Comparison of rat sensory behavioral tasks to detect somatosensory morbidity after diffuse brain-injury

Brain injury disrupts neuronal circuits, impacting neurological function. Selective and sensitive behavioral tests are required to explore neurological dysfunction, recovery and potential therapy. Previously we reported that the Whisker Nuisance Task (WNT), where whiskers are manually stimulated in an open field, shows sensory sensitivity in diffuse brain-injured rats. To further explore this somatosensory morbidity, we evaluated three additional whisker-dependent tasks: Gap Cross Test, a novel Angle Entrance Task and Whisker Guided Exploration Task. Brain-injured (n = 11) and sham (n = 8) rats were tested before midline fluid percussion brain injury (moderate: 2.0 atm) and 1 and 4 weeks after injury. For the WNT, we confirmed that brain-injured rats develop significant sensory sensitivity to whisker stimulation over 28 days. In the Gap Cross Test, where rats cross progressively larger elevated gaps, we found that animals were inconsistent in crossable distance regardless of injury. In the Angle Entrance Task, where rats enter 30 degrees, 40 degrees, 50 degrees or 80 degrees corners, rats performed consistently regardless of injury. In the Whisker Guided Exploration Task, where rats voluntarily explore an oval circuit, we identified significant decreases in the number of rears and reversals and changes in the predominant location (injured rats spend more time in the inside of the turn compared to the outside) after injury and increased thigmotaxis after sham and brain-injury. Both the WNT and Whisker Guided Exploration Task show injury-induced somatosensory behavioral morbidity: however, the WNT remains more sensitive in detecting brain injury, possibly due to imposed whisker stimulation that elicits agitation similar to the human condition.