The responses of auditory ventral-cord neurons ofLocusta migratoria to vibration stimuli

Summary Most of the auditory neurons in the ventral nerve cord ofLocusta migratoria carry information not only from the tympanal organs but also from the subgenual organs (vibration sensors). Six of the eight neuron types studied electrophysiologically respond to at least these two modalities. Artificial sounds (white noise and pure tones varying in frequency and intensity) and sinusoidal vibration (200 Hz with an acceleration of 15.8 cm/s₂ or 2000 Hz and 87 cm/s₂) were used as stimuli.Complex excitatory and/or inhibitory interactions of the signals from both tympanal organs form the discharge patterns of auditory ventral-cord neurons in response to stimulation with air-borne sound. Normally the input of the ipsilateral sense organ dominates. The response patterns of these same neurons elicited by vibration stimuli are formed differently, as follows: (1) the sensory inputs of all subgenual organs are integrated in the responses of the ventral-cord neurons; in a single neuron they have either excitatory or inhibitory effects, but not both. (2) The more legs vibrated, the larger is the response. (3) The subgenual organs in the middle legs are most effective, those in the hind legs least so. (4) Ipsilateral vibration has more effect than contralateral.The six auditory neurons react to vibration combined with air-borne sound in different ways. The B neuron is the only one inhibited by vibration stimuli. The G neuron has been studied more intensively; because its anatomical arrangement and the location of the endings of the subgenual receptor fibers are known, it could be inferred from effects of transection of the connectives that interneurons are interposed between receptor cells and the G neuron.Part of the program Sonderforschungsbereich 114 (Bionach) Bochum, under the auspices of the Deutsche Forschungsgemeinschaft, with the support of the Slovenic Research Society (RSS)     

Endocytosis in flight-stimulated adipokinetic cells ofLocusta migratoria

An ultrastructural morphometric study was made of the influence of flight activity on endocytosis in the adipokinetic cells ofLocusta migratoria. The endocytotic pathway was revealed by the endocytotic tracer horseradish peroxidase. Endocytosis appeared to be stimulated by flight, as indicated by an increase in the number of tracer-containing endocytotic pits and various intracellular endocytotic and lysosomal organelles. This stimulatory effect continued for at least 10 min after cessation of flight. An increase in the numbers of both tracer-labelled endocytotic pits and endosomal tubules was detected in the cell bodies of flight-stimulated adipokinetic cells. Endosomal tubules are supposed to be involved in recycling membrane material to the plasma membrane soon after it has been endocytosed. It is concluded that the increase in endocytosis in the flight-stimulated cell bodies serves to enlarge the uptake of nutritional and/or regulatory substances. An increase in number of tracer-labelled endocytotic pits was also observed in the cell processes of flight-stimulated adipokinetic cells, which was, however, not accompanied by an increase in number of labelled endosomal tubules, the latter being practically absent in the processes. This indicates that the increase in endocytotic activity in the cell processes is a form of adaptive endocytosis that compensates for membrane material added to the plasma membrane during flight-induced exocytotic release of adipokinetic hormones.     

Movements of the hindwings ofLocusta migratoria,measured with miniature coils

Summary Tethered migratory locusts were induced to fly in an airstream for hours at a time, carrying on their extremely delicate hindwings miniature induction coils by which the hindwing movements were recorded in three dimensions.The two coils were mounted at right angles to one another on the central field of the hindwing, which is in close aerodynamic contact with the forewing. Each coil emitted three signals to define the components of a 3-dimensional vector. The movements of the central field can be described completely by the rotations of the two vectors. The main component of the hindwing movement thus becomes accessible to detailed kinematic analysis (Figs. 2, 3).The results obtained with this inductive method are consistent with the few published data based on photogrammetric samples of the movement.The various forms of movement can all be observed during the flight experiment. The movement spectrum is very broad even in an undisturbed flying animal (Figs. 4, 5).Various wingbeat parameters were calculated, including oscillation period, the durations of upstroke and downstroke, and their ratio (Fig. 6).Simultaneous measurement of the movements of the fore- and hindwings has provided the first documentation of the varying interactions of the wings on side of the body during a long flight. Even small changes in the relative positions of the two wings are measurable (Fig. 7).     

Neurochemistry of GABAergic activities in the central nervous system ofLocusta migratoria

Summary The biochemical elements of GABA-ergic synapses in the central nervous tissue were examined by a comparative neurochemical approach. The high concentration of GABA as well as the activities of glutamate decarboxylase and GABA-transaminase suppose a high content of GABAergic elements in the nervous system of the locust.Nerve endings isolated from the ganglia of locusts accumulated exogenous GABA in a carriermediated, sodium dependent process into compartments from where it could partially be released under depolarizing conditions. The transport was stimulated by extracellular chloride, was modulated by specific ionophores (enhanced by valinomycin, inhibited by CCCP) and could effectively be blocked by GABAergic ligands (DABA, muscimol). Binding studies revealed the existence of multiple binding sites for GABA which differ in number, affinity, pharmacology and ion dependency. The putative receptors for GABA (Na⁺-independent binding sites) in locust nervous tissue exceeded the concentrations found in vertebrate brain tissue and showed different binding pharmacology.Abbreviations GABA -amino butyric acid - GAD glutamate decarboxylase - GABA-T GABA-transaminase - DABA diamino butyric acid     

Projections of auditory ventral-cord neurons in the supraesophageal ganglion ofLocusta migratoria

