[Dependence of normal tail regeneration in Xenopus larvae upon a diencephalic factor in the central canal].

Tail regeneration inXenopus larvae is substantially reduced and morphologically disturbed if the continuity of the neural tube at the base of the tail is permanently impaired. This operation is believed to block the transport of a growth factor derived from the diencephalic roof and transmitted to the regeneration site via the central canal. The following experimental data support this hypothesis: 1. Tails transplanted into host larvae and partially amputated after revascularisation but without connection between the transplant and the host neural tube regenerate in the same abnormal manner as do tails in larvae without a continuous neural tube. 2. Simple transsection of the neural tube followed by reunion of the separated parts allows of normal regeneration of the tail provided the patency of the central canal is restored. 3. Occlusion of the ventricles of the brain by injection of agar does not affect normal tail motility but causes the same atypical tail regeneration as does discontinuity of the neural tube. 4. Coagulation of the telencephalon and major parts of the mesencephalic roof leaves tail regeneration unimpaired provided the operation did not lead to an obstruction behind the third ventricle; destruction of the diencephalon has the same effect on regeneration as severance of the neural tube. This effect may still be observed if only a very small part of the diencephalic roof containing the subcommissural organ is coagulated. 5. According to literature the subcommissural organ gives rise to the Reissner's fibre which passes the whole length of the central canal and releases its secretion through the wall of the terminal vesicle into the surrounding tissues. Therefore the subcommissural organ might well be the source of the postulated factor promoting tail regeneration.