Octopamine enhances moth olfactory responses to pheromones, but not those to general odorants

Effects of octopamine on responses of olfactory receptor neurons of Bombyx mori males and females, specialized to the reception of pheromone components and general odorants, respectively, were compared. Injections of octopamine had no effect on the transepithelial potential of antennal sensilla trichodea in both sexes. In males, octopamine increased significantly the amplitude of receptor potentials and nerve impulse responses elicited by the pheromone components bombykol and bombykal. However, the responses of homologous female general odorant-sensitive neurons to linalool and benzoic acid were not affected. In control experiments, injection of physiological saline did not increase the responses in any neuron type.     

Inhibitors of sensillar esterase reversibly block the responses of moth pheromone receptor cells

Three volatile alkyl-thio-trifluoro propanones inhibiting the esterase in olfactory sensilla of the silkmoths Antheraea polyphemus and A. pernyi were used to test the hypothesis that enzymatic pheromone degradation is responsible for the decline of the receptor potential after pheromone stimulation. Test stimuli were the pheromone components (E,Z)-6,11-hexadecadienyl acetate, a substrate for the sensillar esterase, and (E,Z)-6,11-hexadecadienal, not degraded by the esterase. Each compound acts on a separate type of receptor cell. In both receptor cell types the trifluoro propanones caused a partially reversible reduction of sensitivity as indicated by smaller receptor potential amplitudes and lower nerve impulse frequencies. Since application of the esterase inhibitors did not prolong the decline of the receptor potential of the acetate cell, the esterase is not responsible for the rapid pheromone deactivation. When the trifluoro propanones were applied after the pheromone at high concentrations, they rapidly inhibited (repolarized) both receptor cell types. Experiments with local application of trifluoro propanones revealed that the inhibitory effect spreads within seconds along the length of the sensillum. The inhibition of the electrophysiological responses might be due to an antagonistic action of the trifluoro propanones at the pheromone-binding sites, either at the receptor molecules or at the pheromone-binding protein. Accepted: 4 February 1998     

Temporal resolution of odour pulses by three types of pheromone receptor cells inAntheraea polyphemus

Summary Temporal response characteristics of three cell types of maleA. polyphemus, each responding to a different pheromone component, have been measured using series of short (20 ms) pheromone pulses. The stimuli were delivered through capillaries 20 m in diameter and applied to single olfactory sensilla trichodea. Two of three cell types sensitive to (E,Z)-6,11-hexadecadienal and (E,Z)-4,9-tetradecadienyl acetate are able to resolve at least 5 stimuli/s whereas the third, responding to the major pheromone component (E,Z)-6,11-hexadecadienyl acetate, is slower, resolving only about 2 stimuli/s. These results suggest that receptor cells are able to respond to pulses of pheromone concentration as they occur downwind from a point source. The time-averaged number of nerve impulses does not seem to be a reliable measure of the amount of pheromone reaching the sensillum. Responses of the cells thus reflect the non-uniform distribution of pheromone in a plume rather than the average concentration.     

Resolution of pheromone pulses in receptor cells of Antheraea polyphemus at different temperatures

The ability of pheromone receptor cells of male Antheraea polyphemus (Saturniidae) to resolve stimulus pulses was determined at different temperatures (8°, 18°, 28°C). The cells were stimulated by repeated 20-ms puffs of the pheromone components (E, Z)-6, 11-hexadecadienyl acetate and (E, Z)-6,11-hexadecadienal. At higher temperatures, higher frequencies of stimulus pulses were resolved by the nerve-impulse response: about 1.25 pulses per second at 8°C, 2.5 pulses/s at 18°C and 5 pulses/s at 28°C. The decreased ability of receptor cells to resolve stimulus pulses at low temperatures may reduce the male moth's chance of reaching the pheromone source. The peak nerve-impulse frequency increased whereas the duration of nerve-impulse responses to single stimulus pulses decreased at higher temperatures. At a given temperature and stimulus intensity the peak nerveimpulse frequency decreased with shorter intervals between the stimulus pulses, but the duration of the responses remained almost constant. The time needed for recovery from adaptation caused by a single stimulus pulse was longer at lower temperatures. The aldehyde receptor cell recovered more quickly than the acetate cell. At low stimulus concentration, the resolution ability of the acetate cell was strongly decreased, whereas in the aldehyde cell it was only slightly impaired.     

