer Proteins with PDZ domains PDZ domains regulate protein-protein interactions

Metabotropic GABA receptors (GABAB )

Act as autoreceptors to inhibit Ca2+ channels (calcium) leads to reduction in transmitter release (both GABA, shown here, and glutamate)

The effector proteins of G-proteins

Activation of α-subunits cause one or more of the following events (directly or indirectly): • activation of adenylate cyclase (via Gsα or Giα) = cAMP formation & protein kinase A (PKA). • activation of phospholipase C (PLC) (via Gqα) alpha subunits

precursor for nitric oxide

Arginine

Catecholamines

As hormones: catecholamines are released by the adrenal glands in response to psychological stress or low blood sugar levels. Effects typically include increases in heart rate, blood pressure, blood glucose levels, and a general reaction of the sympathetic nervous system. In the CNS (central nervous system), catecholamines act as neuromodulators, influencing the effects of other, classical neurotransmitters.

Transcriptional regulation by CREB CREB = (cAMP response element-binding protein)

CREB is a cellular transcription factor. It binds to DNA sequences called cAMP response elements (CRE), thereby increasing or decreasing the transcription of the downstream genes. CREB is normally unphosphorylated. Its phosphorylation potentiates transcription (--> transcription requires binding of a co-factor to CREB and the RNA polymerase) Activators of CREB: • PKA • Ras / MAPK pathway • CaMK-IV (a variant of CaMK-II) • Ca2+ Important genes transcribed by CREB: • c-fos (an immediate early gene that itself acts as transcription factor for other genes) • the neurotrophic factor BDNF • tryosine hydroxylase • neuropeptides

Synaptic plasticity - LTP

Ca2+ influx through NMDA receptors results in AMPA-R phosphorylation (early phase) and eventually gene transcription and protein synthesis (late phase). calcium NMDA

Biogenic Amines - the Monoamines

Catecholamines: • Dopamine • Norepinephrine (Noradrenaline) • Epinephrine (Adrenaline) Serotonin (5-HT) Histamine

Cell X fires an action potential and releases GABA onto Cell Y. Assuming only GABAA receptors are present on the postsynaptic membrane, which is at rest at -55mV, which ion is responsible for the changes that would be observed?

Chloride

When a GABAA ionotropic receptor is stimulated by GABA in a developing neuron, which ions flow through its channel, and what effect does this have on the postsynaptic cell?

Cl-, which depolarizes the postsynaptic cell

Acetylcholine - the nicotinic AChR

Consists of 5 subunits: in muscle = αα:β:γ:δ in neurons = ααα:ββ (beta, gamma, delta) α-subunits bind acetylcholine Each subunit consists of 4 transmembrane spanning α-helices M2 subunit lines pore

Irreversible Acetylcholinesterase inhibitors

Insecticides (so-called organophosphates), and nerve gases (e.g. Sarin, Soman)

Protein kinases - PKC

DAG causes PKC to move from the cytosol to the membrane where it binds Ca2+ and another phospholipid (PS) This relieves autoinhibition, enabling PKC to phosphorylate proteins

Nuclear Signaling - transcription factors

DNA - A chromosome is packaged and organized chromatin, a complex of macromolecules found in cells, consisting of DNA and protein. The information-carrying macromolecule is a single piece of coiled double-stranded DNA, containing many genes, regulatory elements and other noncoding DNA. The DNA-bound macromolecules (i.e. histones) are proteins that package the DNA and control its functions.

Protein kinases - PKA Inactivation

Downregulation of PKA occurs by a feedback mechanism: One of the substrates that are activated by the kinase is a phosphodiesterase (PDE), which converts cAMP to AMP, thus reducing the amount of cAMP that can activate protein kinase A. Thus, PKA is controlled by cAMP. In addition, the catalytic subunit itself can be down-regulated by phosphorylation

Protein kinases - PKA activation

Each PKA is a holoenzyme that consists of two regulatory and two catalytic subunits. When the concentration of cAMP rises, cAMP binds to the binding sites on the 2 regulatory subunits, which leads to the release of the catalytic subunits. The free catalytic subunits can then catalyze the transfer of ATP terminal phosphates to protein substrates at serine, or threonine residues. This phosphorylation usually results in a change in activity of the substrate protein.

