Rat hypothalamic arcuate neuron response in electroacupuncture-induced analgesia

Electroacupuncture (EA) effects on activity of arcuate neurons of the hypothalamus (ARH) and on magnitude of the digastric electromyogram (dEMG) in the jaw opening reflex were investigated, in both p-chlorophenylalanine pretreated and normal Wistar rats. EA stimulation (300-500 microA, 5 msec pulses, for 15 min) was delivered unilaterally to a meridian Ho-Ku point of anesthetized rats at 3, 45 and 100 Hz. In control animals, EA stimulation at 3, 45 or 100 Hz induced long-lasting suppression of the magnitude of the dEMG activity and changed the spontaneous firing rate of most of the ARH neurons: the rate either increased (type I) or decreased (type II). After low-frequency stimulation, there were significantly more type I neurons than type II; after high-frequency stimulation, there were significantly more type II neurons than type I. In serotonin-depleted rats, however, high-frequency stimulation suppressed dEMG activity only slightly and induced a smaller proportion of type II neurons.