Localization of the corticospinal tract within the porcine spinal cord: Implications for experimental modeling of traumatic spinal cord injury

Spinal cord injury (SCI) researchers have predominately utilized rodents for SCI modeling and experimentation. Unfortunately, a large number of novel therapies developed in rodent models have failed to demonstrate efficacy in human clinical trials which suggests that improved animal models are an important translational tool. Recently, porcine models of SCI have been identified as a valuable intermediary model for preclinical evaluation of promising therapies to aid clinical translation. However, the localization of the major spinal tracts in pigs has not yet been described. Given that significant differences exist in the location of the corticospinal tract (CST) between rodents and humans, determining its location in pigs will provide important information related to the translational potential of the porcine pre-clinical model of SCI. Thus, the goal of this study is to investigate the localization of the CST within the porcine spinal cord. Mature female domestic pigs (n=4, 60kg) received microinjections of fluorescent dextran tracers (Alexa Fluor, 10,000MW) into the primary motor cortex, using image-guided navigation (StealthStation^®), to label the CST. At 5 weeks post-tracer injection animals were euthanized, the entire neuroaxis harvested and processed for histological examination. Serial sections of the brain and spinal cord were prepared and imaged using confocal microscopy to observe the location of the CST in pigs. Results demonstrate that the CST of pigs is located in the lateral white matter, signifying greater similarity to human anatomical structure compared to that of rodents. We conclude that the corticospinal tract in pigs demonstrates anatomical similarity to human, suggesting that the porcine model has importance as a translational intermediary pre-clinical model.

Traumatic injury of cultured astrocytes alters inositol (1,4,5)-trisphosphate-mediated signaling

Our previous studies using an in vitro model of traumatic injury have shown that stretch injury of astrocytes causes a rapid elevation in intracellular free calcium ([Ca2+]i), which returns to near normal by 15 min postinjury. We have also shown that after injury astrocyte intracellular calcium stores are no longer able to release Ca2+ in response to signal transduction events mediated by the second messenger inositol (1,4,5)-trisphosphate (IP3, Rzigalinski et al., 1998). Therefore, we tested the hypothesis that in vitro injury perturbs astrocyte IP3 levels. Astrocytes grown on Silastic membranes were labeled with [3H]-myo-inositol and stretch-injured. Cells and media were acid-extracted and inositol phosphates isolated using anion-exchange columns. After injury, inositol polyphosphate (IPx) levels increased up to 10-fold over uninjured controls. Significant injury-induced increases were seen at 5, 15, and 30 min and at 24 and 48 h postinjury. Injury-induced increases in IPx were equivalent to the maximal glutamate and trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid-stimulated IPx production, however injury-induced increases in IPx were sustained through 24 and 48 h postinjury. Injury-induced increases in IPx were attenuated by pretreatment with the phospholipase C inhibitors neomycin (100 microM) or U73122 (1.0 microM). Since we have previously shown that astrocyte [Ca2+]i returns to near basal levels by 15 min postinjury, the current results suggest that IP3-mediated signaling is uncoupled from its target, the intracellular Ca2+ store. Uncoupling of IP3-mediated signaling may contribute to the pathological alterations seen after traumatic brain injury.

Status epilepticus causes long-term NMDA receptor-dependent behavioral changes and cognitive deficits

PURPOSE

The role of N-methyl-D-aspartate (NMDA)-receptor activation on behavioral and cognitive changes after status epilepticus (SE) is unknown. In this study, behavioral and cognitive changes after SE were evaluated in the short and long term and in rats in which the NMDA receptor was inactivated during SE.

METHODS

Pilocarpine (350 mg/kg) was injected to induce SE. Inhibition of the NMDA receptor during SE was achieved with MK-801 (4 mg/kg). Seizure intensity during SE was monitored by electroencephalography (EEG). After SE, behavioral studies were performed to identify abnormal behavior by using behavioral tests adapted from Moser's functional observational battery. Cognitive changes were assessed by using the Morris Water Maze (MWM).

RESULTS

Pilocarpine-treated animals scored significantly higher on two of the behavioral tests: the Touch test and the Pick-Up test. These behavioral changes occurred very soon after SE, with the earliest changes observed 2 days after SE and persisting for the life of the animal. Inhibition of the NMDA receptor with MK-801 completely inhibited these behavioral changes under conditions that did not alter the duration of SE. In addition, pilocarpine-treated animals exhibited cognitive deficits as determined by using the MWM. Six weeks after SE, the animals displayed significantly longer latencies to locate the hidden platform on this test. The impaired performance on the MWM also occurred as early as 5 days after SE. These cognitive deficits were prevented in animals treated with MK-801 during SE.

CONCLUSIONS

The results indicate that behavioral and cognitive changes occur soon after SE, are permanent, and are dependent on NMDA-receptor activation during SE. NMDA-receptor activation may play an important role in causing cognitive and behavioral morbidity after recovery from SE.