Exam 2

What are the major inhibitory amino acids

GABA and Glycine

What is GABA made from? Via what?

Glutamate via glutamic acid decarboxylase (GAD)

GABA is transported into vesicles via _____

Vesicular GABA transporters (VGAT)

GABA is removed from the synaptic cleft by...... (3 types of transporters)

GAT-1, GAT-2, GAT-3

Removal on neurons:

GABA is either reloaded into vesicles or metabolized to glutamate and succinate by GABA aminotransferase (GABA-T)

Removal on astrocytes:

Glutamate is converted to glutamine by glutamine synthetase --> glutamine can be released by astrocytes ---> taken up by neuron & converted back to glutamate --> remade into GABA

To raise GABA at synapse:

- Block GABA-T (gaba stays & does not get picked up)

- Block GAT1, 2, or 3

What happens to GABA release if you block GAD

decreased production of GABA --> less available in synapse

What about blocking the vesicular transporter (GABA)

GABA is not present to be released (decreased GABA release)

Why won't precursors to GABA work?

Glutamate: excitatory

Glutamine: too standard of a precursor (used for others)

GABA A channels:

-Move ____ into cell

- ________ and ______ occurs at the postsynaptic cell

- __#_ subunits - Various combos of ___ subunits:

1. Cl-

2. Hyperpolarization

3. four: α, β, γ, δ

Both Benzos and barbiturates are......

both have different what kind of binding sites

PAMS & allosteric (binds outside active site)

BZD increases _______ of opening (only if ___ subunit is present)

BZD _____ a subset of GABAa receptors

frequency, γ, potentiate

barbiturates increase ______ of opening

duration

Both BZD & barbiturates have broadly ____ effects but _______ are much stronger.

depressive, barbiturates

NAMS at BZD promote.......

anxiety, arousal, & seizures

Vigabon

- treatment for epilepsy

- responsible for converting GABA transported into neurons into glutamate

-prevents GABA metabolism = increased presynaptic GABA levels

- can affect vision ---> impacts GABAergic interneurons in the retina.

Carbamazepine

- treatment for epilepsy

-Stabilizes inactive state of sodium channels

- reduced neuronal firing

-potentiates SOME GABAa receptors

Lamotrigine

- treatment for epilepsy

-a sodium channel blocker

Ketogenic Diet and Epilepsy: potential mechanisms

- net increase of GABA levels --> suppresses neuronal firing

- inactivation of VGLUT --> less loading GABA in vesicles = lower GLU levels

-altered levels of other NTs (NE, adenosine or 5-HT)

-antioxidant effect

Glutamate Cycle

-EAAT1 & 2 located on astrocytes

-EAAT3 located on presynaptic terminal of neuron

Astrocyte: GLU --> glutamine synthase --> glutamine -> goes through glutamine transporters --> neuron terminal

Neuron terminal Glutamine --> Glutaminase --> Glutamate

VGLUTs load glutamate through vesicles: GLU--> EAAT3 --> VGLUT --> Glutamate in vesicle

VGLUT1 knockout mice

survive birth but begin to die during the third week of life

VGLUT2 knockout mice

die immediately after birth

VGLUT3 knockout mice

are viable but completely deaf; the inner hair cells of the cochlea use glutamate as the neurotransmitter

VGLUT blockers

should reduce levels of GLU released --> used to treat excitotoxicity

NMDA & Long term potentiation

-NMDA receptor is located at post synaptic terminal & responds to GLU

-NMDA has a Mg2+ ion block

- Presynaptic AMPA receptors are activated --> allows influx of Na+

- At sufficient depolarization Mg2+ block is lifted from NMDA Channels

- subsequent stimuli allows for Na+ and Ca2+ influx through NMDA

-Ca2+ is linked to induction of long-term enhancement of signaling at the spine (LTP)

AMPA-kines

drugs that enhance action of AMPA receptors

- maybe by reducing rate of desensitization

- maybe by acting as a PAM

- works in animal models & mixed results in humans

increased neurotransmission --> facilitate LTP --> increase cognitive function (thought to be used in neurodegenerative diseases)

Zinc and NMDA-sensitive glutamate-gated channels (two mechanisms)

Zinc directly inhibits

1) High-affinity binding to N-terminaldomains of Glu NR2A subunits reduceschannel open probability

2) Low-affinity voltage-dependent binding topore-lining residues blocks the channel

Doogie Mouse

NMDA receptor geneticaly altered to stay open longer, allowing more calcium influx, more robust LTP, and enhanced memory

NR2B subunit of NMDA receptor --> over expressed -> greater ratio of NR2B subunits = longer NMDA receptor opening

note: more sensitive to certain forms of pain

Necrosis

Uptake: cell contents are ingested by macrophages with significant inflammation

Membrane: Loss of membrane integrity with cell lysis occurring

Organelles: organelle swelling + lysosomal leaking & random degradation of DNA

Apoptosis

Size: cellular shrinkage with one cell being affected

Uptake: cell contents ingested by neighboring cells with no inflammatory response

Membrane: membrane blebbing & Apoptotic bodies forming

Organelles: mitochondria release prop-apoptotic proteins with the presence of chromatin condensation and non-random DNA degradation.

