Flight Motor Research Articles

Actions Of Putative Amino Acid Neurotransmitters On The Neuropile Arborizations Of Locust Flight Motoneurones

ABSTRACT To characterize the receptors for putative amino acid neurotransmitters present on the dendritic arborizations of flight motoneurones in Locusta migratoria, the effects of pressure applications of glutamate, γ-aminobutyric acid (GABA), aspartate, taurine, glycine and cysteine were studied using an animal preparation in which neuropile intracellular recordings could be made during expression of the flight motor output. A majority of cells responded to glutamate, GABA, aspartate and taurine. At resting potential, glutamate and GABA caused, in different cells, a depolarization, a hyperpolarization or, in a few cells, a biphasic response, all accompanied by a decrease in the size of the evoked and spontaneous postsynaptic potentials (PSPs). At spiking threshold, the responses were always hyperpolarizing. Activation of a chloride conductance mediated the effects of both glutamate and GABA. In some cells, the response to glutamate or GABA desensitized during long-lasting applications, but in most cells the amplitude of the response did not decrease during applications lasting several minutes. Responses to aspartate and glutamate had identical reversal potentials and cross-desensitized. Responses to GABA and taurine had more negative reversal potentials and did not cross-desensitize with those elicited by glutamate or aspartate. Only a few neurones responded to applications of glycine or cysteine at resting potential; they responded with an inhibition of spiking at depolarized potentials. These data suggest that a variety of amino acid receptors are present on the neuropile arborizations of flight motoneurones.

Mesothoracic interneurons involved in flight steering in the locust

1. 1. Twenty-eight interneurons with somata in the mesothoracic ganglion of the locust Locusta appear to be involved in steering in flight. All have their arborizations in the dorsal (flight) neuropil. All make directionally selective responses to visual, ocellar or wind stimuli corresponding to simulated deviations from course in flight. All are directly and/or indirectly postsynaptic to one or more sensory descending neurons (DNs) of the brain, which have been shown to produce steering behaviour when electrically stimulated. Convergence of DNs leads to complex responses by the interneurons. Some receive a variety of additional sensory information derived from thoracic receptors, especially wing proprioceptors and the ear. 2. 2. The membrane potentials of all these interneurons are modulated at flight frequency during fictive flight in deafferented preparations. Nineteen are depolarised in depressor phase (and/ or hyperpolarised in elevator phase); nine are depolarised in elevator phase (and/or hyperpolarised in depressor phase). The modulation derives in at least one case (neuron 016), and presumably in all, from synaptic drive from oscillator or oscillator-follower interneurons. None of the described cells, with the possible exception of IN 313, is thought to be part of the oscillator itself. 3. 3. The 28 ‘steering interneurons’ are characterised and named. Five (016, 035, 036, 302, 313) have been previously described in other contexts. Of these, the first 3 have been renamed; they were previously 116, 135 and 136 of Rowell and Pearson (1983). Four other previously named units are synonomized: 318 of Rowell and Pearson (1983) becomes 302 of Robertson and Pearson (1983), and 120 and 119 of Rowell and Pearson (1983), and 1AA of Elson (1987), all become 016. Two new modifications of the numbering system for locust interneurons are introduced. 4. 4. Five steering neurons are known to make monosynaptic, excitatory or inhibitory connections with flight motor neurons. Individual steering interneurons contribute between 25% and 10% of the total oscillatory drive to individual FMNs. 5. 5. The population of steering interneurons is the site of convergence of oscillator drive and sensory input prior to reaching the motor neuron: this allows sensory modulation of the strength and timing of drive to the individual motor neuron in the appropriate phase of the wing beat cycle, which is required for corrective steering. They are also a point at which the motor drive to the motor neuron is modified by proprioceptive reafference.

Descending neurons supplying the neck and flight motor of diptera: Organization and neuroanatomical relationships with visual pathways

