The closer muscle is a second target for the stretcher inhibitor motoneuron of the crayfish's thoracic limbs

Summary The stretcher inhibitor motoneuron of each thoracic limb of a crayfish (Pacifastacus leniusculus) was consistently found to innervate parts of the closer muscle, in addition to the stretcher muscle; it is thus not a specific inhibitor as previously thought. The common inhibitory motoneuron also innervates parts of both muscles. Some individual closer muscle fibers are inhibited more strongly by one inhibitor, some by the other, and some fairly equally by both; no general rule governing the inhibitors' closer muscle outputs became evident. In the claw, the distal closer fibres with the longest membrane time constants are all strongly inhibited by the stretcher inhibitor, and some by the common inhibitor as well.No other thoracic limb muscles were found to receive the stretcher inhibitor. The opener inhibitor's effects could be detected only in the opener muscle. The common inhibitor inhibits all walking leg muscles effectively. In the cheliped, it consistently inhibits all except the opener muscle, where its output may be vestigial. Its axon emerges through the ganglion's first root, whereas the opener and stretcher inhibitors' axons pass through the second root. The fast and slow excitatory axons to the extensor muscle also exit separately through the first and second roots, as in locusts.Abbreviations CI common inhibitor - EJP excitatory junctional potential - IJP inhibitory junctional potential - OI opener inhibitor - SI stretcher inhibitor     

Comparison of identified leg motoneuron structure and function between larval and adult Manduca sexta

Persistent leg motoneurons of the moth Manduca sexta were investigated in larval and adult animals to compare their dendritic structures, intrinsic electrical properties and pattern of target innervation. The study focused on two identified motoneurons of the prothoracic leg. Despite the complete remodeling of leg muscles, the motoneurons innervated pretarsal flexor muscles in both larval and adult legs. Similarly, although the central dendrites regress and regrow, the branching pattern was similar with the exception of a prominent midline branch that was not present in the adult stage. The intrinsic electrical properties of the motoneurons differed between larval and adult stages. Larval motoneurons had significantly higher membrane input resistances and more depolarized resting membrane potentials than did motoneurons in pharate adults or adults. In all stages, one motoneuron had a low maximal firing frequency, whereas the second motoneuron, which innervated the other half of the muscle, had a high maximum firing frequency. Although the two motoneurons continued to innervate the same halves of the target muscle, their relative effects on muscular contraction were reversed during metamorphosis along with concomitant changes in intrinsic properties. Pretarsal flexor motoneurons in pharate adults (just prior to emergence) displayed properties similar to those in emerged adults. Accepted: 8 January 2000     

Quantitative electron-microscopy analysis of cranial nerves III, IV, and VI and of the extrinsic eye muscles in fog.

A comparative study of the quantitative data of the frog extraocular muscles and the cranial nerves that innervate them was performed. Oculorotatory muscles contain muscle fibres of at least 4 types which are arranged in heterogeneous layers. The zonal arrangement of the muscles does not occur on the cross-sections in the vicinity of muscle insertions. In these regions only two muscle fibre types are present and the total number of fibres is smaller by 70% than in the central region of the muscle. Most numerous are muscle fibres in the rectus inferior muscle, while the smallest number of fibres is found in rectus interior muscle. Three distinct types of nerve fibres are distinguished according to the following criteria: occurrence and thickness of myelin sheath, fibre diameter and ratio "g". The fibres with thin myelin sheaths indicate small diameters (1-5--6- mum) and their ratio "g" equals 0-82 +/- 0-08. They constitute about 30% of the myelinated fibres in the nerve supply of the oculorotatory muscles and about 14% in the supply of the retractor bulbi muscle. Both the value of the ratio "g" and a greater number of these fibres in the nerve supply of the muscles that contain slow contracting muscle fibres indicate that they are rather slow conducting nerve fibres. The range of the diameters of the fibres with thick myelin sheaths is greater (3-5--13-5 mum) and their "g" equals 0-66 +/- 0-06. These fibres constitute about 70% of the myelinated ones in the nerve supply of the oculorotatory muscles and 86% in the supply of the retractor bulbi muscles. The value of the ratio "g" in these fibres indicates that they are fast contracting ones. The smallest diameters are found in the myelinated fibres (0-5--1-7 mum). These fibres occur frequently in all the examined nerves; they constitute 36--47% of the total number of all the nerve fibres. The frog extraocular muscles are characterized by an abundal nerve supply which is reflected in the low innervation ratio (1:4--1:5). On the distal cross-section of nerves the number of nerve fibres is greater than on the proximal ones. Ganglionic neurons occur sporadically around the nerves; in the nerve III synaptic contacts between two neurons were observed.     

