Testosterone modulates pituitary vasotocin receptor expression and adrenal activity in osmotically stressed chicken

Regulation of arginine vasotocin (AVT), avian neurohypophyseal hormone, is an important component of the hypothalamo-pituitary-adrenal axis. Changes in plasma osmolality levels and sex steroids are known to affect AVT gene expression. The present study reports the effect of water deprivation and testosterone treatment independently, as well as simultaneously, on the pituitary vasotocin receptor VT2R expression and adrenal steroidogenic activity in sexually immature male chicken (Gallus gallus). Birds were divided into four groups- control, water deprived (WD), testosterone injected (TE) and TE treated water deprived (TE+WD). WD decreased and TE treatment alone or in combination with WD (TE+WD) increased VT2R expression compared to the control. Expression of pro-opiomelanocortin (POMC) was also studied since this gene is a polypeptide precursor of ACTH and is under the negative feedback of adrenal corticoids. TE treatment as well as WD separately or when coupled together decreased the POMC mRNA expression in the pituitary but stimulated adrenal steroidogenic activity. Further, VT2R expression decreased in TE+WD compared to TE group, but it was not different from the vehicle treated control group suggesting that the suppressive effect of WD on VT2R expression was inhibited by the stimulatory effect of testosterone. Similarly, although both TE and WD decreased POMC expression and increased steroidogenic activity, no further decrease or increase in these parameters was observed when these two (WD and TE) treatments were combined together. Although, the exact mechanism is not clear, data indicate a stimulatory action of testosterone on VT2R expression and adrenal function despite a decreased expression of POMC mRNA. Results also suggest that testosterone treatment to sexually immature birds, in addition to its effect on hypothalamic AVT neurons (earlier study) and pituitary VT2R expression (present study), masks or inhibits osmotic stress-induced alterations in pituitary-adrenal activity.

Age-dependent variation in the RFRP-3 neurons is inversely correlated with gonadal activity of mice

The present study analyzed changes in the expression of RFamide-related peptide-3 (RFRP-3; a mammalian ortholog of avian gonadotropin-inhibitory hormone), in the brain and correlated it with testicular activity of mice of different age groups (day-old, 1-, 3-, 5-, 7-, 9-, 11-, 13-week and 1.5-year-old). Testicular activity after a progressive increase up to 13-week of age declined in the old mice. On the other hand, while immunoreactive (ir) RFRP-3 neurons were not seen in the day-old mice, few appeared in 1-week-old mice, their number and size increased drastically at 3-week of age. This condition remained unaltered until 7-week of age followed by a progressive decline up to the age of 13-week and thereafter increased again in the old age. The present findings indicate that hyperactivity of the ir-RFRP-3 neurons of dorsomedial nucleus of hypothalamus (DMH) observed in prepubertal mice declines in reproductively active mice and increases again in the old mice having declined reproductive performance. It is concluded that aging mice exhibits inverse correlation of RFRP-3 neurons and gonadal activity suggesting that function of RFRP-3 is not initiated until 1-week of age and thereafter it could participate in the regulation of gonadal development.

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.

Temporal phase relation of circadian neural oscillations alters RFamide-related peptide-3 and testicular function in the mouse

In order to study the effect of the temporal synergism of neural oscillations on reproductive regulation and the response of RFamide-related peptide-3 (RFRP-3; a mammalian ortholog of avian gonadotropin-inhibitory hormone), expression of immunoreactive RFRP-3 in the neurons of the dorsomedial nucleus of the hypothalamus was monitored in sexually immature and mature laboratory mice (study I). In study II, the effects of serotonin and dopamine precursors (5-hydroxytryptophan and L-dihydroxyphenylalanine; injected daily, 8 or 12 h apart, for 13 days in 3-week-old mice) on testicular activity and immunoreactive RFRP-3 neurons were studied until 24 days after treatment. Results indicate high levels of expression of immunoreactive RFRP-3 in the sexually immature and 8-hour mice (simulating gonadal suppression), while a low level was noted in mature and 12-hour mice (simulating gonadal stimulation). These findings not only suggest the modulation of gonadal development in mice (during the course of puberty attainment) by changing the temporal phase relation of serotonergic and dopaminergic oscillations (as in some seasonally breeding species), but also demonstrate an inverse correlation of RFRP-3 neurons and gonadal activity in both control and experimental conditions.