How can ischemia cause an increase in glutamate release:

Ischemia = temporary stoppage of blood flow/oxygenation to tissue

- lack of O2 --> interferes with ATP production

- when ATP dependent ion pumps fail --> cell is depolarized

-voltage gated Ca channels open = intercellular Ca2+ levels rise

- stimulates glutamate release --> AVALANCHE

- glutamate activates AMPA & NMDA receptors --> Ca2+ influx in downstream neurons

-excitotoxicity

- second wave: cells that die of necrosis release glutamate into interstitial space, also exciting neighboring cells. --> advantage of having microphages/microglia absorb dying cells

Once blood flow returns --> reperfusion injury --> increased permeability of blood vessels = inflammatory response.

Caffeine as an antagonist

blocks activity

what type of receptors are Adenosine A1

G i/o coupled

what type of receptors are Adenosine A2a

Gs coupled

what type of receptors are Adenosine A2b

G s/q coupled

what type of receptors are Adenosine A3

G i/q coupled

Caffeine at higher doses

-Inhibition of phosphodiesterase: increase cAMP =paralysis in insects

- Blocking of GABAa receptors

- Stimulation of Ca2+ release

- enters toxic range

Malignant hyperthermia

inherited disorder that causes a severe reaction to certain anesthetics

Treatment for malignant hyperthermia

Dantrolene

What genetic mutation is associated with malignant hyperthermia?

Mutation affecting the RYR1 protein in skeletal muscle

What are the two sites on the RYR1 protein responsible for controlling calcium concentration?

A-site and I-site

What is the function of the A-site on the RYR1 protein?

Mediates RYR1 opening with high affinity for calcium

What is the function of the I-site on the RYR1 protein?

Mediates RYR1 closing with low affinity for calcium

What role does magnesium play in the function of the RYR1 protein?

Causes RYR1 protein to close by acting on the I-site

MH: triggering agents

Caffeine, halothane, etc.

- acts by drastically increasing the affinity of the A-site for Ca while simultaneously decreasing the affinity of the I-site in mutant MH proteins.

- Also includes a greatly decreased affinity for Mg.

End result of triggering agents (MH)

increased Ca release due to lowered activation and heightened deactivation threshold.

Most & Least Potent hallucinogens

Most: LSD

Least: Mescaline

How are most hallucinogens administered

they are ingested

Duration of Hallucinogen Effects

begins at 30-90 mins --> LSD trip can last for 6-12 hours

- smoked DMT & Sativa: felt in secs --> peaks in minutes --> gone in an hour

2C-x

Family of psychedelic phenethylamines originally synthesized byAlexander Shulgin

• Early pesticide work with Dow Chemical

• Systematically tested compounds on himself

PCP and ketamine binding site/receptors

noncompetitive antagonists at NMDA receptors

inside the receptors ion channel, separate from the site at which glutamate or NMDA binds

Chronic Use of PCP or Ketamine: negative effects

- Urological signs: bladder pain and incontinence

-deficits in memory/ other cognitive functions

- Grey and White matter abnormalities (chronic ketamine)

-Repeated administration of high doses of ketamine = apoptotic cell death in developing brains of rats and monkeys

This is concern because Ketamine is a common anesthetic agent for pediatric procedures

How can you increase catecholamine synthesis?

administering a precursor

example: LDOPA & treating parkinson's disease

Pathway to dopamine and NE

tyrosine --> TH --> DOPA --> AADC --> DA--> DBH --> NE

Alpha-methyl-para-tyrosine (AMPT)

Blocks TH --> prevention of catecholamine synthesis

After catecholamine synthesis.........

- catecholamines are packaged into vesicles

OR

- is broken down --> decreased levels = sedation and depression

What drug blocks VMAT 2 & 2

reserpine

What type of receptor subtypes are present in DA-ergic system? How many?

