Role of subdermal current shunts in the failure of frogs to regenerate.

Large, uniform, skin-driven currents (20-40 muamp/cm2) leave the ends of limb stumps of post-metamorphic frogs (Rana pipiens) from about the first through the tenth day after amputation. However, right after amputation, while currents of comparable density may leave the periphery of the cut surface, current densities are greatly depressed in the center of this surface. We suggest that this depression is brought about by shunting through the subdermal lymph space (characteristic of anurans but not urodeles); continues in covert form after formation of a wound epithelium; and helps explain the ability of small, imposed currents to initiate frog limb regeneration.     

Anatomy of axolotl flank integument during limb bud development with special reference to a transcutaneous current predicting limb formation

We have compared the anatomy of immature axolotl integument from limb-forming regions with adjacent non-limb-forming regions of the flank, concentrating on the earliest stages of limb bud development. We have extended these observations to include prominent buds just prior to their differentiation. At the ultrastructural level, we note striking differences between these two regions of skin, including a complete loss of hemidesmosomes and tonofilaments in the basal cells of the epidermis; a marked deterioration of the basal lamella; and focal areas of desquamating cells in the apical regions of the bud-all characteristics of limb-forming regions. These observations were made in the same larvae which provided measurements of a steady endogenous electric (ionic) current that either was coincident with or predicted the area of limb bud outgrowth (Borgens et al.: J. Exp. Zool. 228:491-503, 1983). We discuss these physiological measurements, the changes in the anatomy of the bud-forming region, and the relevance of these observations to our theory of early limb formation.     

Electrical responses to amputation of the eye in the mystery snail

Immediately following amputation through the eyestalk of the mystery snail (Pomacea), a persistent ionic current enters the apical amputation surface of the eyestalk stump. The circuit is completed by current driven from undamaged integument of the eyestalk stump and other body regions. The current is relatively steady during the first 10 hours following amputation. Currents subsequently begin a slow decline to base line levels by 60 hours postamputation--a time coincident with wound healing processes. The "battery" driving this ionic current is the internally negative transepidermal potential existing across the snail integument--perhaps the result of a net inward pumping of chloride across the skin. This system is compared to other regeneration models such as the amphibian limb, bone fracture repair, and skin wound healing. We suggest that ionic current may be a control of eye regeneration in the snail.     

Eye regeneration in the mystery snail

Mystery snails (Family Ampullariidae) are aquatic prosobranchs which possess structurally complex eyes at the tip of a cephalic eyestalk. No other sensory organs are found in association with this stalk. These snails possess the ability to regenerate the eye completely after amputation through the mid-eyestalk. Amputation induces gross changes in the cellular character of the entire eyestalk; in particular, an invagination of integumentary epithelium at the apex of the eyestalk stump produces a shallow cleft or "eyecup." Differentiation of all components of the eye apparently occurs by transdetermination of these epithelial cells. Retinal differentiation and the appearance of a new lens is observed as soon as 14 days postamputation. Complete eyes (by external observation), although smaller than the originals, have regenerated by 25 days postamputation. We compare this regeneration to the reconstruction of other animal tissues, in particular the regeneration of amphibian limbs.     

Synthesis,characterization, and electrocatalytic behaviour of hydrothermally grown nanostructured La2O3 and La2O3/K-complex

Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4-N,N-dimethylaminobenzoate-κO)(μ2–4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La₂O₃ nanomaterials to obtain a nanohybrid La₂O₃/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and ¹H and ¹³C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La₂O₃/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La₂O₃/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour.     

Two silicone nontoxic fouling release coatings: Hydrosilation cured PDMS and CaCO3 filled,ethoxysiloxane cured RTV11

Two silicone coatings have been evaluated for barnacle adhesion. One coating is an unfilled hydrosilation cured polydimethylsiloxane (PDMS) network, while the other is a room temperature vulcanized (RTV), filled, ethoxysiloxane cured PDMS elastomer, RTV11^?. The adhesion strength of one species of barnacle, Balanus eburneus, to the hydrosilation coatings is in the range of 0.37–0.60 kg cm^‐2 while the corresponding range for RTV11 is 0.64–0.90 kg cm^‐2. The easier release of B. eburneus from the hydrosilation cured network compared to RTV11 is discussed in relationship to differences in bulk and surface properties. Preliminary results suggest bulk modulus may be the most important parameter in determining barnacle adhesion strength. In light or mechanical property analysis, a re‐evaluation of surface properties and chemical stability is presented.     

