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Updated: Jun 21, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Periaqueductal grey lesions reduce morphine analgesia in the rat
1National Institute for Medical Research, Mill Hill, London NW7 1AA Great Britain.
Abstract:
Many recent experiments have implicated the periaqueductal grey matter (PAG) as a major site of action of morphine in producing analgesia. This hypothesis was tested by investigating the effect of PAG lesions on morphine analgesia. Histologically verified electrolytic lesions were made in the rat mesencephalon which destroyed a large part of the PAG. Rats were subsequently tested for morphine analgesia using the tail flick method. Analgesin produced by morphine administration was markedly reduced in the lesioned rats. Pain thresholds were not altered by the lesions.
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