Discharge patterns of locust visual interneurones

The spike discharges of the descending contralateral movement detector (DCMD) neurone, and of some smaller visual interneurones (S-units), were recorded in the ventral nerve cord of adult Schistocerca gregaria Forsk., in response to a stationary disc (25^o) or a small spot (0.2^o) stimulus. The discharge rate of each neurone was plotted over a period of 5 s exposure; the total number of spikes in this period was also noted. The DCMD response to the 25^o disc was a high-frequency burst falling off quickly to a low rate; the 0.2^o spot evoked a prolonged discharge with an early peak in rate. In S-units the discharge was prolonged with both targets; the rate rose to an early peak in each case, with a much higher rate for the larger disc. For the DCMD the total number of spikes per stimulus (5 s) was greater for the 0.2^o spot; for S-units it was greater for the 25^o disc. Thus an increase of about 30-fold in the number of ommatidia stimulated resulted in a fall in the total DCMD response to about one-quarter; a similar increase evoked a rise of about 6-fold in the S-unit response. When the 25^o disc was presented at progressively reduced intensities the total spike response of the DCMD rose steadily to a maximum at about 2.9 μ W m^-2; using the same procedure the spike output of S-units, initially high, declined monotonically. The role of inhibition in these results is discussed.     

Responses of locust visual interneurones to transiently-illuminated slits,paired spots,annuli and disc arrays

One compound eye of an immobilised locust viewed a large screen on to which could be projected a slit of variable width, parallel thin slits of variable separation, large discs or annuli, pairs of small discs or large arrays of small discs. The on-response in the contralateral cervical connective, for both the DCMD and a smaller axon group (M-spikes), was recorded over a period of 2 sec coinciding with the period of illumination. The normal spontaneous discharge of the connective is described. For a single slit the DCMD response peaked in the range 0.02–0.7° of width subtense, the most common result being 0.05°. The M-axon group showed a negative peak at a corresponding subtense. Comparing the responses to single bars and paired slits of the same overall subtense, it was found that below about 1° these were not discriminated by either type of neurone. At higher subtenses the DCMD showed preference for paired slits, the M-axons for solid bars. Comparing responses to arrays of spots with those to uniformly illuminated areas, neither the DCMD nor the M-axon group showed discrimination at angles less than 1°, but at higher angles the DCMD showed preference for arrays and the M-axons for solid areas. Annuli were more effective stimuli than were discs of the same size. Near the edge of large-area targets it was possible to detect spatial transients in excitability. Two small spots produced interaction over a wide range of separations, affording evidence for wide-range mutual inhibition affecting both types of interneurone, and for short-range facilitation for the M-axon group only.     

Tonic effects of stationary luminous slits on the discharge rates of some locust visual interneurones

The presence of an illuminated slit in the visual field of a locust compound eye produced changes in the tonic discharge rate of the DCMD and three other visual interneurones, recorded in a connective. The DCMD discharge peaked initially in the range of low slit subtenses, but over a period of minutes of exposure its character changed so that there was a rise at high subtenses also. When the luminance of a slit of fixed subtense was increased in steps, there was an initial rise then a sharp fall in discharge, indicating an abrupt onset of inhibition. Lateral spread of inhibition could account for the peak in response to slits, at a subtense falling well within the acceptance angle of a single ommatidium. The results show the ability of some visual interneurones to maintain a changed level of discharge in the presence of a stationary object in the visual field of the eye.     

The locust abdominal muscle receptor organ: response characteristics and its role in the control of segmental distance

A single mutipolar receptor cell is located at the dorsal edge of the lateral internal dorsal muscle in each abdominal segment of the locust (Locusta migratoria). Muscle and receptor cell form the abdominal muscle receptor organ. The receptor cell monitors length changes in the intersegmental muscle, and as a consequence also detects the length of an abdominal segment (cuticule and intersegmental membrane).The muscle receptor organ responds in a phasictonic fashion. The phasic component encodes the rate of change in the stimulus independent from the prevailing length of the muscle receptor organ. The tonic component monitors the absolute length of the muscle.Stimulation of a single muscle receptor organ leads to reflex effects on the ipsilateral longitudinal muscles in at least three adjacent segments. Muscles that shorten the abdomen are activated while their extending antagonists receive reduced activity.The reflex activation of the muscles is polysynaptic. Monosynaptic connections between the receptor and the motoneurones were not found.We identified an interneurone that receives monosynaptic input from the muscle receptor organs in at least three adjacent segments. The interneurone excites motorneurones to the longitudinal muscles of the next posterior segment.Abbreviations aMROII abdominal muscle receptor interneurone 1 - AS3 third abdominal segment - AS4 fourth abdominal segment - AS5 fifth abdominal segment - AS6 sixth abdominal segment - EPSP excitatory postsynaptic potential - MN median nerve - MR multipolar receptor cell - MRO muscle receptor organ - N1 tergal nerve - N2 sternal nerve     

