 |
 Previous Article | Next Article 
The Journal of Neuroscience, September 15, 1998, 18(18):7452-7461
Relationship between Fos Production and Classical Fear
Conditioning: Effects of Novelty, Latent Inhibition, and Unconditioned
Stimulus Preexposure
Jelena
Radulovic,
Jens
Kammermeier, and
Joachim
Spiess
Max Planck Institute for Experimental Medicine, Department for
Molecular Neuroendocrinology, 37075 Goettingen, Germany
 |
ABSTRACT |
The relationship between FOS production in the sensory cortex and
limbic system and the ability of C57BL/6N mice to acquire context- and
tone-dependent freezing were investigated after fear conditioning,
which was achieved by exposure of mice to context only or context and
tone (10 kHz, 75 dB) as conditioned stimuli (Cs) paired with an
electric footshock (0.7 mA, constant) as unconditioned stimulus (Us).
The effect of preexposure to Cs or Cs paired with Us on FOS production
and learning was also tested. It was demonstrated that high
simultaneous FOS production in the parietal cortex, hippocampus, and
amygdala paralleled the ability of mice to acquire strong freezing
responses to novel Cs. After contextual preexposure (latent
inhibition), FOS production could be elicited in the central amygdala
only by shock and in the basolateral amygdala only by tone. Under these
conditions, the ability of mice to acquire contextual freezing
was almost abolished, whereas tone-dependent freezing was reduced.
Lacking FOS production in the central amygdala after preexposure to
context followed by shock (Us preexposure effect) paralleled the
inability of mice to acquire tone-dependent freezing, although the tone
elicited FOS production in the basolateral amygdala. On the basis of
these findings it was concluded that synchronous Cs- and Us-induced FOS
production in several defined forebrain areas was accompanied with
associative learning of novel stimuli, and that a subsequent low level
of FOS production might have been responsible or indicative for delayed
conditioning to those stimuli.
Key words:
fear conditioning; latent inhibition; Us preexposure; FOS; amygdala; hippocampus; parietal cortex; mice; C57BL/6N
| |
INTRODUCTION |
Context- and tone-dependent fear
conditioning may be rapidly induced in rodents after exposure to novel
conditioned (Cs) and unconditioned (Us) stimuli (Blanchard and
Blanchard, 1969 ; Bolles and Collier, 1976). However, fear conditioning
may be markedly delayed by nonreinforced presentation of phasic and
contextual stimuli when the same stimuli are subsequently presented
with a Us, a phenomenon described as latent inhibition. Similarly, preexposure to a Us in a defined context markedly reduces its reinforcing strength when the same Us is later presented with a Cs
(Baker and Mackintosh, 1979).
We have reported previously that C57BL/6N mice acquire a strong
freezing response after context- and tone-dependent fear conditioning performed in a single trial (Stiedl and Spiess, 1997; Radulovic et al.,
1998). This paradigm was demonstrated to be advantageous in studying
the molecular changes in the brain during learning because molecular
events can be monitored during a defined time course of memory
formation, repeated exposures to Cs and Us are avoided, and the effects
of Cs and Us can be dissociated. By using FOS protein as a marker of
neuronal activity (Sagar et al., 1988), we have demonstrated that FOS
production in several forebrain areas is linked to acquisition of
foreground contextual fear conditioning (Milanovic et al.,
1998). Recent investigations of synaptogenesis in FOS-producing
neurons (Kleim et al., 1996) and the use of FOS antisense
oligonucleotides (Mileusnic et al., 1996; Swank et al., 1996) provided
evidence that induction of c-fos may represent a necessary step
toward the formation of long-term memory. However, in our experiments
FOS production did not correlate with the fear response after the
memory test because of a marked reduction of FOS production that was
observed in conditioned and control animals. In agreement with this
observation, Campeau et al. (1997) demonstrated that c-fos expression
in the hippocampus and amygdala of fear-conditioned and control rats
did not differ. These results were in agreement with the finding that
c-fos was downregulated after repeated exposure to the same stimuli
(Papa et al., 1993; Chen and Herbert, 1995; Hess et al., 1995), but
contrasted with observations that FOS production is increased after
reexposure to a Cs (Campeau et al., 1991; Pezzone et al., 1992; Smith
et al., 1992; Beck and Fibiger, 1995).
To obtain additional information on the significance of FOS production
for acquisition of conditioned fear, we have investigated the FOS
production and behavior of mice after context- and tone-dependent fear
conditioning induced by a single training trial. In addition, the
relationship between FOS levels and acquisition of conditioned fear was
studied in mice preexposed to context or to context and shock before
conditioning. This habituation to context or context paired with shock
was performed by monitoring FOS production to determine the brain
structures activated by individual Cs and Us as well as the degree of
convergence of Cs and Us within a particular forebrain area.
| |
MATERIALS AND METHODS |
Animals. Eight-week-old male inbred C57BL/6N mice,
obtained from Charles River (Sultzfeld, Germany), were used in the
experiments. The mice were individually housed in macrolon cages
according to the recommendations of the Society for Laboratory Animal
Science (Germany). Standard pelleted diet and water were offered
ad libitum. Mice were kept in mouse "hotels" 5 d
before the beginning of the experiments. The mouse hotel and the entire
fear-conditioning equipment were located in the same room to prevent
exposure to novelty and transport of mice after the training or before
the testing trials. The mouse hotel was located within a soundproof, nontransparent wooden enclosure equipped with its own air exchange system (air exchange, 60 m3/hr). In the mouse
hotels, the temperature was maintained at 22 ± 1°C, the
humidity was kept at 55 ± 10%, and the 12 hr light/dark cycle
was 7 A.M. to 7 P.M.
