Inhibiton and gamma-aminobutyric acid-induced conductance on locust (Schistocerca gregaria) extensor tibiae muscle fibres

• 1.1. Increases in membrane conductance (g_m) were induced by GABA in distal bundles 32, 33 and 34 of extensor tibiae muscles of the locust (Schistocerca gregaria).
• 2.2. Bath application of GABA (10⁻⁵−5 × 10⁻³ M) induced reductions in muscle fibre space constant (λ).
• 3.3. GABA (5 × 10⁻³ M) induced additional membrane conductance of 2.21 ± 0.03 × 10⁻⁶ S/mm, 0.38 ± 0.03 × 10⁻⁶ S/mm and 0.29 ± 0.06 × 10⁻⁶ S/mm on muscle bundles 34, 33 and 32 respectively. The greater sensitivity of muscle fibres in bundle 34 to GABA is due at least in part to a larger number of GABA receptors on bundle 34 muscle fibres.
• 4.4. The decrement of electrotonic potentials in the presence of GABA were measured over distances of both half fibre length and whole fibre length. Good agreement was obtained between changes in space constant produced by GABA using half fibre length and whole fibre length data.
• 5.5. By taking into account changes in space constant induced by GABA it was possible to demonstrate that presynaptic GABA receptors were involved in the inhibition of slow excitatory postsynaptic potentials by GABA.
• 6.6. “Slow” excitatory postsynaptic potentials recorded under current clamp were inhibited in a dose-dependent manner by GABA. This inhibition was not dependent on muscle-fibre GABA sensitivity and could not be completely accounted for by GABA-induced changes in the cable properties of the muscle fibres.

     

The action of philanthotoxin-343 and photolabile analogues on locust (Schistocerca gregaria) muscle

The effects of philanthotoxin-343 (PhTX-343; tyrosyl-butanoyl-spermine) and photolabile analogues of this synthetic toxin on locust (Schistocerca gregaria) skeletal muscle have been investigated using whole muscle preparations (twitch contractions), single muscle fibres (excitatory postsynaptic currents (EPSCs)) and muscle membrane patches containing single quisqualate-sensitive glutamate receptors (qGluR). Analogues containing an azido group attached to either the butanoyl side-chain of PhTX-343 or as a substitute for the hydroxyl moiety of the tyrosyl residue were about 6 fold more potent antagonists than PhTX-343; those with an azido group located at the distal end of the toxin molecule were generally 2–3 fold less potent than PhTX-343. When these compounds were tested in subdued light, they were reversible antagonists of the muscle twitch, EPSC and qGluR. When a muscle was irradiated with U.V. during application of photolabile toxin combined with either neural stimulation of the muscle orl-glutamate application, antagonism of the twitch, EPSC and qGluR was complete and irreversible.     

FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust (Schistocerca gregaria)

Summary The distribution of FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust, Schistocerca gregaria, has been investigated in serial semithin transverse sections with the use of the peroxidase-antiperoxidase (PAP) technique. The topographical distribution of approximately 120 immunopositive neurons was established. Antiserum against bovine pancreatic polypeptide (BPP) stains the same ganglionic cells as FMRFamide-antiserum, yet this staining is largely blocked after preabsorption to FMRFamide. A comparison of these results with those from other studies suggests that there may be more than one type of endogenous RFamide-like peptide.     

Neuropeptide-degrading endopeptidase activity of locust (Schistocerca gregaria) synaptic membranes.

Locust adipokinetic hormone (AKH, pGlu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2) was used as the substrate to measure neuropeptide-degrading endopeptidase activity in neutral membranes from ganglia of the locust Schistocerca gregaria. Initial hydrolysis of AKH at neural pH by peptidases of washed neural membranes generated pGlu-Leu-Asn and Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2 as primary metabolites, demonstrating that degradation was initiated by cleavage of the Asn-Phe bond. Amastatin protected the C-terminal fragment from further metabolism by aminopeptidase activity without inhibiting AKH degradation. The same fragments were generated on incubation of AKH with purified pig kidney endopeptidase 24.11, and enzyme known to cleave peptide bonds that involve the amino group of hydrophobic amino acids. Phosphoramidon (10 microM), a selective inhibitor of mammalian endopeptidase 24.11, partially inhibited the endopeptidase activity of locust neural membranes. This phosphoramidon-sensitive activity was shown to enriched in a synaptic membrane preparation with around 80% of the activity being inhibited by 10 microM-phosphoramidon (IC50 = 0.2 microM). The synaptic endopeptidase was also inhibited by 1 mM-EDTA, 1 mM-1,10-phenanthroline and 1 microM-thiorphan, and the activity was maximal between pH 7.3 and 8.0. Localization of the phosphoramidon-sensitive enzyme in synaptic membranes is consistent with a physiological role for this endopeptidase in the metabolism of insect peptides at the synapse.     

