Cannabinoid receptors are absent in insects

Area of Science:

• Neurobiology
• Comparative Physiology
• Evolutionary Biology

Background:

• The endocannabinoid system plays a vital neuromodulatory role in mammals and is phylogenetically ancient, present in diverse animal groups.
• Cannabinoid (CB) receptors have been identified across various vertebrate and invertebrate species, highlighting their evolutionary significance.

Purpose of the Study:

• To investigate the presence and function of cannabinoid receptors in terrestrial invertebrates, specifically insects.
• To determine if insects possess functional CB receptors or orthologs of known endocannabinoid system components.

Main Methods:

• Utilized radioligand binding assays with synthetic CB ligands [(3)H]CP55,940 and [(3)H]SR141716A on insect tissues.
• Performed G-protein activation assays using tetrahydrocannabinol (THC) and HU210 in insect tissues.
• Conducted genomic analysis of Drosophila melanogaster to identify orthologs of CB receptors and fatty acid amide hydrolase.

Main Results:

• No specific binding of synthetic CB ligands was observed in a panel of insects, including Apis mellifera and Drosophila melanogaster.
• Tetrahydrocannabinol (THC) and HU210 failed to activate G-proteins in insect tissues, indicating a lack of functional CB receptors.
• No orthologs of human CB receptors or fatty acid amide hydrolase were found in the Drosophila genome.

Conclusions:

• Terrestrial invertebrates, specifically insects, appear to lack functional cannabinoid receptors.
• The absence of CB receptors in insects may be attributed to a lack of endogenous ligands, such as arachidonic acid metabolites.
• This represents a unique loss of a known mammalian neuroreceptor in insects within comparative neurobiology.