The extent of damage following spinal cord injury (SCI) can be reduced by various neuroprotective regimens that include maintaining levels of cyclic adenosine monophosphate (cyclic AMP), via administration of the phosphodiesterase 4 (PDE4) inhibitor Rolipram. The current study sought to determine the optimal neuroprotective dose, route and therapeutic window for Rolipram following contusive SCI in rat as well as its prominent PDE target and putative mechanism of protection. Rolipram or vehicle control (10% ethanol) was given subcutaneously (s.c.) daily for 2 wk post-injury (PI) after which the preservation of oligodendrocytes, neurons and central myelinated axons was stereologically assessed. Doses of 0.1 mg/kg to 1.0 mg/kg (given at 1 h PI) increased neuronal survival; 0.5 mg to 1.0 mg/kg protected oligodendrocytes and 1.0 mg/kg produced optimal preservation of central myelinated axons. Ethanol also demonstrated significant neuronal and oligo-protection; though the preservation provided was significantly less than Rolipram. Subsequent use of this optimal Rolipram dose, 1.0 mg/kg, via different routes (i.v., s.c. or oral, 1 h PI), demonstrated that i.v. administration produced the most significant and consistent cyto- and axo- protection, although all routes were effective. Examination of the therapeutic window for i.v. Rolipram (1.0 mg/kg), when initiated between 1 and 48 h after SCI, revealed maximal neuroprotection at 2 h post-SCI, although the protective efficacy of Rolipram could still be observed when administration was delayed for up to 48 h PI. Importantly, use of the optimal Rolipram regimen significantly improved locomotor function after SCI as measured by the BBB score. Lastly we show SCI-induced changes in PDE4A, B and D expression and phosphorylation as well as cytokine expression and immune cell infiltration. We demonstrate that Rolipram abrogates SCI-induced PDE4B1 and PDE4A5 production, PDE4A5 phosphorylation, MCP-1 expression and immune cell infiltration, while preventing post-injury reductions in IL-10. This work supports the use of Rolipram as an acute neuroprotectant following SCI and defines an optimal administration protocol and target for its therapeutic application.

Methylprednisolone (MP) and interleukin-10 (IL-10) are tissue protective acutely after spinal cord injury (SCI); their combination offers additive protection (Takami et al., 2002a). Our study examined if acute administration of MP (30 mg/kg i.v. at 5 min, and 2 and 4 h after injury) and IL-10 (30 mg/kg i.p. at 30 min after injury) increases the efficacy of Schwann cell (SC) or SC plus olfactory ensheathing glia (SC/OEG) grafts transplanted into rat thoracic cord 1 week after contusive injury. Efficacy was determined by histology, anterograde and retrograde tracing, immunohistochemistry for gliosis and specific nerve fibers, and several behavioral tests. Administration of MP/IL-10 or SC or SC/OEG transplantation significantly increased the total volume of a 9-mm segment of cord encompassing the injury site at 12 weeks. The combination of either SC or SC/OEG transplantation with MP/IL-10 most significantly reduced cavitation. The individual treatments all significantly increased the volume of normal-appearing tissue compared to injury-only controls; however, significant decreases in the volume of normal-appearing tissue were seen when MP/IL-10 and cell grafts were combined compared to MP/IL-10 alone. SC/OEG grafts were effective in promoting serotonergic fiber growth into the graft and led to more reticulospinal fibers caudal to the graft; combination with MP/IL-10 did not further increase fiber number. Only the combination of MP/IL-10 with SC/OEG transplants significantly improved gross locomotor performance (BBB scores) over injury-only controls. MP/IL-10 given prior to SC-only transplants, however, worsened behavioral outcome. Because beneficial effects of MP/IL-10 were not always additive when combined with cell transplantation, we need to understand (1) how tissue protective agents may transform the milieu of the injured spinal cord to the benefit or detriment of later transplanted cells and (2) whether neuroprotectants need to be re-administered at the time of cell grafting or less invasive transplantation techniques employed to reduce damage to tissue spared by an earlier protection strategy.

Hypothermia has been employed during the past 30 years as a therapeutic modality for spinal cord injury (SCI) in animal models and in humans. With our newly developed rat cervical model of contusive SCI, we investigated the therapeutic efficacy of transient systemic hypothermia (beginning 5 minutes post-injury for 4 hours, 33 degrees C) with gradual rewarming (1 degrees C per hour) for the preservation of tissue and the prevention of injury-induced functional loss. A moderate cervical displacement SCI was performed in female Fischer rats, and behavior was assessed for 8 weeks. Histologically, the application of hypothermia after SCI resulted in significant increases in normal-appearing white matter (31% increase) and gray matter (38% increase) volumes, greater preservation (four-fold) of neurons immediately rostral and caudal to the injury epicenter, and enhanced sparing of axonal connections from retrogradely traced reticulospinal neurons (127% increase) compared with normothermic controls. Functionally, a faster rate of recovery in open field locomotor ability (BBB score, weeks 1-3) and improved forelimb strength, as measured by both weight-supported hanging (43% increase) and grip strength (25% increase), were obtained after hypothermia. The current study demonstrates that mild systemic hypothermia is effective for retarding tissue damage and reducing neurological deficits following a clinically relevant contusive cervical SCI.