Dynamics of posttraumatic brain swelling following a cryogenic injury in rats

For evaluation of novel therapeutic regimens against brain edema in experimental models, it is important to know the temporal profile of edema formation. Since development of brain swelling and edema following a cryogenic injury is poorly documented in rats, these parameters have been investigated in this study. 17 Sprague-Dawley rats were used. Three rats (controls) were sham-operated. Their brains were removed 15 min after sham-operation. In all other animals a right parietal cryogenic lesion was applied in ketamine-xylazine anesthesia. Systemic blood pressure was monitored during the perioperative period. Brains were removed in defined intervals following cryogenic injury (0.25, 0.5, 1, 3, 6, 12, 24, and 72 h; n = 3 each). Hemispheres were then separated and weighed for determination of brain swelling, dried and weighed again. Cerebral water content was calculated as the difference of hemispheric wet- and dry-weight. Posttraumatic hemispheric swelling reached its maximum (7.9 +/- 0.4%) as early as 12 h post trauma. During the first hour after injury, brain swelling showed a steep, linear increase to 3.9%, i.e. swelling amounted to 50% of its maximum within one hour. 6 h post trauma swelling was 5.7%. After 12 h brain swelling started to decline. 72 h post cryogenic injury, 6.1% hemispheric swelling were found. Development of brain swelling was paralleled by a linear increase in brain water content of the lesioned hemisphere. The maximum of hemispheric water content was seen 24 h post trauma. In non-lesioned hemispheres only a marginal transient increase in cerebral water content was observed. edema has to be considered when planning therapeutic protocols.