Synaptic modulation by (Endo-) cannabinoids

Endocannabinoids act as a retrograde messenger to regulate GABA release

Opioids as analgesics (painkillers)

Enkephalins, endorphins and dynorphins are released in the periaqueductal gray --> source of pain modulating pathways to the spinal cord (dorsal horn) Enkephalins are also released directly in the spinal cord to blunt the effects of nociceptor activation.

How does the Ca2+ signal get to the Soma?

Functional specialization of dendritic compartments 1)Activation of excitatory synapses leads to generation of IP3 . Phospholipase C (PLC), can be activated by muscarinic AChRs, metabotropic GluRs, and is sensitive to Ca2+ influx through NMDA-Rs. 2)IP3 activates IP3 receptors on the endoplasmic reticulum, triggering a regenerative calcium wave. 3)in the proximal apical dendrite, the Ca2+ wave propagates towards the soma. Elevated [IP3 ] might be necessary for long-range propagation

General features of metabotropic receptors

G-protein coupled receptors (GPCRS) Monomeric proteins consisting of 7 transmembrane domains. Domains II, III, VI, and VII make up the neurotansmitter binding region G-proteins bind to both the loop between domains V and VI and the C-terminus

γ-aminobutyric acid (GABA) and glycine - inhibitory transmitters

GABA GAD = glutamate decarboxylase; catalyzes glutamate to GABA VIATT = vesicular inhibitory amino acid transporter GAT = GABA transporter (removal from synaptic cleft

Cys-loop receptors

GABA Glycine nACh (Nicotinic acetylcholine) serotonin (5-HT3)

inhibitory neurotransmitters

GABA and glycine

Basal ganglia diseases - Parkinson's disease

GABAergic neurons in the striatum are the origin of projections that control (disinhibit) the thalamus, which in turn controls areas in the cortex that initiate movement.

Parkinson's disease

Loss of DA (dopamine) inhibition of GABAergic projection neurons. Balance can be restored by increasing DA function with L-dopa, and/or reducing excitatory drive from cholinergic neurons

Intra-cranial self-stimulation (ICSS) (Olds & Milner, 1954)

Medial Forebrain Bundle MFB contains DA, NE, and 5-HT fibers Initially, ICSS was used as a mapping tool for defining the anatomical boundaries of the reward system

Role of norepinephrine (NE) in ADHD

Methylphenidate (Ritalin) is a norepinephrine and dopamine reuptake inhibitor - works blocks dopamine and NA transporters --> Improves "signal-to-noise" in processing of information. Clonidine is an α2 adrenergic agonist (antihypertensive agent, lowers blood pressure; also mild sedative) --> taken in the evening (after Ritalin) to enable transition to sleep. α2-receptors are autoreceptors (presynaptically) --> inhibits NE release alpha2 NE = norepinephrine

Synaptic current APV = Mg2+ block =

NMDA antagonist only AMPA current remains. no NMDA component, even before APV

glutamate release most likely activates

NMDA receptors first due to the voltage dependence of AMPA receptors

Glutamate Receptors - NMDA-R

NMDA-R serves as coincidence detector: voltage-dependent block by Mg2+ ion needs to be relieved by depolarization, --> requires simultaneous activation of AMPA-Rs influx of Ca2+ acts as second messenger at intracellular signaling pathways --> relevant for synaptic plasticity. NMDA-Rs require glycine as co-agonist magnesium calcium

DA as final common pathway in addiction (dopamine)

