an in vitro gliotoxic effect of serum from animals with experimental allergic encephalomyelitis

Vascular permeability in the peripheral autonomic and somatic nervous systems: controversial aspects and comparisons with the blood-brain barrier

Endothelium, choroidal epithelium, and arachnoid exclude plasma proteins from most parts of the mammalian central nervous system (CNS). Nerve roots, in contrast, have permeable capillaries and permeable pia-arachnoid sheaths. Diffusion of plasma proteins into the cerebrospinal fluid is probably prevented by slow bulk flow along a pressure gradient from the subarachnoid space into the veins of the roots. In nerves, the perineurium prevents diffusion of proteins from the epineurium into the endoneurium. Capillaries within fascicles are permeable to macromolecules, though less so than the microvessels of roots and ganglia. Endoneurial vascular permeability is lowest in rats and mice, but even in these species albumin is normally present in the extracellular spaces around the nerve fibers. The so-called blood-nerve barrier is not equivalent to the blood-brain barrier. Capillaries in sensory and sympathetic ganglia are fully permeable to macromolecules, and extravasated protein is in contact with neuronal cell bodies and neurites. An impenetrable perineurium surrounds each ganglion, but serves no obvious purpose when the vessels inside are as permeable as those outside. The enteric nervous system lacks a perineurium, and the neurons in its avascular ganglia and tracts are exposed to extracellular fluid formed by permeable vessels in adjacent tissues of the gut. The reasons for excluding macromolecules from some parts of the nervous system are obscure. Carrier-mediated transport, which maintains a constant supply of ions, glucose, and other metabolites to cells in the CNS, would be impossible if larger molecules could diffuse freely. Presumably the metabolic needs of ganglia are adequately met by exchange vessels similar to those of nonnervous tissues. Most of the CNS is protected from exogenous toxic substances that bind to plasma proteins. Peripheral neurons and glial cells are damaged by some such substances because of the lack of blood-tissue barriers.

Rat CNS cell culture. Enhancement of neuronal survival and delay of glial proliferation by serum from patients with multiple sclerosis. A morphological study

The addition of serum from multiple sclerosis (MS) patients to the culture medium of dissociated cells from cerebral hemispheres of rat embryos caused a delay in glial proliferation and an enhancement of neuronal survival. Sera from normal individuals and patients with other neurological diseases failed to show this effect. These morphological observations are interpreted as the outcome of inhibition of in vitro gliogenesis.

Tissue culture studies of demyelinating disease: a critical review

Tissue culture studies of human and experimental demyelinating diseases have demonstrated that sera from patients with multiple sclerosis reversibly demyelinate central nervous system cultures. Similar changes are evoked by sera from animals with experimental allergic encephalomyelitis induced by inoculation with whole central nervous system tissue but not by encephalitogenic myelin basic protein. Sera and buffy coat or lymph node cells from humans with idiopathic polyneuritis and animals with experimental allergic neuritis demyelinate cultures of peripheral nervous system tissue. While these studies have contributed to speculations about pathogenetic mechanisms of demyelinating diseases, including the role of both circulating antibodies and delayed hypersensitivity factors, a number of important questions remain unanswered. Among these are the identity of the antigens that evoke antimyelin antibodies and the precise relationship of serum or cellular antimyelin factors to the pathogenesis or clinical course of the demyelinating diseases. Further studies with this technique may provide more complete information about the role of immunological events in induction of disease.

In vivo test for myelinotoxicity of cerebrospinal fluid

A quantitative double blind procedure is described to test the myelinotoxicity of cerebrospinal fluid (SSF) by using optic nerves of Xenopus tadpoles as an in vivo model of a myelinated CNS tract. Only 0.5 ml of unconcentrated CSF is needed for a test and the result is known in 5 days. Groups of 8-10 Xenopus tadpoles received a subcutaneous injection of 12-13 muL of a coded CSF sample or of a saline control solution around the right optic nerve. After 48 h, whole mounts of the right optic nerves were prepared and the slides were randomized before using a differential-interference contrast microscope to count the myelin lesions. The myelinotoxicity of a CSF sample was considered positive (+) when it produced significantly higher (P less than 0.01) counts than the saline control. When P was less than 0.05, the counts were recorded as borderline (+/-) and it was negative (-) when P was greater than 0.05.