Browsing by Author "C.M. Chaturvedi"

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2.45-GHz microwave irradiation adversely affects reproductive function in male mouse, Mus musculus by inducing oxidative and nitrosative stress
(Informa Healthcare, 2014) S. Shahin; V. Mishra; S.P. Singh; C.M. Chaturvedi
Electromagnetic radiations are reported to produce long-term and short-term biological effects, which are of great concern to human health due to increasing use of devices emitting EMR especially microwave (MW) radiation in our daily life. In view of the unavoidable use of MW emitting devices (microwaves oven, mobile phones, Wi-Fi, etc.) and their harmful effects on biological system, it was thought worthwhile to investigate the long-term effects of low-level MW irradiation on the reproductive function of male Swiss strain mice and its mechanism of action. Twelve-week-old mice were exposed to non-thermal low-level 2.45-GHz MW radiation (CW for 2 h/day for 30 days, power density = 0.029812 mW/cm2 and SAR = 0.018 W/Kg). Sperm count and sperm viability test were done as well as vital organs were processed to study different stress parameters. Plasma was used for testosterone and testis for 3β HSD assay. Immunohistochemistry of 3β HSD and nitric oxide synthase (i-NOS) was also performed in testis. We observed that MW irradiation induced a significant decrease in sperm count and sperm viability along with the decrease in seminiferous tubule diameter and degeneration of seminiferous tubules. Reduction in testicular 3β HSD activity and plasma testosterone levels was also noted in the exposed group of mice. Increased expression of testicular i-NOS was observed in the MW-irradiated group of mice. Further, these adverse reproductive effects suggest that chronic exposure to nonionizing MW radiation may lead to infertility via free radical species-mediated pathway. © 2014 Informa UK, Ltd.
Changes in expression of AVT and AVT receptor (VT1) gene in hypothalamus and shell gland in relation to egg laying in white leghorn hen
(Academic Press Inc., 2004) R. Seth; Y.X. Xu; R. Grossmann; C.M. Chaturvedi
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 2h before (-2h), immediately after (0h) and 2h after (+2h) 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 (0h) when compared to 2h before and 2h 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 -2h compared to 0 and +2h 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. © 2004 Elsevier Inc. All rights reserved.
Effect of melatonin on the adrenal and gonad of the common mynah, acridotheres tristis
(1984) C.M. Chaturvedi
Exogenous intraperitoneal administration of melatonin (10 μg per day for 30 days) during peak activity phase of the annual reproductive cycle caused atrophy of the adrenal and gonad in the common mynah, Acridotheres tristis. The adrenal activity was assessed by weight, histology, cortical cord width, cortico-medullary ratio and total cholesterol content; the gonadal activity by weight, histology, cytometric measurements (seminiferous tubule, Leydig cell nuclei and follicular diameter) and total cholesterol content. Single injection of 300 and 600 μg melatonin suppressed the activity of the adrenal as well as the gonad via the neuro-endocrine complex to the same extent as did the daily injections. The present study suggests that melatonin may influence the adrenal and the reproduction of seasonally breeding subtropical common mynahs, although in birds the extent and nature of melatonin control is not yet clear. © 1984 CSIRO.
Effect of photoperiod in the regulation of the annual testicular cycle of a subtropical mammal, the Indian palm squirrel, Funambulus pennanti.
(1995) A.B. Singh; C.M. Chaturvedi
In seasonally breeding subtropical mammal, the Indian palm squirrel (Funambulus pennanti), reproductive recrudescence is initiated before the winter solstice followed by sexually active condition which extends until the end of summer season. Onset of seasonal regression coincides with the annual decrease in daily photoperiod and the increased level of relative humidity resulting from the arrival of monsoon at this latitude. To test the photoperiodic responses, three groups of squirrels were exposed to natural day length (NDL), long day length (LD 15:9), and short day length (LD 6:18) over a period of one year beginning from March. Squirrels of all these groups were exposed to similar ambient temperature and humidity conditions. Initially, the rate of testicular development was similar in control and long day squirrels attaining peak values in May (0.67 cm3) and June (0.7 cm3) respectively. Thereafter, while the gonads of controls regressed, the latter maintained a plateau. On the other hand, the gonads of short day squirrels regressed sharply until June (0.21 cm3) followed by spontaneous recrudescence and finally a plateau (0.55 cm3). These results indicate that initially squirrels are photosensitive (as long days are gonadostimulatory and short days are inhibitory) in the first half of summer season but eventually become refractory to the inhibitory effect of short days. Obviously, an acyclic condition is developed under constant long as well short day conditions maintaining the neuroendocrine-gonadal-axis in a continuously active state. We suggest that in nature although gonadal growth of this species does not synchronize with the increase in daily photoperiod, it is partially regulated by an interplay of annual photocycle and humidity conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of temporal synergism of neural oscillations on photorefractoriness in Japanese quail (Coturnix Coturnix japonica)
(2006) C.M. Chaturvedi; A.C. Tiwari; P. Kumar
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 snowed 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. © 2005 Wiley-Liss, Inc.
