Psych 439 final; reward systems

background on reward

• all animals have reward circuitries to guide behavior

• reward seeking behavior is beneficial and helps focus our behavior

• early in life behavior is driven by immediate rewards (food)

• as we maure more value placed on long term rewards (grades)

• hhowever reward seeking can be maladaptive and lead to risky or poor decision making (excessive gambling, drug taking etc)

medolimbic dopamine circuitry

dopaminergic projection fo from VTA to NAc where dopamine is released (DA)

What are drugs of abuse

drugs have their effects by tapping into brains naturally existing reward circuitry

endogenous ligands

NT or hormones inside body that bind to receptors

eg. dopamine ACH, Estrogen, cortisol

exogenous ligands

drugs or toxins from outside the body that bind to receptors

ex. heroin, nicotine, thc

agonists

molecules that mimic action of a transmitter at a receptor

antagonists

molecules that interfere with or block the actions of transmitter at a receptor

drugs may alterthe presynaptic neuron through effects on…

transmitter production, transmitter release, transmitter clearance

How can drugs alter the presynaptic neuron through effects on transmitter production?

drugs may block synthesis enzymes, axonal transport of raw materials or the ability to store the transmitter

How can drugs alter the presynaptic neuron through effects on transmitter release?

drugs can block APs by blocking ion channels

• autoreceptors that monitor the amount of release and give feedback can also be affected by drugs

How can drugs alter the presynaptic neuron through effects on transmitter clearance?

drugs called reptake inibitors can block reuptake of transmitter, while others allow transmitter to accumulate by blocking enzymes

how can drugs alter postsynaptic systems that respons to released transmitter?

can affect transmitter receptors, and can alter intracellular post synaptic processes

How can drugs alter the post synaptic neuron through effects on transmitter receptors ?

• selective receptor antagonists block postsynaptic receptors from being activated by their NT

• selective receptor agonists bind to recetors and activate them

How can drugs alter the post synaptic neuron through effects on intracellular postsynapptic processes ?

• upregulating or downregulating receptor densities

• activation of second messenger systems

• activation of genes

not everyone who uses drugs becomes addicted, what factors increase/decrease likelihood of addiction?

• biological factors (sex)

• social factors (support, role models)

• environment (availability, normalization)

Whats the problem with drug use?

• repeated exposure changes reward circuitry

• more and more drug needed

• formarly pleasurable acivaties become less so

• continues to seek out drugs despite severe consequences

how does long term drug taking affect behavior and neural circuitry

• chronic use erodes selfcontrol

• strong impulses, highly motivated to obtain drug

• changes in beahviro are driven/accompanied by changes in brain strcutrue that can be long term or permanent

drug impacts at diff stages of dev

• babies; underweight, premature, intellectual dev and behavior affected

• adolescents; academic impacts, risky behavior, puberty is considered second period of orgaization (can render long term changes)

• early drug exposure may increase liklihood of later addicion