Effect of neonatal injection of monosodium glutamate on the analgesia produced by hypothalamic arcuate nucleus stimulation

Hypothalamic arcuate nucleus(ARC) is the principal nucleus containing #beta#-endorphinergic (#beta#-END) neurons in the brain. Neuronal cell bodies in ARC can be destroyed, but sparing the fibers of passage, by neonatal administration of monosodium glutamate(MSG) in rats, which is a valuable model for studying the function of neurons in ARC. In the present experiment this model(MSG-treated rats), was used to investigate the analgesic effect of ARC stimulation by tail stimulation-vocalization test. It -was found that no significant analgesic effect was observed after ARC stimulation in MSG-treated rats. The analgesic effect of ARC stimulation in MSG-treated rats could be recovered after intracerebroveutricular injection of #beta#-END (5#mu#g/ l0#mu#l), but not of dopamine(5#mu#g/ 10#mu#1), which on the contrary, could attenuate the analgesic effect of ARC stimulation in normal rats. Experimental results suggest that the disappearance of analgesic effect of ARC stimulation in MSG-treated rats might be the result of damage of #beta#-END neurons in ARC, and no significant role could be attributed to dopaminergic neurons.