FIG. 4.

Acute stress and fear conditioning and extinction alter spine density on basolateral amygdala (BLA) pyramidal neurons. (A) Digital micrograph demonstrating different spine types on a pyramidal neuron in the BLA. Several photomicrographs were taken at different Z-levels, and merged to increase the number of spines in focus. B, branched; M, mushroom; S, stubby; T, thin. Scale bar: 5 μm. (B) Spine density [mean ± standard error of the mean (SEM)] on first-order to fourth-order branches of BLA pyramidal neurons in the right and left hemispheres in unstressed vs. stressed rats that were either non-conditioned or underwent fear conditioning and extinction. †P < 0.05 for unstressed vs. stressed non-conditioned rats. #P < 0.05 for unstressed non-conditioned rats vs. unstressed rats that underwent conditioning and extinction. ##P < 0.05 for stressed non-conditioned rats vs. stressed rats that underwent conditioning and extinction. (C) Thin spine density (mean ± SEM) on first-order to fourth-order branches of BLA pyramidal neurons in the right and left hemispheres in unstressed vs. stressed rats that were either non-conditioned or underwent fear conditioning and extinction. #P < 0.05 for unstressed non-conditioned rats vs. unstressed rats that underwent conditioning and extinction. ##P < 0.05 for stressed non-conditioned rats vs. stressed rats that underwent conditioning and extinction. (D) Mushroom spine density (mean ± SEM) on first-order to fourth-order branches of BLA pyramidal neurons in the right and left hemispheres in unstressed vs. stressed rats collapsed across learning conditions. §P < 0.05 for unstressed vs. stressed rats. Unstressed, no conditioning, n = 5. Stressed, no conditioning, n = 4. Unstressed, conditioning and extinction, n = 8. Stressed, conditioning and extinction, n = 10.