White Fiber Bundles Research Articles

Is that tractography applicable to cranial nerves: Interest in neuroanatomy and skull base surgery

Introduction The intracranial anatomical distribution of white fibers has long been described from post-mortem brain dissection in latest centuries. Whereas MRI recently brought new possibilities to show the in vivo architecture of the central nervous system, diffusion tensor imaging achieved tracking of white fiber bundles connecting brain areas or projecting sensorimotor pathways. Nonetheless, tracking of small anatomical fibers like cranial nerves remains challenging. Even if they are often seen on T2 steady state sequence along their cisternal segments, their course inside the brainstem or through skull base foramina is difficult to feature. Furthermore, cranial nerves cannot be followed in case of stretching or encasement by skull base tumors. Today, we present a study of cranial nerves tractography and its potential applications in neuroanatomy and skull base surgery. Methods Ten patients, who presented complex skull base tumors, were evaluated by brain MRI with a 32 directions diffusion sequence and a T2 steady state sequence. Distortions due to skull base bone were corrected. Then, fiber tracking was attempted thanks to the Mtrtix3 software. The healthy side was used as control. Post-processing parameters were adapted to each cranial nerve in normal and pathologic conditions. Results Tractography of cranial nerves I to XI (except IV) was performed for various complex skull base tumors: vestibular schwannomes (4), epidermoid cysts (3), meningiomas (3). Small cranial nerves as VI or VII/VIII were difficult to track when stretching around tumors or diffusion signal similar to the tumor. Fiber tracking included cisternal part of nerves but also their trajectory within the brainstem and through the skull base. Discussion and conclusion Tractography was strongly dependent of tracking parameters: design of ROI, fractional anisotropy threshold, curvature angle, number of fibers and minimal length. These have to be refined to track very small white fibers around skull base tumors or along their brainstem course.

Glycogen synthesis from lactate in skeletal muscle of the lizardDipsosaurus dorsalis

The capacity of skeletal muscle to synthesize glycogen from lactate was tested in the iliofibularis muscle of the desert iguana, Dipsosaurus dorsalis. Like other reptiles, Dipsosaurus accumulates significant lactic acid concentrations following vigorous exercise. After 5 min of progressively faster treadmill running at 35 degrees C (final speed = 2.2 km/h), blood lactate concentration increased over 14 mM, which decreased 11 mM after 2 h of recovery. Blood glucose concentration remained unchanged throughout at 8.6 +/- 0.46 mM. The role that muscle gluconeogenesis might play in the removal of post-exercise lactate was evaluated. Animals were run to exhaustion at 1.5 km/h on a treadmill thermostatted at 35 degrees C. Animals (n = 43) ran 6.9 +/- 0.75 min prior to exhaustion. Animals were sacrificed and iliofibularis muscles of both hindlimbs removed and stimulated at 2 Hz for 5 min, reducing twitch tension to 6% of prestimulus tension. Fatigued muscles were then split into red and white fiber bundles and incubated 2 h or 5 h at 35 degrees C in Ringer solution or in Ringer plus 20 mM lactate. In muscles tested in August, red fiber bundles incubated in lactate demonstrated a rate of glycogen synthesis of approximately 1 mg/(g muscle . h). In muscles tested in December, red fiber bundles synthesized glycogen at a reduced rate that was not statistically different than in fiber bundles incubated in Ringer solution without lactate. Glycogen synthesis from lactate was not evident in white fiber bundles in either August or December. The period of peak gluconeogenic capacity coincides with the field active season of Dipsosaurus.(ABSTRACT TRUNCATED AT 250 WORDS)