Early Prenatal Stress Increases Body Weight and Reduces Nociception in Adult Male Rats

Aims: Behavioral responses of 3-month-old male pups from female Wistar rats exposed to daily 1 hour or 3 hour restraint stress during the first 7 days of pregnancy were studied by tail flick and formalin test.
Methodology: Eighteen mature virgin female albino rats (140g-160g) were randomly allocated in a blinded fashion to 3 groups (n=6 each) and mated. Group 1 rats were the control and did not undergo restraint stress. Groups 2 and 3 rats were restrained for 1 hour and 3 hours respectively during the first 7 days of pregnancy. Six male rats only served purpose of copulation. At 3 month of age, 34 pups consisting of 10, 11 and 13 pups delivered by rats in groups 1, 2 and 3 respectively were randomly selected and studied for nociception.
Results: Body weights were higher in both 1 hour and 3 hour prenatally stressed pups compared to that of the control. The latency period during the tail immersion test in the pups prenatally stressed for 3 hour daily but not those stressed for 1 hour daily was significantly higher (p<0.05) compared to that of control. While there were no significant differences in the formalin score in pups prenatally stressed for 1 hour and 3 hour compared to the score of the control during the early phase, the formalin score of the pups prenatally stressed for 3 hour daily but not those stressed for 1 hour daily was significantly lower compared to that of the control during the late phase.
Conclusion: Our findings suggest that early prolonged prenatal stress modulates nociceptive sensitivity in 3-month-old rat and that different mechanisms are responsible for the effects of prenatal stress on acute and persistent pain in the formalin test.