Octopamine modulates the sensitivity of silkmoth pheromone receptor neurons

Effects of octopamine and its antagonist epinastine on electrophysiological responses of receptor neurons of Antheraea polyphemus specialised to the pheromone components (E,Z)-6,11-hexadecadienyl acetate and (E,Z)-6,11-hexadecadienal were investigated. Injections of octopamine and epinastine into the moths had no effect on the transepithelial potential of the antennal-branch preparation nor on the spontaneous nerve impulse frequency in either type of receptor neuron. However, in the presence of continuous low-intensity pheromone stimulation, octopamine significantly increased the nerve impulse frequency in the acetate receptor neuron, but not in the aldehyde receptor neuron. Octopamine and epinastine had no significant effect on the receptor potential amplitudes elicited in both receptor neuron types by pheromone stimulation. However, the peak nerve impulse frequency in the response of both receptor neuron types to pheromone was significantly affected: decreased by epinastine and increased by octopamine over a broad range of pheromone concentrations. In control experiments, injection of physiological saline did not significantly alter the peak nerve impulse frequency. The effect of octopamine was established within 1 h after injection and persisted for about 4 h. The possibility of a direct action of octopamine on the nerve impulse generation by the receptor neurons is discussed. Accepted: 8 January 2000     

Sex pheromone and plant-associated odour processing in antennal lobe interneurons of male Spodoptera littoralis (Lepidoptera: Noctuidae)

Antennal lobe interneurons of male Spodoptera littoralis (Boisd.) were investigated by using intracellular recording and staining techniques. Physiological and morphological characteristics of local interneurons and projection neurons responding to sex pheromone and plant-associated volatiles are described. The interneurons identified were divided into three groups, depending on their physiological response characteristics. Both types of interneurons, local interneurons and projection neurons, were described in all three groups. 1. Interneurons responding exclusively to sex pheromone stimuli, displayed different degrees of specificity. These neurons responded to either one, two, three or all four of the single sex pheromone or sex pheromone-like compounds tested. Most of these neurons also responded to a mixture of the two pheromone components present in the female S. littoralis blend. Two local interneurons and one projection neuron were identified as blend specialists, not responding to the single female produced sex pheromone components, but only to their mixture. Five pheromone specific projection neurons arborized in one or more subcompartments of the macroglomercular complex (MGC) and some of them had axonal branches in the calyces of the mushroom body and in different parts of the lateral protocerebrum. 2. Interneurons responding only to plant-associated volatiles varied highly in specificity. Neurons responding to only one of the stimuli, neurons responding to a variety of different odours and one neuron responding to all stimuli tested, were found. Three specialized local interneurons had arborizations only in ordinary glomeruli. One specialized and three less specialized local interneurons had arborizations within the MGC and the ordinary glomeruli. The projection neurons responding only to plant-associated volatiles had mostly uni- or multiglomerular arborizations within the ordinary glomeruli. 3. Interneurons responding to both sex pheromones and plant-associated stimuli varied in specificity. Individual interneurons that responded to few plant-associated odours mostly responded to several pheromone stimuli as well. Projection neurons responding to most of the plant-associated volatiles also responded to all pheromone stimuli. Two local interneurons responding to both stimulus groups, arborized within the MGC and the ordinary glomeruli. Projection neurons mostly arborized in only one ordinary glomerulus or in one compartment of the MGC. The variation in specificity and sensitivity of antennal lobe interneurons and structure-function correlations are discussed.     

The physiology of an olfactory sensillum of the termite Schedorhinotermes lamanianus: carbon dioxide as a modulator of olfactory sensitivity

There are three morphological types of wall-pore single-walled sensilla on the antennae of Schedorhinotermes lamanianus workers. Among these, the sensilla of the type SW1 always bear two neurons that are distinguishable by their impulse amplitudes in electrophysiological recordings. Both neurons are odour-sensitive and respond with excitation to an equally narrow and strikingly congruent spectrum of odours. 1-Pentanol, 1-hexanol and 2-hexanol cause maximum excitation in both cells. In addition one cell responds to CO₂. Short pulses of CO₂ up to 3 s duration inhibit this cell totally. The duration of total inhibition increases with the logarithm of the CO₂-concentration between 0.06% and 100%. Pulses of CO₂ with concentrations above 0.15% cause an inhibition that lasts longer than the period of stimulation. Prolonged CO₂ -stimuli (> 300 s) with a concentration between 0.5% and 5% CO₂ initially cause total inhibition. However, after 1 to 5 min, activity reappears and reaches a new constant but dose-dependent frequency. None of the stimulatory odours leads to a response in the cell when applied together with CO₂. The sensitivity to odours of this one cell type is switched off by CO₂, whilst CO₂ does not influence the other neuron in the same sensillum. The CO₂-concentration, (high in the centres of termite nests, low outside the nests) may give important information about the context in which an individual receives a signal. The described modulation of odoursensitivity by CO₂ allows the presentation of two hypothetical mechanisms of context-dependent signal interpretation.     

