Processing of Mechanoreceptive Input in Crayfish: An In Vivo and In Vitro Study of the Role of the Cuticular Stress Detectors in Motor Control

Cuticular stress detectors (CSD1 and CSD2) are mechanoreceptors positioned in the proximal parts of the legs of decapod crustaceans. Using a reduced preparation consisting of the isolated thoracic central nervous system and a walking leg of either of the two crayfish species, Procambarus clarkii or Pacifastacus leniusculus, it has been possible to study by means of extracellular and intracellular techniques the physiological properties of the sensory fibres and the reflex responses in the four proximal muscle groups to mechanical and electrical stimulation of the receptor organs. The location of the CSD terminals within the thoracic ganglion was determined by anterograde fillings of the afferent fibres with biocytin. The anterograde fills also showed the absence of any cell bodies within the thoracic ganglion. Thus one can be certain that the CSD nerves contain no motorneurone axons and that all fibres within the CSD nerves belong to sensory cells. These have their cell bodies in the periphery; their orthodromic direction of conduction is from the periphery to the thoracic central nervous system. Most CSD fibres terminate, and branch extensively within the ganglion. Nevertheless, some CSD1 fibres were found to pass through the ganglion and continue rostrally within the ventral nerve cord. Intracellular recordings of impulses arriving in the central ganglion made it possible to identify the physiological properties of single receptor cells when stimulating the receptor organs mechanically. The recordings from CSD2 terminals were found to be in consensus with extracellular recordings from previous studies. CSD1 intracellular recordings revealed a class of sensory fibres not previously described. They were identified as 'high threshold' fibres, for large amplitude, high frequency stimuli were necessary for their activation. These CSD 1 fibres appear to be responsible for the occurrence of a reflex response reversal in anterior levator motorneurones. This is discussed with reference to a possible role of the CSD 1 receptor organ in the control of autotomy. Intracellular recordings from sensory terminals also revealed the presence of centrally coupled sensory afferents. Coupled units often had different conduction velocities, and 'on' units were sometimes coupled with 'off units. Lucifer Yellow usually filled two or more fibres when injected into a single cell. This is in support of central coupling, for the dye is known to cross gap junctions. Some sensory units showed antidromic spike conduction, i.e. from the ganglion to the sense organ, being always coupled to fibres firing orthodromically. It is suggested that the coupling provides a mechanism for amplification of the sensory signals, the antidromic spikes induced by impulses coming from coupled units. This is supported by the finding that stronger mechanical or electrical stimulation of the sensory fibres leads to an increased occurrence of antidromic spikes. Using a number of electrophysiological and pharmacological tests, it has been demonstrated that at least 32% of all the connections recorded between the CSDs and the motorneurones of the four proximal muscle groups are monosynaptic. The reflex responses within one motorneurone group varied. The importance of sensory feedback in shaping the final motor output was studied in preparations showing rhythmic, reciprocal activity in antagonistically operating muscle groups. Rhythmic CSD activity was shown to be able to entrain such fictive locomotor activity. CSD1 activity during normal walking behaviour was studied in an in vivo preparation. Thus, reflex responses could be discussed with knowledge of the natural activation of the CSDs and related to their functional significance in locomotion

Pressure Effect and Specific Heat of RBa2Cu3Ox at Distinct Charge Carrier Concentrations: Possible Influence of Stripes

In YBa2Cu3Ox, distinct features are found in the pressure dependence of the transition temperature, dTc/dp, and in DeltaCp*Tc, where DeltaCp is the jump in the specific heat at Tc: dTc/dp becomes zero when DeltaCp*Tc is maximal, whereas dTc/dp has a peak at lower oxygen contents where DeltaCp*Tc vanishes. Substituting Nd for Y and doping with Ca leads to a shift of these specific oxygen contents, since oxygen order and hole doping by Ca influences the hole content nh in the CuO2 planes. Calculating nh from the parabolic Tc(nh) behavior, the features coalesce for all samples at nh=0.11 and nh=0.175, irrespective of substitution and doping. Hence, this behavior seems to reflect an intrinsic property of the CuO2 planes. Analyzing our results we obtain different mechanisms in three doping regions: Tc changes in the optimally doped and overdoped region are mainly caused by charge transfer. In the slightly underdoped region an increasing contribution to dTc/dp is obtained when well ordered CuO chain fragments serve as pinning centers for stripes. This behavior is supported by our results on Zn doped NdBa2Cu3Ox and is responsible for the well known dTc/dp peak observed in YBa2Cu3Ox at x=6.7. Going to a hole content below nh=0.11 our results point to a crossover from an underdoped superconductor to a doped antiferromagnet, changing completely the physics of these materials.Comment: 6 pages, 5 figures Proccedings of the 'Stripes 2000' Conference, Rome (2000

Ground-based intercomparison of two isoprene measurement techniques

International audienceAn informal intercomparison of two isoprene (C5H8) measurement techniques was carried out during Fall of 1998 at a field site located approximately 3 km west of Boulder, Colorado, USA. A new chemical ionization mass spectrometric technique (CIMS) was compared to a well-established gas chromatographic technique (GC). The CIMS technique utilized benzene cation chemistry to ionize isoprene. The isoprene levels measured by the CIMS were often larger than those obtained with the GC. The results indicate that the CIMS technique suffered from an anthropogenic interference associated with air masses from the Denver, CO metropolitan area as well as an additional interference occurring in clean conditions. However, the CIMS technique is also demonstrated to be sensitive and fast. Especially after introduction of a tandem mass spectrometric technique, it is therefore a candidate for isoprene measurements in remote environments near isoprene sources

Status of the emittance transfer experiment emtex

In order to improve the injection efficiency of the round UNILAC heavy ion beam into the asymmetric acceptance of the SIS18 it would be of great advantage to decreasethe horizontal emittance by a so called emittance transferto the vertical plane. In this contribution the present statusof the emittance transfer experiment EMTEX at GSI will be reported. A short introduction about the theoretical background of the technique will be given, while the mainpart is dedicated to the practical solutions setting up a testbeam line at GSI. Finally, the results of a first commissioning beam time will be presented. The scheduled beam time to apply the emittance transfer technique foreseen in spring 2014 had to be shifted to calendar week 26 in 2014, just after this conference as some components have not been delivered in time by the contractor. The results and comparison to the theoretical predictions you may find in later publications