Parallel processing of mechanosensory inputs from the locust ovipositor by intersegmental and local interneurones

The neural pathways underlying the processing of signals from locust (Schistocerca gregaria) ovipositor hairs by different classes of interneurones are investigated.Spikes in the sensory neurones from these hairs evoke chemically-mediated, unitary EPSPs with a short and constant latency in six identified non-giant projection interneurones with cell bodies in the terminal abdominal ganglion. Five of these interneurones receive direct inputs from the valves ipsilateral to their neuropilar branches, whereas the other receives direct inputs from valves on both sides. The sensory neurone from a single hair makes divergent connections with several interneurones and those from different hairs make convergent connections with a given interneurone. The amplitude of the EPSPs evoked depends on the position of a hair along the proximal-distal axis of the valve, with sensory neurones from more distal hairs generating larger amplitude EPSPs.Deflection of hairs also excites three of the four giant projection interneurones through polysynaptic pathways and some local interneurones in the terminal abdominal ganglion through monosynaptic connections. Branches of non-giant projection interneurones, local interneurones, but not those of the giant interneurones, overlap the axon terminals of the ovipositor hair afferents in the terminal abdominal ganglion.     

Synaptic interactions between nonspiking local interneurones in the terminal abdominal ganglion of the crayfish

Nonspiking local interneurones are the important premotor elements in arthropod motor control systems. We have analyzed the synaptic interactions between nonspiking interneurones in the crayfish terminal (6th) abdominal ganglion using simultaneous intracellular recordings. Only 15% of nonspiking interneurones formed bi-directional excitatory connections. In 77% of connections, however, the nonspiking interneurones showed a one-way inhibitory interaction. In these cases, the presynaptic nonspiking interneurones received excitatory synaptic inputs from the sensory afferents innervating hairs on the surface of the uropods and the postsynaptic nonspiking interneurones received inhibitory synaptic inputs that were partly mediated by the inputs to the presynaptic nonspiking interneurones. The membrane hyperpolarization of the postsynaptic nonspiking interneurones mediated by the presynaptic nonspiking interneurones was reduced in amplitude when the hyperpolarizing current was injected into the postsynaptic interneurones, or when the external bathing solution was replaced with one containing low calcium and high magnesium concentrations. The role of these interactions in the circuits controlling the movements of the terminal appendages is discussed.Abbreviations AL antero-lateral - epsp excitatory postsynaptic potential - ipsp inhibitory postsynaptic potential - PL postero-lateral     

The optomotor yaw response of the desert locust, Schistocerca gregaria

Abstract The optomotor yaw response of the desert locust, Schistocerca gregaria (Forsk.), was investigated under open- and closed-loop conditions. When flying tethered in the centre of a vertically striped hollow sphere, the polarity of response of the locust was always the same as the stimulus. The response, therefore, appears suitable to stabilize body posture against passive rotations around the yaw-axis in free flight. Responses were induced by contrast frequencies up to 150 Hz with a maximum of amplitude at about 20 Hz. The characteristic curve, measured between 0.3 and 160 Hz, is widened up towards higher frequencies as compared with those of bees and flies.
Variability was the most striking feature in the locust's yaw response. The amplitude of modulation not only varied greatly between individuals but also changed with the same visual stimulus in the course of an experiment. We therefore suppose that the locust's turning behaviour is subject to gain control mechanisms and that spontaneous gain modulations are responsible for the observed variability in the stimulus-response conversion.     

