Flight Motor Pattern Research Articles

Adaptive Modifications in the Flight System of the Locust After the Removal Of Wing Proprioceptors

ABSTRACT Previous investigations on the flight system of the locust have found that removal of the wing tegulae in mature locusts (Locusta migratoria) results in an immediate change in the flight motor pattern: the wingbeat frequency (WBF) decreases, the interval between the activity of the depressor and the elevator muscles (the D-E interval) increases, and the phase of the elevator activity in the depressor cycle increases. Here we report the results of a detailed quantitative analysis of these changes. We also examined the flight motor pattern for up to 14 days after removal of the tegulae and found that the changes caused by this operation were not permanent. Beginning on the first day after the operation there was a time-dependent recovery of the WBF, the D-E interval and the phase towards their normal values. In about 80% of the experimental animals the flight motor pattern recovered almost completely. Intracellular recordings from elevator motoneurones showed that this recovery was associated with changes in the pattern of excitatory input to these motoneurones. The modification of activity in elevator motoneurones was dependent on afferent input since complete deafferentation of recovered animals resulted in a motor pattern similar to that following deafferentation of normal animals.

Flight motor pattern in flying and non-flying Phasmida

The insect order Phasmida comprises species with a broad spectrum of wing morphism and flight ability. By monitoring the electrical activity of several pterothoracic muscles the motor output during tethered flight was recorded for several Phasmida, ranging from excellent fliers to non-winged species. Both winged and non-winged species can generate a motor pattern as judged by criteria used to identify the locust flight pattern. However, in non-fliers the probability of expressing this pattern, its duration and precision are reduced. The antagonistic activity of the chosen muscle pairs is clearly different from the motor output during leg movements, which argues for specific motoneuronal coordination released for different behavioural performances. The demonstration of flight motor output in all tested Phasmida indicates that neural structures including their functional connectivity can be maintained independently of the appropriate peripheral structures. With respect to evolution this supports the idea that central neuronal interactions can be more conservative compared to changes in the periphery.

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.

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.

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.

Changes of the hindwing motor pattern associated with phonotactic steering during flight in the cricket,Teleogryllus oceanicus

1. The hindwing movements and flight motor pattern underlying straight flight and negative phonotactic steering of the cricketTeleogryllus oceanicus were investigated by photographing the wing movements and by recording electromyograms (EMG) from hindwing muscles. 2. During straight flight the right and left hindwings showed symmetrical strokes. When the animal turned in response to ultrasonic auditory stimuli the wing stroke was clearly asymmetrical. For animals tethered in an inverted position the hindwing outside the turn showed a lower elevation than the hindwing inside the turn. 3. The straight flight motor pattern showed the elevators were active at 45 to 57% of the depressor cycle. The latency from depressor to elevator activity (D-E) showed a positive correlation with the depressor period whereas the latency from elevator to depressor activity (E-D) was relatively independent of the depressor period. 4. The wing beat frequency increased when the animal steered in response to auditory stimuli. 5. During steering of an animal tethered in an inverted position the elevator muscles on the inside of a turn showed increased activity (double spikes). Also, on the inside of a turn the latency from depressor to elevator activity decreased and the phase of elevator activity in the depressor cycle decreased. On the outside of a turn the elevator muscles were less active. The latency from depressor to elevator activity increased as did the phase of elevator activity in the depressor cycle. 6. The increased activity and earlier firing of the elevators on the inside of a turn is consistent with a greater wing elevation on the same side. Similarly, the decreased activity and later firing of the elevator on the outside of a turn is consistent with a lower wing elevation on that side. These asymmetrical wing strokes seen in the hindwing could be important elements of steering.

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.

A reconsideration of the central pattern generator concept for locust flight

Although it is generally agreed that locusts can generate flight similar rhythmic motor activity in the absence of sensory feedback from the wings, recent studies indicate that functional deafferentation produces significant changes in the flight motor pattern (Hedwig and Pearson 1984). These findings have raised doubts on the adequacy of the central pattern generator concept for the locust flight system (Pearson 1985). In this paper, we re-investigate the effects of deafferentation on the capacity of adult migratory locusts to generate the flight motor pattern. For this purpose, the experimental animals were dissected to various degrees, ranging from head-ventral nerve cord, to isolated pterothoracic nerve cord, and finally single isolated ganglion preparations. Flight motor activity was released by either wind stimulation, the more traditional method, or by applying octopamine (Sombati and Hoyle 1984; Stevenson and Kutsch 1986). In all cases the released motor activity was analysed, giving details of latency, and phase relationships between specific synergistic and antagonistic motor units, and then compared with the flight motor pattern generated by intact tethered locusts.

