Browsing by Author "P.D. Tewary"

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Biochronometry of photoperiodically induced fat deposition in a migratory finch, the Blackheaded bunting Emberiza melanocephala (Aves)
(1983) P.D. Tewary; Vinod Kumar
This investigation attempts to identify the mechanism(s) involved in the fat deposition in a photoperiodic migratory species, the Blackheaded bunting (Emberiza melanocephala). Groups of photosensitive male buntings were exposed to resonance, interrupted night, and ultra‐short‐day light cycles for 35, 42 and 75 days, respectively. Birds were weighed at the beginning and at the end of the experiments. Those exposed to ultra‐short‐day light cycles were also weighed at critical intervals during the treatment period. Our results indicate that: (a) a light‐sensitive rhythm with a period of about 24 hr is involved in the photoperiodic induction of premigratory fattening and weight gain in Blackheaded buntings: (b) buntings possess a bimodal pattern 'of sensitivity to photoperiods that induce fattening, and (c) this endogenous circadian rhythm can be entrained by an ultrashort photophase of 3 h if the latter is coupled with scotophases of specific duration. Copyright © 1983, Wiley Blackwell. All rights reserved
Changes in body weight, ovarian growth, and circulating plasma estradiol level in response to programmed photoperiods in blackheaded bunting, Emberiza melanocephala
(Wiley-Liss Inc., 1999) Manoj Kumar Mishra; P.D. Tewary
Photosensitive female blackheaded buntings (Emberiza melanocephala) were observed at different photoperiodic schedules of increasing duration to study their effect on body weight, ovarian growth, and circulating plasma estradiol level. Continuous-light (24L:0D) and long-day (15L:9D) photoperiodic regimes showed a significant increase, followed by decrease, in body weight, ovarian growth, and circulating plasma estradiol level. The short photoperiod (8L:16D) showed no effect on body weight, ovarian growth, or circulating plasma estradiol level. During 24L:0D and 15L:9D birds became photorefractory and thus unable to maintain an elevated state of body weight, ovarian growth, or plasma estradiol level. On the other hand, the birds exposed to short photoperiod maintained their photosensitive state throughout the period. The peak attained during 24L:0D and 15L:9D treated groups showed little variation. The present findings indicate that long-day and continuous-light, when given for longer durations, causes photorefractoriness (a state in which birds are unable to respond to light) and thus suggest the involvement of endogenous circadian components in regulating reproduction and associated events during photoperiodic manipulation of light/dark cycles in female blackheaded buntings.
Changes in ovarian growth and plasma estradiol concentration in response to photoperiodic transfers in Blackheaded bunting
(1997) Manoj Kumar Mishra; P.D. Tewary
Photosensitive female Blackheaded buntings when exposed to long day (15L/9D) and continuous light (24L/OD) for longer duration showed an increase followed by decrease in ovarian weight and plasma estradiol concentration and thus they become photorefractory. While the birds transferred on continuous dark phase (scoto phase) for 30 days shown to have effective to terminate the photorefractoriness and thus maintained their photosensitivity. The present study reveals that it is the time of exposure of light which plays an important role in maintenance of photosensitivity and photorefractoriness in buntings and thus suggests the presence of an endogenous circadian component which may operate their in.
Circadian Aspect of Photoperiodic Time Measurement in a Female House Sparrow, Passer domesticus
(1995) G. Ravikumar; B. Senthilkumaran; P.D. Tewary; A.K. Goel
Endogenous circadian rhythms are involved in various photoperiodic responses of birds. Investigations involving the mechanisms of photoperiodic time measurement in birds have been confined mainly to temperate zone species using males exclusively. Due to the paucity of experimental evidence on sub tropical birds that have very wide distribution, the present study was performed using subtropical female house sparrows. Photoperiodic sparrows were sub jected to various T cycles for 60 days in which a fixed 3-h photophase was combined with scotophase in cycles of 20-30 h duration. Simultaneously, two groups of birds were also exposed to short days (light:dark = 8L:16D) or long days (15L:9D) as controls. Significant ovarian growth was found only in cycles of 3L:17D, 3L:23D, 3L:25D, and 3L:27D as well as in 15L:9D, whereas no positive response was detected in 3L:19D, 3L:21D, and 8L:16D. Plasma levels of estradiol showed a close relation to ovarian growth. The results indicate that photoperio dic time measurement in house sparrows involves an endogenous circadian rhythm. © 1995, Sage Publications. All rights reserved.
