Learning and memory impairments are common in traumatic brain injury (TBI) survivors. However, there are no effective treatments to improve TBI-induced learning and memory impairments. TBI results in decreased cAMP signaling and reduced cAMP-response-element binding protein (CREB) activation, a critical pathway involved in learning and memory. TBI also acutely upregulates phosphodiesterase 4B2 (PDE4B2), which terminates cAMP signaling by hydrolyzing cAMP. Wehypothesized that a subtype-selective PDE4B inhibitor could reverse the learning deficits induced by TBI. To test this hypothesis, adult male Sprague-Dawley rats received sham surgery or moderate parasagittal fluid-percussion brain injury. At 3 months postsurgery, animals were administered a selective PDE4B inhibitor or vehicle before cue and contextual fear conditioning, water maze training and a spatial working memory task. Treatment with thePDE4Binhibitor significantly reversed the TBI-induced deficits in cue and contextual fear conditioning and water maze retention. To further understand the underlying mechanisms of these memory impairments, we examined hippocampal long-term potentiation (LTP). TBI resulted in a significant reduction in basal synaptic transmission and impaired expression of LTP. Treatment with the PDE4B inhibitor significantly reduced the deficits in basal synaptic transmission and rescued LTP expression. The PDE4B inhibitor reduced tumor necrosis factor-α levels and increased phosphorylated CREB levels after TBI, suggesting that this drug inhibited molecular pathways in the brain known to be regulated by PDE4B. These results suggest that a subtype-selective PDE4B inhibitor is a potential therapeutic to reverse chronic learning and memory dysfunction and deficits in hippocampal synaptic plasticity following TBI.
Bibliographical noteFunding Information:
This work was supported by the National Institutes of Health/National Institute of Neurological Disorders and StrokeR01 NS069721 to C.M.A., R01 NS056072 to C.M.A. and W.D.D., F31 NS089351 to N.M.W., and The Miami Project to Cure Paralysis. M.E.G. acknowledges support by the National Institutes of Health/National Institute of Mental Health R44 MH091791. We thank Jonathan Mendoza, Rosmery Santos, and David Sequeira for technical support, and Dr Xuesheng Mo for synthesis of A33.
© 2016 the authors.
- Long-term potentiation
- Traumatic brain injury