Apparatus. As described previously ( Radulovic et al., 1998;
Stiedl and Spiess, 1997), the experiments were performed by a computerized fear-conditioning system purchased from TSE (Bad Homburg,
Germany). The computer was connected to a control unit containing a
shock and a tone generator. Training took place in an apparatus
consisting of a box [58 cm (length) × 30 cm (width) × 27 cm
(height)] with a gray interior and a 12 V light at the ceiling.
The conditioning and preexposure context consisted of a plexiglass
chamber [35 cm (length) × 20 cm (width) × 20 cm (height)] placed on
a removable shock grid made of stainless steel rods (diameter 4 mm;
bars spaced 0.9 cm apart). The shock grid was connected to a
shocker-scrambler unit delivering shocks of defined duration and
intensity. The shock grid, the floor below the shock grid, and the
chamber were cleaned with 70% aqueous ethanol before each individual
mouse entered the chamber.
The pulsed auditory signal (five counts per second, 10 kHz, 75 dB sound
pressure level) was presented for 30 sec by a high-frequency loudspeaker (Conrad, KT-25-DT).
The shock (0.7 mA, 2 sec, constant) was delivered through a stainless
steel floor grid.
The novel context consisted of a Plexiglas chamber [35 cm (length) × 20 cm (width) × 20 cm (height)] that was exposed to 20 V light, did
not have a rod floor, and was divided in half by inserting a clear
plastic panel connecting the diagonal corners. The chamber was washed
with 1% acetic acid before each individual mouse entered the
chamber.
Fear conditioning. Nine experimental groups of mice
were used in the experiments (Fig. 1).
Three groups were set up for the preexposure procedures. Nonpreexposed
mice (N) were habituated to handling and to the environmental stimuli
of the experimental room for 3 min/d for 6 consecutive d. Two other
groups of mice were preexposed either 3 min to the context (C) or 3 min
to the context and a 2 sec shock (Cs) and then habituated as described above for 5 consecutive d. The habituation procedure was introduced to
completely familiarize the mice with the stimuli of the experimental room and thus prevent any interference of uncontrolled novel stimuli during the experiments. In addition, this procedure markedly reduced generalization of fear response to stimuli other than the Cs in mice of
the Cs preexposure group.
On the training day, the N, C, and Cs preexposed mice were subjected to
three additional training conditions. Mice of each group were exposed
for 3 min to the context (N/C, C/C, and Cs/C groups), or 3 min context
followed by a 2 sec shock (N/Cs, C/Cs, and Cs/Cs groups), or 3 min
context, 30 sec tone, and 2 sec shock (N/CTS, C/CTS, and Cs/CTS
groups). All preexposure and training procedures took place in the same
context.
The contextual memory test was performed 24 hr after the training so
that 12 mice of each experimental group were placed in the
preexposure/conditioning context for 3 min. The tone-dependent memory
test was performed 2 hr later, by exposure of the same mice to a novel
context (3 min) followed by the tone used for conditioning (3 min).
Freezing, defined as the lack of movement except for respiration and
heart beat, was assessed every 10 sec over 18 intervals by a trained
observer who was unaware of the experimental design. The data were
converted to the percentage of samples scored as freezing.
FOS immunohistochemistry. One hour after the training, six
mice of each group and four naive mice were anesthetized with ketamine (130 mg/gm body weight) and xylasine (13 mg/gm body weight) in saline
(0.01 ml/gm, i.p.) and then transcardially perfused with ice-cold
phosphate buffer (0.1 M), pH 7.4, followed by 4%
paraformaldehyde in phosphate buffer, pH 7.4 (150 ml/mouse). Brains
were post-fixed for 48 hr in the same fixative and then immersed for 24 hr each in 10, 20, and 30% sucrose in PBS. After the tissue was
frozen by liquid nitrogen, 50-µm-thick coronal sections were cut on
the cryostat. Every fifth section was collected, starting from the olfactory bulb to the end of the hippocampus. Twelve-well plates (Corning, Corning, NY) were used for performing immunocytochemical staining of free-floating sections as described previously (Milanovic et al., 1998). After elimination of endogenous peroxidase activity by
1% H2O2 in methanol for 15 min, the sections
were saturated with 5% goat serum and 0.3% Triton X-100 in 0.01 M PBS, and then incubated with rabbit anti-FOS antibody
(Oncogene Science), 1:20,000 dilution for 48 hr at +4°C.
Subsequently, the sections were washed and incubated at room
temperature with biotinylated goat anti-rabbit antibody followed by the
ABC complex (Vector ABC kit, Vector Laboratories, Burlingame, CA). For
visualization, DAB was used as chromogen (Sigma fast tablet set). The
sections were mounted, dehydrated, and coverslipped with Eukitt. The
specificity of immunostaining was confirmed on sections that were
incubated with FOS antibody preabsorbed overnight at +4°C with
appropriate synthetic antigenic peptide in tenfold excess over the
amount of antibody (Oncogene Science).
