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Vasotocin and reproductive functions of the domestic chicken
Domestic Animal Endocrinology 25 (2003) 93–99
Vasotocin and reproductive functions of the domestic chicken A. Jurkevich a , R. Grossmann b,∗ a
b
Institute of Ecology, Vilnius University, Akademijos 2, Vilnius LT-2600, Lithuania Institute for Animal Science, Mariensee, Federal Agricultural Research Centre (FAL), Höltystr. 10, 31535 Neustadt a. Rbge., Germany
Abstract The neurohypophyseal hormone arginine vasotocin (AVT) combines both antidiuretic and reproductive activities. In the domestic chicken AVT produces assimetric effects on the reproductive functions of males and females. AVT synthesized in magnocellular diencephalic neurons is released into circulation in a highly coordinated manner contributing to the peripheral control of oviposition in hens. Conversely, parvocellular AVT cells located in the limbic system (bed nucleus of stria terminalis (BST)) are quite different in their properties and, possible, functions. In domestic chickens these cells express AVT in a sexually dimorphic manner and are found solely in males. This sexually dimorphic part of the AVT system is sensitive to gonadal steroids. Experimental data demonstrated that AVT modulates different aspects of reproductive behavior including courtship vocalization and copulation. Sexual differentiation of these limbic vasotocinergic cells show striking correlation with sexual differentiation of masculine behavior. Evidences coming from physiological, anatomical and ethological studies suggest strong implication of the vasotocinergic system in the control of reproductive functions. © 2003 Elsevier Inc. All rights reserved. Keywords: Vasotocin; Reproduction; Chicken; Behavior
1. Introduction The neurohypophyseal hormone arginine vasotocin (AVT) in birds, likewise its homologue arginine vasopressin in mammals, has one of the most remarkable records of documented autonomic and behavioral functions. Because of its important role played in osmoregulation, AVT was defined as antidiuretic hormone in all terrestrial non-mammalian species [1,2]. In birds, AVT shows vasomotor and thermoregulatory effects [3], stimulates ∗
Corresponding author. Tel.: +49-5034-871164; fax: +49-5034-871247. E-mail address: [email protected] (R. Grossmann). 0739-7240/$ – see front matter © 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0739-7240(03)00048-1
94
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
the release of adrenocorticotropic hormone from the pituitary [4,5] and reduces plasma aldosterone [3]. While the neurohypophyseal system of most mammalian species in addition to the antidiuretic hormone produces also oxytocin that controls important reproductive functions such as uterine contractility during partition and milk ejection, and induces some forms of parental behavior, avian AVT combines both antidiuretic and reproductive functions. Moreover, some recent neuroanatomical data point out on its role in regulation of sex-related reproductive behavior [6,7]. The aim of this review is to summarize briefly the sex-related functions of AVT emerging from recent experimental studies in the domestic chickens. 2. AVT and control of oviposition Data obtained from a number of experimental studies have demonstrated that oviposition in the hen is associated with an increase of AVT concentration in the circulation [8–10]. Plasma AVT increases sharply at the time of oviposition inducing the oviduct contractions and decreases within 30 min after an egg has been laid [11]. Oviposition-related elevation of plasma AVT is accompanied by a depletion of AVT concentration in the neurohypophysis [12] suggesting that hormone is likely to be synthesized in hypothalamic magnocellular neurons. However the neurohypophysis is not the only possible source of AVT release during oviposition. AVT was also found to be expressed in the uterus and ovary of laying hens [13]. It needs to be established whether this locally synthesized AVT acts in concert with centrally produced hormone controlling egg lay or it may have a different role as a paracrine regulator of the reproductive system. 3. Brain vasotocin system In the avian neuroendocrine system, neurons producing AVT are obviously among the most abundant. They are concentrated largely within the preoptic and supraoptic brain regions and the paraventricular hypothalamic nucleus. Magnocellular vasotocinergic neurons form the hypothalamo–neurohypophysial–neurosecretory system. AVT is synthesized in these cells and transported along the axon terminals to the neurohypophysis where the peptide is released into the blood stream. In the preoptic area and paraventricular nucleus of the hypothalamus AVT is colocalized in the same cells with chicken gonadotropin releasing hormone I [14] suggesting a possible coordinated response of both neuropeptides in control of reproductive functions. The AVT system includes also a sexually dimorphic population of parvocellular neurons that are located around a conventional border dividing di- and telencephalon. These neurons extend from the mediocaudal part of the preoptic region to the dorsolateral part of the bed nucleus of stria terminalis (BST) (Fig. 1). The role of these brain regions in control of sexual behavior in birds is well-documented [15–17]. Additionally, a dense sexually dimorphic network of AVT-immunoreactive (AVT-ir) fibers is observed in the lateral septum (SL) [18]. In a few bird species investigated so far, males have more AVT-ir cells in the BST and more abundant AVT-ir innervation in the BST and SL than females. In chicken and quail these sex differences are ultimate, with complete absence of the AVT-ir structures in the BST and SL of adult females (Fig. 2) [18,19].
