Polyribosomes redistribute from dendritic shafts into spines with enlarged synapses during LTP in developing rat hippocampal slices.

The presence of polyribosomes in dendritic spines suggests a potential involvement of local protein synthesis in the modification of synapses. Dendritic spine and synapse ultrastructure were compared after low-frequency control or tetanic stimulation in hippocampal slices from postnatal day (P)15 rats. The percentage of spines containing polyribosomes increased from 12% +/- 4% after control stimulation to 39% +/- 4% after tetanic stimulation, with a commensurate loss of polyribosomes from dendritic shafts at 2 hr posttetanus. Postsynaptic densities on spines containing polyribosomes were larger after tetanic stimulation. Local protein synthesis might therefore serve to stabilize stimulation-induced growth of the postsynaptic density. Furthermore, coincident polyribosomes and synapse enlargement might indicate spines that are expressing long-term potentiation induced by tetanic stimulation.