Long-term potentiation of GABAergic synaptic transmission in neonatal rat hippocampus

1. The plasticity of GABAergic synapses was investigated in neonatal rat hippocampal slices obtained between postnatal days 3 and 6 using intracellular recording techniques. Ionotropic glutamate receptor antagonists were present throughout the experiments to isolate GABA, receptor-mediated postsynaptic potentials (GABA(A) PSPs) or currents (GABA(A) PSCs). 2. Repetitive depolarizing pulses (20 pulses, 0.5 s duration, at 0.1 Hz, each pulse generating 4-6 action potentials) induced a long-term potentiation in the slope and amplitude of the evoked GABA(A) PSPs and GABA(A) PSCs. 3. Long-term potentiation was prevented by intracellular injection of the calcium chelator BAPTA (50 mu M), or when the voltage-dependent calcium channels blockers Ni2+ (50 mu M) and nimodipine(10 mu M) were bath applied. 4. Repetitive depolarizing pulses induced a persistent (over 1 h) increase in the frequency of spontaneous GABA(A) PSCs. 5. Repetitive depolarizing pulses induced a lung-lasting increase in the frequency of miniature GABA(A) PSCs, without altering their amplitude or decay-time constant. 6. It is concluded that the postsynaptic activation of voltage-dependent calcium channels leads to a long-term potentiation of GABAergic synaptic transmission in neonatal rat hippocampus. This form of plasticity is expressed as an increase in the probability of GABA release or in the number of functional synapses, rather than as an upregulation of postsynaptic GABA(A) receptor numbers or conductance at functional synapses.