Assessments of Cognitive Function Following Traumatic Brain Injury - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 217

2.1.3. Morris Water Maze
Procedure: Working
Memory

Spatial working memory can be assessed using the same maze
apparatus as described above. In the working memory version of
the MWM, each animal receives eight pairs of trials per day over
fi ve consecutive days. For each pair of trials, animals are randomly
assigned to one of the four possible starting points (North, South,
East, and West) and one of the four possible escape platform
positions (1, 2, 3, and 4). During the eight pairs of trials each, rat
is tested twice from each start position and goal location. For
example, a typical test sequence may be N2, W1, S4, E1, W3, E2,
S3, and N4. On the fi rst trial of each pair (the information trial),
rats are placed in the maze and given 120 s to locate the hidden
platform. If the rat does not fi nd the escape platform in the allotted
120 s, it can be manually guided to the platform. After remaining
on the goal platform for 10 s, animals are promptly placed back
into the maze for the second trial of the pair (test trial). The platform
position and the start position remain unchanged on this trial.
Similar to the information trial, animals are allowed 120 s to locate
the goal and then required to remain there for 10 s. Following the
fi rst pair of trials, the animal is placed in an incubator and given a
4-min inter-trial rest. Between pairs of trials, both the start position
and the goal location are changed.
For the example above:
Trial 1, information trial: N2, starting from the North position, with
the goal in position 2.
Followed promptly by trial 1, test trial, in which animals are
started in the North position, with the goal in position 2.
4-min intertrial interval.
Trial 2, information trial: W1, starting from the West position,
with the goal location in position 1. Followed promptly by trial 2,
test trial, in which animals start from the west, with the goal location
in position 1. This is repeated for all eight trials per day.
The average latency to fi nd the platform is averaged for each
rat for each day. Previous studies using FPI and CCI demonstrated
that sham-injured animals performed signifi cantly better on the
second trial than on the fi rst trial of each pair. However, injured
animals do not signifi cantly differ between fi rst and second trial
goal latencies on any day ( 14, 15 ). These results indicate that injured
animals have a profound and enduring defi cit in spatial working-
memory function on days 11-15 after TBI.

2.2. Fear Conditioning

Fear conditioning has been a relatively underutilized task following
experimental brain injury. In one study, a fear conditioning
protocol was used following injury to investigate hippocampal-
dependant visual-spatial memory (contextual, described below) and
classically conditioned fear (cued). They found that following FPI,
animals displayed hippocampal-dependant contextual fear defi cits,
but no amygdala-dependant cued fear defi cits ( 17 ). In this chap-
ter, we present a typical protocol for contextual-fear conditioning.