Neurobiology

1
Neurobiology
2
Neurobiology of Bipolar Disorder

• Magnetic resonance imaging (MRI)
• Morphometric MRI
• Functional MRI (fMRI)
• Diffusion tensor imaging (DTI)
• Neurochemical studies
• Postmortem studies
• Networks, circuits, signaling
• Stress/HPA axis
• Genetics

3
Useful Neuroimaging Modalities

• MRI structural volume, gray/white, lesions
• fMRI blood flow, blood volume
• MRS neurochemistry
• DTI white matter structure
• PET blood flow, metabolism, receptor binding
• SPECT blood flow, receptor binding

MRI magnetic resonance imaging fMRI
functional MRI MRS magnetic resonance
spectroscopy DTI diffusion tensor imaging PET
positron emission tomography SPECT
single-photon emission computed tomography
4
Structural Studies
5
Anterior Limbic Network
Adapted from Strakowski S, et al. Molecular
Psychiatry. 200510105-116.
6
Structural Changes With BPD ProgressionEpisodes
Are Associated With Brain Tissue Loss
Prefrontal Cortex ? Left inferior
prefrontal gray volumes with ? illness
duration ? Gray matter volume with ?
age Striatum No difference in putamen between
first- and multi-episode patients Cerebellum ?
Cerebellar vermis volume in multi- vs
first-episode patients Amygdala ? Amygdala volume
with ? age in young patients Ventricles ?
Ventricular volume in multi- vs first-episode
patients ? Ventricular volume with ? number of
manic episodes ? Ventricular volume with ? number
of affective episodes
Reviewed in Strakowski S, et al. Molecular
Psychiatry. 200510(1)105-116.
7
Lateral Ventriculomegaly in BPD
Lateral ventricular volume associated with
number of prior manic episodes (r 0.43, P lt
0.02) Not associated with striatal volumes
Lateral Ventricular Volume, Total Cerebrum
First- Episode
Healthy Subjects
Multiple Episodes
Patients With Bipolar Disorder
Strakowski S, et al. Am J Psychiatry.
2002159(11)1841-1847.
8
Structural MRI of Anterior Limbic Network in BPD
30
BPD (n 24)

Healthy volunteers (n 22)
25
Medium effect size Large effect size
20

15
cc

10


5
0
Lat V
PFL/10
Striatum
Thalamus
Amygdala
G. Pallidus
Hippocampus
Amygdala/hippocampal and striatal enlargement
have been shown in several studies
Strakowski S, et al. Arch Gen Psychiatry.
199956(3)254-260. Strakowski S, et al.
Molecular Psychiatry. 200510(1)105-116.
9
Structural MRI of Amygdala in BPD


Significantly larger, P lt 0.001
Significantly smaller, P lt 0.01
Altshuler L, et al. Arch Gen Psychiatry.
199855(7)663-664.
10
Structural MRI Anterior Limbic Network in BP
Adolescents
Amygdala enlargement may be developmental
18

Medium effect size Large effect size
BPD (n 23)
16
14
Healthy subjects (n 20)
12
10
cc
8

6
4
2
0
Striatum
Thalamus
G. Pallidus
Amygdala
DelBello M, et al. Bipolar Disord.
20046(1)43-52.
11
Adjusted Cerebellar Vermis V3 Area in BPD
400
300
Vermal 3 Area x 10-3
200
0
Control
Multiple
First
Vermal volumes inversely correlated with numbers
of affective episodes
DelBello M, et al. Neuropsychopharmacology.
199921(1)63-68.
12
Abnormal Corpus Callosum Myelination in Pediatric
Bipolar Patients

• Corpus callosum signal intensity (CCSI)
  T1weighted MRI as an index of myelination of
  the corpus callosum
• Bipolar patients age 15.5 3.4 years (n 16)
• Healthy subjects age 16.9 3.8 years (n 21)

Values represent signal intensity unadjusted mean
SD

• Abnormalities in the corpus callosum (perhaps due
  to altered myelination) may play a role in the
  pathophysiology of bipolar disorder among
  children and adolescents.