Effect of timed administration of neurotransmitter precursor drugs on testicular activity, body weight and plumage pigmentation in the lal munia Estrilda amandava
(1994) C.M. Chaturvedi; R. Bhatt; S.K. Prasad
Daily injections of L-dihydroxyphenylalanine (L-DOPA, a dopamine precursor) given 12 hr after 5-hydroxytryptophan (5-HTP, a serotonin precursor) during quiescent and progressive phase of annual breeding cycle induced testicular growth, body weight gain and nuptial plumage in autumn breeding sedentary finch E. amandava which exhibits parallel gonadal and body weight cycle. Daily injection of these drugs when given 8 hr apart during progressive phase led to opposite effects in all parameters (testicular growth, body weight and nuptial plumage). Results indicate that 12 hr and 8 hr relationship of neurotransmitter precursor drugs (5HTP and L-DOPA) might have stimulated/inhibited the activity of neuroendocrine-gonadal axis. The findings support the hypothesis that specific phase relation of circadian serotonergic and dopaminergic oscillations account for seasonal reproductive function in lal munia.
Effects of corticosterone, metapyrone, and ACTH on testicular function at different stages of the breeding cycle in migratory redheaded bunting, Emberiza bruniceps
(1990) C.M. Chaturvedi; P.K. Suresh
To study the seasonal reproductive responses, corticosterone (0.2 and 2 μg/day), metapyrone (0.6 mg/day), and ACTH (0.25 IU/day) were administered in male redheaded bunting, Emberiza bruniceps, during different phases of the annual gonadal cycle. All of the three treatments inhibited gonadal growth during the preparatory phase, suggesting that during the early stage of annual gonadal growth, an optimum level of the hormones of pituitary-adrenal axis is essential. In the progressive and breeding phase, while corticosterone administration had no effect, metapyrone inhibited the annual gonadal development, suggesting the necessity of increasing or increased adrenal steroid hormone during this phase. In the regressive phase, while corticosterone enhanced the rate of gonadal regression, metapyrone treatment did not allow the gonad to regress. Further, ACTH administration induced full breeding condition in the regressing gonad. It is suggested that while a higher level of adrenal steroids and a low ACTH (by exogenous corticosterone) may enhance the testicular regression, moderate levels of ACTH (caused by exogenous metapyrone) did not allow regression and increased ACTH levels (by exogenous ACTH) caused full development of the regressing gonad. Thus the sensitivity of the neuroendocrine-gonadal axis not only varies in response to photoperiod, but the reproductive system also responds differently to pharmacological administration of the above three hormones and drugs during different phases of the breeding cycle. © 1990.
Effects of orchidectomy and male hormone administration on the adrenal of common myna, Acridotheres tristis
(1978) C.M. Chaturvedi; J.P. Thapliyal
[No abstract available]
Effects of specific phase relation of serotonergic and dopaminergic drugs on the annual reproductive cycle of spotted munia, Lonchura punctulata
(Triveni Enterprises, 1998) S.K. Prasad; C.M. Chaturvedi
A study of the temporal synergism of serotonergic and dopaminergic drugs in the regulation of seasonality of Indian wild finch, spotted Munia was undertaken. Results indicate that specific phase relationships of serotonergic and dopaminergic activities induced specific seasonal conditions and has similar effect in all the four phases of reproductive cycle. 8-hr temporal relation always induced suppression of increasing or increased gonadal activity. On the other hand, 12-hr relation induced early recrudescence in quiescent phase, increased the rate of growth in progressive phase, maintained higher degree of development in breeding phase and the regression was completely eliminated in postreproductive regressive phase. Body weight also responded in the same way suggesting that these two temporal relationship did not produce any direct effect on the gonad. But, actually affected seasonality of the bird i.e. inducing concurrent increases or decrease in body weight and gonadal growth as occurs in nature (parallel relationship between gonad and body weight cycle) during different phases of annual cycle.
