Eye movements and target fixation during dragonfly prey-interception flights

The capture of flying insects by foraging dragonflies is a highly accurate, visually guided behavior. Rather than simply aiming at the prey’s position, the dragonfly aims at a point in front of the prey, so that the prey is intercepted with a relatively straight flight trajectory. To better understand the neural mechanisms underlying this behavior, we used high-speed video to quantify the head and body orientation of dragonflies (female Erythemis simplicicollis flying in an outdoor flight cage) relative to an artificial prey object before and during pursuit. The results of our frame-by-frame analysis showed that during prey pursuit, the dragonfly adjusts its head orientation to maintain the image of the prey centered on the “crosshairs” formed by the visual midline and the dorsal fovea, a high acuity streak that crosses midline at right angles about 60° above the horizon. The visual response latencies to drifting of the prey image are remarkably short, ca. 25 ms for the head and 30 ms for the wing responses. Our results imply that the control of the prey-interception flight must include a neural pathway that takes head position into account.     

Radiosynthesis and biodistribution of a prosthetic group (¹⁸F-FENMA) conjugated to cyclic RGD peptides

We have recently reported a new N-methylaminooxy-based prosthetic group for the site-selective introduction of 1?F-fluorine under mild acidic aqueous conditions into model peptides functionalized with a Michael acceptor moiety. To further investigate the utility of this methodology, the radiosynthesis of two cyclic RGD peptides was carried out, and in vivo biodistribution and microPET studies were performed in tumor-bearing mice. A cyclic RGD peptide was functionalized with the Michael acceptors trans-β-nitrostyrene carboxylic acid and 3-vinylsulfonylpropionic acid. Radiolabeling was then performed with the prosthetic group O-(2-(2-[1?F]fluoroethoxy)ethyl)-N-methylhydroxylamine (1?F-FENMA) yielding the 1?F-conjugates in moderate yields (8.5-12%). Biodistribution, blocking, and microPET imaging studies were performed in a mouse xenograft model. The vinylsulfonyl-modified conjugate demonstrated good in vitro plasma stability. Biodistribution and microPET studies revealed excellent tumor uptake with low background in key organs and renal elimination as the predominant route of excretion. Blocking studies with coinjected nonlabeled RGD peptide confirmed the in vivo specificity for the integrin α(v)β?. On the other hand, 1?F-FENMA-nitrostyrene-RGD, although stable at conjugation pH 5, was found to rapidly degrade at physiological pH through loss of the 1?F-prosthetic group.     

Plasma biochemical values from apparently healthy free-ranging polar bears from Svalbard

To establish reference values for free-ranging polar bears (Ursus maritimus) at Svalbard, Norway, plasma samples from 15 females and 20 males were analyzed for 28 blood biochemistry parameters. Animals were chemically immobilized (Zoletil: tiletamine and zolazepam) on land at Barents?ya, Edge?ya, and the eastern coast of Spitsbergen in August 1998. All bears were apparently healthy, with ages ranging from 1-22 yr. Females had almost two times higher levels of lipase than males. Several parameters varied with age. Levels of alkaline phosphatase (ALP) and calcium (Ca) decreased with age, being significantly higher in young individuals (< 6 yr) compared to middle-aged (6-13 yr) and older bears (> 13 yr). Globulin was lower in animals < 6 yr of age than in animals > 13 yr of age, while the opposite was the case for albumin. Levels of ALP, Ca, and potassium decreased with age. We found no significant changes in total protein correlated to age, but total protein levels were higher in obese compared to lean individuals. Further, total protein levels were slightly lower and had greater variation compared to data from polar bears in captivity, which may reflect food availability for the latter group. The mean ratio between urea and creatinine was 10.9 and indicated these bears were fasting. These data provide a baseline from which to compare biochemical parameters in captive and free-ranging polar bears and will be especially valuable for future studies of polar bears at Svalbard.     

