Ultrastructure of the muscles of the dorsal diaphragm in Locusta migratoria

Summary The alary muscles of Locusta migratoria adults make up the major tissue of the dorsal diaphragm which separates pericardial and perivisceral sinuses in the abdomen. The alary muscles are striated with a sarcomere at rest measuring about 9 m. The Z-line has a staggered-beaded arrangement with A-bands and I-bands readily discernable. Thick myofilaments are surrounded by 10 or more thin filaments. The sarcoplasm has few mitochondria near the area of the Z-line, dyads are present and sarcoplasmic reticulum is poorly developed. Axons which innervate the alary muscle are either contained within invaginated folds of the sarcolemma of the muscle cells or the muscle cells send finger-like projections to envelop the axons. The synaptic terminals contain synaptic vesicles between 40 and 45 nm in diameter and a few electron-dense granules near or less than 170 nm in diameter. Away from synaptic terminals the axon profiles show few or no granules. The axons are accompanied everywhere by well-developed glial cells. This then is not typical neurosecretomotor innervation, however, the presence of electron-dense granules suggests the possibility of peptidergic neurotransmission.     

Fine structure of the alary muscles of the American cockroach

The alary muscles of the cockroach, Periplaneta americana, are striated with an A-band of 3·0 to 3·5 μm long. Each muscle fibre was 10 to 12 μm in diameter and Z-lines appeared as small discrete units staggered throughout the sarcoplasm. Mitochondria were conspicuously located near the Z-line areas and were absent from the middle portion of the sarcomere. A transverse membrane system was present which formed dyad structures with a relatively sparse sarcoplasmic reticulum. Cockroach alary muscles were innervated by axons containing electron-dense granules of near 100 nm in diameter. These are thought to be typical of ‘neurosecretory’ axons based on their ultrastructural appearance.     

Functional properties of locust locomotor muscles

The ultrastructure of the muscle fibers and the electrical constants and responses of the membrane to microapplication of L-glutamate and acetylcholine were investigated in the longitudinal flight muscle and the flexor tibiae ofLocusta migratoria migratorioides. The twitch flight muscle differs from the slower leg muscle in the smaller size of its sarcomeres and the lower values of the space attenuation factor of the electrotonic potential, time constant, and resistance of the membrane. Microapplication of sodium L-glutamate at strictly definite points of the fibers of both muscles evoked depolarization responses of the membrane. In experiments on normal and denervated muscle, during microapplication of acetylcholine, changes in the level of the membrane potential were never observed. It is concluded that L-glutamic acid is the excitatory mediator of the twitch and slow muscle systems of insects.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 532–538, September–October, 1977.     

Innervation of heart and alary muscles in Sphinx ligustri L. (Lepidoptera)

Summary The origin and orientation of the heart nerves in Sphinx ligustri and Ephestia kuehniella were investigated by scanning electron microscopy using a special technique which involved pinning the dissected specimens on a stabilizing metal pad. The heart and alary muscles in Sphinx particularly their caudal extremity were also examined by transmission electron microscopy. The alary muscles form an incomplete sheath around the heart with a mainly longitudinal fibre orientation, e.i. antagonistically to the fibres of the heart itself. The heart and alary muscles are multiterminally innervated by branches of the transverse segmental nerves. All branches contain a single electron lucent axon; the thickest branches also possess several neurosecretory axons. Swellings of the segmental nerves may indicate the position of nerve cell bodies. There are no lateral heart nerves. Only one type of neuromuscular junction is abundant in the alary muscles but less frequently found in the heart. The terminals originate from the central axon only. They are capped by glial cells, which interdigitate with the muscle cells. They penetrate into the T-system toward the Z-discs and form a complex intercellular space system. Exocytosis of dense-cored vesicles into this perisynaptic reticulum seems likely. Sites of neurohaemal release are distributed along the nerve branches and special nerve endings occur at the level of the ostia. The possible nervous influence upon heart activity is discussed.The transmission electron microscopic part of this investigation was supported by a research scholarship from the Deutsche Forschungsgemeinschaft     

Mechanical properties of locust extensor tibiae muscles

• 1.1. The prothoracic and mesothoracic extensor tibiae muscles of the locust respond to activity in the “slow” extensor tibiae motoneuron (SETi) with very slow contractions and a low fusion frequency, while their phasic contractions are more rapid than those of the metathoracic extensor tibiae muscle.
• 2.2. SETi activity can induce a memory or “catch” effect in which a high tension is maintained by a lower frequency than is needed to develop it. “Catch” tension is reduced by phasic contractions of the muscle or by activity in the inhibitory axon.
• 3.3. A bundle of tonic fibres isolated from the metathoracic extensor tibiae muscle exhibits co-ordinated rhythmic contractions similar to those recorded from intact muscles.
• 4.4. Depolarizations of the tonic fibres coincide with the contractions and are sometimes accompanied by bursts of EPSPs and IPSPs.
• 5.5. The tonic fibres are electrically-coupled.

     

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.     

Interaction of lipophorin with the plasma membrane of locust flight muscles

Binding of high-density lipophorin (HDLp) to a plasma membrane preparation of locust flight muscle tissue was studied using a radiolabelled ligand binding assay and ligand blotting techniques. Analysis at 33 degrees C of the concentration-dependent total binding of tritium-labelled HDLp ([3H]HDLp) to the membrane preparation revealed the presence of a single specific binding site with an equilibrium dissociation constant of Kd = 9 (+/- 2) X 10(-7) M and a maximal binding capacity of 84 (+/- 10) ng X (micrograms protein)-1. Unlabelled HDLp as well as unlabelled low-density lipophorin (LDLp) competed with [3H]HDLp for binding to the identified binding site. In addition, ligand blotting demonstrated that both HDLp and LDLp bind specifically to a 30-kDa protein in the plasma membrane preparation, suggesting the involvement of this protein in the binding of lipophorins to the isolated membranes. A possible relationship between the identified binding of lipophorins and the observed co-purification of lipophorin lipase activity with the plasma membranes is discussed.     

