Pores formed in lipid bilayers and in native membranes by nodularin,a cyanobacterial toxin

Nodularin (NODLN), a cyclic pentapeptide hepatotoxin from the cyanobacterium Nodularia spumigena, induces pores in bilayers of diphytanoyl lecithin (DPhL) and in locust muscle membrane. NODLN increases the surface pressure of a DPhL monolayer; except when the surface pressure of the monolayer is high when the toxin causes a reduction of this parameter. NODLN pores exhibit many open conductance states; the higher state probabilities increasing when the transmembrane pressure is increased. The results from these studies are discussed in terms of two models for a NODLN pore, a torroidal model and a barrel-stave model. The edge energy of the NODLN pore of 1.4× 10^–12 J/m is determined.Abbreviations NODLN Nodularin - MCYST-LR Microcystin-LR - ADDA 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid - DPhL diphytanoyl lecithin Correspondence to: A. G. Petrov     

Characterisation of columnar neurons and visual signal processing in the medulla of the locust optic lobe by system identification techniques

We describe visual responses of seventeen physiological classes of columnar neuron from the retina, lamina and medulla of the locust (Locusta migratoria) optic lobe. Many of these neurons were anatomically identified by neurobiotin injection. Characterisation of neuronal responses was made by moving and flash stimuli, and by two system identification techniques: 1. The first-order spatiotemporal kernel was estimated from response to a spatiotemporal white-noise stimulus; 2. A set of kernels to second order was derived by the maximal-length shift register (M-sequence) technique, describing the system response to a two-channel centre-surround stimulus. Most cells have small receptive fields, usually with a centre diameter of about 1.5°, which is similar to that of a single receptor in the compound eye. Linear response components show varying spatial and temporal tuning, although lateral inhibition is generally fairly weak. Second-order nonlinearities often have a simple form consistent with a static nonlinear transformation of the input from the large monopolar cells of the lamina followed by further linear filtering.Abbreviations LMC large monopolar cell - LVF long visual fibre - RF receptive field - SMC small monopolar cell - SVF short visual fibre     

Physiological responses and central nervous projections of antennal olfactory receptor neurons in the adult desert locust, Schistocerca gregaria (Orthoptera: Acrididae)

Olfactory receptor neurons present in two morphological sensillum types on the male Schistocerca gregaria antenna were for the first time investigated physiologically when stimulated with behaviourally relevant odours. Neurons present in trichoid/basiconic sensilla showed clear excitatory responses to compounds present in the male-produced aggregation pheromone and also to a plant produced compound. Sensilla could be categorised physiologically according to the responses of their receptor neurons to the tested stimuli. Also receptor neurons present in sensilla coeloconica responded to aggregation pheromone components, but always in an inhibitory fashion. These neurons could, however, be excited by a plant produced compound and by some acids present in the nymphal odour. The antennal lobe of the male S. gregaria was observed to contain about 1000 very small glomerular structures. Single receptor neurons were stained from the antenna to the antennal lobe using a cobalt lysine technique. These stainings revealed a multi glomerular axonal branching pattern of antennal receptor neurons.Abbreviations AN antennal nerve - AL antennal lobe - RN receptor neuron     

Responses and locations of neurones in the locust metathoracic femoral chordotonal organ

Summary Insect legs possess chordotonal organs which monitor leg angle, and the direction, velocity and acceleration of leg movements. The locust metathoracic femoral chordotonal organ (mtFCO) has previously been studied morphologically and physiologically, but no detailed analysis of the responses of individual neurones, and their location in the organ has so far been produced. By recording from, and staining mtFCO neurones I have been able to compile for the first time such a map. The distribution of neurone somata in the locust mtFCO is more complex than previously thought: receptors sensitive to both stretch and relaxation of the apodeme are distributed throughout the organ. Seventeen response types were encountered. Neurones with a particular response type have somata in comparable locations within the mtFCO. Comparisons are made between the response types found in the stick insect and those in the locust. The possible functions of some of the responses are discussed.Abbreviation (mt)FCO (metathoracic) femoral chordotonal organ - F-T femur-tibia     

