Transcript Differences Among Inbred Rat Strains in Novelty Seeking

Differences Among Inbred Rat Strains in Novelty Seeking, Locomotor Activity and
Amphetamine Self-Administration
1,2
AC ,
1
ER ,
1,2
S ,
1,2
MT
Meyer
Dawahare
Rahman,
and Bardo
1Department of Psychology, University of Kentucky, Lexington, KY 40536
2Center for Drug Abuse Research Translation, Lexington, KY 40536
Results
Introduction
Number of Self-Infusions
Number of Self-Infusions
30
BUF N=8
30
25
F(10,70)=4.42, p<.001
25
F344 N=7
Strain-dependent differences in the dose effect function for amphetamine selfadministration were obtained.
Among inbred strains, there was no relation between locomotor activity in
inescapable novelty and amphetamine self-administration on the terminal FR5
schedule.
Among inbred strains, there was a relation between novelty preference and
amphetamine self-administration on the terminal FR5 schedule, suggesting a
genetic link between novelty seeking and drug abuse vulnerability.
ACKNOWLEDGMENTS
We acknowledge the expert consultation of Dr. John Crabbe. Research supported by USPHS grant
DA05312.
25
WKY N=5
30
F(10,40)=13.65, p<.001
25
F(10,30)=4.97, p<.001
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20
20
15
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15
10
10
10
10
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5
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0 1 2 3 4 5 6 7 8 9 10 11
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0 1 2 3 4 5 6 7 8 9 10 11
0
0 1 2 3 4 5 6 7 8 9 10 11
0
0 1 2 3 4 5 6 7 8 9 10 11
30
25
BN N=6
F(10,50)=6.40, p<.001
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SHR N=7
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LEW N=6
30
DSS N=9
25
F(10,60)=1.43, NS
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F(10,50)=10.43, p<.001
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F(10,80)=11.63, p<.001
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20
20
20
15
15
15
15
10
10
10
10
5
5
5
5
0
0 1 2 3 4 5 6 7 8 9 10 11
0
0
0 1 2 3 4 5 6 7 8 9 10 11 0 1 2 3 4 5 6 7 8 9 10 11
BD9 N=7
30
FH N=6
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WF N=5
30
WAG N=6
25
F(10,60)=.56, NS
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F(10,50)=4.86, p<.001
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F(10,40)=3.73, p<.001
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F(10,50)=3.95, p=.001
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20
20
20
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10
10
10
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5
5
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0 1 2 3 4 5 6 7 8 9 10 11
0
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0 1 2 3 4 5 6 7 8 9 10 11 0 1 2 3 4 5 6 7 8 9 10 11
FR1
FR1
20g
FR1
20g
Autoshaping
FR1
FR1
20g
Autoshaping
Among the inbred strains,
an ANOVA revealed a
significant interaction
between strain and
session, F(110,640) =
2.02, p<.001. Individual
strain main effects of
session were observed for
the following strains:
BUF, WKY, ACI, BN, LEW,
DSS, FH, WF and WAG,
p<.05.
0
0 1 2 3 4 5 6 7 8 9 10 11
30
Autoshaping
Figure 2. Strain
Differences in
Acquisition of
Amphetamine SelfAdministration During
the Autoshaping
Phase.
ACI N=4
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0
0 1 2 3 4 5 6 7 8 9 10 11
FR1
FR1
FR1
20g
Autoshaping
Sessions
Phase 2: Incremental FR Training
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BUF N=6
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F344 =7
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WKY N=5
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0
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FR1
FR2
FR3
FR4
FR5
BN N=6
0
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FR1
FR2
FR3
FR4
0
FR5
SHR N=4
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FR1
FR2
FR3
FR4
0
FR5
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LEW N=5
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20
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20
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10
10
10
10
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5
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5
0
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FR1
FR2
FR3
FR4
FR5
BD9 N=6
0
25
FR1
FR2
FR3
FR4
0
FR5
25
FH N=5
F(4,16)=3.10, p<.05
FR1
FR2
FR3
FR4
0
FR5
WF N=5
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10
10
10
10
5
5
5
5
FR4
FR5
0
FR1
FR2
FR3
FR4
FR4
FR5
DSS N=6
FR1
FR2
FR3
FR4
An ANOVA revealed a
significant interaction
between strain and FR
value, F(44,212) = 1.52,
p<.03.
FR5
F(4,20)=4.85, p<.01
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FR3
FR3
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FR2
FR2
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FR1
FR1
WAG N=6
20
0
Figure 3. Strain
Differences Across
Incrementing FR
Values in
Amphetamine SelfAdministration.