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

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.

Interneurons in the flight system of the cricketTeleogryllus oceanicus

1. A deafferented preparation of the cricketTeleogryllus oceanicus was developed to investigate the morphological and physiological properties of thoracic neurons which are phasically active with the flight rhythm. 2. Electromyographic recordings from selected wing muscles established properties of the intact flight motor pattern. Deafferentation reduced the repetition frequency of the motor pattern. This reduction was mediated mainly by an increase in the latency from depressor muscle activation to elevator muscle activation. The latency from elevator to depressor muscle activation became less variable. 3. Intracellular recordings were taken from the neuropil segments of flight neurons using glass microelectrodes containing Lucifer Yellow. Two motoneurons were identified. Five phasically active interneurons were identified and are described in this paper. 4. Properties of flight neurons of crickets were very similar to those of locusts. Membrane potential oscillations were initiated and maintained by phasic excitatory and inhibitory synaptic input. Motoneurons tended to fire once per cycle in the absence of other input whereas interneurons fired high frequency bursts of 3 to 6 spikes. Interneurons with short latency connections to flight motoneurons or with the ability to reset the flight rhythm when stimulated, were identified. Flight activity in neurons was modulated by concurrent wind, ventilatory or auditory input. 5. The organization of cricket flight interneurons also was very similar to the organization of locust flight interneurons. Important flight interneurons (i.e. capable of resetting the flight rhythm) originated in the abdominal neuromeres fused with the metathoracic neuromere. Additionally, there was some evidence for the existence of sets of serially homologous interneurons in the three fused neuromeres of the metathoracic ganglionic mass. 6. The results reported here are consistent with the idea that the flight systems of locusts and crickets share a fundamental feature of interneuronal organization that results from the evolutionary origin of the flight system and is not a specific adaptation for flight.

Effects of octopamine, dopamine, and serotonin on production of flight motor output by thoracic ganglia of Manduca sexta.

Effects of biogenic amines on a centrally generated motor pattern in Manduca sexta were examined by pressure injecting nanomole to micromole amounts of octopamine, dopamine or serotonin into thoracic ganglia. Motor output was recorded extracellularly from a pair of antagonistic flight muscles and their motor neurons. The monoamines were found to alter production of a motor pattern that produces rhythmic wing flapping (10 Hz) and exhibits phase relationships similar to those in the flight pattern of intact moths. In mesothoracic ganglia with sensory nerves intact, octopamine (4 X 10(-9) mol) injected into lateral regions evoked regular firing of a single motor neuron, whereas a higher dose (4 X 10(-8) mol) often elicited the flight motor pattern. In the absence of sensory input, these doses of octopamine had little effect. Low doses (10(-10) mol) greatly enhanced motor responses to electrical stimulation of a wing sensory nerve. Dopamine (2 X 10(-10) mol) injected into the medial region of the mesothoracic ganglion elicited the flight motor pattern in the presence or absence of sensory input. Rhythmic output induced by dopamine (5 X 10(-10) mol) was suppressed by injecting serotonin (5 X 10(-10) mol) into the same region. These findings demonstrate that dopamine, octopamine, and serotonin have different effects on motor output in Manduca and suggest that these amines are involved in initiating, maintaining and terminating flight behavior, respectively. Octopamine may elicit flight production by enhancing the efficacy of sensory transmission thereby increasing excitability or arousal. Dopamine may act on interneurons involved in generating the flight motor pattern.

Pre-imaginal flight motor pattern in Locusta

In a wind stream, larval stages of Locusta usually show a tonic muscle activity but they can also exhibit a rhythmic motor output. With ageing such a pattern can be released sooner, the trains become longer. The basic rhythm of 10 Hz does not change. The initial co-contraction of specific muscles is substituted later in development by an antagonistic recruitment. This activity resembles the flight motor pattern of young locusts which lack phasic sensory feedback from the wing region. Azadirachtin, an insect growth regulator, has been used to produce a permanent 5th larval instar. However, the extension of the last larval stage does not lead to a further development of the motor pattern to a level comparable to mature animals.

Neural circuits in the flight system of the locust.

