Figure 1. Reduced hippocampal dendritic spine density after a 5 h stress. A, Structure and organization of the hippocampus, clarifying the location and subcellular domains of a YFP-expressing CA3 pyramidal neuron. The location of the apical dendrites, emerging from stratum pyramidale (sp) and spanning stratum lucidum (sl), radiatum (sr), and lacunosum-moleculare (slm), is shown. Basal dendrites are in stratum oriens (so). EC, Enthorinal cortex. Scale bar, 260 μm. B–D2, Stress leads to spine loss in vulnerable domains of apical dendrites (third- and fourth-order branches in sr). In a 3-month-old, Thy1-YFP-expressing mouse, density of spines on the third/fourth dendritic branches was high under stress-free conditions (D1), and was significantly reduced immediately after a 5 h combined restraint/noise stress (D2), as quantified in C (*p < 0.05). Density of spines on the distal dendritic branches located in slm was not influenced by the acute stress (C, E1, E2). The frames in B denote areas magnified in D1 and E1. Error bars indicate SEM. Scale bars: B, 50 μm; D1–E2, 7 μm.