bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biology of the scrotum. IV. Testis location and temperature sensitivity
Authors: Bedford J. M. , Berrios M. , Dryden G. L. 
Published: June 2005

AbstractWhereas abdominal temperatures have no effect on spermatogenesis in testicondid mammals but inhibit the process completely in scrotal mammals, the inguinal testes of the naturally cryptorchid musk shrew and degu have been found to display an intermediate response. Twelve to 18 weeks after transposition to the abdomen (and so about 1.5°C above its normal inguinal temperature) the weight of the testis was reduced by 27% (musk shrew) and 52% (degu). Nonetheless, spermatogenesis continued in both, though at a lower rate and with a greater proportion of abnormal spermatozoa formed. The ultrastructural anomalies evident in some spermatids of the degu testis transposed to the abdomen were reminiscent of those seen commonly in the germinal epithelium of “normal” men. Natural cryptorchids may thus be useful models in which to discover whether spermatogenesis at a temperature somewhat above the norm for the species compromises the ability of fertilizing spermatozoa to support normal development.The fact that deep‐body temperature induces only a partial suppression of function in the inguinal testis of natural cryptorchids shows that there is no absolute distinction between the scrotal and ascrotal states among mammals with respect to the temperature sensitivity of the testis. That visible sensitivity seems more likely to reflect the adaptation of the metabolically dynamic germinal epithelium to function optimally at the temperature of the location to which the testis migrates, rather than any fundamental incompatability between spermatogenesis and the temperature imposed by homeothermy. External migration of the testis itself may originally have helped the sperm storage region of the associated epididymis to project from and so attain a cooler environment than that beneath the body surface.
Intrafollicular pressure decreases in hamster preovulatory follicles during smooth muscle cell contraction in vitro
Authors: Schroeder Paul C. , Talbot Prudence 
Published: June 2005

AbstractSmooth muscle cells in the base of hamster follicles contract minutes prior to ovulation; during this contraction the profile of the follicle changes from low to tall. Our purpose was to measure intrafollicular pressure, independent of an intact circulatory system to the ovary, at the time when follicular smooth muscles are known to be contracting. Hamster ovaries were removed 13 hours after hCG injection and placed in a culture medium which supports in vitro ovulation. Intrafollicular pressure was measured continuously with a WPI Model 900 Micropressure system, while the follicle was being observed and photographed using a dissecting microscope and Zeiss 35 mm camera. Initial intrafollicular pressure was 2.1 ± 1.1 mmHg (n = 47) in the absence of a blood supply. This pressure decreased slowly (0.03 mmHg/min.) until the transition from a low to tall profile occurred at which time the pressure decreased at a rate of 0.09 mmHg/min. At ovulation, the pressure drops precipitously to 0.0 mmHg. The condition of the follicle, in particular the apex, was examined using scanning electron microscopy (SEM). At 13 hours after hCG, rupture sites had started forming in the apices of 94.3% of the unovulated follicles. In some instances, surface epithelial cells were stretched apart and gaps were present between cells. More often portions of the surface epithelium were missing and the underlying cell layers were exposed. Fluid and erythrocytes were observed passing through the developing rupture sites. Taken together these observations demonstrate that intrafollicular pressure in hamster preovulatory follicles decreases gradually at the time follicular smooth muscle cells contract. We suggest that contraction of follicular SMC is a slow, gradual process which causes formation and/or enlargement of holes in the rupture site. An increase in the size or number of these apertures would lead to increased leakiness and could account for the observed acceleration in the rate of pressure decrease during profile transition. Our observations are the first to correlate changes in intrafollicular pressure with the contraction of smooth muscle cells and condition of the apex.
Factors controlling the ovarian cycle in a temperate zone anuran, the toad Bufo bufo: Food uptake, nutritional state, and gonadotropin
Authors: Jørgensen C. Barker 
Published: June 2005

AbstractThe relations between nutritional state and vitellogenic growth of oocytes were studied in 87 sexually mature female toads Bufo bufo during the postbreeding season before initiation of the next annual ovarian cycle. Recruitment of small oocytes to vitellogenic growth was correlated with resumption of food uptake and the restoration of a positive energy balance in the toads that had become depleted of energy reserves during hibernation and breeding. Treatment with exogenous gonadotropin (hCG) immediately initiated vitellogenic growth, independently of the nutritional state. But the hCG‐induced vitellogenic growth was faster in toads that ate more than the maintenance ration than in those that ate less. hCG also maintained rapid vitellogenic growth in toads that starved after an initial period of feeding during which vitellogenic growth had been resumed. The results support the hypothesis that the period of ovarian quiescence, which normally follows breeding in Bufo bufo, and other anurans from the northern range of distribution of the species, results from inactivation of the hypothalamic‐hypophysial gonadotropic system, and that reactivation of the system depends upon reestablishment of a proper nutritional state of the organism.
Intercalary regeneration in legs of crayfish: Central segments
Authors: Mittenthal Jay E. , Trevarrow William W. 
Published: June 2005