Circuitry in the flight system of the locust, Locusta migratoria, was investigated by use of intracellular recording and staining techniques. Neuronal connections were established by recording simultaneously from neuropile segments of pairs of identified interneurons. Brief depolarizing current pulses delivered to interneurons 301 and 501 reset the flight rhythm in a phase-dependent manner, thus establishing the importance of these neurons in rhythm generation. Interneuron 301 was found to make a strong delayed excitatory connection with 501 and to receive a short-latency inhibitory connection from 501. The circuit formed by 301 and 501 appears suited for promoting rhythmicity in the flight system. The delayed excitatory potential recorded in 501 following each spike of 301 was reversed by hyperpolarizing 501. This potential and short-latency inhibitory postsynaptic potentials from 301 to other interneurons were blocked with the application of picrotoxin. We conclude that the delayed excitation is produced via a disynaptic pathway from 301 to 501, with 301 inhibiting in a graded manner the tonic release of transmitter from one or more unidentified intercalated neurons. Interconnections between the 301-501 circuit and other identified interneurons were discovered. This circuitry can account for two features of the flight motor pattern recorded in deafferented preparations. These features are the constant-latency relationship between depolarizations in elevator and depressor motoneurons and the relatively constant duration of depressor motoneuron bursts. The locust flight system shares general features with other described rhythm-generating systems. These include the occurrence of graded interactions, the probability of multiple oscillatory mechanisms, and a predominance of inhibitory connections. Its uniqueness lies in the way that components and processes are assembled and operate.

Octopamine and chlordimeform enhance sensory responsiveness and production of the flight motor pattern in developing and adult moths

Octopamine and an agonist, chlordimeform, increase the responsiveness of adult and pharate adult Manduca sexta to gentle mechanical stimulation of the wing. Higher doses of chlordimeform elicit almost continuous production of the flight motor pattern in both adults and pharate adults, and the effect persists for more than 24 h. The dose of chlordimeform necessary for this effect increases with age. Mechanical stimulation of the wing of pharate adults elicits several cycles of flight motor pattern, but with repeated stimulation the animal habituates. Habituation is slower in chlordimeform-treated animals than in controls. Injection of octopamine (1-8 X 10(-8) mol) or chlordimeform (3 X 10(-9) mol) into the mesothoracic ganglion elicits the flight motor pattern. The excitatory actions of both compounds can be blocked by cyproheptidine. Chlordimeform (5 X 10(-8) mol) in acetone applied to the wing does not cause a noticeably greater increase in teh electrical activity of sensory neurons than does acetone applied alone; this result suggests that chlordimeform does not act on these peripheral sites or on axonal membranes in general. We suggest that chlordimeform and octopamine act on the thoracic ganglia to alter the level of excitation or effectiveness of synaptic transmission among central neurons, including those involved in producing the flight motor pattern.

Manipulation of the endocrine system ofLocusta and the development of the flight motor pattern

By chemical allatectomy (precocenetreatment) or implantation of corpora allata, precocious adults (adultiforms) and supernumerary larval instars respectively can be produced. Such manipulations of the endocrine system were carried out in order to search for possible hormonal influences on the ontogeny of the flight motor pattern.

The role of sensory inputs in insect flight motor pattern generation

Studies on intact flying locusts are revealing the important part played by phasic sensory inputs in regulating the flight motor output in insects and require a radical revision of the concept of the flight pattern generator.

Dipteran flight motor pattern: invariabilities and changes during postlarval development.

For Calliphora the wingbeat frequency and the underlying motoneuronal activity were recorded during adult life. Wingbeat frequency increases during the ten days following last molt. The activity of motoneurons serving four selected flight muscles (nonfibrillar and fibrillar ones) also increases with age. The motoneuronal activity of young and old flies was analyzed statistically (serial and cross-correlograms, latency and phase histograms). In addition, several wing manipulations were carried out to evaluate the significance of sensory feedback on pattern generation during maturation. These ontogenetic studies suggest a centrally generated motor pattern that (1) is essentially complete with the molt to adulthood, (2) shows a progressive increase in intrinsic activity, and (3) is modulated by sensory feedback from the wing region by the same amount irrespective of age. Similarities in the postlarval development of the flight pattern of neurogenic and myogenic flyers are discussed.

Neural and behavioral correlates of pyrethroid and DDT-type poisoning in the house fly, Musca domestica L

Intact house flies were observed during poisoning caused by several pyrethroid and DDT-type insecticides. The two insecticide classes could be generally distinguished from each other based on differences in symptoms and several physiological correlates. Both insecticide types caused motor unit repetitive backfiring, but the temporal development and stability of repetitiveness were distinctly different between the two classes. Repetitive backfiring always disappeared at low temperatures, but DDT-type backfiring disappeared at lower temperatures than the pyrethroids. trans-Tetramethrin caused a threshold increase in flight motor nerve endings which did not occur in DDT or trans-Barthrin poisoning. Pyrethroids caused “uncoupling” of the flight motor pattern, while DDT-types did not. trans-Barthrin, a methylenedioxyphenyl pyrethroid, was unique in causing both symptoms and physiological aberrations which more closely resembled those of the DDT-types than the pyrethroids.