Biotinylated dextran amine anterograde tracing of the canine corticospinal tract

In this study, biotinylated dextran amine （BDA） was microinjected into the left cortical motor area of the canine brain. Fluorescence microscopy results showed that a large amount of BDA-labeled pyramidal cells were visible in the left cortical motor area after injection. In the left medulla oblongata, the BDA-labeled corticospinal tract was evenly distributed, with green fluorescence that had a clear boundary with the surrounding tissue. The BDA-positive corticospinal tract entered into the right lateral funiculus of the spinal cord and descended into the posterior part of the right lateral funiculus, close to the posterior horn, from cervical to sacral segments. There was a small amount of green fluorescence in the sacral segment. The distribution of BDA labeling in the canine central nervous system was consistent with the course of the corticospinal tract. Fluorescence labeling for BDA gradually diminished with time after injection. Our findings indicate that the BDA anterograde tracing technique can be used to visualize the localization and trajectory of the corticospinal tract in the canine central nervous system.

Chondroitinase ABC treatment of injured spinal cord in rats Evaluation of long-term outcomes

Chondroitin sulfate proteoglycans （CSPGs） which are produced by mature oligodendrocytes and reactive astrocytes can be upregulated after spinal cord injury and contribute to regenerative failure. Chondroitinase ABC （ChABC） digests glycosaminoglycan chains on CSPGs and can thereby overcome CSPG-mediated inhibition. However, many current studies have used an incomplete spinal cord injury model, and examined results after 8-12 weeks of ChABC treatment. In this study, a complete rat spinal cord transection injury model was used to study the long-term effects of ChABC treatment by subarachnoid catheter. Pathology of spinal cord regeneration was compared with control 24 weeks following ChABC treatment using immunohistochemistry and axon tracing techniques. At 24 weeks after injury, neurofilament 200 expression was significantly greater in the ChABC treatment group compared with the transection group. In the ChABC treatment group, axonal growth was demonstrated by a large number of biotinylated dextran amine positive axons caudal to, or past, the epicenter of injury. Biotinylated dextran amine-labeled fibers were found in the proximal end of the spinal cord in the transection alone group. These results confirm that ChABC can promote axon growth, neural regeneration, and repair after spinal cord injury in rats long after the initial injury.

Is Marcus Gunn jaw winking a primitive reflex？ Rat neuroanatomy

AIM： To investigate a possible trigeminal proprioceptive- oculomotor neural pathway and explore possible synaptic connections between neurons in this pathway. Attempt to bring a new insight to mechanism of Marcus Gunn syndrome （MGS）. METHODS： Anterograde and retrograde tract tracing was applied and combined with immunofluorescent stain in rats. After electrophysiological identifying mesencephalic trigeminal nucleus （Vine） neurons, intracellular injection of tracer was performed to trace axon trajectory. RESULTS： Following injections of anterograde tracers into the Vine, labeled terminals were observed ipsilateral in oculomotor and trochlear nuclei （Ill/IV）, as well as in their premotor neurons in interstitial nucleus of Cajal and Darkschewitsch nucleus （INC/DN）. Combining with choline acetyltransferase （CHAT） immunofluorescent stain, it showed that Vme projecting terminals contact upon ChAT positive Ill/IV motoneurons under confocal microscope. By retrograde labeling premotor neurons of the III, it showed that Vme neuronal terminals contact with retrogradely labeled pre-oculomotor neurons in the INCIDN. Axons of intraceiiularly labeled Vme neurons that respond to electric stimuli of the masseter nerve traveled into the ipsilateral III. CONCLUSION： There may exist a trigeminal propdoceptive- oculomotor system neural circuit in the rat, which is probably related to vertical-torsional eye movements. Possible association of this pathway with MGS etiology was discussed.