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Neurohypophysis
Published in Paul V. Malven, Mammalian Neuroendocrinology, 2019
Arginine vasotocin constitutes a molecular compromise, being vasopressinlike at position #8 and oxytocin-like at position #3 (Table 3-1). This molecule is found in neurohypophysial tissue of most submammalian vertebrates, but it also occurs in the neurohypophysis of mammalian fetuses and perhaps in the pineal gland of some adult mammals. The functional role of arginine vasotocin in mammals is unclear, but in bioassays the molecule has both oxytocinergic and vasopressinergic activity.
Pineal Function
Published in Nate F. Cardarelli, The Thymus in Health and Senescence, 2019
Vasotocin is generally reported as arginine vasotocin (AVT). Pavel et al. examined AVT content in the pineal of fetal, neonatal, and adult rats, noting a decrease with age.262 AVT appears to mimic the effects of melatonin when injected into laboratory animals.263
Neurohypophyseal Hormones and Reproductive Hormone Secretion
Published in Craig A. Johnston, Charles D. Barnes, Brain-Gut Peptides and Reproductive Function, 2020
Whether AVP exerts a physiologically important role on the neuroendocrine regulation of gonadotropin secretion is quite controversial. In fact, most of the actions of AVP may be due to its structural similarity to vasotocin, a peptide synthesized in the pineal which has been hypothesized to represent a physiologically relevant antigonadotropic factor. Nonetheless, systemically administered AVP can inhibit the preovulatory surge of LH on proestrus (Cheesman et al., 1977), or the estrogen-induced LH surge in ovariectomized female rats (Salisbury et al., 1980). Two results bring into question the physiological significance of these data. First, AVP is much weaker in its ability to suppress the LH surge than vasotocin (Salisbury et al., 1980; Blask et al., 1978). Second, administration of a potent AVP antagonist throughout the afternoon of proestrus did not significantly affect the preovulatory LH surge observed in vehicle-treated controls (Johnston and Negro-Vilar, 1988). In contrast, a greater release of LH in response to LHRH injection has been reported in castrated male rats who were provided with a simultaneous injection of AVP or vasotocin than in rats treated with LHRH alone (Vaughan et al., 1979a). The intravenous injection of a high dose of AVP has been reported to increase basal presurge LH concentrations in ovariectomized female rats (Salisbury et al., 1980), whereas low doses do not affect basal LH levels in castrated or intact male rats (Vaughan et al., 1979b; Turkelson et al., 1981). A similar ability of AVP to elevate basal LH levels during the luteal phase in female baboons has been reported (Koyama and Hagino, 1983). Once again, because the doses of AVP needed to affect LH secretion are greater than those which would cause elevations in blood pressure, the specificity and physiological significance of the effect of AVP on LH secretion must be questioned. Physiological significance aside, the pharmacological ablity of AVP to alter gonadotropin release does not appear to be mediated directly at the level of the anterior pituitary. Neither basal nor LHRH-stimulated LH release from female rat pituitaries incubated in vitro is affected by AVP administration (Turkelson et al., 1981; Cheung, 1983; Vaughan et al., 1975). Whether AVP may interact as a neurotransmitter in a physiologically relevant manner to influence either static or dynamic LH secretion from the anterior pituitary is not known. However, at present, the importance of this possible influence, even if demonstrated, might be minimal.
The Volumetric Changes of the Pineal Gland with Age: An Atlas-based Structural Analysis
Published in Experimental Aging Research, 2022
Minoo Sisakhti, Lida Shafaghi, Seyed Amir Hossein Batouli
The pineal gland is an interhemispheric neuroendocrine organ that, as a small canonical gland of about 100 mm3, along with habenula nuclei is located medially in the epithalamus of the vertebrate brain, and is surrounded by the structures such as the posterior third ventricle, thalami, and the splenium of the corpus callosum. It contains varied categories of cells such as pinealocytes (80% of the gland), astrocytes, microglia, and more recently evidenced pineal neurons and peptidergic neuron-like cells. This circumventricular organ, as a whole apparatus, concludes mechanisms for synthesis and secretion (into the bloodstream and CSF) of the indoleamine melatonin (N-acetyl-methoxytryptamine)-as the most identified one-, as well as the serotonin, arginine, vasotocin, and some forms of the neurosteroids (Beker-Acay et al., 2016; Khavinson & Lin’kova, 2012; J. Park et al., 2018; Sigurdardottir et al., 2016).
Possible roles of brain derived neurotrophic factor and corticotropin releasing hormone neurons in the nucleus of hippocampal commissure functioning within the avian neuroendocrine regulation of stress
Published in Stress, 2021
Hakeem J. Kadhim, Seong W. Kang, Wayne J. Kuenzel
Activation of parvocellular neurons within the avian hypothalamic paraventricular nucleus (PVN) resulted in an increase of corticotropin releasing hormone (CRH) and arginine vasotocin (AVT) (Kuenzel & Jurkevich, 2010). When CRH and AVT reach the anterior pituitary (APit), CRH binds to two G-protein coupled receptors, CRHR1 and CRHR2; AVT or AVP binds to the V1aR and V1bR. They, in turn, stimulate proopiomelanocortin (POMC) synthesis that is further processed to adrenocorticotropic hormone (ACTH) (Bonfiglio et al., 2011). In adrenal glands, ACTH activates the avian interrenal tissue to produce the stress hormone, corticosterone (CORT) (Herman et al., 2016; Romero, 2004). Stress hormone binds to glucocorticoid receptors (GRs) located on different tissues to provide energy for immediate use (McEwen, 2007) as well as to induce a negative feedback that regulates hypothalamic-pituitary-adrenocortical (HPA) axis activity (Keller-Wood, 2015; Chrousos, 2009; Vandenborne et al., 2005). Additionally, CRH neurons were identified in the nucleus of the hippocampal commissure (NHpC), an extra-hypothalamic structure, suggesting that the NHpC may be involved in the regulation of the stress response (Nagarajan et al., 2017a, 2014; Xie et al., 2010).
24 hour patterning in gene expression of pineal neurosteroid biosynthesis in young chickens (Gallus gallus domesticus L.)
Published in Chronobiology International, 2021
Magdalena Chustecka, Natalia Blügental, Pawel Marek Majewski, Iwona Adamska
Although these biosynthetic pathways are well known, their regulation is not fully understood. The activity of enzymes catalyzing synthesis of neurosteroids can be modulated by various mediators. Neurotransmitters, e.g., dopamine (Baillien and Balthazart 1997), γ-aminobutyric acid (Do Rego et al. 2000), glutamate (Balthazart et al. 2006), as well as hormones, e.g., melatonin (Tsutsui et al. 2008), have been demonstrated to decrease enzyme activity, while endogenous benzodiazepines (Do Rego et al. 2007) or vasotocin/mesotocin (Do Rego et al. 2006) enhance it. Further, the functionally broadly ranging E4BP4 transcription factor, which is highly expressed in many tissues, has been detected in the pineal gland (Yin et al. 2017). In mammals and birds, its principal pineal functions are suppression and down-regulation of Period2 (Per2) mRNA, one of canonical clock genes (Doi et al. 2001; Ohno et al. 2007). E4BP4 also induces activation of cholesterol biosynthetic genes, targets for the sterol regulatory element-binding protein transcription factor (SREBP) (Hatori et al. 2011). Moreover, chicken StAR has the functional capacity for clock-driven expression in preovulatory ovarian follicles (Nakao et al. 2007).