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
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Fig. 1. Low magnification photomicrograph of a 40-m-thick coronal brain section through the septo-preoptic region of adult cockerel showing the distribution of arginine vasotocin immunoreactive cells and fibers. CO, optic chiasm; BSTdl, bed nucleus of the stria terminalis, pars dorsolateralis; BSTvm, bed nucleus of the stria terminalis, pars ventromedialis; LHy, lateral hypothalamus; OM, occipitomesencephalic tract; nCPa, nucleus of pallial commissure; PVN, paraventricular nucleus; SL, lateral septal nucleus; SM, medial septal nucleus; VL, lateral ventricle; 3V, third ventricle. Scale bar = 200 m.
Contrary to the magnocellular neurosecretory system, parvocellular vasotocin neurons may release peptide directly into brain interstitial fluid where it modulates the neural circuits controlling behavior. Such functions were demonstrated by vasopressinergic parvocellular neurons located in the homologous limbic structures (amygdala, BST) of the rat brain [20]. The synthesis of AVT in the sexually dimorphic parvocellular neurons of the Japanese quail is sensitive to testosterone but not to non-aromatisable androgen, 5␣-dihydrotestosterone. Lately strong evidences were provided that aromatization of testosterone into estradiol is essential to stimulate AVT synthesis [21].
4. Development of sex differences in the vasotocin system and sexual behavior Developmental studies in chickens have demonstrated that AVT neurons arise within the BST during embryogenesis in both sexes [22]. First conspicuous AVT-ir cells can be
96
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
Fig. 2. Medium magnification photomicrographs of coronal brain sections illustrating the distribution of AVT-ir cells and fibers in the brain of adult male (A) and female (B) domestic chicken. For abbreviations see Fig. 1. Scale bar = 100 m.
detected already around day 12 of embryonic (E) development. During further development the number of ir cells increases progressively reaching the maximal values both in males and females around hatching. The number of AVT-producing cells in the BST completes differentiation by day 35 posthatch. Recent studies indicated that sexual differentiation of the AVT system is likely to be induced by estrogen-dependent mechanisms. Adult male quail or chickens treated as embryos on E8–E9 with an in ovo injection of estradiol benzoate have virtually completely lost the AVT-ir structures in the BST, medial preoptic nucleus and septum, i.e. they demonstrated a female-like distribution of vasotocinergic fibers and parvocellular perikarya [23,24]. Conversely, the females during the same period of development received single in ovo injections of an aromatase inhibitor that prevents synthesis of endogenous estradiol from testosterone displayed a male-typical distribution of AVT-ir structures. Injections of either estradiol or aromatase inhibitor are not effective when given on E18, i.e. much beyond the critical period for sexual differentiation of behavior [24]. Moreover, experimental manipulations to alter estrogen milieu do not significantly affect the magnocellular component of the AVT system outside of the BST. These facts indicate that embryonic effects of estrogens on the AVT system are time- and region-specific. It is important to note that the embryonic differentiation of the AVT system in chickens and quail demonstrates striking correlation with the differentiation of sexual behavior in these species. In gallinaceous birds, estrogens play a key role in differentiation of sexual