AbstractEach leg of a crayfish embodies two types of morphogenetic fields, a limb field and a sequence of segmental fields. These fields were manifest in grafting operations along the proximodistal axis of legs 3 and 4. The propodite was grafted into more proximal segments—carpopodite, meropodite, or basipodite—in one set of operations. In a second set the propodite was host for a graft from the propodite or carpopodite. After these operations intercalary regeneration yielded complete regenerates, which manifested the limb field, and incomplete regenerates, which showed the segmental field. Complete legs contained all structures present in a normal leg. After some operations complete legs also had supernumerary structures. Several types of incomplete legs regenerated—(1) legs with fusion of the host and graft segments; (2) legs with a joint girdling only part of the leg circumference; and (3) legs with one mosaic segment intercalated to replace two deleted segments. These results show that both limb and segmental fields control intercalation in the tested segments of crayfish legs, as in insect legs. We propose a “mode control hypothesis” to describe the way in which molt cycle phase and healing rate bias the type of field controlling regeneration. Our observations also provide clues about the operation of the fields to generate structures. Homologous parts of the segmental field do not necessarily generate analogous structures in different leg segments. Although intersegmental membrane often develops in conjunction with an apodeme (muscle tendon), in a mosaic joint intersegmental membrane can still develop in the absence of the corresponding apodeme. In a partial joint the length of the segments adjacent to the joint is subnormal, but greater than the length of the segments between which a joint is missing. The jointless region may limit the growth of the jointed region.
Effects of saltwater feeding and reduced food intake on femurs of domestic ducklings
Authors: Wink Carole S. , Armstrong Este , Onge Michele St. 
Published: June 2005

AbstractSeven‐day‐old domestic ducklings were assigned to groups and fed freshwater and food ad libitum (control), 1% NaCl and food ad libitum (stressed), or freshwater and only as much food as the stressed group ate (starved). Tissues were sampled after 3 and 7 days. Other groups of ducklings were fed freshwater and food ad libitum for 9 days (control), 1% NaCl and food ad libitum for 7 days followed by freshwater for 2 days (de‐stressed), or freshwater and the same amount of food as the de‐stressed group for 7 days followed by food ad libitum for 2 days (de‐starved). Body weights were recorded and the femurs were analyzed. Univariate, multivariate, and allometric analyses clearly demonstrate that stressed and starved regimens influence femoral morphology differently. Stressing for 3 days reduced femoral ash and by 7 days had retarded femoral linear growth. Three days fo starvation produced no apparent effect on the femur, but starvation for 7 days reduced the amount of femoral ash/femoral lenght. Furthermore, major differences between stressed and starved ducks disappeared after de‐stressing for 2 days. Studies of bone growht and metabolism may benefit by using this avian model.
Differentiation of the avian secondary palate
Authors: Greene Robert M. , Shah Ravindra M. , Lloyd Martha R. , Crawford B. J. , Suen Roger , Shanfeld Joseph L. , Davidovitch Z. 
Published: June 2005

AbstractThe avian secondary palate exhibits the unique feature of a midline cleft. Cryostat sections indicated that although extensive contact between homologous shelves was present, chick palatal medial edge epithelium (MEE) failed to fuse. The failure of fusion and subsequent clefting of the avian palate were correlated with continued proliferation of the avian MEE, a failure of selective MEE cell death, and an absence of elevated levels of intracellular cAMP. Moreover, immunohistochemical staining for cAMP and microspectro‐photometric quantitation of staining intensity indicated that staining of chick MEE was significantly (p < .01) less than murine MEE at comparable gestational ages. These data indicate that differentiation of the avian secondary palate is fundamentally different than reported for the mammalian palate in that many developmental events known to be associated with normal mammalian palate formation (cessation of MEE proliferation, MEE cell death, elevated levels of MEE cAMP) fail to occur in the chick. The developing avian secondary palate, with its midline cleft, thus provides an interesting and useful model system with which to compare mammalian palate formation where the palate is normally fused in the midline.
Effects of delaying injections of prolactin and actinomycin D on metamorphic changes in thyroxine‐treated Ambystoma tigrinum
Authors: Platt James E. , Luetkehans Daniel L. 
Published: June 2005

