A Tourette Syndrome/ADHD-like Phenotype Results from Postnatal Disruption of CB1 and CB2 Receptor Signalling

Cannabinoid receptor 1 (CB1) signalling is critical for weight gain and for milk intake in newborn pups. This is important as in humans, low birth weight increases the risk for attention-deficit hyperactivity disorder (ADHD). Moreover, some children with ADHD also have Tourette syndrome (TS). However, it remains unclear if insufficient CB1 receptor signalling may promote ADHD/TS-like behaviours. Here, ADHD/TS-like behaviours were studied from postnatal to adulthood by exposing postnatal wild-type CB1 and Cannabinoid receptor 2 (CB2) knockout mouse pups to SR141716A (rimonabant), a CB1 receptor antagonist/inverse agonist. Postnatal disruption of the cannabinoid system by SR141716A induced vocal-like tics and learning deficits in male mice, accompanied by excessive vocalisation, hyperactivity, motor-like tics and/or high-risk behaviour in adults. In CB1 knockouts, rearing and risky behaviours increased in females. In CB2 knockouts, vocal-like tics did not develop, and males were hyperactive with learning deficits. Importantly, females were hyperactive but showed no vocal-like tics. The appearance of vocal-like tics depends on disrupted CB1 receptor signalling and on functional CB2 receptors after birth. Inhibition of CB1 receptor signalling together with CB2 receptor stimulation underlie ADHD/TS-like behaviours in males. This study suggests that the ADHD/TS phenotype may be a single clinical entity resulting from incorrect cannabinoid signalling after birth.