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ADH; Antidiuretic hormone; AVP; Vasopressin Definition

Arginine-vasopressin (AVP) is a nine-amino acid peptide, which is synthesized and released from nerve terminals in the central nervous system (CNS) (Fig. 1). In the brain, AVP acts as a modulator of neuronal function and is involved in the control of stress, anxiety, cognitive behaviors, ► circadian rhythms, and autonomic function. AVP is also released from nerve terminals into the blood stream where it regulates water absorption and urine production

Arginine-Vasopressin. Fig. 1. Arginine-vasopressin (AVP).

in the kidney, and glucose and fatty acid metabolism in the liver, and it increases arterial blood pressure and heart rate.

Pharmacological Properties

The Neuroanatomy of the Central AVP System

AVP is synthesized in neurons of the hypothalamus (Ring 2005). AVP-containing neurons are located in three hypothalamic structures: the supraoptic nucleus (SON), the paraventricular nucleus (PVN), and the suprachiasmatic nucleus (SCN). AVP produced in the SON is transported to nerve terminals of the posterior pituitary and is released in response to changes in plasma osmolality and decreased blood pressure. AVP from the PVN is released into the hypothalamic-hypophyseal portal blood, which supplies the anterior pituitary. The AVP-containing neurons of the PVN also project to the regions of the hindbrain and spinal cord, which are involved in control of the autonomic function. The AVP neurons of the SCN are involved in the control of circadian rhythms. AVP synthesis occurs also in the bed nucleus of the stria terminalis (BST) and the medial amygdaloid nucleus (MeA). The vasopressin neurons in the BST project to the lateral septum, amygdaloid areas, the locus coeruleus, and the dorsal raphe, while MeA neurons project to the ► hippocampus and lateral septum. These neuronal pathways are likely to underlie the effects of AVP on stress, anxiety, fear, and social cognitive behavior (► Social Recognition and Social Learning). The degree of AVP expression in the brain is gender specific, with males having denser AVP levels than females (Frank and Landgraff 2008) due to an effect of ► sex hormones on AVP expression. Sex hormones may exert some of their effects on social cognitive behaviors, such as pair-bonding and parent-offspring relationships, through influencing AVP expression in the CNS.

Arginine-Vasopressin Receptors in the CNS

The biological effects of AVP are mediated via interaction with a family of ► G-protein-coupled receptors (► GPCRs) (Ring 2005). There are four known vasopressin receptor subtypes (V1a, V1b (V3), V2, and oxytocin (OT)) defined on the basis of differences in pharmacology and tissue distribution. Activation of the V1a, V1b, and OT receptors stimulates a number of signal transduction pathways via Gq G-protein coupling to phospholipase C, while activation of the V2 receptor by AVP stimulates adenylyl cyclase via Gs coupling (► Receptors; Functional Assays).

The V1a receptor is the predominant AVP receptor found in the brain, localized in the cortex, hippocampus,

► amygdala, septum, ► hypothalamus, and thalamus. The V1a receptor plays a dominant role in the behavioral effects of AVP. In the periphery, V1a receptors are expressed in vascular smooth muscle cells, hepatocytes,

► platelets, adrenal cortex, uterus cells, kidney, spleen, and testis. The V1b receptor is expressed in corticotrophs of the anterior pituitary and throughout the brain, especially in the pyramidal neurons of the hippocampal CA2 field, although at lower levels than the V1a receptor. In the anterior pituitary, the V1b receptor modulates adrenocor-ticotrophin (ACTH) secretion. The V1b receptor is also expressed in kidney, pancreas, and adrenal medulla, although the functional significance of expression in these tissues is unclear. Vasopressin V2 receptors are primarily expressed in the kidney, where their primary function is to respond to AVP by stimulating mechanisms that concentrate the urine and maintain water homeostasis. The V2 receptor is understood to have a limited expression in the CNS. The OT receptor is expressed in the CNS in the amygdala and hippocampus and brain regions involved in the regulation of stress (► Social Stress) responses and social behavior (► Social Recognition and Social Learning). The OT receptor is also expressed in uterus and mammary gland, where its primary function is to induce uterine contractions and milk ejection.

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Anxiety and Panic Attacks

Anxiety and Panic Attacks

Suffering from Anxiety or Panic Attacks? Discover The Secrets to Stop Attacks in Their Tracks! Your heart is racing so fast and you don’t know why, at least not at first. Then your chest tightens and you feel like you are having a heart attack. All of a sudden, you start sweating and getting jittery.

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