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/