Control of tumbling during the locust jump.

Locust can jump precisely to a target, yet they can also tumble during the trajectory. We propose two mechanisms that would allow the locust to control tumbling during the jump. The first is that prior to the jump, locusts adjust the pitch of their body to move the center of mass closer to the intended thrust vector.

Neuromechanical simulation of the locust jump.

The neural circuitry and biomechanics of kicking in locusts have been studied to understand their roles in the control of both kicking and jumping. It has been hypothesized that the same neural circuit and biomechanics governed both behaviors but this hypothesis was not testable with current technology. We built a neuromechanical model to test this and to gain a better understanding of the role of the semi-lunar process (SLP) in jump dynamics.

AnimatLab: a 3D graphics environment for neuromechanical simulations.

The nervous systems of animals evolved to exert dynamic control of behavior in response to the needs of the animal and changing signals from the environment. To understand the mechanisms of dynamic control requires a means of predicting how individual neural and body elements will interact to produce the performance of the entire system. AnimatLab is a software tool that provides an approach to this problem through computer simulation.

Practical tools for analysing rhythmic neural activity.

This report describes an integrated software package, DataView, which contains a number of tools for analysing rhythmic neural activity. These include simple autocorrelation, a merge-and-drop filter, an enhanced version of the Poisson surprise method and a flexible hill-and-valley analysis tool. The package contains facilities for identifying, examining, and if appropriate, correcting, outliers arising from misidentification or rhythm abnormalities.

Electrical coupling synchronises spinal motoneuron activity during swimming in hatchling Xenopus tadpoles.

The role of electrical coupling between neurons in the swimming rhythm generator of Xenopus embryos has been studied using pharmacological blockade of gap junctions. A conspicuous effect of 18beta-glycyrrhetinic acid (18beta-GA) and carbenoxolone, which have been shown to block electrical coupling in this preparation, was to increase the duration of ventral root bursts throughout the spinal cord during swimming. The left-right coordination, the swimming frequency and the duration of swimming episodes were not affected by concentrations of 18beta-GA which significantly increased burst durations.

Nitric oxide modulation of the electrically excitable skin of Xenopus laevis frog tadpoles.

Nitric oxide (NO) is a highly diffusible signalling molecule with widespread effects on the integrative electrical properties of a variety of neuronal and muscle cells. We have explored the effects of NO on the cardiac-like impulse generated by skin cells of the hatchling Xenopus tadpole. Skin cell impulses propagate from cell to cell via gap junctions and form an unusual sensory system, which triggers escape behaviour at early stages of amphibian development.

DataView: A Tutorial Tool for Data Analysis. Template-based Spike Sorting and Frequency Analysis.

DataView is a Windows program for viewing and analyzing digital data derived from analog signals using A/D acquisition systems. It is primarily designed for research neuroscientists, but its low (or zero) cost makes it a suitable tool for giving students hands-on experience of analysis techniques. It is supplied with many examples of pre-recorded data and also has facilities to allow tutors to use their own - or indeed their students' - experimental results as the dataset for analysis.

Glutamate is a transmitter that mediates inhibition at the rectifying electrical motor giant synapse in the crayfish.

Spike transmission at the electrical synapse between the giant fibres (GFs) and motor giant neurone (MoG) in the crayfish can be blocked by depolarising postsynaptic chemical inhibition, which has previously been shown to be mediated in part by gamma-aminobutyric acid (GABA). The authors show that glutamate applied to the synaptic region of the MoG mimics the depolarisation of the chemical input and can also block spike transmission from the GFs. The glutamate induces an inward current mediated by a conductance increase that is 30-40% of that induced by GABA and that is blocked substantially by picrotoxin.

Escape behaviour in the stomatopod crustacean Squilla mantis, and the evolution of the caridoid escape reaction.

The mantis shrimp Squilla mantis shows a graded series of avoidance/escape responses to visual and mechanical (vibration and touch) rostral stimuli. A low-threshold response is mediated by the simultaneous protraction of the thoracic walking legs and abdominal swimmerets and telson, producing a backwards 'lurch' or jump that can displace the animal by up to one-third of its body length, but leaves it facing in the same direction. A stronger response starts with similar limb protraction, but is followed by partial abdominal flexion.

Fifty years of a command neuron: the neurobiology of escape behavior in the crayfish.

Fifty years ago C.A.G.

Central and peripheral control of the trigger mechanism for kicking and jumping in the locust.

A crucial stage of the locust kick motor program is the trigger activity that inhibits the flexor motorneurons at the end of flexor-extensor coactivation and releases the tibia. One source of this inhibition is the M interneuron, which produces a spike burst at the time of the trigger activity. Previous work has suggested that sensory input resulting from extensor muscle tension may contribute to the M spike burst.

Effect of temperature on a voltage-sensitive electrical synapse in crayfish.