Quantification and data analysis. All sections from the
olfactory bulb to the end of the hippocampus were analyzed
qualitatively. FOS-positive cells were counted in selected forebrain
areas with a Macintosh-based image analysis system (NIH Image), as
described previously (Pomonis et al., 1997). Nuclei were counted
individually and expressed as number of FOS-positive nuclei per 0.1 mm2. The anteroposterior (AP) coordinates of
sections (Franklin and Paxinos, 1997) included for detailed analysis
were as follows: AP  1.22, medial nucleus of the amygdala; AP 1.34
central, cortical, and basolateral nucleus of the amygdala, CA1 region
of the hippocampus and parietal (somatosensory) cortex. The counting
was performed in an area of the same shape and size for each brain
region. Statistical analysis of behavioral and immunohistochemical data
were performed by ANOVA with preexposure and training as a group factor
followed by the Bonferonni-Dunn test for post hoc
comparisons. The results are presented as mean ± SE.
| |
RESULTS |
FOS production after training and behavior during the memory test
of nonpreexposed mice
After the training, FOS production of all nonpreexposed mice (N/C,
N/Cs, and N/CTS groups) was observed throughout numerous cortical,
limbic, diencephalic, and mesencephalic areas. Exposure to context only
(N/C group) significantly increased FOS production in the basolateral
nucleus of the amygdala (t(1,8) = 10.55, p < 0.001), hippocampus (t(1,8) = 6.84, p < 0.001), and parietal cortex
(t(1,8) = 10.64, p < 0.001), in
comparison with naive mice. Statistically significant group differences
were determined within the central and basolateral nuclei of the
amygdala (Figs. 2A, 3). In the central nucleus of the
amygdala, mice of the N/Cs and N/CTS groups produced significantly more
FOS (F(8,45) = 19.824, p < 0.001) than mice of the N/C group. In mice of the N/CTS group, the
number of FOS-positive nuclei in the basolateral amygdala was
significantly higher (F(8,45) = 49.210, p < 0.001) when compared with the mice of the N/C and
N/Cs groups (Figs. 2A, 3). In the other forebrain
areas examined for FOS production, no group differences were detected.
It should be mentioned, however, that FOS production was also detected
in numerous auditory areas, such as the inferior colliculus, medial
geniculate nucleus, and auditory cortex of the N/CTS group. In
additional experiments with mice exposed to context and tone without
shock (data not presented), similar results were observed, except for
the central amygdala, which showed FOS production on a low or
undetectable level.
View larger version (34K):
[in this window]
[in a new window]
|
Figure 2.
A, Fos production in the
forebrain of N/C, N/Cs, and N/CTS groups 1 hr after training. Data
represent mean ± SE of six mice/group. B, Freezing
behavior of the N/C, N/Cs, and N/CTS groups during the context- and
tone-dependent memory test 24 hr after the training. Data represent
mean ± SE of 12 mice/group. Statistically significant
differences: *p < 0.01.
|
|
View larger version (137K):
[in this window]
[in a new window]
|
Figure 3.
FOS production in the central amygdala
(A), basolateral amygdala
(B), hippocampus (C), and
parietal cortex (D) of N/C, N/Cs, and N/CTS
groups. Scale bar, 50 µm.
|
|
During the memory test, mice of the N/C group did not exhibit freezing
behavior. Mice of the N/Cs group had high freezing levels during the
context-dependent but not tone-dependent memory test, whereas mice of
the N/CTS group responded with freezing during the context-dependent as
well as the tone-dependent memory test (Fig. 2B).
FOS production after training and behavior during the memory test
of mice preexposed to context
FOS production in the C/C group of mice (Figs.
4A,
5) was significantly decreased in all
tested areas (p < 0.001) when compared with the
N/C group (Fig. 2A, Table
1). The observed values were similar to
those found in naive mice (data not shown).
View larger version (27K):
[in this window]
[in a new window]
|
Figure 4.
A, Fos production in the forebrain
of of C/C, C/Cs, and C/CTS groups 1 hr after training. Data represent
mean ± SE of six mice/group. B, Freezing behavior
of C/C, C/Cs, and C/CTS groups during the context- and tone-dependent
memory test 24 hr after the training. Data represent mean ± SE of
12 mice/group. Statistically significant differences:
*p < 0.01.
|
|
View larger version (140K):
[in this window]
[in a new window]
|
Figure 5.
FOS production in the central amygdala
(A), basolateral amygdala
(B), hippocampus (C), and
parietal cortex (D) of C/C, C/Cs, and C/CTS
groups. Scale bar, 50 µm.
|
|
View this table:
[in this window]
[in a new window]
|
Table 1.
Significant differences in FOS production of groups
subjected to the same training but different preexposure conditions
|
|
In mice of the C/Cs group, FOS production was induced only in the
central nucleus of the amygdala (Figs. 4A, 5) when
compared with the C/C group (p < 0.001).
However, the number of FOS-positive nuclei in this area was
significantly lower than in the N/Cs (p < 0.05)
or N/CTS group (p < 0.05) (Table 1).
