Recovery from spinal cord injury mediated by antibodies to neurite growth inhibitors

There is little axonal growth after central nervous system (CNS) injury in adult mammals. The administration of antibodies (IN-1) to neutralize the myelin-associated neurite growth inhibitory proteins leads to long-distance regrowth of a proportion of CNS axons after injury. Our aim was: to determine if spinal cord lesion in adult rats, followed by treatment with antibodies to neurite growth inhibitors, can lead to regeneration and anatomical plasticity of other spinally projecting pathways; to determine if the anatomical projections persist at long survival intervals; and to determine whether this fibre growth is associated with recovery of function. We report here that brain stem-spinal as well as corticospinal axons undergo regeneration and anatomical plasticity after application of IN-1 antibodies. There is a recovery of specific reflex and locomotor functions after spinal cord injury in these adult rats. Removal of the sensorimotor cortex in IN-1-treated rats 2-3 months later abolished the recovered contact-placing responses, suggesting that the recovery was dependent upon the regrowth of these pathways.

Recovery of function after spinal cord injury: mechanisms underlying transplant-mediated recovery of function differ after spinal cord injury in newborn and adult rats

Fetal spinal cord transplants placed into the site of spinal cord injury support axonal growth of host systems in both newborn and adult animals. The amount of axonal growth, however, is much more robust in the newborn animals. The current studies were designed to determine if the differences in the magnitude of the anatomical plasticity of host pathways in the presence of transplants is reflected in differences in recovery of function between the neonatal and adult operates. Newborn and adult rats received a midthoracic "overhemisection." Immediately following the hemisection embryonic (E14) spinal cord transplants were placed into the lesion site. All animals were trained and tested as adults, on a battery of qualitative and quantitative tests of motor function. Immunocytochemical methods were used to compare the extent of growth of descending (serotonergic and noradrenergic) and segmental (calcitonin gene-related peptide containing dorsal root axons) pathways in both groups. The growth of descending pathways into the transplants was substantially greater in density and spatial extent after lesions at birth than at maturity. The distribution of segmental dorsal root axons, in contrast, was similar in both groups. Fetal spinal cord transplants promoted recovery of motor function in both newborn and adult operates. The particular aspects of locomotor function which recover differ between the neonatal and adult operates, suggesting that the mechanisms underlying recovery of function must differ between the two groups.

Methods to assess the development and recovery of locomotor function after spinal cord injury in rats

The ability to assess recovery of function after spinal cord injury is a very important part of spinal cord injury research. Recent progress has been made in a number of avenues of treatment designed to ameliorate the consequences of spinal cord injury and enhance recovery of function. This potential for intervention to modify the sequellae of spinal cord injury requires stringent criteria for methods used to evaluate the effects of injury and subsequent recovery of function. Methods which rely on composite ratings of an animal's overall performance, while appropriate for screening groups of animals with spinal cord injury, are not sufficient to demonstrate whether a particular treatment has had a specific effect on motor function or the degree to which function is affected. We have designed a series of sensitive quantitative methods to assess the recovery of locomotor function in rats. The methods examine specific reflex responses and specific components of motor behavior and are sensitive to subtle differences in the pattern of locomotion and individual limb movements. Several of the tests can be used to assess the development of locomotor function as well as the mature response. Postural reflex testing and locomotor function under conditions of graded difficulty are examined and the motor capacity of individual limbs is assessed. Animals are trained to cross runways, to walk on a treadmill, and to climb onto a platform. The animals' performance is videotaped for subsequent quantitative analysis. The pattern of overground and treadmill locomotion is also examined by footprint analysis. Spinal cord injury alters an animal's reflex responses and deficits are evident in locomotor function. Examples are given of the quantitative measurements obtained from analysis of the animals' performance on each of the tests. No single test is sufficient to assess recovery of function after spinal cord injury. Rather, a combination of tests, each examining particular components of normal and recovered motor function, is required. The methods used to assess recovery of locomotor function are specific, are sensitive, and allow individual limb movements to be isolated. Such specific methods allow one to begin to address the mechanisms underlying recovery of function following spinal cord injury.

