Effect of estrogen and its antagonist on the expression of arginine vasotocin (AVT) and its oxytocic-like receptor VT3 in the shell gland of Japanese quail, Coturnix coturnix japonica

Reproductive hormones modulate differentially brain and ovarian vasotocin receptor gene expression in early and late recrudescent catfish, Heteropneustes fossilis

Investigations on the role of the reproductive hormones on VT receptor gene expression are lacking in teleosts. Previously we reported that gonadotropin and steroid hormones modulate the secretion and gene expression of brain and ovarian vasotocin (VT) in the catfish Heteropneustes fossilis. In continuation, in the present study we investigated the role of estradiol-17β (E₂), the maturation-inducing steroid (MIS) 17α, 20β-dihydroxy-4-pregnen-3-one (17, 20β-DP), and human chorionic gonadotropin (hCG) on the expression of VT receptor genes (v1a1, v1a2 and v2a) in the brain and ovary of the catfish in early (previtellogenic, preparatory) and late (post vitellogenic, prespawning) phases of the ovarian cycle. The steroid treatments (in vivo and in vitro) modulated only the v1a1 and v1a2 expression in both tissues, but not the v2a expression. The E₂-induced modulation of the v1a1 and v1a2 gene expression varied with the reproductive phase. In the preparatory phase, E₂ up regulated the expression of brain and ovarian v1a1 and v1a2 gene expression, the response varied with the dose and duration. In the prespawning phase, E₂ inhibited the expression in a dose- and duration-dependent manner. On the other hand, 17, 20β-DP up regulated the expression of brain and ovarian v1a1 and v1a2 in both phases, and the response was higher in the prespawning phase and varied with dose and duration. In contrast to the steroid effects, the hCG treatment modulated the expression of all the VT receptor genes only in the prespawning phase and the response varied with dose and duration. The results indicate differential modulatory roles of steroid hormones and hCG on the VT receptor gene expression, to mediate VT's reproductive or osmoregulatory functions. While the hCG effect on v1a type receptor expression may be steroid- dependent, that of v2a expression seems to be steroid-independent.

Molecular cloning, sequencing and phylogeny of vasotocin receptor genes in the air-breathing catfish Heteropneustes fossilis with sex dimorphic and seasonal variations in tissue expression

Vasotocin (VT) is the ortholog of vasopressin (VP) in non-mammalian vertebrates and is known for multiple functions. Teleost fishes have a complete repertoire of known VP/VT receptor subtypes (vasopressin type, VR): two V1A subtypes (V1Aa and V1Ab or V1a1 and V1a2) and five V2 subtypes (V2A1, V1A2, V2B1, V2B2 and V2C). Full-length cDNAs of v1a1, v1a2 and v2 (v2a1) with ORFs of 1,308, 1,137 and 1,527 bp, respectively, were cloned and characterized in the catfish Heteropneustes fossilis (Siluriformes, Ostariophysi). BLAST analysis revealed that the genes encoded three VT receptors, V1a1, V1a2 and V2 of 436, 379 and 509 amino acid residues, respectively. The predicted proteins showed typical features of the seven-transmembrane domain receptor core structure with hallmark triplets Asp-Arg-Tyr/Asp-Arg-His (DRY/DRH) and the variable intracellular loop III of vertebrate neurohypophysial hormone receptors. Phylogenetic analysis of the deduced protein sequences revealed that they clustered with the V1Aa, V1Ab and V2A1, respectively, of other teleosts. The V2R has a sequence identity of 70-76% with V2A1 than with the V2B type (sequence identity 43-49%). Semiquantitative PCR analysis showed that the receptor gene transcripts were expressed ubiquitously in the tissues examined (brain, pituitary, gonads, liver, muscle, kidney and gills) and displayed sex and seasonal fluctuations in a tissue-specific manner. The results form a basis for functional studies on the VT receptors in the catfish.

