Neuronal and Glial Cell Number in the Hippocampus after Experimental Traumatic Brain Injury: Analysis by Stereological Estimation

Abstract

Fluid percussion (FP) brain injury causes spatial memory dysfunction in rats regardless of injury location (midline vs. lateral). Standard histological analysis of the injured brains shows hippocampal neuronal loss after lateral, but not midline FP injury. We have used the optical volume fractionator (OVF) stereological procedure to quantify neuronal loss and glial proliferation within specific subregions of the hippocampus after midline or lateral FP injury. The OVF method is a design-based cell counting procedure, which combines cellular numerical density estimates (from the optical disector) with volume estimates (generated by point counting and the fractionator stereology method) to produce an estimate of the absolute cell number. Fifteen adult male Sprague-Dawley rats were randomly divided into 3 groups (n = 5/group): midline injury, lateral injury and naive. A single fluid percussion pulse was delivered to anesthetized rats in the injured groups. At 14 days post-injury, strict morphological criteria enabled the estimation of neurons, astrocytes, oligodendrocytes, and microglia in defined hippocampal subregions. The results confirm that hippocampal neurons are selectively vulnerable to brain injury, particularly observed as a significant loss in the hilus following both types of injury and in area CA3 after lateral injury. In contrast, the number of astrocytes and oligodendrocytes remains unaffected by brain injury, regardless of subregion. However, the significant increase in microglia number (bilaterally after midline and ipsilateral following lateral injury) suggests that underlying cellular processes continue weeks following injury. The implications of the observed cell population changes are discussed in relation to the reported cognitive deficits associated with both lateral and midline FP brain injury.

Modulation of the cAMP signaling pathway after traumatic brain injury

“…Accordingly, there are consistent, quantifiable focal and diffuse histopathologies that are all potential therapeutic targets (Dietrich et al, 1994, Bramlett et al, 1997, Ciallella et al, 2002, Grady et al, 2003, Suzuki et al, 2003, Suzuki et al, 2004, Witgen et al, 2005. In our studies, we found that rolipram, a selective PDE IV antagonist, improved histopathology at multiple levels.…”

“…The parasagittal FPI model results in stereotypical neuronal death in the parietal cortex overlying the cortical contusion and in the CA3 region of the hippocampus (Grady et al, 2003, Witgen et al, 2005. Treatment of rolipram during TBI and for 3 days following moderate FPI improved neuronal survival in both the parietal cortex (Fig.…”

“…We chose to pre-treat animals with rolipram to target the acute, rapid inflammatory signaling events initiated by trauma (Kinoshita et al, 2002. Animals were assessed for histopathology at 3 days after TBI because there are reproducible, quantifiable histopathologies at this time point (Dietrich et al, 1994, Bramlett et al, 1997, Suzuki et al, 2003, Suzuki et al, 2004 The parasagittal FPI model results in stereotypical neuronal death in the parietal cortex overlying the cortical contusion and in the CA3 region of the hippocampus (Grady et al, 2003, Witgen et al, 2005. Treatment of rolipram during TBI and for 3 days following moderate FPI improved neuronal survival in both the parietal cortex (Fig.…”

Alterations in Mammalian Target of Rapamycin Signaling Pathways after Traumatic Brain Injury

“…Knockdown of the NMDA-type glutamate receptor 1 in a mere 6% to 7% of CA1 neurons in the hippocampus is enough to significantly impair memory formation (Cheli et al, 2006). The FPI model, without any accompanying hypoxia, does not result in substantial neuronal loss throughout the hippocampus with the exception of the CA3 and hilar subregions, but does result in significant hippocampal-dependent memory impairments (Lyeth et al, 1990;Carbonell et al, 1998;Grady et al, 2003). Accordingly, hippocampal LTP is impaired and subtle structural damage is seen in the hippocampus after TBI (Sanders et al, 2000;Golarai et al, 2001;Scheff et al, 2005).…”

Environmental enrichment increases progenitor cell survival in the dentate gyrus following lateral fluid percussion injury

“…Rodent models of TBI, including the lateral fluid percussion (FP) brain injury model also produce persistent impairments in learning and memory [61], which have been attributed to neuronal injury and dysfunction in the hippocampus [11,27,33,47]. Within the hippocampus, there is a significant loss of neurons in the CA3 pyramidal cell layer and the hilus of the dentate gyrus on theipsilesional side following a FP injury [23]. In addition, in the hilus there is evidence of bilateral injury, which includes damage to neuronal cytoskeletal proteins [34], activation of injury related signal transduction pathways [62], and abnormal electrophysiology [47].…”