Biology Reference
In-Depth Information
Activity counts are obtained from the lower horizontal IR sensors
(along the
x
and
y
axis). Likewise, distance traveled in centimeters
is obtained from the lower horizontal IR, and calculated taking
into account the animal's moving path. Locomotion is defi ned as
the moving distance longer than the whole length of the test ani-
mal. The calculated traveling distance (at any given time period,
called “block,” (i.e., “time bin”) or “total measuring period”), and
speed are two main parameters for locomotor activity (Fig.
2b
).
The
z
-axis photocell beam break counts refl ect the number of beam
interruptions in the upper row of IR sensors and indicate rearing
or climbing activity, which is thought to be part of exploratory
behavior parameters. All IR data (beam break activity counts, loco-
motion, rearing, and rotations) are continuously recorded at a
4-Hz sampling rate. Absolute and percent time in a chosen block
spent in this arousal state are also reported. Mice are most active
within the fi rst 1 h when transferred to a fresh or new cage, and
then their activity levels gradually decrease. After their activity is
stable, treatment with the test drug can be started.
Our fi rst step in verifi cation of the SmartCage™ system was
examination of the accuracy of automatic data analysis by verifi ca-
tion with visual inspection and conventional techniques. The IR
activity and locomotion measures in the SmartCage™ were com-
pared with the video tracking system. The individual mouse was
placed into a freshly prepared home cage and recorded simultane-
ously using the SmartCage™ system and a video camera placed
above the SmartCage™ system. The accumulated traveling distance
at a given time block was automatically calculated by the CageScore™
program (Program associated with the SmartCage™ system; AfaSci,
Inc.). The video images were processed using the video tracking of
rodent activity software (SMART Video Tracking System, San
Diego Instruments). The analyzed data obtained from the two sys-
tems indicated that the pattern in activity levels were identical,
though the absolute value is slightly different when comparing the
SmartCage™ to the video system (Fig.
2b
). This initial validation
indicated that that the activity levels recorded by the SmartCage™
system can adequately identify changes in activity patterns.
To further validate the IR detection, we used well-established
drugs that are known to increase or decrease animal activity. Mice on
day 1 received an injection of vehicle and on day 2 received an injec-
tion of the stimulant cocaine (30 mg/kg, i.p.). Immediately follow-
ing the injection, individual animals in their home cage, complete
with food and water in the top metal rack, were placed into the
SmartCage™ system. The mice were continuously monitored for
24 h following the injection. It is clearly evident via SmartCage™
assessment that cocaine increases distance traveled and rearing activ-
ity following drug administration, lasting for approximately 3 h. In
contrast, vehicle injection mice gradually decreased their activity to a
basal level within half an hour (Fig.
3a
). Conversely, drugs that pro-
duce sedation effects decreased the spontaneous activity measured
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