In dipterous insects, a volume of behavioral and electrophysiological studies promote the contention that three wide-field motion-sensitive tangential neurons provide a necessary and sufficient input to specific channels that drive the torque motor during flight. The present studies describe the results of neuroanatomical investigations of the relationships between motion-sensitive neuropil in the fly optic lobes and descending neurons that arise from a restricted area of the brain and supply segmental neck and flight motor neuropil. The present observations resolve at least 50 pairs of descending neurons supplying flight motor centers in the thoracic ganglia. The majority of descending neurons receive a distributed output from horizontal motion-sensitive neurons. However, the same descending neurons are also visited by numerous small-field retinotopic neurons from the lobula plate as well as hitherto undescribed small tangential neurons. Neuroanatomical studies, using cobalt, Golgi, and Texas red histology, demonstrate that these smaller inputs onto descending neurons have dendrites that are organized at specific strata in retinotopic neuropil and that these correspond to horizontal and vertical motion sensitivity layers. Conclusions that only a restricted number of wide-field neurons are necessary and sufficient for visually stabilized flight may be premature. Rather, neuroanatomical evidence suggests that descending neurons to the flight motor may each be selectively tuned to specific combinations of wide- and small-field visual cues, so providing a cooperative descending network controlling the rich repertoire of visually evoked flight behavior.

Descending neurons supplying the neck and flight motor of diptera: Physiological and anatomical characteristics

In Diptera, dorsal neuropils of the pro-, meso-, and metathoracic ganglia supply motor neurons to neck and flight muscles. Motor circuits are supplied by more than 50 pairs of descending neurons (DNs) whose dendritic trees in the brain are restricted to dorsal neuropils of the deutocerebrum where they are grouped together into discrete clusters. Each cluster is visited by wide-field motion-sensitive neurons and by morphologically small-field retinotopic elements. This organization suggests that flight descending neurons should respond to complex stimuli reflecting panoramic movement and small-field motion. Intracellular recordings, combined with dye filling, confirm this. Certain descending neurons responding to visual flow fields terminate bilaterally in superficial pterothoracic neuropils, at the level of indirect (power) flight muscle motor neurons. Other DNs terminate laterally, and provide segmental collaterals to areas containing neck and direct (steering) flight muscle motor neurons. Such DNs are activated by wide-field directional stimuli corresponding to pitch, roll, or yaw, and to small-field stimuli. Appropriate directional mechanosensory stimuli also activate dorsal descending neurons. The significance of dorsal descending neurons for the control of flight is discussed and compared with studies on course deviation neurons in other insects. It is suggested that, in Diptera, dorsal descending neurons may separately be involved in the control of velocity, stabilization, and steering manoeuvres.

Animal Sonar: Processes and Performance

<i>Animal Sonar: Processes and Performance</i>

Neuronal organisation of the flight motor pattern in the cricket, Teleogryllus commodus

The neuronal organisation of the flight motor pattern in the cricket was investigated using electromyographic and intracellular recording and staining techniques with two objectives: (a) to compare neuromuscular control of the forewings during cricket flight and stridulation, and (b) to provide data for comparison with the well characterised locust flight system.

Chemical deafferentation of the locust flight system by phentolamine

1. Phentolamine was injected into the haemolymph of locusts, Locusta migratoria, and its effects on the flight system were analyzed using electrophysiological techniques. 2. Doses of 150 microliters at 10(-2) M phentolamine inactivated the wing stretch-receptors and tegulae without influencing the central nervous system (CNS). The lack of effect on the CNS was demonstrated by the absence of any effect on the flight motor pattern in animals that had been mechanically deafferented prior to the administration of phentolamine. From these observations we conclude that phentolamine can be used to chemically deafferent the flight system of the locust. Consistent with this conclusion is that the administration of phentolamine in intact animals changed the flight motor pattern so that it resembled the pattern occurring in mechanically deafferented animals. 3. The two main advantages of deafferenting the flight system by injecting phentolamine were a) intracellular recordings from central neurons could be easily maintained during the process of deafferentation, and b) the contribution of different groups of proprioceptors to the generation of the motor pattern could be assessed since not all proprioceptors were inactivated simultaneously. 4. By intracellularly recording from elevator motoneurons and administering phentolamine we confirmed a number of previous results related to the function of the wing stretch-receptors and the tegulae.

