2010. Vol.1, No.5, 367-369
Copyright © 2010 SciRes. DOI:10.4236/psych.2010.15045
Acquisition of Avoidance Responding in the Fmr1
Knockout Mouse
Maria G. Valdovinos1, Kelly Ippolito1, Lauren Nawrocki2, Greg Woods2,
Craige C. Wrenn3
1Department of Psychology, Drake University, Des Moines, USA;
2Neuroscience Program, Drake University, Des Moines, USA;
3Department of Pharmaceutical, Biomedical, and Administrative Sciences, Drake University,
Des Moines, USA.
Received August 26th, 2010; revised November 1st, 2010; accepted November 19th, 2010.
Fragile X Syndrome (FXS) is the most common inherited cause of mental retardation. Much work has been done
characterizing the behavioral phenotype of the animal model of FXS, the Fmr1 knockout mouse. However, very
little literature exists on knockout performance in the active avoidance task. This study evaluated if Fmr1
knockouts differed from wild type littermates in avoidance acquisition. Data revealed no difference in acquisi-
tion between knockouts and wild types.
Keywords: Fragile X Syndrome, Fmr1 Knockout, Active Avoidance
In fragile X syndrome (FXS), the most common inherited
cause of intellectual disability, a repeat of the trinucleotide
sequence CGG (> 200) in the promoter region of the FMR1
gene (located on the X chromosome) leads to a silencing of the
gene. FMR1 silencing results in a lack of fragile X mental re-
tardation protein (FMRP) production (Brown, 2002) and, in the
absence of FMRP, abnormal dendritic development occurs
involving an overgrowth of immature spines (Beckel-Mitchener
& Greenough, 2004; Irwin, Galvez, & Greenough, 2000). The
mechanism by which this occurs is unknown, but is hypothe-
sized to be attributed to enhanced mGluR activity (Bear, Huber,
& Warren, 2004). Since FXS is an X-linked disorder, it is more
common in males than females (Sherman, 2002). Males with
FXS present with specific physical and behavioral phenotypes.
Physically, males with FXS have long narrow faces, prominent
ears, macroorchidism, ophthalmologic problems, and unusual
growth patterns (initial rapid growth followed by a decline in
adolescence) (Hagerman, 2002). Behaviorally, males with FXS
present with hyperarousal and hyperactivity which is some-
times manifested in tantrums (Hagerman, 2002). Additionally,
individuals with FXS are also commonly diagnosed with aut-
ism (Dölen & Bear, 2009).
Research has also demonstrated that individuals with FXS
engage in a high degree of avoidance behavior. One proposed
explanation of this behavior has been the high degree of social
anxiety experienced by those with FXS which appears to mani-
fests itself in the form of social avoidance (e.g., withdrawal,
eye-gaze avoidance, self-injurious behavior (SIB), and aggres-
sion) (Kau, Reider, Payne, Meyer, & Freund, 2000). Indeed, in
a survey of psychotropic medication use among those diag-
nosed with FXS, Valdovinos and colleagues (2009) found that
approximately 36% of their sample were reported to engage in
aggressive behavior, 42% in refusals or opposition, 43% in SIB,
and 25% in withdrawal. These findings are significant as re-
search has demonstrated that in a majority of cases problem
behaviors such as aggression and SIB are maintained by nega-
tive reinforcement or escape from some noxious stimulus (e.g.,
demands, social interactions) (Iwata et al., 1994). Case in point,
in a survey of families with boys diagnosed with FXS, Symons
and colleagues (2003) found that a majority of their sample was
reported to engage or have engaged in self-injurious behavior
and that SIB was more likely to have occurred after the presen-
tation of a difficult demand suggesting an escape function.
Another possible explanation for avoidance behavior in those
diagnosed with FXS is that perhaps those with FXS experience
hyperarousal of the sympathetic nervous system in response to
stimuli (auditory, visual, and tactile) (Hagerman, 2002) as evi-
dence by increased cortisol reactivity (Hessl, Glaser, Dyer-
Friedman, & Reiss, 2006) and increased magnitude of electro-
dermal activity (Miller et al., 1999).
The Fmr1 knockout mouse has been demonstrated to be an
appropriate model for the human condition as similarities have
been observed in both physical and behavioral characteristics
(The Dutch Belgium Consortium, 1994). In assessments of
avoidance behavior in the knockout, data published have been
on the knockout’s performance on the passive avoidance test,
an assessment of learning and memory. Results of have not
revealed any differences between wild type and knockout per-
formance (The Dutch Belgium Consortium, 1994; Qin, Kang,
& Smith, 2005). However, limited data on the performance of
the Fmr1 knockout on the active avoidance test exist. The dif-
ference between these two tasks is that in one test, the ability to
associate one side of a cage (i .e., the dark side as opposed to
bright side) with shock is measured whereas with the other test,
the ability to associate a cue with the shock and subsequent
avoidance of the shock is measured.
Thus, with the human condition in mind, we assessed nega-
tively reinforced behavior in Fmr1 knockout (KO) and wild
type (WT) littermates using an active avoidance test. Given the
research on avoidance behavior in individuals with FXS, we
wanted to determine if the Fmr1 KO would show accelerated
acquisition of avoidance compared to their WT littermates.
Subjects for these experiments were the offspring (N = 10
KO; N = 13 WT) of five breeding pairs obtained from Dr.