ACI N=4
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20
0
FR5
FR1
FR2
FR3
FR4
0
FR5
FR1
FR2
FR3
FR4
FR5
FR Value
Phase 3: Dose Response
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BUF N=5
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F344 N=6
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WKY N=5
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0
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.01
.1
BN N=6
0
40
F(4,20)=1.38, NS
.001
.01
0
.1
SHR N=4
40
.001
.01
0
.1
LEW N=4
40
F(4,12)=2.37, NS
F(4,12)=5.14, p<.05
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30
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10
10
10
40
.001
.01
.1
BD9 N=6
0
40
F(4,20)=0.93, NS
.001
.01
0
.1
FH N=3
40
F(4,8)=3.41, NS
.001
.01
0
.1
WF N=4
40
F(4,12)=2.27, NS
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.1
0
.001
.01
0
.1
.001
.001
.01
.1
An ANOVA revealed a
significant interaction
between strain and dose,
F(44,180) = 2.56, p<.001.
Individual strain main
effects of dose were
observed for the following
strains: BUF, SHR, and
DSS, p<.05.
DSS N=5
.001
.01
.1
WAG N=5
F(4,16)=1.89, NS
30
.001
Figure 4. Strain
Differences Across
Varying Doses of
Amphetamine.
F(4,16)=9.21, p<.001
30
0
ACI N=4
F(4,12)=2.25, NS
F(4,16)=3.37, NS
F(4,20)=1.42, NS
F(4,16)=6.04, p<.01
.01
.1
0
.001
.01
.1
Dose (mg/kg/infusion)
A.
B.
Activity vs. Amphetamine Self-Administration
Novelty Preference vs. Amphetamine Self-Administration
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Number of Self-Infusions
For most strains, the number of amphetamine infusions earned was similar across
gradually increasing FR values, suggesting that intake was regulated for each
strain.
30
F(10,60)=.46, NS
Conclusions
Significant differences in locomotor activity, novelty preference and amphetamine
self-administration were obtained across different inbred rat strains, indicating a
genetic influence for each of these behaviors.
An ANOVA revealed a significant main effect of
autoshaping session, F(10,100) = 8.516, p<.001.
Phase 1: Autoshaping
0
Reliable acquisition of amphetamine self-administration was obtained using an
autoshaping procedure in outbred Sprague-Dawley rats.
Figure 1. Acquisition of Amphetamine SelfAdministration using an Autoshaping Procedure
in Sprague-Dawley Rats.
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WKY
r=-0.056
NS
12
DSS
Number of Self-Infusions
Subjects. Male Sprague-Dawley (SD) outbred rats and male rats from the following
inbred strains were used: ACI; BDIX (BD9); Brown Norway (BN); Buffalo (Buf); Dahl salt
sensitive (DSS); Fawn Hooded (FH); Fischer (F344); Lewis (LEW); Spontaneous hypertensive
rat (SHR); Wistar Albino Glaxo (WAG); Wistar Furth (WF); Wistar Kyoto (WKY). Rats were
housed individually with ad libitum access to food (except as noted) and water in the home
cage, which was maintained in a colony room on a 12-hr/12-hr light/dark cycle.
Drugs. d-Amphetamine sulfate (Sigma; St. Louis, MO) was prepared in 0.9% NaCl
(saline).
Apparatus. Locomotor activity was recorded using an automated monitoring system
with Versamax System software (AccuScan Instruments Inc., Columbus, OH). Activity was
measured as photobeam interruptions, expressed as total distance traveled (cm). Novelty
place preference was measured using an automated conditioned place preference chamber
(ENV-013, Med Associates, St. Albans, VT) consisting of three distinct compartments. Each
chamber was interfaced to a personal computer running MED-PC IV (Med Associates)
software. Amphetamine self-administration was assessed in an operant conditioning chamber
(ENV-001, Med Associates St. Albans, VT) that was enclosed in a sound attenuating
compartment. Located on the front panel of the chamber was a 5 x 4.2 cm opening that
allowed access to a recessed food tray. Two metal response levers on either side of the food
tray were located 7.3 cm above a metal-grid floor. A white cue light was centered above each
response lever. A white house light was centered 20.3 cm above the metal-grid floor on the
wall opposite the response levers. Drug infusions were delivered via a syringe pump. A watertight swivel allowed attachment of the catheter tubing from a 10-ml syringe to the head mount
of the rat within the chamber.
Individual Difference Tests. To assess activity in inescapable novelty, rats were
placed individually in the locomotor apparatus for 30 min. Total distance traveled was
recorded in 5-minute intervals and summed for total distance traveled over the entire 30 min.
On the next day, rats were assessed for novelty place preference. Animals were habituated to
either the black or white compartment (counterbalanced) for 30-min sessions on two
consecutive days. On the following day, animals were placed in the center gray compartment
with access to both the black and white compartments. Time spent in both the black and
white compartments was monitored for 15 min. The percentage of time spent in the novel
compartment was then calculated as the duration in the novel compartment, divided by the
sum of the duration in both the novel and familiar compartments.
