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: • 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. • 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. • 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. • 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. 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. 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. 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 • 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==