C .M. Thiel et al. Brain Research 882 2000 112 –119
115
2.3.5. Statistical analysis Escape behaviour was analysed for both groups using
ANOVA for repeated measures with the blocks of trials 4 levels as factor. Post hoc analysis of significant effects
was performed using Tukey tests. A P-value of 0.05 was required for significance.
3. Results
3.1. Experiment 1: neurochemical and behavioural effects of aversive stimulation and the effects of
background noise
Fig. 2. Extracellular hippocampal ACh levels 10 min samples,
The basal
concentration of
hippocampal ACh
means6S.E.M. in animals that were exposed twice to a 115 dB tone only
mean6S.E.M. in dialysate was 0.5460.12 for animals
3 s duration; dashed lines. All values are expressed as percentage of
exposed to the tone shock stimulation without background
preceding baseline activity B1–B3.
noise, 0.8460.08 pmol 20 ml for animals exposed to the tone without background noise and 0.8960.14 pmol 20 ml
for animals exposed to the tone shock stimulation with tone increased extracellular hippocampal ACh levels
background noise. There were no statistical differences in ANOVA F3,1151.14, P50.376.
basal levels between these groups ANOVA F2,195 Extracellular ACh levels in animals that were exposed to
2.041, P50.157. a constant background noise during the conditioning
Extracellular hippocampal ACh levels in animals, which procedure are shown in Fig. 3. Exposure to the tone shock
were exposed to the conditioning procedure without back- did not increase extracellular hippocampal ACh in these
ground noise, are shown in Fig. 1. Exposure to tone shock animals ANOVA F5,4351.78, P50.138. Also, there
stimulation significantly increased extracellular hippocam- was no effect of the tone alone presented 2 h later.
pal ACh ANOVA F3,2053.85, P50.025 to 180 Behavioural responses are presented in Table 1. Ani-
during tone shock application and to 189 in the sample mals, which were exposed to the tone shock stimulation,
collected after tone shock exposure. Extracellular ACh responded to the shock with running and rearing on the
values returned to baseline after approximately 1 h. The hind limbs. Note, that these behaviours displayed to the
exposure to the tone 2 h later did not increase extracellular tone shock stimulation did not differ quantitatively be-
ACh. tween animals that were exposed to noise and those that
Fig. 2 shows extracellular hippocampal ACh in control were not t-tests, P.0.05. In both groups, there was no
animals which were exposed to the tone without back- behavioural activation during presentation of the tone 2 h
ground noise. Neither the first nor second exposure to the
Fig. 1. Extracellular hippocampal ACh levels 10 min samples, Fig. 3. Extracellular hippocampal ACh in animals that were exposed to a
means6S.E.M. in animals that were exposed to a tone shock stimulation tone shock stimulation solid line and a tone dashed line as animals in
without background noise 3 s 115 dB tone, 60 s 0.3 mA scrambled Fig. 1. In contrast to those, rats were tested under conditions of constant
footshock; solid line followed by the tone only dashed line 2 h later. background noise grey background starting 2 h before and lasting
All values are expressed as percentage of preceding baseline activity throughout and after administration of the stimuli. All values are
B1–B3. expressed as percentage of baseline activity B1–B3.
116 C
Table 1
latencies across the blocks of trials for rats which were not
a
Behavioural activation
exposed to noise n59 and noise exposed animals n59.
Tone shock Tone
Tone shock
A significant time effect for escape latencies was found in
no noise no noise
noise
rats which were not exposed to background noise ANOVA
Locomotion 17.763.8
0.460.4 9.663.8
factor time F3,2454.02, P50.019, indicating that these
Rearing 3.661.3
3.161.5
animals improved in learning to escape from the foot-
Twitching 29.662.8
25.264.6
shock. In contrast, rats which were exposed to noise did
a
The level of twitching and the amount of rearing and locomotion during
not show a decrease in escape latencies with training
the 10 min time interval of tone or tone shock presentation.
ANOVA factor time F3,2450.57, P50.640. Note, that both groups of rats mostly escaped rather than avoided the
later data not shown. Animals in the tone control group shock in most trials. Nevertheless, the number of avoid-
did not show measurable behavioural activation to the ance responses increased from the first to the last block of
presentation of the tone. trials from 0.3 to 1.9 animals not exposed to noise and
from 0.6 to 1.7 animals exposed to noise; ANOVAs, no 3.2. Experiment 2: effects of background noise on active
noise: F3,2456.97, P50.002; noise: F3,2453.08, P5 avoidance learning
0.046, but did not differ between the two groups. The number of escape failures did not change over trials and
Two animals one from each group were excluded from did not differ between the two groups data not shown.
the analysis since they either jumped out of the apparatus or sat on the barrier. Fig. 4 shows the mean escape
4. Discussion
