The role of calcium ions in the synthesis and transport of noradrenaline carrier vesicles in guinea-pig sympathetic neurons in vitro

Nogo-A expression in the intact and injured nervous system

The expression of Nogo-A mRNA and protein in the nervous system of adult rats and cultured neurons was studied by in situ hybridisation and immunohistochemistry. Nogo-A mRNA was expressed by many cells in unoperated animals, including spinal motor, DRG, and sympathetic neurons, retinal ganglion cells, and neocortical, hippocampal, and Purkinje neurons. Nogo-A protein was strongly expressed by presumptive oligodendrocytes, but not by NG2+glia and was abundant in motor, DRG, and sympathetic neurons, retinal ganglion cells, and many Purkinje cells, but was difficult to detect in dentate gyrus neurons and some neocortical neurons. Cultured fetal mouse neocortical neurons and adult rat DRG neurons strongly expressed Nogo-A in their perikarya, growth cones, and axonal varicosities. All axons in the intact sciatic nerve contained Nogo-A and many but not all regenerating axons were strongly Nogo-A immunopositive after sciatic nerve transection. Ectopic muscle fibres that developed among the regenerating axons were also Nogo-A immunopositive. Following injury to the spinal cord, Nogo-A mRNA was upregulated around the lesion and Nogo-A protein was strongly expressed in injured dorsal column fibres and their sprouts which entered the lesion site. Following optic nerve crush, Nogo-A accumulated in the proximal and distal stumps bordering the lesions.

Cryo-electron microscopy of nervous tissue. A review

The present work attempts to demonstrate that cryofixation is a valuable method for the study of the nervous tissue. The use of the newly developed methods of cryofixation and freeze-etching without fixatives or cryoprotectants allows new exciting perspectives for the electron microscopical observation of cellular components, emphasizing their three-dimensional morphological structures. Significant contributions have been made on the fine structure of the cytoskeleton, cell membranes and cell organelles. The components of the cytoskeleton are distributed in different composition through the perikarya, dendrites and axon. The ubiquitous presence of the cytoskeleton suggests a crucial role in the functional activities of the neurons, especially in relation to the intracellular communication and to developmental and regeneration processes. Vitrified cellular membranes of myelin sheaths and rod outer segments have been observed in hydrated state by using cryofixation and cryotransfer techniques. These procedures allow new insights into the supramolecular structure and an approximation of morphological data to the present biophysical membrane model including a critical comparison with the current descriptions gained by conventional electron microscopy.

Microscopic observations on endogenous fluorochromes within a nerve fibre excited by a 325 nm He-Cd laser

A microscopic procedure to observe endogenous fluorochromes in superfused tissues is described. In this procedure, a 325 nm beam from a He-Cd laser is directed through the objective lens of a microscope onto the surface of a brain slice. Fluorescent structures within the tissue can be observed, photographed and measured. A nerve fibre running from the corporis callosi to the dorsal cerebral cortex was studied with this approach. The 325 nm laser beam excited material with an emission peak at 420 nm within a fibre on the cut surface of a rat brain slice superfused with Krebs-Ringer. A similar fibre was observed in vivo in the exposed mouse brain. Packets of the fluorescent material appear to move within the fibre in vitro. The fluorescence of the fibre was rapidly diminished by cyanide, colchicine, rotenone and the withdrawal of Ca2+. Elevation of [K+] in the superfusate caused a "haloing' of the fibre's granularity without decreasing the total fluorescence. This phenomenon is possibly related to the depolarization by [K+] of neurones. Although the structure of the fluorochrome was not established, it is suggested that it may be a neurotransmitter-related substance undergoing axonal movement.

Degeneration of non-myelinated axons in the rat sciatic nerve following lysolecithin injection

Lysolecithin has been used in many studies to induce demyelination in peripheral nerves. In the present investigation lysolecithin (lysophosphatidyl choline) was injected into rat sciatic nerves at a dose of 2-3 microns of a 10 mg/ml solution in order to study the effects of this lipid on cellular elements other than myelin within the nerve. Twenty-four hours after injection, there was splitting of myelin, lysis of Schwann cells, and complete loss of non-myelinated axons and their Schwann cells at the site of injection. Numerous swollen non-myelinated axons containing accumulated organelles were seen just proximal to the site of injection at 48 h. Loss of non-myelinated axons from the distal part of the nerve was also noted at 3 days after injection but 7 days regenerating non-myelinated axons had re-appeared in the distal part of the nerve. Although demyelination, followed by remyelination was prominent feature in the injected segment of the nerve, no damage to myelinated axons was detected. These results suggest that the presence of the myelin sheath protects the large myelinated axons against the action of lysolecithin, but with lysis of Schwann cells, the non-myelinated axons are exposed to the action of lysolecithin. Apart from selective damage to non-myelinated fibres with subsequent degeneration, it is also possible that lysolecithin interferes with axoplasmic flow in non-myelinated axons.

A morphological study of the uptake and orthograde axoplasmic transport of horseradish peroxidase by damaged autonomic neurons in vitro

A preparation comprising the guinea-pig inferior mesenteric ganglion (IMG) and ligated hypogastric nerves was maintained in vitro in a twin-chamber apparatus. Horseradish peroxidase (HRP), added to the ganglion compartment, was taken up via coated pinocytotic vesicles into the neuronal perikarya, and subsequently accumulated in many polymorphic cytoplasmic organelles, but it did not enter the Golgi complex. After 24 h incubation, HRP was also localized in membrane-bounded organelles in the nonmyelinated axons of the hypogastric nerves in the ligated nerve compartment. HRP-labelled organelles accumulated in swollen nonmyelinated axons immediately proximal to the ligation along with other organelles known to undergo fast axoplasmic transport. It is suggested that HRP taken up by the neuronal perikarya subsequently underwent fast axoplasmic transport without passing through the Golgi complex. The organelles in which HRP was transported in an orthograde direction were very similar to those in which the enzyme is known to be transported retrogradely in the same neuronal system. The advantages of this in vitro system for studying the orthograde transport of exogenous protein are discussed.