Neuronal Basis of Innate Olfactory Attraction to Ethanol in Drosophila

The decision to move towards a mating partner or a food source is essential for life. The mechanisms underlying these behaviors are not well understood. Here, we investigated the role of octopamine – the invertebrate analogue of noradrenaline – in innate olfactory attraction to ethanol. We confirmed that preference is caused via an olfactory stimulus by dissecting the function of the olfactory co-receptor Orco (formally known as OR83b). Orco function is not required for ethanol recognition per se, however it plays a role in context dependent recognition of ethanol. Odor-evoked ethanol preference requires the function of Tbh (Tyramine β hydroxalyse), the rate-limiting enzyme of octopamine synthesis. In addition, neuronal activity in a subset of octopaminergic neurons is necessary for olfactory ethanol preference. Notably, a specific neuronal activation pattern of tyraminergic/octopaminergic neurons elicit preference and is therefore sufficient to induce preference. In contrast, dopamine dependent increase in locomotor activity is not sufficient for olfactory ethanol preference. Consistent with the role of noradrenaline in mammalian drug induced rewards, we provide evidence that in adult Drosophila the octopaminergic neurotransmitter functions as a reinforcer and that the molecular dissection of the innate attraction to ethanol uncovers the basic properties of a response selection system.     

Antennal sensory organs in the millipede Eurypauropus ornatus: Fine structure of the flagella and globulus

On the antennal tip of Eurypauropus ornatus are 3 threadlike sensilla—the flagella, and a single spheroid sensillum—the globulus. Each of the 3 flagella is innervated by 2 groups of sensory cells. One group contains 4 cells, the other, 5. All cells of the “four group” and 3 of the “five group” are comprised of single cilia and unbranched dendrites which extend along the lumen of the flagellum. Two cells of the “five group” have double cilia and pairs of unbranched dendrites. One pair also enters the flagellum and the other pair terminates beneath the flagellar base to form a concentric array of lamellae. No pores are present in the cuticular wall. Eight sensory cells innervate the globulus. They are arranged in 3 groups, one triplet and 2 pairs, in addition to a single cell. The single cell contains a pair of cilia whose unbranched dendrites differentiate into tubular bodies that are inserted into the base of the globulus. Each of the other 7 sensory cells has a single cilium. Their unbranched dendrites penetrate into the globulus in 3 groups as described for the sensory cells. The dendrites in each group terminate in an individual pore channel at the globulus tip and completely fuse with the electron-dense material that plugs the pore channel. Based on structural similarities to sensilla having known functions, it is probable that the flagella and the globulus are chemoreceptors, the former responding to odors, the latter sensitive to substances in aqueous solution.     

Sexual differentiation in Mucor: Trisporic acid response mutants and mutants blocked in zygospore development

Spores of a minus strain of Mucor mucedo (Bref.) were treated with 1-methyl-[3-nitro]-1-nitro-soguanidine and mutants were isolated either by testing for zygophore induction with externally supplied trisporic acids (TA) or by mating with wild type plus colonies. Mutants were found defective (Tar^?) or temperature-sensitive (Tar-Ts) in their reaction towards trisporic acids, blocked or temperature-sensitive in their mating with plus strain (Mat^? or Mat-Ts) or temperature-sensitive in zygospore development (Zyg-Ts). The inability to react against externally supplied trisporic acids was not necessarily coupled with an inability to mate with plus strain (phenotype Tar^? Mat⁺). This indicated that the diffusion and uptake of trisporic acids is not a necessary prerequisite to the sexual interaction of Mucor mating types.     

Inositol Phospholipid Hydrolysis by Rat Sciatic Nerve Phospholipase C

Rat sciatic nerve cytosol contains a phosphodiesterase of the phospholipase C type that catalyzes the hydrolysis of inositol phospholipids, with preferences of phosphatidylinositol 4'-phosphate (PIP) greater than phosphatidylinositol (PI) much greater than phosphatidylinositol 4',5'-bisphosphate (PIP2), at a pH optimum of 5.5-6.0 and at maximum rates of 55, 13, and 0.7 nmol/min/mg protein, respectively. Analysis of reaction products by TLC and formate exchange chromatography shows that inositol 1,2-cyclic phosphate (83%) and diacylglycerol are the major products of PI hydrolysis. [32P]-PIP hydrolysis yields inositol bisphosphate, inositol phosphate, and inorganic phosphate, indicating the presence of phosphodiesterase, phosphomonoesterase, and/or inositol phosphate phosphatase activities in nerve cytosol. Phosphodiesterase activity is Ca2+-dependent and completely inhibited by EGTA, but phosphomonoesterase activity is independent of divalent cations or chelating agents. Phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) inhibit PI hydrolysis. They stimulate PIP and PIP2 hydrolysis up to equimolar concentrations, but are inhibitory at higher concentrations. Both diacylglycerols and free fatty acids stimulate PI hydrolysis and counteract its inhibition by PC and lysoPC. PIP2 is a poor substrate for the cytosolic phospholipase C and strongly inhibits hydrolysis of PI. However, it enhances PIP hydrolysis up to an equimolar concentration.     