The dorsal, unpaired, median neurons of the locust metathoracic ganglion

Neurons having large cell bodies in the anterior dorsal median cluster in the metathoracic ganglion of the locust Schistocerca gregaria and the grasshopper Romalea microptera were studied by direct dye injection and reverse filling combined with elyctrical stimulation and recording. Eight, possibly nine, are of the unpaired type, with a T branch leading into left and right axons that leave the ganglion to terminate in muscles. Another six are probably paired, and may be interneurons. Five of the 8 or 9 unpaired neurons have one axonal branch in both N4 and N5, on both sides: the others have but a single branch. One of the nine, DUMETi, has left and right axons exclusively innervating the jumping muscles, and another, DUMDL, has left and right axons exclusively innervating the dorsal longitudinal flight muscles. Neither the locations, sizes or numbers of somata, nor their locations were as constant as is the case for ordinary ventral motoneurons.     

The ultrastructure of locust pleuroaxillary "steering" muscles in comparison to other skeletal muscles

The ultrastructure of locust muscles with different function is examined: the pleuroaxillary flight steering muscle is compared with a typical flight (power muscle) and a typical leg muscle, in particular with respect to sarcomere length, tracheation, mitochondria, and sarcoplasmatic reticulum. The pleuroaxillary muscle exhibits some features characteristic of flight muscles but most of the ultrastructure resembles that of leg muscles. This is in agreement with the innervation of this muscle by an octopaminergic neuron, which also innervates leg muscles but no other flight muscles. It also supports the hypothesis that octopaminergic neurons are important metabolic regulators and that the above muscle types exhibit important differences in energy metabolism.     

Contractile and endurance properties of geniohyoid and diaphragm muscles

Despite the wealth of information about the neural control of pharyngeal dilator muscles, little is known about their intrinsic physiological properties. In the present study the in situ isometric contractility and endurance of a pharyngeal dilator, the geniohyoid muscle, were compared with properties of the diaphragm in 12 anesthetized artificially ventilated cats. The contraction time (means +/- SE) of the geniohyoid (27 +/- 2 ms) was shorter than that of the diaphragm (36 +/- 3 ms; P less than 0.0005), as was the half-relaxation time (29 +/- 2 vs. 45 +/- 4 ms; P less than 0.002). The faster contraction and relaxation of the geniohyoid compared with the diaphragm were appropriately reflected in the shape of the force-frequency curves for the two muscles, with that of the geniohyoid located to the right of the diaphragm force-frequency curve. The endurance properties of the two muscles were assessed using repetitive stimulation at 40 Hz in trains lasting 0.33 s, with one train repeated every second. The ratio of force at the end of 2 min of repetitive stimulation to initial force was 0.67 +/- 0.06 for the geniohyoid and 0.15 +/- 0.03 for the diaphragm (P less than 0.00001). After the repetitive stimulation, the muscle force generated in response to a range of stimulus frequencies was reduced to a greater extent for the diaphragm than for the geniohyoid muscle. These results indicate that the geniohyoid muscle has a faster physiological profile than does the diaphragm yet is relatively resistant to fatigue when driven at high rates.     

Na(+)-Ca2+ exchange in locust striated muscles

High Na+ + Ca2+ exchange rates comparable with those reported for crayfish striated muscle, rat heart and rat brain, were observed in locust striated muscle homogenates and membrane preparations. The Na(+)-Ca2+ exchange followed the 1st order kinetics with a Km value of 18 mumol.l-1 for Ca, the pH optimum was at 8, the temperature optimum at 30 degrees C, and the exchange was inhibited in the presence of sodium in the incubation medium, with a KiNa of approx. 25 mmol.l-1. The present results suggest a high Na(+)-Ca2+ exchange in locust striated muscles which operate on the calcium electrogenesis principle.     

Ultrastructure and orientation of ommatidia in the dorsal rim area of the locust compound eye

In many insect species, a dorsal rim area (DRA) in the compound eye is adapted to analyze the sky polarization pattern for compass orientation. In the desert locust Schistocerca gregaria, these specializations are particularly striking. The DRA of the locust consists of about 400 ommatidia. The facets have an irregular shape, and pore canals are often present in the corneae. Screening pigment is missing in the region of the dioptric apparatus suggesting large receptive fields. The rhabdoms are shorter, but about four times larger in cross-section than the rhabdoms of ordinary ommatida. Eight retinula cells contribute to the rhabdom. The microvilli of retinula cell 7 and of cells 1, 2, 5, 6, 8 are highly aligned throughout the rhabdom and form two blocks of orthogonal orientation. The microvilli in the minute rhabdomeres of retinula cells 3 and 4, in contrast, show no particular alignment. As in other insect species, microvillar orientations are arranged in a fan-like pattern across the DRA. Photoreceptor axons project to distinct areas in the dorsal lamina and medulla. The morphological specializations in the DRA of the locust eye most likely maximize the polarization sensitivity and suggest that the locust uses this eye region for analysis of the sky polarization pattern.