Long-term potentiation and depression: a computer simulation

Synaptic coupling undergoes long-term potentiation (LTP) or depression (LTD) when a train of stimuli respectively at high or low frequency conditions the afferent pathway. It is still debated if the long-lasting synaptic modifications that must occur for LTP and LTD maintenance are pre- and/or post-synaptic, and some form of retrograde messengers between post- and pre-synaptic sites has been proposed, such as nitric oxide (NO) and carbon monoxide (CO). The molecular mechanisms needed to maintain LTP and LTD, and in particular the roles of retrograde signals, are not known, and it is not clear if LTP and LTD are two different mechanisms or the expression of a single process that is able to change synaptic strength bidirectionally. In this paper, we propose a model that is consistent with experimental findings and shed some light on the possible roles of retrograde signals in the maintenance phase of LTP and LTD