Effects of thyroidectomy and replacement therapy on the adrenal and testis of the bird Myna, Acridotheres tristis
(1976) J.P. Thapliyal; C.M. Chaturvedi
Thyroidectomy in Myna, Acridotheres tristis, increased the levels of cholesterol, ascorbic acid and decreased the activity of the adrenal. The size and activity of the testis also decreased following thyroid removal. The weight of the two glands and activity of testis was not affected by 0.25 mg of l-thyroxine. The chemical and histological changes of the adrenal were however reversed. It is suggested that thyroid deficiency leads to reduced output of the trophic hormones from the adenohypophysis of the bird resulting in decreased size and activity of the gonad and of the adrenal.
Elimination of testicular regression by 12-hr temporal relationship of serotonergic and dopaminergic activity in Indian Palm Squirrel, Funambulus pennanti
(Springer-Verlag, 1991) R. Jaiwal; C.M. Chaturvedi
Specific temporal relationship (12-hr) of serotonin and dopamine activity was induced by precursor drugs (5-HTP and L-DOPA) in Indian Palm Squirrel Funambulus pennanti during testicular regression phase. This treatment established breeding condition unlike control, which experienced complete atrophy of testes and accessory sex organs. It is obvious that seasonal testicular regression of Indian Palm Squirrel can be eliminated by 12hr relation of 5-HTP and L-DOPA, which is not a pharmacological effect but actually is an alteration of seasonality in this annually breeding subtropical mammal. It may be concluded that specific phase relation (12-hr) between circadian serotonergic and dopaminergic oscillations may induce breeding condition in regressing gonad of Indian Palm Squirrel during post-reproductive phase of annual gonadal cycle. It is also suggested that inspite of the different environmental factors (photoperiod, humidity etc.) used by different species to time their annual reproduction, basic regulatory mechanism of seasonality appears to be the same, i.e., temporal synergism of neurotransmitter activity. © 1991 Springer-Verlag.
Expression of hypothalamic arginine vasotocin gene in response to water deprivation and sex steroid administration in female Japanese quail
(2004) R. Seth; A. Köhler; R. Grossmann; C.M. Chaturvedi
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.
Functional maturation of neuroendocrine gonadal axis is altered by specific phase relations of circadian neurotransmitter activity in Japanese quail.
(1995) D. Phillips; C.M. Chaturvedi
The present study was designed to ascertain the effects of temporal relationship of circadian neural oscillations on puberty attainment and reproductive growth of Japanese Quail, Coturnix coturnix japonica. Serotonin and dopamine precursors (5-hydroxytryptophan, 5-HTP and L-dihydroxyphenylalanine, L-DOPA; 5 mg/100 g body weight) were injected daily, 8 and 12 h apart in two groups of one-day old chicks, while controls received two daily injections of normal saline. Weekly/biweekly observations (body weight, cloacal gland size, testicular volume and activity, ovarian follicular diameter and rate of egg production) were made until 9 weeks of age, when the experiment was terminated. Results indicate that 8 h relationship completely suppressed gonadal growth even under long photoperiod (LD 16:8), while a 12 h relationship induced precocious sexual maturity and increased the rate of reproduction (spermatogenesis and egg production). It is concluded that circadian phase relationship of serotonergic and dopaminergic activity may not only determine the onset of reproduction in this poultry species, but may also alter the rate of reproduction possibly by affecting photoperiodic mechanism of reproductive regulation.
Influence of different photoperiods on development of gonad, cloacal gland and circulating thyroid hormones in male Japanese quail Coturnix coturnix japonica.