Caetano S, et al. J Affect Disord.
2008108(3)297-301.
13
Ventral Prefrontal Cortex (VPFC) Differences
Across the Lifespan
Bipolar disorder with more rapid decrease in VPFC
during late adolescence/young adulthood
Blumberg H, et al. Biol Psychiatry.
200659611-618.
14
Implications for Patient Care

• Collectively these studies emphasize the
  neuroanatomical consequences of poor adherence to
  treatment or neglecting lifelong treatment
• Every episode leaves a footprint
• Every year is a year of deterioration
• Every episode shortens the time to the next
  episode

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Functional MRI Studies
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fMRI Continuous Performance Test-Identical
Pairs (CPT-IP) A Study of Attention

• Hypothesis anterior limbic network regions
  inappropriately activated during nonemotional
  tasks
• This activation disrupts attentional networks
• To perform task, patients activate compensatory
  areas
• Unmedicated, euthymic bipolar patients compared
  to healthy subjects
• Abnormalities in euthymia may represent
  neurobiological vulnerability factors for BPD
• Task CPT-IP
• Series of numbers, respond when same number
  repeats
• Groups performed the same

Strakowski S, et al. Neuropsychopharmacology.
200429(9)1734-1740.
17
fMRI CPT-IP Task Performance
BPD HS Variable (n 10) (n
10) P-value YMRS 1.6 (1.8) 0.4 (0.8) gt
0.07 HAMD 3.1 (2.5) 1.6 (1.8) gt
0.1 Discriminability 5.9 (2.2) 6.9 (2.5) gt
0.4 Percent correct 94.3 (6.5) 95.6 (5.8) gt
0.7 Percent false 4.0 (3.2) 2.0 (2.8) gt 0.2
Values represent mean (SD). YMRS Young Mania
Rating Scale HAMD Hamilton Depression Rating
Scale
Strakowski S, et al. Neuropsychopharmacology.
200429(9)1734-1740.
18
fMRI CPT in Euthymic BPD
Healthy Volunteers vs Euthymic BPD

• Bipolar patients inappropriately activate mood
  networks during attentional task, with
  compensation for simple task

Areas in which healthy subjects exhibited greater
activation are in blue tones Areas in which
bipolar patients exhibited greater activation are
in yellow/green/red
Strakowski S, et al. Neuropsychopharmacology.
200429(9)1734-1740.
19
fMRI Counting Stroop Task Executive and
Attentional Function

• Hypothesis as task performance fails, subjects
  fail to bring cognitive areas on-line
• Euthymic bipolar patients compared to healthy
  subjects
• Using a counting Stroop task (identify a number
  when it is discordant with the written words)
• More difficult attentional task patients
  struggle with this task
• Abnormalities present in euthymia may represent
  neurobiological vulnerability factors for bipolar
  disorder

Strakowski S, et al. Am J Psychiatry.
2005162(9)1697-1705.
20
fMRI Counting Stroop Task Performance
BPD HS Variable (n
16) (n 16) P-value   Control Task
Performance False hits 12 (16)
2 (2) lt 0.05 Percent correct 85
(17) 97 (3) lt 0.02 Reaction
time, ms 913 (120) 924 (53) gt
0.9   Interference Task Performance False
hits 18 (16) 4 (4) lt
0.008 Percent correct 74 (22) 93
(5) lt 0.006 Reaction time, ms 909
(190) 1013 (52) gt 0.1
Values represent mean (SD)
Strakowski S, et al. Am J Psychiatry.
2005162(9)1697-1705.
21
fMRI Counting Stroop in Euthymic BPD
Healthy Volunteers vs Euthymic BPD

• Failure of secondary error detections and impulse
  control regions in euthymic BPD, with impaired
  task performance

Areas in which healthy subjects exhibited greater
activation are in blue tones Areas in which
bipolar patients exhibited greater activation are
in yellow/orange tones
Strakowski S, et al. Am J Psychiatry.
2005162(9)1697-1705.
22
fMRI Counting Stroop in Euthymic BPD
Medicated vs Unmedicated Euthymic BPD