Biological effects of power frequency magnetic fields: Neurochemical and toxicological changes in developing chick embryos

BACKGROUND: There are several reports that indicate a linkage between exposure to power frequency (50 - 60 Hz) magnetic fields with abnormalities in the early embryonic development of the chicken. The present study was designed to understand whether power frequency electromagnetic fields could act as an environmental insult and invoke any neurochemical or toxicological changes in developing chick embryo model. METHODS: Fertilized chicken eggs were subjected to continuous exposure to magnetic fields (50 Hz) of varying intensities (5, 50 or 100 microT) for a period of up to 15 days. The embryos were taken out of the eggs on day 5, day 10 and day 15. Neurochemical (norepinephrine and 5-hydroxytryptamine) and amino acid (tyrosine, glutamine and tryptophan) contents were measured, along with an assay of the enzyme glutamine synthetase in the brain. Preliminary toxicological investigations were carried out based on aminotransferases (AST and ALT) and lactate dehydrogenase activities in the whole embryo as well as in the liver. RESULTS: The study revealed that there was a significant increase (p < 0.01 and p < 0.001) in the level of norepinephrine accompanied by a significant decrease (p < 0.01 and p < 0.001) in the tyrosine content in the brain on day 15 following exposure to 5, 50 and 100 microT magnetic fields. There was a significant increase (p < 0.001) in glutamine synthetase activity resulting in the significantly enhanced (p < 0.001) level of glutamine in the brain on day 15 (for 100 microT only). The possible mechanisms for these alterations are discussed. Further, magnetic fields had no effect on the levels of tryptophan and 5-hydroxytryptamine in the brain. Similarly, there was no effect on the activity of either aminotransferases or lactate dehydrogenase in the whole embryo or liver due to magnetic field exposure. CONCLUSIONS: Based on these studies we conclude that magnetic field-induced changes in norepinephrine levels might help explain alterations in the circadian rhythm, observed during magnetic field stress. Also, the enhanced level of glutamine can act as a contributing factor for developmental abnormalities.     

Sex differences in the rate of fatigue development and recovery

Background

Many musculoskeltal injuries in the workplace have been attributed to the repetitive loading of muscle and soft tissues. It is not disputed that muscular fatigue is a risk factor for musculoskeltal injury, however the disparity between gender with respect to muscular fatigability and rate of recovery is not well understood. Current health and safety guidelines do not account for sex differences in fatiguability and may be predisposing one gender to greater risk. The purpose of this study was to quantify the sex differences in fatigue development and recovery rate of lower and upper body musculature after repeated bouts of sustained isometric contractions.

Methods

Twenty-seven healthy males (n = 12) and females (n = 15) underwent bilateral localized fatigue of either the knee extensors (male: n = 8; female: n = 8), elbow flexors (male: n = 8; female: n = 10), or both muscle groups. The fatigue protocol consisted of ten 30-second sub-maximal isometric contractions. The changes in maximum voluntary contraction (MVC), electrically evoked twitches, and motor unit activation (MUA) were assessed along with the ability to control the sustained contractions (SLP) during the fatigue protocol using a mixed four-factor repeated measures ANOVA (gender × side × muscle × time) design with significance set at p < 0.05.

Results

There was a significant loss of MVC, MUA, and evoked twitch amplitude from pre- to post-fatigue in both the arms and legs. Males had greater relative loss of isometric force, a higher rate of fatigue development, and were less capable of maintaining the fatiguing contractions in the legs when compared to the females.

Conclusion

The nature of the induced fatigue was a combination of central and peripheral fatigue that did not fully recover over a 45-minute period. The results appear to reflect sex differences that are peripheral, and partially support the muscle mass hypothesis for explaining differences in muscular fatigue.