Related Experiment Video
Updated: Oct 7, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Antisera against endogenous opioids increase the nocifensive response to formalin: demonstration of inhibitory
1Department of Anesthesiology, Medical College of Wisconsin, Medical Education Building, Room M4308, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
Abstract:
The roles of endogenous opioid peptides in the brain in the modulation of nocifensive responses to formalin in ICR mice were studied. Mice were pretreated intracerebroventricularly (i.c.v.) with rabbit antiserum against beta-endorphin, [Leu5]enkephalin, [Met5]enkephalin or dynorphin A-(1-17) 1 h prior to intraplantar injection of formalin (0.5%, 25 microl) and the nocifensive licking responses were then observed. Pretreatment of mice with antiserum against beta-endorphin enhanced the second phase, but not the first phase of the nocifensive responses to formalin. Pretreatment with antiserum against [Leu5]enkephalin also caused a small but statistically significant enhancement of the second phase, but not the first phase of nocifensive responses to formalin. On the other hand, pretreatment with antiserum against [Met5]enkephalin or dynorphin A-(1-17) did not affect the nocifensive response to formalin. Our results indicate that beta-endorphinergic, and to a lesser extent, [Leu5]enkephalinergic systems are activated at the supraspinal sites to attenuate the nocifensive responses to formalin stimulation.
More Related Videos
Related Concept Videos
Analgesia and Pain Management
Opioid Analgesics: Synthetic and Semisynthetic Opioids
Opioid Receptors: Overview
Opioid Analgesics: Morphine and Other Natural Cogeners
Drugs Affecting GI Tract Motility: Opioids as Antidiarrheal Agents
Opioids, widely used antidiarrheal agents, mitigate diarrhea by slowing down...
Nociception

