Frequency of feeding and formation of bone growth marks in frog,Rana cyanophlyctis (Schn.)

Frogs, R. cyanophlyctis (n = 45) divided into four groups, were exposed to different feeding regimens (live guppies were used as food) such as, daily, alternate day, every fourth day and weekly feeding for 5 months, during wet months of the year (April-September). Two toe clippings were made, one at the beginning and the other at the termination of the experiment. Clipped toes were demineralized, and processed for histology. In 6 out of 45 frogs one line of arrested growth (LAG) was present in the phalangeal histology at the beginning of the experiment while, at the termination of experiment 34 out of 43 frogs exhibited one LAG each indicating that in 26 frogs LAG appeared freshly during the experimental period. The fact that LAGs are formed in regularly fed frogs suggests the humid weather/seasonal rainfall may play relatively important role than the feeding in cyclic bone growth and formation of growth marks in this frog.     

Age related changes in ovarian follicular kinetics in the Indian skipper frogRana cyanophlyctis (Schn.)

Changes in ovarian follicular kinetics were studied in relation to aging in the Indian skipper frog Rana cyanophlyctis.Age was determined by skeletochronology, by counting the number of growth rings and lines of arrest of growth from the cross sections of 4th phalange of 4th toe. For follicular kinetics study oocytes were counted under binocular using 10% of Bouin’s fixed ovary and they were classified into first growth phase, medium-sized second growth phase, large-sized second growth phase and atretic follicles. Analysis of phalangeal cross sections indicated that frogs ranging 14–54 g in body weight and 4.9–8.9 cm in body size showed 1–7 year rings. Frogs that weighed 14–16 g showed 1 year ring, and contained immature ovaries; those with 18 g body weight had one to two year rings, in which second growth phase oocytes appeared for the first time in the primiparous ovary. Frogs with 20–54 g body weight showed 2–5 year rings in which ovary contained 5–24% of second growth phase oocytes. Further, body weight, body size, ovarian weight, number and size of second growth phase oocytes and total number of oocytes showed a significant (P < 0.05) positive correlation, while, the number of first growth phase and atretic follicles showed a poor correlation with age. The results suggest that in nature, the age of Rana cyanophlyctis ranges between 1–7 years. Phalangeal growth rings are formed annually. Females attain sexual maturity in 2nd year. Frogs with 2–5 years of age may constitute breeding females. Body weight, body size, ovarian mass, number of second growth phase and total oocytes, and egg size increase with age up to 5 years.     

Effect of photoperiod and temperature on ovarian cycle of the frogRana tigrina (Daud.)

The effect of varying photoperiod regimes (LD: 20,4; 4,20; 6,18; 18,6 and 12,12) on ovarian follicular development was analysed in the frogRana tigrina maintained at ambient and constant 30° ± l°C for 3 months. The experiments were conducted in early recrudescent and quiescent phases. The frogs were fed guppiesad libitum on alternate day. None of the photoperiod regimes had any effect on the ovaries or the fat bodies, whereas exposure to constant high temperature (regardless of photoperiod) during recrudescent phase induced production of greater number of eggs (∼ 18000 vs 13000 in controls) of ovulatory sizes (> 1400 μm) compared to the corresponding controls maintained at ambient temperature. Hence, ovarian mass also increased in these frogs. In the quiescent phase, high temperature merely enhanced growth of previtellogenic oocytes. In both the phases high temperature caused a reduction in the fat bodies over the respective controls, possibly due to increased metabolic activity. The above findings indicate that temperature plays a key role in the regulation of ovarian cycle ofRana tigrina and that the photoperiodic mechanisms may not govern the annual recrudescence of ovaries in the frog. The study also shows that the frog exhibits the phenomenon of “phenotypic plasticity” in its reproductive behaviour by producing significantly greater number of eggs in response to elevated temperature.     

Blood carbohydrates and phosalone poisoning in Rana tigrina (Daudin)

In Rana tigrina, blood levels of total carbohydrates, lactic acid and pyruvic acid were determined in relation to allometric growth in both sexes. The blood carbohydrates content increased in relation to growth and maturity of gonads. Treatment by phosalone resulted in the accumulation of lactic acid in blood suggesting that this organophosphate compound inhibits the normal oxidative metabolism.     