Embryonic diapause in the Australian plague locust relative to parental experience of cumulative photophase decline

The Australian plague locust Chortoicetes terminifera (Walker) exhibits facultative embryonic diapause during autumn. To approximate natural photoperiod changes during late summer and autumn, locust nymphs were reared under different total declines in laboratory photophase (−0.5, −0.75, −1.0, −1.25, −1.5, −1.75, −2 h each lowered in 15 min steps) in a 24 h photoperiod to quantify any effect on the subsequent production of diapause eggs. Induction of diapause eggs was significantly affected by accumulated photoperiod decline experienced by the parental generation throughout all development stages from mid-instar nymph to fledgling adult. The incidence of embryonic diapause ranged from nil at −0.5 h to 86.6% diapause at −2 h. Continued declines in photoperiod for post-teneral locusts (transitioned from −1 h until fledging to −1.75 h) produced a further increase in the proportion of diapause eggs. The results were unaffected by time spent at any given photoperiod, despite a previously indicated maximal inductive photoperiod of 13.5 h being used as the mid-point of all treatments. Implications for the seasonal timing processes of photoperiodism in C. terminifera, which has a high migratory capacity and a latitudinal cline in the timing of diapause egg production across a broad geographic range, are discussed.     

Characterisation of columnar neurons and visual signal processing in the medulla of the locust optic lobe by system identification techniques

We describe visual responses of seventeen physiological classes of columnar neuron from the retina, lamina and medulla of the locust (Locusta migratoria) optic lobe. Many of these neurons were anatomically identified by neurobiotin injection. Characterisation of neuronal responses was made by moving and flash stimuli, and by two system identification techniques: 1. The first-order spatiotemporal kernel was estimated from response to a spatiotemporal white-noise stimulus; 2. A set of kernels to second order was derived by the maximal-length shift register (M-sequence) technique, describing the system response to a two-channel centre-surround stimulus. Most cells have small receptive fields, usually with a centre diameter of about 1.5°, which is similar to that of a single receptor in the compound eye. Linear response components show varying spatial and temporal tuning, although lateral inhibition is generally fairly weak. Second-order nonlinearities often have a simple form consistent with a static nonlinear transformation of the input from the large monopolar cells of the lamina followed by further linear filtering.Abbreviations LMC large monopolar cell - LVF long visual fibre - RF receptive field - SMC small monopolar cell - SVF short visual fibre     

Pigeons and humans are more sensitive to nonaccidental than to metric changes in visual objects

Humans and macaques are more sensitive to differences in nonaccidental image properties, such as straight vs. curved contours, than to differences in metric properties, such as degree of curvature [Biederman, I., Bar, M., 1999. One-shot viewpoint invariance in matching novel objects. Vis. Res. 39, 2885-2899; Kayaert, G., Biederman, I., Vogels, R., 2003. Shape tuning in macaque inferior temporal cortex. J. Neurosci. 23, 3016-3027; Kayaert, G., Biederman, I., Vogels, R., 2005. Representation of regular and irregular shapes in macaque inferotemporal cortex. Cereb. Cortex 15, 1308-1321]. This differential sensitivity allows facile recognition when the object is viewed at an orientation in depth not previously experienced. In Experiment 1, we trained pigeons to discriminate grayscale, shaded images of four shapes. Pigeons made more confusion errors to shapes that shared more nonaccidental properties. Although the images in that experiment were not well controlled for incidental changes in metric properties, the same results were apparent with better controlled stimuli in Experiment 2: pigeons trained to discriminate a target shape from a metrically changed shape and a nonaccidentally changed shape committed more confusion errors to the metrically changed shape, suggesting that they perceived it to be more similar to the target shape. Humans trained with similar stimuli and procedure exhibited the same tendency to make more errors to the metrically changed shape. These results document the greater saliency of nonaccidental differences for shape recognition and discrimination in a non-primate species and suggest that nonaccidental sensitivity may be characteristic of all shape-discriminating species.     

Autoradiographic localization of 3H-histamine accumulation by the visual system of the locust

Summary The uptake of [³H]-histamine into the retina and optic lobe of the locust, Schistocerca americana gregaria was studied by means of autoradiography at the light- and electron-microscopic levels. Light-microscopic autoradiography showed a significant accumulation of [³H]-histamine in several regions of the optic lobe. Dense accumulations of silver grains were concentrated along the medial border of the medullary neuropil and around the entire periphery of the lobula. No significant accumulations of grains were present within the retina or the neuropil zones of the lamina, medulla or lobula.Electron-microscopic autoradiography showed histamine-accumulating cells along the border of the medulla to exhibit electron density and morphology typical of glial cells. Labelled histamine was present within both glial cell bodies and their processes. In the region surrounding the neuropil of the lobula, [³H]-histamine was concentrated within fine glial processes wrapped around neuronal cell bodies and their axons. No neuronal cell bodies or axons showed accumulation of silver grains above background.These results are consistent with previous studies showing the glial uptake of amino acid and biogenic amine putative neurotransmitters. However, the lack of a demonstration of a specific uptake of histamine in neuropil zones makes it difficult to assess the role of histamine uptake in the inactivation of neurally released histamine in the locust visual system.     

