From Synaptic Plasticity to Neurotoxicity: Endocannabinoid Influence on Addiction and Neurodegeneration.

The endocannabinoid system (eCBS) is a versatile neuromodulatory network that orchestrates synaptic plasticity, reward processing, and neuronal homeostasis. Increasing evidence implicates eCBS dysregulation in both addiction and neurodegenerative (ND) disorders, suggesting overlapping molecular and cellular mechanisms underlying these conditions. This review synthesizes recent advances in understanding how eCBS components-cannabinoid receptors (CB1 and CB2), endogenous ligands (anandamide and 2-arachidonoylglycerol), and their metabolic enzymes-modulate dopaminergic and glutamatergic signaling within reward and reinforcement circuits. Chronic exposure to drugs of abuse, including alcohol, opioids, cocaine, and methamphetamine, perturbs eCBS homeostasis, promoting oxidative stress, neuroinflammation, excitotoxicity, mitochondrial dysfunction, and protein aggregation-pathological features common to Alzheimer's, Parkinson's, Huntington's, and amyotrophic lateral sclerosis. These overlapping mechanisms disrupt neuronal integrity and contribute to progressive neurotoxicity, highlighting shared pathogenic pathways between addiction and neurodegeneration. Despite these advances, critical gaps remain in delineating how substance-induced eCBS alterations precipitate neurodegenerative cascades. Addressing these gaps will be essential for harnessing the eCBS as a therapeutic target to mitigate addiction-driven neurotoxicity and age-related cognitive decline.