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

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

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)

Extrathyroidal conversion of thyroxine to triiodothyronine in Calotes versicolor

This article doese not have an abstract

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) circannual 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

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

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

The 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

<span style="font-size:15.0pt;mso-bidi-font-size: 14.0pt;font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; background:white;mso-ansi-language:EN-GB;mso-fareast-language:EN-US;mso-bidi-language: HI;mso-bidi-font-weight:bold" lang="EN-GB">Binding pattern of ¹²⁵Iodine thyroxine and tri-iodothyronine in skin and liver tissues of spotted munia, <i>Lonchura punctulata</i>: Co-relation to seasonal cycles of breeding and molting</span>

478-488Prevalent notion about thyroid hormones is that thyroxine (T4) is a mere precursor and physiological effects of thyroid hormones are elicited by tri-iodothyronine (T3) after mono-deiodination of T4. Earlier studies on feather regeneration and molt done on spotted munia L. punctulata suggest that T4 (mono-deiodination suppressed by iopanoic acid and thyroidectomized birds) is more effective than T3 in inducing feather regeneration. The binding pattern of 125I labeled T4 and T3 has been investigated in the nuclei prepared from skin and liver tissues (samples obtained during different months) of spotted munia using scatchard plot analysis. The results show that binding capacity (Bmax – pmole/80 µgm DNA) of 125I-T3 to nuclei of skin was significantly higher in November as compared to April and June, whereas the binding affinity (Kd-10-9M-1) was significantly lower in November as compared to April and June. During November, Bmax for binding of T3 and T4 did not vary in liver and skin nuclei but Kd varied significantly. Binding capacity of 125I- T3 to skin and liver did not vary but binding affinity of 125I- T4 to skin was approximately 7 times higher than that of liver. The results suggest that T4 does show a variation in binding pattern that co-relates to the molting pattern of spotted munia. These variations might play important role in different physiological phenomenon in this tropical bird. The experiments do point towards the possibility of independent role of T4 as a hormone, however, further experiments need to be done to ascertain the role of T4 in this model and work out the exact molecular mechanism of action. </span

Symposium: endocrinology and physiology of puberty and seasonal breeding in birds

This article does not have an abstract

Higher prevalence of human papillomavirus infection in adolescent and young adult girls belonging to different Indian tribes with varied socio-sexual lifestyle.

Despite high prevalence of human papillomavirus (HPV) infection and cervical cancer in Indian women, no study has been done in tribal populations whose socio-sexual lifestyle is different. Therefore, HPV screening has been carried out in pre-adolescent, adolescent and young adult tribal girls using self-collected urine samples.20-35 ml self-collected midstream urine samples were obtained from a total of 2278 healthy tribal girls (9-25 years) comprising pre-adolescent, adolescent and young adults from three Indian states: Madhya Pradesh, Jharkhand and Chhattisgarh. β-globin positive 2034 samples were employed for HPV detection and genotyping.The overall prevalence of HPV infection in tribal girls was 12.9% (262/2034). More than 65% (172/262) of them were infected with HR-HPV types of which HPV16 was the most predominant type (54%). Young adult girls aged 18-25 years showed a significantly higher prevalence of HPV infection (19.2%; OR = 3.36; 95% CI 2.97-6.34, P<0.001) as compared to that in adolescent (11.4%; OR = 1.82; 95% CI 1.20-2.76, P<0.01) or pre-adolescent girls (6.6%).This is a first study showing significantly a very high prevalence of HPV infection in adolescent and young adult tribal girls possibly due to different socio-sexual behavior, indicating a serious health concern for Indian tribal women