Related Experiment Video

Updated: Aug 14, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
07:23

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities

Published on: July 29, 2014

Analgesia induced by morphine microinjection into the lateral hypothalamus of the rat

P N Fuchs1, R Melzack

  • 1Department of Psychology, McGill University, Montreal, Quebec, Canada.

Experimental Neurology
|August 1, 1995
PubMed

Insights

Electrical stimulation of the lateral hypothalamus (LH) activates endogenous opiate pathways. Morphine microinjection into the LH significantly reduced formalin-induced pain, demonstrating prolonged analgesia.

Area of Science:

  • Neuroscience
  • Pain Research
  • Pharmacology

Background:

  • Electrical stimulation of the lateral hypothalamus (LH) has been shown to produce analgesia for both brief and prolonged pain.
  • The endogenous opiate system plays a crucial role in pain modulation.

Purpose of the Study:

  • To investigate the effect of morphine microinjection into the LH on formalin-induced pain.
  • To determine if the LH engages the endogenous opiate system for analgesia.

Main Methods:

  • Morphine was microinjected into the LH of subjects.
  • Formalin was administered to induce pain.
  • Pain responses were measured over a 25-minute period.

Main Results:

  • A 10-microgram microinjection of morphine into the LH significantly decreased pain responses.
  • The analgesic effect persisted for the entire 25-minute test period.
  • Pain was assessed 25 minutes after formalin injection.

Conclusions:

  • Microinjection of morphine into the LH effectively reduces formalin-induced pain.
  • These findings support the hypothesis that electrical stimulation of the LH engages an endogenous opiate system.
  • The LH is implicated in producing prolonged analgesia through endogenous opiate pathways.

More Related Videos

Intracranial Pharmacotherapy and Pain Assays in Rodents02:26

Intracranial Pharmacotherapy and Pain Assays in Rodents

Published on: April 9, 2019

Partial Sciatic Nerve Ligation: A Mouse Model of Chronic Neuropathic Pain to Study the Antinociceptive Effect of Novel Therapies08:16

Partial Sciatic Nerve Ligation: A Mouse Model of Chronic Neuropathic Pain to Study the Antinociceptive Effect of Novel Therapies

Published on: October 6, 2022

Related Concept Videos

Analgesia and Pain Management01:25

Analgesia and Pain Management

Pain is critical to various clinical pathologies, provoking an urgent need for effective management. Pain, whether acute or chronic, is a complex neurochemical process. Its alleviation depends on the type, with nonopioid analgesics effective for mild to moderate pain, such as musculoskeletal or inflammatory pain, while neuropathic pain responds best to anticonvulsants, tricyclic antidepressants, or serotonin/norepinephrine reuptake inhibitors. For severe acute or chronic pain, opioids may be...