Traumatic brain injury (TBI) results in both focal and diffuse brain pathologies that are exacerbated by the inflammatory response and progress from hours to days after the initial injury. Using a clinically relevant model of TBI, the parasagittal fluid-percussion
brain injury (FPI) model, we found injury-induced impairments in the
cyclic AMP (cAMP) signaling pathway. Levels of cAMP were depressed in the ipsilateral parietal cortex and hippocampus, as well as activation of its downstream target,
protein kinase A, from 15 min to 48 h after moderate FPI. To determine if preventing hydrolysis of cAMP by administration of a
phosphodiesterase (PDE) IV inhibitor would improve outcome after TBI, we treated animals intraperitoneally with
rolipram (0.3 or 3.0 mg/kg) 30 min prior to TBI, and then once per day for 3 days.
Rolipram treatment restored cAMP to
sham levels and significantly reduced
cortical contusion volume and improved neuronal cell survival in the parietal cortex and CA3 region of the hippocampus. Traumatic axonal injury, characterized by
beta-amyloid precursor
protein deposits in the external capsule, was also significantly reduced in
rolipram-treated animals. Furthermore, levels of the pro-inflammatory
cytokines,
interleukin-1beta (IL-1beta) and
tumor necrosis factor-alpha (
TNF-alpha), were significantly decreased with
rolipram treatment. These results demonstrate that the cAMP-PKA signaling cascade is downregulated after TBI, and that treatment with a PDE IV inhibitor improves histopathological outcome and decreases
inflammation after TBI.