Acute toxicity bioassay using Daphnia obtusa as a test organism

The introduction of the cladoceran Daphnia obtusa as a test organism in toxicity bioassays was considered. Development of bioassay included strain isolation, culture conditions, and toxicity test adaptation. Acute toxicity tests for Cr(VI), Mn(II), Cu(II), Cd(II), and Hg(II), phenol, sodium dodecyl sulfate, methanol, ethanol, and paraquat at 24 and 48 h of exposure show a sensitivity within the range reported for other cladocerans or fish. Sensitivity to carbaryl was higher than that found for fish. These results and the spread distribution of the species in the South of South America makes the bioassay a possible good option for the monitoring of toxicants in freshwater systems in the region. © 1996 by John Wiley & Sons, Inc.     

Central precocious puberty in Klinefelter syndrome: A case report with longitudinal follow-up of growth pattern

We report idiopathic central precocious puberty in a boy with Klinefelter syndrome and describe the pattern of linear growth and body proportion from the onset of precocious puberty to final height. The patient was not treated for precocious puberty. He reached adequate adult height, for both general population and normative values of Klinefelter syndrome and normal body proportions. We conclude that precocious puberty in Klinefelter syndrome may result in normal body proportion by inducing a major growth spurt of the trunk rather than in the limbs, and that adult height prognosis is not altered by precocious puberty. Given the possible occurrence of precocious puberty in Klinefelter syndrome, we advise a karyotype analysis in boys with sexual precocity, mainly in those who show small rather than enlarged testes. © 1996 Wiley-Liss, Inc.     

Somatosensory evoked potentials during the ideation and execution of individual finger movements

Scalp somatosensory evoked potentials (SEPs) were recorded in 10 volunteers after median nerve stimulation, in four experimental conditions of hand movements performance/ideation, and compared with the baseline condition of full relaxation. The experimental conditions were (a) self-improvised hand-finger sequential movements; (b) the same movements according to a read sequence of numbers; (c) mental ideation of finger movements; and (d) passive displacement of fingers in complete relaxation. Latencies and amplitudes of the parietal (N20, P25, N33, and P45) and frontal peaks (P20–22, N30, and P40) were analyzed. Latencies did not vary in any of the paradigms. Among the parietal complexes, only the P25-N33 amplitude was significantly reduced in (a), (b), (c), and (d) and the N20-P25 was reduced in (a) and (d); among frontal waves, N30 and P40 were significantly reduced (20–75%) in (a) and (b). Coronal electrodes showed amplitude decrements maximal at the frontal-rolandic positions contralateral to the stimulated side. © 1996 John Wiley & Sons, Inc.     

New synthesis of a highly active δ-MgCl2 for MgCl2/TiCl4/AlEt3 catalytic systems

A good supporting material for Ziegler-Natta type catalysts was obtained by reaction between powdered metallic magnesium and 1-chloro-n-C_mH_2m+1 (m = 3–9). This reaction affords a highly disordered form of MgCl₂ which was characterized by FT-IR spectroscopy and powder X-ray diffraction (XRD) analysis. This MgCl₂ form shows a crystallographic disorder much higher than that exhibited by the products obtained following the commercial activation procedures of α-MgCl₂, either mechanical or chemical. As shown by the XRD spectra, the synthetized MgCl₂ is characterized by the typical structure of the δ-form. Therefore, this MgCl₂ form, in view of its highly disordered structure, appears as a promising material for the preparation of active supported Ziegler-Natta type catalysts. Thus, by titanation of the obtained δ-MgCl₂ we have prepared some supported catalysts which have been tested in the slurry propene polymerizations, showing high activity (136000–138000 gPP/gTi) and good stereoselectivity (82–88% I.I.).     

Central motor tract propagation in man: studies with non-invasive, unifocal, scalp stimulation

Motor-evoked potentials (MEPs) to unifocal, anodal scalp stimulation have been recorded in 45 healthy volunteers from proximal and distal upper limb muscles. Optimal responses were obtained through a pericranial cathode consisting of 6 or more regularly spaced, interconnected plaques whose impedance was carefully balanced with that of a 0.8-cm2 stimulating anode on the scalp. Individual rectangular pulses with threshold intensity (70-86 mA) 100-200 microseconds in duration, with rise-decay times shorter than 50 microseconds resulted more efficient in eliciting individual MEPs in the target muscle. The foci of maximal response for hand and shoulder muscles were localized. The scalp-to-cervical cord conduction time along the motor tracts governing the hand muscles was 5.21 +/- 0.42 ms. This index was highly correlated with the subject's height and stable in time when repeatedly tested. Collision between orthodromically and antidromically propagated motor impulses was obtained by simultaneous stimulation of scalp and median nerve at wrist. Response facilitation was achieved by means of prestimulus voluntary contraction of the target muscle, continuous vibration of its tendon or scalp stimulation with paired shocks. Facilitation of MEPs was obtained by prestimulating the ipsilateral motor cortex 8-24 ms before the stimulation of the one contralateral to the target muscle. This was considered at least in part mediated by transcallosal connections. An efferent volley secondary to scalp stimulation was recorded for the nerve trunk with the near-nerve technique. Segmental and suprasegmental mechanisms underlying MEP facilitation provoked by phasic and tonic contractions of the target muscle have been investigated.     

Simultaneous motor output and sensory input: cortical interference site resolved in humans via neuromagnetic measurements

Neuromagnetic measurements were carried out during median nerve stimulation at the wrist in complete relaxation (a) and during active contraction of the hand muscles (b). Firstly, activity of the generator source responsible for the major component of the sensory evoked magnetic fields (SEFs) was mapped and localized during condition (a) and (b). Then the subtraction maps ((a)-(b)) were obtained and the virtual 'dipole' responsible for the 'interference' (less than or equal to SEFs amplitude) between the afferent input and the motor output was tridimensionally localized in a position compatible with the knee and the convexity of the postcentral gyrus.