Mechanoresponsive neurones in the suboesophageal ganglion of the locust

Abstract. A preparation is described for intracellular recording from the neur-opile of the sub-oesophageal ganglion (SOG) of the locust, while stimulating the labial and maxillary palps with plant material in such a way as to mimic the palpation behaviour which precedes and continues throughout feeding. Twelve neurones responding to simulated palpation were recorded from and stained in the SOG. Axons of three neurones ascended to the brain, six had descending axons and three had all of their processes confined to the suboesophageal ganglion. The major regions of arborization were in the ventrolateral and mediolateral neuropiles of the maxillary and labial neuromeres. All twelve neurones were solely mechanoresponsive. In addition to responding to palpation of one or more of the four palps, five also responded to stimulation of the labrum, one to touching each antenna, and one to mechanical stimulation of each of the six tarsi. In the context of what is known about the role of mechano-stimulation in the control of feeding, and given their particular patterns of input and arborizations, it is suggested that the neurones may be active during food selection and ingestion.     

The effect of wilting on palatability of plants to Schistocerca gregaria,the desert locust

Summary Previous work has shown that host choice by acridids (grasshoppers and locusts) is sensitive to alterations in host quality. In particular, reduced plant water content has been found to increase palatability of certain plant species. To determine if this phenomenon is general, and to gain preliminary information on causes, turgid and wilted plant material of forty-one species was tested using nymphs of the desert locust, Schistocerca gregaria. Twelve plant species (29%) had increased and five (12%) had decreased palatability (as measured by meal size) when wilted. Among fifteen families tested, the increases occurred in six, the decreases in three. The greatest change occurred in Taraxacum officinale; further tests on this plant revealed the increase to be continuous, rising with decreasing water content. The behavioral observations combined with the pattern of the results across plant species suggest that changes are due to alterations in specific deterrents or stimulants, rather than to decreased water content or increased concentrations of amino acids and/or sugars. The implications of these results for understanding drought-associated population outbreaks are discussed.     

The effects of stimulus area and intensity on the on/off ratio of some locust visual interneurones

The on- and off-discharges of three types of locust visual interneurones were recorded in response to luminous discs ranging in subtense from 0.4 to 25°. For the DCMD neurone there was a clear reciprocal relationship between ON and OFF, with large on- and small off-responses at 0.4°, and the reverse at 25° disc subtense. Most of the changeover from almost pure ON to almost pure OFF discharges occurred in the subtense range up to 2°, i.e. within the acceptance angle of one ommatidium or the angle between adjacent ommatidia. This behaviour was not found at low luminance levels, where ON and OFF followed parallel courses. These findings suggest the existence of strong inhibition, augmenting rapidly with increase in target subtense, as also with luminance as shown in separate experiments. For the DCMD the off-response had the characteristics of a simple rebound excitation, following a short period of light exposure.The other visual interneurones (M and S) behaved differently. They did not show reciprocity of ON and OFF, but instead their responses followed parallel courses with increase in subtense, resembling those of the DCMD at low luminance. Nonetheless, like the DCMD, they did show peaking of the on-response at certain subtenses and luminance, although at much higher levels. The inhibitory activity defining the responses of M and S neurones appeared much less effective than that associated with the DCMD. This could be due to greater complexity in their central connexions, of which nothing is known.     

Response decrement in an auditory neurone of the locust

An identified interneurone (SA3) of the suboesophageal ganglion has an axon in both circumoesophageal connectives ascending to the brain. This is a novel morphology for a cell in the auditory system of the locust. The neurone is also novel for its physiological responses to sound in that it displays side-dependent response decrement (habituation). Responses to a tone directed at one ear decrement without affecting responses from the other ear. The responses on the decremented side recover when the opposite ear is stimulated. The decrement is the result of a diminishing amplitude of the compound excitatory post-synaptic potential but no inhibition is seen. Response decrement does not occur if the stimulus frequency is varied.     

