Figure 6. Chronic THC treatment induces long-lasting loss of CB₁ from the plasma membrane of GABAergic axon terminals in a dose-dependent manner.

(a,d) Deconvolved confocal images of axon terminals of perisomatic interneurons, recorded in slices prepared from mice treated with vehicle or THC (i.p. injections twice a day for 6.5 days). (b,e) STORM imaging reveals a dramatic THC-evoked reduction of CB₁ localization points. A CB₁ antibody with improved sensitivity derived from transgenic rabbits (Online Methods) was used to enable reliable visualization of CB₁ receptors at low and high levels alike. (c,f) Visualization of CB₁ localization points in 3D demonstrates an increased intraterminal accumulation of CB₁ in THC-treated animals. (g) Upon chronic administration of 10 mg/kg THC, CB₁ NLP are reduced by 74% (n = 185 and 117 axon terminals from 3 vehicle- and 2 THC-treated animals, Mann-Whitney U test). After a drug-free period of 11.5 days, 53% of CB₁ receptors recovered, but the reduction in NLP (35%) was still significant (n = 283 and 113 boutons from 3 and 3 animals). A longer recovery period of six weeks, however, allowed complete rescue (n = 113 and 92 boutons from 2 and 3 animals). Chronic treatment with a lower (1 mg/kg) dose resulted in a slight (16%) decrease in NLP (n = 129 and 153 boutons from 2 and 3 animals). (h) The remaining CB₁ localization points are shifted towards the center of the axon terminal after high dose of THC (unpaired two-sided t-test). However, internalization was not detectable after recovery for 11.5 days or 6 weeks, or after low dose of THC. Graphs show raw data and median±IQR.