Activity-dependent changes in synaptic efficacy at glutamatergic and GABAergic connections in the immature hippocampus

During development, correlated network activity plays a crucial role in establishing functional synaptic contacts, thus contributing to the development of adult neuronal circuits. In the hippocampus, a region of the brain involved in the formation of declarative memories, network-driven giant depolarizing potentials or GDPs are generated by the synergistic action of glutamate and GABA, which at this developmental stage is depolarizing and excitatory. The depolarizing action of GABA during GDPs results in calcium flux via NMDA receptors and voltage-dependent calcium channels. Calcium, in turn activates different signaling pathways necessary for several developmental processes including synaptogenesis. In previous work from our laboratory it was demonstrated that GDPs and associated calcium transients act as coincident detectors for enhancing synaptic efficacy at poorly developed mossy fibre-CA3 synapses in a Hebbian type of way...