Intersegmental Muscles Research Articles

Hormonal control of muscle atrophy and degeneration in the moth Antheraea polyphemus.

The intersegmental muscles of the giant silkmoth Antheraea polyphemus (Cramer) can undergo two forms of degenerative changes: a wasting atrophy that lasts about 6 days or rapid dissolution that is completed within 30 h. Muscle atrophy is induced by a dramatic decline in the endogenous titres of the steroid moulting hormone 20-hydroxyecdysone. 20-Hydroxyecdysone appears to act as a trophic factor for the muscles as infusion or injection of this steroid blocks further atrophy of the muscle. The normal decline of 20-hydroxyecdysone also allows the muscles to become competent to respond to the peptide eclosion hormone. Eclosion hormone is then released and acts directly on these muscles to induce rapid cell death which is morphologically and physiologically distinct from steroid-regulated atrophy.

Experimental and ultrastructural study of the control of ovulation and parturition in the tsetse fly Glossina fuscipes (Diptera)

Injections of haemolymph, organ extracts and various other substances, as well as in vitro experiments, show that ovary and oviduct extracts on the one hand, and dibutyryl cyclic AMP on the other, enhance ovulation, whereas parturition is stimulated by extracts of the brain, thoracic ganglionic mass, nerve XVII, different parts of the genital apparatus and perhaps proctolin. On the contrary, the proximal neurohaemal organs (corpus cardiacum and perisympathetic organs) appear to contain a substance inhibiting parturition. Lastly, normal intact flies cannot respond to extracts facilitating parturition in decapitated flies. Neuromuscular junctions probably containing peptides and neurotransmitters are described in the muscles of the ovaries, oviducts and the vaginal aperture. Other junctions containing neurotransmitters only are present in uterine and intersegmental muscles. The neurohaemal areas of nerve XVII contain 3 types of peptidergic terminals. From our overall results it is concluded that ovulation is regulated by neurosecretory products released at neuromuscular junctions in the ovaries and oviducts. Parturition control is more complicated. A first neurohormone (parturition-stimulating hormone) appears to be produced in the nerve centres and released in neurohaemal areas located on nerve XVII in the vicinity of the uterus; it enhances the contraction of this organ. A second neurohormone, the parturition-inhibiting hormone may be released in the corpora cardiaca and the median perisympathetic organ. A cephalic nervous factor might exert inhibitory action.

Abdominal stretch reception in Dipetalogaster maximus (Hemiptera: Reduviidae)

Each half abdominal segment in 5th-instar larvae of the giant bloodsucking reduviid, Dipetalogaster maximus, contains 3 stretch receptor neurones, one associated with the tergosternal muscles, one with the ventral intersegmental muscles and one with the dorsal intersegmental muscles. Each of the three receptors respond phasically to the onset of stretch in its respective muscle group, but none show persistent activity upon prolonged stretch. By contrast, stretch of the main abdominal nerves (which run between the thoracic ganglion and the ventral intersegmental muscles of each abdominal segment) is accompanied by a prolonged and sustained pattern of discharge by an as yet unidentified neurone, the rate of discharge being proportional to the degree of stretch. In life, the abdominal nerves become stretched to about 145% of their resting length when the larva takes a bloodmeal. Thus it appears that in Dipetalogaster stretch of the abdominal nerves themselves is the only mechanism for stretch reception after a blood meal.

Neural organization of peptide-activated ecdysis behaviors during the metamorphosis ofManduca sexta

1. At the culmination of each molt, insects shed their old cuticle by a behavior called ecdysis, which generally involves rhythmic peristaltic body movements. We have compared the abdominal peristalsis behaviors produced by the tobacco hornworm,Manduca sexta, during larval-larval molts (‘larval ecdysis’) and at the larval-pupal molt (‘pupal ecdysis’), to see whether the morphological changes during metamorphosis were accompanied by alterations in the motor patterns. 2. At larval ecdysis, caterpillars shed their old cuticle by means of rhythmic peristaltic contractions which run anteriorly along the body, accompanied by coordinated retractions and extensions of the abdominal prolegs (Fig. 2). During the larval-pupal transformation the prolegs are lost, so that at pupal ecdysis the cuticle is shed by peristalsis alone (Fig. 1). 3. Cinematographic analysis of ecdysing larvae and pupae revealed that the peristaltic movements resulted from each abdominal segment being sequentially pulled forward and partially telescoped into the next anterior segment, due to the contraction of intersegmental muscles (ISMs) in the more anterior segment. Despite the marked changes in body morphology which occurred during the larval-pupal transformation, the pattern of the peristaltic contractions produced at larval and pupal ecdysis was the same (Table 1). 4. The neural basis of these behaviors was investigated in semi-intact, deafferented preparations which produced ecdysis motor patterns in response to a peptide hormone, eclosion hormone (EH), which is the normal blood-borne trigger for ecdysis (Fig. 3). The motoneurons which generated the peristaltic motor patterns in larvae and pupae were identified by recording extracellularly from various nerve branches (Figs. 4, 5, 6, 8) and intracellularly from neuronal somata (Figs. 7, 9). 5. The pattern of the motoneuron bursts was the same during both larval and pupal ecdysis (Table 2). The only apparent difference at the two stages was that pupae exhibited a lower level of tonic background motor activity than did larvae (e.g., Figs. 4, 8). 6. Thus, both behavioral and electrophysiological data indicated that the pattern-generating circuitry underlying abdominal peristalsis remained stable during the larval-pupal transformation. In contrast, the loss of the prolegs at pupation and their consequent absence from pupal ecdysis behavior did suggest a possible stage-specific change in the neural circuitry; this possibility is investigated in an accompanying paper (Weeks and Truman 1984).

