Effect of isolation on pain threshold and on different effects of morphine

1. 1. The effect of three periods of isolation (8, 15 and 30 days ) were studied in mice on the pain treshold and the sensitivity to morphine. 2. 2. The pain threshold was unchanged after 8 and 15 days of isolation but increased after 30 days of isolation. 3. 3. The analgesic effect of morphine was unchanged after 8 and 15 days of isolation but increased after 30 days of isolation. 4. 4. The tolerance to morphine analgesia was unchanged after 8 and 15 days of isolation but increased after 30 days of isolation (morphine-induced analgesia was reduced). 5. 5. The physical dependence on morphine induced by precipitated withdrawal was unchanged after 8 and 15 days of isolation but decreased after 30 days of isolation. 6. 6. It is suggested that isolation may modify the metabolism the metabolism/absorption of morphine in a different way according as the treatment is unique or chronic.