This study investigated whether rats exposed to traumatic brain injury and hypoxia experience long-term visual deficits. Rats received a brain injury and were then exposed to hypoxia, mimicking severe human brain injuries. The rats underwent several visual tests over time, including forelimb placement, foot splay, visual cliff, object recognition, and light/dark box tests. In all tests, injured rats performed worse than uninjured rats, showing visual deficits. In foot splay and light/dark box tests, rats tested later showed greater impairment, suggesting visual function continued to decline over time. The results support that brain-injured rats exposed to hypoxia experience visual deficits that remain or worsen over time.

1. .
Mohammed Sarray
Shana King, LaToyia Floyd and Jean Peduzzi Nelson
Traumatic Brain Injury and
Hypoxia Produces Long-term
Visual Deficits in Rats

2. Visual Deficits after Brain Injury
• Visual deficits occurs in more than 50%
of people with brain injury
• Even repeated mild brain injury in rats
causes loss of 50% of retinal ganglion
cells (critical for vision)
• Brain injury causes damage in other
visual areas in the brain
• Hypoxia after injury is associated with
more severe injury
Rationale

3. Hypothesis
Brain-injured rats exposed to hypoxia
exhibit visual deficits that remained or
got worse with time.

4. Background
Previous studies of rats with eye diseases used
the following functional tests to measure
vision:
Forelimb placing
Landing foot splay
Object recognition
Visual Cliff
Light/Dark box

5. Brain Injury Model
•Nude RNU (inbred) rats
anesthetized with isoflurane
•Anesthetized rats received brain
injury using Marmarou model
•Rats are given low oxygen with
isoflurane for 30 min to mimic
severe brain injury in people
Methods
Injury
Marmarou A et al. A new model of diffuse brain injury in rats. Part I: Pathophysiology and biomechanics. J Neurosurg. 1994:80(2):291-300. PMID: 8283269
Hellewell SC et al. Erythropoietin improves motor and cognitive deficit, axonal pathology, and neuroinflammation in a combined model of diffuse traumatic
brain injury and hypoxia, in association with upregulation of the erythropoietin receptor. J Neuroinflammation. 201: 18;10:156.

6. Forelimb Placing Response
Methods
Function
Matsuo T et al. Vision evaluation by functional observational battery, operant behavior test, and light/dark box
test in retinal dystrophic RCS rats versus normal rats. Heliyon 5(6), e01936 (2019).
Rat is held by the tail near a table. Normal rats raise their head and
straighten their forelimbs.

7. Landing Foot Splay
Methods
Function
Matsuo T et al. Vision evaluation by functional observational battery, operant behavior test, and light/dark box test in retinal dystrophic RCS rats versus
normal rats. Heliyon 5(6), e01936 (2019).
• Footpads of the rats are stained
using an ink pad.
• The rat is dropped about 1 foot.
• The distance between hind feet
is measured

8. Virtual Visual Cliff
Methods
Function
Tzameret A, Sher I, Edelstain V et al. Evaluation of visual function in Royal College of Surgeon rats using a depth
perception visual cliff test. Vis Neurosci 36 E002 (2019).
Rats are placed on clear stage and given the option to leave the stage
with a small drop or an illusory large cliff. The checkerboard pattern
makes it difficult to see the cliff. Normal rats avoid the large cliff.

9. Object Recognition Test
Methods
Function
Fazel MF et al. Philanthotoxin-343 attenuates retinal and optic nerve injury, and protects visual function in rats with N-methyl-D-aspartate-
induced excitotoxicity. PLoS One 15(7), e0236450 (2020).
The rat is placed in a container with 2 objects. Later one of
the objects is replaced by an object that is unfamiliar to the
rat. A normal rat will investigate the novel object.

10. Light/Dark Box
• Rats prefer dark areas.
• Rat is placed in a box (100 lux) that has an opening into a
dark box. Note, traditional office lighting: 300-500 Lux
• Time required to enter the dark box was measured.
• Test repeated 3 times.
Methods
Function
Matsuo T et al. Vision evaluation by functional observational battery, operant behavior test, and light/dark box test in retinal dystrophic RCS rats versus
normal rats. Heliyon 5(6), e01936 (2019).

11. Forelimb Placing Response
Results
Function
All normal rats raised their head and
straightened their forelimbs. All
injured rats had slightly subnormal
response.

12. Landing Foot Splay
Results
Function
Rats had a wider landing stance after
injury that got worse with time.

13. Virtual Visual Cliff
Results
Function
Injured rats took longer to dismount from the
platform than normal rats. All of the normal rats
avoided the virtual cliff but 2/3 of injured rats
moved toward cliff.

14. Object Recognition Test
Results
Function
Injured rats take a longer time to explore
a novel object.

15. Light/Dark Box
Results
Function
Rats at 5.5 months after injury took longer
than rats at 3.5 months after injury to move
to dark box.

16. Conclusions
Forelimb placing: The slightly abnormal response of
the injured rats suggests that the rats did not see
the landing well.
Virtual Visual Cliff: Rats took longer to dismount
that may be due to impaired brain processing. Most
injured rats moving to the cliff to dismount suggests
visual deficits are present.

17. Conclusions
Object recognition: Rats took a longer time to
explore the novel object than normal rats due to
visual or memory deficits. This did not change with
increasing time after injury.
Landing foot splay: Rats had a wider landing stance
after injury. Wider stance mean greater stability.
At longer times after injury, the stance got even
wider due to ↑ visual deficits, balance problems
from head injury or size.

18. Conclusions
Light/Dark Box Test: Injured rats took longer
time to enter the dark box in the first trial. The
rats at 5.5 months after injury took even longer
than the rat at 3.5 months after injury. Loss of
sensitivity to light might relate to a continuing
death of retinal ganglion cells.

19. Summary
In all of the functional tests, the injured rats
performed worse than normal rats. In the Landing
Foot Splay and Light/Dark tests, rats with longer
time after injury did worse than rats with less time
after injury. This may reflect continued loss of
retinal ganglion cells. Our findings support brain-
injured rats exposed to hypoxia exhibit visual
deficits that remained or got worse with time.

20. Thank you
for your attention!