Development of the gin trap reflex inManduca sexta: a comparison of larval and pupal motor responses

1. Responses of motor neurons in larvae and pupae of Manduca sexta to stimulation of tactile sensory neurons were measured in both semi-intact, and isolated nerve cord preparations. These motor neurons innervate abdominal intersegmental muscles which are involved in the production of a general flexion reflex in the larva, and the closure reflex of the pupal gin traps. 2. Larval motor neurons respond to stimulation of sensory neurons innervating abdominal mechanosensory hairs with prolonged, tonic excitation ipsilaterally, and either weak excitation or inhibition contralaterally (Figs. 4A, 6). 3. Pupae respond to tactile stimulation of mechanosensory hairs within the gin traps with a rapid closure reflex. Motor neurons which innervate muscles ipsilateral to the stimulus exhibit a large depolarization, high frequency firing, and abrupt termination (Figs. 2, 4B). Generally, contralateral motor neurons fire antiphasically to the ipsilateral motor neurons, producing a characteristic triphasic firing pattern (Figs. 7, 8) which is not seen in the larva. 4. Pupal motor neurons can also respond to sensory stimulation with other types of patterns, including rotational responses (Fig. 3A), gin trap opening reflexes (Fig. 3B), and 'flip-flop' responses (Fig. 9). 5. Pupal motor neurons, like larval motor neurons, do not show oscillatory responses to tonic current injection, nor do motor neurons of either stage appear to interact synaptically with one another. Most pupal motor neurons also exhibit i-V properties similar to those of larval motor neurons (Table 1; Fig. 10). Some pupal motor neurons, however, show a marked non-linear response to depolarizing current injection (Fig. 11).     

Antennal sucrose perception in the honey bee (Apis mellifera L.): behaviour and electrophysiology

Physiological mechanisms of antennal sucrose perception in the honey bee were analysed using behavioural and electrophysiological methods. Following sucrose stimulation of the tip of a freely moving antenna, the latency of proboscis extension was 320–340 ms, 80–100 ms after the first activity in muscle M17 controlling this response. When bees were allowed to actively touch a sucrose droplet with one antenna, contacts with the solution were frequent with durations of 10–20 ms and average intervals between contacts of approximately 40 ms. High sucrose concentrations led to short and frequent contacts. The proboscis response and M17 activity were largely independent of stimulus duration and temporal pattern. Taste hairs of the antennal tip displayed spike responses to sucrose concentrations down to at least 0.1%. The first 25 ms of the response were suitable for discrimination of sucrose concentrations. This time interval corresponds to the duration of naturally occurring gustatory stimuli. Sucrose responses between different hairs on the same antenna showed a high degree of variability, ranging from less than five to over 40 spikes per 0.5 s for a stimulus of 0.1% sucrose. This variability of receptor responses extends the dynamic range of sucrose perception over a large range of concentrations.     

Proboscis extension in the blowfly: directional responses to stimulation of identified chemosensitive hairs

Summary We studied the direction of proboscis extension elicited by stimulating each of an identified array of gustatory sensilla, the largest hairs, on the labellum of the flyPhormia regina. Individual hairs, or pairs of hairs, were stimulated with sucrose or water and the angle of the ensuing extension of the proboscis was recorded. The direction of the response was graded and depended on the identities of the hairs stimulated. Hairs situated on the anterior region of the labellum elicited anterior extensions, mid-level hairs elicited lateral extensions and posterior hairs resulted in posterior extensions. Previous studies of the labellar hairs have been concerned with their encoding of the chemical nature of the stimulus. Our findings show that each hair also relays information about the location of the stimulus. The positional information provided by these sensilla may help the fly to orient itself with respect to a food source.Abbreviation CES central excitatory state     

The interaction of external and internal receptors on the feeding behaviour of the blowfly, Phormia regina