• Effective treatment may improve activation in
  cognitive brain areas

Strakowski S, et al. Am J Psychiatry.
2005162(9)1697-1705.
23
fMRI Caudal and Rostral Ventral Prefrontal
Cortex in Bipolar DisorderState Effects
Depressed
Euthymic
Bipolar vs Healthy
Increased cVPFC in depressed vs euthymic bipolar
disorder
Decreased rVPFC in bipolar vs healthy subjects
Blumberg H, et al. Arch Gen Psychiatry.
200360(6)601-609.
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Summary of fMRI in Bipolar Disorder

• Anterior limbic network overactivated and
  overresponsive in euthymia
• Disrupts cognitive processing and impulse control
• Compensated by compensatory cortical activation
• Compensation during euthymia is vulnerability for
  failure under minor stress loss of compensation
  associated with affective episodes
• Functional abnormalities reflected in task
  performance and, potentially, in neuroanatomy
• Integration of imaging modalities with
  neurocognitive probes critical to clarify
  significance of these findings

Strakowski S, et al. Molecular Psychiatry.
200510(1)105-116.
25
Magnetic Resonance Spectroscopy (MRS)In Vivo
Neurochemistry Studies
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Proton Spectroscopy (1H-MRS)

• 1H-MRS provides a means to look at mechanisms
  underlying functional abnormalities
• Measures neurochemical concentrations in a given
  volume
• N-acetyl aspartate (NAA) neuronal integrity
  metabolic indicator
• Choline-containing compounds (Cho) membrane
  constituent
• Glutamine/glutamate/GABA (Glx)
  neurotransmitters
• Myo-inositol (Ino) second messenger
  systems/membrane constituents
• Creatine (Cr) measure of mitochondrial
  metabolism
• Lactate (Lac) measure of mitochondrial
  metabolism

Strakowski S, et al. Molecular Psychiatry.
200510(1)105-116.
27
1H-MRS Orbital and Prefrontal Gray Matter in
Adults with BPD and Healthy Subjects
NAA N-acetyl aspartate Cho choline Cr
creatine myoI myo-inositol
Cecil K, et al. Bipolar Disord.
20024(6)357-365.
28
1H-MRS Medial Prefrontal Cortex Gray Matter in
At-risk Kids
18
16
14
ARK (n 6)
HK (n 9)
12
Concentration (mM)
10
8
P 0.03, d 0.88
6
4
2
0
NAA
Cho
Cr
myoI
NAA N-acetyl aspartate Cho choline Cr
creatine myoI myo-inositol
Children with a mood disorder and familial risk
for bipolar disorder
Cecil K, et al. J Child Adol Psychopharm.
200313(4)545-555.
29
1H-MRS Cerebellar Vermis in At-risk Kids
18
P 0.07, d 0.38
P 0.07, d 0.38
16
14
ARK (n 9)
HK (n 9)
12
10
Concentration (mM)
8
6
4
2
0
,
NAA
Cho
Cr
myoI
NAA N-acetyl aspartate Cho choline Cr
creatine myoI myo-inositol
Children with a mood disorder and familial risk
for bipolar disorder
Cecil K, et al. J Child Adol Psychopharm.
200313(4)545-555.
30
Proton MRS in BPD Lithium Treatment Effects


Significant difference from baseline
Moore G, et al. Am J Psychiatry.
1999156(12)1902-1908.
31
Neurochemical Changes Associated With Remission
Following Olanzapine Treatment of Adolescent Mania
P lt 0.006
Change in Prefrontal Gray NAA (mM)
Day 0Day 7
Day 7Day 28
DelBello M, et al. Neuropsychopharmacol.
2006311264-1273.
32
Increased Glx and Lactate in Unmedicated Bipolar
Disorder Evidence of Hypermetabolism
P lt 0.01
P lt 0.01
Glx glutamate/glutamine
Dager S, et al. Arch Gen Psychiatry.
200461(5)450-458.
33
Other Relevant 1H-MRS Findings

• Increased Glx and Lac in med-free BPD
• Increase Glx in affective episodes, but not
  euthymia
• NAA is inversely proportional to illness duration
• Lithium decreases Glx, valproate does not
• Phosphorus-MRS supports suggestion of
  mitochondrial abnormalities in bipolar disorder
• Lithium increases NAA (marker of functional and
  structural neuronal integrity)

