Figure 2.
Functional characterization and expression of the mutated CB1R and other components of the eCB system in the striatum of Cnr1 mutant (MT) and WT rats. a, b, Cannabinoid-induced [35S]GTPγS binding (a; interaction effect: F(9,54) = 2.1, p = 0.048), as well as PPR (b; genotype effect: F(1,69) = 13.6, p = 0.001) were significantly higher in MT animals compared with WT littermates. Representative traces for PPR: EPSC amplitudes are normalized to the peak of the first EPSC. In each example, there are three trials superposed (for three different interstimulus intervals). Scale bar, 20 ms. No differences could be observed for sEPSC amplitude (p = 0.27), but the interevent interval was enhanced (p = 0.034) in MT rats. Representative traces for sEPSCs are shown. There are 7 consecutive seconds for each condition (two rows per each). Scale bar, 10 pA; 500 ms (c). Effects of the CB1R antagonist/inverse agonist SR141716 (SR, 2 μm) on field EPSP (fEPSP) were significantly stronger (p = 0.01) in MT rats. Representative traces of field EPSPs recorded before (black) and after (gray) application of SR141716. Scale bar, 0.1 mV; 2 ms (d). CB1R expression did not differ between genotypes. No significant differences could be detected between MT animals and WT controls for protein levels (e) (Western blot analysis) (p = 0.50) and uptake of the CB1R ligand [18F]MK-9470 (assessed in vivo by PET analysis) (p = 0.95) (f). Protein levels of monoacylglycerol lipase (MAGL) were also unaltered (p = 0.73) (g), but FAAH levels were significantly lower in MT (p = 0.043) compared with WT rats (h). No significant differences between the genotypes could be found for expression of AEA (p = 0.62) (i) and 2-AG (p = 0.58) (j). All data are indicated as means ± SEM ([35S]GTPγS: MT/WT n = 4; PPR: MT n = 12; WT n = 13; sEPSC: n = 12; SR on fEPSP: MT: n = 6, WT n = 5; Western blot CB1R: n = 5; PET analysis: n = 6; Western blot FAAH, MAGL: n = 5; AEA, 2-AG: MT: n = 9, WT n = 14; *p ≤ 0.05).