Wet but not slippery: Boundary friction in tree frog adhesive toe pads.

Tree frogs are remarkable for their capacity to cling to smooth surfaces using large toe pads. The adhesive skin of tree frog toe pads is characterized by peg-studded hexagonal cells separated by deep channels into which mucus glands open. The pads are completely wetted with watery mucus, which led previous authors to suggest that attachment is solely due to capillary and viscous forces generated by the fluid-filled joint between the pad and the substrate. Here, we present evidence from single-toe force measurements, laser tweezer microrheometry of pad mucus and interference reflection microscopy of the contact zone in Litoria caerulea, that tree frog attachment forces are significantly enhanced by close contacts and boundary friction between the pad epidermis and the substrate, facilitated by the highly regular pad microstructure.

Correlates of Habituation of a Polysynaptic Reflex in Crayfish In Vivo and In Vitro.

Reflex leg levation habituates during repeated electrical stimulation of mechanosensory afferents in the dactyl of the fifth walking leg of the crayfish, Procambarus clarkii. This was investigated in decerebrate crayfish, and reproduced in an isolated thoracic ganglion preparation. In vivo, trains of stimuli delivered every 2.5 s produced a gradual decrease in the amplitude of the mechanical response, and a concomitant decrease in the number of impulses per burst in the levator muscle myogram. Near complete recovery occurred after 10 min rest, and transient dishabituation was observed after electrical stimulation of the telson. Less frequent or stronger stimuli led to less rapid habituation. In vitro, the same parametric characteristics of habituation were observed in the levator nerve responses, while the intrinsic variability of the reflex was reduced. The response decrement was shown to be unrelated to changes in the afferent excitation. Evoked polysynaptic excitatory postsynaptic potentials (EPSPs) in levator motorneurons decreased in parallel with the levator neurogram. This decrease was unrelated to any change in the resting membrane potential of the levator motorneurons. Interneurons with habituating EPSPs, antagonistic depressor motorneurons with habituating inhibitory postsynaptic potentials and non-habituating responses in other motorneuronal groups were also found. These findings point to a central locus of habituation upstream from the motorneurons, and offer prospects for a detailed investigation of the mechanisms of habituation in a polysynaptic system.

Isometric torque of the finger extensors at the metacarpophalangeal joints.

A pilot study was undertaken to evaluate the isometric torque produced at the metacarpophalangeal joint during finger extension. Fifteen women with normal right hands, aged 21 to 29 years, participated. Each subject was tested for maximal force of isometric extension at the metacarpophalangeal joint angles of 0, 30, and 60 degrees on each of the four fingers. Torque was computed by multiplying the recorded tension and measured length of the proximal phalanx (lever arm). The mean torque for the long finger was significantly greater than the average torque for each of the other three fingers. The mean torque at the joint angle of 60 degrees was significantly greater than at 0 degrees but not at 30 degrees. Reasons for the findings are discussed.

Evaluation of clinical and luteolytic effects of a novel prostaglandin analogue in normal and problem mares.

Alfaprostal (K 11941), a novel prostaglandin F2 alpha analogue was clinically tested in 24 dioestrous mares, 40 anoestrous mares and 31 postpartum mares, all being given 2 or 3 mg intramuscularly. Blood samples were taken for the determination of plasma progesterone levels and the objective confirmation of luteolytic drug effects. Two hundred and thirty-six mares at the same location were used for comparisons of the rates of pregnancy, early embryonic loss and foaling. Alfaprostol was found to act as a potent luteolytic agent with good oestrus induction, follicular development and normal conception (72.6%) and foaling rate (65.3%). No side effects were observed. Treatments commenced early in the season (October), when only 35% of the anoestrous mares showed elevated progesterone levels, but in 80% of anoestrous mares with baseline progesterone levels, alfaprostol initiated heat and ovulation followed by normal fertility.

Primary afferent depolarizations of sensory origin within contact-sensitive mechanoreceptive afferents of a crayfish leg.