Amphetamine Self-administration. Animals were surgically implanted with a
chronic indwelling jugular catheter under anesthesia. Following recovery from surgery, phase
1 began.
Phase 1: Autoshaping. Acquisition of amphetamine self-administration
began using an autoshaping procedure while animals were food restricted (20 g/day). For 5
consecutive days, rats were given a 60-min autoshaping session, followed 30 min later by a
60-min contingent amphetamine self-administration session. During the autoshaping session,
the house light was on and the inactive lever (no programmed consequence) was extended.
For the first 15-min of each autoshaping session, the active lever was extended 10 times at
random intervals and remained extended for 10 sec. If the lever was pressed, a 0.1 mg/kg
infusion of amphetamine was delivered immediately; if the lever was not pressed during the
10-sec extension, a non-contingent infusion of amphetamine was delivered when the lever
retracted. For the remaining 45 min, only the inactive lever was extended. For the contingent
amphetamine self-administration session, both levers were extended and 0.1 mg/kg infusions
of amphetamine were contingent using a FR1/20-sec signaled time out schedule of
reinforcement; during the 20-sec time out interval, both cue lights above the levers were
illuminated and responding was not reinforced. Following the 5 days of autoshaping, rats
underwent 3 more days of 60-min contingent self-administration sessions under food
restriction. Rats were then placed on free feed and phase 2 began.
Phase 2: Incremented FR Schedule. Self-administration continued with the
schedule of reinforcement being incremented from FR1 to FR5, with rats spending 3 days on
each FR value.
Phase 3: Dose Response. Following phase 2, rats then spent 3 consecutive
days on the FR5 at each of the following doses, assessed in descending dose order: 0.056
mg/kg/infusion, 0.03 mg/kg/infusion, 0.01 mg/kg/infusion, and 0.001 mg/kg/infusion.
35 SD N=11
30 F(10,100)=8.52, p<.001
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20
15
10
5
0
0 1 2 3 4 5 6 7 8 9 1011
Sessions
Number of Self-Infusions
Methods
Phase 1: Autoshaping
Number of Self-Infusions
There is now considerable evidence to support a relationship
between individual differences in response to inescapable novelty and
response to stimulant drugs of abuse. Rats categorized as high
responders (HR) self-administer more amphetamine than rats categorized
as low responders (LR; Piazza et al., 1989). While these individual
differences may represent heritable traits, the majority of this evidence has
been derived from experiments using outbred rats (Exner and Clark, 1993;
Gingras and Cools, 1997; Higgins et al., 1994; Hooks et al., 1991; 1992;
Piazza et al., 1989) or using only two inbred strains (Camp et al., 1994;
Kosten et al., 1997). More recently, individual differences in novelty
seeking have been found to also predict response to stimulant drugs.
These latter studies have found that novelty seeking predicts
amphetamine self-administration, with high novelty seekers showing
greater amphetamine self-administration than low novelty seekers (Cain et
al., 2004; 2005). However, these studies also only used rats from an
outbred population.
The purpose of the present experiment was to determine if the
relationship between these predictor and outcome variables is, at least in
part, genetically based. An initial experiment was conducted using outbred
male Sprague-Dawley rats to establish that reliable acquisition of
amphetamine self-administration could be obtained using an autoshaping
procedure. Then, rats from 12 inbred rat strains were screened for their
response to both escapable and inescapable novelty, and assessed for
acquisition of amphetamine self-administration. The various available
strains chosen offered a diversity of characterized phenotypes (traits)
which were useful in analyzing the critical determinants of novelty-seeking
behavior. By holding environmental factors constant in this experiment,
interstrain differences in behavioral responses to amphetamine may be
attributed to differences in the genotype between strains.
SHR
WAG
10
ACI
8
BUF
LEW
6
4
FH
BN
WF
F344
2
BD9
0
0
1000
2000
3000
4000
Distance Traveled (cm)
5000
6000
12
DSS
r=0.601
p <0.05
WKY
SHR
WAG
ACI
10
8
BUF
LEW
6
4
BN
F344
2
0
0.40
FH
WF
BD9
0.45
0.50
0.55
0.60
0.65
0.70
Preference Ratio
Figure 5. Strain Differences in Activity and Novelty Preference as Predictors of Amphetamine Self-Administration
A. Points for each individual strain based on their average locomotor activity and average number of amphetamine infusions on
the FR5 schedule. No significant correlation was obtained.
B. Points for each individual strain based on their average novelty preference and average number of amphetamine infusions on
the FR5 schedule. A significant correlation was found between novelty preference and amphetamine infusions on the FR5, r =
0.601, p < .05.