The effects of prenatal exposure to predictable or unpredictable stress on early development in the rat

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Abstract
Pregnant rats were exposed to differents schedules of noise and light stress, and the developmement of their offspring was studied during the first 2 weeks of life. Motor development was measured by different tests: Righting reflex (Days 2–4); Cliff avoidance (Days 4–10); turning on an inclined plane (Days 5–10); and swimming behavior (Days 6–10). Development of motivation‐involved behavior was measured with a home‐seeking test (Days 6–16). Other developmental landmarks such ss acoustic response (Days 12–14) and eye‐opening (Days 14–17) were also recorded. Thrice‐weekly random stress resulted in a delay in the devlopment of all behaviors studied. Daily stress exposure throughtout pregnancy resulted in smaller litters with heavier pups, but otherwise normal behavioral and physical development. Rats exposed to daily stress during the last week of pregnancy only produced litters that did not differ in size and body weight, but that displayed accelerated development of all parameters (except for eye‐opening) from Day 6 onward. It is concluded that the unpredictabel nature of prenatal stress is responsible for delays in behavior of offspring.