Evaluation of AT121 versus morphine on cortical neurons electrophysiology and dopamine concentrations in hippocampal cells

In order to achieve pain relief without associated tolerance and dependence risks of general opioids like morphine, researchers have designed AT121 as potent safe alternative. In this study, we evaluated the analgesic and neurochemistry effects of AT121, a bifunctional partial agonist at Mu and nociceptin/orphanin FQ peptide (NOP) receptors, compared to morphine in hippocampal neurons for the measurement of dopamine neurotransmitters concentration and action potential of cortical neurons isolated from newborn BALB/c mice. This helps us to predict and assess its success in vivo by detecting the effect of AT121 in vitro. This activates G0/Gi protein pathways while blocking the β-arrestin pathway, significantly delayed action potential generation, prolonged spike duration, and reduced amplitude, without altering firing thresholds or inducing tolerance over a two-hour window. In contrast, morphine has produced similar analgesic effects but with a higher risk of tolerance. Co-administration of AT121 and morphine improved these changes, whereas naloxone failed to reverse AT121's effects, suggesting distinct receptor interactions. Dopamine quantification in hippocampal culture media revealed that morphine, alone or combined with AT121, markedly elevated extracellular dopamine, consistent with its reinforcing properties to morphine on analgesia. Notably, AT121 alone led to significantly lower dopamine levels compared to control, indicating a reduced risk of triggering reward-related pathways. Together, these findings highlight AT121 as a promising candidate for both acute and chronic pain management, and suggest its offering potent analgesia with a lower likelihood of tolerance and addiction following chronic opioid exposure.