Table 2.

Synaptic versus nonsynaptic distribution of δ2 receptor immunoreactivity

TotalParallel fiber synapses with spinesNonsynaptic membranesCytoplasmic compartments
Number of particles349 (100%)311 (89%)12 (3.4%)7 (2%)19 (5.4%)
Relative boundary length100%3.1%96.6%
  • The values represent the number of gold particles. The analysis was based on 40 micrographs covering a total area of ∼500 μm2 (same material as in Figs. 1, 2) and including 66 parallel fiber–spine synapses. No background labeling could be detected over tissue-free resin (0 particles recorded in 50 μm2), and only two particles were recorded over 60 μm2 of neuropil in coprocessed hippocampal sections (synaptic membranes excluded). The areal fraction of spines was 5.7%. Particles were defined as belonging to plasma membranes if they were located within 28 nm of the membrane (Matsubara et al., 1996). The relative boundary length was calculated as described in Materials and Methods.