Nearly all drugs, directly or indirectly, target the brain's reward system by flooding the circuit with dopamine. Drugs of abuse typically release 2 to 10 times the amount of dopamine that natural rewards do Chronic drug use changes monoamine metabolites and uptake transporters. Dopamine D2 receptors are down-regulated to compensate for their drug-induced overstimulation. Thus the brain's capacity to experience pleasure is diminished --> tolerance

Neurotoxins that act on postsynaptic Acetylcholine receptors

Nicotinic and muscarinic AChRs --> classification based on sensitivity for plant alkaloids from tobacco plant (nicotine) and poisonous red mushroom (muscarine)

Nitric oxide (NO) - gaseous (retrograde) messenger

Nitric oxide, is synthesized from arginine and oxygen by various nitric oxide synthase (NOS) enzymes. NO readily passes through membranes NO acts directly within the target cell, without first binding to surface receptors (often considered second messenger) NO is short-lived NO stimulates synthesis of cGMP (via guanyl cyclase) --> second messenger that activates a protein kinase

Molecular targets of signal transduction

Phosphorylation - addition of phosphate group to a molecule, usually a protein. Protein Kinases, enzymes that are the effectors of phosphorylation and catalyze the transfer of a phosphate group from ATP to specific amino acids on proteins. Proteins are phosphorylated predominantly on Serine, Threonine and Tyrosine residues, which account for 86, 12 and 2% respectively of the phosphoproteome --> Serine/Threonine kinases, e.g. PKA, PKC or CaMKII --> Tyrosine Kinases - Protein Phosphatases - enzymes that cleave phosphate from target molecule --> dephosphorylate.

Peptide Neurotransmitters

Pre-propeptides --> rough ER Propeptides --> trans-Golgi network fast axonal transport Proteolytic cleavage, glycosylation, phosphorylation, disulfide bond formation occur after packaging into vesicles Proteolytic processing of prepropeptides (in the vesicle!) can result in several different active peptides (A) and/or the creation of several copies of the same peptide (B) --> different peptides can be released from the same vesicle -->Peptides are also often coreleased with classical neurotransmitters

Acetylcholine metabolism

Precursors = Acetyl coenzyme A and choline Enzyme choline acetyltransferase (ChAT) catalyzes Acetylcholine A vesicular ACh transporter loads ACh into vesicles (~10.000 per vesicle) After release, Acetylcholinesterase breaks up ACh into acetate and choline. Acetylcholinesterase is the target of nerve gases/pesticides A Na+/choline transporter takes choline back up into the presynaptic terminal (sodium)

Serotonin (5-HT)

Regulates Mood and Sleep Implicated in depression, anxiety disorders, schizophrenia. Precursor: Tryptophan = essential amino acid (i.e. can not be synthesized by body, has to be part of diet) --> plentiful in turkey (poultry), chocolate, bananas, milk... Depression, anxiety disorders. Many antidepressants (Prozac; Zoloft) are SSRIs (Selective Serotonin Reuptake Inhibitors) --> block the serotonin transporter (SERT) SERT is target for MDMA (ecstasy) Degraded by MAO Most 5-HT receptors are metabotropic (exception: 5-HT3 receptor) raphe nuclei

Dopamine - Schizophrenia

Schizophrenia is a severely debilitating mental illness with a psychotic disturbance with two groups of symptoms: positive symptoms, such as delusions, hallucinations and bizarre thoughts, and negative symptoms, such as social withdrawal with affective flattening, poor motivation, and apathy. • The potency of typical antipsychotics (haloperidol) depends on their D2 receptor binding affinity. Atypical antipsychotics (clozapine, olanzapine) are only partial DA antagonists (bind also to 5-HT, NE, histamine, ACh receptors) and bind to different kind of DA receptors. • Psychostimulants (e.g. amphetamine) that increase DAergic transmission cause psychotic symptoms.

