Cannabinoid receptors are widely expressed in goldfish: molecular cloning of a CB2-like receptor and evaluation of CB1 and CB2 mRNA expression profiles in different organs

Abstract

Cannabinoids, the bioactive constituents of Cannabis sativa, and endocannabinoids, among which the most important are anandamide and 2-arachidonoylglycerol, control various biological processes by binding to specific G protein-coupled receptors, namely CB1 and CB2 cannabinoid receptors. While a vast amount of information on the mammalian endocannabinoid system does exist, few data have been reported on bony fish. In the goldfish, Carassius auratus, the CB1 receptor has been cloned and its distribution has been analyzed in the retina, brain and gonads, while CB2 had not yet been isolated. In the present paper we cloned the goldfish CB2 receptor and show that it presents a quite high degree of amino acid identity with zebrafish Danio rerio CB2A and CB2B receptors, while the percentage of identity is lower with the pufferfish Fugu rubripes CB2, as also confirmed by the phylogenetic analysis. The sequence identity becomes much lower when comparing the goldfish and the mammalian CB2 sequences; as for other species, goldfish CB2 and CB1 amino acid sequences share moderate levels of identity. Western-blotting analysis shows the CB2 receptor as two major bands of about 53 kDa and 40 kDa, and other faint bands with apparent molecular masses around 70 kDa, 57 kDa and 55 kDa. Since the distribution of a receptor could give information on its physiological role, we evaluated and compared CB1 and CB2 mRNA expression in different goldfish organs by means of quantitative Real-Time PCR. Our results show that both CB1 and CB2 receptors are widely expressed in the goldfish, displaying some tissue specificities, thus opening the way for further functional studies on bony fish and other non-mammalian vertebrates.

The Neuroendocrine Regulation of Food Intake in Fish: A Review of Current Knowledge

“…In goldfish, CB1 and CB2 are both expressed in brain, where CB1 co-localizes with NPY (Cottone et al, 2013). Treatment with low doses of the endocannabinoid receptor agonist anandamide (AEA) increases food intake (Valenti et al, 2005), and food deprivation increases CB1 and AEA brain mRNA levels (Cottone et al, 2009), suggesting the involvement of the ECS in the control of energy intake in Cypriniforme.…”

Developing ‘integrative’ zebrafish models of behavioral and metabolic disorders

“…Taken together, these data suggest the CB1/endocannabinoid system as an emerging target for the treatment of metabolic and behavioral disorders. Importantly, a conserved cannabinoid system (including both CB1 and CB2-like receptors) is present in teleost fish [217][218][219], making zebrafish a likely candidate species to study various cannabinoid-mediated physiological mechanisms [220][221][222]. For instance, activation of CB1 receptor function in transgenic zebrafish promotes hepatic liver accumulation and steastosis [219].…”

Endocannabinoids and Endovanilloids: A Possible Balance in the Regulation of the Testicular GnRH Signalling

“…As indicated above, endocannabinoid activity requires multiple receptors, and this issue is stressed by the discovery of duplicated genes in fish [30, 31], by the detection of several cannabinoid receptor splicing forms [32–34] as well as by the discussed existence of receptors other than CB1/CB2 [5]. In frog, the characterization of cb1 did not revealed any splicing form but nucleotide differences among brain/testis cDNA and genomic sequences together with the corresponding amino acidic variations [18, 19, 29] as a consequence of a possible editing process.…”