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
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behavior. The high levels of estrogens typical to female embryos permanently suppress female capacities to display masculine behavior at adulthood [7]. Male embryos exposed to estradiol as earlier as E12–E13 loss permanently their abilities to copulate at adulthood [25,26]. Detail ethological analysis in chickens revealed no significant changes in the appetitive components of male sexual behavior (courtship) while consummatory components (mounting attempts, treading, and copulation) were suppressed. Curiously, the frequency of aggressive displays towards females has increased. Moreover, estradiol reduced the frequency of crowing and changed some acoustic characteristics of this call. These results along with extensive sexually dimorphic AVT innervation of the brain areas known to be involved in the control of reproductive behavior strongly suggest a role of this peptide in sexual behavior. Available data indicate indeed that AVT regulates male sexual behavior in chickens, pigeons and Japanese quail [27,28], controls courtship singing [29,30], facilitates aggressive behavior in colonial songbirds but inhibits aggression in songbirds with a territorial social organization [30,31]. 5. Conclusion It is a scientific tradition to consider AVT as endocrine regulator of osmotic homeostasis. The results reviewed here obviously demonstrate that AVT plays a significant role in different aspects of reproduction of domestic chickens by modulation of both peripheral and central mechanisms. A surge of AVT released from the hypothalamus evokes, probably in interrelation with some other regulatory factors (see [32]), the oviposition in hen. On the other hand, AVT expression in parvocellular extrahypothalamic neurons depends from the levels of gonadal hormones and correlates with male-typical sexual behavior. These central regulatory effects on the reproductive axis may be mediated by interactions with other neuroendocrine systems such as GnRH-I and/or galanin. Acknowledgements Supported by H.W. Schaumann Stiftung. References [1] Gray DA, Simon E. Mammalian and avian antidiuretic hormone: studies related to possible species variation in osmoregulatory systems. J Comp Physiol 1983;151:241–6. [2] Acher R. Neurohypophysial peptide systems: processing machinery, hydroosmotic regulation, adaptation and evolution. Regul Pept 1993;45:1–13. [3] Robinzon B, Koike TI, Neldon HL, Kinzler SL, Hendry IR, El Halawani ME. Physiological effects of arginine vasotocin and mesotocin in cockerels. Br Poult Sci 1988;29:639–52. [4] Castro MG, Estivariz FE, Iturriza FC. The regulation of the corticomelanotropic cell activity in Aves. II. Effect of various peptides on the release of ACTH from dispersed, perfused duck pituitary cells. Comp Biochem Physiol A 1986;83:71–5. [5] Romero LM, Wingfield JC. Seasonal changes in adrenal sensitivity alter corticosterone levels in Gambel’s white-crowned sparrows (Zonotrichia leucophrys gambelii). Comp Biochem Physiol C 1998;119: 31–6.
