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The time profile of morphine effect on different phases of inhibitory avoidance memory in rat
Mohammad Reza Zarrindast1, Abolfazl Ardjmand, Ameneh Rezayof
1Department of Neuroscience, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Backgrounds:
The amnesic effect of morphine is well known in the laboratory animals. But, it is unclear that morphine at what times can exactly affect different phases of memory, including acquisition, consolidation, and retrieval. Therefore, we investigated the time profile of morphine's amnesic effect on passive (inhibitory) avoidance learning and memory in male Wistar rats.
Methods:
In order to evaluate the outcomes of pre- and post-training administrations of morphine, the animals were trained in a step-through type of passive avoidance task at various time points, and were tested 24 h after training to measure memory retrieval.
Results:
The results showed that acquisition of memory was impaired in the animals that received a dose of 7.5 mg/kg of morphine (Intraperitoneally) at 0, 30 min, and 1 h before training, as evidenced by a decrease in step-through latency on the test day. Post-training administrations of morphine at 30 min and 1h, 4h except for the time immediately after training, did not impair memory consolidation. The results also showed that pre-test administrations of morphine at 0 and 30 min before the test, impaired retrieval of inhibitory avoidance memory.
Conclusion:
Taken together, the results suggest that morphine, when injected at different time points before training, after training, or before testing affects different phases of inhibitory avoidance memory. With regard to the time of injections related to each phase, other experiments can be designed to investigate molecular mechanisms involved in the impairing effect of morphine in each phase.
Insights
Morphine impairs memory acquisition and retrieval when administered at specific times around training and testing in rats. However, it does not affect memory consolidation when given shortly after training.
Area of Science:
- Neuroscience
- Pharmacology
- Behavioral Science
Background:
- Morphine's amnesic effects are known in animal models.
- The precise timing of morphine's impact on memory phases (acquisition, consolidation, retrieval) remains unclear.
Purpose of the Study:
- To investigate the temporal profile of morphine's amnesic effects on passive (inhibitory) avoidance learning and memory.
- To determine how morphine administration timing influences different memory phases.
Main Methods:
- Male Wistar rats were trained in a step-through passive avoidance task.
- Morphine (7.5 mg/kg, intraperitoneally) was administered at various time points before and after training, and before testing.
- Memory retrieval was assessed 24 hours after training.
Main Results:
- Pre-training morphine administration (0, 30 min, 1 h before) impaired memory acquisition.
- Post-training morphine administration (30 min, 1 h, 4 h after) did not impair memory consolidation.
- Pre-test morphine administration (0, 30 min before) impaired memory retrieval.
Conclusions:
- Morphine affects distinct phases of inhibitory avoidance memory depending on injection timing relative to training and testing.
- Further research can explore the molecular mechanisms underlying morphine's dose-dependent effects on memory phases.
