ABSTRACT
The notion that the immature mammalian central nervous system (CNS) may repair and regenerate itself more effectively than that of the adult has been current for all of this century. There are numerous references to sprouting of injured axons in brain and spinal cord of immature animals in Ramón y Cajal’s 1928 monograph which summarised data from experimental observations made on injured spinal cords in young cats and dogs over the three previous decades. All of Ramón y Cajal’s work and most of the subsequent studies dealt with postnatal common laboratory animals, particularly rats and cats. There are few references in the literature to spinal injuries in fetuses, but most of the results of attempts at such experiments seem to have been negative (eg Hooker & Nicholas, 1930). However, there is a small number of reports of successful “regeneration” of injured axons by the outgrowth of neurites and some recovery of function in fetuses (eg Migliavacca, 1928). This perhaps accounts for the fact that there seems to have been a long standing belief that the immature CNS has some capability for regenerative repair that is not present in the adult; the wealth of negative experiments seem to have been largely ignored in favour of the few experiments with more positive outcomes. This is well illustrated by the articles collected together by WF Windle in a monograph entitled “Regeneration in the Central Nervous System” (Windle, 1955) and by Lloyd Guth’s articles (eg 1975). However there were dissenting voices, apparently based on an inability to reproduce the few positive results published (eg Hess, 1955; p1 76 in Windle, 1955). Also Clark’s extensive papers (eg 1942) seem to have been influential in establishing a belief amongst many neuroscientists and neurologists that there is nothing special about the ability of the the developing CNS to repair itself or to sustain repair in the adult, if immature CNS tissue is implanted into injured adult CNS.