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[6] Jurkevich A, Grossmann R, Balthazart J, Viglietti-Panzica C. Gender-related changes in the avian vasotocin system during ontogeny. Microsc Res Tech 2001;55:27–36. [7] Panzica GC, Aste N, Castagna C, Viglietti-Panzica C, Balthazart J. Steroid-induced plasticity in the sexually dimorphic vasotocinergic innervation of the avian brain: behavioral implications. Brain Res Rev 2001;37:178– 200. [8] Nouwen EJ, Decuypere E, Kühn ER, Michels H, Hall TR, Chadwick A. Effect of dehydration, haemorrhage and oviposition on serum concentrations of vasotocin, mesotocin and prolactin in the chicken. J Endocrinol 1984;102:345–51. [9] Tanaka K, Goto K, Yoshioka T, Terao T, Koga O. Changes in the plasma concentration of immunoreactive arginine vasotocin during oviposition in the domestic fowl. Br Poult Sci 1984;25:589–95. [10] Shimada K, Neldon HL, Koike TI. Arginine vasotocin (AVT) release in relation to uterine contractility in the hen. Gen Comp Endocrinol 1986;64:362–7. [11] Koike TI, Shimada K, Cornett LE. Plasma levels of immunoreactive mesotocin and vasotocin during oviposition in chickens: relationship to oxytocic action of the peptides in vitro and peptide interaction with myometrial membrane binding sites. Gen Comp Endocrinol 1988;70:119–26. [12] Sasaki T, Shimada K, Saito N. Changes of AVT levels in plasma neurohypophysis and hypothalamus in relation to oviposition in the laying hen. Comp Biochem Physiol A Mol Integr Physiol 1998;121:149–53. [13] Saito N, Grossmann R. Gene expression of arginine vasotocin in ovarian and uterine tissues of the chicken. Asian-Aust J Anim Sci 1999;12:695–701. [14] D’Hondt E, Eelen M, Berghman L, Vandesande F. Colocalization of arginine-vasotocin and chicken luteinizing hormone-releasing hormone-I (cLHRH-I) in the preoptic-hypothalamic region of the chicken. Brain Res 2000;856:55–67. [15] Putkonen PTS. Electrical stimulation of the avian brain. Ann Acad Sci Fennicae Ser A V Medica 1967;130:1– 95. [16] Barfield RJ. Activation of sexual and aggressive behavior by androgen implanted into the male ring dove brain. Endocrinology 1971;89:1470–6. [17] Adkins-Regan E. Neuroanatomy of sexual behavior in the male Japanese quail from top to bottom. Poult Avian Biol Rev 1996;7:193–204. [18] Jurkevich A, Barth SW, Grossmann R. Sexual dimorphism of arg-vasotocin gene expressing neurons in the telencephalon and dorsal diencephalon of the domestic fowl. An immunocytochemical and in situ hybridization study. Cell Tissue Res 1997;287:69–77. [19] Aste N, Balthazart J, Absil P, Grossmann R, Mühlbauer E, Viglietti-Panzica C, et al. Anatomical and neurochemical definition of the nucleus of the stria terminalis in Japanese quail (Coturnix japonica). J Comp Neurol 1998;396:141–57. [20] Landgraf R. Intracerebellary released vasopressin and oxytocin: measurement, mechanisms and behavioural consequences. J Neuroendocrinol 1995;7:243–53. [21] Viglietti-Panzica C, Balthazart J, Plumari L, Fratesi S, Absil P, Panzica GC. Estradiol mediates effects of testosterone on vasotocin immunoreactivity in the adult quail brain. Horm Behav 2001;40:445–61. [22] Jurkevich A, Barth SW, Kuenzel WJ, Köhler A, Grossmann R. Development of sexually dimorphic vasotocinergic system in the bed nucleus of stria terminalis in chickens. J Comp Neurol 1999;408:46–60. [23] Panzica GC, Castagna C, Viglietti-Panzica C, Russo C, Tlemçani O, Balthazart J. Organizational effects of estrogens on brain vasotocin and sexual behavior in quail. J Neurobiol 1998;37:684–99. [24] Grossmann R, Jurkevich A, Köhler A. Role of estrogen in development of sexually dimorphic vasotocin system in the chicken bed nucleus of stria terminalis. Soc Neurosci Abstr 1999;25:229. [25] Sayag N, Snapir N, Robinzon B, Arnon E, El Halawani ME, Grimm VE. Embryonic sex steroids affect mating behavior and plasma LH in adult chickens. Physiol Behav 1989;45:1107–12. [26] Jurkevich A, Grossmann R, Rimeikiene R, Köhler A. Parallelism in sexual differentiation between the extrahypothalamic vasotocin system and male-typical behaviour of chickens. Trabajos del Instituto Cajal 2000;77:210–2. [27] Kihlström JE, Danninge I. Neurohypophysial hormones and sexual behavior in males of the domestic fowl (Gallus domesticus) and the pigeon (Columba livia Gmel.). Gen Comp Endocrinol 1972;18:115–20. [28] Castagna C, Absil P, Foidart A, Balthazart J. Systemic and intracerebroventricular injections of vasotocin inhibit appetitive and consummatory components of male sexual behavior in Japanese quail. Behav Neurosci 1998;112:233–50.