The effects of temperature on locust ocellar L-neurones and their interconnections

The effects of temperature, over the range 10–40 °C, on properties of locust (Schistocerca gregaria) ocellar L-neurones and of their interconnections have been investigated. At cooler temperatures, a small change in temperature has a larger effect than an equivalent change at warmer temperatures. An increase in temperature leads to the following:

Preparation-dependent distribution of intramembranous particles in freeze-fracture replicas of the neuromuscular junction of the locust Schistocerca gregaria

Summary Freeze-fracture replicas of the neuromuscular junction were prepared from untreated retractor unguis muscles of the locust Schistocerca gregaria that were rapidly frozen by contact with a copper block cooled by liquid helium. These replicas were compared with others prepared from tissue following fixation with glutaraldehyde and cryoprotection in glycerol. Freeze-fracture of rapidly frozen tissue produced replicas of high quality with little evidence of tissue damage by ice crystals in the superficial layers. The gross fracturing characteristics of the neuromuscular junction were consistent with replicas from fixed and cryoprotected tissue; all of the membrane specializations were recognisable but with some alterations in infrastructure. In tissue replicas prepared using either method intramembranous particles in the presynaptic membrane were arranged in a bar-like array. The intramembranous particles of this presynaptic bar array of the rapidly frozen material were large and found on the E-face of the cleaved membrane. This contrasts with the P-face distribution of the comparable particles in muscles fixed in glutaraldehyde and cryoprotected in glycerol, in which they are also smaller and more numerous. This difference in partitioning between rapidly frozen, and fixed, cryoprotected nerve terminals is not found at cholinergic synapses and thus may reflect functional differences between the two types of junction.Indentations of the nerve-terminal membrane occur in replicas from rapidly frozen muscle as well as fixed and cryoprotected muscle suggesting they are not fixation or glycerol-induced artifacts. It is suggested from their position and size that these indentations are more likely to be part of a membrane retrieval system than exocytotic figures.This work was supported by an S.E.R.C. project grant to I.R.D.     

Locust flight metabolism studied in vivo by 31P NMR spectroscopy

Flight metabolism of locusts has been extensively studied, but biochemical and physiological methods have led to conflicting results. For this reason the non-invasive and non-destructive method of ³¹P NMR spectroscopy was used to study migratory locusts, Locusta migratoria, at rest and during flight.

The vasopressin-like immunoreactive (VPLI) neurons of the locust,Locusta migratoria. I. Anatomy

Summary Antiserum to arginine-vasopressin has been used to characterise the pair of vasopressin-like immunoreactive (VPLI) neurons in the locust. These neurons have cell bodies in the suboesophageal ganglion, each with a bifurcating dorsal lateral axon which gives rise to predominantly dorsal neuropilar branching in every ganglion of the ventral nerve cord. There are extensive beaded fibre plexuses in most peripheral nerves of thoracic and abdominal ganglia, but in the brain, the peripheral plexuses are reduced while neuropilar branching is more extensive, although it generally remains superficial. An array of fibres runs centripetally through the laminamedulla chiasma in the optic lobes. Lucifer Yellow or cobalt intracellular staining of single VPLI cells in the adult suboesophageal ganglion shows that all immunoreactive processes emanate from these two neurons, but an additional midline arborisation (that was only partially revealed by immunostaining) was also observed. Intracellularly staining VPLI cells in smaller larval instars, which permits dye to reach the thoracic ganglia, confirms that there is no similar region of poorly-immunoreactive midline arborisation in these ganglia. It has been previously suggested that the immunoreactive superficial fibres and peripheral plexuses in ventral cord ganglia serve a neurohaemal function, releasing the locust vasopressin-like diuretic hormone, F₂. We suggest that the other major region of VPLI arborisation, the poorly immunoreactive midline fibres in the suboesophageal ganglion, could be a region where VPLI cells receive synaptic input. The function of the centripetal array of fibres within the optic lobe is still unclear.Abbreviations AVP arginine vasopressin - DIT dorsal intermediate tract - FLRF Phe-Leu-Arg-Phe - FMRF-amide Phe-Met-Arg-Phe-amide - LDT lateral dorsal tract - LVP lysine vasopressin - MDT median dorsal tract - MVT median ventral tract - SEM scanning electron microscopy - SOG suboesophageal ganglion - VIT ventral intermediate tract - VNC ventral nerve cord - VPLI vasopressin-like immunoreactive     