Neurons discovered in male Helicoverpa zea antennae that correlate with pheromone-mediated attraction and interspecific antagonism

Responses of single receptor neurons in the antennae of male Helicoverpa zea to sex pheromone components and to behavioral antagonists were recorded using a cut-sensillum extracellular recording technique. Three types of sensilla were identified from sampling 325 male-specific sensilla trichodea located at the lateral edge of antennomeres. The majority of these sensilla (71%) contained a receptor neuron tuned to the principal sex pheromone component (Z)-11-hexadecenal. A second sensillar type (10%) contained a receptor neuron that responded only to (Z)-9-tetradecenal. A third sensillar type (19%) contained a large-spiking neuron tuned to the secondary pheromone component (Z)-9-hexadecenal, but this neuron also could be stimulated to equivalent spike frequencies by the same emitted amounts of (Z)-9-tetradecenal. A smaller-spiking neuron in this sensillar type responded to two compounds known to act only as behavioral antagonists, (Z)-11-hexadecen-1-ol and (Z)-11-hexadecenyl acetate, and to (Z)-9-tetradecenal. Cross-adaptation studies confirmed the presence of one large- and one small-spiking neuron in the third sensillar type. Dose-response studies correlated to collected stimuli amounts showed that the large-spiking neuron in the third sensillar type was equally tuned to (Z)-9-hexadecenal and (Z)-9-tetradecenal, whereas the smaller-spiking neuron was far more sensitive to (Z)-11-hexadecen-1-ol and to (Z)-11-hexadecenyl acetate than to (Z)-9-tetradecenal. Accepted: 29 September 1997     

Biogenic amines modulate olfactory receptor neurons firing activity in Mamestra brassicae

The modulatory effects of the biogenic amines octopamine and serotonin on pheromonal receptor neurons of Mamestra brassicae were investigated. The responses to sex pheromone components of two cells types (A and B) in single male long sensilla trichodea were monitored. Cell types A and B do not respond to the same compound. The response of type A to a pulse of the major sex pheromone component increased 5 min after octopamine injection. Responses of type B to other odorants increased after 30 min. In the absence of any pheromone stimulation the background firing activity of type A increased following octopamine injection. This background activity was used to evaluate the kinetics of octopamine and other biogenic amine effects on olfactory receptor neurons. Octopamine increased this background activity in a concentration- and time-dependent manner. Clonidine, an octopamine agonist, was shown to be more powerful in increasing the background activity of olfactory receptor neurons. The effects of octopamine and clonidine were hypothesized to arise from specific receptor activation as chlorpromazine (an octopamine antagonist) was shown to block the effect of octopamine. Serotonin, a known neuromodulator in most animal species, induced a reversible inhibition of spike firing. Altogether, these results indicate that biogenic amines can modulate the sensitivity of olfactory receptor neurons of moths either directly or by an action on adaptation.     

Antennal response of codling moth males, Cydia pomonella L. (Lepidoptera: Tortricidae), to the geometric isomers of codlemone and codlemone acetate

Single sensillum recordings from Cydia pomonella male antennae showed three different types of receptor neurons. The most abundant type was most sensitive to the main pheromone compound (E,E)-8,10-dodecadienol, while its response to the geometric isomers E,Z, Z,E and Z,Z was comparable to a tenfold lower dose of (E,E)-8,10-dodecadienol. This neuron type also responded to the four behaviorally antagonistic isomers of (Δ,Δ)-8,10-dodecadienyl acetate, among which it was most sensitive to the E,E isomer. Cross-adaptation studies showed that these compounds were all detected by the same receptor neuron type. Receptor neurons specifically tuned to (E,Z) or (Z,Z)-8,10-dodecadienol were not found, although these two compounds are behaviorally active. A second type of receptor neuron responded to all isomers of (Δ,Δ)-8,10-dodecadienyl acetate and was most sensitive to the E,E isomer. This neuron type did not respond to any of the isomers of (Δ,Δ)-8,10-dodecadienol. A third receptor neuron type was highly sensitive to the plant compound α-farnesene. The finding that the receptor neuron type tuned to the main pheromone compound responded even to strong behavioral antagonists aids the interpretation of ongoing behavioral studies for the development of the mating disruption technique in codling moth. Accepted: 3 March 2000     