The interaction of sensory activity from internal gut stretch receptors and from external labellar chemosensory hairs has been studied both behaviourally and electrophysiologically in the control of proboscis extension of the blowfly, Phormia regina. Labellar thresholds for proboscis extension, tested behaviourally, do not change significantly up to an hour after feeding in contrast to tarsal thresholds which rise quickly after feeding. Motor activity of the extensor muscle of the haustellum was recorded simultaneously with sensory activity from labellar sensilla. The mean number of muscle spikes per response and the sensory input necessary to trigger a response do not vary with starvation, feeding, or sectioning of the recurrent nerve. Activity of internal stretch receptors seem to interact with tarsal sensory input but apparently do not modulate motor responses triggered by labellar sensory input.     

Differential uptake of fumarate by Candida utilis and Schizosaccharomyces pombe

The dicarboxylic acid fumarate is an important intermediate in cellular processes and also serves as a precursor for the commercial production of fine chemicals such as l-malate. Yeast species differ remarkably in their ability to degrade extracellular dicarboxylic acids and to utilise them as their only source of carbon. In this study we have shown that the yeast Candida utilis effectively degraded extracellular fumarate and l-malate, but glucose or other assimilable carbon sources repressed the transport and degradation of these dicarboxylic acids. The transport of both dicarboxylic acids was shown to be strongly inducible by either fumarate or l-malate while kinetic studies suggest that the two dicarboxylic acids are transported by the same transporter protein. In contrast, Schizosaccharomyces pombe effectively degraded extracellular l-malate, but not fumarate, in the presence of glucose or other assimilable carbon sources. The Sch. pombe malate transporter was unable to transport fumarate, although fumarate inhibited the uptake of l-malate. Received: 15 March 2000 / Received revision: 4 July 2000 / Accepted: 9 July 2000     

Visual ecology of flies with particular reference to colour vision and colour preferences

The visual ecology of flies is outstanding among insects due to a combination of specific attributes. Flies’ compound eyes possess an open rhabdom and thus separate rhabdomeres in each ommatidium assigned to two visual pathways. The highly sensitive, monovariant neural superposition system is based on the excitation of the peripheral rhabdomeres of the retinula cells R1–6 and controls optomotor reactions. The two forms of central rhabdomeres of R7/8 retinula cells in each ommatidium build up a system with four photoreceptors sensitive in different wavelength ranges and thought to account for colour vision. Evidence from wavelength discrimination tests suggests that all colour stimuli are assigned to one of just four colour categories, but cooperation of the two pathways is also evident. Flies use colour cues for various behavioural reactions such as flower visitation, proboscis extension, host finding, and egg deposition. Direct evidence for colour vision, the ability to discriminate colours according to spectral shape but independent of intensity, has been demonstrated for few fly species only. Indirect evidence for colour vision provided from electrophysiological recordings of the spectral sensitivity of photoreceptors and opsin genes indicates similar requisites in various flies; the flies’ responses to coloured targets, however, are much more diverse.     

Labellar lobe spreading in the blowfly: Regulation by taste and satiety

Summary Lobe spreading behavior was studied by recording electromyograms from the muscles which spread the labellar lobes, the retractors of the furca (RF) inPhormia regina. RF responses and lobe spreading could be elicited by stimulating labellar, but not tarsal, taste hairs with sucrose (Fig. 3). RF activity was important to spread the lobes at the beginning of a meal, but was not necessary for continued feeding (Fig. 4).Temporal summation between sugar receptor spikes was necessary to elicit RF responses. Central response decrement occurs independently for different labellar hairs and may participate in the termination of motor responses.RF responses were more probable and more intense when either the sucrose concentration of the stimulus or the number of hairs stimulated was increased (Fig. 7). Stimulation with NaCl had no effect on the response to simultaneous sucrose stimulation of other hairs (Table 1).Feeding caused decreases in the probability and intensity of motor responses, but did not alter chemosensory responses (Figs. 8 and 9). Section of either the recurrent or median abdominal nerves prevented this postingestional inhibition of lobe spreading (Fig. 9).These results are discussed with regard to the possible role that regulation of lobe spreading may play in the control of food intake.This work was supported by United States Public Health Service Training Grant 5T01 GM 00457-13S2 and by a grant from the National Science Foundation to Dr. Vincent G. Dethier. I wish to thank Dr. Dethier for his support and encouragement.     

