Therapeutic hypothermia modulates TNFR1 signaling in the traumatized brain via early transient activation of the JNK pathway and suppression of XIAP cleavage.

Tumor necrosis factor (TNF) plays a critical role in pathomechanisms associated with secondary damage after traumatic brain injury (TBI). The TNF ligand-receptor system stimulates inflammation by activation of gene transcription through the IkappaB kinase (IKK)-NF-kappaB and c-Jun NH(2)-terminal kinase (JNK)-AP-1 signaling cascades. TNF signaling following TBI involves both cell survival and apoptotic pathways, but the mechanism that accounts for the dual role of TNF remains unclear. Multiple studies have reported hypothermia to be protective following TBI, but the precise mechanism has not been clearly defined. Here, TNFR1 signaling pathways were investigated in the cerebral cortex of adult male Sprague-Dawley rats subjected to moderate fluid-percussion TBI and of naïve controls. Another group was subjected to moderate TBI with 30 min of pre- and post-traumatic hypothermia (33 degrees C). Rapid and marked increases in protein expression of TNFR1 and signaling intermediates in both the IKK-NF-kappaB and JNK pathways were induced in traumatized cortices. Hypothermia decreased TNFR1 protein expression acutely in traumatized cortices and stimulated early activation of signaling intermediates in the JNK, but not the IKK-NF-kappaB, signaling pathways. Hypothermia promoted a rapid activation of caspase-3 acutely after injury but suppressed caspase-3 activation at later time points. Moreover, hypothermia treatment suppressed cleavage of X-linked inhibitor of apoptosis protein (XIAP) into fragments induced by TBI. These data suggest that hypothermia may regulate both the JNK signaling cascade via XIAP and the preconditioning pathways that activate caspases. Thus, hypothermia mediates TNFR1 responses via early activation of the JNK signaling pathway and caspase-3, leading to endogenous neuroprotective events.

Experimental intracerebral hemorrhage in the mouse: histological, behavioral, and hemodynamic characterization of a double-injection model.

BACKGROUND AND PURPOSE: A major limitation of intracerebral hemorrhage (ICH) research is the lack of reproducible animal models. The present study was conducted to validate in the mouse the double-injection method of ICH initially developed in the rat. We investigated the effect of intrastriatal injection of blood or cerebrospinal fluid (CSF) on cerebral blood flow (CBF), neurological score, hematoma volume, and brain swelling. METHODS: Male C57BL/6 mice were anesthetized with halothane/nitrous oxide delivered by face mask. Rectal and cranial temperatures were regulated at 37 degrees C to 37.5 degrees C. Mice were placed in a stereotactic frame, and a 30-gauge stainless steel cannula was introduced through a burr hole into the left striatum. Each mouse received a 5-microL injection of either whole blood or CSF (over 3 minutes), followed 7 minutes later by 10 microL injected over 5 minutes. The injection cannula was slowly withdrawn 10 minutes after the second injection. Control mice had only cannula insertion. CBF was studied by laser Doppler perfusion imaging. Neurological status was evaluated on days 1 and 2. After 2 days, hematoma volume and brain swelling were calculated. RESULTS: Physiological values were stable. Mice with ICH but not those with CSF or cannula alone had a marked, persistent neurological deficit and a highly reproducible hematoma, whose mean+/-SEM volume was 2.0+/-0.2 mm3 compared with a lesion size of 0.2+/-0.1 mm3 in mice with CSF. Residual swelling of the ipsilateral hemisphere at 48 hours was 5.7% in the hematoma and 1.5% in the CSF groups. Relative CBF in the neocortex ipsilateral to the injection site declined by approximately 45% to 60% during the first 20 minutes after cannula insertion/injection in all groups but began to renormalize at approximately 25 to 30 minutes in the CSF and cannula-only groups; in the hematoma group, cortical hypoperfusion of approximately 35% to 50% persisted during the 90-minute measurement period. CONCLUSIONS: The present ICH model in mice produces a consistent neurological deficit, hypoperfusion, hematoma volume, and brain swelling. This model closely mimics human hypertensive basal ganglionic ICH and should be useful for the evaluation of pharmaceutical therapies. Laser Doppler perfusion imaging is a useful new technique to quantify relative CBF changes and can be used for studies of dynamic changes of CBF in this in vivo model of ICH in mice.