The contribution of olfactory receptor neurons to the perception of pheromone component ratios in male redbanded leafroller moths

Summary (Z)-11-tetradecenyl acetate (Z-11, 14:AC) must be in a 1009 ratio with (E)-11-tetradecenyl acetate (E-11,14:AC) to produce maximal wing fanning and attraction in male redbanded leafrollers. Earlier electrophysiological studies had indicated that mixtures of these pheromone components elicited responses from olfactory receptor neurons that appeared to differ from those expected on the basis of the responses to the individual components. Here we evaluate whether the behavioral sensitivity to particular ratios of Z- and E-11,14:AC has a correlate in the response properties of olfactory receptor neurons.The stimuli included the ratios of Z- and E-11, 14:AC used in earlier behavioral work plus several different mixtures of the seven components found in the pheromone blend, and equivalent amounts of the individual components. These stimuli were presented over a range of intensities to individual trichoid sensilla on the male antenna. In common with earlier results, the receptor neuron with the larger amplitude action potential responded most strongly to Z-11,14:AC, whereas the companion receptor neuron in the sensillum responded most strongly to E-11,14:AC. In contrast with earlier results, each receptor neuron responded exclusively to its own most effective stimulus, without regard to the presence of any other compound. They failed to respond uniquely to any of the other five compounds in the female pheromone blend, or to any of the tested combinations of these compounds. These minor components also failed to modulate the responses elicited in receptor neurons by appropriate ratios of Z- and E-11,14:AC. Thus, the responses of the two types of olfactory receptor neurons found in trichoid sensilla failed to show an optimum at the pheromone ratio known to elicit peak behavioral activity.Abbreviation RBLR redbanded leafroller moth     

Octopamine and tyramine modulate pheromone-sensitive olfactory sensilla of the hawkmoth <Emphasis Type="Italic">Manduca sexta</Emphasis> in a time-dependent manner

In moths octopamine improved pheromone-dependent mate search time dependently. In the nocturnal hawkmoth Manduca sexta long-term tip recordings of trichoid sensilla were performed to investigate whether biogenic amines modulate pheromone transduction time dependently. At three Zeitgebertimes octopamine, tyramine and the octopamine antagonist epinastine were applied during non-adapting pheromone-stimulation. At ZT 8-11, during the photophase, when sensilla were adapted, octopamine and to a lesser extent tyramine increased the bombykal-dependent sensillar potential amplitude and initial action potential (AP) frequency. In addition, during the photophase, when sensilla are less able to resolve pheromone pulses, octopamine rendered pheromone responses more phasic and sensitive, and raised the spontaneous AP frequency. During the late scotophase, at ZT 22-1, when the antenna appeared maximally sensitized for pheromone pulse detection and endogenous octopamine levels are high, exogenously applied octopamine was ineffective. Epinastine blocked the pheromone-dependent AP response at ZT 8-11 and slightly affected it at ZT 22-1, while it had no effect on the sensillar potential amplitude. Epinastine decreased the spontaneous AP activity during photophase and scotophase and rendered pheromone responses more tonic in the scotophase. We hypothesize that the presence of octopamine in the antenna is obligatory for the detection of intermittent pheromone pulses at all Zeitgebertimes.     