Morphology and physiology of a hair plate sensory organ located on the antenna of the rock lobster Palinurus vulgaris

At the level of the J1 joint of each antenna of the rock lobster Palinurus vulgaris a hair plate sensory organ (hp) similar to those described in insects has been observed. The hp is located on the internal side of the S2 segment of the antenna, close to the soft articulating membrane of the J1 joint. It is formed by a triangular surface of cuticle about 3mm2 in area, covered with numerous hairs of different lengths (Figs. 1 and 2). Details of the hp were studied by scanning electron microscopy (Fig. 2). Physiological stimulation of the hp hairs occurs during medial movement of the J1 joint. Under this condition the soft articulating membrane rolls over the hairs and bends them progressively back onto the cuticle. Flexion of all the hairs corresponds to a medial movement of the J1 through 40 degrees. During this type of movement, the number of successively flexed hairs increases linearly (Fig. 3). Electrophysiological recordings of the hp sensory nerve correlated with selective mechanical stimulation of individual hairs demonstrated that each hair is innervated by a single sensory fiber. This sensory neurone responds phasically when the hair is flexed back onto the cuticle (as during an S2 medial movement) and when it returns to its resting position (as during an S2 lateral movement). Most of the sensory neurones are sensitive to the movement velocity of the hairs (Figs. 4 and 5). When the hair is maintained flexed its sensory neurone discharges tonically (Fig. 4). Electrical stimulation of the hp sensory nerve induced reflex actions in the external and internal rotator muscles of the segment S1. These effects were found to selectively activate the tonic motor command of these muscles (Fig. 6).     

A direct comparison of electrophysiological and behavioural taste responses in the blowfly

Behavioural and electrophysiological taste responses in theblowfly (Calliphora vicina) are measured in successive experiments,using the same flies twice. Inter-individual variations in behaviourare at least partly due to differences in the functioning ofthe tarsal taste hairs; flies with low behavioural thresholdvalues have taste hairs firing with higher rates. The percentageof taste hairs responding with spike trains is not important.Behavioural responses are predominantly influenced by the ‘best’firing hair. The most effective of the parameters describingspike trains seems to bef_t, the firing rate after an ‘infinite’length of stimulation time.     

THE RELATIONSHIP BETWEEN CHEMICAL STRUCTURE AND THE RESPONSE OF BLOWFLIES TO TARSAL STIMULATION BY ALIPHATIC ACIDS

Using the technique of proboscis extension in antennectomized-labellectomized flies, the rejection thresholds of Phormia regina for 18 fatty acids and one mineral acid have been determined. The conclusions reached on the basis of these data may be summarized in the following terms: Tarsal stimulation by acids involves the summation of components from at least two sources. Of these the hydrogen ion is the most important. The other major factor is probably the anion rather than the undissociated acid. The stimulating power of the anions (or free acid molecules) increases with increasing chain length in both the mono- and dicarboxylic series, but the rate of increase decreases as the series is ascended. Acids containing 6 or more carbon atoms are not sufficiently soluble in 0.1 M sucrose to reach the threshold of rejection. Substitution of —H in the acyl grouping by —Cl, —OH, =O or —COOH, the presence of a C=C bond, or a shift from the trans- to the cis- configuration all diminish the effectiveness of the anion (or free acid). But since such alterations also augment the degree of dissociation and consequently the concentration of hydrogen ions, the net result is ordinarily a lowering of threshold in terms of the molar concentration required for rejection.     

