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Neurobiology of Schizophrenia
DR GANESH INGOLE RESIDENT PSYCHIATRY
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• Introduction• Neuro-imaging• Neuro-chemical Abnormalities• Genetics and Neurodevelopment
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INTRODUCTION
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Schizophrenia
• Psychosis– Delusions– Hallucinations– Disorganized speech– Disorganized behaviour– Gross distortions from reality
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Schizophrenia
• Symptom domains– Positive– Negative– Cognitive– Aggressive– Affective
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Schizophrenia
• Positive Symptoms– Delusions– Hallucinations– Distortions in language and communications– Disorganized speech– Disorganized behaviour
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Schizophrenia
• Negative Symptoms– Alogia– Affective blunting– Asociality– Anhedonia– Avolition
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Schizophrenia
• Cognitive domains– Poor concentration– Poor attention– Poor performance– Poor learning – Poor in understanding social cues
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Schizophrenia
• Aggressive Symptom domain– Assaultiveness– Verbally abusive behaviour– Frank violence
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Schizophrenia
• Affective domain– Inability to show expressions– Inability to recognize emotions– Depressed mood– Anxiety– Poor self esteem– Guilt – Suicidal thoughts
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Localization of symptom domains
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NEUROIMAGING
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Structural Abnormalities
• Ventricles- Increased size of lateral ventricles
• Reduced cortical gray volume
• Progressive or static• Reduced symmetry
– Neurodevelopmental
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Prefrontal Cortex
• Anatomical Abnormalities• Functional deficits on neuroimaging• Symptoms of Schizophrenia mimics –
frontal lobotomies and frontal lobe syndrome
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LIMBIC SYSTEM• PM findings and MRI -
decrease in the size of the limbic system including the amygdala, the hippocampus, and the parahippocampal gyrus
• Hippocampus is small, functionally abnormal and has disorganised neurons
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THALAMUS
• Volume shrinkage • Neuronal loss of
medial dorsal nuclei• Number reduced to
30-45%
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Basal ganglia and Cerebellum
• Involved in motor control of movements• Schizophrenia causes odd movements,
gait, facial grimacing• Cell loss and shrinkage in volume• Increase in number of D2 receptors
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Neural Circuits
• Early developmental lesions of dopaminergic tracts
• Disturbances in connectivity in different brain regions
• White matter fibre tracts
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SPECT & PET
• To test DA hyperactivity hypothesis
• Sgnificant, mild elevation in D2 receptor density
• Increase in DA transmission in response to amphetamine challange
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Information Processing in Schizophrenia- DLPFC
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Inappropriate Information Processing
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Neutral Stimuli
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NEUROCHEMICAL ABNORMALITIES
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Neurotransmiters
• Dopamine• Serotonin• Glutamate• Noradrenaline
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Dopamine
• Neurotransmitter • Catecholamine• Synthesized in brain and kidneys
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Dopamine receptors-Location
D1 – Striatum, renal, mesentric vessle
D2 – Striatum, sub.niagra, VTA, pituitary
D3– NA, hypothalamus
D4– Neocortex, midbrain, hippocampus, medulla, heart & kidney
D5– Neocortex, midbrain, hippocampus, medulla
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Dopamine Pathways
• A- Nigrostriatal• B- Mesolimbic• C- Mesocortical• D- Tuberoinfundibular• E- Thalamic Dopamine
pathway
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Dopamine pathways
• Mesolimbic pathway– Ventral tegmental area
of the brainstem to nucleus accumbens in the ventral striatum
– Motivation, pleasure, and reward
– Psychosis, such as delusions and hallucinations
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Mesolimbic Pathway
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Mesolimbic Pathway• Positive, Aggressive symptoms and drug abuse ?to counter negative Symptoms
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Mesocortical Pathway
• Ventral tegmental area to prefrontal cortex
• DLPFC– cognition and
executive functions• VMPFC
– Emotional regulation
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Mesocortical Pathway
• Low Dopamine
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Mesocortical Pathway-VMPFC
•Low Dopamine
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Mesocortical dopamine Hypothesis
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Nigrostriatal pathway
• Substantia nigra to basal ganglia
• Extrapyramidal nervous system
• Motor movements• Deficiencies-
Bradykinesia• Hyperactivity-
Hyperkinetic movement disorders
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5HT – DA interaction at Nigro-striatal Pathway
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Tuberoinfundibular pathway
• Arcuate N of hypothalamus
• Anterior pituitary• Inhibit prolactin
release• Antipsychotic drugs-
increase prolactin– Galactorrhea,
amenorrhea
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Thalamic dopamine pathway
