Tooth eruption: the phase transition theory on biological formation of an orderly structure.

The mechanism of the formation of an orderly structure from random elements in organ development was clarified by studying the maturation of the dental arch in the human mandible. First, an application of methods established in statistical physics to a system of organ development was made possible, and then, the mathematical procedures for quantitative study of the structure and development of the dental arch were established in relation to radiographic data. The experimental results demonstrate that a parallel arrangement of the longitudinal axes of the lateral teeth is formed co-operatively in the dental arch.

Nerve growth factor action on membrane permeation to exogenous substrates in dorsal root ganglionic dissociates from the chick embryo.

An experimental system has been described, in previous studies, where the ability of chick embryo dorsal root ganglionic cells to incorporate radiouridine into RNA declines in the absence of nerve growth factor (NGF), and is promptly restored by delayed supply of the factor. Following these early and fully reversible events, further NGF deprivation causes progressive irreversible damage. The early decline in RNA labeling and its reversion by NGF are accompanied by similar changes in the accumulation of acid-soluble radioactivity from the exogenous radiouridine substrate.

Nerve growth factor-induced rapid activation of RNA labeling in dorsal root ganglionic dissociates from chick embryos.

Dorsal root ganglionic cells, from 8-day chick embryo, undergo anabolic declines when incubated in vitro without Nerve Growth Factor (NGF) or other supportive agents. To determine whether the decline could be opposed by delayed administration of the NGF, cells were incubated without the factor for varying times, then supplies with it and tested periodically with pulses of radiouridine or radioleucine. The decline in RNA labeling was actually reversed by a delayed addition of NGF, and the effect was fully elicited within less than 10 min from the treatment.