Abstract
Conditioning electrical stimulation of the amygdala has an inhibitory effect on two types of nociceptive neurons, NS and WDR neurons, of the rat medullary dorsal horn. The purpose of the present study was to determine whether the activation of cell bodies by glutamate microinjection into the amygdala induces inhibition of both types of nociceptive neurons. The nociceptive neurons were recorded in the medullary dorsal horn of the rat anesthetized with N2O-O2 and 0.5% halothane and immobilized with pancuronium bromide. A peripheral test stimulus (a single rectangular pulse of 2.0 msec in duration) was applied to the facial area, and ipsilateral amygdaloid conditioning stimuli to the recording site were trains of 33 pulses (100-300 μA) delivered at 330 Hz. Glutamate microinjection was conducted through the same electrode as that used for electrical stimulation. Four WDR and three NS neurons were inhibited by the conditioning electrical stimulation in the central, basomedial and basolateral amygdaloid nuclei. Microinjection of 0.5 M monosodium glutamate (5 μl) into these amygdaloid nuclei induced maximal inhibition of these nociceptive neurons (85.4±9.3% for WDR neurons; 66.4±16.6% for NS neurons) at 5 min after injection, and the recovery of inhibition to 50% occurred at about 20-25 min. These findings suggest that excitation of neurons in the amygdala influences sensory-discriminative and motivational-affective components of pain experience. [J Physiol Sci. 2008;58 Suppl:S165]