Processing of antennular input in the brain of the spiny lobster, Panulirus argus

Neurons in the olfactory deutocerebrum of the spiny lobster, Panulirus argus, were recorded intracellularly and filled with biocytin. Recorded neurons arborized in the olfactory lobe (OL), a glomerular neuropil innervated by olfactory and some presumptive mechanosensory antennular afferents. The neurons responded to chemosensory input from the lateral antennular flagellum bearing the olfactory sensilla but not the medial flagellum bearing many non-olfactory chemosensory sensilla. Many neurons received additional mechanosensory input. Thus the OL integrates specifically olfactory with mechanosensory input. OL neurons had multiglomerular arborizations restricted to one or two of the three horizontal layers of the columnar glomeruli. OL local interneurons comprised core neurons with tree-like neurites and terminals in the base of the glomeruli and rim neurons with neurites surrounding the OL and terminals in the cap/subcap. The somata of OL local interneurons lay in the medial soma cluster (100000 somata). OL projection neurons arborized in the base of the glomeruli and ascended via the olfactory glomerular tract to the lateral protocerebrum. A parallel projection pathway is constituted by projection neurons of the accessory lobe, a glomerular neuropil without afferent innervation but intimate links to the OL. The projection neuron somata constituted the lateral soma cluster (200000 somata).Abbreviations AC anterior cluster (cluster 6,7) - AL accessory lobe - aMC anterior subcluster of medial cluster (cluster 9) - A _lNv main antenna I (antennular) nerve - A _lNM antenna I (antennular) motor nerve - A _llNv main antenna II (antennal) nerve - CB central body - CL central layer of accessory lobe - DC deutocerebral commissure - DCN deutocerebral commissure neuropil - dDUMC dorsal subcluster of dorsal unpaired median cluster (cluster 17) - dMC dorsal subcluster of medial cluster (cluster 11) - dVPALC dorsal subcluster of ventral paired anterolateral cluster (cluster 8) G glomerulus - IDUMC lateral subcluster of dorsal unpaired median cluster (cluster 16) - LC lateral cluster (cluster 10) - LF lateral flagellum of antenna I (antennule) - LL lateral layer of accessory lobe - MF medial flagellum of antenna I (antennule) - ML medial layer of accessory lobe - MPN anterior and posterior median protocerebral neuropils - OGT olfactory globular tract - OGTN olfactory globular tract neuropil - OL olfactory lobe - OLALT olfactory lobe-accessory lobe tract - PB protocerebral bridge - pMC posterior subcluster of medial cluster (cluster 9) - PT protocerebral tract - TNv tegumentary nerve - VPMC ventral paired medial cluster (cluster 12) - VUMC ventral unpaired medial cluster (cluster 13) - vVPALC ventral subcluster of ventral paired anterolateral cluster (cluster 8) - ASW artificial sea water - M3 mixture 3 - PRO L-proline - TM TetraMarin extract     

The ultrastructure of the vomero-nasal organ in reptilia

Summary There are three types of cells in the vomero-nasal organ of Lacerta sicula and Natrix natrix: receptor cells, supporting cells and basal cells. The receptor cells bear microvilli and no cilia. In Lacerta centrioles are lacking, indicating that the ciliary apparatus can have no essential significance in the transducer process. In Natrix centrioles occur in the deeper dendritic region. The structural constituents of the dendrites are mitochondria, microtubules and characteristic vesicles the properties of which are described. The perikarya which have uniform structure send off axons of about 0.2 diameter. The supporting cells show signs of a very moderate secretory activity, which is different among the species investigated. The microvilli of the supporting cells are not distinguishable from those of the receptor cells. The dendrites of the latter are completely isolated by the apical parts of the supporting cells. The sheet-like processes of the supporting cells contain strands of tonofilaments and do not cover the perikarya of the receptor cells completely. Thus adjacent sensory cells or dendrites and sensory cells are separated among themselves only by the normal intercellular space. The ratio of sensory cells to supporting cells is about 71. The basal cells resemble the supporting cells and replace these in the lower portion of the epithelium. The typical cellular junctions between sensory cells and supporting cells are described. There are no true tight junctions in the vomero-nasal sensory epithelium, and they are most probably absent from the nasal mucosa too. This absence would seem to indicate special conditions for cellular communication and the accessibility of the intercellular space for certain molecules. There is no sign of regeneration of sensory cells. Both immature blastema cells and degenerating receptor cells are not discernible.     

