Plasticity of postsynaptic density material in optic synapses of the suprachiasmatic nucleus in the senescent rat

Optic synapses in the suprachiasmatic nucleus were studied in senescent rats after 2 weeks of constant light influence (light rats) or darkness (dark rats). The amount of postsynaptic density material was significantly greater in dark rats compared with light rats. Dark rats also showed a higher percentage of asymmetric synapses than light rats. The sizes of synaptic appositions and boutons were also compared. The phenomena observed may indicate supersensitivity and a higher number of excitatory synapses in dark rats and subsensitivity and lower number of excitatory synapses in light rats.