Effects of thyroid status on arginine vasotocin receptor VT2R expression and adrenal function in osmotically stimulated domestic fowl

The role of thyroid hormones in the regulation of adrenal function during stress has been documented in mammals, but only limited reports are available in avian species. The present study was undertaken to analyze the effect of hyper- or hypothyroidism on the adrenal activity under control (hydrated) and osmotically stressed (water deprived, WD) conditions, with special emphasis on the expression of arginine vasotocin receptor VT2 (VT2R) in pituitary corticotrophs. Chickens were made hyper- or hypothyroidic by injecting thyroxine (T4) and 2-thiouracil (TU), respectively for 14 days. After 10 days of injections, one sub-group of both, T4- or TU-treated chickens were subjected to osmotic stress by water deprivation. Hyperthyroidism stimulated adrenal steroidogenic activity compared to euthyroid control birds, but no change was observed in the expression of VT2R. On the other hand, TU-induced hypothyroidism however showed no effect on adrenal gland, but a significant increase in the expression of VT2R was observed. Neither hyper- nor hypothyroidism altered pro-opiomelanocortin (POMC) mRNA levels. Following osmotic stress, no effect was observed either on the adrenal gland or on the VT2R expression in hyperthyroidic birds, but in hypothyroidic birds, osmotic stress stimulated adrenal steroidogenic activity and decreased VT2R expression in comparison to its respective controls (T4 or TU). Expression of POMC mRNA was again unaltered following osmotic stress. Although exact mechanism is not clear, the data indicate that high plasma T4 level stimulates adrenal activity and may also modulate function of the pituitary-adrenal axis during dehydration.

Reproductive responses and nitric oxide activity in Japanese quail, Coturnix coturnix japonica, are altered by specific phase relationships of neural (serotonergic and dopaminergic) oscillations and pineal function

The present study investigates the effects of temporal synergism of 5-hydroxytryptophan (5-HTP) and L-dihydroxyphenylalanine (L-DOPA) and pineal function (pinealectomy and melatonin administration) on gonadal response and nitric oxide (NO) activity in Japanese quail. Three-week-old male quails were divided into 9 groups, as follows: (I) control (treated with normal saline); (II) 8-h and (III) 12-h (receiving L-DOPA after the administration of 5-HTP [5mg/100g body weight] at the interval of 8 and 12h, respectively, over a period of 13 days); (IV) SO (sham operated); (V) Px (pinealectomized); (VI) Veh (vehicle treated control); (VII) Mel (melatonin 25 microg/100g body weight for 45 days); (VIII) 12-h+Veh; and (IX) 12-h+Mel (same as in (III) but further treated with the vehicle or melatonin, respectively, for 32 days). Body weight and cloacal gland volume were recorded weekly, whereas spermatogenesis, plasma testosterone concentration, and total nitrite and nitrate concentration in plasma, hypothalamus, and testes were measured at the termination of the study. Results indicate that compared to the controls, 8-h, Mel, and 12-h+Mel treatments suppressed whereas 12-h and Px stimulated the reproductive system. Further, a significant increase in plasma testosterone, total nitrite, and nitrate in the 12-h and Px groups and a decrease in these concentrations in 8-h, Mel and 12-h+Mel quail were observed. It is evident that 5-HTP and L-DOPA given at the interval of 8h, as well as melatonin, are potent inhibitors of gonadal development, and the gonado stimulatory effect of the 12-h temporal relationship of the neurotransmitter precursors is masked by the inhibitory effect of melatonin. It is concluded that modulation of the daily phase relationship of neural oscillations and pineal function alters gonadal function and NO activity. Further, NO exhibits a parallel relationship with gonadal function in Japanese quail; this relationship appears to be mediated through NO activity, suggesting a causal relationship, although the mechanism between the 2 systems remains a topic of discussion.

