Modeling Behavioral Endophenotypes Related to Alcohol Abuse in Mice Jeanne M. Wehner
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Transcript of Modeling Behavioral Endophenotypes Related to Alcohol Abuse in Mice Jeanne M. Wehner
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Modeling Behavioral Endophenotypes Related to Alcohol Abuse
in Mice
Jeanne M. Wehner Institute for Behavioral Genetics University of Colorado
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What can rodent models do to enhance the studies of alcohol abuse and alcoholism? • Animal models can provide one strategy to study traits that predate the disorder or are associated with the disease including
Broad Categories of Endophenotypes:behavioral, cognitive,
neurophysiological, or neurochemical processes that are associated with risk for alcohol abuse
• Provide multiple different strategies to identify candidate genes regulating these
phenotypes.
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Goal of Using Endophenotypes for Dissection of Complex Disorders
Adapted from Figure 1: Gottesman, I.I. and Gould,T.D.: Amer. J. Psychiatry 2003; 160: 636-645
Decreased complexityof both phenotype and genetic analysis
Example: workingmemory impairments in schizophrenia
Less More # of Genes
Increased complexity of both phenotype and genetic analyses
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All Behavioral Traits are Regulated by Multigenic or Polygenic SystemsModeling of Phenotypes related to the
predisposition to alcoholism and assessing the actions of alcohol
Example 1: The role of -Protein Kinase C Initial sensitivity---Low Responding Anxiety and risk taking Behavioral Disinhibition Ethanol consumption
Example 2: The role of nicotinic cholinergic receptors in mediating alcohol/
nicotine interactions Startle
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Genetic Strategies to Study Complex Behaviors
Polygenic
Genes regulating variation in humans and animals
Strain DifferencesRecombinant Inbreds
& QTL
Single gene
Essential genes forBehaviors, Physiology
etc.
Transgenics andNull Mutants
Selectedlines
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SensitivityAnxiety,
Risk taking Behavioral Disinhibition
Increased alcohol consumption
Modeling Possible Predisposing Factors
What genes regulating these pharmacological and behavioral traits ??
Example 1: Protein Kinase C
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Protein Kinase C is a Central Regulator of Diverse Pathways in the Brain
PKC
AC
Ca/CAM BINDING PROTEINS
LIGAND-GATEDCHANNELS
GABA5HT
MUSCARINIC5HTDA NEUROGRANIN
RECG
R PIP
IPDAG
G
ER
Ca++
3
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PKC Super Gene Family
PRK1PRK2
PKC-PKC-
PKC-PKC-
PKC-PKC-
PKC-
PKC-
PKC-
Neuronal ExpressionPost natal ExpressionPostsynaptic localization
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-PKC Knock-out Mice:
• Created using ES cell technology
• Deletion inserted in -PKC gene
• Lack expression of - PKC protein throughout brain BUT especially important in cerebellum,hippocampus, striatum,
and amygdala• Mild hind limb ataxia in
mutants
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Sensitivity
PKC
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Sensitivity
Low response associated with increased risk for alcoholism: ataxia and other subjective measures (Schuckit et al.)
Increased sensitivity associated with lower risk (Heath et al.)
Confounds in Human Studies:
1. History of alcohol exposure and smoking
(Madden, Heath, Martin) 2. Role of Acute Functional Tolerance
In our animal studies:
Can control #1 but #2 is more difficult
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Dur
atio
n of
LO
RR
(m
in)
0
40
80
120
160
200
MUT HET WT
285.3 + 14.8 mg%
224.9 + 19.9 mg%
230.3 + 44.7 mg%
Sensitivity to High Doses of Ethanol
• Mutants are less sensitive to first exposure to ethanol
• Ethanol Clearance was not different
3.5 g/kg I.P
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What neurotransmitter system could be altered due to loss of -PKC ?
• Reduced ethanol-potentiation of Muscimol-stimulated
chloride flux in microsacs from cerebellum, midbrain, and cortex
Additional Questions???
• Is there an electrophysiological correlate to this?• Is -PKC the only PKC isotype involved?
Alterations in GABAergic system
Harris/Wehner Collaboration (PNAS 92: 3658-3662, 1995)
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PKC Super Gene Family
PRK1PRK2
PKC-PKC-
PKC-PKC-
PKC-PKC-
PKC-
PKC-
PKC-
Neuronal ExpressionPost natal ExpressionPostsynaptic localization
Expressed in many tissuesShown to change with chronic treatment in PC12 cells
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Proctor et al. JPET 305:264-270, 2003
PKC null mutant mice:• more sensitive to ethanol compared to wild types• will self-administer less ethanol (Hodge
et al.)
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Hippocampal Recordings
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We conclude: PKC and PKC isotypes may be important regulators of initial sensitivity for systems that may involve GABAergic function
BUT initial sensitivity is not one precise phenotype
Are low dose behavioral effects different between mutants and wild types? • PKC mutants are also less sensitive to low-dose effects
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Sensitivity Anxiety,Risk taking
PKC
?
Mutation leads to reduced sensitivity
Note: Novelty-seeking has been hardto model
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Ha! I’ve outwittedHa! I’ve outwittedthem at last!them at last!