Circadian basis for the photoperiodic response in the male blackheaded bunting (Emberiza melanocephala)
(1982) Vinod Kumar; P.D. Tewary
Short day (6 hr light in a 24 hr cycle (ld 6 : 18)) inhibits growth and development of the testes in male blackheaded buntings, whereas the same (6 hr) nonstimulatory photoperiods in a 36 hr cycle (ld 6 : 30) induce complete testicular recrudescence and development. In another experiment of 24 hr cycles, using the same (6 hr) main photoperiod, testes were stimulated when the dark period was interrupted by light at 12 to 13 hr after the onset of basic photoperiod (ldld 6 : 6 : 1 : 11). The results appear to conform to the tenets of the external coincidence model. © 1982 Indian Academy of Sciences.
Circadian basis of photoperiodically induced testicular growth in redheaded bunting, Emberiza bruniceps
(1982) P.D. Tewary; B.N. Prasad; V. Kumar
Short day (8L : 16D), pretreated adult male redheaded buntings were held on various light-dark cycles of 20 to 30 h duration, in which a fixed ultra-short photophase of 3 h was combined with scotophases of varying duration. A photoperiodic testicular response was obtained only in 28- and 30-h cycles (3L : 25D and 3L : 27D). The same photo-period (3 h) in 20- to 26-h cycles (3L : 17D, 3L : 19D, 3L : 21D and 3L : 23D) failed to stimulate testicular growth. The results can be interpreted on the assumption that the positive testicular response in this species, under ultra-short-day light cycles, is the result of an advance in the photosensitive phase of the photoperiodic response system so that it coincides at least partly with the external photophase. The results thus appear to conform with the Bünning hypothesis or external coincidence model. © 1982.
Circadian function in the photoperiodic induction of testicular growth in the common indian rosefinch, Carpodacus erythrinus
(1983) Vinod Kumar; P.D. Tewary
The role of circadian mechanism in the photoperiodic induction of gonadal growth was investigated using 46 individuals of a subtropical migratory finch, the common Indian rosefinch (Carpodacus erythrinus), by means of an asymmetrical photoperiodic regime. The regime consisted of a nonstimulatory basic photophase (6 h) in combination with a scotophase, in a 24-h cycle, the scotophase being interrupted by 1 h light at temporally fixed hours. The light interruption between hours 12 and 17 after the onset of the basic photoperiod led to testicular growth, while 1 h light as a continuation of the basic photophase or as an interruption 10, 19 or 21 h after the onset of the basic photophase was not stimulatory. Results clearly indicate that the rosefinch possesses a fine time-measuring device, which involves an endogenous circadian rhythm in photosensitivity. The photosensitive phase appears between hours 12/13 and 17/18 following the onset of the first light period. © 1983.
Circadian periodicity and the initiation of gonadal growth in male blackheaded buntings (Emberiza melanocephala)
(Springer-Verlag, 1981) P.D. Tewary; Vinod Kumar
Photosensitive male blackheaded buntings were held under six different light cycles consisting of a 6-hour main photophase coupled with scotophases of various durations (6L/6 (2 n+1) D). Testicular growth was stimulated in buntings by cycle lengths of 12-(6L:6D), 36-(6L:30D) and 60-hours (6L:54D), but not by cycles of 24-(6L:18D), 48-(6L:42D) and 72-hours (6L:66D). These results are consistent with the Bünning hypothesis and indicate that an endogenous rhythm with a period of approximately 24 hours plays a role in the initiation of testicular growth in this bird. © 1981 Springer-Verlag.
Circadian periodicity in termination of photorefractoriness in the yellow-throated sparrow
(Birkhäuser-Verlag, 1985) P.D. Tewary; P.M. Tripathi
Photorefractory male yellow-throated sparrows (Gymnorhis xanthocollis) were subjected to six resonance light cycles, consisting of 6 h basic photophase coupled with scotophases of longer durations (in cycles of 12 (6L:6D) h, 24 (6L:18D) h, 36 (6L:30D) h, 48 (6L:42D) h, 60 (6L:54D) h and 72 (6L:66D) h). Termination of photorefractoriness was evident in cycles of 24, 48 and 72 h, but not in 12, 36 and 60 h. The results are consistent with the 'external-coincidence' model (Bünning hypothesis) and suggest that endogenous circadian rhythmicity is involved in the termination of photorefractoriness. © 1985 Birkhäuser Verlag Basel.
Circadian periodicity in yellow-throated sparrow as demonstrated by intermittent light experiments.
(1988) P.M. Tripathi; P.D. Tewary
Groups of adult photosensitive male yellow-throated sparrows were subjected to different intermittent light cycles viz. 2L/2D, 3L/3D, 4L/4D, 8L/8D and 12L/12D besides two control groups held on 8L/16D and 18L/6D photoperiodic treatments. Testicular growth occurred in 2L/2D, 3L/3D, 4L/4D and 18L/6D but not in 8L/16D, 12L/12D and 8L/16D photoperiodic regimes. The results of this experiment can be interpreted on the basis of circadian rhythm in photosensitivity in an avian external coincidence model. Our findings suggest that multiple light flashes are more effective than a single broad pulse of light of equal duration.
