Effect of synthetic cannabinoids added to smoked herbal mixtures on GABAergic and glutamatergic synaptic transmission in mouse brain slices

Bela Szabo, Eszter Boros, Mario Lederer. Department of Pharmacology; Albert-Ludwigs-Universität, Freiburg i. Brsg., Germany

Introduction. The CB1 cannabinoid receptor is typically located on axon terminals, and its activation leads to presynaptic inhibition of synaptic transmission. The best known agonist of the CB1 receptor is the phytocannabinoid Δ9-tetrahydrocannabinol. Recently, synthetic cannabinoids were introduced to the drug market: herbal mixtures for smoking (“Spice”, “Lava Red”, “Jamaican Gold”…) are “enriched” with such synthetic cannabinoids. Our aim was to characterize the synaptic effects of two frequently abused synthetic aminoalkylindoles, JWH-018 ((1-pentyl-1H-indol-3-yl)-1-naphthalenyl-methanone) and JWH-210 ((4-ethyl-1-naphthalenyl)(1-pentyl-1H-indol-3-yl)-methanone). The effects of WIN-55212-1 (R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazin-yl]-(1-naphthalenyl)methanone) were also studied for comparison.

Methods. 250 µm-thick sagittal slices were prepared from the cerebella of young (8-18 days old) NMRI mice and superfused at room temperature. Purkinje cells in the cerebellar cortex were patch-clamped and spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs) and evoked glutamatergic excitatory postsynaptic currents (eEPSCs) were recorded.

Results. JWH-210 (10-6 M) lowered the frequency of sIPSCs (by 28 ± 4 %; P<0.05), but did not change their amplitude. JWH-210 (5 x 10-6 M) suppressed the frequency of sIPSCs more strongly (by 52 ± 9 %; P<0.05); again, the amplitude was not changed. The CB1 antagonist taranabant (10-6 M) abolished the effect of JWH-210 (10-6 M) on the frequency of sIPSCs. Depolarization of the postsynaptic Purkinje cells induced an endocannabinoid- and CB1 receptor-mediated suppression of the GABAergic inhibitory input to the Purkinje cells (i.e., DSI occurred). DSI was occluded by superfusion of JWH-210 (5 x 10-6 M). JWH-210 (5 x 10-6 M) suppressed the frequency (by 48 ± 12 %; P<0.05) but not the amplitude of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin (3 x 10-7 M), pointing to presynaptic inhibition of synaptic transmission. JWH-210 (5 x 10-6 M) decreased the amplitude of glutamatergic eEPSCs (by 67 ± 6 %; P<0.05). This was due to presynaptic inhibition, because JWH-210 increased the ratio of the amplitudes of two EPSCs elicited within 40 ms. JWH-018 (10-7 and 10-6 M) did not affect the GABAergic sIPSCs. JWH-018 (5 x 10-6 M) lowered the frequency of sIPSCs (by 43 ± 8 %; P<0.05) without changing their amplitude. WIN-55212-1 (5 x 10-6 M) had a very similar depressive effect on the sIPSCs.

Conclusions. The aminoalkylindoles JWH-210, JWH-018 and WIN-55212-1 inhibit GABAergic synaptic transmission with a presynaptic action. Due to this inhibition they interfere with endocannabinoid-mediated synaptic plasticity. JWH-210 also presynaptically inhibits glutamatergic synaptic transmission. In humans, as additives in herbal mixtures, the synthetic cannabinoids will probably also inhibit GABAergic and glutamatergic synaptic transmission and occlude endocannabinoid-mediated synaptic plasticity. Consequently, impairments of many neuronal functions, including cognitive functions, are to be expected.