Opiate antagonist, naloxone, strongly reduces analgesia induced by stimulation of a raphe nucleus (centralis inferior)

Abstract

The analgesic effects obtained in the cat by central inferior raphe nucleus stimulation are greatly reduced by the administration of a specific opiate antagonist, naloxone. In 12 of 16 cats analgesia, tested by pinches applied on the 4 limbs or the tail, was totally abolished. Analgesia tested by considering the increase of the threshold of the jaw opening reflex was reduced to 44% of the initial value. These results emphasize the relation existing between morphine analgesia and analgesia induced by central stimulation. To try to explain the effects of naloxone, one may suppose that central stimulation releases an endogenous morphine-like substance such as enkephalin.