Effect of estrogen and gonadotropic hormones on the plumage pigmentation in Lal Munia (Estrilda amandava)
(Springer-Verlag, 1963) J.P. Thapliyal; P.D. Tewary
[No abstract available]
EFFECT OF EXOGENOUS 170-ESTRADIOL ON GONADAL PHOTOSTIMULATION IN HOUSE SPARROW, PASSER DOMESTICUS (LINN.)
(Indian Academy of Sciences, 1989) P.D. Tewary; G. Ravikumar
Intramuscular injection of 17β-estradiol inhibited photoperiod induction of gonads in female subtropical house sparrow (Passer domesticus), with no effect on body weight. This suggests that exogenous 17β-estradiol has an antigonadal effect in this species. The effect is due to the negative feedback mechanism of the hormone at the hypothalamo-hypophyseal axis. © (1989), (Indian Academy of Sciences). All Rights Reserved.
Effects of exogenous prolactin on ovarian growth and fattening in the redheaded bunting, Emberiza bruniceps
(1983) P.D. Tewary; B.K. Tripathi; Vinod Kumar
Subcutaneous daily injections of ovine prolactin (PRL) inhibit photoperiodic induction of gonads and fattening in the female redheaded bunting (Emberiza bruniceps). However, birds respond to the same photoperiod (15L:9D) after withdrawal of the exogenous PRL. Further, PRL injections given in late hours during the subjective days induce ovarian regression in the photostimulated females. The results suggest that the PRL has an inhibitory role on gonadal photoperiodic responses in redheaded buntings, and extend our understanding of the regulatory function of PRL in migratory birds. © 1983.
Endogenous circadian rhythm in the photoperiodic ovarian response of the subtropical sparrow, Passer domesticus
(1991) G. Ravikumar; P.D. Tewary
Groups of photosensitive female house sparrows have been kept under night-interruption and intermittent light cycles for a period of 6 weeks. The night-interruption cycle consisted of a basic photophase of 6 h and 1 h photointerruption of the dark phase in the 24 h cycle at different points. Ovarian growth was stimulated under cycles in which photointerruption of the dark phase was made 10 h after the onset of basic photophase. The intermittent light cycles consisted of 2 L:2 D, 3 L:3 D, 4 L:4 D, 8 L:8 D and 12 L:12 D besides two control groups held on 7 L:17 D and 17 L:7 D. Ovarian response was observed only in 2 L:2 D, 3 L:3 D, 4 L:4 D, 12 L:12 D and 17 L:7 D cycles. The results of both the experiments are consistent with an avian external coincidence model and indicate that circadian rhythmicity is involved during the initiation of the female avian reproductive system. © 1991.
Evidence for a circadian component in the photoperiodic mechanism of the blackheaded bunting, Emberiza melanocephala
(1982) P.D. Tewary; Vinod Kumar
Photosensitive male blackheaded buntings were exposed to three different light-dark cycles of 22 to 30 h duration, in which a 3 h photophase was coupled with varying durations of scotophases, for a total duration of 75 days. Gonadal growth was initiated in the 30-h cycle (3L:27D), whereas the same photoperiod (3 h) in 22 h and 24 h cycles (3L:19D, 3L:21D) did not induce testicular recrudescence. The results are consistent with the Bünning hypothesis (external coincidence model), and can be interpreted to mean that the positive ultra-short-day photoperiodic response is the result of an advance in the photosensitive phase of the response system so that it becomes coincident, at least in part, with the environmental photophase. In a further experiment, buntings long-day (20L:4D)-photostimulated for 30 days were transferred to continuous darkness (DD) and short days (8L:16D) for 40 days. When examined at the end, birds in both experiments showed testicular regression. The results are explainable in terms of the external coincidence model, but could be explained also by a relatively simple internal coincidence model. Nevertheless, application of the Law of Parsimony may favour the external coincidence system in the photoperiodic response mechanism of this species. © 1982.
Involvement of a circadian rhythm in the photoperiodic ovarian response of the yellow-throated sparrow, Gymnorhis xanthocollis.
(1989) A.S. Dixit; P.D. Tewary
Groups of the photosensitive female yellow-throated sparrow were placed under various light-dark cycles, in which a fixed ultrashort photophase of 3 h was combined with dark phases of varying duration, resulting in cycles of 18-30 h. Simultaneously, two groups of birds, one in short days (8L/16D) and the other in long days (15L/9D), were kept as controls. Significant ovarian growth, observed at 30 and 60 days, was induced by 3 h ultrashort photophase only if it was introduced in the cycles of 18 h (3L/15D), 20 h (3L/17D), 26 h (3L/23D), 28 h (3L/25D) and 30 h (3L/27D) as well as under long days (15L/9D), whereas there was no response to the ultrashort photophase in cycles of 22 h (3L/19D) and 24 h (3L/21D) and in short days (8L/16D). It seems that there is an ovarian response to the ultrashort day cycles when a phase advance or delay of photosensitivity of the response system repeatedly produces coincidence of the external photophase (3 h) with the photosensitive phase of an endogenous circadian rhythm. The results are thus consistent with the Bünning hypothesis, which suggests the involvement of an endogenous circadian rhythm in photoperiodic time measurement.
