For each synapse on a spine, the number of PEG particles occurring synaptically and nonsynaptically was tallied. For shafts, only the PEG particles at postsynaptic sites were tallied, because nonsynaptic sites lacked clear boundaries. Synapses (axo-spinous or axo-shaft) and spines (spine head and neck) exhibiting one or more PEG particle were categorized as immunolabeled. Four mean values were derived for each animal: the proportion of spines immunolabeled anywhere (synaptic or nonsynaptic); the proportion of axo-spinous synapses immunolabeled at nonsynaptic sites; the proportion of spines labeled at synapses; and the proportion of axo-shaft synapses immunolabeled at the synapse. Treatment effects on the proportion of immunolabeling were analyzed by one-way ANOVA with planned post hoc comparisons (Fisher’s LSD).