Neuroendocrine regulation of stress in birds with an emphasis on vasotocin receptors (VTRs)

The neuroendocrine stress response of vertebrates, particularly mammals, comprises at least two types of neuropeptide containing neurons, corticotropin-releasing hormone (CRH) and vasopressin (VP) neurons, and four receptors [CRH receptor one (CRH-R1) and two (CRH-R2) and VP receptor 1a (V1aR) and 1b (V1bR)]. The avian neuropeptide CRH, a 41-amino acid peptide, has been shown to have the same amino acid sequence as humans while nonapeptide neurohormone arginine-vasotocin (AVT) is regarded as highly conserved having a single amino acid substitution compared to mammalian arginine vasopressin. Similar to mammals, birds have two receptor subtypes (CRH-R1 and CRH-R2) for CRH, however, four vasotocin receptors have been identified. Less is known about the functions of the four avian vasotocin receptors compared to homologous ones found in mammals and other vertebrate classes. Recently, chicken vasotocin receptor two (VT2R) and four (VT4R) have been characterized utilizing immunocytochemistry and an imposed stress test. The purpose of this review is to present evidence that the VT2R and VT4R are involved in the avian stress response and that the cephalic lobe of the anterior pituitary appears specialized for this function as it contains the major population of corticotropes and necessary neuroendocrine receptors to respond to stressors impacting avian species.

Age, photoperiod and estrogen dependent variations in the shell gland and the expression of AVT in the ovary of Japanese quail

Present work was undertaken to describe (i) age dependent (prepuberal-3, 4, 5 and 6 weeks old, puberal and actively laying 8 and 12 weeks old and aged 78 weeks old) (ii) photoperiodic response dependent (photosensitive and photorefractory) and sex steroid dependent (estradiol benzoate and its antagonist tamoxifen treated) variation in the ovary and shell gland activity of Japanese quail (Coturnix coturnix japonica). Further, in view of the role of neurohypophysial peptide arginine vasotocin (AVT) in many physiological processes including age/reproduction related oviposition, expression of ir-AVT was also monitored in the ovary of quail. All the parameters associated with histodifferentiation increased rapidly during the developing stages followed by a decrease in old age, which also increased in reproductively quiescent photorefractory birds following estradiol treatment and decreased in reproductively active photosensitive quail following tamoxifen treatment. Using AVT-specific antibody, expression of immunoreactive AVT (ir-AVT) observed in the ovary of photosensitive quail was not detected in the photorefractory quail. However, administration of estrogen in the photorefractory quail stimulated the growth and activity of ovary and shell gland also resulted in the expression of ovarian ir-AVT. On the other hand, tamoxifen eliminated the localization of ir-AVT in the ovary of photosensitive quail in addition to a decrease in the shell gland protein and alkaline phosphatase activity. It is concluded that estrogen not only affects the growth and differentiation of ovary and oviduct including shell gland but also regulates the expression of ovarian AVT. It is also suggested that in addition to reported paracrine effect of AVT in the shell gland of Japanese quail for oviposition, ovarian AVT may also affect ovarian function (ovulation), and in part, this regulation is estrogen dependent.

Evolving nonapeptide mechanisms of gregariousness and social diversity in birds

Of the major vertebrate taxa, Class Aves is the most extensively studied in relation to the evolution of social systems and behavior, largely because birds exhibit an incomparable balance of tractability, diversity, and cognitive complexity. In addition, like humans, most bird species are socially monogamous, exhibit biparental care, and conduct most of their social interactions through auditory and visual modalities. These qualities make birds attractive as research subjects, and also make them valuable for comparative studies of neuroendocrine mechanisms. This value has become increasingly apparent as more and more evidence shows that social behavior circuits of the basal forebrain and midbrain are deeply conserved (from an evolutionary perspective), and particularly similar in birds and mammals. Among the strongest similarities are the basic structures and functions of avian and mammalian nonapeptide systems, which include mesotocin (MT) and arginine vasotocin (VT) systems in birds, and the homologous oxytocin (OT) and vasopressin (VP) systems, respectively, in mammals. We here summarize these basic properties, and then describe a research program that has leveraged the social diversity of estrildid finches to gain insights into the nonapeptide mechanisms of grouping, a behavioral dimension that is not experimentally tractable in most other taxa. These studies have used five monogamous, biparental finch species that exhibit group sizes ranging from territorial male-female pairs to large flocks containing hundreds or thousands of birds. The results provide novel insights into the history of nonapeptide functions in amniote vertebrates, and yield remarkable clarity on the nonapeptide biology of dinosaurs and ancient mammals. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Neural distribution of vasotocin receptor mRNA in two species of songbird

