Synaptic potentials in the central terminals of locust proprioceptive afferents generated by other afferents from the same sense organ

Afferent neurons from a proprioceptor [the femoral chordotonal organ (FCO)] at the femoro-tibial joint of a locust hindleg carry patterns of spikes to the CNS in which information is coded about the positions and movements of the tibia. Intracellular recordings from the afferents of this organ as they enter the CNS reveal spikes and depolarizing post- synaptic potentials (PSPs) during voluntary or imposed movements of the joint. Some of these PSPs are generated as a result of spikes in other FCO afferents, and can be evoked experimentally by electrical stimulation of the nerve from the organ. One afferent does not appear to synapse directly on another, but instead activates reliable pathways involving other central neurons. Current clamping of individual afferents in isolated ganglia shows that the PSPs are increased in amplitude by hyperpolarizing currents injected into an afferent, and decreased by depolarizing ones. They reverse at about -68 mV (n = 5). At the normal resting potential of the afferents, -72 mV (+/- 0.42 SE, n = 57), the PSPs are therefore depolarizing, and are associated with an increased conductance of the membrane. The changes in membrane potential and conductances associated with the PSPs can be mimicked by pressure injection of GABA into the regions of neuropil that contain the terminals of the afferents. The potential evoked by GABA is associated with an increased conductance of the membrane and reverses at the same potential as the PSPs. GABA also reduces the PSPs evoked in the terminals, either by movements of the FCO or by electrical stimulation of its nerve. The PSPs and the effects of the GABA-evoked potentials are mimicked by the GABA agonist muscimol. The PSPs are blocked reversibly by picrotoxin. The PSPs and the GABA-evoked potentials both alter the excitability of an afferent terminal by reducing the ability of the membrane to support an action potential. It is suggested that the PSPs are depolarizing, inhibitory potentials generated in the terminals of the afferents by central neurons that release GABA, and that their role is to change the efficacy of the afferent spikes at their first output synapses in the CNS. These interactions could form a graded, gain control mechanism for synaptic transmission at the afferent output synapses that is directly dependent on the features of the mechanical movements of the joint

Interacting Gears Synchronize Propulsive Leg Movements in a Jumping Insect

Joint Action Many small insects are impressive jumpers, but large leaps and small bodies pose biomechanical challenges. Burrows and Sutton (p. 1254 ) show that the nymphal planthopper Issus has interlocking gears on their hindleg trochanters that act together to cock the legs synchronously before triggering forward jumps. At the final molt, the gears are swapped for a high-performance friction-based mechanism because the risk of breaking a gear is high, the options for repair during molting are gone, and, moreover, the animal is bigger and stronger. </jats:p

Eyecup muscle action of the crab Carcinus maenas

The muscular control of eyecup movements in the crab Carcinus maenas has been studied by both extracellular and intracellular recording from the nine eyecup muscles. Each muscle involved in optokinetic movements is supplied by a fast and slow axon and each consists of a histologically mixed spectrum of fibres ranging from (Felderstruktur). Muscle 19a, which only participates in the withdrawal reflex consists of phasic fibres only. In general, a fast axon preferentially innervates the phasic fibres and a slow axon the tonic ones. During optokinetic movements the muscles are activated by a complex motor output programme, which is different, not merely the reverse for movements in opposite directions. Both tonic and phasic muscle fibres are active but the latter are only active at greater amplitudes of stimulus movement. Tonic activity is responsible from maintaining the eyecup position in space and for low velocity, small amplitude movements. Phasic activity is recruited during large amplitude movements and is also responsible for fast movement and eyecup tremor. The protective withdrawal reflex overrides any other eyecup movement and involves the firing of two axons in the optic tract, one supplying a group of two, the other a group of three muscles. One of the muscles involved in this eyecup withdrawal movement away from the mid-line is also active during horizontal optokinetic movements of the eyecup towards the mid-line. It is suggested that interpretation of eyecup muscle activity is more intelligible if the whole group of muscles, rather than the individual muscles themselves, is regarded as the functional unit

Epigenetic remodelling of brain, body and behaviour during phase change in locusts