Organization of the auditory pathway in the thoracic ganglia of noctuid moths

We describe the neuroarchitecture of the noctuid thoracic nerve cord and use this framework to interpret the organization of the auditory pathway responsible for escape behaviour in noctuid moths. Noctuid moths possess only two auditory receptors (A1, A2), in each ear. The axon of the A1 cell projects initially to a glomerulus located ventrally and medially in the metathoracic ganglion, where it bifurcates. One branch ascends in the ventral intermediate tract to the brain, the other descends in the ventral intermediate tract into abdominal neuromeres of the metathoracic ganglion. Both axons arborize in the median ventral and ring tracts in each neuromere. The central projections of the A2 cell remain largely within the metathoracic ganglion. The axon bifurcates at the midline and directs arborizations dorsally to the dorsal intermediate and median dorsal tracts, and ventrally into the ring tract where the arborizations overlap those of the A1 afferent. The afferent projections remain ipsilateral to the ear of origin. We describe a posterior auditory association area in the metathoracic ganglion in which the major arborizations of several identified interneurones overlap those of the A1 afferent and make monosynaptic connections with it. These interneurones all respond tonically to sound stimuli. We have also identified the projections of the A1 afferent, interneurones, and motor neurones in the segmentally equivalent anterior auditory association area of the mesothoracic ganglion. An interneurone with major arborizations in the same tracts as the A1 afferent, and receiving monosynaptic input from it, is described. The arborizations of higher order interneurones lie mainly in dorsal tracts along with those of flight motor neurones. All the interneurones in this anterior centre respond phasically or phasic/tonically to sound stimuli. The relevance of this anatomical organization for predator avoidance behaviour is considered and the organization of auditory pathways in tympanate insects compared.

Synchronous activity of flight neurons in the mesothoracic ganglion of the locust

1. Coordinated movements of the wings during flight in the locust result from coordinated activity of flight neurons in the thoracic ganglia. Many flight interneurons and motoneurons fire synchronous bursts of action potentials during the expression of the flight motor pattern. The mechanisms which underlie this synchronous firing were investigated in a deafferented preparation of Locusta migratoria. 2. Simultaneous intracellular recordings were taken from flight neurons in the mesothoracic ganglion using glass microelectrodes filled with fluorescent dye. 3. Three levels of synchronous activity between synergistic motoneurons and between the right and left partners of bilaterally symmetrical pairs of interneurons were observed: bursting which was loosely in phase but which showed little correlation between the temporal parameters of individual bursts in the two neurons; bursting which showed synchrony of the beginning and end of bursts; and bursts which showed highly synchronous spike-for-spike activity. 4. Direct interactions between the neurons had little or no part to play in maintaining any of the levels of synchrony, even in instances of very close synchrony (spikes in different neurons occurring within 1 ms of each other). Highly synchronous firing was a consequence of common synaptic input impinging on neurons with similar morphological and physiological properties.

Neural circuits mediating visual flight control in flies. II. Separation of two control systems by microsurgical brain lesions

The role of 2 sets of interneurons in the optic lobes of blowflies in visual course control was studied by means of brain lesions. The first set comprises the cells HS and H2, which respond to global horizontal motion. The second set are the FD-cells, which respond selectively to local horizontal motion. All these cells are output neurons of the third optic ganglion of flies and are thought to be coupled via descending neurons to the flight motor system. In 2 series of experiments specific cells of these 2 sets were inactivated by microsurgical brain lesions L1 and L2 respectively. The effects of the lesions on visual course control were tested by measuring the yaw torque responses of the animals in restrained flight before and after the operation. The flies were stimulated in these tests with monocular and binocular motion of periodic gratings moving in either the horizontal or the vertical direction. Lesion L1 in the right side of the brain inactivates the right HS-cells and the left H2- and FD-cells. This leads to a complete block of the response to binocular clockwise horizontal motion and a reduction of the response to monocular motion from front to back on the right side of the animal. Application of L1 also leads to a pronounced response to binocular motion from front to back not observed in normal animals. The response to monocular vertical motion is unaffected. Lesion L2 reduces all responses to monocular and binocular horizontal motion present in normal animals. The behavioral effects of the lesions are highly specific and consistent with predictions based on the well-known anatomical and physiological properties of the neural circuitry investigated. The results demonstrate directly that the HS-, H2-, and FD-cells control motion-induced steering maneuvers in flight.

Integration of ultrasound and flight inputs on descending neurons in the cricket brain.

