We next sought to determine whether lower CB1R mRNA levels were specific to mPFC in GAD67+/− mice or were also found in other cortical brain regions, such as the supplementary motor area. First, as expected (17), in WT mice CB1R expression was lower in supplementary motor area (402.5 ± 51.9 nCi/g) than in mPFC (477.0 ± 62.4 nCi/g) and CB1R mRNA levels were highly correlated between these two cortical regions (r=0.86, p<0.001). Similar to mPFC, mean CB1R mRNA levels were 11.0% lower in GAD67+/− mice (358.3 ± 47.7 nCi/g) relative to WT mice (402.5 ± 51.9 nCi/g), although this difference did not reach statistical significance (t12=1.66; p=0.123). The reduced strength of the finding in the supplementary motor area relative to mPFC may reflect the lower baseline levels of CB1R expression in motor areas (17); indeed, we previously suggested that reduced CB1R mRNA is likely to be an effective compensatory response to a deficit in GAD67 expression only in regions, like the PFC, with high levels of CB1R expression (6).