The distribution of GABA-like immunoreactivity in relation to ganglion structure in the abdominal nerve cord of the locust (Schistocerca gregaria)

Summary An antiserum raised against GABA was used to stain the abdominal nervous system of the locust. To interpret the results, however, it was first necessary to describe the structure of the free abdominal and terminal ganglia. This was done on the basis of ethyl-gallate staining. The free abdominal ganglia are similar in structure to the abdominal neuromeres of the metathoracic ganglia. The terminal ganglion is composed of four neuromeres (representing ganglia 8–11), but only three can be distinguished in the adult on morphological grounds. The eighth neuromere resembles the free ganglia, but the ninth lacks DCI (dorsal commissure I) and the T tracts. In the tenth, only DCII and III are recognisable of the commissures, but two more posterior ones of uncertain homology are also present. Immunocytochemistry reveals three populations of somata in each abdominal ganglion. Of these only one, the medial posterior group, is found in the thoracic ganglia. DCIV and the supra-median commissure are composed of stained neurites, DCII and V contain both unstained neurites and DCI, III and VI are unstained. With the exception of the median ventral tract, all the longitudinal tracts contain some stained axons.     

The binding of the insect selective neurotoxin (AaIT) from scorpion venom to locust synaptosomal membranes

The binding of the radioiodinated insect selective neurotoxin from the venom of the scorpion Androctonus australis (AaIT), to synaptic plasma membrane vesicles derived from osmotically shocked insect synaptosomes was studied under kinetic and equilibrium conditions. The integrity of these vesicles and the existence of membrane potential and its modifiability were demonstrated by assays of the uptake of the lipophilic cation tetraphenylphosphonium. It has been shown that ¹²⁵I-labeled AaIT binds specifically and reversibly to a single class of noninteracting binding sites of high affinity ($\text{K}{}_{\mathrm{<mtext>d</mtext>}}{}^1\text{= 1.2–3}\text{nM}$) and low capacity (1.2–2.0 pmol/mg protein). The values of the rate association and dissociation constants k₁ and k_?1 are, respectively, 1.36 · 10⁶ M^?1 · s^?1 and 1.9 · 10^?3 s^?1, and are in a good accordance with the equilibrium constant. The use of various ionophores and changes in external potassium concentration shown to modify the membrane potential of the present neuronal preparation, did not affect the binding of ¹²⁵I-AaIT, thus indicating its voltage-independence. Veratridine, tetrodotoxin, sea anemone toxin and the α and β scorpion toxins specific for vertebrates did not affect the binding of ¹²⁵I-AaIT. Furthermore, the above scorpion toxins were devoid of specific binding to the present insect neuronal preparation. Two additional insect toxins derived from the venom of the scorpion Buthotus judaicus, BjIT₁ (spastic-excitatory toxin, homologus to the AaIT) and BjIT₂ (flaccidity inducing-depressory toxin), were both shown to displace the ¹²⁵I-AaIT with a high affinity (K_d = 2.2 and 1.3 nM, respectively). These data are compared and discussed in light of the information concerning the interaction of scorpion venom toxins affecting vertebrates with mammalian neuronal tissues.