Ibudilast-Mediated Suppression of Neuronal TLR4 in the Prefrontal Cortex Mitigates Methamphetamine-Induced Neuroinflammation and Addictive Behaviours

Abstract

Methamphetamine (METH) use leads to addiction, neurotoxicity, and neuroinflammation. Ibudilast, a toll-like receptor 4 (TLR4) inhibitor, has been shown to reduce METH-induced neuroinflammation and self-administration, but its specific role in neuronal TLR4 signalling and associated behavioural outcomes remains poorly understood. This study examined Ibudilast's effects on METH reward, drug-seeking behaviour, and TLR4 signalling in a rat self-administration model. Ibudilast was found to dose-dependently reduce METH intake and motivation for the drug, as evidenced by a downward shift in the dose–response curve and a decrease in breakpoint. Additionally, Ibudilast suppressed both cue- and METH priming-induced drug-seeking behaviours. Western blot analysis revealed elevated TLR4, p-NF-κB and IL-6 in the prefrontal cortex after 14 days of METH self-administration. These increases were significantly attenuated by Ibudilast treatment. Furthermore, local administration of Ibudilast in the prefrontal cortex led to a reduction in METH intake and motivation, as well as decreased TLR4 expression in this brain region. Immunofluorescence staining was revealed that TLR4 was expressed predominantly in neurons and microglia, with METH-induced upregulation of neuronal TLR4 being linked to apoptosis. Ibudilast restored normal spatial interactions between neurons and microglia, thereby mitigating neuroinflammation and neuronal damage. Furthermore, local injection of Ibudilast in the prefrontal cortex led to a reduction in METH intake and motivation, as well as decreased expression of TLR4 in the brain region. These findings underscore the critical role of neuronal TLR4 in METH addiction and highlight Ibudilast's therapeutic potential in addressing METH-related neuroinflammation and behavioural dysregulation.