2-Arachidonoylglycerol mobilization following brief synaptic stimulation in the dorsal lateral striatum requires glutamatergic and cholinergic neurotransmission
Several forms of endocannabinoid (eCB) signaling have been described in the dorsal lateral striatum (DLS), however most experimental protocols used to induce plasticity do not recapitulate the firing patterns of striatal-projecting pyramidal neurons in the cortex or firing patterns of striatal medium spiny neurons. Therefore, it is unclear if current models of eCB signaling in the DLS provide a reliable description of mechanisms engaged under physiological conditions. To address this uncertainty, we investigated mechanisms of eCB mobilization following brief synaptic stimulation that mimics in vivo patterns of neural activity in the DLS. To monitor eCB mobilization, the novel genetically encoded fluorescent eCB biosensor, GRABeCB2.0, was expressed in corticostriatal afferents of C57BL6J mice and evoked eCB transients were measured in the DLS using a brain slice photometry technique. We found that brief bouts of synaptic stimulation induce long lasting eCB transients. Inhibition of monoacylglycerol lipase, prolonged the duration of the eCB transient, while inhibition of diacylglycerol lipase inhibited the peak amplitude, suggesting that 2-AG is the predominate eCB generated following brief synaptic stimulation. 2-AG transients were robustly inhibited by AMPA and NMDA receptor antagonists, DNQX and DL-AP5 respectively. Additionally, the 2-AG transient was inhibited by the muscarinic M1 receptor (M1R) antagonist, VU 0255035, and augmented by the M1R positive allosteric modulator, VU 0486846, indicating that acetylcholine (ACh) release is required for efficient 2-AG production. The dopamine D2 receptor (D2R) agonist, quinpirole, inhibited the 2-AG transient. However, in slices from mice lacking D2Rs on cholinergic interneurons (CINs), quinpirole did not inhibit the 2-AG transient, demonstrating that D2Rs on CINs can modulate 2-AG production. The AMPA receptor or NMDA receptor antagonists, DNQX or DL-AP5 respectively, occluded 2-AG augmentation by VU 0486846 suggesting that converging glutamatergic and cholinergic signals are required for efficient 2-AG production following brief synaptic stimulation. Collectively, these data uncover unrecognized mechanisms underlying 2-AG mobilization in the DLS.