Biochemistry of an Olfactory Purinergic System: Dephosphorylation of Excitatory Nucleotides and Uptake of Adenosine

Abstract: The olfactory organ of the spiny lobster, Panu-lirus argus , is composed of chemosensory sensilla containing the dendrites of primary chemosensory neurons. Receptors on these dendrites are activated by the nucleotides AMP, ADP, and ATP but not by the nucleoside adenosine. It is shown here that the lobster chemosensory sensilla contain enzymes that dephosphorylate excitatory nucleotides and an uptake system that internalizes the nonexcitatory dephosphorylated product adenosine. The uptake of [³H]-adenosine is saturable with increasing concentration, linear with time for up to 3h, sodium dependent, insensitive to moderate pH changes and has a K _m of 7.1 μ M and a V_max of 5.2 fmol/sensillum/min (573 fmol/μg of protein/min). Double-label experiments show that sensilla dephosphorylate nucleotides extracellularly; ³H from adenine-labeled AMP or ATP is internalized, whereas ³²P from phosphate-labeled nucleotides is not. The dephosphorylation of AMP is very rapid; ³H from AMP is internalized at the same rate as ³H from adenosine. Sensillar 5'-ectonucleotidase activity is inhibited by ADP and the ADP analog α,β-methylene ADP. Collectively, these results indicate that the enizymes and the uptake system whereby chemosensory sensilla of the lobster inactivate excitatory nucleotides and clear adenosine from extracellular spaces are very similar to those present in the internal tissues of vertebrates, where nucleotides have many neuroactive effects.     

Der Feinbau olfaktorischer Sensillen des Seidenspinners (Insecta,Lepidoptera)

Zusammenfassung Die Sensilla (S.) trichodea und S. basiconica auf den Antennen des Seidenspinners,Bombyx mori, wurden nach chemischer Fixierung, Gefriersubstitution und Gefrierätzung im Transmissionselektronenmikroskop untersucht. Es lassen sich fünf Typen von Sensillen unterscheiden, deren olfaktorische Funktion aus elektrophysiologischen Versuchen bekannt ist, mit Ausnahme des letzten Typs.Lange S. trichodea undhalblange S. trichodea I sind jeweils von zwei Sinneszellen innerviert, deren Rezeptorfortsätze (Dendriten) im wesentlichen unverzweigt bleiben. Diegroßen S. basiconica haben meist drei, diekleinen S. basiconica nur eine Sinneszelle; die Dendriten dieser Rezeptorzellen verzweigen sich büschelförmig beim Eintritt in das Haarlumen. Erstmals wird ein Zwischentyp beschrieben: diehalblangen S. trichodea II ähneln hinsichtlich der Innervation den S. basiconica, sind aber wegen der Form und Größe des Sinneshaars als S. trichodea zu klassifizieren. Für jeden Typ werden die Abmessungen der Rezeptorfortsätze sowie die Zahl und Verteilung der reizleitenden Poren und Porentubuli in der Haarwand angegeben.Auf der männlichen Antenne sind die langen S. trichodea am zahlreichsten; sie enthalten hochempfindliche Sexuallockstoffrezeptoren (mittlere Anzahl pro Antenne: 17 000 Sensillen mit 34 000 Sinneszellen). Beim Weibchen sind diese Sensillen in der Zahl auf etwa 35% reduziert und mit Sinneszellen anderer Spezifität und geringerer Empfindlichkeit ausgerüstet. Die beiden Dendriten der langen S. trichodea unterscheiden sich bei beiden Geschlechtern stark im mittleren Durchmesser und der Anzahl der cytoplasmatischen Mikrotubuli; beim Männchen reichen beide bis zur Haarspitze, beim Weibchen endet der dünnere Fortsatz bereits im proximalen Haardrittel. Die Cuticula der Sinneshaare ist von Poren durchbrochen (: 2–7 Poren/²; : 2–5 Poren/²), die stets in der Nähe von charakteristischen Stufen in der Haaroberfläche münden. Jeder Porenkanal führt in ca. fünf Porentubuli, die bis ins Haarlumen reichen und dort enden, zum Teil in Kontakt mit der Rezeptormembran der Dendriten. Die Häufigkeit solcher Tubulus-Membrankontakte ist in distalen Haarabschnitten größer als in proximalen. Der dickere Dendrit weist etwa viermal so viel Kontakte auf wie der dünnere. Die beiden Rezeptorzellen dieser Sensillen stellen funktionell verschiedene Reaktionstypen dar, was mit den beobachteten morphologischen Unterschieden zusam menhängen dürfte.Die S. basiconica haben 20 Poren pro ² ihrer Oberfläche und 12–23 Porentubuli pro Pore; dadurch erreichen oder übertreffen sie die viel größeren S. trichodea in der Gesamtzahl der Porentubuli pro Sinneshaar. Auf den S. trichodea steigt die Zahl der Poren pro Oberflächeneinheit zur Spitze hin stetig an, während die Zahl der Poren pro Haarlängeneinheit einen konstanten Wert annimmt. Eine Hypothese über die Morphogenese dieser Verteilung wird aufgestellt.Die funktionelle Bedeutung der äußeren Epicuticulaschichten und der Porentubulussysteme für die Reizleitung wird diskutiert. Ausgehend von beliebigen Orten ihres Auftreffens auf dem Sinneshaar können die Duftmoleküle zunächst durch zweidimensionale Diffusion entlang der Haaroberfläche zu den Poren gelangen und anschließend durch eindimensionale Diffusion über Porenkanäle und Porentubuli die Rezeptormembran erreichen. Die berechneten Diffusionszeiten sind kürzer als die bekannten Rezeptorlatenzen; die Reizleitung kann also durch Diffusion hinreichend erklärt werden und erfordert keine kompliziertere Hypothese.