Recordings from the central branches of single identified dactyl sensory afferent (DSA) neurons in a crayfish in vitro preparation were performed to study modifications of the sensory message occurring before the first central synapse. These afferents comprised hairs and force-sensitive mechanoreceptors with phasic and phasotonic response characteristics in the terminal segment (dactyl) of the crayfish leg. More than one afferent spike size was often observed in intracellular recordings from these afferents, thus indicating the presence of electrical coupling between the central processes of DSA fibers. Additionally, in identified DSA fibers with large spike sizes, primary afferent depolarizations (PADs) of up to 15 mV were observed, which sometimes triggered antidromic spikes in the afferent. Nevertheless, PADs were clearly inhibitory, because they shunted the afferent spikes. They exhibited the following properties. First, each PAD was preceded by an afferent spike from a neighboring hair, indicating that the PADs had a sensory rather than central origin. Second, PADs could follow high frequencies of afferent discharges without failure, a property suggestive of monosynaptic connections, but because PAD latencies varied by +/-0.5 ms it is more likely that they were mediated by a disynaptic pathway. Third, although PADs were evoked in an extremely reliable manner, their amplitude varied in a quantal manner. Most unitary PADs were the result of the release of < 12 quanta, the mean quantal content lying between 4 and 5; quantal size was large, approximately 1 mV. Fourth, PADs showed facilitation in some fibers, whereas in others they became much smaller when occurring at brief intervals. We suggest that PADs may be an efficient and parsimonious way to limit sensory inflow in space and time, allowing the crayfish to identify precisely both weak and strong mechanical stimuli.

Force dependent response reversal mediated by low- and high-threshold afferents from the same mechanoreceptor in a crayfish leg.

1. The reflex responses initiated by cuticular stress detector one (CSD1) afferents in anterior levator motor neurnons in the fifth walking leg of crayfish were studied in an in vitro preparation by means of intracellular recordings. 2. The response in the anterior levator reversed with strong mechanical stimulation. Inhibitory responses were correlated with the activation of low-threshold CSD1 units, excitatory responses with the activation of high-threshold CSD1 units. Two opposing reflexes thus originate from the same sense organ at different levels of stimulation. 3. Some low-threshold units were inactive at stimulus strengths that activated the high-threshold units. Other low-threshold units remained active. Their reflex effects were reduced by either pre- or postsynaptic mechanisms. 4. Functionally, this force dependent response reversal could be important in switching from postural/locomotor responses to defensive responses such as limb autotomy.

Synaptic connections of the cuticular stress detectors in crayfish: mono- and polysynaptic reflexes and the entrainment of fictive locomotion in an in vitro preparation.

The reflex connections made by Cuticular Stress Detector afferents (CSD1 and CSD2) with motorneurones of the four proximal muscle groups in the 5th walking legs of crayfish (Procambarus clarkii, Pacifastacus leniusculus) have been studied in an in vitro preparation. Reflex responses to mechanical stimulation of the CSDs were studied in single neurones by means of intracellular techniques. Within each motorneurone pool, both excitatory and inhibitory reflex responses occurred, although sometimes no reflex connections were found. When present, they could be classified into 'levation' and 'depression' reflexes, corresponding to negative and positive feedback effects respectively. Each motorneurone receives input from a number of different CSD afferents (mean values between 3.0 and 5.8). Using electrophysiological and pharmacological tests, it was demonstrated that at least 32% of all connections were monosynaptic. In preparations showing fictive locomotion, phasic CSD stimulation was shown to be able to entrain anterior levator and depressor motorneurone activity in 95% of cases. The results thus demonstrate the importance of sensory feedback from the CSDs in shaping the final motor output.

Sensitive and specific method for rapid identification of Streptococcus pneumoniae using real-time fluorescence PCR.

Molecular surveillance of pathogens has shown the need for rapid and dependable methods for the identification of organisms of clinical and epidemiological importance. As the leading cause of community-acquired pneumonia, Streptococcus pneumoniae was used as a model organism to develop and refine a real-time fluorescence PCR assay and enhanced DNA purification method. Seventy clinical isolates of S. pneumoniae, verified by latex agglutination, were screened against 26 negative control clinical isolates employing a TaqMan assay on a thermocycler (LightCycler). The probe, constructed from the lytA gene, correctly detected all S. pneumoniae genomes without cross-reaction to negative controls. The speed and ease of this approach will make it adaptable to identification of many bacterial pathogens and provide potential for adaptation to direct detection from patient specimens.