In response to ultrasonic stimuli, tethered flying crickets perform evasive steering movements that are directed away from the sound source (negative phonotaxis). In this study we have investigated the responsiveness to ultrasound of neurons that descend from the cricket brain, and whether flight activity facilitates the responsiveness of these neurons. 1. Ultrasonic stimuli evoke descending activity in the cervical connectives both ipsilateral and contralateral to the sound source. 2. Both the amount of descending activity and the latency of this response in the cervical connectives are linearly correlated with ultrasonic stimulus intensity, regardless of the cricket's behavioral state. 3. Flight activity significantly increases the amount of descending activity evoked by ultrasound at all stimulus intensities, and significantly decreases the latency of the response in the cervical connectives compared with non-flying crickets. Flight activity, however, does not significantly affect the activity in an interneuron (Int-1) carrying ultrasound input to the brain. Thus, the increase in the amount of descending activity produced during flight activity is due to the integration of input from Int-1 and the flight motor system to ultrasound-sensitive neurons in the cricket brain. 4. Descending units recorded in the cervical connectives originate in the cricket brain. A reduction in the amount of descending activity is correlated with a decrease in the magnitude of the negative phonotactic response of the abdomen during flight activity, suggesting that these descending units play a role in eliciting negative phonotaxis.

Metamorphosis of Wing Motor System in the Silk Moth, Bombyx mori: Origin of Wing Motor Neurons: (flight motor neuron/insect/neural development).

The origin of the peripheral nerve and motor neurons that innervate the adult mesothoracic dorsal longitudinal muscles (DLMs) was examined in the silk moth, Bombyx mori. The anatomical features of the peripheral nerve and motor neurons were investigated by dissection, electron microscopy, and cobalt back-fill staining at different pupal stages. These studies showed that the peripheral nerve (IIN1c) that innervates the adult DLMs originates from a branch (db branch) of the larval mesothoracic dorsal nerve that innervates the larval DLMs. During metamorphosis the larval nerve shortens or lengthens locally without change in its basic branching pattern, and the db branch moves towards the mesothoracic ganglion to become the IIN1c. All the adult DLM motor neurons are from larval ones. Nine of the 14 larval DLM motor neurons survive during metamorphosis to become adult DLM motor neurons, and 5 disappear in early pupal stages.

Reflections on Organisms: Examples from the Neurobiology of Insect Rhythmic Movements

Consideration of organisms is necessary for neurobiologists interested in the neural bases of behavior, because a behavioral act performed by an intact animal defines the problem to be solved and also constitutes the context in which the nervous system operates. In addition, observations of behaving organisms can introduce new preparations for study of general questions. Examples are given from rhythmic gill movements of Corydalus cornutus , insect flight, and development of the moth flight motor. In a concluding section, questions are raised about possible philosophical and judgmental influences on the current tensions between holistic approaches expressed in organismic biology and reductionist approaches expressed in biotechnology.

Neural Mechanisms Underlying Axial/Appendicular Steering Reactions in Locust Flight

SYNOPSIS. Steering during flight in the locust involves complex changes in wingbeat, bending of thorax and head, and ruddering movements of abdomen and hindlegs. Most of these behavioral subcomponents involve coordinated modification of axial and appendicular musculature control. Some of the mechanisms underlying this neural modification have been analysed at the cellular level. During steering via wingbeat, sensory information about course deviations leads to highly coordinated and asymmetric changes in the flight motor's output through the following mechanisms. Identified feature detector neurons in the locust brain integrate sensory information concerning specific types of course deviation. Each of these descending detector neurons makes connections with a population of thoracic interneurons. These thoracic interneurons have two important properties. First, they relay deviation information to flight motoneurons. Second, they are under the gating control of the flight central oscillator. Through this gating control the descending sensory signal is phase-coupled to the flight rhythm and delivered to appropriate flight motoneurons in one and the same step. Although most of the recent cellular studies have been aimed at unraveling the neural basis of wingbeat alterations, similar (but not identical) principles of neural organization seem to be involved in the steering reactions produced by axial motor systems.

Morphological study of flight motor neurons in the cricket.

The motor innervation of the major flight muscles powering the fore- and hindwings of the cricket Teleogryllus oceanicus was investigated. The morphology of the motor neurons was determined by filling them via their axons in the periphery with either Lucifer Yellow or cobalt chloride followed by silver intensification. Details of the location of branches of motor neurons within the ganglion were obtained by serially sectioning ganglia containing filled neurons. For each flight muscle at least two motor neurons were found. The somata of motor neurons were located in two clusters in the ganglion, the anterior lateral cluster and the posterior lateral cluster. Motor neurons in the same cluster had similar morphologies. Most of the arborizations of these motor neurons were in the dorsal neuropil with a few branches in the lateral intermediate neuropil. The morphology of flight motor neurons was compared with the morphology of leg motor neurons in consideration of the possible functional organization of the ganglion. A comparison was made between motor neurons innervating homologous muscles of the cricket and the locust to determine the extent of the difference between the flight systems of these two groups.

