Anna Maria Angioy

Macroglomeruli for fruit odors change blend preference in Drosophila

The olfactory circuitry of Drosophila melanogaster is becoming increasingly clear. However, how olfactory processing translates into appropriate behavioral responses is still poorly understood. Using a sibling species approach, we tested how a perturbation in the olfactory circuitry affects odor preference. In a previous study, we found that the sibling species of D. melanogaster, the specialist D. sechellia, overrepresents a sensillum, ab3, the A neuron of which is sensitive to hexanoate esters, characteristic of the species’ sole host, the Morinda citrifolia fruit. Concordantly, the corresponding glomerulus, DM2, is enlarged. In this study, we found that the ab3B neuron, the expansion of which was previously assumed to be pleiotropic and of no ecological significance, is in fact tuned to another morinda fruit volatile, 2-heptanone (HP). Axons of this neuron type arborize in a second enlarged glomerulus. In behavioral experiments we tested how this has affected the fly’s odor preference. We demonstrate that D. sechellia has a reversed preference for the key ligands of these macroglomeruli, especially at high concentrations. Whereas D. melanogaster was repelled by high concentrations of these odors, D. sechellia was highly attracted. This was the case for odors presented singly, but more notably for blends thereof. Our study indicates that relatively simple changes, such as a shift in sensillar abundance, and concordant shifts in glomerular size, can distort the resulting olfactory code, and can lead to saltatory shifts in odor preference. D. sechellia has exploited this to align its olfactory preference with its ecological niche.

NEW INSIGHT INTO THE ANTENNAL CHEMOSENSORY FUNCTION OF OPIUS CONCOLOR (HYMENOPTERA, BRACONIDAE)

Abstract The presence of taste and olfactory chemosensilla is demonstrated by using both morphological and electrophysiological techniques on antennae of Opius concolor, a parasitoid of tephritid larvae. Observation under the Scanning Electron Microscope revealed the presence of large sensilla trichodea with an apical pore, and of flat plates (sensilla placodea) extending almost the entire length of each antennomere. By means of currently used electrophysiological techniques, it was possible to record both the gustatory activity generated by sensilla trichodea following contact with KC1 100 mM and sucrose 100 mM solutions, and olfactory activity probably generated by sensilla placodea in response to volatile stimuli. The analysis of gustatory activity showed that each sensillum trichodeum consisted of at least three chemosensory units. This supports the assumption that in O. concolor single sensilla may, by providing different spike discharge patterns, which depend on the quality and intensity of the stim...

Influence of age on the electroantennogram response of the female blowfly (Phormia regina) (Diptera: Calliphoridae)

Abstract By means of electroantennogram recording techniques, we have monitored the antennal olfactory sensitivity, from the time of eclosion until complete egg maturation, of female blowflies (Phormia regina) fed either a protein diet or a protein free one. The tested stimuli were swormlure-4 (SL-4) which is a potent lure for calliphorid flies, 1-hexanol as a reference stimulus and air as a control. After taking the electroantennograms, egg and ovarian development were evaluated. Stimulation with SL-4 and 1-hexanol evoked electroantennograms increasing in amplitude with age regardless of whether or not flies were fed protein during the first 5 days of adult life. In the protein-fed flies eggs were fully developed whereas those of the no-protein group remained undeveloped. The peak olfactory sensitivity occurs at a time when the female fly begins to search for an oviposition substrate.

Morphology and EAG mapping of the antennal olfactory receptors in Dacus oleae

EAGs were recorded from various locations on the flagellar surface of the antennae of the olive fly Dacus oleae stimulated with compounds of behavioural significance to this species. This information was compared with data on the typology and distribution patterns of the olfactory sensilla. Results showed that: a) 3 types of olfactory sensilla are present on the antennae: long basiconica, short grooved basiconica and trichodea; b) 1‐hexanol, ethanol and volatiles belonging to the oily fraction of the olive pulp are the strongest stimuli, while those of the water fraction are little or not effective; c) EAG amplitude values vary as a function of the recording location on the flagellar surface; d) a significant correlation was found, for 2 stimuli of the oily fraction, between EAG amplitude and population density of long sensilla basiconica, thus suggesting this type as specifically responding to these substances.

Reflex cardiac response to various olfactory stimuli in the blowfly, Protophormia terraenovae

In the present investigation it is shown that a reflex change in the heart activity of Protophormia flies is evoked by olfactory stimulation with several volatile substances, and particularly with those which are repellent for blowflies. Among these, i-pentanal and hexanal vapours evoked a fast, highly persistent cardiac response, whereas in the case of hexanol and ammonia vapours the response resulted slower and could be suppressed as a function of repeated stimulation.

