Hyperplasia in the brain of amblystoma.

Abstract

An experimental study of the effect on the brain of Amblystoma of the transplantation of an additional nasal placode has given some rather curious and interesting results. When a right nasal placode from an Amblystoma embryo is transplanted into the reentrant angle between the optic cup and nasal placode of a host, there results either complete fusion, partial fusion, or the maintenance of complete integrity of the two placodes. When the union is more or less complete, a majority of the experiments show an augmentation in size of the olfactory nerve through the addition to it of axones derived from the neuro-epithelium of the transplant. The ingrowth of the enlarged olfactory nerve trunk into the cerebral hemispheres results in an increase of the cellular content of the olfactory bulb amounting to approximately 30 per cent. No such increase occurs in those instances where the transplant has made no contribution to the olfactory nerve.

In the experimental embryos where the transplant did not fuse with the placode of the host, the outgrowing fibers from the neuro-epithelium of the transplant pursued either one of two courses. In a majority of cases they established connection with the pars dorsalis thalami with resulting hyperplasia of a restricted region in the central gray. Several experiments resulted in the axones from the transplant joining the ophthalmic branch of the Vth cranial nerve, ascending along it and terminating in the ophthalmic ganglion. Here again hyperplasia of the cellular elements in the ganglion occurred.

It is suggested that the growth of axones into a field of growing neuroblasts is a factor in producing cell: proliferation, the degree of which is dependent upon the number of ingrowing nerve units.