---

The fine structure of olfactory sensilla in the silk moth (insecta, lepidoptera)

Summary The sensilla (s). trichodea and s. basiconica on the antennae of the silk moth,Bombyx mori, were studied under the transmission electron microscope. Chemical fixation, freeze substitution and freeze etching methods were used. The following results have been obtained: Five sensillum types were distinguished, the olfactory function of which is known from electrophysiological recordings, except for the last one. Thelong s. trichodea and themedium-sized s. trichodea I are innervated by two sensory cells which have essentially unbranched receptor processes (dendrites). Commonly thelarge s. basiconica contain three sensory cells, thesmall s. basiconica only one; the dendrite of these receptor cells branch multiply when entering the hair lumen. For the first time an intermediate type has been described: themedium-sized s. trichodea II, which resemble the s. basiconica in their branching innervation, but must be classified as s. trichodea because of the form and size of the sense hair. For each type, the dimensions of the receptor processes, as well as the number and distribution of the stimulus conducting pores and pore tubules in the hair wall are noted.On the male antenna the long s. trichodea are most abundant; they contain the highly sensitive sex pheromone receptors (mean number per antenna: 17 000 sensilla with 34 000 sense cells). In the female these sensilla are reduced in number to about 35% and supplied with receptor cells of different specificity and lower sensitivity. In both sexes, the two dendrites of the long s. trichodea differ markedly in their mean diameter, and the number of cytoplasmatic microtubules. In the male moth both receptor processes reach the hair tip, whereas in the female the thinner one invades only the proximal third of the sense hair. The cuticle of the hair wall is perforated by pores (: 2–7 pores per ²; : 2–5 pores per ²), which mostly open to the outside near to characteristic steps in the hair surface. Each pore canal leads into about five pore tubules, which proceed towards the hair lumen, where they end, partly in contact with the receptor membrane of the dendrites. Distal parts of the sense hairs show such tubule-membrane contacts more frequently than proximal regions. The number of contacts counted on the thicker dendrite is about four times greater than on the thinner one. In these sensilla, the two receptor cells constitute functionally different reaction types, which may relate to the observed morphological differences.The s. basiconica have about 20 pores per ² of the hair surface, and 12–23 pore tubules per pore: thus, these sensilla have the same or even a greater number of pore tubules per sensillum than the much larger s. trichodea. In the s. trichodea the number of pores per unit surface increases steadily towars the hair tip, while the number of pores per unit length of the hairs soon reaches a constant value. A hypothesis about the morphogenesis of this distribution is given.The functional significance of the epicuticular surface layers and of the pore tubule systems is discussed under the aspect of stimulus conduction. Starting from the site of impact anywhere on the sense hair, odour molecules may diffuse two-dimensionally along the hair surface to the pores, and then proceed by one-dimensional diffusion through pore canals and pore tubules until they eventually reach the receptor membrane at the end of a tubule. The calculated conduction times are shorter than the known receptor latencies; thus, the transport mechanism can be explained by diffusion and does not need a more complex hypothesis.