In the C/CTS group, in comparison with the C/C and C/Cs groups, the
number of FOS-positive nuclei was significantly higher in the
basolateral (p < 0.001) and central
(p < 0.01) nuclei of the amygdala (Figs.
4A, 5). In those areas, FOS production did not differ
from that of the N/CTS group. However, in all other brain areas, such
as the hippocampus (p < 0.001), parietal cortex (p < 0.001), medial amygdala
(p < 0.001), and cortical amygdala (p < 0.001), the FOS levels were significantly
lower than the FOS production of the N/CTS group.
Mice preexposed to context differed significantly from nonpreexposed
mice in their ability to acquire context- and tone-dependent conditioned fear (F(8,99) = 419.629, p < 0.001). Mice of the C/Cs and C/CTS groups
exhibited low freezing levels during the contextual memory test (Fig.
4B). The mice of the C/CTS group showed increased freezing during the tone-dependent memory test (Fig.
4B), but the freezing scores were significantly lower
than those of the N/CTS mice subjected to the same training
(p < 0.001).
FOS production after the training and behavior during the memory
test of mice preexposed to context followed by shock
Cs preexposure of mice (Figs.
6A,
7) resulted in a significantly lower FOS
production in all brain structures of the Cs/C and Cs/Cs groups
(p < 0.001) when compared with the N/C and N/Cs groups (Table 1). In addition, mice of the Cs/Cs group had
significantly lower (p < 0.01) FOS levels in
the central nucleus of the amygdala than mice of the C/Cs group (Figs.
4A, 5, 6A, 7). In mice of the Cs/CTS group, significantly higher FOS production
(p < 0.001) was detected only in the
basolateral nucleus of the amygdala when compared with the Cs/C and
Cs/Cs groups (Figs. 6A, 7). In this anatomical
structure, FOS production of the Cs/CTS group did not differ
(p = 0.403) from the N/CTS group (Figs.
2A, 3, 4A, 5; Table 1), but in all
other brain areas it was significantly lower (p < 0.001). Similar results were obtained in additional experiments with
mice preexposed to context and reexposed to context and tone (data not
shown).
View larger version (26K):
[in this window]
[in a new window]
|
Figure 6.
A, Fos production in the
forebrain of of Cs/C, Cs/Cs, and Cs/CTS groups 1 hr after training.
Data represent mean ± SE of six mice/group. B,
Freezing behavior of Cs/C, Cs/Cs, and Cs/CTS groups during the context-
and tone-dependent memory test 24 hr after the training. Data represent
mean ± SE of 12 mice/group. Statistically significant
differences: *p < 0.01.
|
|
View larger version (143K):
[in this window]
[in a new window]
|
Figure 7.
FOS production in the central amygdala
(A), basolateral amygdala
(B), hippocampus (C), and
parietal cortex (D) of Cs/C, Cs/Cs, and Cs/CTS
groups. Scale bar, 50 µm.
|
|
Mice of the Cs/Cs and Cs/CTS groups acquired a strong context-dependent
fear response that did not differ from the response of the N/Cs and
N/CTS groups. However, tone-dependent conditioned fear was
significantly reduced (F(8,99) = 419.629, p < 0.001) in the Cs/CTS group (Fig.
6B) when compared with the N/CTS and C/CTS
groups.
| |
DISCUsSION |
Widespread FOS production of nonpreexposed mice was observed in
numerous brain areas, including the nuclei of the amygdala, hippocampus, and parietal cortex, in agreement with previous mapping studies (Handa et al., 1993; Papa et al., 1993). These data were interpreted as the response of animals to novel environmental stimuli.
The observed differences between the N/C, N/Cs, and N/CTS groups
confirmed and extended our previous results (Milanovic et al., 1998)
indicating that the shock used as a Us in the N/Cs and N/CTS groups
elicited marked FOS production in the central nucleus of the amygdala,
whereas exposure to a tone as a novel Cs in the N/CTS group resulted in
high FOS levels in the basolateral nucleus of the amygdala.
Repeated exposure of mice to the same Cs (C/C group) or Cs/Us (Cs/Cs
group) resulted in a significant decrease of FOS levels and thus
demonstrated that reduction of FOS production occurred after
nonassociative as well as associative learning and that it was not
affected by the emotional state of the mice as suggested previously
(Sandner et al., 1993). These results contrasted with the observation
that conditioned fear elicits c-fos mRNA and FOS production in the
limbic system on reexposure of mice to a Cs (Campeau et al., 1991;
Pezzone et al., 1992; Smith et al., 1992; Beck and Fibiger, 1995). It
is difficult to explain the observed discrepancy. On the basis of our
own experience, novel stimuli accidentally used before the training may
have to be considered. We were only able to prevent this type of
interference by extensive habituation of the mice to the training
environment, the experimenter, and the lack of any transport before
handling. Our results also contrasted with the observation that
specific brain areas express c-fos mRNA after learning in instrumental
paradigms (Castro Alamancos et al., 1992; Bertaina and Destrade, 1995;
Hess et al., 1995; Kleim et al., 1996). This discrepancy may be
attributable to the differences between classical and operant
conditioning and primarily attributable to the fact that animals do not
need to perform a particular task during classical conditioning.
