During and after degeneration of the optic nerve afferents in the rat suprachiasmatic nucleus (SCN) postsynaptic density (PD) material is added to existing symmetrical and asymmetrical appositions of non-optic synapses on optic target neurons. If the correlation between thickness of the postsynaptic density and excitatory or inhibitory function of a synapse holds in this nucleus, the change in morphology of synapses could mean that some inhibitory synapses turn into excitatory contacts.