- metabotropic

- 5

D1 & D5 (G...... coupled)

Gs coupled

also know as "D1 like"

D2, D3, D4 receptors

separate family --> Gi/o coupled

Also know as "D2 like"

dopaminergic system: D1 & D2 signalling

alpha1 receptors (four main areas)

1. Blood vessels: vasoconstriction, increased BP, increased contractibility of the heart

2. eye: Mydriasis (dilation)

3. bladder: relaxation

4. prostate: contraction

alpha2 receptors (two main areas)

1. blood vessels: decreased blood pressure

2. smooth muscles (GI tract): decreased GI tone and motility

beta1 receptors (2 main areas)

1. heart: increased heart contraction and increased heart rate

2. kidney: increased renin secretion, increased angiotensin, and increased blood pressure

beta2 receptors (4 main areas)

1. smooth muscle (GI tract): decreased GI tone and motility

2. Lungs: bronchodilation

3. uterus: relaxation of uterine smooth muscle

4. Liver: activation of glycogenolysis, and increased blood sugar

Alpha1 Adrenergic Blockers

opposite functions of sympathetic nervous system --> decreased smooth muscle contraction and blood vessel dilatation

treats hypertension and benign prostatic hyperplasia

Beta1

main subtype of the heart

propranolol: what does it block? What does it do?

blocks β-receptors in the heart, reducing contractile force

makes anxiety FEEL less overwhelming

How do you make serotonin

Tryptophan —> TH —> 5-HTP —> AADC —> 5HT—> serotonin

What will given Tryptophan do?

increase production of 5HT

Serotonin Cycle:

5-HT released by vesicles —> 5HT transporter (SERT) takes it back into serotonergic neuron —> Transported into vesicles by VMAT2—> Metabolized by MAO to 5-HIAA

What is the target for SSRIs

SERT

What does reserpine do as a VMAT2 blocker

Depletes 5-HT —> is then broken down when not protected in vesicles

Which MAO is located in neurons vs gilal cells?

MAO-A is located in neurons, MAO-B is located in gilal cells.

Serotonin receptors and appetite (reduced food intake)

5-HT1B or 5-HT2C receptor agonists, and 5-HT6 antagonists produce
hypophagia (reduced food intake)

Serotonin receptors and appetite (increased food intake)

5-HT1A agonists can lead to hyperphagia (increased food intake).

Where are 5-HT3 receptors located?

On the peripheral terminals of the vagus nerve

Chemo and 5-HT3 receptors

induces vomiting

antagonists can be used to treat the nausea

Pathological Aggression

Prevalent in men —> comorbidity with a lot of things such as substance abuse, depression, and anxiety disorders.

Pathological aggression: threat perception and risk assessments

alteration can affect aggression —> reactive aggression associated with poor recognition of facial cues

Pathological aggression: circuit

amygdala —> orbito frontal and orbital prefrontal cortex (OPF cortex)

Lesion of the OPF cortex……

massive agression

Arsenic toxicity: target organs

Blood, Kidneys, CNS, digestive, and keratinized tissues

Arsenic has a high affinity for a…..

sulfhydryl chemical group (thiol)

Amino acids that contain sulfur:

cysteine and methionine

Where are skin affects of arsenic seen at

hands and feet

Arsenic poisoning: impedes….. and may also alter……

DNA repair system & DNA methylation (alters gene expression)

Brain barrier to prevent metal insults from blood beyond the BBB

choroid plexus (CP)

True or false: Cadmium can cross BBB

true

cd concentration in blood is about —— times higher than found in the brain cortex

2.5x

the CP contains abundant WHAT binding ligands

metal

BBB and CP structures in young Individuals…. does it make it easier or harder for Cd to reach the brain

NOT FULLY DEVELOPED & EASIER —> DEVELOPMENTAL TOXIN

Itai Itai disease

• Chronic Cd poisoning that happened in japan

• 1912-1942

• ‘it hurts it hurts’ disease

• Cd orginated from downstream of major mining site

• Link to Cd was not id’ed until 1968

• softening of the bone as Cd substitutes Ca

Dimercaprol: what is it?

• BAL

• drug of choice fr treatment of gold, lead, arsenic, copper, and mercury toxicity

• used as an antidote to the chemical weapon Lewisite

How is Dimercaprol administered

Deep IM injection

Dimercaprol: What does it do?

- Extracellular and intracellular cation scavenged

• Enhances fecal and urinary elimination

• Diffuses into brain and RBC's

• IS TOXIC ITSELF WITH A NARROW THERAPEUTIC RANGE

What else is Dimercaprol useful for?

Apparently also useful for some snake-bites
• Zinc-dependent metalloproteinases in viper venom
• Chelates the zinc

EDTA

• second line of treatment for lead toxicity

• more effective when given early in acute poisoning

• CHELATES ONLY EXTRACELLULAR LEAD

• may also induce CNS toxicity if BAL therapy not initiated first

EDTA —> when does therapy start? How is it administered?

• 4 hrs after BAL is given

• Only given via IV by continuous infusion