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Morphine-induced impairment of spatial memory acquisition reversed by morphine sensitization in rats

Maryam Farahmandfar1, Seyed Morteza Karimian, Nasser Naghdi

  • 1Department of Physiology, Tehran University of Medical Sciences, Tehran, Iran.

Behavioural Brain Research
|March 16, 2010
PubMed

Insights

Morphine impairs spatial memory in rats, but this effect is reversed in morphine-sensitized rats. Opioid receptors appear crucial for this memory reversal, suggesting potential therapeutic targets.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Behavioral Science

Background:

  • Morphine, an opioid analgesic, can significantly impact cognitive functions, including spatial memory.
  • Understanding the neurobiological mechanisms underlying morphine's effects on memory is crucial for managing pain and addiction.

Purpose of the Study:

  • To investigate the impact of morphine sensitization on spatial memory acquisition in rats using the Morris water maze (MWM).
  • To explore the role of opioid receptors in the reversal of morphine-induced amnesia in sensitized rats.

Main Methods:

  • Rats were sensitized to morphine via daily subcutaneous injections for 3 days, followed by a 5-day withdrawal period.
  • Spatial memory acquisition was assessed using the MWM task, including training and probe trials.
  • The effect of naloxone, an opioid antagonist, on morphine-induced amnesia reversal was evaluated.

Main Results:

  • Single pre-training doses of morphine (2.5-7.5 mg/kg) impaired spatial memory acquisition in the MWM, with maximal impairment at 5 mg/kg.
  • Morphine-induced amnesia was significantly reversed in morphine-sensitized rats (15-20 mg/kg).
  • Naloxone administration (1-2 mg/kg) prior to morphine during sensitization reduced the reversal of amnesia in sensitized rats.

Conclusions:

  • Morphine sensitization effectively reverses the impairment of spatial memory acquisition caused by morphine.
  • Opioid receptors likely play a significant role in the observed reversal of morphine-induced amnesia.
  • These findings highlight the complex interplay between opioid exposure, sensitization, and cognitive function.

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