The nude mouse: an in vivo model for demonstrating cross-species trophic nerve function

The distribution of alkaline phosphatase activity in normal and cross-species regenerated rat and mouse taste buds

Alkaline phosphatase (ALK Pase) activity can be detected histochemically in the taste buds of rats but not mice. Since taste buds develop, regenerate and are maintained under the influence(s) of the sensory nerve it was decided to study cross-species regenerated buds of these two animals to determine whether the nerve also regulated ALK Pase development in taste cells. Grafts of rats sensory ganglion and mouse tongue or mouse ganglion and rat tongue were combined in the anterior chamber of the eyes of immunologically-deficient nude mice and the cross-species buds that developed at 35 days were examined histochemically for ALK Pase. The results revealed that the rat nerve did not cause ALK Pase to appear in any buds found in mouse tongue grafts and that mouse nerve could support buds containing ALK Pase in rat tongue tissue. Because the cross-species regenerated buds were histochemically characteristic of those normally found in rat or mouse tongue, there is no evidence that the foreign nerve altered gene expression for ALK Pase in the target organ, and the action of the nerve on gustatory epithelium appears to be that of activation and maintenance.

Neurotrophic control of RNA synthesis in amphibian striated muscle

When frog sartorius muscles are incubated in culture for 3 days, a 98% increase in RNA synthesis by the muscles is seen. A portion of this increase (60--100% in different experiments) is prevented by the presence of a 2 cm distal nerve stump left attached to the muscle, or by the addition to the culture medium of nerve and spinal cord extracts from frog, rat or cow. The effect of the nerve stump and the extract is seen under conditions of neuro-muscular blockade by 50 mg/l gentamicin sulfate present in the culture medium. Autoradiography of 1 micrometer sections of muscles previously labeled with [3H]uridine shows that isotope incorporation is largely confined to muscle fibers rather than connective tissue. Muscles cultured for 3 days display normal action and resting potentials either in the presence or absence of extract. The results are discussed in terms of control of muscle RNA synthesis by substances present in motor neurons.