Probing pain aversion in rats with the "Heat Escape Threshold" paradigm.

Area of Science:

• Neuroscience
• Pain Research
• Animal Models

Background:

• Pain aversion is a significant burden for patients.
• Existing animal models for pain aversion often involve complex cognitive processes, complicating result interpretation.
• Unconditioned escape behaviors are increasingly used to measure pain aversion, but current methods are limited in applicability to rats.

Purpose of the Study:

• To introduce and validate a novel "Heat Escape Threshold" (HET) paradigm for assessing heat aversion in rats.
• To demonstrate the HET paradigm's utility in various preclinical pain models.

Main Methods:

• Development and application of the Heat Escape Threshold (HET) paradigm in Sprague-Dawley rats.
• Utilized inflammatory pain models (carrageenan), real-time place avoidance (RTPA), systemic morphine administration, and intra-lateral parabrachial nucleus (LPBN) glutamate antagonist injections.
• Assessed both affective (HET, RTPA) and reflexive (Hargreaves test) pain responses.
• Investigated opioid-withdrawal pain models.

Main Results:

• The HET paradigm robustly and reproducibly detected heat aversion in inflammatory pain models in both male and female rats.
• Carrageenan-induced heat aversion in males was associated with real-time place avoidance.
• Morphine more effectively reduced HET and RTPA measures of heat aversion than reflexive responses.
• Blocking excitatory transmission to the LPBN reversed carrageenan-induced affective and reflexive pain behaviors.
• Opioid withdrawal robustly increased heat aversion without affecting reflexive heat responses.

Conclusions:

• The Heat Escape Threshold (HET) paradigm is a validated and reliable tool for measuring heat aversion in rats.
• The HET paradigm is sensitive to affective-motivational aspects of pain, offering advantages over traditional methods.
• This novel paradigm facilitates preclinical pain research and the development of targeted pain therapies.