Octopamine

Functions

Cellular effects

Octopamine exerts its effects by binding to and activating receptors located on the surface of cells. These receptors have mainly been studied in insects, where they can be divided into distinct types:

1. OctαR (alpha-adrenergic-like), are structurally and functionally similar to noradrenergic alpha-1 receptors in mammals. There are multiple subtypes of the OctαR receptor. For example, the kissing bug (Rhodnius prolixus) has Octα1-R, Octα2R.
2. OctβR (beta-adrenergic-like), are structurally and functionally similar to noradrenergic beta receptors in mammals. There are multiple subtypes of the OctβR receptor. For example, the fruit fly (Drosophila melanogaster) has DmOctβ1R, DmOctβ2R, and DmOctβ3R.
3. OAMB. The diversity of this receptor is relatively unknown. The fruit fly (Drosophila melanogaster) has two distinct isoforms which are functionally distinct: OambK3 and OambAS.
4. TyrR (mixed octopamine/tyramine receptors), which are structurally and functionally similar to noradrenergic alpha-2 receptors in mammals. Receptors in the TyrR class, however, are generally more strongly activated by tyramine than by octopamine.

Phylogenetic studies claim that in ancient bilaterians such as Platynereis dumerilii there is a co-existence of norepinephrine, tyramine and octopamine receptor signaling. However, due to partial overlapping in their signalling functionality tyramine and octopamine receptors have been lost in vertebrates.

In vertebrates no octopamine-specific receptors have been identified. Octopamine binds weakly to receptors for norepinephrine and epinephrine, but it is not clear whether this has any functional significance. It binds more strongly to trace amine-associated receptors (TAARs), especially TAAR1.

Invertebrates

Octopamine was first discovered by Italian scientist Vittorio Erspamer in 1948 in the salivary glands of the octopus and has since been found to act as a neurotransmitter, neurohormone and neuromodulator in invertebrates. Although Erspamer discovered its natural occurrence and named it, octopamine had actually existed for many years as a pharmaceutical product. It is widely used in energy-demanding behaviors by all insects, crustaceans (crabs, lobsters, crayfish), and spiders. Such behaviors include modulating muscle tension, flying, ovulation and egg-laying, and jumping.

In non-insect invertebrates

In lobsters, octopamine seems to direct and coordinate neurohormones to some extent in the central nervous system, and it was observed that injecting octopamine into a lobster and crayfish resulted in limb and abdomen extension.

In the nematode, octopamine is found in high concentrations in adults, decreasing egg-laying and pharyngeal pumping behaviors with an antagonistic effect to serotonin.

Octopaminergic nerves in the mollusc may be present in the heart, with high concentrations in the nervous system.

In non-''Drosophila'' insects

In insects, octopamine is released by a select number of neurons, but acts broadly throughout the central brain, on all sense organs, and on several non-neuronal tissues. In the thoracic ganglia, octopamine is primarily released by DUM (dorsal unpaired median) and VUM (ventral unpaired median) neurons, which release octopamine onto neural, muscular, and peripheral targets. These neurons are important for mediating energy-demanding motor behaviors, such as escape-induced jumping and flight. For example, the locust DUMeti neuron releases octopamine onto the extensor tibia muscle to increase muscle tension and increase relaxation rate. These actions promote efficient leg muscle contraction for jumping. During flight, DUM neurons are also active and release octopamine throughout the body to synchronize energy metabolism, respiration, muscle activity and flight interneuron activity. Octopamine in locusts is four times more concentrated in the axon than in the soma, and decreases the locust's myogenic rhythm.

In the honey bee, octopamine has a major role in learning and memory. In the firefly, octopamine release leads to light production in the lantern.

In larvae of the oriental armyworm, octopamine is immunologically beneficial, increasing survival rates in high-density populations.

The emerald cockroach wasp stings the host for its larvae (a cockroach) in the head ganglion (brain). The venom blocks octopamine receptors and the cockroach fails to show normal escape responses, grooming itself excessively. It becomes docile and the wasp leads it to the wasp's den by pulling its antenna like a leash.

In ''Drosophila''

Octopamine affects almost every process of the fruit fly and is widely present in both the adult and larval fly. A non-exhaustive list of some of the areas in which Octopamine modulates:

• Learning and memory
• Ovulation and Egg-Laying
• Locomotion
• Muscle Physiology
• Aggression
• Alcohol and drug tolerance
• Feeding
• Microbiome and gut physiology
• Sleep
• Modulating effects of exercise
• Metabolism

Vertebrates

In vertebrates, octopamine replaces norepinephrine in sympathetic neurons with chronic use of monoamine oxidase inhibitors. It may be responsible for the common side effect of orthostatic hypotension with these agents, though there is also evidence that it is actually mediated by increased levels of N-acetylserotonin.

