Georges E. Ouaknine

New trend in neuroscience: low-power laser effect on peripheral and central nervous system (basic science, preclinical and clinical studies).

The present review summarizes findings in our continuing study of the use of low-power laser irradiation (LPLI) in the treatment of severely injured peripheral (PNS) and central nervous systems (CNS). The radiation method was proposed by Rochkind and has been modified over the last 13 years. LPLI in specific wavelengths and energy density maintains the electrophysiological activity of severely injured peripheral nerve in rats, preventing scar formation (at injury site) as well as degenerative changes in the corresponding motor neurons of the spinal cord, thus accelerating regeneration of the injured nerve. Laser irradiation applied to the spinal cord of dogs following severe spinal cord injury and implantation of a segment of the peripheral nerve into the injured area diminished glial scar formation, induced axonal sprouting in the injured area and restoration of locomotor function. The use of laser irradiation in mammalian CNS transplantation shows that laser therapy prevents extensive glial scar formation (a limiting factor in CNS regeneration) between a neural transplant and the host brain or spinal cord. Abundant capillaries developed in the laser-irradiated transplants, and was of crucial importance in their survival. Intraoperative clinical use of laser therapy following surgical treatment of the tethered spinal cord (resulting from myelomeningocele, lipomyelomeningocele, thickened filum terminale or fibrous scar) increases functional activity of the irradiated spinal cord. In a previous experimental work, we showed that direct laser treatment on nerve tissue promotes restoration of the electrophysiological activity of the severely injured peripheral nerve, prevents degenerative changes in neurons of the spinal cord and induces proliferation of astrocytes and oligodendrocytes. This suggested a higher metabolism in neurons and improved ability for myelin production under the influence of laser treatment. The tethering of the spinal cord causes mechanical damage to neuronal cell membranes leading to metabolic disturbances in the neurons. For this reason, we believe that using LPLI may improve neuronal metabolism, prevent neuronal degeneration and promote improved spinal cord function and repair. The possible mechanism of LPLI is investigated. Using electron paramagnetic resonance in cell culture models, we found that at low radiation doses, singlet oxygen is produced by energy transfer from porphyrin (not cytochrome as commonly assumed) which is known to be present in the cell. At low concentration, singlet oxygen can modulate biochemical processes taking place in the cell and trigger accelerated cell division. On the other hand, at high concentration, singlet oxygen damages the cell.(ABSTRACT TRUNCATED AT 400 WORDS)

Paraganglioma of the pituitary fossa: diagnosis and management

Paraganglioma of the sellar area is extremely rare with only six cases having been reported in the literature. Surgical removal of these tumors is difficult, and the transsphenoidal approach usually results in limited resection. Most authors who published reports on this tumor recommended radiation therapy after partial removal of the tumor. However, considering the benign nature of these tumors, the risk of radiation-induced endocrine insufficiency and optic neuropathy and the lack of proven effectiveness of radiotherapy, its value remains controversial.We describe a 48-year-old woman with parasellar paraganglioma who presented with headaches, visual loss and oligomenorrhea. Magnetic resonance imaging (MRI) showed an invasive tumor in the sellar and parasellar areas which extended to both cavernous sinuses and compressed the optic chiasm and the left internal carotid artery. Surgery by the transsphenoidal approach enabled only limited biopsy of the tumor. The patient was reoperated by an extended pterional approach which resulted in a subtotal removal of the tumor and adequate decompression of the adjacent structures. She received no adjuvant treatment during the 8-year postsurgical follow-up and remained in good health. A repeated MRI showed no change in the size of the residual tumor. Contrary to the therapeutic recommendations described in previous reports, we favor postoperative adjuvant therapy only if the symptoms or signs of cranial nerve compression persist following maximal tumor removal, or if there is evidence of subsequent growth of residual tumor.

Organization of layers II-III connections in human visual cortex revealed by in vitro injections of biocytin.

In the search for cortical mechanisms subserving psychological phenomena, a better understanding of human cortical circuitry is crucial. In this report we describe aspects of intrinsic connectivity of supragranular layers in human visual cortex, revealed by extracellular injections of the anterograde tracer biocytin in vitro. Human cortical slices were obtained from visual association cortex in the posterior-medial portion of the dorsal bank of the occipital lobe, removed during neurosurgical tumor ablations. Small iontophoretic injections of biocytin into layers II-III revealed intense Golgi-like staining of axonal projections emanating from the injection sites. Vertically descending axons are grouped in bundles 20 microns in diameter which are spaced 15 microns apart. Some of these axons enter the white matter and send long oblique and horizontal collaterals. The main horizontal spread of the axons could be observed in layers II-III and V. The bulk of projections extends to a distance of 1.5 mm in layers II-III and 1.1 mm in layer V. Few individual axons could be observed at greater distances. In contrast, layer IV is almost devoid of horizontal connections, forming a clear gap between supra- and infragranular layers. Axon collaterals in the infragranular layers project mostly in a descending oblique direction with long horizontal collaterals in lower layer VI.

Primary intramedullary spinal melanoma: Diagnostic and treatment problems

A 76-year old female patient with 9 year history of right mastectomy for an infiltrating ductal breast cancer and no evidence of recurrent nor metastatic disease, was admitted due to pain in the lower thoracic area radiating bilaterally to the posterior aspect of the chest wall at the same level, difficulties in micturition, urinary hesitancy, and progressive weakness of the lower limbs. Primary intramedullary spinal tumor was demonstrated by a MRI study of the spine, partially resected, and found to be a malignant melanoma on pathological study. Postoperative irradiation and administration of dexamethasone did not improve the neurologic status.