No abstract

Pieces of fetal spinal tissue were transplanted into the site of complete midthoracic spinal transections in neonatal rat pups (transplant rats). The development of locomotion in these animals was compared with that of unoperated control rats and rats that received spinal transections alone (spinal rats). Reflex, treadmill and overground locomotion, staircase descent, and horizontal ladder crossing for a water reward were tested in control, spinal, and transplant rats from 3 weeks to adulthood. All tests were readily performed by control animals. Most spinal rats were unable to make many linked weight-supported steps on these tasks. Transplant rats were variable in their locomotor capabilities, but a subset of rats were able to demonstrate coordinated and adaptable locomotion on these tasks. Some transplant rats performed better on more challenging tasks, suggesting that motor strategies for these tasks used different information, perhaps from descending systems. Transplanted tissue survived, and in most cases there was immunocytochemical staining of serotonergic fibers passing into and caudal to the transplant, supporting the conclusion that descending systems grew through the transplanted tissue. Integration with the host tissue was often poor, suggesting that nonspecific or trophic effects of the transplant might also contribute to the development of locomotor function. Therefore several mechanisms may contribute to the repair of injured spinal cord provided by transplants that permit the development of useful locomotion.

The purpose of this study was 1). to characterize the morphology of lumbar commissural neurons (CNs) with reticulospinal inputs and 2). to quantitate their activity during locomotor rhythm generation. Intraaxonal recordings at the L4-7 level of the spinal cord were obtained in 67 neurons in the decerebrate, paralyzed cat. Fourteen of them were subsequently nearly fully visualized following their intraaxonal injection with the tracer neurobiotin. All 14 were CNs with axons projecting across the midline of the spinal cord. Their somata were located mainly in lamina VIII and additionally in laminae VII-VI. Most of the lamina VIII CNs were excited monosynaptically from reticulospinal pathways. They were judged to be interneuronal CNs if they had no, or a short, rostral projection. These CNs commonly gave off multiple axon collaterals in and around their somata's segmental level. They projected mainly to laminae VIII-VII and some additionally to lamina IX. Some laminae VIII and the laminae VII-VI CNs were excited polysynaptically from reticulospinal pathways or were not excited. They were judged to be long propriospinal or ascending tract CNs because they had only an ascending axon. Most lamina VIII CNs discharged rhythmically during fictive locomotion evoked by stimulation of the mesencephalic locomotor region, exhibiting one peak per locomotor cycle. The peak was in phase with neurographic activity of either a left or a right hindlimb extensor nerve. These results suggested that lamina VIII CNs are reciprocally connected bilaterally at each segmental level. Such an arrangement suggests their participation in the generation and coordination of reciprocal and bilateral locomotor activity.

OEF ratios on QSM-OEF images at 7 Tesla showed a good correlation with those on PET-OEF images in patients with unilateral steno-occlusive internal carotid artery/middle cerebral artery lesions, suggesting that noninvasive OEF measurement by MRI can be a substitute for PET.