Dager S, et al. Arch Gen Psychiatry.
200461(5)450-458. Michael N, et al.
Psychopharmacol. 2003168(3)344-346. Chang K,
et al. Biol Psychiatry. 200353(11)1059-1065. Win
sberg M, et al. Biol Psychiatry.
200047(6)475-481. Friedman S, et al. Biol
Psychiatry. 200456(5)340-348 Moore C, et al.
Bipolar Disord. 20002(3 pt 2)207-216.
Glx glutamate/glutamine Lac lactate NAA
N-acetyl aspartate
34
1H-MRS Summary

• 1H-MRS suggests abnormalities in
• Mitochondrial metabolism
• Membrane metabolism
• Second messenger systems
• Some abnormalities may predate illness onset
  (eg, vermis), others may develop over time
• Glutamatergic excitotoxicity may be mechanism for
  progressive brain changes

Dager S, et al. Arch Gen Psychiatry.
200461(5)450-458. Michael N, et al.
Psychopharmacol. 2003168(3)344-346. Chang K,
et al. Biol Psychiatry. 200353(11)1059-1065. Win
sberg M, et al. Biol Psychiatry.
200047(6)475-481. Friedman S, et al. Biol
Psychiatry. 200456(5)340-348 Moore C, et al.
Bipolar Disord. 20002(3 pt 2)207-216.
35
Diffusion Tensor Imaging (DTI)White Matter
Imaging
36
Diffusion Tensor Imaging in Bipolar Disorder

• Preliminary study (BPD, HS, N 9 per group)
• Prefrontal/periventricular regions of interest
  (ROI)
• Examined fractional anisotropy (FA) and trace
  apparent diffusion coefficient (TADC)
• FA significantly differed between groups TADC no
  difference between groups
• Conclusions
• FA but not TADC differences
• Suggest loss of axonal bundle coherence. This
  loss may contribute to the prefrontal cortical
  pathology in bipolar patients

White matter fractional anisotropy ROI BPD HS
p d 15 mm above AC 0.22 (.04) 0.25
(.04) .21 0.7 20 mm above AC 0.20 (.04) 0.23
(.03) .11 0.8 25 mm above AC 0.18 (.03) 0.22
(.04) .04 1.0 30 mm above AC 0.18 (.02) 0.22
(.03) .01 1.3 Total 0.78 (.12) 0.91 (.12) .05 1.0
Adler C, et al. Bipolar Disord.
20046(3)197-203.
37
Postmortem Studies
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Neuron Numbers and Amygdala Volume in Subjects
Diagnosed With Bipolar Disorder or Schizophrenia

• Postmortem investigation
• N 12 healthy controls, 10 bipolar disorder, 16
  schizophrenia
• Nissl-stained sections
• Total number, numeric density, somata size of
  neurons, nuclear volume
• Lateral (LN), basal (BN), accessory basal (AB),
  and cortical (CO) amygdalar nuclei
• No significant differences between groups for
  age, sex, postmortem time interval, brain weight,
  hemisphere or cause of death

Berretta S, et al. Biol Psychiatry.
200762(8)884-893.
39
Volume and Total Number of Neurons Are Decreased
in the Lateral Nuclei of Bipolar Disorder
Subjects
29.0 ? volume P 0.01 vs
healthy control 41.1 ? total numbers of
neurons 14.5 ? numeric density of neurons
Berretta S, et al. Biol Psychiatry.
200762(8)884-893.
40
Networks/Circuits/Signaling in Bipolar Disorder
41
Neurotransmitter and Neuropeptide
SystemsImplicated in the Pathophysiology of
Bipolar Disorder

• Noradrenergic system
• Dopaminergic system
• Serotonergic system
• Cholinergic system
• GABAergic system
• Glutamatergic system

Goodwin F, Jamison K. Manic Depressive Illness.
Oxford University Press New York, NY2007.
42
Circuits, Synapses, and Cellular Plasticity