Transcripts of the six Drosophila actin genes accumulate in a stage- and tissue-specific manner

We have surveyed expression of the six Drosophila actin genes during ontogeny. Unique portions of cloned actin genes were used to monitor levels of respective mRNAs in developmentally staged whole organisms and dissected body parts. We find that each gene is transcribed to form functional mRNA, which accumulates with a distinct pattern. Two of the genes, act5C and act42A, are expressed in un-differentiated cells and probably encode cytoplasmic actins. Act57A and act87E are expressed predominantly in larval, pupal, and adult intersegmental muscles; act88F in muscles of the adult thorax; and act79B in the thorax and leg muscles. These composite data define three main patterns of actin gene expression which are correlated with changing Drosophila morphology, particularly muscle differentiation and reorganization.

Programmed cell death, degradation of myosin during the involution of the intersegmental muscles in Manduca sexta

1. 1. Involuting intersegmental muscle of Manduca sexta contained a 67–70 K dalton fragment of myosin. 2. 2. The fragment was identified by precipitation with monospecific anti-MHC (myosin heavy chain) serum and by the fact that when endogenously-labelled myosin was degraded the label appeared in the fragment. 3. 3. The molecular weight of the remaining myosin was unchanged, but some myosin in degenerating fibers had a pI of 5.8, slightly more acid than the normal 5.9. 4. 4. Leupeptin-sensitive proteolytic activity in extracts did not rapidly degrade myofilament proteins. 5. 5. These results suggest that proteolysis is initiated by a small alteration of the MHC, followed by endopeptidic cuts. Leupeptin-sensitive enzymes are probably involved only in the later stages of proteolysis.

Spontaneous degradation of insect myosin during metamorphic cell death. Conditions for proteolysis

Department of Biology, Molloy College, Rockville Centre, NY 11570, U.S.A. The intersegmental muscles of the Sphingiid moth, Manduca sexta, degenerate completely within 48 hr after the emergence of the adult. Although lysosomal proteases are present in the tissue, the mechanisms for initiation and control of lysis are not known. Conditions for in vitro proteolysis were therefore investigated. A 70,000 dalton fragment of myosin, seen in spontaneously-degenerating muscle, was generated occasionally in vitro, at pH 6.5. M. sexta intersegmental muscle myosin, with an initial subunit size of 220,000 daltons, was shown to degrade spontaneously in vitro to 170,000 daltons, at pH 6.5 and to 127,000 daltons, at pH 8.5. Exogenous addition of Ca 2+ or ATP did not affect these results. Cathepsins B and D were present in high quantities during times of active lysis and were likewise unaffected by Ca 2+. Native or iodinated (Bolton-Hunter) insect myosin was cleaved to 130,000 daltons by rat liver cathepsin B and to 145,000 daltons by rat liver cathepsin D. Our interpretation is that a protease or proteases acting at or near neutral pH initiates the degradation of myosin, and that in vitro and potentially in vivo, lysosomal cathepsins terminate the digestion.

Superextension and supercontraction in locust ovipositor muscles

A ten times elongation of certain abdominal intersegmental muscles occurs in female locusts during digging prior to oviposition. During and after oviposition the muscles contract, shortening by up to 90% or more, restoring the resting positions of the abdominal segments. Discontinuous Z-discs permit supercontraction at the resting length and then fragment into Z-bodies when the muscle is stretched, so enabling it to superextend without loss of the contractile property. In this superextended state the fibres resemble smooth muscles. After oviposition, the muscle fibres contract but the sarcomeres are not restored completely, some of the Z-bodies being unevenly distributed in the recontracted fibres. Locust ovipositor muscle has the most extreme example of Z-disc disagregation known from the insects and is the insect muscle which approaches most closely the smooth muscle condition. Two types of motor nerve innervate this muscle, one is ordinary and the other, containing granules, resembles an octopaminergic fibre possibly involved in regulating a catch mechanism in the muscle. The physiological requirements for egg-laying with an extensible ovipositor, which is also part of the normally functioning abdomen, are well met by the ultrastructural specializations of locust ovipositor muscles.

