CB1 cannabinoid receptor expression in brain regions associated with zebrafinch song control

Cannabinoids have been used for millennia through various preparations of C annabis sativa;. Despite this long history of use, the physiological signif icance of cannabinoid signaling in the vertebrate CNS is not well understoo d. High CB1 cannabinoid receptor densities in mammalian telencephalon and t he results of behavioral studies suggest that cannabinoids play a role in c ognitive function, learning, and memory. Since a network of discrete brain regions in zebra finch telencephalon controls song learning, we hypothesize d that cannabinoid signaling may be relevant to songbird vocal development and behavior. Radioligand binding experiments using the cannabinoid a,agoni st [H-3]CP-55940 allowed identification of a dense population of high-affin ity cannabinoid binding sites in zebra finch neuronal membranes. Northern b lotting and RT-PCR experiments demonstrated expression of a predominant zeb ra finch CB1 mRNA of similar to 5.5 kb. Expression of this CB1 mRNA appears to change over the course of vocal development within the caudal telenceph alon. As zebra finch caudal telencephalon contains the higher vocal center (HVC) and the robust nucleus of the archistriatum (RA), regions involved in song learning and production, we further investigated CB1 expression in th ese areas using in situ hybridization. In situ hybridization revealed that CB1 mRNA is expressed at high levels within both HVC and RA. Overall, these data demonstrate the presence of CBI signaling systems within songbird tel encephalon, notably within regions known to be involved in song learning an d production. High-level CBI expression in song regions suggests a potentia l role for cannabinoid signaling in zebra finch vocal development. (C) 2000 Elsevier Science B.V. All rights reserved.