CB1 Cannabinoid Receptors in the central nervous system of Podarcis sicula.

The endocannabinoid system is an important intercellular signaling system in which are involved cannabinoid receptors, endocannabinoids (endogenous transmitters) and different enzymes (McPartland et al., 2002). Two types of cannabinoid receptors have been characterized, CB1 and CB2 receptors. While CB2 receptors are mainly express by cells of the immune system, CB1 receptors are indeed expressed in many brain regions where they have a relevant neuromodulatory role (Felder and Glass,1998). The endocannabinoid system appears to be phylogenetically ancient, because its homologs are expressed in the genoma of many organism. The phylogenetic distribution of this system is yet poorly known and its components are apparently evolved separately in different epochs (McPartland, 2004). Genes encoding orthologues of the mammalian CB1 receptor have been identified in a fish, an amphibian and a bird, indicating that CB1 receptors may occur throughout the vertebrates (Elphick and Egertová, 2001). To our knowledge few is known regard CB1 receptors in the reptilian species. In the present work we have studied the occurrence and distribution of the CB1 receptors in the brain of the reptile Podarcis sicula. The study was performed on 6µm serial section of P. sicula brains enclosed in paraffin and processed by ABC technique and the use of the polyclonal antiserum anti-CB1 receptor at the working dilution of 1/800. CB1-immunoreactivity (IR) was observed through all the CNS of P. sicula. The immunoreactivity appeared specific but with a different distribution between the several areas. CB1-IR was more abundant in the optic chiasma, in the transitional area between diencephalon and mesencephalon and in the optic tectum, where we in particular observed CB1(+) fibres. Few CB1-IR structures were also observed in the telencephalon, confined in the central area, and in the cerebellum. These preliminary data prove the occurrence of CB1-receptors also in the lizard brain and agree with the hypothesis that the CB1 receptors of the other vertebrates have a structural homology with that of mammals (Cesa et al., 2002).