Analgesia induced by electrical stimulation of the inferior centralis nucleus of the raphe in the cat

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Abstract
In the cat, electrical stimulation of the inferior central nucleus of the raphe (CI) induced a powerful analgesia. This stimulation totally suppressed the behavioral reactions elicited by strong pinches applied to the tail or to the 4 limbs; it strongly modified the threshold of the jaw opening reflex obtained by tooth pulp stimulation and considerably affected the behavioral reactions elicited by continuing such stimulation. The mechanism of analgesia from the inferior raphe nucleus may be similar to that already described in the dorsal raphe nucleus. The analgesia obtained by stimulation of raphe nuclei seemed to be sustained by serotoninergic mechanisms and relationships between these are discussed. In preliminary experiments, analgeisa induced by CI stimulation was suppressed by administration of naloxone, a specific opiate antagonist.