Cannabinoid CB₁ Receptor Activation Mitigates <i>N</i>-Methyl-<scp>d</scp>-aspartate Receptor-Mediated Neurotoxicity

Alzheimer's disease (AD) is characterized by synaptic dysfunction and excitotoxicity, yet effective therapeutic strategies remain limited. This study explores the functional and physical interplay between cannabinoid CB₁ receptors (CB₁Rs) and <i>N</i>-methyl-d-aspartate receptors (NMDARs), which are implicated in AD pathology. Using bioluminescence resonance energy transfer and imaging assays in HEK-293T cells, we demonstrate a direct interaction between CB₁R and the N1 subunit of NMDAR, supporting the formation of receptor complexes. Functional assays further reveal a bidirectional negative crosstalk: NMDA attenuates CB₁R-mediated cAMP inhibition, while CB₁R activation reduces NMDA-induced calcium influx and mitogen-activated protein kinase signaling pathway activation. This negative crosstalk suggests the existence of receptor-receptor interactions with functional consequences. Complexes of CB₁Rs and N₁ subunits of NMDARs are present in both neurons and microglia, and their expression is upregulated in response to Aβ_1-42 and in cells derived from the APP_Sw/Ind AD model mice. However, upregulation did not always correlate with stronger CB₁R-NMDAR cross-modulation, suggesting that cell-specific signalosome composition shapes the signaling outcome. Functionally, CB₁R activation confers neuroprotection: It rescues neurite loss induced by NMDA and Aβ_1-42, highlighting the therapeutic potential of modulating CB₁R-NMDAR interactions. These findings support a model in which CB₁R-NMDAR interactions, through dynamic functional cross-modulation, finely tune excitotoxic and inflammatory signaling pathways. This mechanism offers therapeutic prospects for addressing cannabinoid-glutamatergic interactions.