No potential (but conductance) change (if ECl- = RMP) =

Shunting inhibition Hyperpolarization (if ECl- more negative thanRMP) extracellular chloride more negative than resting membrane potential

Signal Transduction increases from step 1 to last

Signal 'X' X Receptor 1st Messenger Effector Molecule 1 2nd Messenger Effector Molecule 2

Cells alter internal chemistry in response to external signals

Signal transduction: is the process by which extracellular signals are communicated to specific domains within the cell Requires 3 steps: Signal, receptor, and target molecule that mediates the cellular response

mGluRs - metabotropic glutamate receptors

Slow responses; can be excitatory or inhibitory 3 groups based on pharmacology and second messenger linkages: • Group I (mGluRs 1 and 5) - excitatory, Gq -coupled (-->PLC --> ion channels; increase NMDA) - mostly postsynaptic • Group II (mGluRs 2 and 3) - inhibitory, Gi /Go - coupled (-->reduce cAMP), decrease transmitter release; decrease NMDA - mostly presynaptic, and on glia cells • Group III (mGluRs 4, 6, 7, and 8) - inhibitory, Gi /Go - coupled (--> reduce cAMP), decrease transmitter release; decrease NMDA - mostly presynaptic

Parkinson's Disease - movement disorder Loss of Dopamine neurons

Symptoms: • Tremor • Muscle Rigidity • Akinesia (difficulty in initiating movement) • Bradykinesia (slowness in the execution of movement) • Postural instability • ~2% of population will develop PD during their lifetime • Age of onset typically 58-60, very rare in those < 30 years • Treatment - replacement of lost DA (dopamine) with L-DOPA or DA agonists. Efficacy typically decreases over time. • Cause is unknown. Genetic component? Environmental toxicity? Nerve cell damage in the brain causes dopamine levels to drop, leading to the symptoms of Parkinson's

Heterotrimeric G-proteins Termination

The Gα subunit eventually hydrolyzes the attached GTP to GDP through its own enzymatic activity, allowing it to re-associate with Gβγ forming the "resting" G-protein.

Activated PKA Catalytic units phosphorylate substrate proteins

The active subunits catalyze the transfer of phosphate from ATP to specific serine or threonine residues of protein substrates. The further effects can be divided into: A) Direct protein phosphorylation - PKA directly either increases or decreases the activity of a protein (e.g. an ion channel). B) Protein synthesis - PKA phosphorylates specific proteins (CREB) that bind to promoter regions of DNA, causing increased expression of specific genes. In general, this mechanism takes more time (hours to days).

Nuclear Signaling - Transcription factors

The amount of protein present in cells is determined by the rate of transcription of DNA into RNA. Transcription factors allow RNA polymerase to assemble on the DNA promoter region and to begin transcription.

small molecule neurotransmitters

acetylcholine amino acids (glutamate, GABA, glycine) Biogenic amines ((catecholamines = epinephrine, norepinephrine, dopamine), serotonin, histamine)

Opioids - Reward and drug addiction

The μ opioid receptors have a high affinity for enkephalins (Leu-enkephalin and Met-enkephalin) and beta-endorphin, but low affinity for dynorphins. Morphine (heroin, once it is deacetylated) and codeine bind to μ opioid receptors. Effects upon binding are: intense euphoria, decreased pain perception, and anxiolytic effects (relief of anxiety) However, rapid development of tolerance and high addiction potential Main locus of action in the VTA

excitatory neurotransmitters

acetylcholine, glutamate, catecholamines, ATP

While the nature of adenosine's actions on central circuits is not well understood, adenosine is thought to have an inhibitory or relaxing effect because of which of the following observations?

The consequences of xanthine (e.g., caffeine) blockade of adenosine receptors

Proteins called GTPase-activating proteins (GAPs) accelerate the hydrolysis of GTP to GDP. Thus GAPs regulate the activity of G-proteins and terminate the transduced signal.

The effector (e.g. adenylyl cyclase) itself may also possess GAP activity, which helps deactivate the pathway.