One study noted that octopamine might be an important amine that influences the therapeutic effects of inhibitors such as monoamine oxidase inhibitors, especially because a large increase in octopamine levels was observed when animals were treated with this inhibitor. Octopamine was positively identified in the urine samples of mammals such as humans, rats, and rabbits treated with monoamine oxidase inhibitors. Very small amounts of octopamine were also found in certain animal tissues. It was observed that within a rabbit's body, the heart and kidney held the highest concentrations of octopamine. Octopamine was found to be 93% eluted by urine within 24 hours of being produced in the body as a byproduct of Iproniazid in rabbits.

Pharmacology

Octopamine has been sold under trade names such as Epirenor, Norden, and Norfen for use in medicine as a sympathomimetic drug, available by prescription. However, very little information exists concerning its clinical usefulness or safety. It has been studied as an antihypotensive agent and has been shown to increase blood pressure when administered intravenously, intramuscularly, and buccally at sufficiently high doses, whereas oral administration was ineffective.

Octopamine is an analogue of sympathomimetic catecholamines like norepinephrine and phenethylamines like tyramine. However, octopamine has 400- to 2,000-fold lower affinity for the mammalian α- and β-adrenergic receptors than norepinephrine. In any case, it can produce significant sympathomimetic effects, like pressor responses, at sufficiently high doses.

In mammals, octopamine may mobilize the release of fat from adipocytes (fat cells), which has led to its promotion on the internet as a slimming aid. However, the released fat is likely to be promptly taken up into other cells, and there is no evidence that octopamine facilitates weight loss. Octopamine may also increase blood pressure significantly when combined with other stimulants, as in some weight loss supplements.

The World Anti-Doping Agency lists octopamine as a banned substance for in competition use, as a "specified stimulant" on the 2019 Prohibited List.

In contrast to various other phenethylamines, octopamine is a poor or negligible substrate of the dopamine transporter (DAT).

Insecticides

The octopamine receptor is a target of insecticides, as its blockage leads to decreased cyclic adenosine monophosphate (cAMP) levels. Essential oils can have such a neuro-insecticidal effect, and this octopamine-receptor mechanism is naturally utilized by plants with active insecticidal phytochemicals.

Biochemical mechanisms

Mammals

Octopamine is one of four primary endogenous agonists of human trace amine-associated receptor 1 (TAAR1) together with 3-iodothyronamine, dopamine and tyramine.

Invertebrates

Octopamine binds to its respective G-protein coupled receptors (GPCRs) to initiate a cell signal transduction pathway. At least three groups of octopamine GPCR have been defined. OctαR (OCTOPAMINE1 receptors) are more closely related to α-adrenergic receptors, while OctβR (OCTOPAMINE2 receptors) are more closely related to β-adrenergic receptors. The Octopamine/Tyramine receptors (including Oct-TyrR) can bind both ligands, and display agonist-specific coupling. Oct-TyrR is listed in both OCTOPAMINE and TYRAMINE RECEPTORS gene groups.

Biosynthesis

In insects

Octopamine acts as the insect equivalent of norepinephrine and has been implicated in regulating aggression in invertebrates, with different effects on different species. Studies have shown that reducing the neurotransmitter octopamine and preventing coding of tyramine β-hydroxylase (an enzyme that converts tyramine to octopamine) decreases aggression in Drosophila without influencing other behaviors.

Chemistry

Octopamine, or para-octopamine, also known as 4,β-dihydroxyphenethylamine, is a substituted phenethylamine derivative. It is related to analogues including phenylethanolamine (β-hydroxyphenethylamine), tyramine (para-tyramine; 4-hydroxyphenethylamine), and norfenefrine (meta-octopamine; 3,β-dihydroxyphenethylamine), among others.

