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Updated: May 1, 2026

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

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Treatment with steroid hormones and morphine alters general activity, sexual behavior, and opioid gene expression in

E Teodorov1, R Camarini2, M M Bernardi1

  • 1Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, Av dos Estados, 5001, Brazil.

Life Sciences
|April 5, 2014
PubMed
Abstract

Insights

Chronic morphine alters rat behavior and opioid receptor expression, indicating opioid system activation and sex hormones impact these patterns quickly. Keywords: morphine, opioid receptors, behavior, sex hormones, rats.

Area of Science:

  • Neuroscience
  • Endocrinology
  • Pharmacology

Background:

  • Brain opioid peptides inhibit gonadotropin secretion.
  • Opioid peptides (β-endorphin, enkephalin, dynorphin) act via specific receptors (μ, δ, κ).

Purpose of the Study:

  • To investigate the effects of chronic morphine on behavior and opioid receptor expression.
  • To examine changes in hypothalamus, striatum, and periaqueductal gray in female rats with induced estrus.

Main Methods:

  • Ovariectomized female rats received daily morphine for 6 days.
  • Evaluated general activity, sexual behavior, and opioid receptor (Oprm1, Oprd1, Oprk1) gene and protein expression.

Main Results:

  • Morphine increased locomotion/grooming, decreased immobility and sexual behavior.
  • Increased μ opioid receptor (MOR) gene/protein in striatum; decreased κ opioid receptor (KOR) protein in hypothalamus.
  • Increased MOR gene in periaqueductal gray and KOR gene in striatum in sexually behavior-tested animals.

Conclusions:

  • Opioid system activation and sex hormones rapidly alter behavioral and molecular patterns.
  • Suggests a short-term interplay between opioids, hormones, and neural pathways.
Keywords:
General activityOpioid systemSexual behaviorSexual hormones

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