Summary The neuropile regions in the supraesophageal ganglion ofLocusta migratoria were revealed by Bodian staining of frontal and parasagittal sections.A combined recording and staining technique (CoS method, Rehbein et al., 1974) was used to identify physiologically five different types of auditory ventral cord neurons and mark the course of their axons and the positions of the terminal arborizations. The boundaries of the projection regions are described; they include the various multimodal neuropile regions in the ventrolateral protocerebrum.Previously demonstrated instances of convergence with neurons of other sensory systems, and others likely to exist, are considered with respect to their possible significance in neuronal processing within the auditory system.Supported by the Deutsche Forschungsgemeinschaft, as part of the program Sonderforschungsbereich Bionach, Bochum. The investigations were done at Lehrstuhl für Allgemeine Zoologie, Ruhr-UniversitÄt, D-4630 Bochum     

Octopamine- and dopamine-sensitive adenylate cyclase in the brain ofLocusta migratoria during its development

Octopamine- and dopamine-sensitive adenylate cyclases were studied in the brain of Locusta migratoria during its metamorphosis. In the adult brain the effects of octopamine and dopamine on adenylate cyclase were additive, suggesting the presence of separate populations of adenylate cyclase-linked receptors for octopamine and dopamine. There are no separate receptors for noradrenaline. Octopamine stimulates adenylate cyclase in both adult and larval brain; however, in adult brain octopamine is more potent than in larval brain. Dopamine stimulates adenylate cyclase activity only in adult brain. The sensitivity of adenylate cyclase to octopamine changes during the development of the animal. Phentolamine and cyproheptadine are potent antagonists of octopamine-stimulated adenylate cyclase, while propranolol has a weak effect. No cytosol factor which would modulate either basal or octopamine-stimulated adenylate cyclase was found. The effect of GTP and octopamine on adenylate cyclase was synergistic in adult brain but not in larval brain, while the effect of GppNHp and octopamine was synergistic in both adult and larval brains.     

Comparative studies on cholinergic activities in the central nervous system ofLocusta migratoria

Summary Comparative studies on biochemical and pharmacological aspects of cholinergic transmission in the cerebral ganglion of locust and the mouse cerebral cortex were performed. The results point to common features and significant differences in the cholinergic pharmacology of insect and vertebrate nervous system: ACh content as well as AChE and ChAT activities reflect a highly cholinergic innervation of the locust cerebral ganglion. While the nicotinic ACh-receptor type predominates in locust nervous system, the muscarinic type is the main receptor type in mouse brain.The kinetic data for the high affinity choline uptake of locust synaptosome preparations corroborate the cholinergic properties of nerve endings from locust head ganglion.Abbreviations ACh acetylcholine - ChAT cholineacetyltransferase - AChE acetylcholinesterase - QNB quinuclidihylbenzilate - -BTX -bungarotoxin The author is indebted to Prof. Lueken for support and encouragement during the course of this work. I also gratefully acknowledge the excellent technical assistance of Mrs. M. Düwel. This work was financially supported by the Deutsche Forschungsgemeinschaft (Br 712/2-2).     

Development of the tympanal organ in larvae of the migratory locust (Locusta migratoria)

Summary The tympanal organ of the migratory locust acquires its definitive form during larval development. All the receptor cells (90–100) are present in the 1st instar, whereas the differentiation of the tympanum and the cuticular structures it bears proceeds in steps from one instar to the next. The elevated process is the earliest such structure to appear (2nd instar); it is followed by the pyriform vesicle (3rd instar) and folded body (4th instar). The styliform body first appears in the imago. Although the typical arrangement of the receptor cells is already discernible in the 1st instar, some of the attachment sites change during development, the final configuration appearing only in the imago.Supported by the Deutsche Forschungsgemeinschaft (Ka 498/2)     

Flight motor patterns recorded in surgically isolated sections of the ventral nerve cord ofLocusta migratoria

Summary In the locust,Locusta migratoria, the pairs of connectives between the three thoracic ganglia and in the neck were transected in all possible combinations. Each of these preparations was tested for the production of rhythmic flight motor activity, with sensory input from the wing receptors intact and after deafferentation. The motor activity elicited in these preparations was characterized by intracellular recordings from motoneurons and electromyographic analyses.The motor patterns observed in locusts with either the neck or the pro-mesothoracic connectives severed (Figs. 2, 3, and 4) were very similar to the flight motor pattern produced by animals with intact connectives. The activity recorded in mesothoracic flight motoneurons of locusts with either only the meso-metathoracic connectives cut or both the meso-metathoracic and the neck connectives transected were similar to each other. Rhythmic motor activity could be observed in these preparations only as long as sensory feedback from the wing receptors was intact. These patterns were significantly different from the intact motor pattern (Figs. 5, 6, and 7). Similar results were obtained when the mesothoracic ganglion was isolated from the other two thoracic ganglia, although the oscillations produced under these conditions were weak (Fig. 8 upper). In the isolated metathorax no rhythmic flight motor activity could be recorded (Fig. 8 lower), even when wing afferents were intact.Considering the differences between the motor patterns observed in the various preparations these results suggest that the ganglia of the locust ventral nerve cord do not contain segmental, homologous flight oscillators which are coupled to produce the intact flight rhythm. Instead they support the idea that the functional flight oscillator network is distributed throughout the thoracic ganglia (Robertson and Pearson 1984). The results also provide further evidence that sensory feedback from the wing sense organs is necessary for establishing the correct motor pattern in the intact animal (Wendler 1974, 1983; Pearson 1985; Wolf and Pearson 1987 a).Abbreviations CPG central pattern generator - EMG electromyogram