Behavioral thermoregulation in the migratory locust: a therapy to overcome fungal infection

We examined under laboratory conditions the thermopreference of the migratory locust, Locusta migratoria migratorioides, following infection by the entomopathogenic fungus Metarhizium anisopliae var. acridum and its influence on mycosis. Infected locusts raised their body temperature more frequently than healthy conspecifics through selection of high temperatures in a heat gradient. Thermoregulation did not, however, alter the frequency of feeding events nor the amount of food eaten by infected L. migratoria. A thermoregulation regime of a minimum of 4 h/day substantially increased survival of inoculated insects (by 85%). However, the therapeutic effect decreased when thermoregulation was delayed following inoculation of the pathogen. Thermoregulation reduced locust mortality but did not completely eliminate the fungus from infected hosts; the fungus grew and killed the insects when thermoregulation was interrupted. We suggest that periodic, short bouts of thermoregulation, when performed from the onset of infection and for an extended period of time, are sufficient to provide a therapeutic effect to infected hosts. Such thermoregulatory capacity of locusts may limit the potential of fungal pathogens as biological control agents under certain ecological conditions.     

细菌sRNA对环境胁迫的响应机制

细菌小RNA (Small RNAs,sRNAs)是一类长度大约在40?400个核酸之间,不编码蛋白质的RNA,在细菌适应环境方面起重要的调节作用。当环境中温度、营养、外膜蛋白、pH、铁等条件改变时,sRNA常常通过连接双组分信号转导系统和调节蛋白,来传递压力信号并调节应激响应,其作用方式一般是通过碱基互补配对的方式与靶mRNA结合,从而调控靶mRNA的翻译和稳定性;或直接与靶标蛋白质结合,调节靶标蛋白质的生物活性。本文总结了细菌在多种环境压力下,sRNA的调控响应机制。     

Responses and locations of neurones in the locust metathoracic femoral chordotonal organ

Summary Insect legs possess chordotonal organs which monitor leg angle, and the direction, velocity and acceleration of leg movements. The locust metathoracic femoral chordotonal organ (mtFCO) has previously been studied morphologically and physiologically, but no detailed analysis of the responses of individual neurones, and their location in the organ has so far been produced. By recording from, and staining mtFCO neurones I have been able to compile for the first time such a map. The distribution of neurone somata in the locust mtFCO is more complex than previously thought: receptors sensitive to both stretch and relaxation of the apodeme are distributed throughout the organ. Seventeen response types were encountered. Neurones with a particular response type have somata in comparable locations within the mtFCO. Comparisons are made between the response types found in the stick insect and those in the locust. The possible functions of some of the responses are discussed.Abbreviation (mt)FCO (metathoracic) femoral chordotonal organ - F-T femur-tibia     

Muscle contraction and relaxation-response time in response to on or off status of visual stimulus

Background

It is unclear whether response time is affected by a stimulus cue, such as a light turned on or off, or if there are differences in response to these cues during a muscle contraction task compared with a muscle relaxation task. The objective of this study was to assess the response time of a relaxation task, including the contraction portion of the task, to a stimulus of a light turned on or off. In addition, we investigated the effect of the pre-contraction level on the relaxation task.

Results

Contraction response time was significantly shorter during the light-on status than during the light-off status (P <0.01), and relaxation response time in each maximum voluntary contraction was significantly longer during the light-on status than during the light-off status (P <0.01). The relaxation response time became longer in order of 25% to 75% maximum voluntary contraction regardless of light-on or -off status, and was significantly longer than the contraction response time (P <0.05-0.01).

Conclusions

This study found that as the contraction level increased, the relaxation response time became longer than the contraction response time regardless of light status. However, contraction response time or relaxation response time findings were opposite to this during the light-on status and light-off status: contraction response time became shorter in the light-on status than in the light-off status and relaxation response time became longer in the light-on status than in the light-off status. These results suggest that the length of each response time is affected by motor control in the higher order brain and involves specific processing in the visual system.     

Visual control of steering in locust flight: the effects of head movement on responses to roll stimuli

The contribution of head movement to the control of roll responses in flying locusts (Locusta migratoria) has been examined (i) on a flight balance, recording the angles through which the locust turns when following an artificial horizon; (ii) by recording activity in a pair of flight muscles in restrained conditions; and (iii) by observations on free flying locusts. Responses were compared when the head was free to turn about the thorax, as normal, and when the head was waxed to the thorax, blocking any relative motion between the two (head-fixed). These experiments suggest that the major signal generating corrective roll manoeuvres is the visual error between the angle of the head and the horizon, rather than a signal that includes a measure of the head-thorax angle.