INTRINSIC CHANGES IN DEVELOPING RETINAL NEURONS RESULT IN REGENERATIVE FAILURE OF THEIR AXONS

The failure of mature mammalian central nervous system axons to regene rate after transection is usually attributed to influences of the extr aneuronal milieu. Using explant cocultures of retina and midbrain tect um from hamsters, we have found evidence that these influences account for failure of regrowth of only a small minority of retinal axons. Fo r most of the axons, there is a programmed loss of ability to elongate in the central nervous system, We show that there is a precipitous de cline in the ability of retinal axons to reinnervate tectal targets wh en the retina is derived from pups on or after postnatal day 2, even w hen the target is embryonic. By contrast, embryonic retinal axons can regrow into tectum of any age, overcoming growth-inhibiting influences of glial factors.