Reduced reactivity of the middle cerebral artery and its large branches after cold lesion

Arterial hypotension triggers perifocal depolarizations and aggravates secondary damage in focal brain injury

Perifocal depolarizations (PFD) have been observed after traumatic brain injury, are known to disturb cerebrovascular reactivity and thus may contribute to the morphological consequences of brain injury. In this investigation, the role of PFD was studied in focal brain lesions with/without induction of delayed hypotension. Cerebral freeze lesions were induced in anesthetized normotensive rats that underwent perfusion fixation of brains 5 min, 4 h or 24 h after lesioning, respectively, to obtain quantitative histopathology. In additional groups, a 45-min period of moderate hypobaric hypotension was applied 15 min post-trauma and brains were perfusion fixed after 4 h or 24 h. In a second series, the direct current (DC) potential and cortical laser-Doppler flow (LDF) were measured adjacent to lesions under normotensive or hypotensive conditions. Sham procedures were carried out in rats that underwent hypotension alone. Lesioning resulted in a significant LDF decrease to 50% of baseline, further decreased during hypotension to less than 40% of control (P < 0.05). Sham animals had LDF values between 60 and 70% of control when subjected to hypotension. Focal brain injury always induced a negative DC shift shortly after lesioning. In 6 of 8 rats that underwent cold lesion plus hypotension, a second PFD was observed approximately 2.5 min after onset of hypotension accompanied by a relative LDF increase by 25 +/- 12%. Lesion expansion was significantly worsened by hypotension (8.19 +/- 0.56 mm(3) at 24 h) compared with normotensive rats (7.01 +/- 0.3 mm(3) at 24 h, P < 0.01). We conclude that hypotension triggers depolarizations by an ischemic mechanism that contributes to final tissue damage.

Time course of apoptotic cell death after experimental neurotrauma

Traumatic or ischemic brain injury may give rise to the development of secondary brain damage. In the present study the time course of TUNEL staining which is widely used to delineate apoptotic reaction pattern was followed after experimental neurotrauma in order to test the hypothesis that apoptotic cell death may be involved in the development of secondary brain damage. Neurotrauma was induced in male Wistar rats by applying a cold probe to the exposed dura over the temporo-parietal cortex. Animals were sacrificed between 1 and 72 hours after trauma and coronal sections prepared from the lesioned area and adjacent tissue. The TUNEL staining was employed to detect DNA-fragmentation and conventional HE staining of sequential slices to delineate the extent of the lesion. Occurrence of positively stained cells was detected by a computer-based quantification system and stored on hard disk. TUNEL-positive nuclei were observed as early as one hour after lesion and peaked at 3 hours. There after, the number of cells detected decreased steadily. Histological examination revealed two different types of morphology in TUNEL-positive cells. A small proportion termed type I-cells displayed additional signs of apoptotic cell death such as nuclear condensation and fragmentation while type-II were considered to undergo necrotic cell death. Thus, TUNEL staining proved to be an unspecific marker of apoptotic cell death in the present study. Nevertheless, the data suggest that apoptotic cell death does not contribute substantially to the final extent of cold induced brain tissue damage.