AN ELECTRON MICROSCOPE STUDY OF CULTURED RAT SPINAL CORD

Explants prepared from 17- to 18-day fetal rat spinal cord were allowed to mature in culture; such preparations have been shown to differentiate and myelinate in vitro (61) and to be capable of complex bioelectric activity (14–16). At 23, 35, or 76 days, the cultures were fixed (without removal from the coverslip) in buffered OsO₄, embedded in Epon, sectioned, and stained for light and electron microscopy. These mature explants generally are composed of several strata of neurons with an overlying zone of neuropil. The remarkable cytological similarity between in vivo and in vitro nervous tissues is established by the following observations. Cells and processes in the central culture mass are generally closely packed together with little intervening space. Neurons exhibit well developed Nissl bodies, elaborate Golgi regions, and subsurface cisternae. Axosomatic and axodendritic synapses, including synaptic junctions between axons and dendritic spines, are present. Typical synaptic vesicles and increased membrane densities are seen at the terminals. Variations in synaptic fine structure (Type 1 and Type 2 synapses of Gray) are visible. Some characteristics of the cultured spinal cord resemble infrequently observed specializations of in vivo central nervous tissue. Neuronal somas may display minute synapse-bearing projections. Occasionally, synaptic vesicles are grouped in a crystal-like array. A variety of glial cells, many apparently at intermediate stages of differentiation, are found throughout the otherwise mature explant. There is ultrastructural evidence of extensive glycogen deposits in some glial processes and scattered glycogen particles in neuronal terminals. This is the first description of the ultrastructure of cultured spinal cord. Where possible, correlation is made between the ultrastructural data and the known physiological properties of these cultures.

THE APPLICATION OF TISSUE CULTURE TO THE STUDY OF EXPERIMENTAL ALLERGIC ENCEPHALOMYELITIS. II. SERUM FACTORS RESPONSIBLE FOR DEMYELINATION

1. In the presence of a source of complement, the gamma 2 globulin fraction of rabbit EAE serum results in complete demyelination of myelinated cultures of rat cerebellum. Exposure of the serum to homologous or heterologous brain specifically removes the myelinotoxic activity whereas exposure to non-nervous tissue does not. Polylysine has no effect upon the cultures or upon the demyelinative potency of EAE, whereas heparin inhibits activity presumably through an effect on complement. 2. With the fluorescent antibody technique, the EAE globulins are specifically localized to the myelin sheaths and glial cell membranes during the process of demyelination. As demyelination proceeds, the globulins become localized within the neuroglia in a homogeneous manner which contrasts sharply with the punctate pattern observed in control experiments. 3. The "delayed sensitivity" and classical antibody interpretations of experimental allergic encephalomyelitis are discussed. It is suggested that several factors may be responsible for the pathogenesis of EAE, one of which may well be a myelinotoxic antibody.

CENTRAL CARDIOVASCULAR ACTIONS OF GAMMA-AMINOBUTYRIC ACID

The vasomotor and cardiac effects of gamma-aminobutyric acid (GABA) administered by different routes were studied in cats and dogs. The cat was resistant to the action of GABA administered intravenously or into a vertebral artery. Intrathecal injection of GABA into the cat depressed the vasomotor reponse to spinal compression. In dogs, intravenous, intrathecal or intraventricular injection, or topical application of GABA to the floor of 4th ventricle consistently produced hypotension and depressed the reflex and direct excitability of the vasomotor neurones, located at the supraspinal and spinal levels. Bradycardia observed after intravenous and intraventricular injections of GABA into dogs was abolished by stellate ganglionectomy but not by vagotomy. It has been attributed to depression of the central sympathetic neurones.