Olfaction in the female sheep botfly

The nasal botfly Oestrus ovis (Diptera, Cyclorrhapha: Oestridae) is a myiasis-causing insect species, which affects the health of sheep, goats and humans. Gravid females are viviparous and larviposit into the animal’s nostrils. Host-searching and larvipositing flies are visually guided and influenced by climatic conditions, whereas olfaction seemed to play no role in this process. However, here, we show that the antennae of adult O. ovis female flies are relatively small but well developed and inhabited by several types of olfactory sensilla. Further, we show that the antennal lobes of this species receive input from antennal afferents and consist of a clearly defined glomerular organisation. We also give the first evidence of the fly’s ability to detect several synthetic odour compounds. Our findings provide a morpho-functional basis for future investigations on olfactory-mediated behaviour of this insect pest.

Impaired sense of smell in a Drosophila Parkinson's model.

Parkinson’s disease (PD) is one of the most common neurodegenerative disease characterized by the clinical triad: tremor, akinesia and rigidity. Several studies have suggested that PD patients show disturbances in olfaction at the earliest onset of the disease. The fruit fly Drosophila melanogaster is becoming a powerful model organism to study neurodegenerative diseases. We sought to use this system to explore olfactory dysfunction, if any, in PINK1 mutants, which is a model for PD. PINK1 mutants display many important diagnostic symptoms of the disease such as akinetic motor behavior. In the present study, we describe for the first time, to the best of our knowledge, neurophysiological and neuroanatomical results concerning the olfactory function in PINK1 mutant flies. Electroantennograms were recorded in response to synthetic and natural volatiles (essential oils) from groups of PINK1 mutant adults at three different time points in their life cycle: one from 3–5 day-old flies, from 15–20 and from 27–30 days. The results obtained were compared with the same age-groups of wild type flies. We found that mutant adults showed a decrease in the olfactory response to 1-hexanol, α-pinene and essential oil volatiles. This olfactory response in mutant adults decreased even more as the flies aged. Immunohistological analysis of the antennal lobes in these mutants revealed structural abnormalities, especially in the expression of Bruchpilot protein, a marker for synaptic active zones. The combination of electrophysiological and morphological results suggests that the altered synaptic organization may be due to a neurodegenerative process. Our results indicate that this model can be used as a tool for understanding PD pathogensis and pathophysiology. These results help to explore the potential of using olfaction as a means of monitoring PD progression and developing new treatments.

Reflex cardiac response to a feeding stimulus in the blowfly Calliphora vomitoria L.

Abstract Evidence is presented on the effectiveness of taste chemosensory stimulation in evoking reflex heart-beat reversal in the blowfly, Calliphora vomitoria L. Electrophysiological activity of the heart and input from stimulated taste sensilla were simultaneously recorded in intact and operated insects. The reflex cardiac response to taste stimulation could still be evoked in headless flies and after transection at the abdominal level of nerve fibres running to the heart. Upon repeated stimulation, the cardiac reflex was abolished in intact insects, while it was persistently evoked even on performing iterative stimulations in operated insects. It is suggested that cephalic ganglia regulate the degree of excitation of the thoracicoabdominal ganglion which, on the incoming input from taste chemosensilla, actually promotes reflex heart-beat reversal in this insect.

Cyclic sensitivity variations in the labellar chemosensilla ofCalliphora

Cyclic variations in the sensitivity of labellar chemosensilla are time-related to ovarian development inCalliphora. It is assumed that a single endocrine mechanism controls both sensitivity of chemosensilla and ovarian function.

Neuropeptide F peptides act through unique signaling pathways to affect cardiac activity

Elucidating how neuropeptides affect physiology may result in delineating peptidergic mechanisms and identifying antagonists for application in basic and translational science. Human neuropeptide Y (NPY) regulates cardiac activity; frequently invertebrates contain orthologs of vertebrate peptides. We report invertebrate NPY-like neuropeptide F (NPF) arrested the signal frequency of the slow phase of the cardiac cycle (EC50 = 1 pM); however, signal frequency of the fast phase was affected only minimally. Neuropeptide F decreased the duration of the slow phase by ~70% (EC50 = 0.6 pM), but increased the duration of the fast phase by ~57% (EC50 = 10nM). Short NPF-1 (sNPF-1) decreased the signal frequency of the slow phase by ~70% (EC50 = 9 nM); yet, signal frequency of the fast phase was unaffected. Short NPF-1 decreased the duration of the slow phase ~55% (EC50 ~50 nM), but increased the duration of the fast phase ~20% without dose dependency. Neuropeptide F and sNPF-1 increased isoelectric period duration. This novel report demonstrated NPY-like peptides are cardioactive but functionally unique. These data contribute to understanding how invertebrate orthologs affect cardiovascular activity. Dipteran fast and slow phases may be generated from separate pacemakers in the abdominal heart and in the anterior thoracocephalic aorta, respectively. Thus, our research suggests NPF and sNPF-1 act through different mechanisms to regulate cardiac activity. Invertebrate NPY-like peptides act in olfaction and feeding yet mechanisms which are associated with their cardioactive effects remain unknown; our work may provide evidence linking their roles in sensory response and cardiac activity.