James Malter’s lab at the University of Wisconsin Waisman
Center. The Fmr1 KO mice were originally developed by Wil-
liam Greenough (University of Illinois, Urbana, Illinois) and
backcrossed > 6 times to C57BL/6 mice. Breeding pairs con-
sisted of a female heterozygous for a null mutation in Fmr1
(McKinney, Grossman, Elisseou, & Greenough, 2005) and a
male wild type. Breeding in this manner produced male
offspring that were either wild type (WT) or hemizygous (Fmr1
KO) for the null mutation. All breeding was conducted at Drake
University and genotyping was performed by polymerase chain
reaction at the Waisman Center (Madison, WI). Mice were
weaned at 3 weeks of age, housed individually, maintained on a
light to dark schedule of 12/12 hours, and had ad lib access to
food and water. Principles of laboratory animal care (NIH
publication No. 86-23, revised 1985) were followed.
Mice were trained to actively avoid a mild footshock (0.5
mA, 2 sec) by moving between chambers in an automated two-
chambered shuttle box (San Diego Instruments, San Diego,
CA). An avoidance trial commenced with the onset of a cue
lamp. If the mouse failed to move into the other chamber during
cue lamp onset (maximum of 10 sec), footshock was adminis-
tered. If the mouse moved into the other chamber during cue
lamp onset, avoidance was recorded by the computer. Follow-
ing a 30-min acclimation period, mice were placed into a clean
activity monitor. Sessions consisted of 15 avoidance trials and
were conducted once a day for 10 days (Monday through Fri-
As shown in Figure 1 (l eft panel), avoidances increased with
training (two-way repeated measures ANOVA; main effect of
day, (F(9,21) = 34.05, p < 0.001). However, there was no sig-
nificant effect of genotype, (F(1, 21) = 0.19, p = 0.67) or inte-
raction between day and genotype (F(9, 189) = 0.76, p = 0.66).
The right panel of Figure 1 illustrates data for the number of
escape responses, which is the number of times mice crossed to
the dark side of the chamber once shock was delivered. Again,
there was a main effect of day (F(9, 21) = 27.76, p < 0.001) but
there was no effect of genotype (F(1, 21) = 2.14, p = 0.16) or
interaction between day and genotype (F(9, 189) = 1.28, p =
0.25). Figure 2 (left panel) shows the number of inter-trial in-
terval crosses for both Fmr1 KO and WT. As with the other
measures, there was a main effect of day (F(9,21) = 13.78, p <
0.001) but no effect of genotype (F(1, 21) = 0.72, p = 0.41) or
interaction between day and genotype (F(9, 189) = 1.39, p =
0.20). Finally, the right panel of Figure 2 depicts data for the
average latency of crossing after presentation of the cue light.
For each mouse on each day a latency score was calculated by
taking the mean latency of the 15 trials. Trials in which there
were no avoidances were assigned a latency of 10 sec. The data
points on the graph are group means of these latency scores.
Two-way repeated measures ANOVA revealed main effect of
day (F(9,21) = 28.88, p < 0.001) but not genotype (F(1, 21) =
0.32, p = 0.58) or interaction between day and genotype (F(9,
189) = 0.74, p = 0.68).
Based on the high degree of avoidance behavior observed in
individuals with FXS, we had hypothesized that the Fmr1 KO
mice would demonstrate a more rapid acquisition of avoidance
responding than their WT counterparts. These data, however,
demonstrate that Fmr1 KO do not have enhanced avoidance
learning which is similar to what was observed in the passive
avoidance test (The Dutch Belgium Consortium, 1994; Qin et al.,
2005). Performance on negatively reinforced behavior (lever
press) has also been evaluated in the Fmr1 KO (Brennan, Al-
beck, & Paylor, 2006). Researchers had found that although
WT mice were able to avoid shock delivery as the study pro-
gressed, the Fmr1 KO mice were not. It appeared that an ope-
rant avoidance task may not be the most appropriate paradigm
to study avoidance responding in the Fmr1 KO as the Fmr1 KO
never acquired the lever-pressing response. Our data suggest
that although the Fmr1 KO mouse is a valid model for many of
the behaviors often observed in those with FXS, with regards to
aversion of noxious stimuli, this mouse might not demonstrate
the heightened aversion often observed in individuals diag-
nosed with FXS. Further research should be conducted with
other behavioral tests to determine if heightened avoidance of
noxious stimuli is present in the Fmr1 KO model and thus con-
gruent with what is observed in humans with FXS.
Day of Training
0 1 2 3 4 5 6 7 8 910 11
Number of Avoidances
WT (n = 13)
Fmr1 KO (n = 10)
Day of Training
0 1 2 3 4 5 6 7 8 910 11
Number of Escapes
Figure 1.
Left Panel: Number of avoidance crossings for wild type (WT) (N = 13) versus Fmr1 knockout (KO) (N = 10) mice per day of active avoidance train-
ing. Right Panel: Number of shock escape crossings for WT versus Fmr1 KO mice per day of active avoidance training.
Day of Training
0 1 2 3 4 5 6 7 8 910 11
Number of Crosses
WT (n = 13)
Fmr1 KO (n = 10)
Day of training
0 12 34 56 78 910 11
Latency to avoid (s)
Figure 2.
Left Panel: Number of inter-trial interval (ITI) crossings for WT versus Fmr1 KO mice per day of active avoidance training. Righ t Panel: Mean la-
tency to cross into dark chamber after cue light presentation for WT versus Fmr1 KO mice per day of active avoidance training.
Ac knowledg ements
This research was supported by a Drake University Faculty
Research Grant and the Drake Undergraduate Science Colla-
borative Institute (DUSCI) Summer Research Fellowship Pro-
gram. We also wish to thank Cara Westmark and James Malter
at the University of Wisconsin Waisman Center for breeding
pairs and genotyping services. Correspondence concerning this
article should be addressed to Maria G. Valdovinos, Drake
University, Department of Psychology, 2507 University Ave,
Des Moines, IA 50312. (phone: 515-274-2847) (email: maria.
va ldo vinos@dra
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