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[29] Maney DL, Goode CT, Wingfield JC. Intraventricular infusion of arginine vasotocin induces singing in a female songbird. J Neuroendocrinol 1997;9:487–91. [30] Goodson JL. Vasotocin and vasoactive intestinal polypeptide modulate aggression in a territorial songbird, the violet-eared waxbill (Estrildidae: Uraeginthus granatina). Gen Comp Endocrinol 1998;111:233–44. [31] Goodson JL. Territorial aggression and dawn song are modulated by septal vasotocin and vasoactive intestinal polypeptide in male field sparrows (Spizella pusilla). Horm Behav 1998;34:67–77. [32] Ubuka T, Sakamoto H, Li D, Ukena K, Tsutsui K. Developmental changes in galanin in lumbosacral sympathetic ganglionic neurons innervating the avian uterine oviduct and galanin induction by sex steroids. J Endocrinol 2001;170:357–68.
Vasotocin and reproductive functions of the domestic chicken A. Jurkevich a , R. Grossmann b,∗ a
b
Institute of Ecology, Vilnius University, Akademijos 2, Vilnius LT-2600, Lithuania Institute for Animal Science, Mariensee, Federal Agricultural Research Centre (FAL), Höltystr. 10, 31535 Neustadt a. Rbge., Germany
Abstract The neurohypophyseal hormone arginine vasotocin (AVT) combines both antidiuretic and reproductive activities. In the domestic chicken AVT produces assimetric effects on the reproductive functions of males and females. AVT synthesized in magnocellular diencephalic neurons is released into circulation in a highly coordinated manner contributing to the peripheral control of oviposition in hens. Conversely, parvocellular AVT cells located in the limbic system (bed nucleus of stria terminalis (BST)) are quite different in their properties and, possible, functions. In domestic chickens these cells express AVT in a sexually dimorphic manner and are found solely in males. This sexually dimorphic part of the AVT system is sensitive to gonadal steroids. Experimental data demonstrated that AVT modulates different aspects of reproductive behavior including courtship vocalization and copulation. Sexual differentiation of these limbic vasotocinergic cells show striking correlation with sexual differentiation of masculine behavior. Evidences coming from physiological, anatomical and ethological studies suggest strong implication of the vasotocinergic system in the control of reproductive functions. © 2003 Elsevier Inc. All rights reserved. Keywords: Vasotocin; Reproduction; Chicken; Behavior
1. Introduction The neurohypophyseal hormone arginine vasotocin (AVT) in birds, likewise its homologue arginine vasopressin in mammals, has one of the most remarkable records of documented autonomic and behavioral functions. Because of its important role played in osmoregulation, AVT was defined as antidiuretic hormone in all terrestrial non-mammalian species [1,2]. In birds, AVT shows vasomotor and thermoregulatory effects [3], stimulates ∗
Corresponding author. Tel.: +49-5034-871164; fax: +49-5034-871247. E-mail address: [email protected] (R. Grossmann). 0739-7240/$ – see front matter © 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0739-7240(03)00048-1
94
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
the release of adrenocorticotropic hormone from the pituitary [4,5] and reduces plasma aldosterone [3]. While the neurohypophyseal system of most mammalian species in addition to the antidiuretic hormone produces also oxytocin that controls important reproductive functions such as uterine contractility during partition and milk ejection, and induces some forms of parental behavior, avian AVT combines both antidiuretic and reproductive functions. Moreover, some recent neuroanatomical data point out on its role in regulation of sex-related reproductive behavior [6,7]. The aim of this review is to summarize briefly the sex-related functions of AVT emerging from recent experimental studies in the domestic chickens. 