G-Protein Coupled Receptors (GPCR)

The human genome encodes roughly 800 G protein-coupled receptors, which detect photons (light), hormones, growth factors, drugs, and other endogenous ligands. G proteins are activated by G protein-coupled receptors, they are inactivated by RGS proteins. --> Receptors stimulate GTP binding. --> RGS proteins (Regulators of G protein signaling, also called GAPs - GTPase-Activating Proteins) stimulate GTP hydrolysis via GTPases. Ras small GTPases. GAP: GTPase-Activating Proteins

Ionotropic receptors

The nicotinic Acetylcholine receptor (nACh)

Which of the following statements about EPSPs in the central nervous system is false? a. They are much larger than end plate potentials. b. EPSPs occurring close together in time can summate and help bring a neuron to threshold. c. Multiple EPSPs arriving together at different locations on the dendritic tree can summate and help bring a neuron to threshold. d. Their effect in the central nervous system can be nullified by IPSPs e. All of the above are false; none is true.

They are much larger than end plate potentials.

The transmitter GABA excites immature cortical neurons because

immature GABA-receptive neurons express many Na+/K+/Cl- co-transporters.

precursor for serotonin

Tryptophan

Effector pathways associated with G-Protein coupled receptors

Two principal signal transduction pathways of G protein-coupled receptors: 1) the adenylyl cyclase - cAMP signal pathway (via Gαs and Gαi ), and 2) the Phospholipase C signal pathway (via Gαq ) galphas and galphai

Precursor for catecholamines

Tyrosine

Catecholamines - Tyrosine hydroxylase

Tyrosine hydroxylase = rate limiting enzyme in synthesis of all catecholamines Can be phosphorylated by at least 9 distinct protein kinases (including PKA, CaMKII, PKC). Upregulated by: • Stress • caffeine • nicotine • morphine Downregulated by: • antidepressants

Second messengers: Adenylate Cyclase and cyclic AMP

Upon binding of the alpha subunit of the G-protein, Adenylate cyclase catalyzes the conversion of ATP to 3',5'- cyclic AMP (cAMP) cAMP acts as a second messenger by interacting with and regulating other proteins such as protein kinase A

Dopamine synapse

VMAT = vesicular monoamine transporter DAT = Dopamine transporter COMT = catechol O-methyltransferase; enzyme that degrades all catecholamines MAO = monoamine oxidase, enzyme that degrades all Monoamines located both intra- and extracellularly --> inhibiting MAO increases availability of DA --> MAO inhibitors = treatment for depression and Parkinson's disease HVA = homovanillic acid

Physiological effects of (Endo-) cannabinoids

Various effects, including • inhibition of adenylate cyclase, • modulation of voltage-dependent calcium, and • potassium channels

The presence of which of the following compounds or proteins in a cell makes it quite likely that the cell is a GABAergic neuron? a. Pyridoxal phosphate b. Glutamic acid decarboxylase c. GABA transaminase d. γ-hydroxybutyrate e. Glutamine

b. Glutamic acid decarboxylase

Which of the following is not a catecholamine? a. Dopamine b. Histamine c. Norepinephrine d. Epinephrine e. All of the above are catecholamines.

b. Histamine

Based upon the distribution of endocannabinoid receptors in the brain, it can be surmised that these compounds have a likely influence on a. neocortex. b. the hippocampus. c. basal ganglia d. the hypothalamus. e. All of the above

b. the hippocampus.

