Safe Sound Exposure in the Fetus and Preterm Infant

The mammalian auditory cortex normally undergoes rapid and progressive functional maturation. Here we show that rearing infant rat pups in continuous, moderate-level noise delayed the emergence of adultlike topographic representational order and the refinement of response selectivity in the primary auditory cortex (A1) long beyond normal developmental benchmarks. When those noise-reared adult rats were subsequently exposed to a pulsed pure-tone stimulus, A1 rapidly reorganized, demonstrating that exposure-driven plasticity characteristic of the critical period was still ongoing. These results demonstrate that A1 organization is shaped by a young animal's exposure to salient, structured acoustic inputs-and implicate noise as a risk factor for abnormal child development.

A study was made of the effects of prenatal stress on the reactivity of the hypothalamic-pituitary adrenal (HPA) axis in male and female offspring. Rat dams were subjected to noise and light stress on an unpredictable basis throughout pregnancy. At 28 days of age mRNA for POMC, proenkephalin and prodynorphin were measured in the hypothalamus of the offspring. A marked reduction was found in POMC mRNA in PS females (PSF) but not in males (PSM), but the other mRNA's did not differ from controls (C). At 60 days of age, PSF has 3 times higher resting levels of serum corticosterone (COR) and significantly lower dexamethasone (DEX)3H hippocampal binding sites than CF. Overnight adrenalectomy abolished the difference in DEX binding. After 10 min exposure to open field PS males and females voided more fecal pellets and made fewer center entries than C offspring, testifying to increased emotionality. Open field stress caused a 3-5-fold rise in circulating COR in all groups within 15 min, which returned to baseline by 90 min in all rats except PSF. These data show that prenatal stress can cause permanent alterations in the behavior of both sexes in stressful situations but appears to cause a selective effect on the HPA axis in the female rat.