Variation of acceptance thresholds in the blowfly by increasing sugar concentrations in the food

Summary Aduld blowflies,Phormia regina M., were raised on different concentrations of sucrose. The thresholds of the behavioral responses to tarsal stimulation were elevated in blowflies raised on high concentrations of sucrose. The relationship between the median acceptance thresholds and the raising concentration of sucrose was logarithmically linear. Two groups of experimental flies were prepared: (1) coated flies, in which only D-type chemosensory hairs could respond physiologically, and (2) treated flies, in which all chemosensory hairs except D-type hairs functioned physiologically. Proboscis extension responses were ascertained in both groups. Median acceptance thresholds for the coated and treated flies, respectively, were presumed to be logarithmically linear in relation to the raising concentration of sucrose. It was supposed that D-type sugar receptor impulses initiate mainly the proboscis extension responses under the 0.01 M sucrose threshold and that B-type sugar receptor impulses initiate the responses above the 0.01 M sucrose threshold. Median acceptance thresholds for whole labellar stimulation were elevated to 0.026 M sucrose in blowflies raised on 1.0 M sucrose. Median acceptance thresholds were again lowered in blowflies raised on sucrose of more than 1.0 M.This research was supported in part by ITO foundation and Scientific Research Fund from the Ministry of Education of Japan.     

Pollination biology in the Snowy Mountains of Australia: Comparisons with montane Colorado,USA

Various aspects of the pollination biology of the alpine flora of Kosciusko National Park, NSW, were examined from late December 1983 until the end of March 1984, including flowering phenology, corolla tube lengths, flower colour, ultraviolet reflectance patterns, visitation rates to the flowers and proboscis lengths of the flower-visiting insects. An average of 5.3 species flowered in each of 13, 2 m×2 m montane plots and 5.6 species in the 13 alpine plots. The maximum number in flower simultaneously averaged 4.1 species in the montane and 3.3 in the alpine plots; flowering peaked in mid-January, Corolla tube lengths of the flora averaged 1.73 mm. The most common floral colour was white or predominantly white (40 species), followed by yellow (14 species). Only six of the 38 species (16%) examined had some type of reflectance pattern; the remaining species all absobed ultraviolet. Flies appeared to be the major pollinators. The insects collected in the study area comprised 60 species of Diptera, 33 species of Hymenoptera, and several species each of Lepidoptera and Coleoptera. On average, 14.4% of flowers watched during 379 observation periods (10 min each) were visited. On average, each plant species was visited by 6.4 species of flies, 2.4 species of bees, wasps or sawflies, one species of butterfly or moth and 0.3 species of beetles. Visitation rates increased over the growing season, and were significantly affected by ambient temperature (positively), light levels (positively) and wind speed (negatively). The maximum proboscis length for the 25 most common species of bees was 2.76 mm, but 18 of 51 species of flies had proboscis lengths longer than this. The mean proboscis length for all 25 species of bees was 1.68 mm, and for 51 species of flies was 2.31 mm. Proboscis lengths for flies were positively correlated with the average corolla length for the plant species they visited. For bees, however, the range in proboscis lengths was relatively small and did not show this pattern. There appear to be significant differences between the plant-pollinator community of alpine Australia and other alpine areas where bumblebees are common pollinators. These differences include shorter proboscis and corolla tube lengths, and perhaps an increased diversity and significance of flies as pollinators.     