Corticosterone- or metapyrone-induced alterations in adrenal function and expression of the arginine vasotocin receptor VT2 in the pituitary gland of domestic fowl, Gallus gallus

The avian neurohypophyseal hormone arginine vasotocin (AVT) is known to be involved in the regulation of adrenocorticotropin (ACTH) release by interacting with the VT2 receptor (VT2R), which is homologous to the mammalian vasopressin V1b receptor (V1bR). To study the role of glucocorticoid in the expression and regulation of the VT2R, corticosterone (1 or 5mg/bird/day) or metapyrone (10 or 50mg/kg body weight/day) were administered daily for 8 days to white leghorn chickens. While low doses were ineffective, a high dose of corticosterone upregulated, while metapyrone downregulated, pituitary VT2R mRNA expression and ir-VT2 in the cephalic lobe of the anterior pituitary. Further, although no change was observed in the expression of POMC mRNA, adrenal activity (as judged by the changes in total cholesterol, 3beta HSD, cortical cord width and cortico-medullary ratio) exhibited suppression or stimulation following treatment with corticosterone or metapyrone, respectively. In view of the classical negative feedback effect of glucocorticoids at the level of hypothalamic CRH neurons and pituitary corticotrophs, high corticosterone level-induced suppression of the CRH-ACTH axis may have been masked by VT2R-mediated stimulation of corticotrophs, and hence the POMC mRNA level did not change. The same argument could be used for metapyrone. It is concluded that expression of the VT2 receptor is regulated by glucocorticoids in chicken. These findings confirm a role for AVT, mediated by the VT2 receptor, in regulating ACTH secretion during stress and suggest that corticotroph VT2 receptor levels may be dynamically regulated depending on the HPA axis activity.

Osmotic stress induced alteration in the expression of arginine vasotocin receptor VT2 in the pituitary gland and adrenal function of domestic fowl

The role of arginine vasotocin in the regulation of the pituitary-adrenal axis of domestic fowl was analyzed by studying the expression of its recently cloned pituitary receptor VT2 and adrenal activity following osmotic stress. Four days of water deprivation induced an increase in plasma osmolality-a known stimulator of AVT synthesis and release from hypothalamic magnocellular neurons. Water deprivation also decreased pituitary mRNA levels for both the VT2 receptor and for pro-opiomelanocortin (POMC). Despite a decrease in the expression of VT2 mRNA, immunoreactive-VT2 receptor levels in the pituitary increased, suggesting a possible role for post-transcriptional mechanisms in the regulation of this receptor. Further, adrenal activity (as judged by adrenal weight, cholesterol content, 3beta hydroxysteroid dehydrogenase, cortical cord width and cortico-medullary ratio) showed stimulation in water-deprived chicken as compared to control. On the basis of present findings, it is concluded that water deprivation down regulates the mRNA expression of AVT receptor VT2 as well as POMC but stimulates adrenal function. It is also suggested that in addition to the release of magnocellular AVT into the neurohypophysis to act as antidiuretic hormone following water deprivation, AVT may also modulate HPA axis to cope with the osmotic stress.

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

Avian neurohypophysial hormone arginine vasotocin (AVT) is known to regulate shell gland contractility during oviposition. While studying the role of estrogen in the expression and regulation of AVT and its oxytocic-like receptor VT3, using in situ hybridization and immunohistochemistry, it was observed that the expression of AVT and its receptor was not detected in the shell gland of sexually immature Japanese quail. However, administration of estrogen to these birds not only stimulates the growth and activity (as assessed by increased mucosal fold length, total protein content and alkaline phosphatase level) of the shell gland but also upregulates the expression of AVT and VT3. Further, administration of estrogen antagonist tamoxifen to sexually mature bird shows opposite results. On the other hand, localization of ir-AVT, observed in the ovary of sexually mature bird, was not detected in the estrogen treated sexually immature quail. It is concluded that estrogen not only affects the growth and differentiation of avian oviduct, but also regulates the expression of shell gland AVT and its receptor VT3. Present findings suggest that the locally synthesized AVT acts in a paracrine way to upregulate VT3 receptor and thus facilitates the endocrine function of neurohypophysial AVT during oviposition.