The neurohypophyseal hormones vasopressin and oxytocin are produced and released within the mammalian brain, where they act via multiple receptor subtypes. The neural distributions of these receptors, for example, V1a and oxytocin receptors, have been well described in many mammals. In birds, the distribution of binding sites for the homologous neuropeptides, vasotocin (VT) and mesotocin, has been studied in several species by using synthetic radioligands designed to bind to mammalian receptors. Such binding studies, however, may not reveal the specific distributions of each receptor subtype. To identify and map the receptors likely to bind VT and mesotocin, we generated partial cDNA sequences for four VT receptor subtypes, VT1, VT2 (V1b), VT3 (oxytocin-like), and VT4 (V1a), in white-throated sparrow (Zonotrichia albicollis) and zebra finch (Taeniopygia guttata). These genes shared high sequence identity with the homologous avian and mammalian neurohypophyseal peptide receptors, and we found evidence for VT1, VT3, and VT4 receptor mRNA expression throughout the brains of both species. As has been described in rodents, there was striking interspecific and intraspecific variation in the densities and distribution of these receptors. For example, whereas the VT1 receptor mRNA was more widespread in zebra finch brain, the VT3 (oxytocin-like) receptor mRNA was more prevalent in the sparrow brain. Although VT2 (V1b) receptor mRNA was abundant in the pituitary, it was not found in the brain. Because of their association with brain regions implicated in social behavior, the VT1, VT3, and VT4 receptors are all likely candidates for mediating the behavioral effects of VT.

Effect of estrogen and tamoxifen on the shell gland AVT and VT3R of scotosensitive and scotorefractory Japanese quail

The neurohypophyseal hormone arginine vasotocin (AVT) found in most vertebrate species is known to modulate different aspects of reproduction in quail. AVT system is sensitive to gonadal steroids. Previous studies have shown that estradiol benzoate stimulates the proliferation of shell gland and increases the AVT and the vasotocin 3 receptor (VT3R) in long day length. This study was undertaken to investigate the effect of estrogen and tamoxifen on AVT as well as its receptor VT3 under the short day condition (6L:18D). Estradiol benzoate (EB) was administered daily in sexually quiescent (scotosensitive) condition for 15days. After the initial period of sexual quiescence, the quail of control group exhibited sexual development (scotorefractory condition). Thereafter, scotorefractory quail were administered with anti-estrogen tamoxifen, which eliminated the reoccurrence of scotosensitivity. Immunohistochemical and in-situ hybridization studies indicate the expression of AVT and VT3R transcripts in both scotosensitive as well as scotorefractory conditions. Administration of EB to scotosensitive female quail produced an increase in AVT and VT3 while tamoxifen suppressed them in scotorefractory quail. The results indicate that in quail myometrium the expression of VT3R is upregulated by estrogen when kept under short day condition.

Age-dependent expression of AVT and its oxytocic-like receptor VT3 in the shell gland of Japanese quail, Coturnix coturnix japonica

The avian neurohypophyseal hormone AVT is an important regulatory hormone involved in many physiological processes including oviposition; an age-related phenomenon, through its action on the shell gland. In this study, immunohistochemistry and in situ hybridization was performed to study the expression of immunoreactive (ir) AVT and its oxytocic-like receptor VT3 transcript in the ovary/shell gland of Japanese quail representing sexually immature, mature and old condition. Our results indicate that ir-AVT is present in the ovary of sexually active adult only, but in the shell gland it is observed in both sexually active adult and sexually quiescent old quail. Further, VT3 gene transcript although not detected in the shell gland of sexually immature birds, has been found abundantly in the myometrium of shell gland of sexually active adult quail with a slight decrease in old birds. It is concluded that in addition to the ovarian function and shell gland activity, the expression of AVT and VT3 receptor in the shell gland also varies with the age dependent reproductive/egg laying performance of the Japanese quail. Our findings also suggest that (i) local synthesis of AVT and the expression of its oxytocic-like VT3 receptors is estrogen dependent and (ii) shell gland AVT upregulates its VT3 receptor (paracrine role) in advance to facilitate the role of neurohypophyseal AVT during oviposition.