The data obtained from the preexposure experiments provided further
evidence that novelty represented the major factor triggering FOS
production. Therefore, it was possible to analyze the brain areas
activated by individual novel Cs and Us. The results demonstrated that
the strongest FOS production was observed after exposure of mice to
novel contextual stimuli (N/C group), resulting in high FOS levels in
the parietal cortex, the hippocampus, and all nuclei of the amygdala
except for the central nucleus. When shock was introduced as a novel
stimulus (C/Cs group), FOS production was induced only in the central
nucleus of the amygdala, whereas exposure to a tone as a novel stimulus
(Cs/CTS group) resulted in FOS production in the basolateral nucleus.
These results indicated that the shock does not converge with the
contextual and auditory stimuli within the cortical, hippocampal, and
amygdaloid brain areas. In contrast, Cs/Us convergence at the
hippocampal level was demonstrated during trace conditioning of the
eyeblink response with the finding that both Us and Cs altered the
neural activity of the CA1 hippocampal area (Mcechron and
Disterhoft, 1997). The observed discrepancy may be attributable to
different neural pathways mediating conditioned fear and conditioned
eyeblink responses.
Although FOS production in the central nucleus of the amygdala was
induced only by shock (C/Cs group) and not by context or tone, the FOS
level within this nucleus was significantly enhanced when shock used as
a novel Us was paired with novel contextual (N/Cs group) or auditory
(C/CTS group) stimuli. It appears therefore that brain areas activated
by a novel Cs have the capacity to facilitate the responsiveness
of the central amygdala to a Us paired with the Cs. This interaction
seems to occur only when both the Cs and Us are novel, because in the
Cs/CTS group of mice, which were twice exposed to context and shock,
the novel tone could not enhance FOS production in the central
amygdala.
The contextual and auditory Cs used in the present experiments mainly
elicited FOS production in different forebrain areas. An exception was
the basolateral nucleus of the amygdala, where both Cs induced FOS.
Although the highest FOS level in this area was found when novel
contextual and auditory stimuli were applied simultaneously (N/CTS
group), each Cs applied individually (N/C and Cs/CTS groups) also
elicited FOS production, thereby suggesting that contextual and phasic
Cs converge within the basolateral amygdala. This result is consistent
with the finding that the basolateral amygdala (Kim and Fanselow, 1992)
is required for both context- and tone-dependent fear conditioning.
The series of behavioral studies performed after different preexposure
conditions strongly suggested a relationship between FOS production
after the training and the learning efficiency monitored during the
memory test. High FOS levels detected throughout the forebrain of
nonpreexposed mice paralleled their ability to acquire strong
contextual (N/Cs and N/CTS groups) and tone-dependent freezing (N/CTS
group). These findings are in agreement with results pointing to
significant roles of the amygdala (Helmstetter, 1992; Kim and Fanselow,
1992; Fanselow et al., 1994), hippocampus (Kim and Fanselow, 1992;
Phillips and LeDoux, 1992; Chen et al., 1996), and parietal cortex
(Thinus et al., 1996) in acquisition of context- and tone-dependent
freezing as well as of other autonomic responses reflecting fear
(Roozendaal et al., 1991). Accordingly, C and Cs preexposure
resulted in reduction of FOS production in certain forebrain areas as
well as in impaired acquisition of conditioned fear.
Significant decrease of contextual freezing of the C/Cs and C/CTS
groups paralleled the low FOS level in the hippocampus, parietal
cortex, and cortical and medial nuclei of the amygdala. Thus it
appeared that activation of the central amygdala elicited by the Us
after contextual preexposure was not sufficient for acquisition of
context-dependent freezing. The tone-dependent freezing response of the
C/CTS group was also significantly reduced, but to a lesser extent,
implying that simultaneous activation of the basolateral and central
amygdala may be sufficient for acquisition of tone-dependent freezing.
This finding is in agreement with the observation that the involvement
of hippocampus is not required for acquisition of tone-dependent fear
(Selden et al., 1991; Kim and Fanselow, 1992; Phillips and LeDoux,
1992). The significance of simultaneous FOS production in the
basolateral and central amygdala for tone-dependent fear conditioning
was further supported by the finding that the Cs/CTS group, in which FOS production was detected only in the basolateral but not central amygdala, acquired very weak tone-dependent freezing. On the
basis of these findings it was concluded that synchronous FOS
production, followed most probably by activation of specific molecular
cascades (Morgan and Curran, 1991), in defined brain areas is
accompanied by associative learning involving novel stimuli.
Interestingly, the novel neutral stimuli used as Cs exhibited a
much stronger capacity to induce the production of the FOS protein than
the novel aversive stimulus used as Us.
Activation of certain brain areas during latent inhibition has been
reported previously using a conditioned emotional response procedure
and using FOS as a marker of neural activity. Latent inhibition was
induced by preexposure of rats to both contextual and auditory Cs and
resulted in reduction of the FOS production in most of the brain
areas, except for the nucleus accumbens, dentate gyrus, and subiculum,
where an increase was detected (Sotty et al., 1996). In those and other
areas, however, we could not find any increase of the FOS protein after
reexposure to the same Cs and Us (data not shown). We assume that this
discrepancy may be attributable to numerous differences in the
experimental conditions, such as the type of the learning procedure,
sequence and number of stimuli presentations during the preexposure and
training, number of training trials, interference of novel stimuli, and the time point of FOS immunodetection.