Sodium chloride reduces growth and cytosolic calcium,but does not affect cytosolic pH,in root hairs of Arabidopsis thaliana L

The effects of salinity (NaCl) stress on growth, cytosolic Ca(2+) gradients and cytosolic pH homeostasis of root hairs of Arabidopsis thaliana are assessed here. Neither cytosolic Ca(2+) nor pH at the hair apex were significantly affected by 20 min exposure of up to 90 mM NaCl or of up to 5 mM extracellular Ca(2+). Exposure to increasing NaCl concentrations, up to 90 mM, for 2 d or 6 d reduced hair extension, and this inhibition was relieved by supplemental extracellular Ca(2+). Such extended salinity stress reduced the magnitude of the Ca(2+) gradient in the apical 12 microm of hairs at all NaCl concentrations tested (up to 90 mM), including NaCl concentrations that did not reduce hair extension. The magnitude of the tip-focused gradient was also reduced in root hairs of plants grown with low (0.5 mM) extracellular Ca(2+) when compared to those in 5 mM extracellular Ca(2+), regardless of the presence of NaCl. Up to 90 mM NaCl did not affect cytosolic pH of root hairs in any of the treatments. It is concluded that NaCl inhibition of root hair extension in the long term may operate via alterations in the tip-focused Ca(2+) gradient that regulates root hair growth. However, NaCl-induced alterations in this gradient do not always lead to detectably altered growth kinetics. Short-term signalling events in response to NaCl may operate by a means other than altering Ca(2+) at the root hair apex. Salinity stress in root hairs does not appear to be mediated by effects on cytosolic pH.     

Drosophila melanogaster prefers compounds perceived sweet by humans

To understand the functional similarities of fly and mammalian taste receptors, we used a top-down approach that first established the fly sweetener-response profile. We employed the fruit fly Drosophila melanogaster, an omnivorous human commensal, and determined its sensitivity to an extended set of stimuli that humans find sweet. Flies were tested with all sweeteners in 2 assays that measured their taste reactivity (proboscis extension assay) and their ingestive preferences (free roaming ingestion choice test). A total of 21 sweeteners, comprised of 11 high-potency sweeteners, 2 amino acids, 5 sugars, 2 sugar alcohols, and a sweet salt (PbCl2), were tested in both assays. We found that wild-type Drosophila responded appetitively to most high-potency sweeteners preferred by humans, even those not considered sweet by rodents or new world monkeys. The similarities in taste preferences for sweeteners suggest that frugivorous/omnivorous apes and flies have evolved promiscuous carbohydrate taste detectors with similar affinities for myriad high-potency sweeteners. Whether these perceptual parallels are the result of convergent evolution of saccharide receptor-binding mechanisms remains to be determined.     

Pollen feeding in the eucalypt nectar fly, Drosophila flavohirta

Abstract. Adults of the eucalypt nectar fly, Drosophila flavohirta Malloch (Diptera: Drosophilidae), feed on Eucalyptus pollen. Flies of both sexes gather pollen with the proboscis, forming a large mass of pollen on the anterior surface of the extended proboscis. Pollen gathering alternates with quiescent periods when the moistened pollen load is continually vibrated. No pollen was found in the adult gut, and it is suggested that hydration of the pollen causes release of nutrients which are then imbibed. This 'external digestion' is reminiscent of that employed by heliconiine butterflies.     

The sensitivity of the labellar sugar receptors of Phormia regina in relation to feeding

The hypothesis that behavioural feeding threshold of P. regina modulates and is modulated by the sensitivity of the labellar contact chemoreceptors is not supported by the examination of individual flies.Sensitivity (number of impulses fired in the first second of stimulation) of the sugar receptors in selected labellar hairs of flies of known age was recorded periodically on a fixed schedule for up to 72 hr. Experimental flies were hand fed 2.0 M fructose once every 24 hr. No correlations between feeding or age and receptor sensitivity were found. Statistically significant changes in firing frequency did occur but were unrelated to feeding and age.The proboscis extension response, on which behavioural threshold measures are based, is known to be triggered by the first few sugar receptor spikes of sufficient frequency. Neither age nor feeding significantly affected the number or frequency of impulses during the first 50 msec of stimulation.     

