Effects of corticosterone on mild auditory fear conditioning and extinction; role of sex and training paradigm

Abstract

Multiple lines of evidence suggest that glucocorticoid hormones enhance memory consolidation of fearful events. However, most of these studies involve male individuals. Since anxiety, fear, and fear-associated disorders present differently in male and female subjects we investigated in mice whether male and female mice perform differently in a mild, auditory fear conditioning task and tested the modulatory role of glucocorticoid hormones. Using an auditory fear conditioning paradigm with different footshock intensities (0.1, 0.2, and 0.4 mA) and frequencies (1× or 3×), we find that intraperitoneal injections with corticosterone (2 mg/kg) immediately after training, altered freezing behavior when repeated footshocks were applied, and that the direction of the effects were opposite in male and female mice. Effects were independent of footshock intensity. In male mice, corticosterone consistently increased freezing behavior in response to the tone, whereas in female mice, corticosterone reduced freezing behavior 24 h after training. These effects were not related to the phase of the oestrous cycle. In addition, corticosterone enhanced extinction learning for all tones, in both male and female mice. These results emphasize that glucocorticoid hormones influence memory consolidation and retrieval, and underscore sex-specific effects of glucocorticoid hormones in modulating conditioned fear responses.

Figure 1.

Training and testing paradigm cued fear conditioning. (A) Mice are trained in a fear conditioning paradigm with one or three 30 sec tones, coupled with a 2-sec footshock of varying intensity (“training”). Immediately following training, mice were injected i.p. with corticosterone (2 mg/kg) or saline. Twenty-four hours later, mice were introduced in a novel environment, and reexposed to the same 30 sec tone for six times (“retrieval”). (B) The effects of sex, footshock intensity and footshock frequency on freezing behavior after reexposure to a single tone at retrieval. All mice received a saline injection following training. A main effect was observed for footshock intensity (F_(2,65) = 40.89, P = 0.001), footshock frequency (F_(1,65) = 31.78, P = 0.001), and sex (F_(1,65) = 14.01, P = 0.001), and an interaction effect was found between sex × intensity (F_(2,65) = 3.31, P = 0.05), and between sex × frequency × intensity (F_(2,65) = 4.18, P = 0.02).

Figure 2.

The effect of corticosterone on freezing behavior. (A) Freezing levels to the first tone. A significant interaction effect was observed between sex × frequency × treatment (F_(1,133) = 10.25, P = 0.002), and corticosterone increased freezing only in male mice after a training paradigm with three footshocks (P = 0.049). (B) Average freezing behavior over the six tones. Corticosterone resulted in an overall effect on freezing behavior to the tones during retrieval, although differently in male and female mice (sex*treatment effect: F_(1,133) = 17.21, P < 0.001).

Figure 3.

The effects of corticosterone on extinction learning, as measured by the difference in freezing levels between tone 1 and tone 6 at retrieval. There was a significant interaction effect of sex × frequency × treatment (interaction effect: F_(1,134) = 4.8, P = 0.03). *Indicates significant difference between saline and corticosterone-treated mice after a similar training frequency and intensity.