• Bipolar disorder is not just too little or too
  much of individual neurotransmitters or
  neuropeptides it is a
• Disorder of synapses and circuits
• Abnormality of the regulation of cellular
  plasticity cascades
• Aberrant information processing mediating
  various functions
• Biological mechanisms underlying neuroplasticity
• Alterations in gene transcription
• Intracellular signaling cascades
• Modifications in synaptic number and strength
• Variations in neurotransmitter release
• Modeling of axonal and dendritic architecture

43
Cellular Signaling Cascades

• Regulate multiple neurotransmitter and
  neuropeptide systems implicated in BPD
• Targets for hormones that have been implicated in
  pathophysiology of BPD
• Monoamine and neuropeptide pathways originate and
  project heavily to limbic-related regions
  (hippocampus, hypothalamus, brain stem)
• Abnormalities in cellular signaling cascades that
  regulate diverse physiological functions may
  explain the extensive medical comorbidities
  associated with BPD
• Many of these pathways play important roles in
  synaptic plasticity and long-term atrophic
  processes

44
Signaling NetworksNeuroprotection BDNF, bcl-2

• BDNF (brain-derived neurotrophic factor)
• Important in neurogenesis, neuronal survival
  and maturation of neural pathways
• In adults, important for synaptic plasticity,
  dendritic growth, and long-term memory
• BDNF acts at the tyrosine kinase receptor B
  (Trk B) on target cells
• Inhibits cell death cascades via MAP kinases
  and upregulation of bcl-2
• Reduced serum levels of BDNF in depressed
  patients and patients with bipolar disorder
  (both depressive and manic phases)
• Bcl-2
• Localized to outer mitochondrial membrane, ER,
  and nuclear membrane
• Major downstream target of the ERK MAPK
  cascades
• Inhibits apoptotic and necrotic cell death
• Neurotrophic effects promotes neurite
  sprouting, outgrowth, axonal regeneration
• Lithium and valproate activate the ERK MAP
  kinase cascade (upregulate cell
• survival proteins)

MAPK mitogen activated protein kinase ERK
extracellular receptor-coupled kinase
Schloesser R, et al. Neuropsychopharmacology.
200833(1)110-133. Post R. J Psychiatr Res.
200741(12)979-990.
45

• Mitochondrial Dysfunction and Bipolar Disorder

• Mitochondria important role in the regulation
  of intracellular
• calcium and signaling
• Mitochondrial dysfunction in BPD
• Impaired energy metabolism in the brain of BPD
  patients
• Comorbidity of bipolar disorder with
  mitochondrial diseases
• Effects of mood stabilizers on mitochondria
• Increased mitochondrial DNA deletion in the
  brain of BPD patients
• Association of mitochondrial DNA
  mutations/polymorphisms in BPD
• It has been proposed that mitochondrial DNA
  mutations or
• polymorphisms result in altered mitochondrial
  Ca2 regulation,
• and ultimately altered neuroplasticity

Kato T. CNS Drugs. 200721(1)1-11.
46
Mitochondrial Dysfunction and Bipolar Disorder
? PME in Bipolar Depression and Mania
? Intracellular pH
? PME in Bipolar Euthymia
? Glutamate/Glutamine
? Phosphocreatine
? Lactate
Altered Phosphomonoester (PME) Levels
? Choline
Energy Shortage ? ATP
Shift toward Glycolysis
? Myo-inositol
Mitochondrial Dysfunction
Altered Phospholipid Metabolism
? N-acetyl aspartate
Adapted from Stork C, Renshaw P. Molecular
Psychiatry. 200510(10)900-919.
47
Stress, Hypothalamic-Pituitary-Adrenal (HPA)
Axis, and Bipolar Disorder
48
HPA Axis Dysregulation in Bipolar Disorder

• HPA axis hyperactivity prominent in BPD
• Significant hypersecretion of cortisol state
  dependent abnormalities
• Dexamethasone non-suppression
• Abnormal response to physical and psychological
  stressors
• Chronic elevation of glucocorticoids

Goodwin F, Jamison K. Manic Depressive Illness.
Oxford University Press New York, NY 2007.
49
Cytokines and Hypothalamic-Pituitary-Adrenal
(HPA)-axis

