Diverse speed response properties of motion sensitive neurons in the fly’s optic lobe

Speed and acceleration are fundamental components of visual motion that animals can use to interpret the world. Behavioral studies have established that insects discriminate speed largely independently of contrast and spatial frequency, and physiological recordings suggest that a subset of premotor descending neurons is in this sense speed-selective. Neural substrates and mechanisms of speed selectivity in insects, however, are unknown. Using blow flies Phaenicia sericata, intracellular recordings and dye-fills were obtained from medulla and lobula complex neurons which, though not necessarily speed-selective themselves, are positioned to participate in circuits that produce speed-selectivity in descending neurons. Stimulation with sinusoidally varied grating motion (0–200°/s) provided a range of instantaneous velocities and accelerations. The resulting speed response profiles are indicative of four distinct speed ranges, supporting the hypothesis that the spatiotemporal tuning of mid-level neurons contains sufficient diversity to account for the emergence of speed selectivity at the descending neuron level. This type of mechanism has been proposed to explain speed discrimination in both insects and mammals, but has seemed less likely for insects due to possible constraints on small brains. Two additional recordings are suggestive of acceleration-selectivity, a potentially useful visual capability that is of uncertain functional significance for arthropods.     

Blue lipophorin from Podisus maculiventris

A chromoprotein responsible for the blue coloration of the hemolymph in the spined soldier bug, Podisus maculiventris (Say), was isolated and identified as lipophorin. With the exception of its blue color the lipoprotein shares similar molecular characteristics with the hemolymph lipophorins of other Hemipterans and insects of several different orders. Its ability to carry a blue chromophore, biliverdin IX γ, adds a new feature to this multifunctional lipoprotein. © 1992 Wiley-Liss, Inc.     

Localized adaptation processes in olfactory sensilla of Saturniid moths

Receptor potentials and nerve impulses were recorded extracellularlyfrom the two olfactory cells innervating most sensilla trichodeaon the antenna of male Antheraea polyphemus and Antheraea pemyimoths that respond to two key compounds, the sex pheromone components(E)-6, (Z)-11-hexadecadienyl acetate and (E)-6, (Z)-11-hexadecadienal.Stimulation with the key compound of one receptor cell auto-adaptsthis cell and also cross-adapts the other cell in the same sensillumbut cross-adaptation is weaker than auto-adaptation. Local stimulationexperiments demonstrate that sections of the olfactory receptorcell can be selectively adapted as monitored by the receptorpotential response. The mechanism of impulse generation canadapt separately from the mechanism generating the receptorpotential as indicated by an altered relationship between impulseresponse and receptor potential. These results demonstrate multipleand distributed adaptation processes in an olfactory bipolarneuron as studied in a time domain of seconds. Cross-adaptationmay indicate extracellular alterations caused by excitationof one cell but could also be caused by direct inhibitory actionof the stimulus compound.