Correlation of nitric oxide (NO) activity and gonadal function in Japanese quail, Coturnix coturnix japonica following temporal phase relation of serotonergic and dopaminergic oscillations

Nitric oxide (NO), a highly reactive and short-lived radical, is considered to be an important trigger molecule for several physiological mechanisms including gonadotrophin releasing hormone (GnRH) secretion in mammals, although there is no such information in avian literature. On the other hand, specific temporal phase relation of circadian neural (serotonergic and dopaminergic) oscillations is reported to modulate reproductive activity in many avian species including Japanese quail. The present study was undertaken to investigate the correlation of NO activity and gonadal function of Japanese quail. In experiment I, the effect of serotonin and dopamine precursors, (5-hydroxytryptophan (5-HTP) and L-dihydroxyphenyalanine (L-DOPA) respectively; 5 mg per 100g body weight) administered at intervals of 8 or 12h over a period of 13 days, was studied on reproductive responses and NO activity. Measurements of body weight, cloacal gland size, testosterone concentration, spermatogenesis, nitrite-nitrate concentration in plasma, hypothalamus and testes, and NADPH-diaphorase (NADPH-d) activity in testes were made on the 2nd, 3rd, 6th and 11th days of treatment and 2nd and 30th day post-treatment. In experiment II, quail were divided into five groups including the control. One experimental group received 13 daily injections of 5-HTP and L-DOPA at intervals of 8h along with 0.1 ml of normal saline administered orally (8-hr+Veh), while another group of 8-hr quail received NO donor (sodium nitroprusside (SNP), 5 mg per 100 g body weight) orally (8-hr+SNP). The third experimental group received 5-HTP and L-DOPA at intervals of 12h along with normal saline (12-hr+Veh), while the fourth group of quail along with 5-HTP and L-DOPA at intervals of 12h also received the NOS inhibitor (N-nitro-L-arginine methyl ester, L-NAME, 25 microg per 100 g body weight) intraperitoneally (12-hr+L-NAME) for 13 days. This experiment was terminated after 21 days of the treatment. Results indicate that 5-HTP and L-DOPA administered 8h apart (8-hr) suppressed but if given 12h apart (12-hr) stimulated the reproductive system and NO activity compared to the control. These effects were apparent on the 6th day of injections and were maintained 30 days following the termination of the treatment. A significant decrease in nitrite and nitrate concentration and NADPH-d activity in reproductively inhibited 8-hr group and an increase in reproductively stimulated 12-hr quail was also evident. In contrast, these activities were stimulated in 8-hr+SNP quail and were suppressed in 12-hr+L-NAME group quail. It is concluded that activity of the reproductive system and NO activity waxes and wanes simultaneously in Japanese quail. Moreover, experimental modulation of gonadal activity (following changes in the phase relation of serotonergic and dopaminergic activity) or NO activity (following the administration of NO modulator or inhibitor) affects each other maintaining a parallel relation between the two systems. Further, it is interesting to note that the gonado-stimulatory effect of SNP overpowers the gonado-inhibitory effects of the 8-hr time interval and inhibitory effects of L-NAME mask the stimulatory effects of 12-hr temporal relation of 5-HTP and L-DOPA administration. These findings strongly suggest that reproductive effects may be induced via changes in NO activity, however the exact mechanism by which NO drives gonadal axis needs to be ascertained.

Changes in vasotocin immunoreactivity of paraventricular nuclei and adrenal function of Japanese quail in relation to different phases of sexual development

In relevance to osmoregulatory and reproductive functions, activity of hypothalamic neurosecretory neurons may also vary seasonally. The current study was performed to determine annual changes in ir-AVT neurons of hypothalamus and adrenal gland function. We examined changes in ir-AVT neuron by immunohistochemical method and plasma testosterone was measured by enzyme immunoassay. The steroidogenic interrenal activity was studied by histological and biochemical methods. Birds were sampled in February (quiescent), April (recrudescent), June (breeding) and November (regressive). A significant and gradual increase in the number of ir-AVT neurons was observed from quiescent to breeding phase which decreased during regressive phase of annual gonadal cycle. The gradual increase in ir-AVT neurons along with annual gonadal activity of quail were accompanied by increase in plasma levels of testosterone. These results indicate a functional interaction between sex steroid and AVT synthesizing neurons. Adrenal activity (as judged by weight, ascorbic acid content, cortical cord width and cortico-medullary ratio) was also maximum during breeding phase. It is thus postulated that domesticated quail when exposed to natural day length (NDL), exhibits seasonal/annual cyclicity in vastocinergic activity and adrenal function which may be due to difference in sex steroid hormone.