Involvement of circadian rhythm in response to ultrashort photoperiods in blackheaded bunting, emberiza melanocephala
(1997) Manoj Kumar Mishra; P.D. Tewary
Groups of photosensitive adult female blackheaded buntings were exposed to various ultrashort days photoperiodic regimes for 60 days in which a fixed 3 h photophase was coupled with dark phases in cycles of 22 to 32 hours duration. One group of buntings was kept in long days (15L:9D) as control. Significant increase in ovarian weight and circulating plasma estradiol concentration was marked in the cycles of 30 h (3L:27D), and 32 h (3L:29D) photoperiodic schedules as well as in control group (15L:9D), whereas there was no response in the cycles of 22 h (3L:19D) and 24 h (3L:21D). It seems that the response to ultrashort day cycles is due to a phase advance or delay in photosensitivity of the response system repeatedly shows coincidence of the external photophase (3 h) with the photoinducible phase of an endogenous circadian rhythm. Therefore, the present result appears to be consistent with Bünning hypothesis suggesting the involvement of an endogenous circadian component in the female blackheaded bunting. © 1997 Akadémiai Kiadó, Budapest.
Involvement of threshold photoperiod in control of reproductive rhythmicity in migratory blackheaded bunting, emberiza melanocephala
(Marcel Dekker Inc., 1999) Manoj Kumar Mishra; P.D. Tewary
To explore the need for minimum threshold photoperiodicity in regulation of metabolic and reproductive activities of a migratory finch, various programmed light-dark (LD) schedules, such as P1(3L/21D), P2 (6L/18D), P3 (9L/15D), P4 (12L/12D), P5 (15L/9D), P6 (18L/6D), P7 (21L/3D), and P8 (24L/0D), have been used on photosensitive female blackheaded buntings for 42 days. Results indicate that the photoperiodic thresholds of 3h, 6h, and 9h completely failed to have any response on buntings, while threshold photo- periodicities of 12h, 15h, 18h, 21h, and 24h had significant effect (P < .001) on body weight, ovarian weight, and circulating plasma estradiol concentration, suggesting the role of the photoperiod as a primary environmental source to regulate various metabolic and reproductive functions. Further, it has been suggested that the threshold photoperiod in this species appears to be of 12h duration.
Participation of the circadian component in the photoperiodic mechanism of the blackheaded bunting, Emberiza melanocephala
(1985) Vinod Kumar; P.D. Tewary; A.S. Dixit
Groups of photosensitive male blackheaded buntings (Emberiza melanocephala) were subjected to continuous darkness (DD), short days (8L:16D), alternating DD and long days (15L:(D), and alternating 8L:16D and 15L:9D after photostimulation (15L:9D) for either 15 or 30 days. The effect of transfer to any of these regimes on the size of the testes was found to be dependent on the size attained at the time of transfer. However, the rate of testis regression, after 15 days or 30 days of 15L:9D, after transfer to DD, once begun, was the same as in the group transferred to 8L:16D. (Testicular regression did not begin immediately upon transfer to DD or 8L:16D, but, development continued for about 10 days in the birds photostimulated for 15 days.) Similarly, alternating long days could not maintain the testis size when they had attained their maximal size. A significant growth occurred in birds transferred after 15 days, in contrast to those transferred after 30 days of photostimulation. These observations are compatible with an external coincidence model, but could also be explained by an internal coincidence model. Application of the Law of Parsimony may favour an explanation that combines an external coincidence model and the established "carry-over" function of the neuroendocrine-gonadal system in photoperiodic birds. © 1985.
Photoperiodic control of ovarian growth in the subtropical house sparrow, Passer domesticus: evidence of an external coincidence system.
(1990) G. Ravikumar; P.D. Tewary
Groups of adult female house sparrows (Passer domesticus) were placed under short days (8L/16D) and continuous darkness (DD) after photostimulation by long days (15L/16D) for either 25 or 40 days and another two groups of photostimulated birds were continued on long day (15L/9D) photoperiod. Two groups of photosensitive birds were subjected to 8L/16D or DD and they treated as controls. The rate of ovarian regression was nearly the same under transfer to 8L/16D or DD. Birds placed under long days maintained ovarian growth and this exclude the possibility of refractoriness. However, the photosensitive birds placed under 8L/16D or DD did not show any ovarian growth. The results of these experiments seem to support Bünning - Pittendrigh external coincidence model.