Stress-induced attenuation of acoustic startle in low-saccharin-consuming rats

Exposure to stress can lead to either increased stress vulnerability or enhanced resiliency. Laboratory rats are a key tool in the exploration of basic biobehavioral processes underlying individual differences in the effect of stress on subsequent stressors' impact. The Occidental low (LoS) and high (HiS) saccharin-consuming rats, which differ in emotional reactivity, are useful in this effort. In the present study, footshock affected acoustic startle amplitude 4 h later among LoS but not HiS rats. Surprisingly, shock attenuated startle rather than sensitizing it, a finding not previously reported for male rats exposed to shock. Attenuation was blocked by administering the anxiolytic drug alprazolam prior to stress, implicating anxiety in the effect. Preliminary tests provided no evidence of mediation by adenosine or corticosterone. This novel result encourages further study of the stressor and dispositional variables that modulate the timecourse of effects of stress on startle and identification of its mechanisms.