AbstractAs a part of our continuing effort to understand the nature of the inhibition of thyroxine‐induced metamorphosis by prolactin in the tiger salamander, we examined the effects of delaying the initiation of prolactin treatment for progressively longer time intervals following the injection of a metamorphosing dose of thyroxine. Prolactin continued to inhibit gill resorption when given either 2 or 4 days following thyroxine, but the magnitude of the inhibition appeared to diminish. Delay of prolactin treatment until day 6 abolished the inhibition. In contrast, tail fin regression appeared to be inhibited in an undiminished fashion by prolactin given 2, 4, or 6 days following thyroxine. Body weight loss was inhibited in a similar manner. In a second experiment, actinomycin D, a transcription inhibitor, was observed to inhibit metamorphic changes. A delay of 5 days in the administration of this drug relative to thyroxine treatment produced a significant reduction in its inhibition of gill resorption, tail fin regression, and body weight loss. Surprisingly, late (day 5 following thyroxine) treatments with prolactin still produced a significant inhibition of fin regression and weight loss even when the inhibitory dose of actinomycin D was given on day 5 along with the prolactin. These results are discussed with respect to their implications concerning our understanding of the mechanism of prolactin action during amphibian metamorphosis.
Male fertility in Drosophila melanogaster: Genetics of the vermilion region
Authors: Geer Billy W. , Lischwe Timothy D. , Murphy Kevin G. 
Published: June 2005

AbstractMale sterility is one of three phenotypic effects of mutations at three loci in region 9F4 to 10C2 of the polytene X chromosome of Drosophila melanogaster, female sterility and reduced viability being other mutant effects. The male sterile (ms) alleles at these loci are allelic with lethal mutations. Male sterile mutations are induced at lower frequencies than lethal mutations at these loci by EMS. Because gene products of two of the loci are essential to larval development and the product of the other locus is essential to pupal development, the occurrence of ms mutations is not restricted to loci whose products function solely in developing adult tissue. Mutations at a locus in 10A2‐5 cause male sterility without adversely influencing viability or female fertility. We conclude that many loci whose products function in nonreproductive tissue can mutate to a form for which male sterility is a secondary effect. Another group of loci encode products that function exclusively in reproductive tissue.
Comparative feeding and breeding strategies of a sympatric pair of leopard frogs (Rana pipiens complex)
Authors: Frost John S. 
Published: June 2005

AbstractOvary weight and fat body weight relative to total body weight were ascertained from samples of Rana magnaocularis and Rana forreri taken routinely from sympatric populations of the two species. Relative fat body weight reaches a maximum in R. forreri in October and November, about 2 months later than in R. magnaocularis (August and September). Relative ovary weight in R. forreri reaches a maximum in July and August, some 8 to 9 months after the fat body peak. In R. magnaocularis, in contrast, maximum relative ovary weight occurs in November, December, and January, only about 2 to 4 months later than the fat body peak. Both species may capitalize on abundant food in late summer to increase fat storage. Maturation of the ova and the laying of eggs are almost completely asynchronous for the two species, however. These differences are considered from the standpoint that they may represent an example of reproductive character displacement via temporal competitive exclusion.
Quantitative study on the reproduction of two strains of agamic planarians Dugesia gonocephala and Dugesia tigrina
Authors: Zaccanti Francesco , Tognato Giovanni 
Published: June 2005

AbstractIn two asexual planarian strains (Dugesia gonocephala and Dugesia tigrina), reproduction by transverse fission and regeneration is observed under normal conditions and upon decapitation and reserpine treatment. The pattern of asexual reproduction processes in planarians, as it results from our quantitative observations compared with the literature data, indicates that autotomy and regeneration processes have an extremely wide range of possible expressions. In such a heterogeneous situation it is still possible to suppose the existence of a negative cephalic control of fissiparity, similar to the ones involved in general tissue organization and in the regeneration of planarians.
Refractive index gradients subserve optical isolation in a light‐adapted reflecting superposition eye
Authors: Nilsson D.‐E. 
Published: June 2005

AbstractThe freshwater shrimp Macrobrachium rosenbergii (de Man) has reflecting superposition compound eyes. Upon adaptation from dark to light conditions, the eye converts from superposition to apposition optics by screening pigment migration. The clear zone, typical of dark‐adapted superposition eyes, persisted after adaptation to 500 lux, when the eye optically behaved like an apposition eye. In this state, optical isolation is maintained by a proximal refractive‐index gradient in the crystalline cone, which only requires the proximal pigment to be in the light‐adapted position around the junction between the cone and rhabdom. Thus, the distal pigment need not invade the clear zone for the eye to convert to apposition optics. This mechanism probably decreases the time required for light adaptation. Furthermore, as a result of total internal reflections in the cone tip, the proximal gradient increases the acceptance angle.
The effects of pulsed magnetic fields on chick embryo cartilaginous skeletal rudiments in vitro
Authors: Archer C. W. , Ratcliffe N. A. 
Published: June 2005

