Induction of long-term potentiation (LTP) of the synaptic connection betwee
n two hippocampal glutamatergic neurons in a neural network formed in cell
culture resulted in a specific pattern of potentiation at other connections
within the network. We found that potentiation propagated from the site of
induction retrogradely to glutamatergic or GABAergic synapses received by
the dendrites of the presynaptic neuron and laterally to those made by its
axonal collaterals onto other glutamatergic cells. In contrast, synapses ma
de by the same presynaptic neuron onto GABAergic cells were not affected, a
nd there was no postsynaptic lateral or forward propagation to other synaps
es received or made by the postsynaptic neuron. In addition, there was no s
econdary propagation to synapses not directly associated with the presynapt
ic neuron. Both induction and propagation of LTP required correlated spikin
g of the postsynaptic cell as well as the activation of the NMDA subtype of
glutamate receptors. Such selective propagation suggests the existence of
a long-range cytoplasmic signaling within the presynaptic neuron, leading t
o a specific pattern of coordinated potentiation along excitatory pathways
in a neural network.