Bidirectional plasticity expressed by GABAergic synapses in the neonatal rat hippocampus

1. Activity-dependent plasticity of GABAergic synaptic transmission was investigated in neonatal rat hippocampal slices obtained between postnatal day (P) 2-10 using intracellular recording techniques. In all experiments, AMPA receptors were blocked by continual application of CNQX (10 mu m). 2. Between P2 and P4, tetanic stimulation (TS) evoked NMDA receptor-dependent long-term depression of monosynaptic GABA(A) EPSPs (LTD(GABAA)). In contrast, when NMDA receptors were blocked by D-AP5 (50 mu m), the same TS evoked long-term potentiation of GABA(A) EPSPs (LTP(GABAA)). 3. Between P6 and P10, TS failed to produce either LTP or LTD of hyperpolarizing monosynaptic GABA(A) IPSPs under the same recording conditions. However, when GABAergic potentials were rendered depolarizing (KCl-filled electrode) TS induced with LTP(GABAA) or LTD(GABAA) in the presence or absence of D-AP5, respectively. 4. Both LTP(GABAA) and LTD(GABAA) were specific to the conditioned pathway and could be sequentially expressed at the same synapses. Potentiation of GABAergic synaptic efficacy was induced more easily following previous induction of LTD(GABAA) than in naive slices. 5. In conclusion, early in development, bidirectional synaptic plasticity is expressed by GABA(A) receptors and the activation (or not) of NMDA receptors determines the induction of either LTP(GABAA) or LTD(GABAA).