Vasotocin is an

oligopeptide An oligopeptide ('' oligo-'', "a few"), is a peptide consisting of two to twenty amino acids, including dipeptides, tripeptides, tetrapeptides, and other polypeptides. Some of the major classes of naturally occurring oligopeptides include aerugi ...

homologous to

oxytocin Oxytocin is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. Present in animals since early stages of evolution, in humans it plays roles in behavior that include Human bonding, ...

and

vasopressin Mammalian vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the ''AVP'' gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It ...

found in all non-mammalian vertebrates (including

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

es, and

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

s) and possibly in mammals during the fetal stage of development. Arginine vasotocin (AVT), a hormone produced by neurosecretory cells within the

posterior pituitary The posterior pituitary (or neurohypophysis) is the posterior lobe of the pituitary gland which is part of the endocrine system. Unlike the anterior pituitary, the posterior pituitary is not glandular, but largely a collection of axonal projec ...

gland (neurohypophysis) of the brain, is a major endocrine regulator of water balance and osmotic homoeostasis and is involved in social and sexual behavior in non-mammalian vertebrates. In mammals, it appears to have biological properties similar to those of oxytocin (stimulating reproductive tract contraction as in egg laying or birth) and vasopressin (diuretic and antidiuretic effects). It has been found to have effects on the regulation of

REM sleep Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the s ...

. Evidence for the existence of endogenous vasotocin in mammals is limited and no mammalian gene encoding vasotocin has been confirmed. AVT (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Arg-Gly-NH2), which occurs in the

lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

, represents the ancestral form in the phylogeny of the vertebrate neurohypophysial hormones. Gene duplication and point mutation have produced two distinct lineages, one involved in reproduction (oxytocin-like peptides) and the other in

osmoregulation Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration ...

(vasopressin-like peptides). These hormones have remained highly conserved throughout evolution. Each is a peptide of nine amino acids derived from a preprohormone precursor by proteolytic cleavage, with an intramolecular disulfide bridge between the

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

(Cys) residues; the C-terminal

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

(Gly) residue is amidated. Six of the residues have been found to be invariant in homologous peptides from numerous species of vertebrates. The vasopressin-like peptides, which differ in positions 3 and/or 8, include AVT and the mammalian hormones

arginine vasopressin Mammalian vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the ''AVP'' gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It ...

(Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2, with

isoleucine Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the depro ...

-3 of AVT changed to

phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the chemical formula, formula . It can be viewed as a benzyl group substituent, substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of ...

) and lysine vasopressin (isoleucine-3 changed to phenylalanine and

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

-8 changed to

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group ( ...

). The oxytocin-like peptides, which differ in positions 4 and/or 8, include

(Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, with arginine-8 of AVT changed to

leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-Car ...

), mesotocin (arginine-8 changed to isoleucine), and isotocin (

glutamine Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...

-4 changed to

serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − ...

and arginine-8 changed to isoleucine); they differ from the vasopressin-like peptides in having a neutral amino acid in place of a basic amino acid at position 8. Oxytocin occurs in placental mammals; mesotocin occurs in amphibians, reptiles, and birds, and isotocin occurs in fishes.

Biosynthesis

AVT is synthesized as a preprohormone that includes a second peptide, neurophysin VT ( neurophysins are carrier proteins that are secreted along with their passenger hormones); intracellular proteolytic processing generates the mature peptides. In the chicken (Gallus gallus), the 161-amino acid vasotocin-neurophysin VT preprohormone is encoded by the gene AVP, which is considered homologous to the mammalian genes encoding arginine vasopressin.Gallus gallus (chicken) > Removal of the 19-amino acid N-terminal signal peptide generates the prohormone, which is hydrolysed to AVT (derived from amino acids 20-28) and neurophysin VT (derived from amino acids 32-161). The existence of two AVT preprohormones with different sequences in fishes (such as

chum salmon The chum salmon (''Oncorhynchus keta''), also known as dog salmon or keta salmon, is a species of anadromous salmonid fish from the genus ''Oncorhynchus'' (Pacific salmon) native to the coastal rivers of the North Pacific and the Beringian Arctic ...

, Oncorhynchus keta) is evidence for gene duplication.

