Astrocytic disruption and cognitive impairment following sub-acute fentanyl administration in male rats

Fentanyl is a potent, fast-acting synthetic opioid that has played a major role in the opioid overdose crisis in the United States for over five decades, with opioid-related deaths increasing sharply in recent years. This study investigates the behavioral, histological, and molecular changes in the hippocampus of rats subjected to sub-acute fentanyl exposure. Two groups of rats were studied: one group received multiple fentanyl injections over approximately one week, while the control group received no fentanyl. A battery of behavioral tests related to memory and depression-including the Y-maze, shuttle box, tail suspension test, elevated plus maze, Barnes maze, Morris water maze, and forced swimming test-was administered. Electrophysiological assessments, including field potential recording and electromyography (EMG), were conducted to evaluate neural activity. Western blot analysis was performed to quantify the expression of brain-derived neurotrophic factor (BDNF) and RE1-silencing transcription factor (REST), while immunohistochemical analyses assessed hippocampal cellular alterations. Results showed that sub-acute fentanyl administration impaired behavioral performance in memory assessment tests (Y maze (P < 0.05), shuttle box (P < 0.01)). However, fentanyl did not alter spatial memory assessed by Morris water maze and Barnes maze relative to controls. Moreover, LTP was decreased in fentanyl group compared to the control group (P < 0.01). Locomotor activity (P < 0.05) and EMG latency (P < 0.01) were also diminished following fentanyl exposure. Notably, increased astrogliosis (P < 0.01) and astrocyte reactivity (P < 0.001) were observed, indicating significant disruptions in astrocyte neurobiology. Furthermore, BDNF expression was reduced (P < 0.001), whereas REST expression was elevated (P < 0.001) in the fentanyl-treated group. These findings offer initial insights into the neurobiological effects of fentanyl, underscoring the potential role of astrocytes in fentanyl-induced cognitive dysfunction and the broader implications for memory-related neuroregeneration.