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Cognition & Reward (Schizophrenia (Symptomatology (Positive symptoms
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Cognition & Reward
Schizophrenia
Symptomatology
affects 1% population
been around a long time (1,000s years)
Costs nations more than cancer
symptoms universal across culture
appeasrs gradually over 3-5 years
negative symptoms first
cognitive symptoms later
positive symptoms years later
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cognitive symptoms
- difficulty sustaining attention
- low psychomotor speed
- learning and memory issues
- poor abstract thinking
- poor problem solving
Heritibility & genetics
adpotion and twin studies indicate sizable heritability
not a single gene disorder
having 'schizophrenia gene' increases susceptibility from trauma/stress/environment
Rare mutation of DISC1 gene
regulation of neurogenesis
neuronal migration
postsynaptic density in excitatory neurons
mitochondria function
increase chances of schizophrenia by 50
increases insicence of MDD, autism, bipolar
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concordance in monochorionic (same placenta) MZ twins higher
60% monochorionic, 11% dichorionic MZ
Neuropathology
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Structural changes
- ventricular englargement
- associated with loss of neurons
- reduced grey matter in:
- temporal lobes
- frontal lobes
- hippocampus
- Faulty cellular arrangement (asymmetry) in:
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Neurocognitive deficits
- all associated with frontal lobe
- lower IQ
- attention deficits
- planning and information processing
- working memory deficits
- sensory motor gating
- antisaccade task
- oculolotor function
hypofrontality
decreased activity
dlPFC esp.
attention to everything
P50 second click not habituated
PPI small pulse doesn't prepare for second
Neurochemistry
Dopamine hypothesis
caused by abnormality in DA system
overactivity in mesolimbic - positive (VTA to NAc)
underactivity in mesocortical - negative (VTA to pFC)
Evidence
Dopamine agonists psychotomimetic
L-DOPA, cocaine, amphetamine
antipsychotics ameliorate effects
CPZ DA antagonist
since CPZ typical antipsychotics
work on positive symptoms (although ~20-30% don't respond)
Block D2 receptors
dose required and D2 receptor affinity closely matched
more evidence
PET experiment
IBZM reversible antagonist - competes with DA for binding site
displacement after amphetamine measured
more DA actiity (IBZM displacement) in striatum associated with positive symptoms
issues
only covers positive not negative symptoms
atypical (low D2 affinity) drugs work better
negative symptoms associated with underactivity in mesocortical DA pathway
obverse of DA overactivity
long term drug treatment
antipsychotics cause parkinson's type symptoms:
- slowness movement
- lack of facial expression
- general weakness
~1/3 patients tardive dyskinesia
unable to stop moving
atypical antipsychotics
Clozapine
first
low affinity for D2 (higher for D3, D4 and 5HT)
only drug which reduces suicide rate
not widely used
lots of side effects:
weight gain, sedation, hypersalivation, tachycardia, hypotension, neutropenia
Glutamate hypothesis
~50% of neurons use glutamate as neurotx
in mammals balanced with GABA
both neurotx influence almost every area and chemical in brain
evidence that NMDA receptor implicated in schiz
NMDA receptor (4 subunits)
ionotropic
mutations in subunits
evidence that mice(!) display schizopherenic symptoms with NMDA receptor subtypes selectively knocked out
Hypothesis
NMDA receptor hypofunction
- why neg symptoms are treatment resistant
- onset in early adulthood
- why disorder has structural changes and cognitive deficits
Evidence
NMDA receptor antagonists (PCP, Ketamine)
cause positive, negative & cognitive symptom similarities
glutamate agonists improve both +ve and -ve symptoms
positive symptoms
in healthy brain, glutamate projected from PFC into VTA
if not function, VTA doesn't get inhibitory singals from PFC
negative symptoms
in healthy brain, glutamtate from PFC to VTA
overstimulate GABA interneuron
from VTA DA projection to dlPFC and dmPFC
disrupted in schiz
less dopamine
Recent developments
Neuroinflamatory hypothesis
brain's immune (microglia) hyperactive in schizo risks
animal study support for pro-inflamatory agents and schiz symptoms
reversed with antipsychotics or antibiotics which reduce microglial activation
not just involved in pathogen control
neuronal death & survival
synaptogenesis
synaptic pruning
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Estrogen hypothesis
more schiz in men than women
later onset in women than men
women respond better to treatment
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Depression
heritibility & genetics
moderate - 2 - 3 times more likely if relatives have it
several genes linked
charecteristics of MDD related to different genes
monoamine hypothesis
depressive symptoms are caused by insufficient monoaminergic neurons
monoamine agonists should reverse the symptoms
Monoamines:
- Catecholamines
- dopamine
- norepinephrine (noradrenaline)
- epinephrine (adrenaline)
- indolamines
depression: norepinephrine & serotonin
synthesised in the soma
transported down to the bouton
reuptake by transporters
enzyme MAO and COMT to breakdown monoamines
Evidence
lower levels of serotonin metabolite found in CSF of depressives
lower levels of dopamine and norepinephrine metabolites in CSF
Reserpine caused depression
prevents packaging of monoamines in vesicles
all effective antidepresants affect serotonin and norepinephrine
amphetamines & MDMA elevate monoamine levels
Criticism
accute decrease in serotonin levels only affects depressives (or those susceptible)
although SSRI & SNRI increase levels of 5HT & NE quickly, action of drugs takes weeks
Antidepressants
MAO inhibitors
inhibit breakdown of Monoamines in presynaptic terminal
increase pool of monoamines available for loading in vesicle
side effects
Tricyclic
inhibit reuptake of NE & 5HT
SSRI
prozac most effective for adolescents and children
SNRI
serotonin & Norepinephrine reuptake
Stress-diathesis hypothesis
(neurogenic hypothesis)
hyperactive HPA axis
high blood levels of cortisol
high brain levels of CRH
Reduced hippocampal volume
correlates with days of untreated depression
administer artificial cortisol
in controls, body stops producing cortisol until CRH administered
in depressives, body still produces cortisol, produces more after CRH
BDNF is reduced by stress
BDNF has been shown to protect cells agaist neuronal death
BDNF reduced in depression
Amygdala threat
HPA axis activation
cortisol released
cortisol to hippocampus (cortisol/glucocorticoid receptors)
negative feedback to HP
chronic stress
increased Ca2+ influx
excitotoxicity
cells die
hippocampus loses negative feedback to HPA
Treatment
antidepressants produce neurogenesis in hippocampus
2-4 weeks for new neurons (coincides with delay in SSRI)
Addiction
DSM V
impaired control (1-4)
social impairment (5-7)
risky use (8-9)
pharmacological (tolerance/withdrawal) (10-11)
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Direct
coke/speed - increase at synapese
nicotine
direct VTA stimulation by nicotinic receptors
indirect
opiod/cannibanoids
inhibit GABA projections onto VTA, allowing to fire
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