different attributes associated with spinal cord injuries. Depending on the purpose of the study and the specific aspect of the injury to be investigated, researchers determine which animal model most closely replicates the injury in humans (Tables 3-2 and 3-3). In 2000, the International Spinal Research Trust published guidelines that describe four characteristics that are required for an optimal model of spinal cord injury (Ramer et al., 2000):
The nature and the extent of the lesion should be precisely defined. If there is doubt about the extent of a lesion or whether axons have been spared, then interpretations of regeneration can be misleading.
A histological method should be available to detect the growth of axons through the lesion.
A method should be available to analyze the functional synaptic transmission beyond the lesion by measuring the electrical activity that neurons use to communicate with one another.
A behavioral measure should be available that is capable of detecting restoration of known circuits.
It is important to examine therapies in a system that best mimics the condition of the individual with a spinal cord injury. For example, therapies designed for individuals with chronic conditions should not be tested in animal models immediately after the animal has received the injury but should be tested only after the animal is in the chronic stage of the injury (Kwon et al., 2002a; Houle and Tessler, 2003; Kleitman, 2004). Further-
TABLE 3-2 Value of Animal Models for Spinal Cord Injury Research