Light has no role in spermatogenesis in the frog Rana cyanophlyctis (Schneider)

The effect of 3 months exposure to short day length (L:D, 9:15) on spermatogenesis in R. cyanophlyctis was studied. There was no difference in the qualitative and quantitative aspect of spermatogenesis between control frogs exposed to ambient photoperiod (L:D, 12.16:11.44) and frogs exposed to short day light. The present findings indicate that light has no role in spermatogenesis in the frog.     

Video Scanning for Determination of the Proportion of Cortical Tissue in the Avian Adrenal Gland

The use of a video scanning apparatus (Leitz, T.A.S.) for the determination of the corticomedullary proportion in histological sections of the avian adrenal gland is described and statistically evaluated. When the video scanning method was applied to material from groups of domestic hens, which had been exposed to different experimental conditions, the results were similar to those obtained through the integrating method as described by Siller et al. (1975). The mean values obtained by both methods did not differ significantly, and there was a highly significant correlation between the counts for both methods applied on the same sections. When applying the video scanning method to 16 sections from four adrenals, repeated measurements on each of the sections showed considerable variation. However, this variation was found to be significantly smaller than the variation among the sections. It is suggested that the video scanning method could be made more precise by improvement of the staining procedure. However, on relatively large samples it seems to give reliable results, and it has a great advantage in reducing the tedious work involved in other available methods.     

A Polydnavirus ANK Protein Acts as Virulence Factor by Disrupting the Function of Prothoracic Gland Steroidogenic Cells

Polydnaviruses are obligate symbionts integrated as proviruses in the genome of some ichneumonoid wasps that parasitize lepidopteran larvae. Polydnavirus free viral particles, which are injected into the host at oviposition, express virulence factors that impair immunity and development. To date, most studies have focused on the molecular mechanisms underpinning immunosuppression, whereas how viral genes disrupt the endocrine balance remains largely uninvestigated. Using Drosophila as a model system, the present report analyzes the function of a member of the ankyrin gene family of the bracovirus associated with Toxoneuron nigriceps, a larval parasitoid of the noctuid moth Heliothis virescens. We found that the TnBVank1 expression in the Drosophila prothoracic gland blocks the larval-pupal molt. This phenotype can be rescued by feeding the larvae with 20-hydroxyecdysone. The localization of the TnBVANK1 is restricted to the cytoplasm where it interacts with Hrs and Alix marked endosomes. Collectively, our data demonstrate that the TnBVANK1 protein acts as a virulence factor that causes the disruption of ecdysone biosynthesis and developmental arrest by impairing the vesicular traffic of ecdysteroid precursors in the prothoracic gland steroidogenic cells.     

Levels of liver glycogen during normal and radiation-induced metamorphosis in Rana cyanophlyctis

This study shows that significant changes in the pattern of glycogen deposition are brought about by irradiation with 2,000 R gamma-rays. The sharp fall during the 1st week can be attributed to its emergent mobilization. However, glycogen stored in the liver during the 2nd and 3rd week prior to the resorptive process substantiates the fact that tadpoles complete metamorphic transformations in spite of sublethal irradiation.     

Involvement of the Endoplasmic Reticulum of Chromaffin Cells of the Rat Adrenal Gland in Calcium Signaling

We studied the involvement of the endoplasmic reticulum (ER) in calcium signaling in rat chromaffin cells. For this purpose, the following agents influencing the activity of the ER were used: (i) Caffeine that activates the release of Ca²⁺ from the endoplasmic store and (ii) thapsigargin that suppresses accumulation of calcium in the ER. The intracellular Ca²⁺ concentration was measured with the help of a calcium-sensitive dye, Fura-2AM, using the microfluorescent technique. Applications of caffeine led to a rise in the level of free Ca²⁺ in the cell cytosol and also to a decrease in the amplitude of calcium transients induced by depolarization of the plasma membrane under the action of a hyperpotassium solution. Under conditions of repeated caffeine applications, the amplitude of transients decreased to 9% of its initial value, which is explained by exhaustion of the calcium stores. The action of caffeine was restored when the calcium stores were re-filled under the action of depolarization of the plasma membrane. Thapsigargin completely removed the effect of caffeine and did not influence KCl-induced transients. Therefore, our experiments are indicative of a significant importance of the ER calcium stores for calcium signaling in chromaffin cells, which allows us to hypothesize that these stores play an important role in the control of secretion of catecholamines.