So far, the phenomenon of latent inhibition has been explained mainly
by decreased attentional processes during encounter of stimuli. A major
role has been attributed to various neurotransmitter systems (Dunn et
al., 1993; Baxter et al., 1997). The present findings extend these
observations, suggesting that reduction of FOS may reflect the decrease
of Cs processing underlying latent inhibition. The same molecular
changes seem to be involved in the Us preexposure effect, thus
providing a relatively simple molecular basis for a phenomenon that has
been described by numerous adaptational (Taylor, 1956; Kamin, 1961; Mis
and Moore, 1973), associative (Tomie, 1976), and cognitive (Baker and
Mackintosh, 1979) psychological models. Taking into account that a
causal relationship between FOS production and learning has been
demonstrated recently, as mentioned above (Mileusnic et al., 1996;
Swank et al., 1996), the results obtained in this study suggested that learning impairments induced by Cs and Cs/Us preexposure might have
been caused by downregulation of FOS production in specific brain
areas. This explanation would be consistent with the hypothesis that
reduced processing of Cs and Us, which occurs when they are learned as
consistent predictors of certain events, prevents subsequent association of the same Cs and Us with other events.
| |
FOOTNOTES |
Received May 22, 1998; accepted July 7, 1998.
This work was supported by the Max Planck Society, Germany. We thank
Dr. Ragna Lohman and Dr. Oliver Stiedl for helpful discussions. We also
thank Karin Birkenfeld for technical assistance with the immunohistochemistry. Almuth Burgdorf and Svea Dettmer are acknowledged for their help in the preparation of this manuscript.
Correspondence should be addressed to Jelena Radulovic, Max Planck
Institute for Experimental Medicine, Department for Molecular Neuroendocrinology, Hermann-Rein-Strasse 3, 37075 Goettingen, Germany.
| |
REFERENCES |
-
Baxter MG,
Holland PC,
Gallagher M
(1997)
Disruption of decrements in conditioned stimulus processing by selective removal of hippocampal cholinergic input.
J Neurosci
17:5230-5236[Abstract/Free Full Text].
-
Baker AG,
Mackintosh NJ
(1979)
Pre-exposure to the Cs alone, Us alone, or Cs and Us uncorrelated: latent inhibition, blocking by context, or learned irrelevance?
Learn Motiv
10:278-294.
-
Beck CHM,
Fibiger HC
(1995)
Conditioned fear-induced changes in behavior and in the expression of the immediate early gene c-fos: with and without diazepam pretreatment.
J Neurosci
15:709-720[Abstract].
-
Bertaina V,
Destrade C
(1995)
Differential time courses of c-fos mRNA expression in hippocampal subfields following acquisition and recall testing in mice.
Brain Res Cogn Brain Res
2:269-275[Medline].
-
Blanchard RJ,
Blanchard DC
(1969)
Crouching as an index of fear.
J Comp Physiol Psychol
67:370-375[ISI][Medline].
-
Bolles RC,
Collier AC
(1976)
The effect of predictive cues on freezing in rats.
Anim Learn Behav
4:6-8.
-
Campeau P,
Hayward MD,
Hope BT,
Rosen JB,
Nestler EJ,
Davis M
(1991)
Induction of the c-fos proto-oncogene in the rat amygdala during unconditioned and conditioned fear.
Brain Res
565:349-352[ISI][Medline].
-
Campeau S,
Falls WA,
Cullinan WE,
Helmreich DL,
Davis M,
Watson SJ
(1997)
Elicitation and reduction of fear: behavioral and neuroendocrine indices and brain induction of the immediate-early gene c-fos.
Neuroscience
78:1087-1104[ISI][Medline].
-
Castro Alamancos MA,
Borrell J,
Garcia Segura M
(1992)
Performance in an escape task induces fos-like immunoreactivity in a specific area of the motor cortex of the rat.
Neuroscience
49:157-162[ISI][Medline].
-
Chen C,
Kim J,
Thompson RF,
Tonegawa S
(1996)
Hippocampal lesions impair contextual fear conditioning in two strains of mice.
Behav Neurosci
110:1177-1180[ISI][Medline].
-
Chen X,
Herbert J
(1995)
Regional changes in c-fos expression in the basal forebrain and brainstem during adaptation to repeated stress: correlations with cardiovascular, hypothermic and endocrine responses.
Neuroscience
64:675-685[ISI][Medline].
-
Dunn LA,
Gail ES,
Kilts CD
(1993)
Effects of antipsychotic drugs on latent inhibition: sensitivity and specificity of an animal behavioral model of clinical drug action.
Psychopharmacology
112:315-323[Medline].
-
Fanselow MS,
Kim JJ,
Yipp J,
De Oca B
(1994)
Differential effects of the N-methyl-D-aspartate antagonist DL-2-amino-5-phosphonovalerate on acquisition of fear of auditory and contextual cues.
Behav Neurosci
108:235-240[ISI][Medline].
-
Franklin KBJ,
Paxinos G
(1997)
In: The mouse brain in stereotaxic coordinates. San Diego: Academic.