• Arise from multiple sites– Periaqueductal gray matter– Ventral mesencephalon– Hypothalamic nuclei– Lateral parabrachial nucleus• Sleep and arousal mechanisms • Gating info passing through thalamus to the
cortex and other brain areas• Schizophrenia- Normal
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Serotonin
• Serotonin receptors present in many brain areas
• Cortical receptors- excitatory• Enhances downstream glutamate release
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5HT2A Receptors Decreases DA Release
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5HT2A Receptors Decreases DA Release
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Blocking 5HT2A Receptors Increase DA Release
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Cortical 5HT1A Receptors
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Cortical 5HT1A Receptors
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Nigral &Striatal 5HT2A decrease DA release
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Nigral &Striatal 5HT2A decrease DA release
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Raphe 5HT1A Increase DA release
Serotonin binding at raphe nucleus inhibits serotonin release
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Raphe 5HT1A Increase DA release
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Glutamate
• Excitatory neurotransmitter
• Master switch of brain
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Glutamate Dysfunction
• Abnormalities in synapse formation during neurodevelopment
• Genetic abnormalities• Dysconnectivity- Parvalbumin–containig
GABA interneurons• Deficit in GABA• Glutamate hyperactivity• Increased Dopamine
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Glutamate Dysfunction
•Normal Receptors
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Glutamate Dysfunction
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Glutamate Pathways in Brain
• A- Cortico-brainstem• B- Cortico-striatal• C- Hippocampal-striatal• D- Thalamo-cortical• E- Cortico-thalamic• F-Cortico-
cortical(direct)• E- Cortico-
cortical(Indirect)
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Cortico- brainstem • Cortical Pyramidal neurons
to brainstem• Raphe for serotonin• VTA and substantia nigra for
dopamine• Locus coeruleus for
norepinephrine• Key regulator• Direct innervation to other
pathways- excitatory• Indirect- Inhibitory
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Cortico-brainstem Pathway
• Communicates with Mesolimbic pathway in VTA
• Hypoactive NMDA receptors
• Excess Glutamate• Excess DA NA
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NMDA Receptor Hypofunction- Negative Symptoms
• Hypoactive NMDA receptors
• Cortico-brainstem –Overactive
• Excess Glutamate at VTA• Excess stimulation of
braistem pyramidal neurons
• Inhibition of Mesocortical DA neurons
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Cortico-striatal
• Cortical pyramidal neurons to striatal complex
• Cortico-striatal– Dorsal striatum• Cortico-accumbens- nucleus accumbens• Both terminate in GABA neurons of globus
pallidus
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Hippocampal- Accumbens
• Hippocampus to nucleus accumbens• Terminate into GABA neurons• In turn project into Globus pallidus
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NMDA Receptor Hypofunction- Positive Symptoms
• Glutamate at ventral Hippocampus
• Binds to NMDA receptors on GABAeric interneurons
• Pyramidal Glutamate receptors to Nucleus accumbens
• Inhibits Glutamate release at VTA- Normal GABA to Globus pallidus
• Normal DA
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NMDA Receptor Hypofunction- Positive Symptoms
• NMDA receptors hypoactive
• Glutamatergic pathway to NA overactive
• Excess stimulation of GABAergic neurons VTA
• Decreased GABA from Globus Pallidus
• Disinhibition of Mesolimbic pathway
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Thalamo-cortical
• Thalamus to cortex• Process sensory information
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Cortico-Thalamic
• Cortex to Thalamus• Modulates reaction of neurons to sensory
info
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Cortico-cortical
• Direct– Excitatory – Pyramidal neurons excite directly each other
• Indirect– Inhibitory– Through GABA interneurons
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Norepinephrine
• Noradrenergic projections from locus coeruleus to cortex
• A1 receptors on Glutametargic neurons
• Glutamate release in brainstem
• Releases GABA• Inhibits DA release
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Cortical Alpha 1 Receptors
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GENETICS AND NEURODEVELOPMENT
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Genetics
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Subtle Molecular Abnormalities
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Stress Diathesis Model
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Neurodevelopment
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Multiple Susceptibility-1
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Multiple Susceptibility-2
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Genes Causing Abnormal Synaptogenesis
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Synapse Formation
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References• Benjamin James Sadock, Virginia Alcott Sadock,
Pedro Ruiz,2007,Schizophrenia,Synopsis of Psychiatry,11th edition,300-323
• Stephen M Stahl, Psychosis and scizophrenia, Antipsychotic agents, Stahl’s Essential Psychopharmacology, 4th edition, 79-236
• Anissa AD, Olivier G, Integrating the Neurobiology of Schizophrenia
• JN Vyas, Shree Ram Ghimire, Schizophrenia:Neurobiology, Textbook of postgraduate Psychiatry, 3rd edition,237-246
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THANK YOU