Correlation between thrombin-induced prostacyclin production and inositol trisphosphate and cytosolic free calcium levels in cultured human endothelial cells

Cultured human umbilical vein endothelial cells (HUVEC) stimulated with thrombin are known to synthesize prostacyclin at least in part from arachidonate released by phospholipase A2, an enzyme directly activated by calcium. In this study, thrombin stimulation of Quin 2-loaded HUVEC caused rapid and dose-dependent rises in inositol trisphosphate (IP3) and cytosolic free calcium (Ca2+i) levels which preceded a similarly dose-dependent rise in prostacyclin production measured as 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) by radioimmunoassay (ED50 = 0.6-0.7 units/ml for all three effects). Thrombin induced these effects in the absence of extracellular calcium (EGTA) or in the presence of either 8-bromo-cAMP or the calmodulin inhibitor W7. Thrombin inactivated with either diisopropyl fluorophosphate or D-Phe-Pro-Arg-chloromethyl ketone was inactive. In contrast, Quin 2-loaded cultured bovine aortic endothelial cells failed to respond to thrombin, although stimulation with trypsin elevated IP3 and Ca2+i levels and increased 6-keto-PGF1 alpha production. Restimulation of HUVEC with thrombin or histamine 5 min after an initial stimulation with thrombin (2 units/ml for 5 min) failed to induce a second rise in either IP3 or Ca2+i levels or further production of 6-keto-PGF1 alpha, whereas restimulation with ionomycin in the presence or absence of extracellular calcium elevated Ca2+i levels and induced further 6-keto-PGF1 alpha production. However, if the initial stimulation with thrombin was terminated by addition of D-Phe-Pro-Arg-chloromethyl ketone within 10-60 s, restimulation with a second dose of thrombin induced second rises in both IP3 and Ca2+i levels and additional 6-keto-PGF1 alpha production that were greatest when the initial thrombin stimulus was briefest. These results are consistent with the conclusion that IP3 acts as a second messenger by which thrombin elevates Ca2+i levels and initiates prostacyclin synthesis in HUVEC and that in vivo endothelial cells may be stimulated multiple times to synthesize prostacyclin if each period of stimulation is brief.     

Hygroreceptor identification and response characteristics in the stick insectCarausius morosus

Summary Simultaneous recordings were made from 3 sensory units in an easily identifiable sensillum on the 12th antennal segment ofCarausius morosus. Impulse frequency (F) of one unit rose sharply when either the temperature (T) or the partial pressure of water vapor (Pw) was suddenly lowered. F of another rose sharply either when T was suddenly lowered or Pw was raised. F of the third was hardly affected by sudden changes in T but rose abruptly when Pw fell (Fig. 1). The reactions of the first may be explained by enthalpic cooling and is considered a cold cell. Those of the second may be attributed to changes in relative humidity (Hr) and is thus termed a moist cell. The third is taken to be the latter's antagonist, a dry cell.A 90%-probability that a single moist cell of average differential sensitivity will correctly discriminate between two humidity levels is not reached until the difference between the two is 38% Hr. The dry cell requires a difference of only 7.5% (Table 1). The basis for discrimination is a single presentation of each level.The power to discriminate Hr steps is better in both cell types. For a single moist cell of average differential sensitivity the difference required between the steps for a 90%-probability of correct discrimination is only 6.3% Hr; for the dry cell, 3.5% Hr. Basis for discrimination: a single presentation of each step. Step range: 5% to 55% Hr.Abbreviations F impulse frequency in impulses per second (imp/s) - Hr orHR relative humidity in % - Ps saturation pressure of water vapor in torr - Pw partial pressure of water vapor in torr - r correlation coefficient - T temperature in °C Dedicated to Prof. Dr. F. Schaller on the occasion of his 65th birthday