Search

Evidence was presented earlier that a host-cell receptor for the highly neurotropic rabies virus might be the acetylcholine receptor. The amino acid sequence of the glycoprotein of rabies virus was compared by computer analysis with that of snake venom curaremimetic neurotoxins, potent ligands of the acetylcholine receptor. A statistically significant sequence relation was found between a segment of the rabies glycoprotein and the entire sequence of long neurotoxins. The greatest identity occurs with residues considered most important in neurotoxicity, including those interacting with the acetylcholine binding site of the acetylcholine receptor. Because of the similarity between the glycoprotein and the receptor-binding region of the neurotoxins, this region of the viral glycoprotein may function as a recognition site for the acetylcholine receptor. Direct binding of the rabies virus glycoprotein to the acetylcholine receptor could contribute to the neurotropism of this virus.

Rabies virus was found on mouse diaphragms and on cultured chick myotubes in a distribution coinciding with that of the acetylcholine receptor. Treatment of the myotubes with alpha-bungarotoxin and d-tubocurarine before the addition of the virus reduced the number of myotubes that became infected with rabies virus. These findings together suggest that acetylcholine receptors may serve as receptors for rabies virus. The binding of virus to acetylcholine receptors, which are present in high density at the neuromuscular junction, would provide a mechanism whereby the virus could be locally concentrated at sites in proximity to peripheral nerves facilitating subsequent uptake and transfer to the central nervous system.

The effects of tissue explants and nerve homogenates on cholinesterase activity of muscle of the newt Triturus in organ culture were measured. Sensory ganglia, ganglia separated from muscle by a Millipore filter, spinal cord, liver, and nerve homogenates produced greater activity of muscle cholinesterase than occurred in untreated muscle cultured for the same period of time. Boiled ganglia, kidney, oviduct, and spleen were ineffective. This procedure serves as a convenient bioassay for a neurotrophic process and indicates that the trophic effect is mediated by a diffusible chemical substance produced by nerves.

Peroxidase-conjugated antibodies were used to determine the histologic and cytologic localization of bovine and human tissue factor (thromboplastin). Tissue factor antigen was found in highest concentration in the intima of blood vessels, particularly in the plasma membranes of endothelial cells and in human atheromatous plaques. Tissue factor was also found limited to the plasma membranes of many cell types. The presence of tissue factor in the plasma membranes of endothelial cells and atheromata suggests that it may play a significant role in hemostasis and thrombosis.

Material staining with aldehyde fuchsin appeared in sensory ganglion cells supplying a regenerating limb or nerve-induced blastema and in regenerating nerve fibers within the blastema. With the electron microscope, large (1000 to 2500 angstroms), dense granules were observed in the perikarya and within end bulbs of peripheral nerves. Secretory materials may be elaborated and transported by neurons during limb regeneration and induction in the newt.

Neurosecretory granules of Hydra littoralis were isolated by differential centrifugation. Excised midsegments of hydra that were exposed to the fraction containing neurosecretory granules developed additional heads at any site, as they regenerated. Hence neurosecretory granules may contain a factot that regulates or stimulates growth in normal and regenerating hydra.