Impaired Learning Due to Noise Stress During Pregnancy in Rats Offspring

Abstract

Background: Environmental noise is a known stressful factor,that induces alterations of various physiological responses in the exposed individuals. Extensive evidences from animal and human studies have indicated that stress influences cognitive functions. Studies have shown that chronic exposure to noise during pregnancy impairs neurobehavioral and reproductive functions and also reduces the body weight of the offspring. It seems that prenatal noise stress during last three months of fetal life damages the neurons in special areas of brain involved in cognition and impairs the activity of hypothalamuspituitary- adrenal (HPA) axis. It is known very little about the effect of prenatal noise stress on learning. The aim of present work was to determine the effect of prenatal chronic intermittent noise stress on learning in rats. Methods: Fifteen Wistar pregnant rats were exposed chronically to intermittent white noise (90-120dB, 350Hz) during the last two weeks of their pregnancy periods (dark cycle, 07:00Pm-07:00Am). Stressed and nonstressed puppies bred under normal condition up to 3 months of age. Both stressed and nonstressed adult male and female rats were trained in an equal 3 arms Y-maze with 20-25 Volts D.C. electrical footshock and a 12 Watts light stimuli as an active avoidance learning. Animals were trained one session daily and criterion condition response (CCR) was 90 percent of last session of training. Results: Data showed that chronic exposure to noise during pregnancy impairs learning of stressed male rats significantly at all sessions (P<0.01). However, in the stressed female rats the response was decreased significantly only at the first two sessions (P<0.05). Conclusion: The results indicate that prenatal noise stress may damage the neurons in special areas of brain such as hippocampus and alters cognition and behavioral functions.
Keywords: noise stress, pregnancy, learning, rat.