Which of the following is not a class of opioid peptides? a. Dynorphins b. Endorphins c. Enkephalins d. Endocannabinoids e. All of the above are opioid peptides.

d. Endocannabinoids

In terms of size, which of the following are the largest neurotransmitters? a. Biogenic amines b. Amino acid transmitters c. Neuropeptide transmitters d. Purinergic transmitters e. Gaseous transmitters

c. Neuropeptide transmitters

Which of the following is not a feature of glutamate signaling systems? a. The presence of multiple glutamate receptor families with different ionic selectivities b. Voltage-dependent gating of certain types of glutamate receptor c. The passage of large amounts of magnesium and calcium by NMDA receptors d. The use of specialized proteins for loading glutamate into vesicles e. The use of specialized proteins for removing glutamate from the synaptic cleft

c. The passage of large amounts of magnesium and calcium by NMDA receptors

Excitotoxicity

can occur in some forms of epilepsy and head trauma.

precursor for acetylcholine

choline and acetyl CoA

Dopamine - Addiction

cocaine inhibits monoamine reuptake Amphetamine and methamphetamine increase monoamine release

Cocaine acts a. on GABAA receptors. b. as an MAO inhibitor. c. by blocking serotonin reuptake. d. by blocking dopamine reuptake. e. by blocking biogenic amine vesicular transporters.

d. by blocking dopamine reuptake.

The banded krait uses the neurotoxin _______ to paralyze its prey .a. nicotine b. muscarine c. conotoxin d. α-bungarotoxin e. δ-tubocurarine

d. α-bungarotoxin

Sensitization

describes the opposite response to repeated drug administration

In the CNS, catecholamines act as neuromodulators, influencing the effects of other, classical neurotransmitters

do not evoke EPSP or IPSP by themselves, rather make EPSP / IPSP larger or smaller alter ion channels to modulate cell's excitability, so that when synaptic inputs arrive the neuron is either more ready to fire action potentials or hyperpolarized / less excitable Specific effects depend on: Receptor subtypes involved Intracellular signaling pathways activated Brain area / circuitry involved Type of postsynaptic cell (e.g. pyramidal cell vs. interneuron)

Biogenic amines

dopamine, norepinephrine, epinephrine, serotonin, histamine

Acetylcholine is used as a neurotransmitter at a. the neuromuscular junction. b. preganglionic synapses of the autonomic (visceral motor) nervous system. c. postganglionic synapses of the sympathetic nervous system. d. widely distributed synapses in the central nervous system. e. All of the above

e. All of the above

Glutamate is a. the most commonly used neurotransmitter in the brain. b. neurotoxic at high concentrations. c. a nonessential amino acid. d. often synthesized from glial-synthesized glutamine. e. All of the above

e. All of the above

inhibits inhibition

endocannabinoids

rate limiting step for endocannabinoids

enzymatic modification of lipids

precursor for glutamate and GABA

glutamate

rate limiting step for glutamate

glutaminase

rate limiting step for histine

histidine decarboxylase

Reward and Addiction

• Addictive drugs induce pleasurable states (positive reinforcement), or relief from distress (negative reinforcement), thus motivating repeated drug use. • The defining feature of addiction is compulsive, out-of-control drug use, despite negative consequences. • Drugs of abuse are both rewarding and reinforcing. Rewards are stimuli that are perceived as intrinsically positive, and reinforcing stimuli are those that increase the probability that behaviors will be repeated. • Addictive drugs target the brain reward circuit, which includes the dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens and other forebrain structures. This circuit normally controls the response to natural reinforcers such as food, water, and sex, • Repeated use of addictive drugs produces multiple unwanted changes in the brain that may lead to tolerance, sensitization, dependence, and addiction.

(Ionotropic GABA receptors (GABAA and GABAC)) Both benzodiazepines and barbiturates (or alcohol) facilitate the ability of GABA to activate the receptor and opening of the chloride channel, (different binding sites and mechanisms)

• Barbiturates increase the length of channel openings • Benzodiazepines increase the frequency of channel openings.

Ca2+/calmodulin dependent protein kinase type II (CaMKII)

• Calcium binds to calmodulin • Ca2+/calmodulin activates CaMKII by displacing the inhibitory domain from the catalytic subunit

Dephosphorylation - Protein phosphatases

• Can be grouped into three main classes based on sequence, structure and catalytic function. The largest class of PPs is the phosphoprotein phosphatase family, which -among others- contains PP-1, PP-2A, and PP-2B (calcineurin)

Myasthenia Gravis - It occurs when communication between nerve cells and muscles becomes impaired.