References

References

1. (5 June 2023). "FDA's New Dietary Supplement Ingredient Directory {{!}} Foley & Lardner LLP".
2. (1974). "The physiological disposition of p-octopamine in man". Naunyn-Schmiedeberg's Archives of Pharmacology.
3. (January 2010). "Trace amine metabolism in Parkinson's disease: low circulating levels of octopamine in early disease stages". Neuroscience Letters.
4. (September 2006). "Determination of octopamine, synephrine and tyramine in Citrus herbs by ionic liquid improved 'green' chromatography". Journal of Chromatography A.
5. (1979). "Mechanism of central action of octopamine". Polish Journal of Pharmacology and Pharmacy.
6. (2017-09-26). "Cloning and Functional Characterization of Octβ2-Receptor and Tyr1-Receptor in the Chagas Disease Vector, ''Rhodnius prolixus''". Frontiers in Physiology.
7. (July 2005). "Identification and characterization of a novel family of Drosophila beta-adrenergic-like octopamine G-protein coupled receptors". Journal of Neurochemistry.
8. (2009-03-05). "The octopamine receptor OAMB mediates ovulation via Ca2+/calmodulin-dependent protein kinase II in the Drosophila oviduct epithelium". PLOS ONE.
9. (2005). "Evolutionary aspects of octopaminergic systems with emphasis on arthropods". Arthropod Structure & Development.
10. (January 2017). "Ancient coexistence of norepinephrine, tyramine, and octopamine signaling in bilaterians". BMC Biology.
11. (2009). "Active Substances in the Posterior Salivary Glands of Octopoda. II. Tyramine and Octopamine (Oxyoctopamine)". Acta Pharmacologica et Toxicologica.
12. (February 1962). "On the identification of octopamine in mammals". The Journal of Biological Chemistry.
13. (October 2013). "Action of octopamine and tyramine on muscles of Drosophila melanogaster larvae". Journal of Neurophysiology.
14. (January 1993). "A Multifunctional Role for Octopamine in Locust Flight". Annual Review of Entomology.
15. (December 2003). "Octopamine receptor OAMB is required for ovulation in Drosophila melanogaster". Developmental Biology.
16. (March 2015). "The octopamine receptor octß2R is essential for ovulation and fertilization in the fruit fly Drosophila melanogaster". Archives of Insect Biochemistry and Physiology.
17. (2014-08-06). "The octopamine receptor Octβ2R regulates ovulation in Drosophila melanogaster". PLOS ONE.
18. (2009-03-05). "The octopamine receptor OAMB mediates ovulation via Ca2+/calmodulin-dependent protein kinase II in the Drosophila oviduct epithelium". PLOS ONE.
19. (December 2003). "Distinct octopamine cell population residing in the CNS abdominal ganglion controls ovulation in Drosophila melanogaster". Developmental Biology.
20. (October 2015). "A Follicle Rupture Assay Reveals an Essential Role for Follicular Adrenergic Signaling in Drosophila Ovulation". PLOS Genetics.
21. (September 1988). "Activation of DUM cell interneurons by ventral giant interneurons in the cockroach, Periplaneta americana". Journal of Neurobiology.
22. (1982-04-01). "Octopamine in insects: neurotransmitter, neurohormone, and neuromodulator". Canadian Journal of Zoology.
23. (April 1980). "Serotonin and octopamine produce opposite postures in lobsters". Science.
24. (May 1982). "Serotonin and octopamine in the nematode Caenorhabditis elegans". Science.
25. (January 1981). "Occurrence and synthesis of octopamine in the heart and ganglia of the mollusc Tapes watlingi". Comparative Biochemistry and Physiology Part C: Comparative Pharmacology.
26. (2009-01-01). "Neuromuscular Transmission Modulation at Invertebrate Neuromuscular Junctions". Academic Press.
27. (December 1999). "Octopamine in invertebrates". Progress in Neurobiology.
28. (August 1992). "A new specific antibody reveals octopamine-like immunoreactivity in cockroach ventral nerve cord". The Journal of Comparative Neurology.
29. (April 1994). "Octopamine-like immunoreactivity in the dorsal unpaired median (DUM) neurons innervating the accessory gland of the male cockroach Periplaneta americana". Cell and Tissue Research.
30. (April 1978). "The identification of an octopaminergic neurone and the modulation of a myogenic rhythm in the locust". The Journal of Experimental Biology.
31. (November 2001). "Missing link in firefly bioluminescence revealed: NO regulation of photocyte respiration". BioEssays.
32. (June 2001). "Nitric oxide and the control of firefly flashing". Science.
33. (December 2020). "Immunological regulation by a β-adrenergic-like octopamine receptor gene in crowded larvae of the oriental Armyworm, Mythmina separata". Developmental and Comparative Immunology.
34. (2007). "How to make a zombie cockroach". Nature.
