Received 23 May 2015, accepted for publication 2August 2015

Background & Aims: Stressful events during gestation have important effects on the later physical and mental health of the offspring. The present study aimed to identify effects of co-administration of stress and morphine in prenatal period and re-exposure to stress at the end of infancy on corticosterone blood levels and pentylentetrazol-induced epileptic behaviors in rat.

Materials and Methods: Pregnant rats were divided to six groups of control, stress, saline, morphine, stress-saline and stress-morphine. In the stressed group, rats were stressed and held immobile for three consecutive days started on day 15 of pregnancy. The rats in saline and morphine groups received saline and morphine in the same days. In the morphine/saline-stress groups, rats were exposed to stress and received morphine/saline simultaneously. On postnatal day 22, half of the pups re-exposed to stress, and pentylentetrazol-induced epileptic behaviors of each rat were assessed. Blood samples were collected to determine corticosterone level.

Results: Latency of first epileptic behavior decreased significantly in stress-morphine group compared to other groups. Re-exposure to stress significantly led to a decrease in number of clonic seizure. There was no significant difference between the experimental groups in duration of clonic attacks and mortality rate. The level of corticosterone showed a significant increase in stressed pups and decreased in morphine group.

Conclusion: these results indicated that co-administration of morphine and restraint stress during late pregnancy had profound impact on neurochemical development and might alter vulnerability to PTZ-induced epileptic behaviors. Prenatal stress is more powerful than postnatal stress on influencing neural development and seizure susceptibility in rats.