Neuronal loss as evidenced by automated quantification of neuronal density following moderate and severe traumatic brain injury in rats

Abstract

Traumatic brain injury causes widespread neurological lesions that can be reproduced in animals with the lateral fluid percussion (LFP) model. The characterization of the pattern of neuronal death generated in this model remains unclear, involving both cortical and subcortical brain regions. Here, 7 days after moderate (3 atmospheres absolute [ATA]) or severe (3.8 ATA) LFP, we estimated neuronal loss by using immunohistochemistry together with a computer-assisted automated method for quantifying neuronal density in brain sections. Neuronal counts were performed ipsilateral to the impact, in the parietal cortex ventral to the site of percussion, in the temporal cortex, in the dorsal thalamus, and in the hippocampus. These results were compared with the counts observed at similar areas in sham animals. We found that neuronal density was severely decreased in the temporal cortex (-60%), in the dorsal thalamus (-63%), and in area CA3 of the hippocampus (-36%) of injured animals compared with controls but was not significantly modified in the cortices located immediately ventral to the impact. Total cellular density increased in brain structures displaying neuronal death, suggesting the presence of gliosis. The increase in the severity of LFP did not change the pattern of neuronal injury. This automated method simplified the study of neuronal loss following traumatic brain injury and allowed the identification of a pattern of neuronal loss that spreads from the dorsal thalamus to the temporal cortex, with the most severe lesions being in brain structures remote from the site of impact.

Altered hypermetabolic response to cortical spreading depolarizations after traumatic brain injury in rats

“…Severe LFP injury rapidly induced a consistent decrease in rCBF and [Glc]b in a cortical area known to degenerate seven days post-LFP injury, which we designated as a potential traumatic penumbra. 3 In this brain area at risk of neuronal injury, spontaneous SDs induced similar patterns of rCBF and [Glc]b changes to those observed in the control group, suggesting hypermetabolism. However, PbtO 2 and [Lac]b displayed an initial biphasic pattern followed by a prolonged decrease.…”

“…This severe LFP injury produced a $60% decrease in neuronal density in the temporal cortex lateral to the impact seven days after trauma (Figure 1(b)). 3 Without external intervention, this cortical area is therefore bound to degenerate and represents a traumatic penumbra. After LFP injury, animals were again placed in the stereotaxic frame under light anesthesia (0.8-1.5% isoflurane in 30% oxygen with air) for 5 h. Between 30 min and 1 h after LFP injury, arterial blood gas analysis was performed in nine animals under mechanical ventilation.…”

“…(a) Experimental timeline after LFPI. Sensors were implanted in the temporal cortex, a brain area that undergoes a 60% decrease in neuronal density within the first seven days after LFPI (orange area in (b) adapted from Balança et al 3 with permission). (c) Median and interquartile range (IQR) of regional cerebral blood flow (rCBF in %, n ¼ 12 in both groups), brain tissue partial pressure of oxygen (PbtO 2 in mmHg, n ¼ 6 in both groups), glucose and lactate extracellular brain concentrations ([Glc]b in mmol/l, n ¼ 6 in both groups and [Lac]b in mmol/l, n ¼ 6 in both groups), at the onset and the end of the recording period in control group (blue) and TBI-induced group (red).…”

“…In animal models of TBI, the majority of neurons in such zones die within a few days of the initial insult. [1][2][3] On computed tomography scans in patients, this area often shows hypodensity in acute and subacute stages and atrophy later on. On the basis of these observations, the concept of a pericontusional or traumatic ''penumbra'' was developed, by analogy with the outer zone of focal cerebral ischemia.…”

Mapping the functional connectome in traumatic brain injury: What can graph metrics tell us?

“…Indirect damage can occur via several mechanisms such as mechanical forces, metabolic changes, and presynaptic hyperexcitability (Potts et al, 2009). This is further supported by studies using animal models of indirect and direct TBI trauma (Balanca et al, 2016;Igarashi et al, 2007;Park et al, 2007;Park et al, 2006). As graph theoretical analyses can be applied to a large number of network nodes, future studies should include subcortical regions as ROIs.…”