Fig. 2. Corticosterone persistently disrupts synaptic plasticity in APP transgenic rats.

A In a longitudinal study design, transgenic (TG) rats received single daily s.c. injections of CORT (either 10 mg/kg, closed circles, or 5 mg/kg, open circles) for 3 days. Strong high frequency conditioning stimulation (sHFS, arrowhead) was applied repeatedly in the hippocampus of freely behaving rats over a 2.5 month period. The time course of sHFS-induced potentiation from the same animals is displayed before (B, 0 month), 2 h after (C, 0.5 month), 1 (D, 1.5 month) and 2 (E, 2.5 month) months after the last injection, starting at 4 months. Red and blue colours indicate CORT 10 or CORT 5 treatments, respectively (online version only). Insets show representative field EPSP traces at the times indicated. Calibration bars: vertical, 1 mV; horizontal, 10 ms. The magnitude of potentiation 3 h post-sHFS (last 10 min) at the different recording sessions is plotted for 10 mg/kg (F) and 5 mg/kg (G) CORT-treated rats, for individuals (left hand panel) and groups (right hand panel). The ♯ symbol stands for a statistical comparison between pre- and 3 h post-HFS values at each recording session within one group (paired t test) whereas an * indicates a comparison between groups. LTP was significantly inhibited at 0.5, 1.5, and 2.5 month in the TG CORT 10 group (one-way ANOVA with repeated measures). In contrast, the magnitude of LTP was not significantly different between recording sessions in the TG CORT 5 group. One symbol, p < 0.05; two symbols, p < 0.01; three symbols, p < 0.001. Values are mean ± S.E.M. % pre-HFS baseline EPSP amplitude.