Reflex modulation in locusts walking on a treadwheel intracellular recordings from motoneurons

Summary In locusts (Locusta migratoria) walking on a treadwheel, afferents of tarsal hair sensilla were stimulated via chronically implanted hook electrodes (Fig. 1). Stimuli applied to the middle leg tarsus elicited avoidance reflexes (Fig. 2). In quiescent animals, the leg was lifted off the ground and the femur adducted. In walking locusts, the response was phase-dependent. During the stance phase, no reaction was observed except occasional, premature triggering of swing movements; stimuli applied near the end of the swing phase were able to elicit an additional, short leg protraction.Central nervous correlates of phase-dependent reflex modulation were observed by recording intracellularly from motoneuron somata in walking animals. As a rule, motoneurons recruited during the swing phase showed excitatory stimulus-related responses around the end of the swing movement, correlated to the triggering of additional leg protractions (Figs. 3, 4, 5). Motoneurons active during the stance phase were often inhibited by tarsal stimulation, some showed only weak responses (Figs. 8, 9, 10). Common inhibitory motoneuron 1 was excited by tarsal stimulation during all phases of the leg movement (Figs. 6, 7). In one type of flexor tibiae motoneuron, a complex response pattern was observed, involving the inversion of stimulus-related synaptic potentials from excitatory, recorded during rest, to inhibitory, observed during long-lasting stance phases (Figs. 11, 12).The results demonstrate how reflex modulation is represented on the level of synaptic input to motoneurons. They further suggest independent gain control in parallel, antagonistic pathways converging onto the same motoneuron as a mechanism for reflex reversal during locomotion.Abbreviations CI ₁ common inhibitory motoneuron (1) - EMG electromyogram - Feti fast extensor muscle of the tibia     

Inhibitory motoneurons in arthropod motor control: organisation,function, evolution

Miniaturisation of somatic cells in animals is limited, for reasons ranging from the accommodation of organelles to surface-to-volume ratio. Consequently, muscle and nerve cells vary in diameters by about two orders of magnitude, in animals covering 12 orders of magnitude in body mass. Small animals thus have to control their behaviour with few muscle fibres and neurons. Hexapod leg muscles, for instance, may consist of a single to a few 100 fibres, and they are controlled by one to, rarely, 19 motoneurons. A typical mammal has thousands of fibres per muscle supplied by hundreds of motoneurons for comparable behavioural performances. Arthopods—crustaceans, hexapods, spiders, and their kin—are on average much smaller than vertebrates, and they possess inhibitory motoneurons for a motor control strategy that allows a broad performance spectrum despite necessarily small cell numbers. This arthropod motor control strategy is reviewed from functional and evolutionary perspectives and its components are described with a focus on inhibitory motoneurons. Inhibitory motoneurons are particularly interesting for a number of reasons: evolutionary and phylogenetic comparison of functional specialisations, evolutionary and developmental origin and diversification, and muscle fibre recruitment strategies.     

Musculature and innervation of the neck of the desert locust,Schistocerca gregaria (Forskål)

The innervation of each of the muscles involved in mediating head movement in the desert locust Schistocerca gregaria is described in detail. The number of motor neurones to each muscle and the neutral pathway and ganglion of origin of each are deduced from both histological and electrophysiological evidence. Only two of the muscles are, on histological evidence, innervated by as few as four different neurones, while several receive more than ten, and one at least 13. Individual muscles are shown physiologically to receive, in a few cases, as many as six different motor neurones. At least six muscles are innervated by motor neurones originating in more than one ganglion. One group of four muscles consisting in total of less than 100 muscle fibres receives more than 20 different motor neurones from three different ganglia through three or four different nerve roots. In these muscles, many single muscle fibres receive innervation from at least two different ganglia. It is concluded that the segmental nature of an insect muscle can not be deduced solely from a knowledge of the ganglion of origin of the motor innervation to that muscle. The innervation patterns that exist today must reflect past evolutionary development, but changes in the peripheral distribution of motor neurones, or migration of motor neurone cell bodies from one ganglion to another, or the development of additional motor neurones, or several of these factors together, must have formed a part of that development.     