-
Handa RJ,
Nunley KM,
Bollnow MR
(1993)
Induction of c-fos mRNA in the brain and anterior pituitary gland by a novel environment.
NeuroReport
4:1079-1082[ISI][Medline].
-
Helmstetter FJ
(1992)
Contribution of the amygdala to learning and performance of conditional fear.
Physiol Behav
51:1271-1276[Medline].
-
Hess Us,
Lynch G,
Gall CM
(1995)
Regional patterns of c-fos mRNA expression in rat hippocampus following exploration of a novel environment versus performance of a well-learned discrimination.
J Neurosci
15:7796-7809[Abstract].
-
Kamin LJ
(1961)
Apparent adaptation effects in the acquisition of a conditioned emotional response.
Can J Psychol
15:176-188[Medline].
-
Kim JJ,
Fanselow MS
(1992)
Modality-specific retrograde amnesia of fear.
Science
256:675-677[Abstract/Free Full Text].
-
Kleim JA,
Lussnig E,
Schwarz ER,
Comery TA,
Greenough WT
(1996)
Synaptogenesis and Fos expression in the motor cortex of the adult rat after motor skill learning.
J Neurosci
16:4529-4535[Abstract/Free Full Text].
-
Mcechron MD,
Disterhoft JF
(1997)
Sequence of single neuron changes in CA1 hippocampus of rabbits during acquisition of trace eyeblink conditioned responses.
J Neurophysiol
78:1030-1044[Abstract/Free Full Text].
-
Milanovic S,
Radulovic J,
Laban O,
Stiedl O,
Henn F,
Spiess J
(1998)
Production of the FOS protein after contextual fear conditioning of C57BL/6N mice.
Brain Res
784:37-47[Medline].
-
Mileusnic R,
Anokhin K,
Rose SP
(1996)
Antisense oligodeoxynucleotides to c-fos are amnestic for passive avoidance in the chick.
NeuroReport
7:1269-1272[Medline].
-
Mis RW,
Moore JW
(1973)
Effect of preacquisition UCs exposure on classical conditioning of the rabbit's nictitating membrane response.
Learn Motiv
4:108-114.
-
Morgan JI,
Curran T
(1991)
Stimulus-transcription coupling in the nervous system: involvement of the inducible proto-oncogenes fos and jun.
Annu Rev Neurosci
14:421-451[ISI][Medline].
-
Papa M,
Pellicano MP,
Welzl H,
Sadile AG
(1993)
Distributed changes in c-fos and c-jun immunoreactivity in the rat brain associated with arousal and habituation to novelty.
Brain Res Bull
32:509-515[ISI][Medline].
-
Pezzone MA,
Lee WS,
Hoffman GE,
Rabin BS
(1992)
Induction of c-fos immunoreactivity in the rat forebrain by conditioned and unconditioned aversive stimuli.
Brain Res
597:41-50[ISI][Medline].
-
Phillips RG,
LeDoux JE
(1992)
Differential contribution of amygdala and hippocampus to cued and contextual fear conditioning.
Behav Neurosci
106:274-285[ISI][Medline].
-
Pomonis JD,
Levine AS,
Billington CJ
(1997)
Interaction of hypothalamic paraventricular nucleus and central nucleus of the amygdala in naloxone blockade of neuropeptide Y-induced feeding revealed by c-fos expression.
J Neurosci
17:5175-5182[Abstract/Free Full Text].
-
Radulovic J, Kammermeier J, Spiess J (1998) Generalization of
fear responses in C57BL/6N mice subjected to one-trial foreground
contextual fear conditioning. Behav Brain Res, in press.
-
Roozendaal B,
Koolhaas JM,
Bohus B
(1991)
Central amygdala lesions affect behavioral and autonomic balance during stress in rats.
Physiol Behav
50:777-781[Medline].
-
Sagar SM,
Sharp FR,
Curran T
(1988)
Expression of c-fos protein in the brain: metabolic mapping at the cellular level.
Science
240:1328-1331[Abstract/Free Full Text].
-
Sandner G,
Oberling P,
Silveira MC,
Di Scala G,
Rocha B,
Bagri A,
Depoortere R
(1993)
What brain structures are active during emotions? Effect of brain stimulation elicited aversion on c-fos immunoreactivity and behavior.
Behav Brain Res
58:9-18[ISI][Medline].
-
Selden NRW,
Everitt BJ,
Jarrard LE,
Robbins TW
(1991)
Complementary roles for the amygdala and hippocampus in aversive conditioning to explicit and contextual cues.
Neuroscience
42:335-350[ISI][Medline].
-
Smith MA,
Banerjee S,
Gold PW,
Glowa J
(1992)
Induction of c-fos mRNA in rat brain by conditioned and unconditioned stressors.
Brain Res
578:135-141[ISI][Medline].
-
Sotty F,
Sandner G,
Gosselin O
(1996)
Latent inhibition in conditioned emotional response: c-fos immunolabelling evidence for brain areas involved in the rat.
Brain Res
737:243-254[Medline].
-
Stiedl O,
Spiess J
(1997)
Effect of tone-dependent fear conditioning on heart rate and behavior of C57BL/6N mice.
Behav Neurosci
111:703-711[Medline].
-
Swank MW,
Ellis AE,
Cochran BN
(1996)
C-Fos antisense blocks acquisition and extinction of conditioned taste aversion in mice.