Peptide and steroid regulation of muscle degeneration in an insect.

Two types of cell death occur in the intersegmental muscles of the giant silkmoth Antheraea polyphemus. The first results from a slow atrophy of the fibers, and the second is a rapid, programmed dissolution of the muscle. Both types appear to be mediated by endocrine factors. The slow atrophy is brought about by the decline in the steroid molting hormone 20-hydroxyecdysone and can be prevented with exogenous steroid. The rapid degeneration is triggered by the peptide eclosion hormone, but the sensitivity of the muscle to the peptide depends on the history of exposure of the muscle to 20-hydroxyecdysone.

Activation by anoxia of latent lactic acid dehydrogenase isozymes in insect intersegmental muscles ( Manduca sexta, sphingidae)

1. An isozyme of lactic dehydrogenase is activated within 30 min in muscles of Manduca sexta larvae when the insects are exposed to anoxia. 2. The activated enzyme is lost when the insects are returned to air; returning them to 100% oxygen causes more rapid inactivation. 3. The enzyme is not activated or inactivated in vitro, nor does cycloheximide block activation or inactivation. 4. Prolonged exercise also activates the enzyme. 5. Apparently the intersegmental muscles are hypoxic when working. 6. The appearance of the enzyme shortly before the muscles involute suggests that the muscle is hypoxic at that time.

Transegmental electrical coupling between adjacent intersegemental muscles in the tobacco hawkmoth ( Manduca sexta)

The lateral intersegmental muscles of pharate adult tobacco hawkmoths ( Manduca sexta), exhibited electrical coupling across the segmental boundary. The degree of electrical coupling was constant throughout adult development. These muscle fibres did not appear to be dye coupled in that neither cobalt ions nor the flourescent dye Lucifer Yellow CH passed between cells. Electrical coupling was unaffected by cellular acidification with CO 2. Data are presented which suggest that this electrical coupling may be through the extracellular space rather than some membrane specialization. It is further speculated that many invertebrates may show this form of electrical coupling due to the metameric architecture of certain skeletal muscles.

Changes in fine structure of the ventral intersegmental abdominal muscles in the adult of Rhodnius prolixus

In Rhodnius prolixus, after the imaginal molt, the intersegmental muscles completely lose their contractile material, and are transformed into thin strands containing nuclei. It is possible that these muscular strands are finally pinched off as mononucleated myoblasts. These residual muscles apparently maintain a normal innervation—which persists to the end of the imago's life. Moreover, they appear to show some aspects of synthetic activity after the adult has been fed: in this case, there is a growth of the ‘rough endoplasmic reticulum’ and elaboration of specialized fibrous inclusions.

Metamorphic degeneration of intersegmental muscles in cabbage white butterfly, Pieris brassicae L. ( Lepidoptera: Pieridae)

An attempt has been made in this paper to demonstrate how 2 sets of homologous muscles in the same species differ in their developmental disintegration. The degeneration of persisting intersegmental muscles in the cabbage white butterfly, Pieris brassicae was found to be significantly different from that occurring in certain intersegmental muscles during larval-pupal metamorphosis. The degeneration, beginning deep within the muscles fibre, was characterized by disintegration of mitochondria, the appearance of lysosome-like structures, autophagosomes, membranous bodies and vacuoles which appeared to enclose lysosome-like structures, and complete degeneration of myofibrillar remnants. The T-tubules, nerve endings and, occasionally, the sarcoplasmic reticulum remained unaffected even during the late stages of muscle degeneration. Phagocytes did not appear to play a role during the initial stages of muscle degeneration. The initial degradation of myofilaments appeared to take place outside of lysosomes and presumably in an environment rich in Ca 2+ since the mitochondria which sequester and store this ion are the first to be affected. However, the mechanisms controlling the catabolism of muscle cells appear to be complicated and the degradative events are varied even within the same species.