(1992) C.M. Chaturvedi; L. Dubey; D. Phillips
One day old chicks of Japanese quail were exposed to different photoperiods (LD, 8:16, 13.5:10.5, 16:8 and LL) and observations (testes weight, cloacal gland size, body weight and circulating thyroxine and triiodothyronine) were taken at the age of 3, 5, 7, 9 and 16 weeks. Results indicate that immediate reproductive development occurred in birds exposed to long photoperiods (greater than 12 hr). Growth under LD 8:16, was not apparent till 7th week and by 16 weeks, degree of gonadal development was similar in all the birds, irrespective of photoperiodic treatment. Whereas body weight of the intermediate and long day (LD 13.5:10.5, 16:8 and LL) treated birds increased upto 5th week and remained constant thereafter. But the chicks maintained under short day length (LD 8:16), showed spontaneous increase till the end of the study and birds were much heavier compared to all other groups. Plasma T4 concentration increased with increasing age till 9th week and remained unaltered thereafter. On the other hand T3 level did not change till 7th week followed by a decline. It is suggested that the initiation and degree of gonadal growth in quail depends on the availability of daily photoperiod, until the achievement of full breeding condition. Peak level of T4 observed in 9 week old birds may be involved in the development of photorefractoriness at that age.
Interaction of cyproterone acetate and photoperiod in regulation of gonadal development and body fat of the red headed bunting Emberiza bruniceps
(1987) P.K. Suresh; C.M. Chaturvedi
[No abstract available]
Light responses of thyroidectomized Common Myna Acridotheres tristis
(1980) C.M. Chaturvedi; J.P. Thapliyal
Under normal day length, the gonads of thyroidectomized Common Myna, Acridotheres tristis, decreased and those of sham-operated Common Myna increased significantly. Long photoperiod (15L:9D) stimulated and short photoperiod (6L:18D) inhibited the development of gonad of sham-operated and thyroidectomized birds. It is suggested that, while thyroidectomy had an inhibitory influence, long photoperiod stimulated the hypothalamo-hypophyseal-gonadal axis of athyroidic birds. © 1980, All rights reserved.
Phase relation of neurotransmitter affecting drugs (5-HTP and L-DOPA) alters photo-sexual response (scotosensitive and scotorefractory) in Japanese quail
(Triveni Enterprises, 1998) Renu Bhatt; C.M. Chaturvedi
To understand the effect of temporal phase relation of circadian serotonergic and dopaminergic activity on the short day (LD 6 : 18) response of Japanese quail, 5-hydroxytryptophan (Serotonin precursor, 5-HTP) and L- dihydroxyphenylalanine (Dopamine precursor, L-DOPA) were administered daily in six different relationships (0, 4, 8, 12 16 and 20hr). After the initial period of sexual quiescence (Scotosensitivity), quail of the control as well as all the treated groups exhibited sexual development i.e. scotorefractoriness (increase in gonadal activity and cloacal gland size). Thereafter, while quail of 0 and 4hr groups remained reproductively stimulated other groups showed regression. Obviously 0 and 4 hr relation between the administration of two neurotransmitter precursor drugs eliminated reoccurrence of scotosensitivity and maintained continuous breeding condition (scotorefractoriness). These findings suggest that Japanese quail exhibits gonadal cyclicity even under constant short days and this endogenous cycle may be altered by specific phase relation of circadian serotonergic and dopaminergic activities.
Photoperiodism in Japanese quail (Coturnix coturnix japonica) with special reference to relative refractoriness.
(1993) C.M. Chaturvedi; R. Bhatt; D. Phillips
Cloacal gland (an androgen dependent sex accessory) of Japanese quail exhibits full breeding condition as long as these were maintained under long days (LD 16:8). When shifted to short daylength (LD 6:18), scotosensitivity (cloacal gland regression) was observed up to 5 weeks, followed by scotorefractoriness (cloacal gland development). There was a regression in cloacal gland volume of the birds when shifted to intermediate daylength (LD 13.5:10.5 and 13:11) after 12 weeks of exposure to long days (relative refractoriness) but no regression when shifted to relatively short days (< 14 hr) after 3 weeks of exposure to long daylength. Birds maintained under constant short photoperiod (LD 6:18) exhibited cyclicity. Shift experiments (quail reared and maintained under continuous light; LL, were shifted to LD 16:8, 13:11 and 8:16, similarly quail maintained under LD 16:8 were shifted to rest three photoperiods and so on) made to compare the cloacal gland responses indicated that if the difference between two photoperiods (previous and shifted one) was more the percentage of difference in cloacal gland response was also high. Short daylength (LD 8:16) was always gonadoinhibitory for the quail previously exposed to any daylength (13L, 16L or 24L) and 16L and 24L were always stimulatory for the quail previously exposed to other daylength (8L, 13L, 16L). But, when the birds were shifted to 13L, photoresponses cannot be generalized and it depends on the photoperiod to which quail were exposed previously (i.e. photoperiodic history).
