The effect of certain anions on muscle resting potential in Tenebrio molitor

Experiments were carried out on longitudinal ventral muscles of the mealworm larva (Tenebrio molitor) using conventional microelectrode methods. Both sodium nitrate and sodium sulphate depolarized the fibres markedly, whereas sodium propionate exerted an hyperpolarizing influence. It is concluded that the differences in the mode of action are due to different permeabilities of the membrane to the applied anions. The results obtained confirm also the concept of a multi-ionic electrode with respect to insect muscle fibres.

Developmental changes in the glutamate receptor at the insect neuromuscular synapse

Developmental changes in the glutamate receptors were studied using insect (Tenebrio molitor) neuromuscular synapses. Bath-applied L-glutamate produced depolarization of the postsynaptic membrane of larva muscle, whereas in imago muscle L-glutamate produced both depolarization and hyperpolarization with conductance increase. Iontophoretically applied glutamate distinguished two types (depolarization and hyperpolarization) of receptors in the imago muscle. Quisqualic acid and ibotenic acid mimic depo- and hyper-type response by L-glutamate respectively. Kainic acid blocks the excitatory postsynaptic potentials in both larva and imago, with little effect on the resting conductance of the postsynaptic membrane. As the nerve terminal spike was abolished by kainate it is suggested that kainate mainly acts on the nerve terminal.

Postsynaptic effects of nickel ions at the insect neuromuscular junction

The effect of extracellular nickel on the excitatory postsynaptic response at the insect neuromuscular junction was studied in the segmental muscle of the larval mealworm Tenebrio molitor. The response to L-glutamate applied iontophoretically (glutamate potential, GP) was potentiated in the presence of Ni2+ though the excitatory postsynaptic potential (EPSP) was reduced. It seems unlikely that Ni2+ acts at the same binding site as L-glutamate does since the value of the limiting slope of double logarithmic plots for the action of glutamate was increased in the presence of Ni2+. The potentiation of GP in the presence of Ni2+ cannot be ascribed to competition between Ni2+ and Ca2+ since GP amplitude did not show any dependence on the concentration of Ca2+. Nickel ions did not alter the reversal potential of excitatory postsynaptic current (EPSC) and glutamate current (GC) under the voltage clamp condition, whereas the amplitude of GC was potentiated in the presence of Ni2+. The time constant of the decay of EPSC showed a weak voltage dependency: the more depolarized the membrane, the more prolonged the time constant. In the presence of 1 mM Ni2+ the amplitude of miniature EPSCs (MEPSCs) increased and the half decay time was prolonged significantly. These results suggest that Ni2+ interacts with charged groups near the glutamate receptor-channel complex so that the kinetics of the channel are altered.

Drugs that block calmoduLin activity inhibit cell-to-cell coupling in the epidermis of Tenebrio molitor

In many cell systems, the permeability of membrane junctions is modulated by the cytoplasmic level of free Ca++. To examine whether the calcium-dependent regulatory protein calmodulin is involved in this process, the ability of anticalmodulin drugs to influence the cell-to-cell passage of injected current and an organic tracer was tested using standard intracellular glass microelectrode techniques. Several antipsychotics and local anesthetics were found to block junctional communication in the epidermis of the beetle Tenebrio molitor. Treatment of the epidermis with chlorpromazine (0.25 mM) raised intercellular resistance two- to threefold within 20 to 25 min; cell-to-cell passage of electrical current was abolished within 41 +/- 5 min. Loss of electrotonic coupling was accompanied by a block in the cell-to-cell movement of the organic tracer carboxyfluorescein. The reaction is fully reversible, with normal electrotonic coupling being restored within 2 to 4 hr. Other antipsychotics and local anesthetics had similar effects on cell coupling. The order of potency found was: trifluoperazine greater than thioridazine greater than D-butaclamol greater than chlorprothixine = chlorpromazine greater than L-butaclamol greater than dibucaine greater than tetracaine. The relative uncoupling potencies of these drugs correlate well with their known ability to inhibit calmodulin-dependent phosphodiesterase activity. Other anesthetic compounds, procaine and pentobarbital, did not block cell-to-cell communication. Altering the extracellular Ca++ concentration did not affect the rate of uncoupling by antipsychotics, while chelation of extracellular Ca++ with EGTA raised electrotonic coupling. The effect of three metabolic inhibitors on coupling was also examined. Iodoacetate uncoupled the epidermal cells while DNP and cyanide did not. These results are discussed in terms of possible mechanisms by which calmodulin may control junctional communication in this tissue.