Effect of photoperiod and estrogen on expression of arginine vasotocin and its oxytocic-like receptor in the shell gland of the Japanese quail

The avian neurohypophysial hormone arginine vasotocin (AVT) is an important regulatory hormone involved in many physiological processes including fluid balance, blood pressure regulation, stress responses and reproductive events including oviposition. The mechanisms by which AVT stimulates myometrial contraction during oviposition are not well established in birds. In the present study, immunohistochemistry and in situ hybridization were used to localize AVT and the oxytocin-like VT3 receptor in the shell gland of Japanese quail (Coturnix coturnix japonica). Using an AVT-specific antibody, immunoreactive AVT (ir-AVT) was observed in the myometrium of both photosensitive and photorefractory birds. Similarly, VT3 receptor gene transcripts were detected in the myometrial layer of the shell gland of both photosensitive and photorefractory birds. Body mass, shell gland mass and length of mucosal folds of the shell gland of photosensitive birds was higher compared to that of photorefractory birds. Treatment of photorefractory birds with estrogen increased shell gland activity (mass and length of mucosal folds) and levels of both AVT and VT3 receptor mRNA, whereas treatment of photosensitive birds with the estrogen antagonist tamoxifen decreased shell gland activity and levels of both AVT and VT3 receptor mRNA. Our results suggest that shell gland contractility in response to AVT may be regulated during the reproductive cycle of the Japanese quail and that, in part, this regulation is estrogen-dependent.

Tissue localization of collagenase and leucine aminopeptidase in the bovine filarial parasite Setaria cervi

BACKGROUND

Like other helminth proteases, filarial proteases have also been shown to require for parasite survival inside the host and mediate various physiologic processes such as tissue invasion, feeding, embryogenesis and host immune evasion. Many of these proteases have shown potential for vaccines and chemotherapeutic agents against active filarial infections. Setaria cervi is a bovine filarial parasite and serves as a good parasite model for the studies in lymphatic filariasis. Recently, a 175 kDa collagenase and leucine aminopeptidase (LAP) have been purified and characterized from the bovine filarial parasite S. cervi and shown to be potential vaccine candidate and diagnostic marker, respectively for human lymphatic filariasis. However, their tissue localizations and putative roles in the parasite biology have not yet been examined and thus remain unclear. Therefore, the current study attempts to localize and explore the putative roles of these two enzymes in S. cervi.

METHODS

The tissue distributions of 175 kDa collagenase and leucine aminopeptidase in S. cervi were examined by immunohistochemical and histochemical methods, respectively. Immune sera obtained from the jirds immunized with collagenase served as primary antibody, rabbit anti-mouse IgG-HRP conjugate as secondary antibody and DAB as the substrate for the immunostaining of collagenase. Leu-betaNA was used as the substrate for the histochemical staining of LAP.

RESULTS

Both the collagenase and LAP were present in the body wall; however, they differ in their distribution pattern in different layers of body wall. Collagenase was mainly localized in epicuticle, cuticle, syncytial hypodermis and the nerve cord region whereas LAP was more concentrated in epicuticle, longitudinal muscle layers and almost absent or very faintly stained in syncytial hypodermis and nerve cord region. Both collagenase and LAP showed their common distributions in intestine, uterus and mature eggs, growing embryos and mf. Very strong immunostaining of collagenase in the outer body surface of the parasite indicates its major role in host-parasite relationship whereas the presence of LAP in muscular region suggests its role in tissue remodeling. The common presences of collagenase and LAP in the S. cervi intestine, ovary, uterus, eggs and mf suggest that they also have collaborative roles in molting, nutrition and embryogenesis. The data obtained on their immunological characterizations and their presence in important parasite organs give strong indication that they are critical for the survival of filarial parasite and thus can be good vaccine candidates and/or diagnostic markers for human lymphatic filariasis.

CONCLUSION

The manuscript reports for the first time the tissue distribution of collagenase and LAP in the bovine filarial parasite S. cervi and discuss their putative roles in vivo. Our findings also open the avenue to examine the roles of these two proteases in vivo, which will require further experiments like using their natural substrates and/or specific inhibitors in each tissues.