• Chronic Stress Response (chronic activation
  maladaptive)
• Compromised immune function
• HPA-axis dysfunctional feedback regulatory system
• Chronic state of inflammation
• ? Cortisol production, ? Acute phase reactants,
  ?IL-1, IL-2, IL-6, TNFa
• Hippocampal atrophy
• Recurrent stress and recurrent mood episodes may
  lower threshold for cellular death/atrophy in
  response to physiological and pathological events
• Cytokines activate the Acute Stress Response
  (acute activation adaptive)
• Adaptation and survival
• Glucocorticoids inhibit the production of
  proinflammatory cytokines and stimulate
  production of anti-inflammatory cytokines

Wilson C, et al. J Amer Geriatrics Soc.
200250(12)2041-2056. McEwen B. Ann N Y Acad
Sci. 200410321-7.
50
Cytokine Profiles in Bipolar Disorder
P lt 0.001 Manic vs Controls P lt 0.05 Depressed
vs Controls

• Similar results have been reported with other
  proinflammatory cytokines, ie, IL-1, IL-6
• The effect on anti-inflammatory cytokines is
  less consistently reported
• The current study found no significant
  differences in IL-10

OBrien S, et al. J Affect Disord.
200690(2-3)263-267.
51
Genetics of Bipolar Disorder
52
Genetics Familial Factors

• Risk of illness in a first degree relative 10X
  general population
• Risk of illness for an identical twin 63
• Calculated heritability for bipolar disorder from
  twin studies 0.78
• Risk of affective disorder in offspring with 1
  parent with BPD 2729
• Risk of affective disorder in offspring with 2
  affected parents 5074

Goodwin F, Jamison K. Manic Depressive Illness.
Oxford University Press New York, NY 2007.
53
Genetics

• Two broad approaches used to search for genes
  involved in disease
• Linkage Studies Establish location of genes
  involved in disease susceptibility by identifying
  markers that occur in a greater than random
  frequency in affected family members or in
  affected siblings candidate genes can be
  investigated within these narrowed regions
• Association Studies Compare variations in genes
  that encode proteins thought to have a role in
  the disease state in affected patients and
  healthy controls

McGuffin P. Actas Esp Psiquiatr. 200836(1)48-50.
54
Genome-wide Association StudyCase-Control Study
of Bipolar Disorder

• 2,000 established bipolar cases compared with
  3,000 controls
• Microarray-based technology
• Strongest signal at Chromosome 16p12
• Several genes at this locus could have relevance
  to BPD
• PALB2 involved in stability of nuclear
  structures (chromatin, nuclear matrix)
• NDUFAB1 encodes a subunit of Complex I of the
  mitochondrial respiratory chain
• DCTN5 encodes a protein involved in
  intracellular transport interacts with DISC1
  implicated in schizophrenia
• Other loci of interest
• KCNC2 encodes a voltage-gated potassium channel
• GABRBI GABA A receptor
• GRM7 metabotropic glutamate receptor
• SYN3 synapsin III

The Wellcome Trust Case Control Consortium.
Nature. 2007447(7)661-683.
55
Promising Linkage Regions and Candidate Genes
Associated With Bipolar Disorder

• Linkage Regions
• 4p16, 4q35
• 6q22
• 8q24
• 12q24
• 13q31-33
• 16p12
• 18p11-q12, 18q22-23
• 21q22
• 22q11-13

• Candidate Genes
• 5-HTT Serotonin transporter
• MAOA Monoamine oxidase A
• TH Tyrosine hydroxylase
• COMT Catechol-O-methyl transferase
• DRD2 Dopamine D2 receptor
• DRD4 Dopamine D4 receptor
• BDNF Brain-derived neurotrophic factor
• G72/G30 D-amino acid oxidase activator

Large sample sizes needed for these
investigations
Goodwin F, Jamison K. Manic Depressive Illness.
Oxford University Press New York, NY 2007.
56
Neurobiology of Bipolar DisorderTherapeutic
Implications

• A greater understanding of the structural,
  neurophysiological, and neurochemical alterations
  associated with this illness will enhance the
  options for therapeutic intervention
• Abnormalities in the regulation of cellular
  plasticity cascades are part of the
  pathophysiology of bipolar disorder
• Bipolar disorder is a genetically influenced,
  complex, multifaceted illness