Evolution of the arthropod neuromuscular system. 2. Inhibitory innervation of the walking legs of a scorpion: Vaejovis spinigerus (Wood, 1863), Vaejovidae, Scorpiones, Arachnida

Inhibitory motoneurons which supply the leg musculature are identified and characterized in the scorpion, Vaejovis spinigerus (Wood, 1863) (Vaejovidae, Scorpiones, Arachnida). (1) Successive intracellular muscle fiber recordings from antagonists, and correlation of the monitored inhibitory postsynaptic potentials with spikes in motor nerves, suggest supply of the scorpion leg musculature by common inhibitory motoneurons. (2) Anti-GABA immunohistochemistry is combined with transmission electron microscopy to estimate the number of inhibitory motor axons present in the main leg nerve. The number of immunoreactive axons decreases toward more distal leg segments, from 14 to 18 in the basis to 6-8 in the tibia. No immunoreactive axons are detected beyond the tibia. (3) The distribution of putative inhibitory neurons in the subesophageal ganglion mass is determined by anti-GABA immunohistochemistry, revealing notable similarities to the situation in pterygote insects. This provides a framework for the characterization of the inhibitory motoneurons. (4) Backfills from leg nerves are combined with anti-GABA immunocytochemistry to identify inhibitory motoneurons in the central nervous system. Putative inhibitory motoneurons occur in three clusters per hemi-segment. Two clusters are located near the posterior edge of the neuromere, one lateral, the other more medial, and both contain ca. 8-10 cell bodies. The third cluster consists of two somata located contralaterally, just off the ganglion midline.     

Arrangement of supramandibular and suprahyoid motoneurons in the rat; a fluorescent tracer study

The arrangement of the motoneurons innervating the supramandibular and suprahyoid muscles was studied in Wistar albino rats using two fluorescent tracers: nuclear yellow and true blue. All supramandibular motoneurons were found within the trigeminal motor nucleus; they appeared to be somatotopically arranged. The suprahyoid motoneurons were located in an accessory trigeminal-facial motor complex. No overlap of the motoneuron pools of the supramandibular and suprahyoid muscle group was observed. Only motoneurons ipsilateral to the treated muscles were labeled. It was shown that a one-to-one relationship always exists between motoneuron and muscle.     

Identification of common excitatory motoneurons in Drosophila melanogaster larvae

In insects, four types of motoneurons have long been known, including fast motoneurons, slow motoneurons, common inhibitory motoneurons, and DUM neurons. They innervate the same muscle and control its contraction together. Recent studies in Drosophila have suggested the existence of another type of motoneuron, the common excitatory motoneuron. Here, we found that shakB-GAL4 produced by labels this type of motoneuron in Drosophila larvae. We found that Drosophila larvae have two common excitatory motoneurons in each abdominal segment, RP2 for dorsal muscles and MNSNb/d-Is for ventral muscles. They innervate most of the internal longitudinal or oblique muscles on the dorsal or ventral body wall with type-Is terminals and use glutamate as a transmitter. Electrophysiological recording indicated that stimulation of the RP2 axon evoked excitatory junctional potential in a dorsal muscle.     

