New methods have been recently developed to explore selectively presynaptic inhibition of Ia afferents in humans. They have allowed us to describe a highly specialized organisation in these pathways. A differential control has been disclosed during voluntary movements among various motoneuronal pools: at the onset of a selective voluntary contraction presynaptic inhibition of Ia afferents projecting to the 'contracting' motoneurons is strongly decreased whereas presynaptic inhibition of Ia afferents to antagonistic or synergistic motoneuronal pools, not involved in the contraction, is increased. Indirect arguments suggested that these modulations are centrally patterned. A differential control has been also disclosed between upper and lower limb pathways. Using transcranial magnetic stimulation to induce a descending corticospinal volley, we have shown that a corticospinal volley inhibits preferentially 'presynaptic interneurons'at the lumbar spinal level, an effect which is strengthened by a cutaneous input whereas it preferentially activates 'presynaptic interneurons' at the cervical spinal level, an effect which is inverted by a cutaneous input. 相似文献
The venom of the North African scorpion Androctonus mauretanicus mauretanicus possesses numerous highly active neurotoxins that specifically bind to various ion channels. One of these, P05, has been found to bind specifically to calcium-activated potassium channels and also to compete with apamin, a toxin extracted from bee venom. Besides the highly potent ones, several of these peptides (including that of P01) have been purified and been found to possess only a very weak, although significant, activity in competition with apamin. The amino acid sequence of P01 shows that it is shorter than P05 by two residues. This deletion occurs within an α-helix stretch (residues 5–12). This α-helix has been shown to be involved in the interaction of P05 with its receptor via two arginine residues. These two arginines are absent in the P01 sequence. Furthermore, a proline residue in position 7 of the P01 sequence may act as an α-helix breaker. We have determined the solution structure of P01 by conventional two-dimensional 1H nuclear magnetic resonance and show that 1) the proline residue does not disturb the α-helix running from residues 5 to 12; 2) the two arginines are topologically replaced by two acidic residues, which explains the drop in activity; 3) the residual binding activity may be due to the histidine residue in position 9; and 4) the overall secondary structure is conserved, i.e., an α-helix running from residues 5 to 12, two antiparallel stretches of β-sheet (residues 15–20 and 23–27) connected by a type I′ β-turn, and three disulfide bridges connecting the α-helix to the β-sheet. 相似文献
A plasmon waveguide resonance (PWR) sensor is proposed for studying the interaction between gold nanoparticles and proteins. The ability of the PWR sensor to operate in both TM and TE Polarizations, i.e. its polarization diversity, facilitates the simultaneous spectroscopy of the nanoparticles surface reactions using both polarizations. The response of each polarization to streptavidin‐biotin binding at the surface of gold nanoparticles is investigated in real time. Finally, using the principles of multimode spectroscopy, the nanoparticle's surface reactions are decoupled from the bulk solution refractive index variations.
Schematic diagram of the NP‐modified PWR sensor 相似文献
Group members present physical and physiological differences according to their age, sex or social status, which could generate
motivation differences among individuals during travel. In spite of these divergences of interest among individuals, the group
succeeds more often than not in making a collective decision about departure time and which direction to take. To reach a
consensus decision, animals should exchange information relating to characteristics of group movement through different communication
channels. The main purpose of this study is to understand the function of behaviour patterns displayed during movements of
white-faced capuchins (Cebus capucinus). We designed experiments in which we provoked collective movements involving a binary choice. During experiments, a video
camera recorded the behaviour of each capuchin, which enabled us to determine which individuals displayed a behavioural pattern
during travel and how this behaviour influenced the other group members. We found that looking backwards seemed to permit
the recruitment of group mates during collective movement. This behaviour also seemed to allow the quantification of the number
of followers, since the emitter modified its locomotion speed according to this number. In this preliminary study, we showed
that visual behaviour was used to recruit and monitor group mates during collective movements and provided information on
mechanisms involved in maintaining cohesion and coordination among group members during travel. 相似文献
Cone-rod dystrophies are inherited dystrophies of the retina characterized by the accumulation of deposits mainly localized to the cone-rich macular region of the eye. Dystrophy can be limited to the retina or be part of a syndrome. Unlike nonsyndromic cone-rod dystrophies, syndromic cone-rod dystrophies are genetically heterogeneous with mutations in genes encoding structural, cell-adhesion, and transporter proteins. Using a genome-wide single-nucleotide polymorphism (SNP) haplotype analysis to fine map the locus and a gene-candidate approach, we identified homozygous mutations in the ancient conserved domain protein 4 gene (CNNM4) that either generate a truncated protein or occur in highly conserved regions of the protein. Given that CNNM4 is implicated in metal ion transport, cone-rod dystrophy and amelogenesis imperfecta may originate from abnormal ion homeostasis. 相似文献
Glycerotoxin (GLTx) is capable of stimulating neurotransmitter release at the frog neuromuscular junction by directly interacting with N-type Ca2+ (Cav2.2) channels. Here we have utilized GLTx as a tool to investigate the functionality of Cav2.2 channels in various mammalian neuronal preparations. We first adapted a fluorescent-based high-throughput assay to monitor glutamate release from rat cortical synaptosomes. GLTx potently stimulates glutamate secretion and Ca2+ influx in synaptosomes with an EC50 of 50 pm. Both these effects were prevented using selective Cav2.2 channel blockers suggesting the functional involvement of Cav2.2 channels in mediating glutamate release in this system. We further show that both Cav2.1 (P/Q-type) and Cav2.2 channels contribute equally to depolarization-induced glutamate release. We then investigated the functionality of Cav2.2 channels at the neonatal rat neuromuscular junction. GLTx enhances both spontaneous and evoked neurotransmitter release causing a significant increase in the frequency of postsynaptic action potentials. These effects were blocked by specific Cav2.2 channel blockers demonstrating that either GLTx or its derivatives could be used to selectively enhance the neurotransmitter release from Cav2.2-expressing mammalian neurons. 相似文献
Exocytosis of neurotransmitter containing vesicles supports neuronal communication. The importance of molecular interactions involving specific lipids has become progressively more evident and the lipid composition of both the synaptic vesicle and the pre-synaptic plasma membrane at the active zone has significant functional consequences for neurotransmitter release. Several classes of lipids have been implicated in exocytosis including polyunsaturated fatty acids and phosphoinositides. This minireview will focus on recent developments regarding the role of phosphoinositides in neurosecretion. 相似文献