A new stress model, a scream sound, alters learning and monoamine levels in rat brain.

Most existing animal models for stress involve the simultaneous application of physical and psychological stress factors. In the current study, we described and used a novel psychological stress model (scream sound stress). To study the validity of it, we carried out acute and chronic scream sound stress. First, adult Sprague-Dawley (SD) rats were randomly divided into white noise, stress and background groups. The white noise group and stress group were treated with white noise and scream sound for 4h in the morning respectively. Compared with white noise and background groups, exposure to acute scream sound increased corticosterone (CORT) level and decreased latency in Morris water maze (MWM) test. The levels of noradrenaline (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were altered in the striatum, hypothalamus and hippocampus of stress rats. Second, adult SD rats were randomly divided into background and stress groups, which were treated with scream sound for three weeks. Exposure to chronic scream sound suppressed body weight gain, increased corticosterone (CORT) level, influenced the morphology of adrenal gland, improved spleen and thymus indices, and decreased latency in MWM test. NE, DA, DOPAC, HVA and 5-HIAA levels were also altered in the brain of stress rats. Our results suggested that scream sound, as a novel stressor, facilitated learning ability, as well as altered monoamine levels in the rat brain. Moreover, scream sound is easy to apply and can be applied in more animals at the same time.