**1. Introduction**

Arginine Vasopressin (AVP) and oxytocin (OXT) are peptide hormones found in most mammals that have vital physiological and behavioral actions. The major sites of AVP production are the paraventricular (PVN) and supraoptic (SON) nuclei in the hypothalamus, although AVP and its receptors are found in numerous brain nuclei and peripheral tissues. AVP's physiological roles, which are mediated through both peripheral and central mechanisms, include regulating fluid homeostasis and blood pressure. It is also an important component of the endocrine stress response through its actions in the posterior pituitary gland, where it is a secretagogue of ACTH, stimulating the release of corticosteroid stress hormones and catecholamines from the adrenal glands. The three receptor subtypes for AVP are V1a, V1b, and V2. V2 receptors mediate the fluid regulating actions of AVP in the periphery, where the behavioral and central endocrine functions of AVP are mediated by the V1a and V1b receptors in the brain. These receptors are also involved in the central control of cardiovascular activity.

Oxytocin's major physiological roles are to facilitate uterine contractions during birth through a positive feedback mechanism during the second and third stages of labor, and to mediate milk letdown. In lactating mammalian mothers, OXT initiates milk letdown in the mammary glands, and the release of OXT is stimulated by suckling. OXT has one known receptor which has several alleles. The focus of the present chapter will be on the social behavior functions of both AVP and OXT. While some of these actions are mediated the PVN and SON, several other behaviorally active brain regions will also be discussed.

The behavioral roles of oxytocin and vasopressin have been studied and characterized in several animal species over the past few decades, and these findings have recently stimulated related work in humans. While the specific direction of the effects often vary between species, the general behavioral functions of AVP and OXT, as well as several related ancestral peptides, are conserved across taxa. The study of the diversity of these systems in birds [1] and fish [2] has been particularly useful in identifying the mechanisms

© 2012 Nephew, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Nephew, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

of the effects of these peptides on behavior. Although the behavioral roles of OXT and AVP are good examples of effective translation from animal models to clinical study for some topics, such as autism, there is still a need for increased communication and collaboration on many relevant issues, especially gender differences and stress related mood disorders. Both animal and human studies on depression and anxiety indicate that these neuropeptides have gender specific roles, and administering treatments developed in male animals and humans to females may be ineffective or have adverse consequences. The objectives of this review chapter are to present an updated summary of the gender specific behavioral roles of OXT and AVP in both animals and humans and stimulate translationally relevant gender specific studies on these hormones. The need for more female specific studies in this area is great, and this need will be underscored throughout the chapter. Behavioral topics covered include affiliation, aggression, parental behavior, depression/anxiety, and memory. Clinical topics discussed include depression, anxiety, addiction, and autism. Due to the broad scope of these objectives, this review chapter will highlight selected research and review papers on each topic, but will not be comprehensive.

Behavioral Roles of Oxytocin and Vasopressin 51

knockout mice display elevated aggression which is postulated to be the result of decreased fearfulness [13]. One potential explanation for this inconsistency is indirect effects through AVP due to the neuroanatomical and biochemical similarities between the two neuropeptide systems. The increased aggression in OXT knockout mice may be mediated by

In polygamous male meadow voles (*Microtus pennsylvanicus*), paternal experience is associated with increases in OXT receptor binding in the accessory olfactory nucleus, bed nucleus of the stria terminalis, lateral septum, and lateral amygdala [14]. It was concluded that central OXT infusion increased the tolerance of the offspring by the father. Combined treatment with both an OXT antagonist and an AVP antagonist decrease male parental behavior in reproductively naïve male prairie voles, where treatments with only one antagonist did not affect the expression of alloparenting [15]. It appears that male prairie vole paternal behavior may rely on the neural effects of both peptides. Mandarin voles (*Lasiopodomys mandarinus)*, which are biparental and express parental behavior towards foster pups, increase central OXT expression following the development of male alloparental behavior. This increased expression may be mediated by elevated estrogen receptor alpha [16]. In support of this association between OXT and mammalian paternal expression, a recent primate study reported that icv OXT increased the transfer of food from fathers to their offspring [17]. Similar effects of OXT in male primates are supported by

Peripheral OXT has antidepressant effects in both young and old rats, and the effects in older rats are associated with enhanced memory [18, 19]. In the mouse tail suspension test, both systemic and central OXT decrease immobility time, which indicates that OXT decreased helplessness [20]. In contrast to these results, intracerebroventricular (icv) OXT did not affect behavior in the forced swim test of depressive like behavior in male rats selected for high or low anxiety, although it did have an anxiolytic effect [21]. Furthermore, isolated prairie vole males exhibit both anhedonia and increased plasma OXT following a resident intruder test of aggression [22]. As has been hypothesized for OXT elevation following maternal aggression, this increase could be due to the stress of the interaction, and may not be a causal factor for anhedonia. It is possible that anhedonia targeting tests of depressive behavior, such as saccharin preference or a naturally occurring reward mediated behavior (sexual behavior,

Most of the research on OXT and learning and memory has been limited to male models [23]. OXT mediates social recognition in several species [24], and male OXT knockout mice exhibit social amnesia [6], while other forms of memory are not affected. This effect on social

a compensatory increase in AVP in these males.

clinical data which will be discussed later in this review.

**2.4. OXT and male animal models of depression and anxiety** 

maternal behavior), would reveal consistent anti-depressive actions of OXT.

**2.5. OXT and male animal learning and memory** 

**2.3. OXT and animal paternal behavior** 