Ich danke Frl. B. Müller für ihre stete, sorgfältige Hilfe, Prof. L. Bachmann und Dr. W. Schmitt von der TU München für die Benützungsmöglichkeit der Gefrierätzanlage und ihren erfahrenen Rat, Dr. G. Adam von der Universität Konstanz sowie meinen Seewiesener Kollegen, Dr. W. A. Kafka, Dr. K.-E. Kaissling und Dr. E. Priesner, für viele anregende Diskussionen und konstruktive Kritik.     

Ammonia attracts the haematophagous bug Triatoma infestans : behavioural and neurophysiological data on nymphs

1) Nymphs of the haematophagous bug Triatoma infestans (Heteroptera: Reduviidae) are attracted to volatiles from their own faeces on a servosphere. 2) Biological substrates attractive to triatomines release NH₃: wetted triatomine faecal papers release NH₃ at 256 ppb NH₃ from a 60-g source and stale rabbit urine at 394 ppb from 200 ml. Ammonia released from aqueous NH₃ also attracts bugs at doses of 3 ppb and 17 ppb on the servosphere. 3) Bugs typically show negative anemotaxis in a stimulus-free air-stream on the servosphere. At onset of stimulation with ammonia from either biological substrates or aqueous NH₃ the bugs stop, move their antennae, turn and walk upwind, i.e. odour-mediated anemotaxis. 4) At lower NH₃ doses a latency in attraction is recorded, but this latency disappears when the relative humidity of the stimulus delivery air-stream is dropped from 90 to 35%. 5) Electrophysiological recordings from single olfactory sensilla on antennae of Triatoma nymphs reveal two different types of NH₃-excited receptors, both within grooved-peg sensilla. The responses of one of these receptor cells to NH₃ has been studied in detail and shows that the action potential discharge rate is dose-dependent over the range 2–200 ppb. 6) The amplitudes of electroantennograms recorded from Triatoma nymphs to NH₃ are dose dependent over the range 5–550 ppb. Accepted: 16 January 1997     

The organization of the chemosensory system in Drosophila melanogaster: a rewiew

This review surveys the organization of the olfactory and gustatory systems in the imago and in the larva of Drosophila melanogaster, both at the sensory and the central level. Olfactory epithelia of the adult are located primarily on the third antennal segment (funiculus) and on the maxillary palps. About 200 basiconic (BS), 150 trichoid (TS) and 60 coeloconic sensilla (CS) cover the surface of the funiculus, and an additional 60 BS are located on the maxillary palps. Males possess about 30% more TS but 20% fewer BS than females. All these sensilla are multineuronal; they may be purely olfactory or multimodal with an olfactory component. Antennal and maxillary afferents converge onto approximately 35 glomeruli within the antennal lobe. These projections obey precise rules: individual fibers are glomerulus-specific, and different types of sensilla are associated with particular subsets of glomeruli. Possible functions of antennal glomeruli are discussed. In contrast to olfactory sensilla, gustatory sensilla of the imago are located at many sites, including the labellum, the pharynx, the legs, the wing margin and the female genitalia. Each of these sensory sites has its own central target. Taste sensilla are usually composed of one mechano-and three chemosensory neurons. Individual chemosensory neurons within a sensillum respond to distinct subsets of molecules and project into different central target regions. The chemosensory system of the larva is much simpler and consists essentially of three major sensillar complexes on the cephalic lobe, the dorsal, terminal and ventral organs, and a series of pharyngeal sensilla.     

Receptor-transporting protein 1 short (RTP1S) mediates translocation and activation of odorant receptors by acting through multiple steps

Odorant receptor (OR) proteins are retained in the endoplasmic reticulum when heterologously expressed in cultured cells of non-olfactory origins. RTP1S is an accessory protein to mammalian ORs and facilitates their trafficking to the cell-surface membrane and ligand-induced responses in heterologous cells. The mechanism by which RTP1S promotes the functional expression of ORs remains poorly understood. To obtain a better understanding of the role(s) of RTP1S, we performed a series of structure-function analyses of RTP1S in HEK293T cells. By constructing RTP1S deletion and chimera series and subsequently introducing single-site mutations into the protein, we found the N terminus of RTP1S is important for the endoplasmic reticulum exit of ORs and that a middle region of RTP1S is important for OR trafficking from the Golgi to the membrane. Using sucrose gradient centrifugation, we found that the localization of RTP1S to the lipid raft microdomain is critical to the activation of ORs. Finally, in a protein-protein interaction analysis, we determined that the C terminus of RTP1S may be interacting with ORs. These findings provide new insights into the distinct roles of RTP1S in OR translocation and activation.