PKC null mutants may be risk takers...
Slide from Jason Keller, Wehner lab
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Elevated Plus Maze
Mirrored Chamber Test
Open Field Arena
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PE
RC
EN
T O
F T
OT
AL
EN
TR
AN
CE
S
INT
O O
PE
N A
RM
0
10
20
30
40
50
CL
OS
ED
EN
TR
AN
CE
S
0
5
10
15
ELEVATED PLUS MAZE
*
Mutants demonstrate less anxiety or greater exploration of novel places
MUT HET WT
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LA
TE
NC
Y
TO
EN
TE
R (
se
c)
0
50
100
150
200
250
300
PE
RC
EN
T O
F T
IME
IN
CH
AM
BE
R
0
2
4
6
8
10
12
14
16
EN
TR
AN
CE
S
0
1
2
3
4
MIRRORED CHAMBER
MUT HET WT
**
**
PKC mutants appear less anxious and again are willing to explore novel places
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Open-field Studies
Security is a nice wall to hug!
That eagle will never get me. I aminvincible!!!
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*
Latency to Center Time in Center Total Activity
SEC
0
100
200
300
400
Mutant
Wild Type
Sec
0
10
20
30
40
50
CM X
10
-3
0
2
4
6
8
10
12
*
*
**
Open-field behavior under white light in PKC mice
Mutants are more willing to explore center and spend more time there consistent with increased risk taking or less anxiety
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SensitivityAnxiety
Risk taking BehavioralDisinhibition
PKC
?
Mutation leads to reduced sensitivity
Mutation leads toreduced anxiety or increasedRisk taking
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Human Genetic Modeling of Behavioral Disinhibition
Behavioral Disinhibition
ConductDisorder
SubstanceAbuse
AttentionDeficit
Disorder
NoveltySeeking
•Experimentation is driven by environmental factors•Severe Substance Abuse with early onset has a large genetic component• Colorado Adolescent Drug Dependence Research Center***
From Young et al:Amer. J. Med. Genetics96: 684-695***
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Measuring impulsivity inthe mouse
• Appetitive learning using an operant paradigm
Slide from Dr. Barbara Bowers
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SIGNALED APPETITIVE TASK
DRL task: differential reinforcement of low rate of responding
1. Mice deprived to 85% of normal weight
2. Mice learn to nose poke for a food reward. (FR 1, FR 3)
3. Mice learn to associate reward with the presentation of a clicker sound .
4. Mice must learn to withhold their nose-poking response until tone to gain a reward on a variable schedule. Clock is reset when nose poke is not appropriate response.
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Efficiency Ratio for Withholding Responses for
Impulsivity Task
Inbred Strainsurvey provides firstevidence for genetic regulation of the withholdingresponse
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Impulsivity is negatively correlated with Ethanol consumption
r = -.63; P<.05
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% CONDITIONED RESPONSES
DAYS
0 2 4 6 8 10 12
% C
ON
DIT
ION
ED
RE
SP
ON
SE
S
10
20
30
40
50
60
70
80
90
PKC WildtypesPKC Mutants
0 2 4 6 8 10 12
0.0
0.1
0.2
0.3
0.4
0.5
0.6PKC WildtypesPKC Mutants
DAYS
EF
FIC
IEN
CY
RA
TIO
IMPULSIVITY TASK
Bowers and Wehner (2001) J.Neuroscience:
21: RC180 (1-5)
PKC Null mutants are impaired on withholdingresponses to receivethe sucrose reward
• What neurotransmittersystem mediates thisresponse? 5HT 2 a/c receptors???- Bowers
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SensitivityAnxiety
Risk takingBehavioral disinhibition
Increased alcohol consumption ???
PKC
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PERCENT ETHANOL
2 4 6 8 10 12
GR
/KG
0
2
4
6
8
10
12
14
16PKC MUTANT PKC WILDTYPE
FEMALE
ETHANOL CONSUMPTION IN PKC MICE
PERCENT ETHANOL
2 4 6 8 10 121
2
3
4
5
6
7
8MALE
PKC mutants consume more ethanol in a free- choice 2 bottle choice test
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SACCHARIN PREFERENCE
PERCENT SACCHARIN0.05 0.10 0.15 0.20
PR
EF
ER
EN
CE
RA
TIO
50
55
60
65
70
75
80
85
90
95
100
PKC MUTANTPKC WILDTYPE
NICOTINE CONSUMPTION
MICROGRAM/ ML0 20 40 60 80 100 120
MG
/KG
/24H
RS
0
2
4
6
8
10
There is no difference in saccharin and nicotine preference or consumption based on genotype
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Increased alcohol consumption
Sensitivity BehavioralDisinhibition
Anxiety,Risktaking
PKC
Mutation leads toreduced anxietyor increased risk taking
Mutation leads to reduced sensitivity
Mutation leads to increased impulsivity
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Conclusions about PKC
-PKC mutation has pleiotropic effects on phenotypes that may predispose individuals to greater risk of alcohol abuse
Translating these results to humans
• Are there human polymorphisms in the -PKC gene?