The sense organs on the mouth parts of the Desert locust (Schistocerca gregaria)

The "hairs" and various types of sensilla present on the mouth parts of Schistocerca gregaria are described. The distribution of the sensilla on the clypeo-labrum, labium and theHmaxillae has been plotted in detail, and the general distribution of all types of sensilla on each of the mouth parts is described.
A comparison is made between the distribution of certain sensilla on the clypeo-labrum in first instars and adults.
The probable role of the sensilla in feeding is discussed.     

The body temperature of the desert locust Schistocerca gregaria

Summary The internal equilibrium body temperatures of hoppers (nymphs) of Schistocerca gregaria were studied in the field. The data obtained are here compared with theoretical estimates of the thermal balance resulting from the factors assumed to be concerned in heat loss and heat gain.In the field, the equilibrium body temperature of quiescent hoppers shaded from direct sunshine was up to 3.2° higher than the air temperature when the latter was about 25° or less, but was lower than the air temperature when this was above about 31°. In sunlight, body-temperature excesses increased linearly with total radiation intensity between 0.15 and 1.25 cal/cm²/min. Differences in orientation to the sun gave rise to differences in equilibrium body temperature of as much as 6°. At relatively low radiation intensities (about 0.5 cal/cm²/min) the equilibrium body temperatures were found to vary with a power of the wind speed of about 0.35. There were no demonstrable significant differences in equilibrium body temperature or rate of change of body temperature between hoppers having opposite extremes of possible coloration.Except in hoppers shaded from sunlight and those exposed to low radiation intensities there was good agreement between the observed equilibrium temperatures and those expected on theoretical grounds. This provides evidence of the relative importance of the factors concerned in thermal balance.The relation between body temperature and behaviour is discussed.