Effect of long and short photoperiod on vasotocin neurons of paraventricular nuclei and adrenal function of water deprived Japanese quail

The responses of magnocellular neurons of paraventricular nuclei (PVN) and changes to adrenal activity to water deprivation in Japanese quail maintained under gonado-inhibitory and stimulatory photoperiods were examined. Water deprivation of 4 days resulted in a 12% decrease in body weight of sexually regressed short day (SD, 6L:18D) quail, while the decrease was more (18%) in sexually stimulated long day (LD, 16L:8D) quail. The increase in plasma osmolality following water deprivation was also more (47%) in LD than to SD quail (36%). Under the LD condition, quail had increased numbers, sizes and immunostaining of ir-AVT neurons of PVN compared to SD condition. A significant increase in the number of ir-AVT neurons was observed following 4 days of water deprivation in both SD and LD quail compared to their respective fully hydrated controls. However, the degree of response was more under the LD compared to the SD condition suggesting that gonado-stimulatory long days increase the activity/response of the AVT system. Increased adrenal ascorbic acid content (i.e., activity) was also observed to quail of LD when compared to SD treatment. However, osmotic stress led to adrenal hypertrophy and hyperactivity of quail of both of the photoperiodic regimes. Our findings indicate that not only osmotic stress but also photo-gonadal stimulation upregulates the expression of hypothalamic AVT genes and increases the localization of ir-AVT in many neurons of PVN. The above results support the existence of a parallel adrenal-gonad relationship and increase in adrenal function during osmotic stress, which also leads to simultaneous increase in AVT system. We conclude that photo-sexual conditions alter hypothalamic vasotocinergic and adrenal activity in Japanese quail and the degree of stimulation of the two systems following osmotic stress is higher under gonado-stimulatory LD conditions.

Effect of temporal synergism of neural oscillations on photorefractoriness in Japanese Quail (Coturnix Coturnix Japonica)

Circadian rhythms in many metabolic functions including neural (transmitters) and hormonal secretion appear to change with physiological condition. It is also reported that seasonal changes in photoperiodism/reproduction and other metabolic conditions may result from a temporal interaction of circadian neural oscillations that change seasonally. To test this hypothesis, the present study was designed to study the effect of temporal synergism of two neural oscillations (serotonin and dopamine) on relative photorefractoriness of Japanese quail. Serotonin and dopamine precursor drugs (5-HTP, 5-hydroxytryptophan and L-DOPA, L-dihydroxyphenylalanine) were administered (intraperitonially 5 mg/100 g body weight) at six different time intervals of 0, 4, 8, 12, 16 and 20 hr in sexually mature quail (>12 weeks old). The birds of control group received two daily injections of normal saline. The treatment was given for 13 days in continuous condition of light and then the quail were shifted to intermediate daylength (LD 13.5:10.5 for experiment 1) and short daylength (LD 8:16 for experiment 2). Six weeks following treatment, birds in intermediate daylength showed regressed cloacal gland and testicular activity except in 12-hr group, which exhibited gonadostimulatory condition. But birds of all the groups in short daylength showed complete regression of cloacal gland after 4 weeks of the treatment. In experiment 3, reproductively quiescent relative photorefractory quail maintained under intermediate daylength (LD 13.5:10.5) received 13 daily injections of 5-HTP and L-DOPA at the interval of 12 hr. At 6 weeks post-treatment, it was observed that unlike cloacal gland of control quail, which remained regressed, that of 12-hr quail showed significant development. These findings indicate that 12-hr temporal interaction of 5-HTP and L-DOPA administration maintained reproductive system in stimulated condition and prevented reproductive regression in photorefractory quail, but did not prevent the onset of scotosensitivity. It is concluded that the 12-hr temporal relationship of circadian serotonergic and dopaminergic oscillations not only eliminates photorefractoriness but may also re-establish photosensitivity in relative photorefractory quail. These findings suggest the regulatory role of neural oscillations and their temporal interaction in the regulation of neuroendocrine-gonadal axis with special reference to photosensitivity/refractoriness.

