Activity dependent plasticity of postsynaptic density structure in the ventral cochlear nucleus of the rat.

Young adult male rats were anaesthetised with urethane and exposed to either 24 h of silence or 24 h of repetitive 77 dB tones in a sound-proofed anechoic chamber. The influence of these two conditions on the ultrastructure of the synaptic appositions made by auditory afferents in the anterior ventral cochlear nucleus (end bulbs of Held) was compared. Both the cross-sectional area and the mean thickness of the postsynaptic density (PSD) in the rats exposed to tones were significantly reduced when compared with rats maintained in silence. Similarly, the degree of curvature of the apposition was significantly reduced. The results of these experiments provide further evidence that the postsynaptic density material is a plastic structure significantly influenced by the amount of activity in the presynaptic element.