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Zusammenfassung Das innere Gleichgewicht der Körpertemperatur von vorzugsweise fünften Larvenstadien der Wüstenheuschrecke wurde unter Freilandbedingungen in Beziehung zu Lufttemperatur, relativer Luftfeuchtigkeit, Strahlungsintensität, Windgeschwindigkeit und Aktivität gemessen.Die verschiedenen Faktoren, die das Temperaturgleichgewicht der Heuschrecken beeinflussen, werden theoretisch behandelt. Die unter bestimmten Kombinationen der Umweltbedingungen zu erwartenden Gleichgewichts-Körpertemperaturen werden aus den theoretischen Werten für die verschiedenen beteiligten Faktoren errechnet und mit den unter entsprechenden Freilandbedingungen beobachteten Werten verglichen.Ohne Sonneneinstrahlung und unter relativ windstillen Bedingungen wurde bei ruhenden Larven des fünften Stadiums eine Gleichgewichts-Temperatur des Körpers gefunden, die bis zu 3,2° höher lag als die Lufttemperatur, wenn diese ca. 25° oder weniger betrug. Dieser Überschuß hatte eine abnehmende Tendenz bei Lufttemperaturen bis zu etwa 31° und über dieser Schwelle waren die Gleichgewichts-Temperaturen des Körpers im allgemeinen niedriger als die entsprechenden Lufttemperaturen. Theoretisch würde zu erwarten sein, daß unter diesen Umweltbedingungen das Temperaturgleichgewicht des Körpers in allen Niveaus annähernd der Lufttemperatur entspräche. Folglich scheint hier ein physiologischer Mechanismus zu bestehen, mit dessen Hilfe die Insekten in Abwesenheit von Sonnenschein und unter den Bedingungen schwacher Konvektion ihre Körperausgleichstemperaturen bei niedrigen Lufttemperaturen erhöhen, bei hohen senken können.Es war nicht möglich, im Freiland nachzuweisen, daß Unterschiede in der relativen Luftfeuchtigkeit irgendeinen signifikanten Einfluß auf die ausgeglichenen Körpertemperaturen in dem untersuchten Bereich (Sättigungsdefizit von 2 bis 27 mm) ausübten. Die erwarteten maximalen Differenzen der Gleichgewichts-Körpertemperaturen lagen in diesem Bereich des Sättigungsdefizits in einer Größenordnung von nur 0,5°.Unter relativ ruhigen Freilandbedingungen zeigten die Heuschrecken im Sonnenschein Körpertemperaturüberschüsse, die bei einer totalen Strahlungsintensität zwischen 0,15 und 1,25 cal/cm²/min annähernd linear anstiegen (von einem Mittel von 2–10° bei fünften Larvenstadien). Die in diesem Strahlungsintensitätsbereich gemessenen Übertemperaturen des Körpers stimmten einigermaßen gut mit Werten überein, die von anderen Untersuchern unter Laboratoriumsverhältnissen festgestellt wurden. Unter 0,40 cal/cm²/min waren die beobachteten Körpertemperaturüberschüsse im allgemeinen höher als theoretisch zu erwarten gewesen wäre. Die Körpertemperatur von Larven des ersten Stadiums nahm rascher zu als die von Larven des fünften, jedoch nur bis zu einem niedrigeren Niveau; auch das stimmte gut mit den theoretischen Vorstellungen und mit der Laborerfahrung überein. Die Einstellreaktion der Heuschrecken zur Sonne ergab beobachtete Unterschiede in der Gleichgewichts-Körpertemperatur bis zu 6° zwischen Larven des fünften Stadiums, die sich in Richtung der Sonnenstrahlen eingestellt hatten, und solchen, die im rechten Winkel zur Sonnenrichtung auf dem Boden standen; die erwarteten Unterschiede waren von der gleichen Größenordnung.Im Sonnenschein variierten die erwarteten Intensitätsproportionen zwischen der Ausgleichstemperatur und der Windgeschwindigkeit zwischen 0,5 und 0,6 mit dem Sättigungsdefizit. Bei Strahlungsintensitäten von etwa 1,10 cal/cm²/min stimmten die beobachteten Körpergleichgewichtstemperaturen engstens mit den erwarteten überein, aber bei geringeren Strahlungsintensitäten von etwa 0,50 cal/cm²/min variierten die Meßwerte mit einer Intensitätsproportion zur Windgeschwindigkeit von etwa 0,35. Darin zeigt sich möglicherweise, daß bei niederen Strahlungswerten die Körperausgleichstemperaturen zu höheren Werten tendieren als zu erwarten war.Das beobachtete Ansteigen der Körperausgleichstemperatur von ungefähr 1° bei dritten Larvenstadien und von 2–3° bei fünften Larvenstadien befindet sich in Übereinstimmung mit dem für entsprechende Umweltbedingungen errechneten.Zwischen Larven extrem entgegengesetzter Färbungstypen konnten keine Unterschiede in den Körperausgleichstemperaturen oder dem Ausmaß der Körpertemperaturänderung nachgewiesen werden.Mit Ausnahme der vor direkter Sonnenbestrahlung geschützten Heuschrecken unter relativ ruhigen Bedingungen und der Heuschrecken, die niederen Strahlungsintensitäten ausgesetzt waren, bestand eine gute allgemeine Übereinstimmung zwischen den beobachteten und den erwarteten Gleichgewichts-Körpertemperaturen. Es wurde deshalb geschlossen, daß die durchgeführten Bestimmungen Beweise für die relative Bedeutung der für den Temperaturhaushalt verantwortlichen Faktoren darstellen. Zur Erzeugung beträchtlicher Überschüsse der Körpertemperatur über die Lufttemperatur hat die Strahlung die größte Bedeutung. Für den Wärmeabfluß nach außen werden die durch Konvektion entstehenden Wärmeverluste, die insgesamt 94% oder mehr betragen, als bei weitem am wichtigsten angesehen.Einige mögliche Beziehungen zwischen Körpertemperatur und Verhalten werden besprochen.

     

Partial purification and some properties of pyruvate carboxylase from the flight muscle of the locust (Schistocerca gregaria)

A procedure is described for the partial purification of pyruvate carboxylase (pyruvate:CO2 ligase (ADP-forming), EC 6.4.1.1) from the flight muscle of the locust (Schistocerca gregaria). Characterisation of the kinetic properties of this enzyme indicates that it is activated by acetyl-CoA, is insensitive to inhibition by di- and tricarboxylic acids and exhibits an apparent Km for HCO3-(16 mM) which differs by an order of magnitude from that observed for other pyruvate carboxylases. It is suggested that activation of this locust flight muscle pyruvate carboxylase during the rest leads to flight transition may result from increases in the concentrations of pyruvate and HCO3- under these conditions.     

Neurobiology of polarization vision in the locust Schistocerca gregaria

The polarization pattern of the blue sky serves as an important reference for spatial orientation in insects. To understand the neural mechanisms involved in sky compass orientation we have analyzed the polarization vision system in the locust Schistocerca gregaria. As in other insects, photoreceptors adapted for the detection of sky polarization are concentrated in a dorsal rim area (DRA) of the compound eye. Stationary flying locusts show polarotactic yaw-torque responses when illuminated through a rotating polarizer from above. This response is abolished after painting the DRAs. Central stages of the polarization vision system, revealed through tracing studies, include dorsal areas in the lamina and medulla, the anterior lobe of the lobula, the anterior optic tubercle, the lateral accessory lobe and the central complex. Physiological analysis of polarization-sensitive (POL) neurons has focussed on the optic tubercle and on the central complex. Each POL neuron was maximally excited at a certain e-vector (phimax) and was maximally inhibited at an e-vector perpendicular to phimax. The neurons had large visual fields, and many neurons received input from both eyes. The neuronal organization of the central complex suggests a role as a spatial compass within the locust brain.     