• Are they associated with any measures of risk for alcoholism or drug abuse?
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Gene structure of PRKCG:Location of SNPs Selected
6526bp 8958bp
1
3332bp 6072bp
2 3 1876 154 5 8 10119 141213
16 17
Drs. Marissa Ehringer• SNP association analyses on subjects from ColoradoAdolescent Drug Dependence Center
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Example 2:
• Collaborative work with Allan Collins, IBG
• The role of nicotinic receptors in mediating sensitivity to ethanol’s effects the startle response
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Background for study of nicotine and ethanol
on startle response• Most alcoholics are heavy smokers
• Common genes may influence sensitivity to nicotine and ethanol
• Startle response is a simple behavior that is altered by both ethanol and nicotine
• FH+ and FH- individuals differ in basal acoustic startle and after ethanol consumption
• Ethanol can modulate function of 42 nAChRs in vitro
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NEURONAL NICOTINIC RECEPTOR STRUCTURENEURONAL NICOTINIC RECEPTOR STRUCTURE
B.
Na+
Ca++
A.
Alpha 2, 3, 4, 5, 6, 7..9,10 Beta 2, 3, 4
42* highly expressed in Brain
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a2
In Situ Hybridization for nAChR Subunits from Michael Marks, CU
a3
a4
a5 a6 a7
b2 b3 b4
Sections approximately –1.8 mm Bregma
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Drawing from Dr. Karen Stevens
ACOUSTIC STARTLE
• Acoustic startle measured at 100-120 dB• Dose-response analyses for effects of nicotine and ethanol
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Multiple strategies to provide converging evidence
1. Long Sleep/Short Sleep mice
2. LS X SS Recombinant inbred strains 3. Nicotinic receptor mutants
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GAASLTESKPTGSPASLKTRPSQLPVSDQTSPCKCTCKEPSPVSPITVLKAGGTKAPPQHLP
GAASLTESKPTGSPASLKTRPSQLPVSDQASPCKCTCKEPSPVSPITVLKAGGTKAPPQHLP
Region of displayed sequence
Extracellular
Intracellular
4 Missense Mutation in LS X SS RI STRAINS
•LS and SS RI strains have a polymorphism at position 529
LS-like = ThreonineSS-like = Alanine
• Confers a change in receptor function
From: Dr. Jerry Stitzel, Institute for Behavioral Genetics
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Creation of LS X SSRecombinant
Inbred (RI) Strains
strain 1(LS)
strain 2(SS)
X
F1 X F2
20 generations ofbrother-sister matings
RI Strains
1 2 3 4 5 6 7 8 ….22
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100 110 120dB
• Strains containing the T529 variant were less sensitive to the effects of ethanol on acoustic startle.
• A/T polymorphism accounted for 56% of variation.
• Tritto et al. (2002) showed same relationship for nicotine’s effects
startle
• Suggests a role for 4-containing receptors in mediating the effects of ethanol on startle
• Animal models were needed to test this role of 4-containing receptors more directly.
Results in LSXSS Recombinant Inbreds
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Extracellular
IntracellularS
Leucine 9’ Serine Mutation: Gain of function mutation increases sensitivity to acetylcholine and nicotine
•In brain usually in heteromer as 42
•Acetycholine• Nicotine
• Do alcohol and nicotine have any common sites of
action?
Gain of Function Mutation in 4 Nicotinic Subunit
Labarca et al.PNAS: 98: 2786-2791, 2001
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2 Null Mutants
• Virtually all -containing nAChRs include the 2 subunit.
42 receptors are eliminated in 2 null mutants. • The 2 null mutants have reduced sensitivity to
nicotine on multiple measures.
Prediction: Gain of function mutants should be MORE
sensitive to ethanol Null mutants should be LESS sensitive to ethanol
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Ethanol Effects on Startle in 4 and 2 mice
• 4 L9’S Hetsare more sensitive to the effects of ethanol
• 2 mutants are less sensitive to the high-dose effects of ethanol
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Conclusions and Future Studies
• 42-containing receptors may play important roles in modulating the effects of ethanol and nicotine on acoustic startle response • Evaluate the A529T 4 subunit polymorphism using a knock-in mouse line Drs. Gregg Homanics (PITT) and Jerry Stitzel
(IBG)
Translating this to humans
Dr. Marissa Ehringer: examining nicotinic gene familyDr. Kent Hutchinson: 4 with startle response
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Alcoholism
Analyze phenotypes of interest in mice
Find genetic mouse modelsto suggest candidate genes
Human SNPanalysis
Association studies
New Animal Model with human SNP
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Contributors to the work
PKC WORK Nicotinic Work
Dr. Barbara Bowers Dr. Allan CollinsDr. Sheree Logue Dr. Jeremy OwensDenise Hix Dr. Seth Balogh Jill Miyamoto Jason Keller
Other CU labsDr. William Proctor (UCHSC)Dr. Marissa Ehringer Dr. Jerry Stitzel
Mutant linesDr. Asa Abeliovich Dr. Henry LesterDr. Susumu Tonegawa Dr. Marina Picciotto Dr. Robert Messing
FUNDED by NIAAA