• Chronic condition that causes muscle fatigue (incidence rate 1:200.000) • Typically begins as "ocular myasthenia" • Can become generalized and potentially life-threatening (problems chewing, swallowing, breathing) • Characterized by a decrease in EPP (end plate potential) • Treated with reversible acetylcholine-esterase inhibitors (e.g. neostigmine) In MG, that attack interrupts the connection between nerve and muscle — the neuromuscular junction. Myasthenia gravis is characterized by autoantibodies against the acetylcholine receptor (AChR-Ab) Autoantibodies are antibodies (immune proteins) that mistakenly target and react with a person's own tissues or organs

Cocaine and amphetamines inhibit the re-uptake of dopamine

• Cocaine blocks the dopamine transporter (DAT), i.e. blocks dopamine re-uptake. This increases the lifetime of dopamine in the synaptic cleft. • Amphetamines increase dopamine release and block re-uptake. ---> Amphetamines enter the presynaptic terminal (via DAT, or through direct diffusion) and release dopamine from the vesicles by making the dopamine transporters work in reverse.

3 groups of endogenous opioid receptor ligands

• Endorphins (endogenous morphine) • Enkephalins • Dynorphins

Heterotrimeric ("large") G-proteins

• G-protein binds to the receptor • G protein is composed of 3 subunits (α, β, γ) • the alpha subunit binds either to guanosine triphosphate (GTP) or guanosine diphosphate (GDP) • G proteins function as molecular switches. They are "on" when they bind GTP, they are "off" when they bind GDP. alpha, beta, gamma

Phospholipase C (PLC) and IP3 -DAG signaling

• G-protein coupled receptors (Gαq ) activate PLC. • PLC cleaves PIP2 into inositol - 1,4,5-triphosphate (IP3 , soluble) and diacylglycerol (DAG, membrane bound). IP3 stimulates the release of calcium ions from the endoplasmic reticulum whereas DAG is an activator of protein kinase C (PKC). galphaq

Phospholipase C (PLC) and IP3 -DAG signaling = PKC activation

• G-protein coupled receptors (Gαq ) activate PLC. • PLC cleaves PIP2 into inositol -1,4,5-triphosphate (IP3 , soluble) and diacylglycerol (DAG, membrane bound). • IP3 stimulates the release of calcium ions from the endoplasmic reticulum, whereas DAG is an activator of protein kinase C (PKC).

There are several classes of Gα subunits: alpha

• Gsα (stimulatory), • Giα (inhibitory), • Gqα Gsalpha Gialpha Gqalpha

The effects of GABA agonists (e.g. benzodiazepines [Valium] and barbiturates) are

• anxiolytic (anxiety-reducing) • anesthetic • sedative-hypnotic • anti-convulsive

5 groups of Neuropeptides

• brain / gut peptides • Opioid peptides • Pituitary peptides • Hypothalamic releasing hormones • "other peptides"

Irreversible Acetylcholinesterase inhibitor characteristics

• Irreversible Acetylcholinesterase inhibitors completely inhibit ACh breakdown • The lethal effect results from "overstimulation" (persistent depolarization) of the postsynaptic membrane, particularly muscle cells. • The main effect is neuromuscular paralysis (leading to respiratory failure within 5 min), preceded by cognitive and severe autonomic symptoms. • Treatment involves combined administration of a muscarinic receptor antagonist (e.g. atropine) and the AChE antagonist pralidoxime, which paradoxically restores AChE function (--> Pralidoxime attaches to the site where the cholinesterase inhibitor has attached, then attaches to the inhibitor, removing the organophosphate from cholinesterase, allowing it to work normally again)

Mitogen-activated protein kinase (MAPK)

