Regeneration of central nervous system axons into an acellular tube in the absence of distal tissue

Axonal growth and glial migration from co-cultured hippocampal and septal slices into fibrin-fibronectin-containing matrix of peripheral regeneration chambers: a light and electron microscope study

In order to investigate whether a fibrin-fibronectin-containing matrix of a peripheral regeneration chamber could promote the growth of central nervous system neurons, hippocampal and septal slices were co-cultured in the presence of this acellular substrate. In introducing the peripheral matrix into a 2-mm-long tube between hippocampal and septal slices, a spatio-temporal sequence of cell migration and axonal growth was described by light and electron microscopy. Axons were able to elongate directly into the flocculent material constituting the matrix and a possible neurite-promoting activity was implicated in this process as axonal growth was not detected in direct contact with rat plasma coagulated with calcium, or chicken plasma coagulated with thrombin, used as control matrices. However, in the 3 different substrates tested, astrocytes were able to migrate and dilated astroglial processes containing intermediate filaments were detected. Axonal processes were observed growing on the glial cell surface. GFAP-positive phagocytic cells, that could be of the same origin as astrocytes, were involved in matrix removing. Neuronal growth and glial migration arose from hippocampal and septum slices and acetylcholinesterase-containing fibers were seen in the bridging structure suggesting that cholinergic axons were able to progress to the hippocampal slice. This technique appeared to provide a model in which axonal growth and cell migration can be studied 'in vitro' in a 3-dimensional environment.

A new in vivo model to study the influence of the microenvironment in the regeneration of the central nervous system

In order to study the 'in vivo' regenerative capacity of the central nervous system, a semipermeable tube was placed in the axis of the lesioned nigrostriatal pathway of adult rats. In spite of a correct positioning of the tube, no growing central nervous processes were observed within the tube after 3 to 6 weeks when it was left empty. However, when the lumen of the tube was previously filled with a pre-degenerated sciatic nerve, unmyelinated and myelinated fibers were observed growing in the peripheral graft. Since the content of the tube can be modified, it appears that this model can be used to test the capability of cellular or acellular microenvironments to promote the 'in vivo' regeneration of the mammalian central nervous system fibers.

Fetal tectal or cortical tissue transplanted into brachial lesion cavities in rats: influence on the regrowth of host retinal axons

Fetal neural tissue was transplanted into suction lesions of the left brachium and pretectal region in young rats. Tectal tissue was grafted into 6-18-day-old rats and cortical tissue was transplanted into 17-20-day-old animals. The aim was to determine whether grafts could potentiate the regrowth of damaged retinal axons and, as a consequence, stimulate the axons to reenter their host target, the superior colliculus (SC). Fifteen to 581 days after transplantation, host retinal projections were traced by injecting the right eye with horseradish peroxidase (HRP). Parallel series of frozen brain sections were stained for HRP histochemistry, acetylcholinesterase, Nissl, or neurofibrils. At all ages studied, grafts survived and grew within the wound cavity; survival was better in the older animals. Most cortical grafts and a small number of tectal grafts filled the wound cavity and formed complete tissue bridges across the lesion. The majority of tectal grafts were attached to one or the other side of the lesion and were connected to the opposite lesion face by glial and connective tissue membranes that formed over the lesion site. In many animals that received tectal transplants, host retinal axons were traced growing into the grafts. Regenerating axons innervated specific, localized areas within the grafts, and it appeared that the axons retained the ability to recognize their appropriate target cells within the graft neuropil. Comparable ingrowth into cortical grafts was not observed. Optic axons were occasionally seen reentering the superficial layers of the host SC; however, compared to fetal tectal grafts, the density of host SC innervation was sparse. The implications of these data are discussed with regard to the possible use of fetal neural tissue grafts as reconstructive tissue bridges in the mammalian central nervous system.