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AbstractArginine vasopressin (AVP) has previously been shown to promote disruption of the blood−brain barrier, exacerbate edema, and augment the loss of neural tissue in various forms and models of brain injury. However, the mechanisms underlying these AVP actions are not well understood. These mechanisms were studied in AVP-deficient Brattleboro rats (Avpdi/di), and their parental Long-Evans strain, using a controlled cortical impact model of traumatic brain injury (TBI). The increased influx of inflammatory cells into the injured cortex in wild-type versus Avpdi/dirats was associated with higher levels of cortical synthesis of the CXC and CC chemokines found in wild-type versus Avpdi/dirats. These chemokines were predominantly produced by the cerebrovascular endothelium and astrocytes. In astrocyte and brain endothelial cell cultures, AVP acted synergistically with tumor necrosis factor-α (TNF-α) to increase the TNF-α-dependent production of CXC and CC chemokines. These AVP actions were mediated by c-Jun N-terminal kinase (JNK), as shown by Western blotting and pharmacological inhibition of JNK activity. The activity of JNK was increased in response to injury, and the differences in the magnitude of its post-traumatic activation between Avpdi/diand wild-type rats were observed. These data demonstrate that AVP plays an important role in exacerbating the brain inflammatory response to injury. [ABSTRACT FROM AUTHOR]