Cannabinoid receptors in invertebrates

Area of Science:

• Evolutionary Biology
• Neuroscience
• Zoology

Background:

• Cannabinoid receptors (CB1 and CB2) are well-characterized in vertebrates.
• The presence and distribution of cannabinoid receptors in invertebrates remain controversial due to conflicting evidence.
• Previous research suggested CB1 receptor loss as a shared trait in Ecdysozoa.

Purpose of the Study:

• To systematically review existing literature on invertebrate cannabinoid receptors.
• To experimentally investigate the presence of cannabinoid receptors in understudied invertebrate clades.
• To clarify the evolutionary history and phylogenetic distribution of cannabinoid receptors.

Main Methods:

• Conducted a systematic literature review with expanded search parameters.
• Performed [3H]CP55,940 ligand binding assays on neural membranes from seven representative invertebrate species.
• Utilized CB1-selective antagonist SR141716A to confirm specific binding.

Main Results:

• Specific binding of [3H]CP55,940 was detected in neural membranes of Ciona intestinalis, Lumbricusterrestris, Peripatoides novae-zealandiae, Jasus edwardi, and Panagrellus redivivus.
• No specific binding was observed in Actinothoe albocincta (Cnidaria) or Tethya aurantium (Porifera).
• The presence of CB1 receptors in nematodes, onychophorans, and crustaceans does not support, but also does not contradict, the Ecdysozoa hypothesis.

Conclusions:

• Cannabinoid receptors likely evolved in the last common ancestor of bilaterians.
• Secondary loss of cannabinoid receptors may have occurred in insects and other clades.
• The evolutionary history of cannabinoid receptors in basal metazoans remains unclear due to conflicting data in Cnidarians and absence in sponges.