Hatching rhythms in the desert locust, Schistocerca gregaria

ABSTRACT. The eggs of Schistocerca gregaria (Orthoptera, Acrididae) incubated under natural conditions hatch only within a few of hours on either side of dawn. This gated hatching is controlled by a circadian clock that is phase set by the diel fluctuations in the temperature of the soil surrounding the eggs. There is a circadian fluctuation in haemolymph sugar concentration which is initiated at least 4 days before hatching. However, eggs hatch arrhythmically unless given cycled temperature incubation for at least 10 days of a 12–13-day incubation. Increase in acetylcholine esterase content of the brain during the penultimate day suggests that increased hatching rhythmicity occurring at this time is the result of increased neural organization. Embryonic activity and respiration show no circadian rhythm but do provide confirmatory evidence of a quiescent phase prior to hatching. This quiescent phase is an integral part of gated hatching behaviour.     

Allatostatin-like immunoreactivity in the abdomen of the locust Schistocerca gregaria

A polyclonal antibody against allatostatin 1 (AST-1) of cockroach Diploptera punctata was used to investigate the distribution of AST-like immunoreactivity within the abdomen of the locust, Schistocerca gregaria. In the abdominal ganglia, AST-like immunoreactivity was found in both cell bodies and neuropile. In ganglia 6 and 7, staining was found in serial homologous cell bodies in anterior dorsolateral and dorsomedial, and posterior ventrolateral and ventromedial locations. In the terminal ganglion, the numerous immunoreactive somata were smaller in size than those in the unfused ganglia. The combination of backfill experiments with immunocytochemistry showed that, in abdominal ganglion 7, one neuron of the ventromedian cell body cluster and two of the ventrolateral cluster innervated the oviduct, which itself was covered with a dense mesh of AST-immunoreactive varicosities. Combining electron microscopy with immunohistochemistry revealed AST-like immunoreactivity in dense-core vesicles located in neurohaemal-like terminals lacking structures normally found in synapses. A mesh of AST-immunoreactive varicosities was also found on the muscles of the spermatheca and the spermathecal duct. In addition, a mesh of strongly stained varicosities was present in the distal perisympathetic organs (neurohaemal organs in the abdomen) and on the lateral heart nerves (a putative neurohaemal release zone). These data indicate that AST is an important neuroactive substance that is probably involved in multiple tasks in the control of the locust abdomen.     

Location of repetitious DNA in the chromosomes of the desert locust (Schistocerca gregaria)

A modified Giemsa staining technique and the in situ hybridisation technique, have been used to investigate the localisation of highly repeated sequences in the karyotype of the locust Schistocerca gregaria. The centromeric regions are stained densely with Giemsa and further Giemsa-stained bands occur at the telomeric region of the short (S) chromosomes. RNA complementary to repetitious DNA hybridised to loci scattered along the whole length of the chromosomes, with concentrations of grains at the centromeric regions of all the chromosomes and also at the telomeric regions of the S chromosomes.     

Intracellular application of polyamine and polyamine amide inhibits the quisqualate-sensitive ionotropic glutamate receptor of locust (Schistocerca gregaria) muscle

The effects of intracellularly-applied philanthotoxin-343 (PhTX-343) on single channel currents gated by quisqualate-sensitive glutamate receptors (qGluR) of locust leg muscle have been studied. PhTX-343 initially increased qGluR channel open probability, mainly by virtue of an increase in mean channel open time, but this was followed by a decrease in channel open probability, sometimes to zero, because of a decline in the frequency of channel openings and a decline in mean channel open time. These results suggest that antagonism of qGluR by PhTX-343 can arise, in part, through binding of the toxin to a site or sites on the intracellular domain of this receptor.     

Studies on the mid-gut of the desert locust, Schistocerca gregaria.

ABSTRACT. The gross morphology of the mid-gut musculature of the desert locust, Schistocerca gregaria is described. Some of the electrophysiological characteristics of the external longitudinal muscle fibres were examined. The membrane potentials have mean values of -24.7mV (SE ± 7.3). Spontaneous post-synaptic potentials were recorded, and the responses of the muscle fibres to electrical stimulation of their nerve supply studied.