Expression of hypothalamic arginine vasotocin gene in response to water deprivation and sex steroid administration in female Japanese quail

Arginine vasotocin (AVT) is a neurohypophyseal hormone involved in reproductive function and control of osmoregulation in birds. In view of the dual function of AVT, the present experiment was designed to observe the effect of water deprivation (WD) and sex steroid [estradiol benzoate (EB) and testosterone propionate (TP)] treatment independently, as well as simultaneously, on the profile/activity of the hypothalamic AVT system. WD resulted in a significant increase in plasma osmolality, sodium ion concentration and AVT concentration, but administration of sex steroids had no significant influence on these parameters. By contrast, the amount of hypothalamic AVT transcript (northern analysis) and the size of immunoreactive vasotocin (ir-AVT) neurons and hybridization signals (in the form of silver grains), representing AVT mRNA in corresponding neurons of paraventricular nuclei (PVN), increased significantly in all the treated groups compared with controls. Our findings indicate that although sex steroid administration has no effect on plasma osmolality and AVT concentration, unlike water deprivation, it may stimulate the profile/activity of AVT neurons of PVN,supporting the possibility of sex steroid receptors on these neurons. It is concluded that in quail, osmotic stress not only upregulates the expression of the AVT gene in existing neurons but also recruits many more neurons to increase the rate of AVT synthesis and secretion, while sex steroids appear to have a stimulatory effect only on the existing number of neurons and only at the level of transcription/translation and hence may influence/modulate hypothalamic AVT gene expression in response to osmotic stress. This study also suggests an interrelationship between reproduction and AVT system/function in birds.

Changes in expression of AVT and AVT receptor (VT1) gene in hypothalamus and shell gland in relation to egg laying in white leghorn hen

Oviposition is a complex phenomenon involving various regulatory mechanisms at the neuroendocrine levels. Present study was designed to access the changes in arginine vasotocin (AVT) and its receptor (VT1) gene expression in relation to the time of egg laying of white leghorn hen. The expression of AVT gene (Northern blot analysis and in situ hybridization) in the hypothalamus and localization of ir-AVT in the magnocellular neurons of paraventricular nuclei was studied 2 h before (-2 h), immediately after (0 h) and 2 h after (+2 h) egg laying. Simultaneous changes in the AVT and VT1 receptor gene in the shell gland, which finally responds to AVT for smooth muscle contraction and expulsion of egg, were also determined by semi-quantitative reverse transcriptase-polymerase chain reaction. The findings indicated increased hypothalamic AVT gene expression immediately after egg laying (0 h) when compared to 2 h before and 2 h after egg laying. AVT receptor gene expression in the shell gland also followed the same pattern. However, AVT gene expression in the shell gland, unlike that of hypothalamus was higher at -2 h compared to 0 and +2 h of oviposition. While highly significant increase was noted in plasma AVT concentration at the time of egg laying, other parameters such as plasma osmolality and ionic concentration (Na(+), K(+), Ca(2+), and Cl(-)) did not show any change. It is suggested that in addition to increased hypothalamic AVT transcript and peripheral release, local synthesis of AVT in the shell gland (paracrine release) may contribute to the contraction of shell gland smooth muscles during egg laying. Moreover, these findings clearly indicate temporal correlation of AVT and its receptor gene expression in different tissues during oviposition.

Water deprivation and circadian changes in plasma arginine vasotocin and mesotocin in the domestic hen (Gallus domesticus)

Possible circadian variations in plasma levels of arginine vasotocin (AVT) and mesotocin (MT) were assessed in domestic hens (Gallus domesticus) under a 12h:12h light-dark (LD) schedule. Blood samples were taken at 4h intervals, and neurohypophyseal hormone levels were determined by radioimmunoassay. Marked circadian changes in both AVT and MT were observed in hens provided free access to water. Minimal and maximal AVT levels occurred at 08:00 and 20:00, respectively. Minimal MT levels occurred at 20:00, whereas maximal MT levels occurred over a broad time period of 04:00 to 12:00. In water-deprived hens, plasma AVT levels were elevated at each time point, and the circadian variations in plasma AVT and MT levels were attenuated. These results demonstrate that rhythmicity in neurohypophyseal function in a lower vertebrate species, like that in mammals, is disrupted by osmotic stress.