A comparative study of pheromone perception in two species of Noctuid moths

The electrical activity of single olfactory receptor neurons in male soybean looper (SBL) Pseudoplusia includens(Walker) and cabbage looper (CL) Trihoplusia ni(Hübner) moths was evaluated in response to stimulation with fixed amounts of the individual components of their respective pheromone blends. In common with earlier observations in the CL, there are at least two classes of morphologically distinct pheromone sensitive sensilla on the antenna of male SBL, each of which contains two olfactory receptor neurons. In both species, one class of sensilla contains an olfactory receptor neuron sensitive to (Z)-7-dodecen-1-ol acetate (Z-7, 12:AC), the major component in each insect's blend, and a companion receptor neuron which is sensitive to (Z)-7-dodecen-1-ol (Z7,12: OH). In both species the second class of sensilla contains an olfactory receptor neuron which is sensitive to one of the minor components of the pheromone blend. (Z)-5-dodecen-1-ol acetate (Z-5,12:AC) is an effective stimulus in SBL, whereas (Z)-7-tetradecen-1-ol acetate (Z-7,14:AC) is an effective stimulus in CL. However, these two stimulatory compounds have been identified only in the female CL gland; neither has been found in the SBL gland. Thus, in contrast to the CL, which has receptor neurons which are responsive exclusively to conspecific pheromone components, the SBL has a class of receptor neurons which is responsive to a minor component of another species' pheromone blend. Field-trapping assays in which Z-5,12:AC is added to the SBL blend suggest that this single CL component is a powerful inhibitor of male SBL behavioral responses to conspecific pheromone blends. The difference observed in the specificity of the receptor neurons in this second class of sensilla are thus believed to play an integral role in the isolation processes that are maintained between these two species and may well account for the observed behavioral differences in their responses to heterospecific pheromone blends.     

The macroglomerular complex of the antennal lobe in the tobacco budworm moth Heliothis virescens : specified subdivision in four compartments according to information about biologically significant compounds

The functional organisation of the male specific macroglomerular complex in Heliothis virescens has been studied by tip recordings of sensilla trichodea type 1 combined with cobalt-lysine stainings and by intracellular recordings of antennal lobe projection neurons combined with neurobiotin stainings. The antennal lobe, the macroglomerular complex and the stained axons/dendrites were reconstructed by camera-lucida. Some were further computer reconstructed in three dimensions. The results showed that: 1) The macroglomerular complex consisted of four anatomically separated compartments; 2) A large compartment (the cumulus) at the entrance of the antennal nerve received input from receptor neurons responding to the major pheromone component; 3) Another large compartment, located dorso-medially of the cumulus (the dorso-medial compartment) received input from receptor neurons tuned to the second pheromone component; 4) Two ventrally located compartments received input from two receptor neuron types, co-localized in the same sensillum. Each neuron type responded strongest to one of two interspecifically acting signals, shown to interrupt the pheromone attraction. 5) The function of the dorso-medial compartment was further verified by selective arborizations in this compartment by a projection neuron showing strong response to antennal stimulation with the second pheromone component. At low concentration, the neuron responded synergistically to stimulation with the binary pheromone mixture. Accepted: 29 July 1998     

Acceleratory nervous regulation of juvenile myogenic hearts in the isopod crustacean Ligia exotica

We examined regulation of the myogenic heart by two identified cardioacceleratory neurons (CA1, CA2) in early juveniles of the isopod Ligia exotica. Repetitive stimulation of either the CA1 or CA2 axon increased the frequency and plateau amplitude of the action potential and decreased the maximum hyperpolarization of the cardiac muscle. These effects were larger with increasing stimulus frequency. The rate of increase in the frequency caused by CA1 stimulation was significantly larger than that by CA2. No impulse activity of the cardiac ganglion was induced by acceleratory nerve stimulation. The frequency of the muscle activity was decreased by injection of a hyperpolarizing current into the muscle during stimulation of the acceleratory nerve. In a quiescent heart, acceleratory nerve stimulation caused an overall depolarization in the muscle membrane and the amplitude of the depolarization induced by CA1 stimulation was significantly larger than that by CA2. These results suggest that CA1 and CA2 neurons regulate the myogenic heart affecting directly the cardiac muscle; the CA1 neuron produces more potent effects than does the CA2 neuron.     

