exam 2 Flashcards
striatum
major target of dopamine (DA) axon terminals
major components of brainstem
midbrain, pons, medulla oblongota
striatum components and their functional roles
- nucleus accumbens- pleasure, motivation, reward cues,
- caudate- dorsomedial; goal-directed actions; flexible; rapidly acquired behaviors
- putamen - dorsolateral; habits, inflexible, automatic behaviors
nigrostriatal pathway
substantia nigra –> dorsal striatum
movement and stereotypies
mesolimbic pathway
VTA –> ventral striatum (nucleus accumbens) and amygdala
mesocortical pathway
VTA –> prefrontal cortex
What is the function of the basal ganglia?
Input and output structures
Output targets
voluntary movement, action selection, procedural learning, and habits
Input structure: cortex (glutamatergic - excitatory)
output structures: SNr, GPi (GABAergic- inhibitory)
Targets of output: Thalamus, superior colliculus, PPN
input and output structures of basal ganglia
input structures: cortex; glutamatergic (excitatory)
output structures: GPi, SNr; GABAergic (inhibitory)
indirect ptathway
how is dopamine involved (and not involved) in different components of reward learning?
not involved: liking
involved in: wanting and reward prediction
what is “reward prediction error” and how is dopamine involved?
learning about cues/actions related to reward
positive- increased activity with unexpected reward (activates D1 and DIRECT pathway)
zero- unchanged baseline for expected rewards
negative- decreased activity with unexpected reduction of reward (activates D2 and INDIRECT pathway)
decrease in dopamine firing when an expected reward is omitted
factors that influence addiction vulnerability
- properties of drug
- individual differences (genetic and env.)
- drug-induced neuroadaptations
individual differences that increase/protect addiction vulnerability
increase:
1. high impulsivity (reduced D2 receptors in striatum)
2. history of trauma/ stress (enhanced habit learning & reduced behavioral inhibition)
protect
1. environmental enrichment
(showed reduced place-preference)
what are the effects of chronic stress?
- enhanced habit learning (DLS)- DLS more dominant than DMS
- reduced behavioral inhibition (loss of PFC)
what behaviors are associated with prefrontal cortex?
self-control; behavioral inhibition; executive function
drug-induced neuroadaptations that increase addiction likelihood
- enhanced drug motivation (sensitization)
- enhanced habit learning (DLS)
- reduced behavioral inhibition (PFC) (resistance to neg consequences)
lesions in DMS and DLS
DMS- habitual responding
DLS- goal-directed responding
5-HT
serotonin
MDMA
- never used clinically
- can enhance communication and openness
- club drug during 1980s-90s
- Schedule 1
- orally; long half-life (8hrs)
- effects at low doses: increased energy; increased hr and temp
- high doses: mild hallucinogenis; hyperthermia; dehydration; stroke; increased hr
- acute adverse effects: hyperthermia, dehydration
Catecholamine synthesis and inactivation
synthesis: tyrosine
inactivation: reuptake via transporters and/or enzymatic degradation (metabolism)
Catecholamine transporters
VMAT2 (all have this vesicular monoamine transporter- package into vesicles)
Catecholamine enzymes and metabolites
enzymes: MAO (monoamine oxidases), COMT (catechol-o-methyltransferase)
metabolites: 1) dopamine: HVA (humans), DOPAC(rats)
2) Norepinephrine: MHPG
6-OHDA
-causes catecholamine lesions
- damages/ destroys catholamniergic neurons
what releases catecholamines?
amphetamines
how does cocaine and methylphenydate affect dopamine system?
inhibit catecholamine reuptake
Dorsal noradrenergic bundle (DNAB)
originates at locus coeruleus in pons
cognition, arousal, attention
ventral noradrenergic bundle (VNAB)
- originates from medullate
- aversive aspects of stress
what did pharmacological studies show?
- DA antagonists (but not NE antagonists) disrupt amphetamine reinforcement
- DAT blockage is responsible for reinforcing effects of cocaine and amphetamine
what did lesion studies show?
- Using 6-OHDA to lesion DA affects cocaine reinforcements
- If destroy dopamine cells in striatum→ don’t get reinforced anymore
what did neurochemical studies show?
Repeated amphetamine treatment produces sensitization of locomotor and reinforcing effects, and DA levels in striatum
what did genetic knockout and knockin studies show?
knockout: already have high dopamine -> increased locomotion
knockin: showed decreased reinforcement
Stimulant-induced DA in nucleus accumbens (mesolimbic)
locomotion & reinforcement
Stimulant-Induced DA in dorsal striatum (nigrostriatal)
stereotypies