Neurobehavioral functional deficits following closed head injury in the neonatal pig

Abstract

Neurobehavioral deficits in higher cortical systems have not been described previously in a large animal model of diffuse brain injury. Anesthetized 3-5 day old piglets were subjected to either mild (142 rad/s) or moderate (188 rad/s) rapid non-impact axial rotations of the head. Multiple domains of cortical function were evaluated 5 times during the 12 day post-injury period using tests of neurobehavioral function devised for piglets. There were no observed differences in neurobehavioral outcomes between mild injury pigs (N=8) and instrumented shams (N=4). Moderately injured piglets (N=7) had significantly lower interest in exploring their environment and had higher failure rates in visual-based problem solving compared to instrumented shams (N=5) on days 1 and 4 after injury. Neurobehavioral functional deficits correlated with neuropathologic damage in the neonatal pigs after inertial head injury. Injured axons detected by immunohistochemistry (beta-APP) were absent in mild injury and sham piglets, but were observed in moderately injured piglet brains. In summary, we have developed a quantitative battery of neurobehavioral functional assessments for large animals that correlate with neuropathologic axonal damage and may have wide applications in the fields of cardiac resuscitation, stroke, and hypoxic-ischemic brain injury.

Figure 1

Open field test space. (A) piglet starting position. (B) small blue ball with rattle, (C) small yellow ball with rattle. Both (B) and (C) function as color discrimination stimuli and movement with noise. (D) large blue ball movement without noise. (E) foam padding, tactile stimulus.

Figure 2

Open field testing: percent of minute-long intervals that sniffing the floor behavior was observed comparing 1^st and 2^nd segment and INJ and SHAM. * denotes statistically significant differences (p < 0.05).

Figure 3

Open field testing: percent of minute-long intervals that sniffing the wall behavior was observed comparing 1^st and 2^nd segment and INJ and SHAM. * denotes statistically significant differences (p < 0.05).

Figure 4

Proximity of INJ and SHAM to Pig X during the initial three minutes and the last three minutes of the socialization segment of the open field testing. * denotes statistically significant differences (p < 0.05).

Figure 5

Balance beam test, average errors for successful trials * denotes statistically significant differences (p < 0.05).

Figure 6

Balance beam test, average time to food reward for successful trials. * denotes statistically significant differences (p < 0.05).

Figure 7

Schematic depicting a composite of the regional distribution of injured axons (filled circles) and subarachnoid hemorrhage (heavy black lines) for selected slices of the 5 INJ brains examined

Figure 8

Maximal rotational accelerations and peak changes in rotational velocity for mild piglets (x’s), moderate piglets (filled squares) both scaled from a 35g to 500g brain, and anthropomorphic doll shakes without impact with padded chest (filled circles) or rubber stopper (open diamonds). The dashed line depicts the sagittal acceleration threshold associated with a 50 percent probability of concussion for a 500gm brain mass, derived from primate studies by Ommaya et al. (Ommaya 1966).