Ligand binding to six recombinant pheromone-binding proteins of<Emphasis Type="Italic"> Antheraea polyphemus</Emphasis> and<Emphasis Type="Italic"> Antheraea pernyi</Emphasis>

Binding properties of six heterologously expressed pheromone-binding proteins (PBPs) identified in the silkmoths Antheraea polyphemus and Antheraea pernyi were studied using tritium-labelled pheromone components, (E,Z)-6,11-hexadecadienyl acetate (³H-Ac1) and (E,Z)-6,11-hexadecadienal (³H-Ald), common to both species. In addition, a known ligand of PBP and inhibitor of pheromone receptor cells, the tritium-labelled esterase inhibitor decyl-thio-1,1,1-trifluoropropanone (³H-DTFP), was tested. The binding of ligands was measured after native gel electrophoresis and cutting gel slices. In both species, PBP1 and PBP3 showed binding of ³H-Ac1. In competition experiments with ³H-Ac1 and the third unlabelled pheromone component, (E,Z)-4,9-tetradecadienyl acetate (Ac2), the PBP1 showed preferential binding of Ac1, whereas PBP3 preferentially bound Ac2. The PBP2 of both species bound ³H-Ald only. All of the six PBPs strongly bound ³H-DTFP. Among unlabelled pheromone derivatives, alcohols were revealed to be the best competitors for ³H-Ac1 and ³H-Ald bound to PBPs. No pH influence was found for ³H-Ac1 binding to, or its release from, the PBP3 of A. polyphemus and A. pernyi between pH 4.0 and pH 7.5. The data indicate binding preference of each of the three PBP-subtypes (1–3) for a specific pheromone component and support the idea that PBPs contribute to odour discrimination, although to a smaller extent than receptor activation.Abbreviations Ac1 (E,Z)-6,11-hexadecadienyl acetate - Ac2 (E,Z)-4,9-tetradecadienyl acetate - Ald (E,Z)-6,11-hexadecadienal - AMA 1-amino-anthracene - cpm counts per min - DTFP decyl-thio-1,1,1-trifluoropropanone - ES-MS electrospray mass spectrometry - OH (E,Z)-6,11-hexadecadienol - PAGE polyacrylamide gel electrophoresis - PCR polymerase chain reaction - PBP pheromone-binding protein - SDS sodium dodecyl sulphate - Z-11 OH Z-11 hexadecenolCommunicated by G. Heldmaier     

A comparison of responses from olfactory receptor neurons of<Emphasis Type="Italic"> Heliothis subflexa</Emphasis> and<Emphasis Type="Italic"> Heliothis virescens</Emphasis> to components of their sex pheromone

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons in sensilla trichodea on male antennae of the heliothine species Heliothis subflexa and the closely related congener H. virescens. A large percentage of sensilla (72% and 81%, respectively, of all sensilla sampled) contained a single odor-responsive receptor neuron tuned to the major pheromone component of both species, Z-11-hexadecenal. A second population of sensilla on H. subflexa antennae (18%) housed receptor neurons that were tuned to Z-9-hexadecenal but also responded with less sensitivity to Z-9-tetradecenal. A similar population of sensilla (4%) on H. virescens male antennae housed receptor neurons that were shown to be tuned specifically only to Z-9-tetradecenal, with no response to even high dosages of Z-9-hexadecenal. A third population of sensilla (comprising 8% and 16% of the sensilla sampled in H. subflexa and H. virescens, respectively) housed two olfactory receptor neurons, one of which was tuned to Z-11-hexadecenyl acetate and the other tuned to Z-11-hexadecenol. In H. subflexa the Z-11-hexadecenyl acetate-tuned neuron also responded to Z-9-tetradecenal with nearly equivalent sensitivity. The behavioral requirements of males of these two species for distinct pheromonal blends was, therefore, reflected by the subtle differences in the tuning properties of antennal olfactory receptor neurons.Abbreviations MGC macroglomerular complex - ORN olfactory receptor neuron - Z9–14:Ald (Z)-9-tetradecenal - Z9–16:Ald (Z)-9-hexadecenal - Z11–16:Ac (Z)-11-hexadecenyl acetate - Z11–16:Ald (Z)-11-hexadecenal - Z11–16:OH (Z)-11-hexadecenol     