AbstractThe biological response of cultured 7‐day embryonic chick tibiae to small alternating currents induced by pulsed magnetic fields (PMFs) was investigated. It was found that continuous exposure to PMFs over 7 days did not alter the overall DNA content of rudiments nor the incorporation of 3H‐thymidine when compared with control tibiae. The overall collagen content of explants was slightly reduced by PMF exposure whilst the incorporation of 3H‐proline was significantly suppressed. The synthesis of sulphated glycosaminoglycans was also measured in terms of 35SO4− incorporation, but PMF treatment failed to alter the levels of isotope incorporation.These results suggest that, whereas noncollagenous, and possibly collagenous, protein synthesis is affected by PMF exposure, glycosaminoglycan synthesis is not. Histological and electron microscopical observations substantiated this interpretation and revealed selective inhibition of matrix secretion in the periphery of the proliferative epiphyseal zones in experimental explants. High‐power electron microscope examination of these zones showed that PMF‐exposed matrix was sparsely invested with fibrous protein while elements of the stellate reticulum had formed large aggregates which were often clumped about the cell membrane. The results are discussed in terms of the possible role of naturally occurring potentials in the development and maintenance of connective tissue systems such as cartilage and bone.
Epigenesis in developing avian scales. II. Cell proliferation in relation to morphogenesis and differentiation in the epidermis
Authors: Tanaka Shoji , Kato Yoshihiro 
Published: June 2005

AbstractThroughout the early development of chicken scale epidermis, consisting of discrete placode and interplacode cell populations, morphogenesis and differentiation were examined from the standpoints of cell proliferation. From day 9.25 to day 11, active cell proliferation was observed only in the interplacode region, whereas the number of constituent cells increased considerably within the placode. After 26 hr of continuous labeling with [3H]thymidine (3H‐TdR) in ovo, three regions could be recognized: (1) unlabeled placode on the distal edge, (2) labeled placode in both lateral and proximal sites to the unlabeled placode, and (3) extensively labeled interplacode on the most proximal site of the scale.Examination of the distribution pattern of labeled cells has demonstrated that a fraction of the cells in the interplacode transits and annexes only to the proximal side of the placode. Cells transit after mitosis, accompanied with changes in morphology and proliferation activity. During the period of cell transition, orientation of mitosis paralleled completely along the proximodistal axis of the scale. Cell marking with carbon particles was carried in organ cultures from day 10, and the changes in the position of marked cells were observed. The results confirm those obtained after continuous labeling with 3H‐TdR. Various combinations of pulse‐chase experiments with 3H‐TdR clearly demonstrated the establishment of a cell lineage in which cells were aligned along the axis of the scale according to order of their birth. Along with a sudden resumption of active proliferation after day 11, a new class of cells (suprabasal cells) differentiated upward from the basal cells on the top region of the hump scale. At the first stage of development of suprabasal cells from day 11 to day 11.75, the direction of mitoses became preferentially polarized in the direction of axis vertical to the basal lamina. The important coordination of cell proliferation in relation to morphogenesis and cell differentiation is discussed.
Modulation of melanosome ultrastructure in cultured embryonic pigment cells
Authors: Garcia Raul I. , Szabo George 
Published: June 2005

AbstractMelanosomes synthesized by embryonic chick retinal pigment cells in vitro are of a different size and shape than those made in ovo and in vivo. Ultrastructurally, the melanosomes made by cultured cells are small, spherical, contain an irregular internal matrix, and appear similar to the pheomelanosomes found in red hair and feathers. This modulation in melanosome ultrastructure in cultured retinal pigment cells does not appear to be caused by an irreversible change in differentiated capability but to a response of cells to the culture environment. Cells grown in embryo extract‐free and serum‐free defined media were found to synthesize melanosomes of normal size and shape in vitro, although at a much reduced number. The predominant melanosome type found was still the smaller, spherical variety. It appears that some still unknown factors in the culture environment have produced a shift to a different type of melanogenesis.
The relationship between age and body size of individuals in isolated clutches of the terrestrial slug, Limax maximus (linnaeus, 1858)
Authors: Prior David J. 
Published: June 2005

AbstractThe variability of the relationship between age and growth rate was analyzed using isolated clutches of eggs from the terrestrial slug, Limax maximus. The slugs that hatched from isolated clutches of eggs were weighed every 30 days until they were 150 days old. The weights of the slugs at every age were highly variable. For example, the range of weights at 150 days was 0.21–8.15 gm, which represents a 39‐fold difference. In addition, there was considerable variation in the age of slugs that weighed the same. The mean weights of slugs in clutch T4 at 90 days and of slugs in clutch T2 at 150 days were the same (2.19 gm). Also the ranges of weights at 30 and 150 days indicate that there were 30‐day‐old slugs that weighed the same as some 150‐day‐old slugs. The large variability of growth rate of Limax indicates that age‐related studies of gastropod molluscs will require knowledge of the hatch dates, as well as developmental or biochemical staging schemes.