Invariance of Oscillator Interneurone Activity During Variable Motor Output by Locusts

ABSTRACT Simultaneous intracellular recordings were made in locusts from (a) flight motor neurones and (b) output interneurones of the flight oscillator. The insects were mounted with the head at the centre of rotation of an artificial horizon. During fictive flight, these animals responded to simulated deviations from course with the changes in motor output appropriate to course-correction manoeuvres, as previously described. In the motor neurone of depressor muscle MN98 (meso-thoracic second basalar) these changes take the form of systematic variation in amplitude in the cyclical depolarization seen in the neurone in flight which, in turn, leads to variation in the number of action potentials per cycle (from 0·3) and in the latency of the first spike (up to 19 ms difference). These changes are closely related to the perceived movement of the horizon. The oscillator output, as recorded in metathoracic interneurone 511, shows, in contrast, very little change. The fraction of its variation which is correlated with horizon movement is vanishingly small (e.g. for number of action potentials per burst r2 = 0·008). The exteroceptive sensory inputs which modify motor output during steering do not, therefore, affect the oscillator appreciably. Thus, by exclusion, the motor patterns of compensatory steering are due exclusively to summation of the oscillator drive with the sensory inputs. This takes place in the motor neurones and especially in the premotor interneurones, as previously described.

Induced neuroma formation and target muscle perturbation in the giant fiber pathway of the Drosophila temperature-sensitive mutant shibire.

The temperature-sensitive mutation shibire (shi) in Drosophila melanogaster is thought to disrupt membrane recycling processes, including endocytotic vesicle pinch-off. This mutation can perturb the development of nerves and muscles of the adult escape response. After exposure to a heat pulse (6 h at 30° C) at 20 h of pupal development, adults have abnormal flight muscles. Wing depressor muscles (DLM) are reduced in number from the normal six to one or two fibers, and are composed of enlarged fibers that appear to represent fiber fusion; large spaces devoid of muscle fibers suggested fiber deletion. The normal five motor axons are present in the peripheral nerve PDMN near the ganglion. However, while some motor axons pass dorsally to the extant fibers, other motor axons lacking end targets pass into an abnormal posterior branch and terminate in a neuroma, i.e., a tangle of axons and glia without muscle target tissue. Hemisynapses are common in axons of the proximal PDMN and within the neuroma, but they are rarely seen in control (no heat pulse) shi or wild-type flies. All surviving muscle fibers are innervated; no muscle tissue exists without innervation. Fibrillar fine structure and neuromuscular synapses appear normal. Fused fibers have dual innervation, suggesting correct and specific matching of target tissue and motor axons. Motor axons lacking target fibers do not innervate erroneous targets but instead terminate in the neuroma. These results suggest developmental constraints and rules, which may contribute to the orderly, stereotyped development in the normal flight system. The nature of the anomalies inducible in the flight motor system in shi flies implies that membrane recycling events at about 20 h of pupal development are critical to the formation of the normal adult nerve-muscle pattern for DLM flight muscles.

Forewing movements and motor activity during roll manoeuvers in flying desert locusts

Desert locusts, tethered on a roll torque meter and flying in a wind tunnel are surrounded by an artificial horizon (Fig. 1). Flight motor activity and movement of forewings are monitored continuously. Movements of the artificial horizon elicit roll manoeuvers of the animal with latencies of several seconds; concomitant changes in flight motor pattern and wing movement can be correlated with the animal's roll angle and roll torque. Flight sequences with constant torque and roll angle (steady state) have been analysed with the following results. Wing Kinematics. A phase difference between the movements of the forewings on either side is correlated with roll angle (Fig. 3). Pronation of a forewing is always greater on the side to which the animal rolls, i.e. on the side that produces less lift (Fig. 5). In some experiments the slope of the wing tip path is also decreased (Fig. 5). In both cases, the aerodynamic angle of attack is decreased and the forewing on this side produces less lift. In most experiments, changes in pronation are less pronounced in the contralateral wing (Fig. 11). All factors contribute to a net roll torque that sustains the animal's roll angle. Other kinematic parameters of forewing movement, e.g. wing stroke amplitude, were not found to be correlated with roll angle and torque (Fig. 4). Motor Pattern. Activity of several flight muscles (depressors M97, M98, M99, and M129; elevators M83, M84, and M90) was investigated for changes in burst length and temporal coordination in response to roll stimuli. Most flight muscles fired only once per wing beat cycle in our preparations. Thus, burst length was not found to be correlated with roll angle. Time intervals of firing between all muscle pairs investigated change in correlation with the torque and roll angle (Fig. 9). All mesothoracic muscles are active earlier-relative to the ipsilateral metathoracic subalar muscle M129-during roll to the ipsilateral side than during roll to the contralateral side. Correlations Between Motor and Movement Pattern. The phase of muscle firing within the wing beat cycle varies with roll angle (roll torque). The first basalar M97 and second tergosternal M84 muscles, when referenced e.g. to the upper (M97) or lower (M84) reversal point of the wing tip trajectory, are active earlier on the side the animal turns to (Fig. 10). The onset of the first basalar M97 relative to the beginning of downstroke is correlated with maximum pronation and roll angle (Fig. 11). Mechanisms of Lift Control. Wing pronation, which is very important for lift production is controlled by the central nervous system by altering the phase of muscle activity within the wing beat cycle.