• MAPK - specifically the extracellular signal-regulated kinase (ERK) subfamily - phosphorylate transcription factors, proteins that regulate gene expression (e.g. CREB) • MAPK are kinases that themselves are activated by other kinases

Calmodulin, or CaM

• Many of the proteins that CaM binds are unable to bind calcium themselves, and they use CaM as a calcium sensor and signal transducer. • CaM can also make use of the calcium stores in the endoplasmic reticulum. • CaM undergoes a conformational change upon binding to calcium, which enables it to bind to specific proteins for a specific response. • CaM can bind up to four calcium ions, and can undergo post-translational modifications, such as phosphorylation, acetylation, methylation and proteolytic cleavage, each of which has potential to modulate its actions.

Ionotropic Receptors

• Membrane spanning region forms ion channel. • Comprised of 4-5 protein subunits. • Mediate rapid postsynaptic effects (millisecond time scale) • Glutamate receptors (NMDA, nonNMDA) • nicotinic acetylcholine receptor (nAChR • 5-HT3 receptor • GABA receptor • Glycine receptor • Purinergic receptors

Receptors are specific to a given signal Receptors act through different mechanisms

• Most neurotransmitters (includes ionotropic & metabotropic receptors • Cholesterol derived hormones • Cell-cell adhesion molecules (requires direct contact)

Signal Amplification and temporal control

• Most signal transduction pathways serve not only to communicate signals to specific intracellular domains but to amplify them as well. • In addition, different signaling pathways allow for control of cellular responses on various time scales

Targets of DA receptor signaling cascades ( dopamine )

• Protein kinases (PKA, PKC) • Protein phosphatases (Calcineurin) • Ion channels (K+, Na+, Ca2+) • Ionotropic receptors (AMPA, NMDA, GABAA) • Transcription factors (CREB) • Other targets (TH, DAT)

Extracellular signaling molecules

• Small soluble organic molecules e.g. Neurotransmitters, amino acids, sugars, nucleotides • Inorganic ions (e.g. Zn2+) • Diffusable gases (e.g. CO & NO) • Peptides • Lipophilic organic molecules (e.g. endocannabinoids) • Cell-surface expressed proteins

block nicotinic AChRs (Nicotinic acetylcholine receptors) (antagonists)

• Snake poisons, α-bungarotoxin or cobra α-neurotoxin • Curare (plant toxin) • Conotoxins from fish hunting marine cone snails (other conotoxins block glutamate receptors, or voltage-gated Na+ and Ca2+ channels) alpha-bungarotoxin alpha-neurotoxin sodium channels calcium channels

induce increases in catecholamine synthesis

• Stress • caffeine • nicotine • morphine

Calcium stores

• The endoplasmic reticulum (ER) and the mitochondria have higher Ca2+ levels compared with the cytoplasm. • The ER has two pharmacologically different Ca2+ stores, both of which are opened by physiological cellular events: one by the activation of IP3 metabolism (PLC), and the other one by elevation of cytosolic Ca2+ itself (Ryanodine-store) (e.g. caffeine modulates Ca2+ stores in heart and brain) • Mitochondria act as a slow Ca2+ buffer.

Transcription factors either stimulate or inhibit RNA polymerase activity

• Transcriptional Activators enhance gene expression. • Transcriptional Repressors decrease gene expression.

Calcium as a Messenger

• Under baseline conditions, the cytosol is largely kept devoid of Ca2+ (10-9 M); --> outside: 10-3 M Ca2+ is either pumped out of the cell, sequestered in internal stores in the ER lumen and mitochondrial matrix, or bound by calcium-binding proteins. Opening of voltage-gated Ca2+ channels or Ca2+ permeable ionotropic receptors allows influx of extracellular Ca2+. IP3 receptors and ryanodine receptors in the ER membrane allow flow of Ca2+ from internal stores into the cytosol. ER = Endoplasmic reticulum membrane