Asha Chandola-Saklani

Circulating thyroid hormone concentrations in relation to seasonal events in the male Indian garden lizard, Calotes versicolor

Circulating thyroxine (T4) and triiodothyronine (T3) were estimated by RIA in plasma samples of Calotes versicolor collected over a period of 28 months. Monthly observations on seasonal events, viz., molting, whole body O2 consumption, abdominal fat deposition, and testes weight were also made. Plasma T4 ranged from 0.16 to 4.63 ng/ml and T3 from 0 to 1.76 ng/ml during the course of the year. Peaks of T4 and T3 could be related with prehibernating (October/November) and posthibernating (March/April) periods, when scale shedding and O2 consumption were also enhanced. Maximum abdominal fat deposition was found in prehibernatory months (October/November). Thyroid hormone levels declined sharply with entry into hibernation. Abdominal fat deposits gradually decreased, being almost depleted by the end of hibernation. The gradual increase in thyroid hormone concentration in the later half of hibernation may be associated with increased lipolysis and preparation of the oncoming reproductive period. Although T4 and T3 profiles were apparently parallel, discrepancies were observed. Posthibernatory peak of T4 was maintained much longer than that of T3 which declined earlier. Also the rise in the prehibernatory T3 concentration was delayed as compared to that in T4.

Pinealectomy and LL Abolished Circadian Perching Rhythms but Did Not Alter Circannual Reproductive or Fattening Rhythms in Finches

In the subtropical finch, spotted munia (Lonchura punctulata), circanual rhythms (of gonads, fattening, feeding) have been demonstrated in an information-free environment of continuous illumination (LL), rendering it an ideal model for research on the physiology of the circannual clock. In an attempt to understand the involvement, if any, of the circadian system in the genesis of circannual rhythms, we studied the effect of pinealectomy (LL 15 lux) and strong continuous illumination (LL 300 lux), both known to abolish circadian rhythms, on the circadian perch-hopping rhythm and on the circannual rhythm of reproduction and fattening in the same birds. While both pinealectomy and LL 300 lux treatments abolished the circadian rhythm of motor activity, they had no effect on the circannual rhythms of gonadal size and fattening. If the endogenous circadian rhythm in perch-hopping can be taken to reflect the circadian clock mechanism associated with gonadal functioning, present results suggest that circannual rhythm of reproduction in spotted munia is independent of circadian events.

Daily increments of light hours near vernal equinox synchronize circannual testicular cycle of tropical spotted munia.

In some long-lived organisms, particularly in tropical birds and migrants that spend part of the year close to the equator, endogenous circannual rhythms have been demonstrated in seasonal events like reproduction, molt, and migration. These, like the circadian rhythms, are expressed only in constant conditions of illumination with a periodicity deviating from 1 yr. If birds followed this periodicity, they would soon be out of phase with the annual calendar and perish and, therefore, they would need to be synchronized. However, almost nothing is known as to how synchronization is achieved in birds. Herein, with the help of a suitable model, viz., the tropical spotted munia and long-term experiments conducted in series over a 5-yr period, we provide direct evidence for the first time indicating that the segment of annual photocycle with maximal rate of increase prior to vernal equinox (approximately between mid-February and mid-March) synchronizes the circannual reproductive cycle with the monsoon period of ample food supply through a phase delay. Data also indicate, contrary to the prevalent view, that birds in the tropics can perceive minor changes in day-length, that birds respond to progressive changes in day-length as distinct from responding to fixed photoperiods of particular durations, and that birds can actually distinguish the quality of the environmental signal, viz., vernal equinox from early spring, or increasing days of spring from decreasing days of autumn. The underlying mechanisms, although yet to be identified, appear to involve a gonado-inhibitory rather than the conventional gonado-stimulatory response to increasing day-length. The photoperiodic responses of spotted munia are distinctly different from that of any “long-day” birds described thus far and do not conform to the prevalent “circadian coincidence” hypothesis of photoperiodism.