Effect of light and incubation temperature on production by species of Fusarium of metabolites toxic to larvae of Tenebrio molitor L

Larvae of Tenebrio molitor L., Gembloux strain, race F, having an initial weight of 10 mg were reared for 4 weeks at 27 +/- 0.25 degrees C 65 +/- 5% relative humidity on rye seed incubated with single isolates of four strains of Fusarium. The fungi had been cultured in total darkness or in constant light at a temperature of 8, 14, 20 or 24 degrees C. Two isolates of Fusarium poae (Peck). Wollenw. (7450 and 7452) retarded growth more than the third isolate of this species or than the isolate of Fusarium accuminatum Ell. & Ev. Nutritional value of rye seed decreased with increasing temperature, but declined to a larger extent when Fusarium species were present than when they were absent. The results suggest that changes in weight and mortality of larvae are good criteria for determining toxicity of fungal metabolites in Insects.

[Effect of adrenocorticotropin fragments on the memory of Tenebrio molitor beetles]

Fragments of the adrenocorticotropic hormone ACTH1-24 and ACTH5-7 facilitate memory in the beetle T. molitor, the effect being observed at different stages after learning. An analogue of ACTH5-7 which contains D-phenylalamine, as well as D-phen7-ACTH4-7, inhibit memorization (the results checked 1 day after learning) and induce some other disturbances in the behaviour of beetles. To the 10th day of learning, the effects of the analogues cannot be distinguished from those of L-Phe7-fragments. The results obtained are compared with the known effect of ACTH fragments on memory in vertebrates.

The time course of the electroretinogram of compound eyes in insects and its dependence on special recording conditions

Electroretinograms recorded from slowly moving insects like the mealworm beetle Tenebrio molitor and the stick insect Carausius morosus are shown to be distorted by the use of electrodes of stainless steel and silver/silver chloride wires, unless they are used in conjunction with amplifiers having extremely high input resistance. Undistorted electroretinograms can also be recorded using micropipettes filled with a suitable electrolyte. The undistorted ERG of Tenebrio molitor is monophasic, as described by Autrum (1950) for Dixippus, and as expected from his rule.

Passive exchanges during water vapour absorption in mealworms (Tenebrio molitor): a new approach to studying the phenomenon

The weights of single mealworms were continuously recorded at 20 degrees C during exposure to periods of constant humidity and to abrupt changes in atmospheric vapour pressure. Two exchange stages were recognized in each animal. Weight changes were either limited to slow losses, suggesting transpiration through the external cuticle, or showed more rapid humidity-dependent gains as well as losses. Rapid exchanges indicated that water was gained or lost through permeable barriers, from a fluid compartmet of significantly lower vapour pressure than the haemolymph, equivalent to about 90% R.H. Weight gains and losses during humidity changes provided evidence of a significant, passively exchanging fluid compartment located between the exchange surface and absorbing mechanism. Weight changes in faecal pellets following their elimination provide further support for a rectal site of atmospheric absorption.

Sodium activity of insect blood: physiological significance and relevance to the design of physiological saline

The apparent activity coefficients for sodium (gamma'Na) in the blood of six insect species have been calculated from measurements made with sodium-selective electrodes and a flame photometer. In every case gamma Na was significantly lower than that for this cation in free solution (gammaNa). In Periplaneta americana gammaNa varied considerably, during a period of 90 days, so that a relatively constant sodium activity (aNa) was maintained in the blood in the face of large variations in the total sodium content measured by flame photometry. Despite the relative constancy of aNa (of around 0.088M) appreciable fluctuations were observed in the sodium and potassium content of nervous connective over a period of 140 days. The values of aNa and aK were used to devise a satisfactory cockroach saline for use in experiments with isolated nerve cords.