Different responses of nitric oxide synthase inhibition on morphine-induced antinociception in male and female rats

Abstract The roles of gonadal hormones and nitric oxide on pain perception and their interaction have been widely investigated. In the present study the chronic effect of l-NAME (NOS inhibitor) on morphine-induced antinociception in male and female rats was investigated. Forty rats were divided into four groups: (1) female (2) female-LN (3) male (4) and male-LN. The animals of groups 2 and 4 received daily injection of l-NAME (10mg/kg) during 3 weeks. The animals of control groups 1 and 3 received 2ml/kg saline instead of l-NAME. Finally, all animals were tested on the hot plate test (52±0.2°C; Cut-off 80s) to evaluate the antinociceptive effects of morphine. The hot plate test was performed for base record 15min before the injection of morphine (10mg/kg; s.c.) and consequently it was repeated every 15min after the injection. There were no significant differences in baseline latencies among all groups. Reaction times after injection of morphine in female-LN were higher than in the female control group ( p p