Number and sensitivity of three types of pheromone receptor cells inAntheraea pernyi andA. polyphemus

Summary Three types of receptor cells responding respectively to the pheromone components (E,Z)-6,11-hexadecadienyl acetate (AC₁, (E,Z)-6,11-hexadecadienal (AL) and (E,Z)-4,9-tetradecadienyl acetate (AC₂) occur in different combinations in the sensilla trichodea on male antennae ofAntheraea polyphemus andA. pernyi. The numbers of cells sensitive to AC₁ and AL and the average sensitivities of these cells are about equal, and higher than those of the AC₂-cells. The cells sensitive to AC₂ are relatively common in the small hairs positioned on the anterior side of the antenna. The product of three experimental values — (i) the relative number of each cell type, (ii) the average relative sensitivity of the cells and (iii) the estimated relative release rate of the respective pheromone component from the female gland — suggest that the distance from the female over which a compound can be detected or, the potential active space, is different for each pheromone component.Abbreviations EAG electroantennogram - SEM scanning electron microscope     

Activity modulation in cockroach sensillum: the role of octopamine

The plasticity of sensory perception is provided partially by modulation of receptor cells. The electrical activity of American cockroach chemoreceptor cells in response to sex pheromone was measured under the influence of octopamine treatment and tracheal anoxia. Both experimental procedures caused decreased electroantennograms but affected spike activity differently: octopamine treatment increased firing rate, whereas anoxia decreased it. Spike frequency under octopamine treatment was elevated in response to pheromone stimulation and at background activity. Experiments with perfusion of isolated antennae showed a direct effect of octopamine on spike activity of pheromone sensilla, and excluded the possibility of indirect effects via octopamine-dependent release of other biologically active substances. The suggested mechanism of octopamine action is receptor cell membrane depolarization.     

Guanosine 3',5'-cyclic monophosphate reduces the response of the Moth's olfactory receptor neuron to pheromone

The effects of the membrane-permeable dibutyryl guanosine 3', 5'-cyclic monophosphate (db-cGMP) on the bombykol-elicited receptor current and nerve impulse activity were studied using the open sensillum recording technique. db-cGMP was applied to the outer dendritic membrane of the olfactory receptor neuron of the moth Bombyx mori. db-cGMP reduced the amplitude of the overall receptor current activated by a pulse of strong pheromone stimuli as well as diminished the nerve impulse frequency elicited by continuously applied weak pheromone stimuli. The observed inhibition of the response to pheromone was due to size reduction of an elementary receptor current that elicits the nerve impulses and underlies the overall receptor current. It is suggested that cGMP is a factor which may adjust cell sensitivity to odour and play a role in olfactory adaptation.     

Firing properties of the soma and axon of the abdominal stretch receptor neurons in the crayfish (Astacus leptodactylus)

