Option E:

Neurobiology & Behavior

E4: Neurotransmitters &

synapses

• Presynaptic neurons release NT into the

synaptic cleft to create graded potentials in

postsynaptic neurons

• Some presynaptic neurons generate

excitatory postsynaptic potentials (EPSPs)

• Others generate inhibitory postsynaptic

potentials (IPSPs)

• If the combination of signals reaches a

threshold level, an action potential will be

generated in the postsynaptic neuron

E.4.1

E.4.1 – Review Resources on WikiSpace

E.4.1

Neurotransmitters

• 2 Major Players:

• Released by only a few neurons but connect to 1000s all over the brain!

• Serotonin

– Affected by many drugs (cocaine, amphetamines, LSD, alcohol)

– Many brain processes regulated • Body temp, sleep, mood, appetite, pain

• Problems OCD, anxiety disorders, depression

• Most anti-depressants increase S levels!

• Dopamine

– “Reward Pathway”

– Motor control, memory, motivation, emotional response, reward/desire, addiction, hormonal regulation, maternal behavior, sensory processes

– Can cause hallucinations and schizophrenia if not working properly; can cause Parkinson’s disease if neurons die in one of 3 major pathways

Glutamate and GABA (Gamma-Aminobutyric Acid)

• Brain’s major “workhorse” NTs

• >50% all brain synapses release glutamate, >30% release GABA

• GABA is inhibitory

– Stops action potentials

• Glutamate is excitatory

– Starts or propagates action potentials

• Work together: brain’s overall level of excitation

• Many drugs affect one/both of these

– Tranquilize or stimulate the brain

Alcohol

Decreases

Glu

activity

Caffeine

inhibits

GABA

release

PCP

increases

activity

Caffeine

increases

activity

Alcohol

increases

activity

Tranquilizers

increase

activity

Genetic Science Learning Center (2011, January 24) Beyond the Reward Pathway. Learn.Genetics. Retrieved January 30, 2011, from http://learn.genetics.utah.edu/content/addiction/reward/pathways.html

E.4.2 CNS decision making result of interaction btw

EPSN and IPSN at synapses

• Decision making in the CNS involves the

integration of multiple nerve impulses at

various synaptic junctions

• Some presynaptic neurons are excitatory

(cause depolarisation) while others are

inhibitory (cause hyperpolarisation)

• Excitatory and inhibitory presynaptic

neurons function by releasing different

neurotransmitters

E.4.2 CNS decision making result of interaction btw

EPSN and IPSN at synapses

• The net effect of these signals are

generally summative (either spatial or

temporal)

• Summation can lead to the selection of

alternative neuronal pathways in the

frontal cortex of the brain involved in

decision making processes

E.4.2

E.4.2

E.4.3 Explain how psychoactive drugs may either increase postsynaptic

transmission (stimulants) or decrease postsynaptic transmissions

(depressants).

• Whereas stimulants produce psychomotor

arousal and increased alertness,

depressants slow down brain activity and

relax muscles

• Both act primarily on the CNS and can

cause a chemical dependency, leading to

substance abuse

• Addictions affect the brain and personality

by either increasing or decreasing

postsynaptic transmissions

Drugs ARE Addictive

• Not just Heroin, Cocaine, Crack and Meth!!

• Alcohol, Nicotine, “Weed,” “X”, Pain Pills, Ritalin, any Rx...

• This is serious business.

• Drugs are toxic substances.

• Long-term drug use is bad for your health.

• But even a single-use can KILL YOU.

E.4.3 Explain how psychoactive drugs may either increase postsynaptic

transmission (stimulants) or decrease postsynaptic transmissions

(depressants).