Fusimotor innervation in the cat

The motor innervation of cat spindles was examined in hindlimb muscles using a variety of techniques employed in light and electron microscopy. Observations were made on teased, silver preparations of 267 spindles sampled from the peroneal, flexor hallucis longus, and soleus muscles, hereafter referred to as the PER/FHL/SOL series. The γ innervation. Trail endings are almost invariably present, and innervate both bag and chain muscle fibres. Trail fibres accounted for 64.6 to 74.8% of the total fusimotor supply to samples of spindle poles in the PER/FHL/SOL series, the mean number of fibres per pole varying from 2.7 to 5.0 in the different muscles, and the mean number of ramifications (areas of synaptic contact) per fibre being 3.7. By contrast, the p?innervation of a spindle pole generally consists of a single fibre supplying only one plate. In the above samples p(2) fibres accounted for 4.1 to 28.0% of the total fusimotor supply, and the mean number of fibres per pole varied from 0.3 to 1.2 in the different muscles. Ninety per cent of p(2) plates innervate bag fibres. The α innervation. The structure of p?plates as seen in both light and electron microscopy compares very closely with that of extrafusal plates. After nerve section p?plates degenerate at the same time as extrafusal plates, being the first of the three types of fusimotor ending to disappear. The frequency of the p?innervation is similar to that of the p?innervation. In the same samples of PER/FHL/SOL spindle poles as above p? fibres accounted for 6.0 to 28.8% of the total fusimotor supply, the mean number of fibres per pole varying from 0.25 to 2.1 in the different muscles. The majority of p? fibres enter a pole to terminate in one plate only. Seventy-five per cent of the plates innervate bag fibres. The three types of fusimotor ending are thus not selectively distributed to the two types of intrafusal muscle fibre. All three types of fusimotor fibre may branch within the spindle so as to innervate both bag and chain fibres. Bag fibres receive both types of plate ending as well as trail endings. Most chain fibres receive trail endings only; the rest receive either a p?or a p?plate innervation in addition, 25% of the p?and 10% of the p?innervation being distributed to chain fibres. The significance of this nonselective innervation is interpreted as indicating that the type of contraction elicited by stimulating a fusimotor fibre depends upon the type of ending initiating it rather than upon the type of muscle fibre executing it. Reasons are given for concluding that the dynamic response is controlled via the p?and p?plates, and that the static response is controlled by the trail endings. The participation of the α fibres in mammalian fusimotor innervation, previously regarded as a vestigial feature, proved to be widespread in the muscles studied and more prevalent in fast muscles (FHL, peroneus digiti quinti) than slow (soleus). A low frequency of p?innervation is offset by a high frequency of p?(as in peroneus longus), and vice versa (as in FHL). It is unlikely that collaterals from slow α fibres innervating type B muscle fibres are wholly responsible for the high frequency of the p?innervation in FHL, and it is suggested that collaterals may also be derived from fast α fibres innervating type C muscle fibres. The possibility of there being some motor fibres of α conduction velocity and with an exclusively fusimotor distribution is also taken into account.     

A modified walking rhythm employed during righting behavior in the cockroachGromphadorhina portentosa

Summary Electromyograms were recorded from leg muscles of the cockroachGromphadorhina during walking and righting under free-ranging and tethered conditions. Two muscles which are essentially synergistic during walking become antagonistic during righting (Fig. 3, 4). This explains in part the difference in the direction of the leg stroke in the two behaviors (Fig. 2). Other properties of the muscle activity are very similar during the two rhythms: the same motoneurons appear to be active (Fig. 5, 6); cycle frequencies are the same; the burst length of one motoneuron studied varies with burst frequency in a generally similar manner in both behaviors (Fig. 7); inter-leg coordination is the same (Fig. 9); and transganglionic coupling characteristic of walking can occur while a leg on one side is engaged in walking, and its contralateral homologue is engaged in righting (Fig. 10). Although other properties of the leg rhythms are different in walking and righting, these differences appear to result from dissimilarities in sensory feedback. It is concluded that although the two leg rhythms are superficially quite different, the underlying central neuronal rhythms are very similar, and possibly result from activity in the same central oscillatory cell or circuit.We thank Carol Smith for technical assistance. This work was supported by NIH grant #NS09083-05. Computation was done at the New York State Veterinary College Computer Facility which is supported by NIH grant RR 326.     