Action potentials (APs) and impulse responses in the soma and axon of the rapidly and slowly adapting (SA) abdominal stretch receptor neurons of the crayfish (Astacus leptodactylus) were recorded with single microelectrode current-clamp technique. Impulse frequency response to constant current injection was almost constant in the SA neuron while the response decayed completely in the rapidly adapting (RA) neuron. Mean impulse frequency responses to current stimulations were similar in the receptor neuron pairs. In the RA neuron additional current steps evoked additional impulses while a sudden drop in the current amplitude caused adaptation. Impulse duration was dependent on the rate of rise when current ramps were used. Adaptation was facilitated when calculated receptor current was used. Exposing the neuron to 3 mmol/l TEA or scorpion venom resulted in partly elongated impulse responses. SA neuron could continuously convert the current input into impulse frequency irrespective of previous stimulation conditions. Exposing the SA neuron to 3 mmol/l TEA or 1 mmol/l Lidocaine reduced impulse duration to large current stimulations. The SA neuron fired spontaneously if it was exposed to 5-10 mmol/l Lidocaine or 10(-2) mg/ml Leiurus quinquestriatus venom. The action potential (AP) amplitudes in the RA soma, RA axon, SA soma, and SA axon were significantly different between components of all pairs. Duration of the AP in the axon of the RA neuron was significantly shorter than those in the RA soma, SA soma, and SA axon. Diameter of the RA axon was larger than that of the SA axon. Non-adapting impulse responses were promptly observed only in the SA axons. The results indicate that the RA neuron is a sort of rate receptor transducing the rapid length changes in the receptor muscle while the SA neuron is capable of transducing the maintained length changes in the receptor muscle. The differences in firing properties mainly originate from the differences in the active and passive properties of the receptor neurons.     

Neofunctionalization in an ancestral insect desaturase lineage led to rare Δ6 pheromone signals in the Chinese tussah silkworm

The Chinese tussah silkworm, Antheraea pernyi (Lepidoptera: Saturniidae) produces a rare dienoic sex pheromone composed of (E,Z)-6,11-hexadecadienal, (E,Z)-6,11-hexadecadienyl acetate and (E,Z)-4,9-tetradecadienyl acetate, and for which the biosynthetic routes are yet unresolved. By means of gland composition analyses and in vivo labeling we evidenced that pheromone biosynthesis towards the immediate dienoic gland precursor, the (E,Z)-6,11-hexadecadienoic acid, involves desaturation steps with Δ⁶ and Δ¹¹ regioselectivity. cDNA cloning of pheromone gland desaturases and heterologous expression in yeast demonstrated that the 6,11-dienoic pheromone is generated from two biosynthetic routes implicating a Δ⁶ and Δ¹¹ desaturase duo albeit with an inverted reaction order. The two desaturases first catalyze the formation of the (E)-6-hexadecenoic acid or (Z)-11-hexadecenoic acid, key mono-unsaturated biosynthetic intermediates. Subsequently, each enzyme is able to produce the (E,Z)-6,11-hexadecadienoic acid by accommodating its non-respective mono-unsaturated product. Besides elucidating an unusually flexible pheromone biosynthetic pathway, our data provide the first identification of a biosynthetic Δ⁶ desaturase involved in insect mate communication. The occurrence of this novel Δ⁶ desaturase function is consistent with an evolutionary scenario involving neo-functionalization of an ancestral desaturase belonging to a gene lineage different from the Δ¹¹ desaturases commonly involved in moth pheromone biosynthesis.     

Antennal lobe projection destinations of Helicoverpa zea male olfactory receptor neurons responsive to heliothine sex pheromone components

We used single sensillum recordings to define male Helicoverpa zea olfactory receptor neuron physiology followed by cobalt staining to trace the axons to destination glomeruli of the antennal lobe. Receptor neurons in type A sensilla that respond to the major pheromone component, (Z)-11-hexadecenal, projected axons to the cumulus of the macroglomerular complex (MGC). In approximately 40% of these sensilla a second receptor neuron was stained that projected consistently to a specific glomerulus residing in a previously unrecognized glomerular complex with six other glomeruli stationed immediately posterior to the MGC. Cobalt staining corroborated by calcium imaging showed that receptor neurons in type C sensilla sensitive to (Z)-9-hexadecenal projected to the dorsomedial posterior glomerulus of the MGC, whereas the co-compartmentalized antagonist-sensitive neurons projected to the dorsomedial anterior glomerulus. We also discovered that the olfactory receptor neurons in type B sensilla exhibit the same axonal projections as those in type C sensilla. Thus, it seems that type B sensilla are anatomically type C with regard to the projection destinations of the two receptor neurons, but physiologically one of the receptor neurons is now unresponsive to everything except (Z)-9-tetradecenal, and the other responds to none of the pheromone-related odorants tested.