Graded expression patterns of ephrin-As in the superior colliculus after lesion of the adult mouse optic nerve

The idea has been put forward that molecules and mechanisms acting during d evelopment are re-used during regeneration in the adult, for example in res ponse to traumatic injury in order to re-establish the functional integrity of neuronal circuits. Members of the Eph family of receptor tyrosine kinas es and their 'ligands. the ephrins, play a prominent role during developmen t of the retinocollicular projection in rodents, where EphA receptors and e phrin-As are expressed in gradients in both the retina and the superior col liculi (SQ. We were interested in investigating whether EphA family members are also expressed or re-expressed in the adult after optic nerve lesion, since the presence of axon guidance information is an important prerequisit e for a topographically appropriate re-connection by retinal ganglion cell (RGC axons. This analysis was encouraged by results showing that RGC axons do not exert guidance preferences in response to membranes from adult unles ioned SC, but in response to membranes from the adult deafferented SC. We f ound a graded expression pattern of ephrin-As in the SC both before and aft er deafferentation, which was remarkably similar to those found during deve lopment. EphA receptor levels were reduced in the SC after deafferentation and the expression patterns of the EphB family were not changed. In particu lar, the presence of a graded ephrin-A expression in the deafferented SC su ggests that - if robust regeneration of RGC axons can be achieved - topogra phic guidance information as a likely requirement for a functionally succes sful re-establishment of the retinocollicular projection is available. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.