Conditioned hyperalgesia depends on the pain sensitivity measure

Area of Science:

• Pharmacology
• Neuroscience
• Behavioral Science

Background:

• Conflicting reports exist on conditioned hyperalgesia during morphine tolerance development.
• Some researchers propose tolerance reduces stimulus processing, not via compensatory interactions.

Purpose of the Study:

• To investigate conditioned hyperalgesia using both hot-plate and tail-flick tests in the same animals.
• To determine if measurement procedures influence observed conditioned responses.

Main Methods:

• Animals were tested for conditioned hyperalgesia on hot-plate and tail-flick tests.
• Conditioned responses were assessed in drug-free animals and after low-dose morphine challenge.

Main Results:

• Tail-flick tests in drug-free animals did not show conditioned compensatory hyperalgesia.
• Tail-flick conditioning effects were observed only with a low morphine dose.
• Hot-plate tests in drug-free animals replicated conditioned hyperalgesia.

Conclusions:

• Measurement of conditioned responses in drug-free animals is dependent on the assessment procedure.
• Findings support theories of morphine tolerance involving compensatory response interactions.