Abstract The environment has a central role in shaping developmental trajectories and determining the phenotype so that animals are adapted to the specific conditions they encounter. Epigenetic mechanisms can have many effects, with changes in the nervous and musculoskeletal systems occurring at different rates. How is the function of an animal maintained whilst these transitions happen? Phenotypic plasticity can change the ways in which animals respond to the environment and even how they sense it, particularly in the context of social interactions between members of their own species. In the present article, we review the mechanisms and consequences of phenotypic plasticity by drawing upon the desert locust as an unparalleled model system. Locusts change reversibly between solitarious and gregarious phases that differ dramatically in appearance, general physiology, brain function and structure, and behaviour. Solitarious locusts actively avoid contact with other locusts, but gregarious locusts may live in vast, migrating swarms dominated by competition for scarce resources and interactions with other locusts. Different phase traits change at different rates: some behaviours take just a few hours, colouration takes a lifetime and the muscles and skeleton take several generations. The behavioural demands of group living are reflected in gregarious locusts having substantially larger brains with increased space devoted to higher processing. Phase differences are also apparent in the functioning of identified neurons and circuits. The whole transformation process of phase change pivots on the initial and rapid behavioural decision of whether or not to join with other locusts. The resulting positive feedback loops from the presence or absence of other locusts drives the process to completion. Phase change is accompanied by dramatic changes in neurochemistry, but only serotonin shows a substantial increase during the critical one- to four-hour window during which gregarious behaviour is established. Blocking the action of serotonin or its synthesis prevents the establishment of gregarious behaviour. Applying serotonin or its agonists promotes the acquisition of gregarious behaviour even in a locust that has never encountered another locust. The analysis of phase change in locusts provides insights into a feedback circuit between the environment and epigenetic mechanisms and more generally into the neurobiology of social interaction.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Jumping performance of flea hoppers and other mirid bugs (Hemiptera, Miridae).

The order Hemiptera includes jumping insects with the fastest take-off velocities, all generated by catapult mechanisms. It also contains the large family Miridae or plant bugs. Here we analysed the jumping strategies and mechanisms of six mirid species from high speed videos and from the anatomy of their propulsive legs and conclude that they use a different mechanism in which jumps are powered by the direct contractions of muscles. Three strategies were identified. First, jumping was propelled only by movements of the middle and hind legs which were respectively 140% and 190% longer than the front legs. In three species with masses ranging from 3.4 to 12.2 mg, depression of the coxo-trochanteral and extension of femoro-tibial joints accelerated the body in 8-17 ms to take-off velocities of 0.5 to 0.8 m s$^{-1}$. The middle legs lost ground contact 5-6 ms before take-off so that the hind legs generated the final propulsion. The power requirements could be met by the direct muscle contractions so that catapult mechanisms are not implicated. Second, other species combined the same leg movements with wing beating to generate take-off during a wing downstroke. In the third strategy, up to four wing beat cycles preceded take-off and were not assisted by leg movements. Take-off velocities were reduced and acceleration times lengthened. Other species from the same habitat did not jump. The lower take-off velocities achieved by powering jumping by direct muscle contractions may be offset by eliminating the time taken to load catapult mechanisms

Mantises exchange angular momentum between three rotating body parts to jump precisely to targets.

Flightless animals have evolved diverse mechanisms to control their movements in air, whether falling with gravity or propelling against it. Many insects jump as a primary mode of locomotion and must therefore precisely control the large torques generated during takeoff. For example, to minimize spin (angular momentum of the body) at takeoff, plant-sucking bugs apply large equal and opposite torques from two propulsive legs [1]. Interacting gear wheels have evolved in some to give precise synchronization of these legs [2, 3]. Once airborne, as a result of either jumping or falling, further adjustments may be needed to control trajectory and orient the body for landing. Tails are used by geckos to control pitch [4, 5] and by Anolis lizards to alter direction [6, 7]. When falling, cats rotate their body [8], while aphids [9] and ants [10, 11] manipulate wind resistance against their legs and thorax. Falling is always downward, but targeted jumping must achieve many possible desired trajectories. We show that when making targeted jumps, juvenile wingless mantises first rotated their abdomen about the thorax to adjust the center of mass and thus regulate spin at takeoff. Once airborne, they then smoothly and sequentially transferred angular momentum in four stages between the jointed abdomen, the two raptorial front legs, and the two propulsive hind legs to produce a controlled jump with a precise landing. Experimentally impairing abdominal movements reduced the overall rotation so that the mantis either failed to grasp the target or crashed into it head first.GPS was supported by HFSP grant LT00422/2006-C. DAC was funded by a Leverhulme Trust grant F/09 364/K to S.R. Ott, University of Leicester, whom we thank for his support.This is the accepted manuscript. The final version is available at http://www.cell.com/current-biology/abstract/S0960-9822%2815%2900086-X