Decompressive craniectomy reduces white matter injury after controlled cortical impact in mice

Abstract

Reduction and avoidance of increases in intracranial pressure (ICP) after severe traumatic brain injury (TBI) continue to be the mainstays of treatment. Traumatic axonal injury is a major contributor to morbidity after TBI, but it remains unclear whether elevations in ICP influence axonal injury. Here we tested the hypothesis that reduction in elevations in ICP after experimental TBI would result in decreased axonal injury and white matter atrophy in mice. Six-week-old male mice (C57BL/6J) underwent either moderate controlled cortical impact (CCI) (n=48) or Sham surgery (Sham, n=12). Immediately after CCI, injured animals were randomized to a loose fitting plastic cap (Open) or replacement of the previously removed bone flap (Closed). Elevated ICP was observed in Closed animals compared with Open and Sham at 15 min (21.4±4.2 vs. 12.3±2.9 and 8.8±1.8 mm Hg, p<0.0001) and 1 day (17.8±3.7 vs. 10.6±2.0 and 8.9±1.9 mm Hg, p<0.0001) after injury. Beta amyloid precursor protein staining in the corpus callosum and ipsilateral external capsule revealed reduced axonal swellings and bulbs in Open compared with Closed animals (32% decrease, p<0.01 and 40% decrease, p<0.001 at 1 and 7 days post-injury, respectively). Open animals were also found to have decreased neurofilament-200 stained axonal swellings at 7 days post-injury compared with Open animals (32% decrease, p<0.001). At 4 weeks post-injury, Open animals had an 18% reduction in white matter volume compared with 34% in Closed animals (p<0.01). Thus, our results indicate that CCI with decompressive craniectomy was associated with reductions in ICP and reduced pericontusional axonal injury and white matter atrophy. If similar in humans, therapeutic interventions that ameliorate intracranial hypertension may positively influence white matter injury severity.

Keywords: axonal injury; controlled cortical impact; intracranial pressure; traumatic brain injury; white matter.

FIG. 1.

Controlled cortical impact with immediate bone flap replacement (Closed) resulted in elevations in intracranial pressure (ICP). (A) ICP measurements in mice survived for 24 h after injury or Sham surgery. (** p<0.001, Tukey test). (B) ICP measurements in mice survived for 7 days after injury or Sham surgery. (* p<0.01, ** p<0.001, Tukey tests).

FIG. 2.

Controlled cortical impact with immediate bone flap replacement (Closed) resulted in increased beta amyloid precursor protein (β-APP) stained axonal swellings. (A–C) β-APP staining in the pericontusional white matter of Sham, Open, and Closed mice respectively at 1 day post-injury; scale bar 250 μm. (D–I) Higher magnification of the pericontusional white matter at 1 day and 1 week post-injury; scale bars 25 μm. (J, K) Stereological quantification of numbers of β-APP positive axonal swellings per cubic millimeter of the ipsilateral corpus callosum and external capsule: J at 1 day post-injury and K at 1 week post injury (*p<0.01, **p<0.001, #p<0.0001 compared with Sham, Tukey test).

FIG. 3.

Controlled cortical impact with or without immediate bone flap replacement did not result in increased beta amyloid precursor protein (β-APP) stained axonal swellings in the contralateral white matter. (A–C) β-APP staining in the contralateral white matter of Sham, Open, and Closed mice respectively at 1 day post-injury; scale bar 250 μm. (D–I) Higher magnification of the contralateral white matter at 1 day and 1 week post-injury; scale bars 25 μm.

FIG. 4.

Controlled cortical impact with immediate bone flap replacement (Closed) resulted in increased neurofilament-200 (NF200) stained axonal swellings. (A–C) NF200 staining in the percontusional white matter of Sham, Open, and Closed mice, respectively, at 1 day post-injury; scale bar 250 μm. (D–I) Higher magnification of the pericontusional white matter at 1 day and 1 week post-injury; scale bars 25 μm. Arrows denote NF200 positive axonal swellings. (J, K) Stereological quantification of numbers of NF200 positive axonal swellings per cubic millimeter of the ipsilateral corpus callosum and external capsule: J at 1 day post-injury and K at 1 week post-injury (*p<0.01, #p<0.0001 compared with Sham, Tukey test).

FIG. 5.

Controlled cortical impact with immediate bone flap replacement (Closed) resulted in increased white matter atrophy 4 weeks after injury. (A–I) Exemplar images of the ipsilateral corpus callosum and external capsule from three rostral-caudal sections per mouse; scale bar 250 μm. (J) Estimation of white matter volume of the ipsilateral corpus callosum and external capsule by the Cavalieri method at 1 month post-injury or Sham surgery. (*p<0.01, #p<0.001 compared with Sham, Tukey test).

FIG. 6.

Controlled cortical impact with immediate bone flap replacement (Closed) resulted in decreased NeuN positive cells in the hippocampus. (A–L) NeuN staining of the hippocampus of Sham, Open, and Closed mice, respectively; scale bar 200 μm. (M–N) Stereological quantification of numbers of NeuN positive cells per cubic millimeter of the ipsilateral CA3 region of the hippocampus: M at 1 day post-injury and N at 1 week post-injury (*p<0.05, # p<0.01 compared with Sham, Tukey test).

FIG. 7.

Controlled cortical impact with immediate bone flap replacement (Closed) resulted in decreased NeuN positive cells in the hippocampus at 1 month post-injury. (A–F) NeuN staining of the hippocampus of Sham, Open, and Closed mice, respectively; (scale bar 200 μm. (G) Stereological quantification of numbers of NeuN positive cells per cubic millimeter of the ipsilateral CA3 region of the hippocampus. (*p<0.05, #p<0.01 compared with Sham, Tukey test).

FIG. 8.

Scatterplots of 15 min post-injury intracranial pressure (ICP) measurements with 1 week post-injury stereological quantification of (A) beta amyloid precursor protein (β-APP) positive axonal swellings in the ipsilateral corpus callosum and external capsule; (B) neurofilament-200 (NF200) positive axonal swellings in the ipsilateral corpus callosum and external capsule; (C) NeuN positive cells in the ipsilateral CA3 region of the hippocampus. r Spearman correlation, *p<0.05.