Effects of neonatal administration of monosodium gluta-mate on morphine-, acupuncture- and stress-analgesia in adult rats

Monosodium glutamate(MSG) was given to neonatal rats from the 5th d after birth at a dose of 2 g/kg qd x5 d. 10% NaCI was given as an iso-osmotic control. The analgesic experiments were performed 105 d later. Pain thresholds were measur-ed by tail stimulation-vocalization test. It was found that hypothalamic ar-cuate nucleus (HAN) neurons were dam-aged markedly by MSG. No significant dif-ferences in the baseline pain thresholds were seen between the MSG-treated group (0.21±0.09 mA) and the control group (0.23±0.11). After ip morphine 5 mg/kg, acupuncture and stress, the pain thresh-olds in the MSG-treated group increased only t0 0.45±0. 24, 0.29±0.20 and 0. 27±0.18, respectively,which were significant-ly lower than those of the control groups (0.9±0.5, 0.6±0.5 and 0.5±0.3, respec-tively). The results suggested that HAN play-ed an important role in morphine anal-gesia, acupuncture analgesia and stress analgesia, as an endogenous analgesic structure.