Inhibiting cortical protein kinase A in spinal cord injured rats enhances efficacy of rehabilitative training

Exp Neurol. 2016 Sep;283(Pt A):365-74. doi: 10.1016/j.expneurol.2016.07.001. Epub 2016 Jul 8.


Elevated levels of the second messenger molecule cyclic adenosine monophosphate (cAMP) are often associated with neuron sprouting and neurite extension (i.e., neuroplasticity). Phosphokinase A (PKA) is a prominent downstream target of cAMP that has been associated with neurite outgrowth. We hypothesized that rehabilitative motor training following spinal cord injuries promotes neuroplasticity via PKA activation. However, in two independent experiments, inhibition of cortical PKA using Rp-cAMPS throughout rehabilitative training robustly increased functional recovery and collateral sprouting of injured corticospinal tract axons, an indicator of neuroplasticity. Consistent with these in vivo findings, using cultured STHdh neurons, we found that Rp-cAMPS had no effect on the phosphorylation of CREB (cAMP response element-binding protein), a prominent downstream target of PKA, even with the concomitant application of the adenylate cyclase agonist forskolin to increase cAMP levels. Conversely, when cAMP levels were increased using the phosphodiesterase inhibitor IBMX, Rp-cAMPS potently inhibited CREB phosphorylation. Taken together, our results suggest that an alternate cAMP dependent pathway was involved in increasing CREB phosphorylation and neuroplasticity. This idea was supported by an in vitro neurite outgrowth assay, where inhibiting PKA did enhance neurite outgrowth. However, when PKA inhibition was combined with inhibition of EPAC2 (exchange protein directly activated by cAMP), another downstream target of cAMP in neurons, neurite outgrowth was significantly reduced. In conclusion, blocking PKA in cortical neurons of spinal cord injured rats increases neurite outgrowth of the lesioned corticospinal tract fibres and the efficacy of rehabilitative training, likely via EPAC.

Keywords: PKA; Single pellet grasping; Spinal cord injury; cAMP.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 1-Methyl-3-isobutylxanthine / pharmacology
  • Analysis of Variance
  • Animals
  • CREB-Binding Protein / metabolism
  • Cell Line, Transformed / metabolism
  • Cell Line, Transformed / pathology
  • Cells, Cultured
  • Cerebral Cortex / enzymology*
  • Cerebral Cortex / metabolism
  • Cyclic AMP / analogs & derivatives
  • Cyclic AMP / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Disease Models, Animal
  • Female
  • Ganglia, Spinal / cytology
  • Microglia / metabolism
  • Microglia / pathology
  • Neurites / drug effects
  • Neurites / physiology
  • Neurons / drug effects
  • Neurons / metabolism
  • Phosphodiesterase Inhibitors / pharmacology
  • Pyramidal Tracts / metabolism
  • Rats
  • Rats, Inbred Lew
  • Recovery of Function / physiology
  • Spinal Cord Injuries / pathology*
  • Spinal Cord Injuries / rehabilitation*
  • Thionucleotides / metabolism


  • Phosphodiesterase Inhibitors
  • Thionucleotides
  • adenosine-3',5'-cyclic phosphorothioate
  • Cyclic AMP
  • CREB-Binding Protein
  • Crebbp protein, rat
  • Cyclic AMP-Dependent Protein Kinases
  • 1-Methyl-3-isobutylxanthine