CHARACTERIZATION OF CB1 RECEPTORS ON RAT NEURONAL CELL-CULTURES - BINDING AND FUNCTIONAL-STUDIES USING THE SELECTIVE RECEPTOR ANTAGONIST SR141716A

This study was undertaken to characterize further the central cannabin oid receptors in rat primary neuronal cell cultures from selected brai n structures, By using [H-3]SR 141716A, the specific CBI receptor anta gonist, we demonstrate in cortical neurons the presence of a high dens ity of specific binding sites (B-max = 139 +/- 9 fmol/mg of protein) d isplaying a high affinity (K-D = 0.76 +/- 0.09 nM), The two cannabinoi d receptor agonists, CP 55940 and WIN 55212-2, inhibited in a concentr ation-dependent manner cyclic AMP production induced by either 1 mu M forskolin or isoproterenol with EC(50) values in the nanomolar range ( 4.6 and 65 nM with forskolin and 1.0 and 5.1 nM with isoproterenol for CP 55940 and WIN 55212-2, respectively). Moreover, in striatal neuron s and cerebellar granule cells, CP 55940 was also able to reduce the c yclic AMP accumulation induced by 1 mu M forskolin with a potency simi lar to that observed in cortical neurons (EC(50) values of 3.5 and 1.9 nM in striatum and cerebellum, respectively), SR 141716A antagonized the CP 55940- and WIN 55212-2-induced inhibition of cyclic AMP accumul ation, suggesting CB1 receptor-specific mediation of these effects on all primary cultures tested. Furthermore, CP 55940 was unable to induc e mitogen-activated protein kinase activation in either cortical or st riatal neurons. In conclusion, our results show nanomolar efficiencies for CP 55940 and WIN 55212-2 on adenylyl cyclase activity and no effe ct on any other signal transduction pathway investigated in primary ne uronal cultures.