Control of extracardiac haemolymph pressure pulses in Tenebrio molitor

The pupae of Tenebrio exhibit periodic pulsations in the haemolymph pressure which are independent of the heartbeat. Tensometric records of the extracardiac pulses show certain specific modifications caused by changes in either the internal or external environment. Chronological changes in the pulse pattern were associated with adult morphogenesis and ecdysis. The abdominal pump controlling extracardiac pressure pulsations is independent of the brain or of any other cephalic part of the nervous system. The nerve impulses controlling the pump arise only in the mesothoracic ganglion. They are carried by the connectives to certain abdominal ganglia from which they are further transmitted to the contracting intersegmental abdominal muscles. The extracardiac pulses in haemolymph pressure aid in the maintenance of water balance and respiration and assist with the circulation of haemolymph through the appendages.

Fine structure of degenerating abdominal motor neurons after eclosion in the sphingid moth, Manduca sexta.

Ultrastructural aspects of the natural degeneration of a group of six motor neurons in the fourth abdominal ganglion of Manduca sexta are described. These motor neurons innervate intersegmental muscles that degenerate and disappear immediately after adult eclosion. The first detectable changes in the cell bodies appear 12h after eclosion and include disruption of the endoplasmic reticulum and an increase in the size and number of lamellar bodies. At 32h the nuclear membranes rupture, and the membranous and granular cytoorganelles segregate in different parts of the cell. At that stage the surrounding glial cells participate in the digestion of material from the degenerating neurons. From 72h onward the remaining neuronal structures become disrupted, and are finally transformed into a single, large lamellar body (residual body) within the glial profile. The degeneration pattern differs significantly from that of embryonic vertebrate neurons.

Nervous system of 6th stage western spruce budworm larvae, Choristoneura occidentalis freeman (lepidoptera: Tortricidae)

The central and peripheral nervous systems of the 6th-stage larvae of the female western spruce budworm, Choristoneura occidentalis Freeman, were studied. Two pairs of nerve branches were found that appear to be unique in these larvae. One pair originates from the corpora cardiaca and innervates a pair of dorsoventral muscles on both sides of the pharynx. The other pair arises from the dorsolateral surface of the subesophageal ganglion and innervates the dorsal longitudinal intersegmental muscles of the prothorax. Branches of lateral nerve 1 of the mesothorax were found to innervate structures on the cuticle, specifically the L setal complex of that segment, and what appear to be stretch receptors. We were particularly interested in the innervation of these structures because of their possible involvement in increasing the effectiveness of insecticide poisoning.

Ultrastructural study of the normal degeneration of the intersegmental muscles of Anthereae polyphemus and Manduca sexta (Insecta, Lepidoptera) with particular reference of cellular autophagy.

AbstractIn studying ultrastructural changes in metamorphosis‐related degeneration of intersegmental muscles in Antheraea polyphemus, particular attention was directed to the mechanisms and timing of degradation of organelles and myofilaments. At emergence, the muscles are typical slowly contracting insect muscles, with a few dense body lysosomes and occasional autophagic vacuoles containing mitochondria. During the early phases of degradation the number of autophagic vacuoles, dense bodies, and lamellar bodies increases rapidly, along with an expansion of the Golgi system and the T system. Free glycogen particles and glycogenosomes are demonstrated by the PATAg test.Between 7 and 20 hours after ecdysis the T system continues to expand, the fibers subdivide, and the contractile system is degraded. Myofibrils fragment; myofilaments are not enclosed in isolating membranes at the time of their dissolution. The destruction of individual filaments occurs rapidly, with few intermediate stages being seen, while thick filaments tend to disappear earlier than thin filaments and Z‐line material. The process is generalized and not confined to specific regions of the fiber. Autophagy destroys cell organelles in apparent synchrony with the first signs of nuclear pycnosis.By 20 to 30 hours after emergence, the fibers are reduced to lamellae of polynucleate sarcoplasm containing no organized contractile material. The sarcoplasm is filled with autophagic vacuoles containing mitochondria, dense lamellar or residual bodies, and ribosome‐rich sarcoplasm. The number of mitochondria is drastically reduced at this time.In the final phases of involution (40–49 hours after emergence) shedding of the residual sarcoplasm precedes the expulsion of the pycnotic nuclei into the hemocoele.These results indicate that autophagy is responsible for the selective destruction of mitochondria, glycogen particles, ribosomes, and other organized sarcoplasmic structures. The one exception is the dissolution of the myofilaments, a process which remains undefined but which appears to be independent of lysosomal activity.

Loss of enzymes in dying cells

During the programmed cell death of intersegmental muscles in Manduca sexta, the activities of several enzymes begin to decrease at different times. The rate of loss of these activities also varies among organelles and is dependent on other factors. Myofilament proteins begin to disappear as early as 4 days before the emergence of the adult. An enzyme digesting ATP at acid pH increases 3-fold in total activity, and more than 10-fold in relative activity over the same period.