Recovery of function after spinal cord hemisection in newborn and adult rats: differential effects on reflex and locomotor function

It is often assumed that the response of the immature nervous system to injury is more robust and exhibits greater anatomical reorganization and greater recovery of function than in the adult. In the present experiments the extent of recovery of function after spinal cord injury at birth or at maturity was assessed. We used a series of quantitative tests of motor behavior to measure reflex responses and triggered movements and to examine different components of locomotion. Rats received a midthoracic "over-hemisection" at birth or as adults. The neonatal operates were allowed to mature and the adult operates were allowed to recover. The animals were trained to walk on a treadmill and to cross runways of varying difficulty. The animals were tested for reflex responses and triggered movements, videotaped while crossing the runways, and footprinted while walking on the treadmill. The adult operates had greater deficits in the reflex responses than the neonatal operates. The adult operates lost the contact placing response and had a decreased hopping response in the ipsilateral limb, while these responses were not impaired in the neonatal operates. Although the contact placing response in the neonatal operates was spared, a greater stimulus was necessary to induce the response than in control animals. In contrast, the neonatal operates had greater deficits in locomotion. Footprint analysis revealed that the animals' base of support was significantly greater after the neonatal injury than after the adult injury, and deficits in limb rotation were larger in the neonatal operates than in the adult operates. Both groups crossed the grid with a similar number of steps but the adult operates made significantly more errors with the hindlimb ipsilateral to the lesion than the contralateral one, while the neonatal operates made an equivalent number of errors with both limbs. The neonatal operates took longer to execute the climb test and used a different movement pattern than the adult operates. The neonatal operates had a different locomotor pattern than the adult operates. Despite greater recovery of reflex responses after spinal cord injury at birth, the pattern of locomotion exhibits greater deficits when compared with the same lesion in the adult. Just as the anatomical consequences of injury to the developing nervous system are not uniform, similarly, the behavioral consequences are also not uniform. Spinal cord injury before the mature pattern of locomotion has developed results in a different motor strategy than after injury in the adult.(ABSTRACT TRUNCATED AT 400 WORDS)

Spinal cord transplants enhance the recovery of locomotor function after spinal cord injury at birth

Fetal spinal cord transplants placed into the site of a neonatal spinal cord lesion after the response of immature CNS neurons to injury. The transplants prevent the retrograde cell death of immature axotomized neurons and support the growth of axons into and through the site of injury. In the present experiments we used a battery of locomotor tasks to determine if these transplants are also capable of promoting the recovery of motor function after spinal cord injury at birth. Embryonic (E14) spinal cord transplants were placed into the site of a spinal cord "over-hemisection" in rat pups. Three groups of animals were used: 1) normal control animals, 2) animals with a spinal cord hemisection only, and 3) animals with a spinal cord transplant at the site of the hemisection. Eight to twelve weeks later, the animals were trained and videotaped while crossing runways requiring accurate foot placement and footprinted while walking on a treadmill. The videotapes and footprints were analyzed to obtain quantitative measures of locomotor function. Footprint analysis revealed that the animals' base of support during locomotion was increased by a neonatal hemisection. The base of support in animals with transplants was similar to control values. Animals with a hemisection rotated their hindlimbs further laterally than did control animals during locomotion. A transplant at the site of injury modified this response. Normal animals were able to cross a grid runway quickly with only a few errors. In contrast, animals with a hemisection took a longer time and made more errors while crossing. The presence of a transplant at the site of injury enabled the animals to cross the grid more quickly and to make fewer errors than the animals with a hemisection only. Animals that received the transplants demonstrated qualitative and quantitative improvements in several parameters of locomotion. Spinal cord transplants at the site of neonatal spinal cord injury result in enhanced sparing or recovery of motor function. We suggest that this transplant induced recovery of function is a consequence of the anatomical plasticity elicited by the transplants.

Extension of the critical period for developmental plasticity of the corticospinal pathway

The corticospinal tract (CST) of the rat undergoes a prolonged period of postnatal development. Lesions of the presumptive CST pathway at birth are followed by the aberrant rerouting of the developing corticospinal axons around the lesion site through adjacent undamaged CNS tissue. This developmental plasticity becomes severely restricted by 5-6 days of age, so the axons are no longer capable of growth around the site of injury. The aim of the current study was to determine whether altering the environment at the site of injury by filling the lesion with transplanted fetal spinal cord tissue could prolong the critical period for developmental plasticity of the corticospinal pathway. The spinal cord was damaged (overhemisection) at three stages in the development of the corticospinal (CS) pathway: 1) prior to the arrival of CS axons, 2) after the axons elongated through the cord but prior to synaptogenesis, and 3) after both axonal elongation and synaptogenesis were completed. One to 9 months later, anterograde neuronal tracing with horseradish peroxidase was used to assess the growth of the corticospinal pathway with or without a fetal transplant at the site of injury, and the pattern of labeling was compared with that observed in adult nonlesioned control animals. Our results indicate that the presence of a transplant prolongs the critical period for developmental plasticity of the CST. Transplants elicited growth of CST axons throughout the postnatal period examined. CST axons damaged prior to synaptogenesis exhibited more robust growth than those lesioned after synaptogenesis had been completed. These results suggest that both environmental and neuronal factors interact to regulate the response of immature CS neurons to injury.