Complex innervation of three neck muscles by motor and dorsal unpaired median neurons in crickets

Summary In the crickets, Gryllus campestris and Gryllus bimaculatus, the innervation of the dorso-ventral neck muscles M62, M57, and M59 was examined using cobalt staining via peripheral nerves and electrophysiological methods. M62 and M57 are each innervated by two motoneurons in the suboesophageal ganglion. The four motoneurons project into the median nerve to bifurcate into the transverse nerves of both sides. M62 and M57 are the only neck muscles innervated via this route. These bifurcating axon-projections are identical to those of the spiracular motoneurons in the prothoracic ganglion innervating the opener and closer muscle of the first thoracic spiracle in the cricket. The morphology of their branching pattern is described. The neck muscle M57 and the opener muscle of the first thoracic spiracle are additionally innervated by one mesothoracic motoneuron each, with similar morphology. These results suggest, that in crickets, the neck muscles M57 and M62 are homologous to spiracular muscles in the thoracic segments. The two neck muscles M62 and M59 (the posterior neighbour of M57) receive projections from a prothoracic dorsal unpaired median (DUM) neuron that also innervates dorsal-longitudinal neck muscles but not M57. In addition, one or two mesothoracic DUM neurons send axon collaterals intersegmentally to M59. This is the first demonstration of the innervation of neck muscles by DUM neurons.     

A Neuro-Mechanical Model of a Single Leg Joint Highlighting the Basic Physiological Role of Fast and Slow Muscle Fibres of an Insect Muscle System

In legged animals, the muscle system has a dual function: to produce forces and torques necessary to move the limbs in a systematic way, and to maintain the body in a static position. These two functions are performed by the contribution of specialized motor units, i.e. motoneurons driving sets of specialized muscle fibres. With reference to their overall contraction and metabolic properties they are called fast and slow muscle fibres and can be found ubiquitously in skeletal muscles. Both fibre types are active during stepping, but only the slow ones maintain the posture of the body. From these findings, the general hypothesis on a functional segregation between both fibre types and their neuronal control has arisen. Earlier muscle models did not fully take this aspect into account. They either focused on certain aspects of muscular function or were developed to describe specific behaviours only. By contrast, our neuro-mechanical model is more general as it allows functionally to differentiate between static and dynamic aspects of movement control. It does so by including both muscle fibre types and separate motoneuron drives. Our model helps to gain a deeper insight into how the nervous system might combine neuronal control of locomotion and posture. It predicts that (1) positioning the leg at a specific retraction angle in steady state is most likely due to the extent of recruitment of slow muscle fibres and not to the force developed in the individual fibres of the antagonistic muscles; (2) the fast muscle fibres of antagonistic muscles contract alternately during stepping, while co-contraction of the slow muscle fibres takes place during steady state; (3) there are several possible ways of transition between movement and steady state of the leg achieved by varying the time course of recruitment of the fibres in the participating muscles.     

Identified nonspiking interneurons in leg reflexes and during walking in the stick insect

In the stick insect Carausius morosus identified nonspiking interneurons (type E4) were investigated in the mesothoracic ganglion during intraand intersegmental reflexes and during searching and walking.In the standing and in the actively moving animal interneurons of type E4 drive the excitatory extensor tibiae motoneurons, up to four excitatory protractor coxae motoneurons, and the common inhibitor 1 motoneuron (Figs. 1–4).In the standing animal a depolarization of this type of interneuron is induced by tactile stimuli to the tarsi of the ipsilateral front, middle and hind legs (Fig. 5). This response precedes and accompanies the observed activation of the affected middle leg motoneurons. The same is true when compensatory leg placement reflexes are elicited by tactile stimuli given to the tarsi of the legs (Fig. 6).During forward walking the membrane potential of interneurons of type E4 is strongly modulated in the step-cycle (Figs.8–10). The peak depolarization occurs at the transition from stance to swing. The oscillations in membrane potential are correlated with the activity profile of the extensor motoneurons and the common inhibitor 1 (Fig. 9).The described properties of interneuron type E4 in the actively behaving animal show that these interneurons are involved in the organization and coordination of the motor output of the proximal leg joints during reflex movements and during walking.Abbreviations CLP reflex, compensatory leg placement reflex - CI1 common inhibitor I motoneuron - fCO femoral chordotonal organ - FETi fast extensor tibiae motoneuron - FT femur-tibia - SETi slow extensor tibiae motoneuron     

The role of delayed excitation in the co-ordination of some metathoracic flight motoneurons of a locust