The effects of temperature on transmission through the voltage-sensitive giant motor synapse (GMS) were investigated in crayfish both experimentally and in computer simulation. The GMS is part of the fast reflex escape pathway of the crayfish and mediates activation from the lateral giant (LG) command neurone to the motor giant (MoG) flexor motoneurone. The investigation was motivated by an apparent mismatch between the temperature sensitivity of the activation time constant of the GMS, with a Q10 reported to be close to 11, and that of the active membrane properties of LG and MoG, which are thought to have Q10 values close to 3.

The influence of proprioceptors signalling tibial position and movement on the kick motor programme in the locust.

Four main proprioceptors monitor tibial position in the hindleg of the locust: the femoral chordotonal organ (FCO), the lump receptor, the suspensory ligament receptors and Brunner's organ. The influence of these proprioceptors on quantitative aspects of the kick motor programme has been investigated. The parameters measured were the duration of the initial flexion burst, the duration of co-activation of flexor and fast extensor tibiae (FETi) motoneurones, the number of FETi spikes during the co-activation, the interval between the kick and post-kick flexion, the number of FETi spikes occurring in this interval and the duration of post-kick flexion activity.

The concerted activity in parallel proprioceptive pathways controls the initiation of co-activation in the locust kick motor programme.

To jump and kick the locust uses a catapult mechanism implemented by a three-stage motor programme: initial flexion of the hind tibiae, co-activation of the antagonist flexor and extensor tibiae motor neurons and trigger inhibition of the flexor motorneurons. The transition from stage 1 to stage 2 thus involves a switch from the normal alternate activation to co-activation of the antagonist tibrae motorneurons. However, co-activation has never been observed when the central nervous system has been isolated from the leg.

A simple method for the removal of mains interference from pre-recorded electrophysiological data.

Motivation: A common problem with electrophysiological recording is the contamination of the signal of interest with interference generated at mains frequency. Standard filtering techniques are often inappropriate because the signal of interest has components spectrally close to the mains frequency.

Results: A digital subtraction method is described for removing mains frequency interference from pre-recorded data.

Peripheral control of the gain of a central synaptic connection between antagonistic motor neurones in the locust.

The metathoracic fast extensor tibiae (FETi) motor neurone of locusts is unusual amongst insect motor neurones because it makes output connections within the central nervous system as well as in the periphery. It makes excitatory chemical synaptic connections to most if not all of the antagonist flexor tibiae motor neurones. The gain of the FETi-flexor connection is dependent on the peripheral conditions at the time of the FETi spike.

Quasi-reversible photo-axotomy used to investigate the role of extensor muscle tension in controlling the kick motor programme of grasshoppers.

The jump and kick of the grasshopper are behaviours which are potentially critical for the survival of the animal, and whose maximal performance depends upon optimizing the rate and level of tension development in the extensor tibiae muscle of the hind legs. In experimental conditions extensor tension control can be reduced to a single motoneuron, the fast extensor tibiae (FETi). The axon of FETi can be cut using dye-mediated laser photoaxotomy without damaging the central or peripheral portions of that neuron or any other neuron innervating the leg.

Two classes of vesicles are present and change in relative proportion during post-embryonic development of rectifying electrical synapses in the crayfish.

The size and shape of vesicles at junctional appositions of the rectifying electrical synapses between the medial giant fibre and motor giant neurone of the crayfish were measured during the first 2 months after hatching. Summed data over this period reveal a bimodal distribution in vesicle diameter. From the day of hatching until about 7 days of age, small vesicles (circa 25 nm diameter) predominate.

Structural and functional post-embryonic development of a non-rectifying electrical synapse in the crayfish.

The post-embryonic development of the non-rectifying septate synapse between homologous lateral giant (LG) fibre segments has been investigated using electron microscopy and electrophysiology. In adults, the LG-LG synapse is characterized by closely apposed membranes (approximately 4 nm separation) traversed by regularly spaced particles, and large (60-80 nm) spherical vesicles on both sides of the junction. In newly hatched crayfish the junction between lateral giant fibre segments comprises regions of close membrane apposition as seen in the adult along with non-specialized areas of wide (10-15 nm) membrane separation.

Different types of rectification at electrical synapses made by a single crayfish neurone investigated experimentally and by computer simulation.

The rectification properties of electrical synapses made by the segmental giant (SG) neurone of crayfish (Pacifastacus leniusculus) were investigated. The SG acts as an interneurone, transmitting information from the giant command fibres (GFs) to the abdominal fast flexor (FF) motoneurones. The GF-SG (input) synapses are inwardly-rectifying electrical synapses, while the SG-FF (output) synapses are outwardly rectifying electrical synapses.

Postsynaptic modulation of rectifying electrical synaptic inputs to the LG escape command neuron in crayfish.

The lateral giant (LG) tail-flip escape system of crayfish is organized to provide a massive convergence of mechanosensory inputs onto the LG command neuron through electrical synapses from both mechanosensory afferents and interneurons. We used electrophysiological techniques to show that the connections between three major mechanosensory interneurons and LG rectify, and that their inputs to LG can be reduced by postsynaptic depolarization and increased by postsynaptic hyperpolarization. The mechanosensory afferents and interneurons are excited by sensory nerve shock, and the components of the resulting LG PSP can be similarly modulated by the same postsynaptic potential changes.