EphA/ephrin-A interactions regulate epileptogenesis and activity-dependent axonal sprouting in adult rats

The Eph family of tyrosine kinase receptors and their ligands, ephrins, are distributed in gradients and serve as molecular guidance cues for axonal patterning during neuronal development. Most of these molecules are also expressed in mature brain. Thus, we examine here the potential roles of such molecules in plasticity and activity-dependent mossy fiber sprouting of adult CNS. We show that the ligand ephrin-A3 and the receptor EphA5 are expressed in complementary gradients in the adult rat mossy fiber system. Using the kindling model, we demonstrate that exogenous immunoadhesins that affect the interaction of endogenous EphA receptors and ephrin-A ligands modulate the development of kindling, one type of long-term plasticity, in mature rat brain. These immunoadhesins, combined with epileptogenic stimulations, alter both the extent and the pattern of collateral axonal sprouting in the mossy fiber pathway. Our results suggest that EphA receptors and ephrin-A ligands modify neuronal plasticity and may serve as spatial cues that modulate the development and pattern of activation-dependent axonal growth in adult CNS.