Summary Intracellular recordings have been made from the somata of two metathoracic flight motoneurons, one innervating an elevator muscle of the hindwing, the tergosternal muscle 113 and the other a depressor, the first basalar muscle 127. The locust,Ghortoicetes terminifera was mounted ventral side uppermost with the thorax restrained and opened for access to the thoracic ganglia. Patterns of electrical activity recorded from the thoracic muscles were similar to those shown by a locust during flight when tethered in a more normal posture. In flight the left and right 113 motoneurons each receive a single impulse together at every stroke of the wing, with the 127 muscles active in approximate antiphase. A spike in a 113 motoneuron causes a delayed wave of excitation simultaneously upon itself and its contralateral partner (Fig. 2). The epsp's which form these waves summate and may cause a spike which follows the original one with a delay equal to the wingbeat period. The delayed excitation of the contralateral motoneuron is of larger amplitude than the ipsilateral one so that spikes in either motoneuron must activate separate but symmetrical pathways. A single spike may cause multiple waves in either motoneuron, each separated by intervals equal to the wingbeat period (Fig. 3). In the pathway must be neurons capable of reverberation.A spike in a 113 motoneuron causes a delayed excitation of the ipsilateral 127 motoneuron so that its membrane potential is lowered antiphasically to that of 113 (Fig. 17). A spike in a 127 motoneuron has no effect on the 113 motoneurons. In flight these pathways causing delayed excitation may co-ordinate the motoneurons.The left and right 113 motoneurons receive common synaptic inputs from at least two sources (Fig. 8). These occur as bursts of epsp's at intervals approximately equal to or multiples of the wingbeat period and in the absence of flight. Epsp's of sufficient amplitude cause a spike in the motoneuron which is in the correct phase in the flight pattern relative to any other active motoneurons (Fig. 9). During sustained flight epsp's contribute to the wave of depolarization that the motoneuron undergoes at each wingbeat (Fig. 11). In the absence of the epsp's the motoneuron does not oscillate on its own. At the end of flight bursts of epsp's may continue at the flight frequency long after all activity in the muscles has ceased.Beit Memorial Research Fellow.     

Calcitonin gene-related peptide expression at endplates of different fibre types in muscles in rat hind limbs

Calcitonin gene-related peptide (CGRP) occurs only in some motoneurons. In this study, the presence of CGRP in motor endplates in relation to muscle fibre types was examined in slow (soleus muscle) and fast [tibialis anterior (TA) and extensor digitorum longus (EDL)] leg muscles of the rat. CGRP was detected by use of immunohistochemical methods, and staining for the mitochondrial-bound enzyme NADH-TR was used for demonstration of fibre types. The fibres showing low NADH-TR activity were interpreted as representing IIB fibres. All such fibres located in the superficial portion of TA were innervated by endplates displaying CGRP-like immunoreactivity (LI), whereas in the deep portion of TA some of these fibres lacked CGRP-LI at their endplates. Thirty per cent of the IIB fibres in EDL showed CGRP-LI at the endplates. All fibres in TA and EDL displaying high NADH-TR activity and interpreted as type-IIA fibres, lacked CGRP-LI in their motor innervation. One third of the fibres with intermediate NADH-TR activity in TA exhibited CGRP-LI at their endplates, whereas in EDL only few such fibres displayed CGRP-LI in the endplate formation. These fibres are likely to belong to type-IIX or type-I motor units. CGRP-LI was very rarely detected at the endplates in the soleus muscle. These observations show that distinct differences exist between the slow muscle, soleus, and the fast muscles, TA and EDL, but that there are also differences between the different types of fibres in TA and EDL with respect to presence of CGRP-LI at the endplates. As CGRP-LI was frequently detected at endplates of IIB fibres, it is likely that CGRP has a particular role related to the differentiation and maintenance of these fibres.     