Mechanism of Action of Various

Psychoactive Drugs

http://outreach.mcb.harvard.edu/animations/synapse.swf

http://www.jellinek.nl/brain/index.html

Good intro (slide 16) & Details

Alcohol

• How it works (GABA, synapse) http://www.thirteen.org/closetohome/animation/gaba-anim-main.html

• Dopamine, serotonin, endorphin, GABA and Glutamate

• Stimulates GABA, which inhibits APs, makes you calm

Alcohol Binds to GABA receptor @ allosteric site

GABA binds too, stays bound longer than normal & more frequently

• Inhibits Glutamate, which reduces the excitatory effect of Glu on other neurons

Alcohol binds to Glu receptor, changes shape, Glu can’t bind, no signals conveyed to post-synaptic neuron, no action potential propagates

• Stimulates Dopamine (reward center: happy, euphoric) can lead to addiction; brain adapts, less sensitive to dopamine, produce less, depression

• Stimulates Serotonin also (happy, euphoric)

• Slows down info txfr: learning, memory

THC

• Tetrahydrocannabinol

• Disrupts Anandamide (NT) action

– Normally, impulse, NT released to cleft,

transmit AP to post-syn neur, reuptake into

pre-synaptic neuron

– THC mimics anandamide, binds to receptors

and sends the message, then unbinds, broken

down (reward center; GABA and dopamine)

• * http://www.jellinek.nl/brain/index.html animation

slide 9

• THC stops GABA release, which normally slows the

release of dopamine

• More dopamine released

Cocaine

• Heart attacks common

• Overheating

• Brain damage

• EVEN AFTER A LOW DOSE, you’re 24x more likely than normal to have a heart attack.

• How it works: dopamine/synapse

• http://www.thirteen.org/closetohome/animation/coca-anim2-main.html

• http://www.jellinek.nl/brain/index.html

– Normally, dopamine released to cleft, transmit AP, unbinds, uptake by presyn neur

– Cocaine binds to reuptake ptns, block access, dopamine bounces around in cleft, sending signal repeatedly

– Cocaine also induces NT release into cleft, more dopamine in cleft, more signals transmitted

– Reward center

– Receptors gradually destroyed, need more and more until totally numb to it

Nicotine

• Low doses, only binds to receptors in

brain

• High enough doses (smoking, and patch,

and gum...) binds to brain AND muscle

receptors

– Paralyze muscles that control breathing

– Cause a heart attack

• Smoking...VERY ADDICTIVE! WHY?!

– fast delivery

– tobacco smoke is taken into the lungs,

nicotine seeps into lung blood where it

can quickly travel to the brain.

– Affects brain regions that facilitate

addiction

Synergistic Effects are Especially Dangerous

• Example: Heroin and alcohol

– Both suppress breathing, in different ways

– Normal: Excit. Glut + Inhib GABA in balance;

regular breathing

– Alcohol decreases Excit Glut effects

• Can lead to unconsciousness

• If body’s ridding itself of the toxin (puking) while

you’re unconscious...you can die by aspiration

– Heroin increases Inhib GABA effects

– Suppresses the impulse to breathe

Stimulants

• Amphetamines, Ecstasy/MDMA, Methampetamines

• Increase dopamine & norepinephrine (adrenaline-like hormone) levels

– Increased motor activity, heart rate, blood pressure, narrowing of blood vessels

– Heart attack: increased motor activity increased O2 demand of heart; reduced blood supply b/c narrowed vessels

– Brain damage: increased BP, increased risk of ruptured b vessel in brain; narrowed vessels reduce blood flow around brain

– Overheating: dopamine regulates body temp; altering levels body can’t cool itself. Can increase @ dangerous levels, organ failure, death

• kills brain cells or YOU...if you’re “partying” in a hot place...pretty likely you’ll overheat

Is Addiction Genetic?

• Your proteins (receptors) are encoded by your genes

• Differences in alleles

• Ptns can bind differently

– Differences in likelihoods of becoming addicted

• More to it, but it’s one piece of the puzzle

• Inside the Teenage Brain (video)

• http://www.pbs.org/wgbh/pages/frontline/shows/teenbrain/

Mental Illness + Addiction

• Do drugs cause mental illness?

• Do they make the symptoms worse?

• http://learn.genetics.utah.edu/content/addi

ction/issues/mentalillness.html

http://learn.genetics.utah.edu/content/addiction/drugs/mouse.html

http://learn.genetics.utah.edu/content/addiction/reward/