The imaginal ecdysis of the cricket (Teleogryllus oceanicus)

1. The activities of individual motor neurons have been recorded by electromyography from the muscles of unrestrained, successfully ecdysing crickets. 2. As the behavior progresses, each muscle becomes involved in stereotyped patterns of contractions corresponding to a sequence ofmotor programs (Carlson, 1977). For example, muscle 71d participates in 3 programs: (1) Pushups (A1, Fig. 3), (2) Proximal Leg-segment Extrication (B7, Fig. 3), and (3) Distal Leg-segment Extrication (B11, Fig. 3). These motor programs are recruited in tandem, and involve 3 different modes of coordination (Figs. 5A, 7C, 8-bout 55). 3. In this study, 3 motor programs were selected for intensive analysis: (1) Pushups — bilaterally symmetric contractions of front leg muscles; (2) Abdominal Peristalsis (B1, Fig. 3) — longitudinally sequential contractions of abdominal intersegmental muscles; and (3) Proximal Legsegment Extrication — bilaterally alternating contractions of the leg muscles. 4. The entire 4 h period of ecdysis can be recorded bilaterally from right and left muscles 71d, and the motor output underlying all 3 motor programs in which they participate is interrupted by regular interbout intervals (Figs. 4A, 7A, 8, 9). 5. Abdominal peristaltic waves (Fig. 6A, E) occur between bouts of rhythmical contractions by thoracic motor programs (Fig. 9C2), and thus occur at the bout frequency of other programs. 6. During Leg Extrication, the strengths of successive contractions by muscles 71d vary in register with each bout cycle. The strongest contractions occur near the centers of bouts, and are produced by longer bursts of higher frequency impulses (Fig. 7C). Additional motor neurons may be recruited during strong contractions, subject to the “size principle” (see Henneman, 1965). 7. While motor neuron activation varies sinusoidally within each bout cycle, the period of successive burst changes only vary gradually (Fig. 7B, C, 8). This fact implies that the bout generating oscillator does not influence the contraction generating oscillator as it modulates motor neuron activity. The motor neurons must therefore be independent of the oscillator which drives the alternating contractions that extricate the legs. 8. An hypothesis is presented in which “non-spiking interneurons”, are the major components of central oscillators underlying rhythmical contractions, and a series of these, located in each of the segmental ganglia, generate bouts of activity. 9. During a major peak in the intensity of the behavior, which occurs during the Ecdysial Phase, concurrent peaks in bout, burst, and intraburst impulse frequencies of the neurons involved in Proximal Leg-segment Extrication occur (Fig. 10). As interbout intervals shrink, and the burst frequency increases, additional bursts are recruited during each bout, and a second motor neuron is recruited (Fig. 8). 10. Since sensory feedback from areas of newly exposed cuticle are known to accelerate the bout oscillator (Carlson, 1977), it is hypothesized that acceleration of the burst frequency and concurrent increases in average firing rates for motor neurons, which accompany the major intensity peak of the Ecdysial Phase result from sensory feedback. 11. Sensory feedback provides immediate control of the strength of contractions by individual muscles during Pushups (Figs. 5C, 9B1, 9C1), and prolongs motor programs (compare Fig. 9A2 with 9B2, 9C2), without disrupting coordination. 12. It is concluded that a multilayered system of central control which includes more than 48 motor programs, a temporal bout structure, and 4 functionally distinct behavioral phases, cooperates with sensory feedback mechanisms to permit the successful completion of the nearly 4 h of stereotyped behavior which results in the ecdysis of the cricket.

Correlated structural and contractile properties in specialized fibers of a woodlouse Armadillidium vulgare (Latr.)

AbstractIn order to define the ultrastructural differences between slow‐contracting (tonic) muscles with differing abilities to develop tension, observaticns were made on Armadillidium vulgare, comparing muscle structure and function. The latero‐ventral muscles, by means of which the animal holds itself rolled up in a tight ball, were compared with the dorsal intersegmental muscles. which pull it back to a normal stance. The morphological differences found are easily interpreted in the light of the different functions of the two types of muscle. Where the muscles are more powerful, and have to hold considerable tension, the contractile system is stronger (myosin filaments are 7 μm long and 200 Å thick; the ratio of thin to thick filaments is 6 or 7: 1; there is a thick filament density of 610 filaments per μm2). In the dorsal intersegmental muscles, which have less resistance, the system is simpler: myosin filaments are 4 μm long and 150 Å thick; the ratio of thin to thick filaments is 4: 1; and the thick filament density is lower — 510 filaments per μm2.