The role of the frontal ganglion in foregut movements of the moth,Manduca sexta

Two types of rhythmic foregut movements are described in fifth instar larvae of the moth, Manduca sexta. These consist of posteriorly-directed waves of peristalsis which move food toward the midgut, and synchronous constrictions of the esophageal region, which appear to retain food within the crop. We describe these movements and the muscles of the foregut that generate them.The firing patterns of a subset of these muscles, including a constrictor and dilator pair from both the esophageal and buccal regions of the foregut, are described for both types of foregut movement.The motor patterns for the foregut muscles require innervation by the frontal ganglion (FG), which lies anterior to the brain and contains about 35 neurons. Eliminating the ventral nerve cord, leaving the brain and FG intact, did not affect the muscle firing patterns in most cases. Eliminating both the brain and the ventral nerve cord, leaving only the FG to innervate the foregut, generally resulted in an increased period for both gut movements and muscle bursts. This manipulation also produced increases in burst durations for most muscles, and had variable effects on the phasing of muscle activity. Despite these changes, the foregut muscles still maintained a rhythmic firing pattern when innervated by the FG alone.Two nerves exit the FG to innervate the foregut musculature: the anteriorly-projecting frontal nerve, and the posteriorly-directed recurrent nerve. Cutting the frontal nerve immediately and irreversibly stopped all muscle activity in the buccal region, while cutting the recurrent nerve immediately stopped all muscle activity in the pharyngeal and esophageal regions. Recordings from the cut nerves leaving the FG showed that the ganglion was spontaneously active, with rhythmic activity continuing within the nerves. These observations indicate that all of the foregut muscle motoneurons are located within the FG, and the FG in isolation produces a rhythmic firing pattern in the motoneurons. We have identified several motoneurons within the FG, by cobalt backfills and/or simultaneous intracellular recordings and fills from putative motoneurons and their muscles.Abbreviations BC Buccal Constrictor - BC1 buccal constrictor motoneuron 1 - BC2 buccal constrictor motoneuron 2 - BD Buccal Dilator - BD1 buccal dilator motoneuron 1 - EC Esophageal Dilator - EC1 esophageal dilator motoneuron 1 - EC2 esophageal dilator motoneuron 2 - EC3 esophageal dilator motoneuron 3 - ejp excitatory junction potential - FG frontal ganglion - psp postsynaptic potential     

Nerve-muscle interactions regulate motor terminal growth and myoblast distribution during muscle development

Interactions between motoneurons and muscles influence many aspects of neuromuscular development in all animals. These interactions can be readily investigated during adult muscle development in holometabolous insects. In this study, the development of the dorsolongitudinal flight muscle (DLM) and its innervation is investigated in the moth, Manduca sexta, to address the specificity of neuromuscular interactions. The DLM develops from an anlage containing both regressed larval template fibers and imaginal myoblasts. In the adult, each fiber bundle (DLM1-5) is innervated by a single motoneuron (MN1-MN5), with the dorsal-most fiber bundle (DLM5) innervated by a mesothoracic motoneuron (MN5). The DLM failed to develop following complete denervation because myoblasts failed to accumulate in the DLM anlage. After lesioning MN1-4, MN5 retained its specificity for the DLM5 region of the anlage and failed to rescue DLM1-4. Thus specific innervation of the DLM fiber bundles does not depend on interactions among motoneurons. Myoblast accumulation, but not myonuclear proliferation, increased around the MN5 terminals, producing a hypertrophied adult DLM5. Therefore, motoneurons compete for uncommitted myoblasts. MN5 terminals subsequently grew more rapidly over the hypertrophied DLM5 anlage, indicating that motoneuron terminal expansion is regulated by the size of the target muscle anlage.     

A model of pattern generation of cockroach walking reconsidered

Cockroaches that have been decapitated or that have cut thoracic connectives can show rhythmic bursting in motoneurons to intrinsic leg muscles. These preparations have been studied as models for walking and to evaluate the functions of leg proprioceptors. The present study demonstrates that headless cockroaches walk extremely poorly and slowly with considerable discoordination of motoneuronal activity, these preparations show rhythmic motoneuron bursting that is similar to righting responses (attempts to turn upright) of intact animals when placed on their backs, and bursting is inhibited when a headless animal is turned or turns itself upright. Thus, rhythmic motoneuron activity of these preparations is most probably attempted righting rather than walking. It is concluded that the headless cockroach is useful for understanding the motor mechanisms underlying righting and walking but is not of value in assessing the functions of proprioceptive feedback.