Discrimination of oilseed rape volatiles by the honeybee: combined chemical and biological approaches

Honeybees (Apis mellifera L.) were individually subjected to a classical conditioning procedure in order to obtain an olfactory conditioned proboscis extension response. To relate the behavioural response directly to antennal detection abilities, a technique was developped for coupling proboscis extension responses and electroantennogram recordings, with the stimulation being provided by the effluent of a gas chromatograph (GC). Bees were conditioned with a six-component mixture being part of oilseed rape (Brassica napus L.) floral volatiles, and tested with the individual components separated by GC. Responses of the conditioned bees were compared to those of unconditioned bees. No behavioural response was obtained in the control group, neither to the individual components nor to the mixture. Conditioning induced behavioural responses for three components, and an increase of electroantennogram responses for all components. A second experiment was conducted with an air entrainment extract of oilseed rape flower volatiles. Behavioural responses of conditioned and unconditioned bees were recorded. Responses obtained from conditioned bees tested with the air entrainment extract showed six groups of behaviourally active GC peaks. Unconditioned bees showed the same pattern of responses but at a lower level. The coupled technique described here appears to be a reliable tool for locating active components in a synthetic as well as in a natural mixture of floral volatiles. The effects of conditioning on odour discrimination and on its sensory correlates are discussed.     

Effects of ethanol,octanoic and decanoic acids on fermentation and the passive influx of protons through the plasma membrane of Saccharomyces cerevisiae

Ethanol, octanoic and decanoic acids are known toxic products of alcoholic fermentation and inhibit yeast functions such as growth and fermentation. pH-stat measurements showed that, in a concentration range up to 20 mg/l, octanoic and decanoic acids increase the rate of passive H⁺ influx across the plasma membrane of Saccharomyces cerevisiae IGC 3507. Decanoic acid was more active than octanoic acid, which agrees with its higher liposolubility. The fatty acids probably act as H⁺ carriers, since the magnitude of the effect depended on pH and correlated with the concentration of protonated fatty acids. Esterification of the fatty acids partially abolished the enhancing effect on passive H⁺ influx. Passive H⁺ influx showed saturation kinetics with half-maximal activity at 6.6 M H⁺ (pH 5.2). Contrary to previous findings, ethanol inhibited H⁺ influx exponentially up to a concentration of 8% (v/v). At higher concentrations, ethanol reactivated H⁺ influx; the original rate of H⁺ uptake was reached at 14% (v/v) ethanol. In the same concentration ranges that affected passive H⁺ influx, ethanol, octanoic and decanoic acids inhibited the fermentation rate. This inhibitory effect of the fatty acids on fermentation rate depended on liposolubility, pH, and esterification in the same way as that found for their effect on passive H⁺ influx. Inhibition of fermentation by octanoic and decanoic acids could therefore result from their effect on the rate of passive H⁺ influx. Correspondence to: S. Stevens     

The anion-carrier mediated uncoupling effect of dicarboxylic fatty acids in liver mitochondria depends on the position of the second carboxyl group.

Effects of dicarboxylic fatty acids with varying positions of the carboxyl groups on respiration and membrane potential of liver mitochondria were studied. Tetradecylmalonic acid (a fatty acid with two carboxyl groups in the alpha-position) efficiently uncoupled oxidative phosphorylation similarly to palmitic acid with the same number of carbon atoms. Similarly to the uncoupling by palmitic acid, the coupling effects of carboxyatractylate and glutamate changed reciprocally with changes in pH of the incubation medium: on increasing the pH from 7.0 to 7.8, the coupling effect of carboxyatractylate increased and that of glutamate decreased. A dicarboxylic fatty acid with the second carboxyl at the end of the alkyl chain in the omega-position (alpha, omega-tetradecyldicarboxylic acid) stimulated respiration of the mitochondria at a significantly higher concentration than myristic acid with the same number of carbon atoms, but unlike the latter nearly failed to decrease the transmembrane potential DeltaPsi. Neither carboxyatractylate nor glutamate inhibited the respiration stimulated by this dicarboxylic fatty acid.