Experimental Models of Partial Lesion of Rat Spinal Cord to Investigate Neurodegeneration, Glial Activation, and Behavior Impairments

Abstract

The article demonstrates two experimental models of spinal cord partial injury in rats: a contuse model promoted by the NYU impactor system and a partial hemitransection model achieved by a stereotaxic-posi-tioned adjustable wire knife. By means of a defined impact weight (10 g) and a digital optical potentiometer linked to a computer, the impactor transferred and registered a moderate or a severe contusion to the rat spinal cord at a low thoracic level after dropping the weight from distances of 25 mm and 50 mm, respectively, to the dorsal surface of the exposed dura spinal cord. Impact curve was calculated and the parameters of the trauma, like impact velocity, cord compression distance and cord compression rates were obtained in order to demonstrate trauma severity. To promote partial hemitransection, rats were positioned in a spinal cord unit of a stereotaxic apparatus and lesion was made with the adjustable wire knife spatially oriented. By means of a computerized infrared motion sensor-home cage activity monitor and a noncomputerized evaluation of motor behavior using the inclined plane and the motor score of Tarlov tests, behavior was analyzed in an acute period postlesion. Rats were sacrificed and spinal cords were processed for routine staining to show neurons and for GFAP and OX42 immunohistochemistry to demonstrate glial cells. The tissue labelings were quantified using computer assisted stereology by means of an optical disector and microden-sitometric image analysis by means of quantification of gray values of discriminated profiles. While partial hemitransection model favored a more accurate control of the lesion location, the contuse model allowed us to perform different degrees of lesion severity. A close correlation between behavioral impairment and severity of trauma was seen in the rats submitted to spinal cord contusion. The stereologic lesion index showed a correlation between severity of trauma and tissue damage by 7 days and demonstrated a time-dependent secondary degeneration after moderate but not after severe spinal cord contusion from 7 to 30 days after injury. Long-lasting activations of astrocytes and microglia seen by persisted increases in the specific mean gray values of immu-noreactivities were also found in all levels of the white and gray matters of the partial hemitransected spinal cord until 3 months postinjury which can he related to wound/repair events and paracrine trophic support to spinal cord remaining neurons. The results showed that controlled partial lesions may provide an important toll to study trophism and plasticity in the spinal cord.

Key Words:

• astrocyte
• microglia
• behavior
• stereology
• image analysis
• immunohistochemistry