NeuroReport
7:1866-1870[ISI][Medline].
-
Taylor JA
(1956)
Level of conditioning and intensity of the adaptation stimulus.
J Exp Psychol
51:127-130[Medline].
-
Thinus BC,
Save E,
Rossi AC,
Tozzik A,
Ammassari TM
(1996)
The differences shown by C57BL/6 and DBA/2 inbred mice in detecting spatial novelty are subserved by a different hippocampal and parietal cortex interplay.
Behav Brain Res
80:33-40[Medline].
-
Tomie A
(1976)
Interference with autoshaping by prior context conditioning.
J Exp Psychol
2:324-334.
Copyright © 1998 Society for Neuroscience 0270-6474/98/18187452-10$05.00/0
This article has been cited by other articles:
|
|
|
|
 
C. E. Canal, Q. Chang, and P. E. Gold
Intra-amygdala injections of CREB antisense impair inhibitory avoidance memory: Role of norepinephrine and acetylcholine
Learn. Mem.,
August 26, 2008;
15(9):
677 - 686.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. Knapska, K. Radwanska, T. Werka, and L. Kaczmarek
Functional Internal Complexity of Amygdala: Focus on Gene Activity Mapping After Behavioral Training and Drugs of Abuse
Physiol Rev,
October 1, 2007;
87(4):
1113 - 1173.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. G. Reijmers, B. L. Perkins, N. Matsuo, and M. Mayford
Localization of a Stable Neural Correlate of Associative Memory
Science,
August 31, 2007;
317(5842):
1230 - 1233.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. Knapska, G. Walasek, E. Nikolaev, F. Neuhausser-Wespy, H.-P. Lipp, L. Kaczmarek, and T. Werka
Differential involvement of the central amygdala in appetitive versus aversive learning
Learn. Mem.,
March 1, 2006;
13(2):
192 - 200.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. B. Keeley, M. A. Wood, C. Isiegas, J. Stein, K. Hellman, S. Hannenhalli, and T. Abel
Differential transcriptional response to nonassociative and associative components of classical fear conditioning in the amygdala and hippocampus
Learn. Mem.,
March 1, 2006;
13(2):
135 - 142.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. B. Rosen
The Neurobiology of Conditioned and Unconditioned Fear: A Neurobehavioral System Analysis of the Amygdala
Behav Cogn Neurosci Rev,
March 1, 2004;
3(1):
23 - 41.
[Abstract]
[PDF]
|
|
|
|
|
|
|
A. Fischer, F. Sananbenesi, C. Schrick, J. Spiess, and J. Radulovic
Distinct Roles of Hippocampal De Novo Protein Synthesis and Actin Rearrangement in Extinction of Contextual Fear
J. Neurosci.,
February 25, 2004;
24(8):
1962 - 1966.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
F. Sananbenesi, A. Fischer, C. Schrick, J. Spiess, and J. Radulovic
Mitogen-Activated Protein Kinase Signaling in the Hippocampus and Its Modulation by Corticotropin-Releasing Factor Receptor 2: A Possible Link between Stress and Fear Memory
J. Neurosci.,
December 10, 2003;
23(36):
11436 - 11443.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Desmedt, S. Hazvi, and Y. Dudai
Differential Pattern of cAMP Response Element-Binding Protein Activation in the Rat Brain after Conditioned Aversion as a Function of the Associative Process Engaged: Taste versus Context Association
J. Neurosci.,
July 9, 2003;
23(14):
6102 - 6110.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Savonenko, T. Werka, E. Nikolaev, K. Zielinski, and L. Kaczmarek
Complex Effects of NMDA Receptor Antagonist APV in the Basolateral Amygdala on Acquisition of Two-Way Avoidance Reaction and Long-Term Fear Memory
Learn. Mem.,
July 1, 2003;
10(4):
293 - 303.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. J. Colombo, J. J. Brightwell, and R. A. Countryman
Cognitive Strategy-Specific Increases in Phosphorylated cAMP Response Element-Binding Protein and c-Fos in the Hippocampus and Dorsal Striatum
J. Neurosci.,
April 15, 2003;
23(8):
3547 - 3554.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. J. Ressler, G. Paschall, X.-l. Zhou, and M. Davis
Regulation of Synaptic Plasticity Genes during Consolidation of Fear Conditioning
J. Neurosci.,
September 15, 2002;
22(18):
7892 - 7902.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Fischer, F. Sananbenesi, C. Schrick, J. Spiess, and J. Radulovic
Cyclin-Dependent Kinase 5 Is Required for Associative Learning
J. Neurosci.,
May 1, 2002;
22(9):
3700 - 3707.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. Schauz and M. Koch
Blockade of NMDA Receptors in the Amygdala Prevents Latent Inhibition of Fear-Conditioning
Learn. Mem.,
November 1, 2000;
7(6):
393 - 399.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
J. Radulovic, A. Ruhmann, T. Liepold, and J. Spiess
Modulation of Learning and Anxiety by Corticotropin-Releasing Factor (CRF) and Stress: Differential Roles of CRF Receptors 1 and 2
J. Neurosci.,
June 15, 1999;
19(12):
5016 - 5025.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
Top
Abstract
Introduction