Regulation of seasonal reproduction by neurotransmitter affecting drugs in spotted munia, Lonchura punctulata
(2003) S.K. Prasad; C.M. Chaturvedi
Timed daily injection of serotonin precursor, 5-HTP (5-Hydroxytryotophan) and dopamine precursor, L-DOPA (Dihydroxyphenylalanine) determine seasonality in wild finch spotted munia. Lonchura punctulata, which does not utilize photoperiod to tune their seasonal reproduction. These effects are due to serotonergic and dopanunergic activities and not due to serotomn and dopamine alone. Further, L-DOPA was effective when converted into dopamine and not into nor-adrenaline or adrenaline, the next biosynthetic product of dopamine. The findings suggest that seasonal changes in the reproductive functions may be related to seasonal changes in the phase relationship between daily rhythms in serotonergic and dopaininergic activity in the central nervous system.
Reproductive phase dependent circadian variation in hypothalamic concentration of serotonin, dopamine and peripheral thyroxine levels in Japanese Quail following 5-HTP and L-DOPA administration at specific time intervals
(2006) A.C. Tiwari; P. Kumar; S. Singh; D. Sharma; C.M. Chaturvedi
Temporal phase relations of circadian hypothalamic neurotransmitters are reported to regulate seasonal reproduction in some avian species. Present experiments were designed to study circadian variation in the hypothalamic concentration of neurotransmitters (serotonin and dopamine) and the plasma thyroxine level in sexually active (long day) and inactive (short day) Japanese Quail. A significant circadian cycle was noted in the hypothalamic content of both serotonin and dopamine, but with different patterns. In breeding Quail, peak activity of serotonin and dopamine was noted at 10.00 A.M. and 10.00 P.M. respectively i.e. at the interval of 12 hours. However, during sexually quiescent condition, peaks of both neurotransmitters occurred at 2.00 P.M. i.e. having a 0-hour temporal relationship. During the breeding phase, the plasma thyroxine level showed a biphasic pattern with two circadian peaks at 10.00 A.M. and 10.00 P.M. whereas in the non-breeding condition a single peak was observed at 10.00 A.M. In the second experiment, to study the effect of temporal synergism of neurotransmitter precursor drugs on circadian cycles, two groups of Quail were administered daily with serotonin precursor 5-HTP (5-hydroxytryptophan) and dopamine precursor L-DOPA (L-dihydroxyphenylalanine) (5mg/100g body weight) 12 hour (12-hr) and 8 hour (8-hr) apart over a period of 11 days under continuous conditions of light and then transferred to long day length for 15 days when the experiment was terminated. When compared to controls, the 12-hr condition induced breeding while the 8-hr condition led to a non-breeding condition. The circadian pattern of serotonin levels of control and 12-hr Quail was similar to that of a normal sexually active bird, while that of the 8-hr Quail showed the pattern of a sexually inactive bird. The plasma thyroxine level exhibited a biphasic pattern in 12-hr Quail, which was similar to a normally breeding bird, whereas unlike sexually inactive birds, the thyroxine concentration in 8-hr Quail was relatively low and did not show significant cyclicity. Interestingly, the plasma testosterone level of 12-hr Quail followed a more or less similar pattern with peak activities coinciding with that of thyroxine i.e. biphasic in the sexually active condition (12-hr and control) but a single peak in the quiescent (8-hr) condition. These findings suggest that the temporal phase relation of circadian serotonergic and dopaminergic oscillator varies as a function of reproductive status of the bird, and breeding/non-breeding conditions may be induced experimentally by changing the phase relation of these oscillations. © 2006 Taylor & Francis.