T3 fails to mimic certain effects of T4 in munia birds: physiological implications for seasonal timing

The comparative effects of equimolar doses of thyroxine (T4) and tri-iodothyronine (T3) were studied on fattening, gonadal status and moulting in thyroidectomized female spotted munia. The effects of suppression of peripheral conversion of T4 to T3 were also studied on these parameters. T4 administration led within 10 days to a significant regression of gonads and mobilization of fat, the response being linear. T3 had no effect on these parameters at any dose level. However, both T4 and T3 were effective, the former to a greater extent in stimulating feather regeneration in the same birds. Inhibition of peripheral monodeiodination of exogenous T4 in thyroidectomized (Tx) birds by iopanoic acid (IOP) did not suppress T4 response, but resulted in greater regression of gonads and fat mobilization; however, IOP alone was ineffective. Long-term suppression of peripheral monodeiodination of endogenous T4 in intact birds with IOP suppressed follicular growth and fat deposition but enhanced moult. Hormonal profiles of T4 and T3 indicated that seasonal moult-inducing, anti-gonadal and anti-fattening effects of the thyroid gland are reflected by circulating T4 but not T3 in the munia bird. It may be concluded that T4 may be more potent than T3 in eliciting certain biological actions and that T3 may not mimic all T4 effects. Contrary to general opinion T4-induced effects need not necessarily be mediated through its prior conversion to T3, giving it an independent hormonal role. This may be a mechanism evolved by passerine birds which are generally known to be iodine-deficient, to preclude the simultaneous occurrence of seasonal events requiring high energy and nutrition, such as moulting, reproduction and migration.

Effect of pinealectomy on free-running reproductive cycle of tropical spotted munia

SummaryThe breeding cycle of the tropical spotted munia (Lonchura punctulata) is regulated by the photoperiodic synchronization of an endogenous circannual rhythm. Since the pineal gland has been implicated in circadian periodicity, in an attempt to understand the functioning of the mechanism(s) involved in photoperiodic synchronization of the circannual clock in the spotted munia the effect of pinealectomy on the reproductive cycle was studied in birds maintained in normal entrained (natural day length, NDL) and free-running (constant light, LL) conditions.Results indicate that pinealectomy had no effect in LL but that the reproductive cycle was altered marginally (in the first cycle only), and the body weight cycle drastically, in NDL conditions. It seems that the marginal effects observed on the overt reproductive cycle in the entrained condition may not be through the circannual oscillator itself but may perhaps reflect interference with processes involved in photoperiodic synchronization of the circannual rhythm. Alternatively, these effects could also result from general metabolic disturbances caused in the body by the absence of the pineal gland.

Evidence for the role of thyroxine as a hormone in the physiology of a lizard.

In vivo effects of thyroxine (T4) and triiodothyronine (T3) were studied in male lizards. T4 or T3 (0.5 to 2 nmol) was administered per day over 10 days to surgically thyroidectomized male lizards (35 +/- 2.0 g) and the responses were measured in terms of scale shedding, whole body oxygen consumption (OC), and testicular weight. T3 was more effective in stimulating OC as compared to T4. T4 accelerated scale shedding to a greater extent as compared to T3. T4 was more effective than T3 in restoring the decline in the gonadal weight of thyroidectomized animals. Effect of inhibition of peripheral conversion of T4----T3 by iopanoic acid (IOP) was studied on the above response parameters. IOP at both dose levels inhibited extrathyroidal conversion of T4----T3. The T4-stimulated increase in OC of IOP-treated animals was suppressed, clearly indicating that the T4 effect could be attributed to its conversion to T3. But in these same animals, IOP failed to inhibit T4-stimulated scale shedding and gonadal weight. As the proportion of T4 converted to T3 decreased as a result of IOP treatment, the effectiveness of T4 increased in terms of scale shedding and restoration of gonadal weight. From these studies it appears that all effects of T4 in lizards need not necessarily be mediated via conversion to T3.

Environmental and hormonal control of vernal migration in redheaded bunting (Emberiza bruniceps)

This paper reviews the factors and mechanisms which result in the development of the metabolic state characteristic of migration with special reference to a palaeotropic migrant the redheaded bunting,Emberiza bruniceps. Changes in climatic conditions and food supply act as proximate triggers of migratory behaviour in partial migrants. Typical migrants like buntings use daylength as a cue but the exact mechanism of how photoperiodic information is translated in terms of migratory events is still not known. Almost entirely the photoperiodic effects have been explained on the basis of the involvement of hypothalamo/hypophyseal system. We feel mechanism(s) other than those acting through neuroendocrine system may be equally important. Furthermore the role of temperature has not been adequately explored so far. Our observations indicate the possibility that redheaded buntings might integrate the information received from photoperiod with environmental temperature (and other factors?) resulting in the development of migratory state. The physiological control of avian migration is much less understood. Majority of papers have centered around the ‘gonadal hypothesis’ of Rowan supporting or contradicting it without providing conclusive evidence. Pituitary prolactin has also been shown to be implicated although the mechanism of action is only speculative.Conclusive evidence for the involvement of thyroid hormones (thyroxine, T4; triiodothyronine, T3) in the physiological timing of migration has been produced attributing independent roles to T4 and T3. It is suggested that seasonal variation in peripheral conversion of T4 to T3 could serve as an effective strategy to render available the required thyroid hormones T4 and/or T3 during different phases of the year thus accounting for the metabolic switch over from T4-dependent moult to T3-dependent migratory fat deposition and zugunruhe and also ensuring preclusion of simultaneous occurrence of these mutually incompatible events. Considering that the number of environmental and physiological factors influence this mechanism and considering that thyroid hormone molecule has been put to a wide range of usage during the course of evolution the mechanism(s) of peripheral conversion of T4-T3 may assume great flexibility and have selective value-especially in migration which is known to have evolved several times in diverse avian families.The attractiveness of this hypothesis lies in the fact that it has potential to explain the both physiological development of the metabolic state of migration and at the same time the physiological timing of migration not only with respect to the cycle of environment but also with respect to other conflicting seasonal events (moult and reproduction).