Proprioceptive input patterns elevator activity in the locust flight system.

1. In the locust, Locusta migratoria, the roles of two groups of wing sense organs, hind wing tegulae and wing-hinge stretch receptors, in the generation of the flight motor pattern were investigated. A preparation was employed that allowed the intracellular recording of neural activity in almost intact tethered flying locusts or after selective manipulations of sensory input. The functions of the two sets of receptors were assessed 1) by studying the phases of their discharges in the wingbeat cycle (Fig. 3), 2) by the selective ablation of input from the receptors (Figs. 4-7), and 3) by the selective stimulation of the receptor afferents (Figs. 8-12). 2. Input from the tegulae was found to be responsible for the initiation of elevator activity (Figs. 9 and 10) and for the generation of a distinct initial rapid depolarization (Figs. 4, 5, and 8) characteristic of elevator motor neuron activity in intact locusts (Figs. 1 and 16). 3. Input from the wing-hinge stretch receptors was found to control the duration of elevator depolarizations by the graded suppression of a second late component of the elevator depolarizations as wingbeat frequency increased (Figs. 6, 7, 11, and 12). The characteristics of this late component of elevator activity suggested that it is generated by the same (central nervous) mechanism that produces the elevator depolarizations recorded in deafferented animals (Fig. 2). Apparently this late component contributes to the intact pattern of elevator depolarizations only at lower wingbeat frequencies and is abolished by the action of stretch-receptor input at frequencies above approximately 15 Hz (Figs. 1, 2, and 4). At these high wingbeat frequencies elevator activity is dominated by the rapid depolarizations generated as a result of tegula input. 4. The present study demonstrates 1) that the timing of elevator motor neuron activity is determined by phasic afferent input from tegulae and stretch receptors and 2) that input from the stretch receptors controls the duration of elevator activity in the wingbeat cycle following the wing movement that was responsible for the generation of the receptor discharge.

Demonstration of functional connectivity of the flight motor system in all stages of the locust

The development of the flight motor pattern was studied by recording from the thoracic muscles of locusts of various developmental stages. In response to a short wind stimulus, larval locusts generate unpatterned motor activity, whereas newly moulted adults generate the flight pattern (Fig. 1A). The latter is equivalent to the mature adult flight pattern, although more irregular and of lower frequency. Experiments with highly deafferentated locusts indicate that the switch from the larval tonic to adult phasic flight pattern and subsequent increase in frequency are not dependent on phasic peripheral feedback from moving body structures (Fig. 1B). By using octopamine, flight motor activity could be released without need of the wind stimulus (Fig. 2). This corresponded to the normal wind released flight pattern of intact locusts, although the frequency was lower (Fig. 8). Following octopamine treatment, the response to wind stimulation was enhanced. Wind then released in deafferentated adults long flight sequences of significantly elevated frequency (Fig. 3). Although flight is essentially an adult specific behaviour, octopamine was finally found to release flight motor activity in all larval stages (Fig. 7). We conclude that major steps in the development of the flight motor circuitry are completed by the end of embryogenesis. Thus, in contrast to previous assumptions (cf. Bentley and Hoy 1970; Kutsch 1974a; Altman 1975), postembryonic changes in neither the central, nor peripheral nervous system appear to be of major importance for the ontogeny of the locust flight motor program. Whether developmental changes in the wind sensory system of the head, or levels of neurohormones such as octopamine, are related to the newly acquired responsiveness of freshly moulted adult locusts to the normal flight releasing stimulus is discussed.