2. AVT and control of oviposition Data obtained from a number of experimental studies have demonstrated that oviposition in the hen is associated with an increase of AVT concentration in the circulation [8–10]. Plasma AVT increases sharply at the time of oviposition inducing the oviduct contractions and decreases within 30 min after an egg has been laid [11]. Oviposition-related elevation of plasma AVT is accompanied by a depletion of AVT concentration in the neurohypophysis [12] suggesting that hormone is likely to be synthesized in hypothalamic magnocellular neurons. However the neurohypophysis is not the only possible source of AVT release during oviposition. AVT was also found to be expressed in the uterus and ovary of laying hens [13]. It needs to be established whether this locally synthesized AVT acts in concert with centrally produced hormone controlling egg lay or it may have a different role as a paracrine regulator of the reproductive system. 3. Brain vasotocin system In the avian neuroendocrine system, neurons producing AVT are obviously among the most abundant. They are concentrated largely within the preoptic and supraoptic brain regions and the paraventricular hypothalamic nucleus. Magnocellular vasotocinergic neurons form the hypothalamo–neurohypophysial–neurosecretory system. AVT is synthesized in these cells and transported along the axon terminals to the neurohypophysis where the peptide is released into the blood stream. In the preoptic area and paraventricular nucleus of the hypothalamus AVT is colocalized in the same cells with chicken gonadotropin releasing hormone I [14] suggesting a possible coordinated response of both neuropeptides in control of reproductive functions. The AVT system includes also a sexually dimorphic population of parvocellular neurons that are located around a conventional border dividing di- and telencephalon. These neurons extend from the mediocaudal part of the preoptic region to the dorsolateral part of the bed nucleus of stria terminalis (BST) (Fig. 1). The role of these brain regions in control of sexual behavior in birds is well-documented [15–17]. Additionally, a dense sexually dimorphic network of AVT-immunoreactive (AVT-ir) fibers is observed in the lateral septum (SL) [18]. In a few bird species investigated so far, males have more AVT-ir cells in the BST and more abundant AVT-ir innervation in the BST and SL than females. In chicken and quail these sex differences are ultimate, with complete absence of the AVT-ir structures in the BST and SL of adult females (Fig. 2) [18,19].
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
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Fig. 1. Low magnification photomicrograph of a 40-m-thick coronal brain section through the septo-preoptic region of adult cockerel showing the distribution of arginine vasotocin immunoreactive cells and fibers. CO, optic chiasm; BSTdl, bed nucleus of the stria terminalis, pars dorsolateralis; BSTvm, bed nucleus of the stria terminalis, pars ventromedialis; LHy, lateral hypothalamus; OM, occipitomesencephalic tract; nCPa, nucleus of pallial commissure; PVN, paraventricular nucleus; SL, lateral septal nucleus; SM, medial septal nucleus; VL, lateral ventricle; 3V, third ventricle. Scale bar = 200 m.
Contrary to the magnocellular neurosecretory system, parvocellular vasotocin neurons may release peptide directly into brain interstitial fluid where it modulates the neural circuits controlling behavior. Such functions were demonstrated by vasopressinergic parvocellular neurons located in the homologous limbic structures (amygdala, BST) of the rat brain [20]. The synthesis of AVT in the sexually dimorphic parvocellular neurons of the Japanese quail is sensitive to testosterone but not to non-aromatisable androgen, 5␣-dihydrotestosterone. Lately strong evidences were provided that aromatization of testosterone into estradiol is essential to stimulate AVT synthesis [21].
4. Development of sex differences in the vasotocin system and sexual behavior Developmental studies in chickens have demonstrated that AVT neurons arise within the BST during embryogenesis in both sexes [22]. First conspicuous AVT-ir cells can be
96
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
Fig. 2. Medium magnification photomicrographs of coronal brain sections illustrating the distribution of AVT-ir cells and fibers in the brain of adult male (A) and female (B) domestic chicken. For abbreviations see Fig. 1. Scale bar = 100 m.