Short-day experience is not a prerequisite for the termination of photorefractoriness in the reproductive cycle of baya weaver,Ploceus philippinus

In most photoperiodic avian forms (irrespective of temperate or tropical distribution) including the baya weaver,Ploceus philippinus, seasonal reproduction comes to an end due to the development of a photoperiodically controlled photorefractory phase when birds cease to respond to the stimulatory effect of long days. In the present paper photoperiodic control of the termination of photorefractory phase has been examined by studying the effect of short-day exposure lasting 4–6 months on long-day response of birds. Results indicate that unlike in other photoperiodic birds short-day exposure of winter is not a prerequisite for the termination of photorefractory phase in the reproductive cycle of baya weaver. Artificial long days on the other hand hasten the termination of this phase. Refractory phase in baya weaver, therefore, unlike that in temperate forms, is a temporary state resulting most likely from a sequel of physiological events triggered by long days of spring/summer which temporarily mask the photostimulatory response. Spontaneous termination of photorefractoriness in birds of tropical habitats may have a selective value imparting to the reproductive cycle the necessary elasticity for adaptation to diverse ecological conditions.

Comparison of an alternative and existing dbs matrix for estimation of thyroid stimulating hormone (tsh) in adults.

Nikku Yadav. Currently, Whatman 903 (W-903) filter paper is the only filter paper that has been used for collection of blood samples in thyroid hormones. This commercially available filter paper has so expensive which is not suitable for epidemiological study conducted in developing countries. We therefore introduced a new matrix for collection of blood samples and also compared with commercial available matrix, Whatman filter paper (W-903). We used two matrices initially for standardisation purpose viz., the conventional Whatman dbs cards (#903 10531018) & pre coated TLC silica gel matrix (60F254, Merck 20x20 Cm), the latter with cost-effectiveness in view. Both were subjected to validation for optimum working conditions. The assay characteristics for Whatmann DBS card and TLC matrix were found to be as follows: correlation coefficient 0.982 & 0.976, slope 0.070 & 0.068, coefficient of variation 0.32-0.77% & 0.40-0.85%, sensitivity 0.0287 & 0.0286 mIU/L and interassay variation 0.40% & 0.50 respectively. The assay characteristics of the calibration curve for FT4: correlation coefficient 0.926 , slope 0.094, coefficient of variation 0.84-4.12% and inter assay variation 3.03% for TLC silica matrix. Drying time (0.5, 1.5, 2.5, 3.5 , 4.5 ,5.5 h), elution time (1.0, 3.0, 5.0-16 h), percent recovery (83-98%) and linearity at varying dilutions were determined. Stability studies for TSH samples were conducted at variable temperatures and half life found to be temperature dependent viz.,24.54 days, RT; 180.45, 4C; 206.25 days, -20C. Owing to its cost-effectiveness and comparable results, TLC silica matrix was preferred for subsequent studies under optimized conditions.

Acoustic variations in the geographically isolated populations of L punctulata in India.

Atul Kathait. Birds use verity of acoustic signals for their daily communication. These signals are very important for their daily life in individual recognition, food hunting, prey alarm etc. For successful reproduction acoustic signals are very important in mate recognition and attraction. However signals are very much affected by local habitat and geographical pressures and well reflected in populations and genetic structure. In present work geographical variation in the calls of L punctulata has been investigated. Results indicate that L punctulata is mono-syllabic in morning calls. Spectrographically no variations were observed across all locations. However in parametric comparisons variations were observed across all geographical regions. Population level acoustic signatures were seen in majority of individuals. UPGMA tree based on the parametric distance indicates population level structure in both notes with some admixture. This indicates the possibility of local level difference in genetic structure of L punctulata.