Neuronal nicotinic acetylcholine receptors (nAChRs) are widely distributed within the brain where they contribute to regulate high cognitive functions. The loss of the cholinergic function in Alzheimer's disease patients, along with the well-known memory enhancing effect of nicotine, emphasises the role of cholinergic signalling in memory functions. The hippocampus, a key structure in learning and memory, is endowed with nAChRs localised at pre and postsynaptic levels. In previous work on the immature hippocampus we have shown that, at low probability (P) synapses, activation of 7 nAChRs by nicotine or by endogenously released acetylcholine persistently enhanced glutamate release and converted "presynaptically silent" synapses into functional. Here we show that in the same preparation, at high P synapses, nicotine induces long-term depression of AMPA- and NMDA-mediated synaptic currents. This effect was mediated by presynaptic -7 and 2-containing receptors and was associated with an increase in paired pulse ratio and in the coefficient of variation. High P synapses could be converted into low P and vice versa by changing the extracellular Ca2+/Mg2+ ratio. In these conditions nicotine was able to persistently potentiate or depress synaptic responses depending on the initial P values. A bi-directional control of synaptic plasticity by nicotine would considerably enhance the computational properties of the network during a critical period of postnatal development thus contributing to sculpt the neuronal circuit.