Hyphessobrycon platyodus (Teleostei: Characiformes), a new species from the Rio Madeira basin, Brazil, with comments on how multicuspid teeth relate to feeding habits in Characidae.

A new species of Hyphessobrycon is described from the Rio Juma, a tributary of the lower Rio Aripuanã-Rio Madeira basin, Amazonas, Brazil. Hyphessobrycon platyodus can be distinguished from its congeners by the: presence of an elongated dorsal fin in adult males, 25-28 branched anal-fin rays and absence of dark blotches from the dorsal fin and caudal peduncle. The presence of multicuspid teeth in species of Characidae and its relation with feeding habits are briefly commented on.

Behaviour, feeding habits and ecology of the blind catfish Phreatobius sanguijuela (Ostariophysi: Siluriformes).

The subterranean fish Phreatobius sanguijuela, originally described from Bolivia, was captured in different wells near São Francisco do Guaporé, Rondônia State, Brazil. Thirty wells were investigated in April and July 2012, and September 2013. These surveys resulted in the capture of 58 individuals from eight wells and comprised three to 14 individuals per well. The capture of the individuals allowed a detailed evaluation of their colours in life, behaviour in the field and in captivity, aspects of their biology, confirmation of the species identification and provided new diagnostic characteristics to distinguish between P. sanguijuela and Phreatobius dracunculus. Cannibalism, territorialism, agonistic interactions and phototaxis behaviour were not observed. Phreatobius sanguijuela exhibited cryptobiotic habits and two behaviours under stressful conditions. The analysis of stomach contents reveals that this species apparently feeds on invertebrates, almost exclusively on earthworms. The sex ratio was 1:1. The absence of opercular movement during the resting period associated with intense blood irrigation of the skin indicates a possible cutaneous respiration as an alternative form of gas exchange. Local people often mistake P. sanguijuela for helminths and have the habit of releasing non-native fishes into the wells or to use chemicals to eliminate them. The consequence of this habit for the conservation of the species requires further evaluation.

Intermittent reperfusion fails to prevent posttourniquet neurapraxia.

This study examined the effects of intermittent reperfusion on peripheral nerve function. Rabbits were randomized to undergo 4 hours of 350 mm Hg tourniquet compression to a hind limb either continuously, interrupted by a single 10-minute reperfusion interval after 2 hours, or interrupted by 10 minutes of reperfusion after each hour. A control group had the tourniquet applied for 4 hours but it was never inflated. The animals were examined clinically for neuromuscular dysfunction and the structure and function of the peripheral nerves were evaluated 1 week after tourniquet compression. Animals that underwent compression had a foot drop and decreased toe-spread reflex. There was greater intraneural edema and slower nerve conduction velocity in nerve segments that were directly compressed by the tourniquet but no apparent abnormalities in segments distal to the tourniquet. Intermittent reperfusion failed to diminish the clinical, structural, or functional consequence of the neurologic injury.

Comparison of functional deficits in the rabbit tibialis anterior following tourniquet ischemia and tourniquet compression.

The purpose of this study was to measure the contractile properties of skeletal muscle after direct compression with a tourniquet and to compare these properties with those found after a similar period of tourniquet ischemia. A rabbit model of tourniquet compression of the tibialis anterior was developed and tested for this investigation. Fifty-seven animals then were divided into four protocol groups: (a) thigh tourniquet (ischemia) at 350 mm Hg (46.7 kPa), (b) leg tourniquet (compression) at 350 mm Hg (46.7 kPa), (c) leg tourniquet at 125 mm Hg (16.7 kPa), and (d) controls. A significant decrease in maximum tetanic tension was demonstrated in all three experimental groups. Direct compression at 350 mm Hg resulted in the greatest decline in maximum tetanic tension (22.6% of control), followed by compression at 125 mm Hg (30.5%) and ischemic injury (40.2%). In addition, direct compression at 350 mm Hg resulted in a significantly greater loss of force-generating capacity when compared with the ischemic group (p < 0.01). A similar pattern was noted for the rate of rise in maximum tetanic tension. Gross histologic examination of the tibialis anterior sections was consistent with the results of functional testing, with the more severe abnormalities noted in the compressed specimens. These results clearly demonstrate that tourniquet compression injury results in a more significant loss of functional strength and contractile speed than tourniquet ischemia. Further investigations on the safe limits of tourniquet use thus should be directed toward measuring the effect of the pneumatic tourniquet on the underlying soft tissues.

Effects of an antioxidant in a rabbit model of tourniquet-induced skeletal muscle ischemia-reperfusion injury.

The purpose of this study was to evaluate the effects of U74006F, a new antioxidant, on isometric contractile function after tourniquet-induced ischemia-reperfusion injury. Twenty-six NZW rabbits underwent either 2 or 4 hr of thigh tourniquet compression. Animals were randomized to receive U74006F or an equal volume of its citrate vehicle. When tibialis anterior function was tested 2 days later, there was no difference between treatment groups in peak tension, rate of force production, contraction time, half relaxation time, or resistance to fatigue. The use of U74006F failed to improve functional outcome in this model of ischemia-reperfusion injury.

Stochastic distribution of a short region of Z-DNA within a long repeated sequence in negatively supercoiled plasmids.

We have analyzed, at nucleotide resolution, the progress of the B-to-Z transition as a function of superhelical density in a 2.2-kilobase plasmid containing the sequence d(C-A)31.d(T-G)31. The transition was monitored by means of reactivity to two chemical probes: diethyl pyrocarbonate, which is sensitive to the presence of Z-DNA, and hydroxylamine, which detects B-Z junctions. At a threshold negative superhelical density between about 0.048 and 0.056, hyper-reactivity to diethyl pyrocarbonate appears throughout the CA/TG repeat and remains as the superhelical density is further increased. However, there is no reactivity characteristic of B-Z junctions until the superhelical density reaches 0.084, when single cytosines at each end of the repeat become hyper-reactive to hydroxylamine. A two-dimensional gel analysis of this system by others (Haniford, D. B., and Pulleyblank, D. E. (1983) Nature 302, 632-634) indicates that only about half of the 62 base pairs of the CA/TG repeat undergo the initial transition at omega = 0.056. Our results indicate that this region of Z-DNA is free to exist anywhere along the CA/TG repeat and is probably constantly in motion. Well defined B-Z junctions are seen only when there is sufficient supercoiling to convert the entire CA/TG sequence to Z-DNA. The implications for possible B-Z transitions in chromosomal domains of different sizes are discussed.