Pheromone-modulated optomotor response in male gypsy moths,Lymantria dispar L.: Directionally selective visual interneurons in the ventral nerve cord

In response female pheromone the male gypsy moth flies a zigzagging path upwind to locate the source of odor. He determines wind direction visually. To learn more about the mechanism underlying this behavior, we studied descending interneurons with dye-filled micro-electrodes. We studied the interneuronal responses to combinations of pheromone and visual stimuli.

The mapping of visual space by identified large second-order neurons in the dragonfly median ocellus

In adult dragonflies, the compound eyes are augmented by three simple eyes known as the dorsal ocelli. The outputs of ocellar photoreceptors converge on relatively few second-order neurons with large axonal diameters (L-neurons). We determine L-neuron morphology by iontophoretic dye injection combined with three-dimensional reconstructions. Using intracellular recording and white noise analysis, we also determine the physiological receptive fields of the L-neurons, in order to identify the extent to which they preserve spatial information. We find a total of 11 median ocellar L-neurons, consisting of five symmetrical pairs and one unpaired neuron. L-neurons are distinguishable by the extent and location of their terminations within the ocellar plexus and brain. In the horizontal dimension, L-neurons project to different regions of the ocellar plexus, in close correlation with their receptive fields. In the vertical dimension, dendritic arborizations overlap widely, paralleled by receptive fields that are narrow and do not differ between different neurons. These results provide the first evidence for the preservation of spatial information by the second-order neurons of any dorsal ocellus. The system essentially forms a one-dimensional image of the equator over a wide azimuthal area, possibly forming an internal representation of the horizon. Potential behavioural roles for the system are discussed.     

A novel prosthetic group for site-selective labeling of peptides for positron emission tomography

Efficient methodologies for the radiolabeling of peptides with [(18)F]fluoride are a prerequisite to enabling commercialization of peptide-containing radiotracers for positron emission tomography (PET) imaging. It was the purpose of this study to investigate a novel chemoselective ligation reaction comprising conjugation of an [(18)F]-N-methylaminooxy-containing prosthetic group to a functionalized peptide. Twelve derivatives of general formula R1-CO-NH-Lys-Gly-Phe-Gly-Lys-OH were synthesized where R1 was selected from a short list of moieties anticipated to be reactive toward the N-methylaminooxy group. Conjugation reactions were initially carried out with nonradioactive precursors to assess, in a qualitative manner, their general suitability for PET chemistry with only the most promising pairings progressing to full radiochemical assessment. Best results were obtained for the ligation of O-[2-(2-[(18)F]fluoroethoxy)ethyl]-N-methyl-N-hydroxylamine 18 to the maleimidopropionyl-Lys-Gly-Phe-Gly-Lys-OH precursor 10 in acetate buffer (pH 5) after 1 h at 70 degrees C. The non-decay-corrected isolated yield was calculated to be 8.5%. The most encouraging result was observed with the combination 18 and 4-(2-nitrovinyl)benzoyl-Lys-Gly-Phe-Gly-Lys-OH, 9, where the conjugation reaction proceeded rapidly to completion at 30 degrees C after only 5 min. The corresponding non-decay-corrected radiochemical yield for the isolated (18)F-labeled product 27 was 12%. The preliminary results from this study demonstrate the considerable potential of this novel strategy for the radiolabeling of peptides.     

Prey pursuit and interception in dragonflies

Perching dragonflies (Libellulidae; Odonata) are sit-and-wait predators, which take off and pursue small flying insects. To investigate their prey pursuit strategy, we videotaped 36 prey-capture flights of male dragonflies, Erythemis simplicicollis and Leucorrhinia intacta, for frame-by-frame analysis. We found that dragonflies fly directly toward the point of prey interception by steering to minimize the movement of the prey's image on the retina. This behavior could be guided by target-selective descending interneurons which show directionally selective visual responses to small-object movement. We investigated how dragonflies discriminate distance of potential prey. We found a peak in angular velocity of the prey shortly before take-off which might cue the dragonfly to nearby flying targets. Parallax information from head movements was not required for successful prey pursuit. Accepted: 11 November 1999