Role of the amygdala opioid system in the effects of stress on the post-learning sleep patterns of male Wistar rats.

Objectives: Three physiological processes interact: sleep, learning, and stress. It is essential to understand how stress affects and interacts with the link between sleep, learning, and memory since it has long been recognized that sleep plays a crucial role in memory consolidation and learning. Through naloxone injection in the baso lateral amygdala (BLA), this study intends to shed light on the interactions between stress, learning, and sleep, as well as the function of the opioid system and its impact on brain-derived neurotrophic factor (BDNF) production in the hippocampus.

Materials and methods: Male Wistar rats (n=77) in eleven groups were implanted with electroencephalogram (EEG) and electromyography (EMG) recording electrodes, and the BLA area was bilaterally cannulated. Recordings of Rapid Eye Movement (REM) and Non-Rapid Eye Movement (NREM) sleep and wakefulness steps were made for the three hours prior to and three hours following the implementation of the immobility stress protocol and learning with the Barnes maze for three consecutive days. Also, the animals' memory was tasted 48 hr later. Before the stress and learning procedure, naloxone was injected into each BLA three times in a row at a dosage of 0.05 μg or 0.1 μg in a volume of 0.5 μl. A molecular biomarker of learning and stress, BDNF, was also examined.

Results: The study demonstrated that the immobility stress model lowers REM and NREM sleep. On the other hand, putting the learning technique into practice results in more REM and NREM sleep, and stress situations do not stop this rise after learning. Naloxone injections in the BLA region also enhance learning and memory, preventing stress-related REM and NREM sleep loss. Additionally, stress lowers BDNF expression in the hippocampal region. BDNF expression rises in the hippocampus throughout the learning process, and naloxone administration in the BLA area also raises BDNF expression in the hippocampus.

Conclusion: Stress generally reduces REM, NREM, and BDNF expression in the hippocampal region. Under stress, using the learning protocol increases REM, NREM sleep, and BDNF. Naloxone injection in BLA improves memory and learning, reducing stress-induced memory loss.