Periadolescent morphine exposure alters subsequent behavioral sensitivity to morphine in adult rats.

Little research has been conducted investigating the long-term impact of opioid exposure during adolescence. These experiments were conducted to determine the behavioral effects of morphine exposure during periadolescence (postnatal days 30-32) versus young adulthood (postnatal days 65-67) on subsequent sensitivity to morphine. Male Sprague-Dawley rats were treated with three days of saline (S-S-S), one day of 10 mg/kg morphine followed by two days of saline (M-S-S), or three days of morphine (M-M-M). Unlike adult-treated counterparts, periadolescent M-M-M-treated rats showed greater locomotor response to morphine compared to S-S-S or M-S-S cohorts five weeks after treatment, suggesting age- and exposure-dependent differences in opioid sensitivity.