Vasotocin is an

oligopeptide An oligopeptide, often just called peptide ('' oligo-'', "a few"), consists of two to twenty amino acids and can include dipeptides, tripeptides, tetrapeptides, and pentapeptides. Some of the major classes of naturally occurring oligopeptides incl ...

homologous to

oxytocin Oxytocin (Oxt or OT) is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytocin ...

and

vasopressin Human 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 then travel ...

found in all non-mammalian vertebrates (including

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

es, and

amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...

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. The posterior pituitary is not glandular as is the anterior pituitary. Instead, it is largely a collection of axonal ...

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 and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream viv ...

. 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 an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...

, 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 o ...

(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 formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

(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 (carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinogeni ...

(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 Human 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 then trave ...

(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 deprot ...

-3 of AVT changed to

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

) 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 guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the am ...

-8 changed to

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −C ...

). 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- ca ...

), 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 − form un ...

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 Neurophysins are carrier proteins which transport the hormones oxytocin and vasopressin to the posterior pituitary from the paraventricular and supraoptic nucleus of the hypothalamus, respectively. Inside the neurosecretory granules, the analogous ...

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 A ...

, 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 Pair or PAIR or Pairing may refer to: Government and politics * Pair (parliamentary convention), matching of members unable to attend, so as not to change the voting margin * ''Pair'', a member of the Prussian House of Lords * ''Pair'', the Frenc ...

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). As su ...

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. The species are: Previously, both species were classified as a single species ...

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 have stout conical bills adapted for eating seeds and nuts and often have colourful plumage. They occupy a great range of habitats where they are usua ...

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 () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...

and

Paraventricular Nucleus The paraventricular nucleus (PVN, PVA, or PVH) is a nucleus in the hypothalamus. Anatomically, it is adjacent to the third ventricle and many of its neurons project to the posterior pituitary. These projecting neurons secrete oxytocin and a smaller ...

. In a study conducted with male

Japanese quail The Japanese quail (''Coturnix japonica''), also known as the coturnix quail, is a species of Old World quail found in East Asia. First considered a subspecies of the common quail, it is now considered as a separate species. The 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 Wor ...

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 groups. Co ...

. 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 overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual; although it can be channeled into creative and practical outlets for some. It may occur either reacti ...

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 tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...

,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