Figure 1.

Synapse density in stratum radiatum of CA1 in young and aged estrogen (OVX + E₂)- and vehicle (OVX + Veh)-treated groups. Ultrastructural images from a representative young animal illustrating the disector method. For each animal, 15 pairs of adjacent digital images were taken. One section was considered the reference (a) and the other the look-up (b). Only synaptic profiles (*) contained in the reference but not in the corresponding look-up planes were counted. [Note: (●), Solid circles denote profiles contained in both planes.] This procedure was repeated by switching the reference and look-up sections. (c) Analysis revealed a significant increase in young OVX + E₂ compared with OVX + Veh (P < 0.005) but no difference between aged OVX + E₂ and OVX + Veh (P > 0.38). The young OVX + E₂ were significantly different from both aged groups (both P values < 0.0001).