Selective glutamate receptor antagonists can induce or prevent axonal sprouting in rat hippocampal slice cultures

After the transection of the Schaffer collateral pathway in hippocampal slice cultures, reactive sprouting is induced in the CA3 area, and eventually synaptic transmission between areas CA1 and CA3 is restored. Using this model, we have studied the role of ionotropic glutamate receptors in the initiation of axonal sprouting and the regeneration of functional synapses. We show that neither reactive sprouting nor functional recovery of synaptic transmission occur in the presence of the non-N-methyl-D-aspartate (NMDA) receptor antagonist 6-nitro-7-sulfamoylbenzoquinoxaline-2,3-dione (CNQX). In contrast, the NMDA receptor antagonists methyl-10, 11-dihydro-5-H-dibenzocyclohepten-5,10-imine (MK-801) or 3-(RS)-2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP) did not interfere with these processes. Moreover, we observed that the application of NMDA receptor antagonists induced massive axonal sprouting and an increase in the frequency of miniature excitatory postsynaptic currents in unlesioned cultures. Our results thus indicate that NMDA and non-NMDA receptors exert a differential effect on reactive sprouting and the recovery of synaptic transmission after injury in the hippocampus. Activation of non-NMDA receptors appears necessary for these processes to occur, whereas activation of NMDA receptors suppresses growth-associated protein -43 expression and axonal outgrowth.