detected already around day 12 of embryonic (E) development. During further development the number of ir cells increases progressively reaching the maximal values both in males and females around hatching. The number of AVT-producing cells in the BST completes differentiation by day 35 posthatch. Recent studies indicated that sexual differentiation of the AVT system is likely to be induced by estrogen-dependent mechanisms. Adult male quail or chickens treated as embryos on E8–E9 with an in ovo injection of estradiol benzoate have virtually completely lost the AVT-ir structures in the BST, medial preoptic nucleus and septum, i.e. they demonstrated a female-like distribution of vasotocinergic fibers and parvocellular perikarya [23,24]. Conversely, the females during the same period of development received single in ovo injections of an aromatase inhibitor that prevents synthesis of endogenous estradiol from testosterone displayed a male-typical distribution of AVT-ir structures. Injections of either estradiol or aromatase inhibitor are not effective when given on E18, i.e. much beyond the critical period for sexual differentiation of behavior [24]. Moreover, experimental manipulations to alter estrogen milieu do not significantly affect the magnocellular component of the AVT system outside of the BST. These facts indicate that embryonic effects of estrogens on the AVT system are time- and region-specific. It is important to note that the embryonic differentiation of the AVT system in chickens and quail demonstrates striking correlation with the differentiation of sexual behavior in these species. In gallinaceous birds, estrogens play a key role in differentiation of sexual
A. Jurkevich, R. Grossmann / Domestic Animal Endocrinology 25 (2003) 93–99
97
behavior. The high levels of estrogens typical to female embryos permanently suppress female capacities to display masculine behavior at adulthood [7]. Male embryos exposed to estradiol as earlier as E12–E13 loss permanently their abilities to copulate at adulthood [25,26]. Detail ethological analysis in chickens revealed no significant changes in the appetitive components of male sexual behavior (courtship) while consummatory components (mounting attempts, treading, and copulation) were suppressed. Curiously, the frequency of aggressive displays towards females has increased. Moreover, estradiol reduced the frequency of crowing and changed some acoustic characteristics of this call. These results along with extensive sexually dimorphic AVT innervation of the brain areas known to be involved in the control of reproductive behavior strongly suggest a role of this peptide in sexual behavior. Available data indicate indeed that AVT regulates male sexual behavior in chickens, pigeons and Japanese quail [27,28], controls courtship singing [29,30], facilitates aggressive behavior in colonial songbirds but inhibits aggression in songbirds with a territorial social organization [30,31]. 5. Conclusion It is a scientific tradition to consider AVT as endocrine regulator of osmotic homeostasis. The results reviewed here obviously demonstrate that AVT plays a significant role in different aspects of reproduction of domestic chickens by modulation of both peripheral and central mechanisms. A surge of AVT released from the hypothalamus evokes, probably in interrelation with some other regulatory factors (see [32]), the oviposition in hen. On the other hand, AVT expression in parvocellular extrahypothalamic neurons depends from the levels of gonadal hormones and correlates with male-typical sexual behavior. These central regulatory effects on the reproductive axis may be mediated by interactions with other neuroendocrine systems such as GnRH-I and/or galanin. Acknowledgements Supported by H.W. Schaumann Stiftung. References [1] Gray DA, Simon E. Mammalian and avian antidiuretic hormone: studies related to possible species variation in osmoregulatory systems. J Comp Physiol 1983;151:241–6. [2] Acher R. Neurohypophysial peptide systems: processing machinery, hydroosmotic regulation, adaptation and evolution. Regul Pept 1993;45:1–13. [3] Robinzon B, Koike TI, Neldon HL, Kinzler SL, Hendry IR, El Halawani ME. Physiological effects of arginine vasotocin and mesotocin in cockerels. Br Poult Sci 1988;29:639–52. [4] Castro MG, Estivariz FE, Iturriza FC. The regulation of the corticomelanotropic cell activity in Aves. II. Effect of various peptides on the release of ACTH from dispersed, perfused duck pituitary cells. Comp Biochem Physiol A 1986;83:71–5. [5] Romero LM, Wingfield JC. Seasonal changes in adrenal sensitivity alter corticosterone levels in Gambel’s white-crowned sparrows (Zonotrichia leucophrys gambelii). Comp Biochem Physiol C 1998;119: 31–6.
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