Physiological effects

AVT combines both antidiuretic and reproductive activities similar to those of oxytocin and vasopressin. The physiological actions of AVT in birds are mediated through diverse receptor subtypes VT1, VT2, VT3 and VT4.Jurkevich A, Grossmann R (2003). Vasotocin and reproductive functions of the domestic chicken. Domest Anim Endocrinol. 25(1):93-9. AVT and synthetic analogs injected into monkeys cause reabsorption of osmotically free water and changes in excretion of sodium and potassium ions in the kidneys.Buravkova LB, Larina IM, Korolkov VI, Dobrokhotov IV, Grigorev AI (2003). Bull Exp Biol Med. 142(6):714-6. AVT produces distinct effects on the reproductive functions of male and female domestic chickens. In laying hens, AVT synthesised in magnocellular diencephalic neurons is released into circulation in a highly coordinated manner, contributing to the peripheral control of oviposition. In males, parvocellular AVT cells located in the limbic system (bed nucleus of stria terminalis) express AVT. This expression is sensitive to gonadal steroids and is correlated with sexual differentiation of masculine behavior such as courtship vocalization and copulation.

Behavioral effects

Several animal studies have been conducted that explore the behavioral effects of AVT. The main findings of these studies have revealed that AVT plays an integral role in the

pair bonding In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of young and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is frequently ...

behavior and

social hierarchy Social stratification refers to a society's categorization of its people into groups based on socioeconomic factors like wealth, income, race, education, ethnicity, gender, occupation, social status, or derived power (social and political). ...

in non-mammalian vertebrates. In a study conducted with

zebra finch The zebra finches are two species of estrildid finch in the genus ''Taeniopygia'' found in Australia and Indonesia. They are seed-eaters that travel in large flocks. Species The species are: Previously, both species were classified as ...

es, increased levels of AVT were linked to an increase in aggressive, competitive behavior in non-paired male finches, but were subsequently related to an increase in defensive behavior after the

finch The true finches are small to medium-sized passerine birds in the family Fringillidae. Finches generally have stout conical bills adapted for eating seeds and nuts and often have colourful plumage. They occupy a great range of habitats where the ...

es had been paired. However, this study also found that blocking AVT receptors did not directly affect pair bonding ability. The shift in behaviors were explained by the location of the release of AVT in the brain. Competitive aggressive behavior was found to be linked with AVT release in the BSTm, whereas defensive, nest-protecting behavior was linked with AVT release in the neurons of the

Hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

and

Paraventricular Nucleus The paraventricular nucleus (PVN) is a nucleus in the hypothalamus, located next to the third ventricle. Many of its neurons project to the posterior pituitary where they secrete oxytocin, and a smaller amount of vasopressin. Other secretions ...

. In a study conducted with male Japanese quail, AVT was found to have an effect on later social interactions amongst the species. Immediately after injection with AVT, the

quail Quail is a collective name for several genera of mid-sized birds generally placed in the order Galliformes. The collective noun for a group of quail is a flock, covey, or bevy. Old World quail are placed in the family Phasianidae, and New ...

s displayed less aggressive behavior (pecking). However, the next day, the

that were injected with AVT displayed more dominant behavior towards familiar birds, but not unfamiliar birds. This study shows that AVT may play a role in establishing social hierarchy. A study that investigated the role of social construction and AVT compared territorial and non-territorial species of tropical

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in group ...

. Experimenters administered Manning compound, an AVT agonist to the fish and found that, after treatment, non-territorial species displayed more territorial behavior whereas territorial species displayed less territorial behavior. Research suggests that the effects of AVT on

aggression Aggression is behavior aimed at opposing or attacking something or someone. Though often done with the intent to cause harm, some might channel it into creative and practical outlets. It may occur either reactively or without provocation. In h ...

may be influenced by the social construction of the species. For example, in a study done with

Rainbow Trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributary, tributaries of the Pacific Ocean in North America and Asia. The steelhead (sometimes called steelhead trout) is an Fish migration#Classification, ...

,Backström T, and Winberg S. Arginine vasotocin influence on aggressive behavior and dominance in rainbow trout. Physiology and Behavior. 2009; 96(3): 470-475. increased levels of AVT were associated with more subordinate behavior. It is currently hypothesized that the contrasting effects of AVT are related to the distinction between territorial versus colonial social systems. In a territorial species, such as

, AVT is linked to less dominant behavior. This may be due to the differences in the distribution of AVT receptors in territorial and colonial species.

Sources

External links

* {{Oxytocin and vasopressin receptor modulators Neuropeptides Oxytocin receptor agonists Vasopressin receptor agonists Nonapeptides