Involvement of adrenal and thyroid activity in the annual testicular regression of red headed bunting (Emberiza bruniceps)

Thyroid and adrenal activities are closely associated with reproductive cycle and any alteration in these endocrine functions may cause changes in the pituitary-gonadal axis. To understand this interrelationship during testicular senstive phase (month of April) male birds were injected with metapyrone(corticosterone synthesis blocks 1 microg/bird/day & 10 microg/bird/day) and newmercazol (thyroxine synthesis blocks 10 microg/bird/day) over a period of 12 weeks. During late breeding phase (month of August) two sets of birds having large gonad (photosensitive) and regressed gonad (photorefractory) were injected with metapyrone (10 microg/bird/alternate day). Results indicate that decreased activity of both adrenal and thyroid, extended the breeding phase but rate of regression decreased only in the case of bird receiving higher level of metapyrone.However,in the second group rate of gonadal regression was slow only in those bird where treatment was started during photosensitive phase. It may be suggested that optimum level of activity of adrenal and thyroid function are essential for termination of reproduction and any alteration in these function may alter seasonal pattern of neuroendocrine gonadal axis.

A sexual dimorphism in hypothalamic arginine vasotocin (AVT) gene expression and AVT plasma levels in the Japanese quail (Coturnix coturnix japonica) in response to water deprivation

To examine a possible sexual dimorphism in the osmotic control of arginine vasotocin (AVT) release in birds, age-matched male and female Japanese quail were subjected to water deprivation. The observed increased plasma osmolalities were accompanied by increased plasma AVT levels. Plasma mesotocin levels did not change with water deprivation. The sensitivity of the osmotic control of AVT release as determined by the slope of the relationship between plasma AVT levels and plasma osmolalities was significantly (P < 0.05) higher in males than in females. By Northern blot analysis, levels of hypothalamic AVT gene transcripts were increased 2.3 +/- 0.14- and 3.5 +/- 0.13-fold in water-deprived male and female Japanese quail, respectively, compared to normally hydrated birds. Our data suggest gender-related differences in the osmotic control of AVT release and in hypothalamic AVT gene expression in the Japanese quail.

Effect of gonadotrophin and sex steroid on the scotoresponses of day old chicks of Japanese quail, Coturnix coturnix japonica

Luteinizing hormone (LH) and testosterone propionate (TP) were tested for their effects on the development of scotorefractoriness in Japanese quail. Day old chicks of both the sexes were divided into four groups and treated with normal saline, LH (1 microg/100 g body weight) and two doses of TP (100 microg/100 g body weight- TP1 and 1 mg/100 gm body weight- TP2) over a periods of 14 weeks. In the male chicks, compared to control, LH treatment advanced and low dose of TP suppressed the development of scotorefractoriness, while high dose of TP inhibited it completely and maintained the birds in scotosensitive state. On the other hand, in females, LH treatment increased the rate of sexual development resulting in the onset of egg laying earlier than that of control, but both the doses of steroid hormone suppressed ovarian development. It is suggested that, LH treatment not only induced a higher degree of reproductive development in short day quail but may also advance sexual maturity as under long daylength. Further, both the doses of male hormone had negative feedback effect on neuroendocrine axis and eliminated the attainment of scotorefractoriness i.e., reproductive development under short days.

Arginine vasotocin gene expression in hypothalamic neurons is up-regulated in chickens drinking hypertonic saline: an in situ hybridization study

Osmotic stress stimulates the release of the avian hypothalamic neuropeptide arginine vasotocin (AVT) into the peripheral circulation. We conducted the present study to investigate the effects of salt-loading on AVT secretion and AVT gene expression in specific hypothalamic nuclei in chickens. White Leghorn chickens were provided food ad lib and either water or 2% NaCl to drink. Both plasma osmolality and plasma AVT levels were significantly increased in chickens that drank 2% NaCl for either two or four days compared to that in chickens that drank water. Results from in situ hybridization analysis demonstrated an increase in the number of neurons expressing AVT mRNA in the supraoptic (SON) and paraventricular nuclei (PVN) in chickens provided 2% NaCl to drink compared to chickens that were provided water to drink. The number of grains per neuron increased in the PVN, but not in the SON of osmotically stimulated birds. Thus, increased osmolality resulting from ingestion of hypertonic saline is an effective stimulus to increase hypothalamic AVT mRNA content in chickens.