Following the paired presentation of stimuli, asymmetric synapses responded with an increase in GluR1 immunoreactivity, regardless of the location of the synapse (spine or shaft). However, following the unpaired presentation of stimuli, the asymmetric synapses at the two types of locations responded oppositely: synapses formed along the spine remained unchanged or slightly elevated in GluR1 immunoreactivity, whereas synapses formed along shafts decreased GluR1 immunoreactivity. Although the number of synapses analyzed along the dendritic shaft was smaller than that for the spines, the magnitude of the change at axo-shaft synapses was sufficiently large to be detectable.