35. (December 2005). "Parasitoid wasp uses a venom cocktail injected into the brain to manipulate the behavior and metabolism of its cockroach prey". Archives of Insect Biochemistry and Physiology.
36. (May 2020). "Concerted Actions of Octopamine and Dopamine Receptors Drive Olfactory Learning". The Journal of Neuroscience.
37. (December 2012). "Layered reward signalling through octopamine and dopamine in Drosophila". Nature.
38. (November 2003). "Dopamine and octopamine differentiate between aversive and appetitive olfactory memories in Drosophila". The Journal of Neuroscience.
39. (February 2019). "Tyramine action on motoneuron excitability and adaptable tyramine/octopamine ratios adjust ''Drosophila'' locomotion to nutritional state". Proceedings of the National Academy of Sciences of the United States of America.
40. (November 2012). "The role of octopamine and tyramine in Drosophila larval locomotion". The Journal of Comparative Neurology.
41. (March 2004). "Tyramine and octopamine have opposite effects on the locomotion of Drosophila larvae". Journal of Neurobiology.
42. (September 2018). "Modulation of neuromuscular synapses and contraction in Drosophila 3rd instar larvae". Journal of Neurogenetics.
43. (May 2014). "Octopamine neuromodulation regulates Gr32a-linked aggression and courtship pathways in Drosophila males". PLOS Genetics.
44. (2014-06-12). "Drosophila insulin-producing cells are differentially modulated by serotonin and octopamine receptors and affect social behavior". PLOS ONE.
45. (January 2014). "Regulation of aggression by obesity-linked genes TfAP-2 and Twz through octopamine signaling in Drosophila". Genetics.
46. (August 2004). "Molecular Genetic Analysis of Ethanol Intoxication in Drosophila melanogaster". Integrative and Comparative Biology.
47. (December 1998). "Y do we drink?". Cell.
48. (June 22, 2005). "Bar Flies: What our insect relatives can teach us about alcohol tolerance". Naked Scientist.
49. (22 August 2005). "'Hangover gene' is key to alcohol tolerance". New Scientist.
50. (December 2019). "Linking physiological processes and feeding behaviors by octopamine". Current Opinion in Insect Science.
51. (November 2019). "A Neural Circuit Arbitrates between Persistence and Withdrawal in Hungry Drosophila". Neuron.
52. (May 2021). "Gut microbiome modulates Drosophila aggression through octopamine signaling". Nature Communications.
53. (November 2018). "A gut microbial factor modulates locomotor behaviour in Drosophila". Nature.
54. (June 2014). "Monoamines and sleep in Drosophila". Behavioral Neuroscience.
55. (September 2012). "Interaction between sleep and metabolism in Drosophila with altered octopamine signaling". The Journal of Biological Chemistry.
56. (June 2020). "Alpha- and beta-adrenergic octopamine receptors in muscle and heart are required for Drosophila exercise adaptations". PLOS Genetics.
57. (July 2020). "Variation in mobility and exercise adaptations between Drosophila species". Journal of Comparative Physiology A.
58. (August 2020). "Hazardous effects of octopamine receptor agonists on altering metabolism-related genes and behavior of Drosophila melanogaster". Chemosphere.
59. (October 2016). "Octopamine controls starvation resistance, life span and metabolic traits in Drosophila". Scientific Reports.
60. (January 2015). "Physiological functions and pharmacological and toxicological effects of p-octopamine". Drug and Chemical Toxicology.
61. (September 2005). "Hemodynamic effects of ephedra-free weight-loss supplements in humans". The American Journal of Medicine.
62. "Prohibited In Competition – Stimulants". WADA.
63. (March 2020). "TAAR1 and Psychostimulant Addiction". Cell Mol Neurobiol.
64. (April 2021). "Amphetamines signal through intracellular TAAR1 receptors coupled to Gα13 and GαS in discrete subcellular domains". Mol Psychiatry.
65. (January 2001). "The antidepressant-sensitive dopamine transporter in Drosophila melanogaster: a primordial carrier for catecholamines". Mol Pharmacol.
66. (November 2001). "Insecticidal activity of essential oils: octopaminergic sites of action". Comparative Biochemistry and Physiology. Toxicology & Pharmacology.
67. (2010-09-01). "Mechanism of action of insecticidal secondary metabolites of plant origin". Crop Protection.
68. (20 February 2018). "Trace amine receptor: TA₁ receptor". International Union of Basic and Clinical Pharmacology.
69. (January 2022). "Ulotaront: A TAAR1 Agonist for the Treatment of Schizophrenia". ACS Medicinal Chemistry Letters.
70. (16 October 2018). "Gene Group: OCTOPAMINE RECEPTORS". FlyBase.
71. (September 2008). "A subset of octopaminergic neurons are important for Drosophila aggression". Nature Neuroscience.