Organization of inputs to motoneurons during fictive respiration in the isolated lamprey brain

Summary The intracellular activity of motoneurons during fictive respiration in the isolated lamprey brain was investigated. In association with each respiratory cycle three distinct PSP phases were observed: an early, low amplitude EPSP phase; a large, brief EPSP phase that drove action potentials; and a subsequent IPSP phase (Fig. 1). Selective midline and trigeminal lesions, and trigeminal stimulation, demonstrated that the large excitatory and inhibitory phases were generated by a previously described pair of central pattern generators located in the trigeminal region of the medulla (V) (Figs. 3, 4). Lesion studies further showed that the low amplitude excitatory input could be produced independently of the trigeminal pacemakers (Figs. 3, 5), near the region of the medulla that contains the respiratory motoneurons (VII, IX, and X).In addition to normal fictive respiration, the isolated brain was found to produce several variations of the respiratory pattern. These motor programs, coughs, arousal breathing, and weak breathing, were distinguished from the normal respiratory pattern by their much longer burst durations, distinctive underlying synaptic input, and separate coordinating mechanism (Figs. 6–8). Activity similar to these motor programs could be independently produced by the caudal medulla after both trigeminal central pattern generators had been removed (Figs. 5, 6). Lesion studies, and the observation that respiratory-related neural activity ceased in the trigeminal region during the production of these long-duration programs, suggest that the caudal medulla also contains paired central pattern generators involved in lamprey respiration (Figs. 5, 9, 10).Abbreviations CPG central pattern generator - HRP horseradish peroxidase     

End buds: non-ampullary electroreceptors in adult lampreys

Summary Shared anatomical and physiological characters indicate that the low-frequency sensitive electrosensory system of lampreys is homologous with those of non-teleost fishes and amphibians. However, the ampullary electroreceptor organs which characterize all of these gnathostomes are not found in lampreys. Experimental anatomical and physiological studies reported here demonstrate that the epidermal end buds are the electroreceptors of adult lampreys.End buds, consisting of both sensory and supporting cells, are goblet-shaped with the top (25–60 m diameter) at the epidermal surface and the stem directed toward the dermis (Fig. 1A). Short lines or clusters of 2–8 end buds (Fig. 1B) are distributed over both trunk and head. Injections of horseradish peroxidase (HRP) into vitally-stained end buds labeled anterior lateral line afferents terminating in the ipsilateral dorsal nucleus (Fig. 2A) — the primary electrosensory nucleus of the lamprey medulla. Conversely, after HRP injection into the dorsal nucleus HRP-filled fibers and terminals were present on ipsilateral end buds (Fig. 2B).End buds are usually not visible without staining. However, in adult sea lampreys the presence of end buds was histologically confirmed in skin patches containing the receptive fields of electroreceptor fibers recorded in the anterior lateral line nerve. Additionally, in the rare instance of two silver lampreys in which end buds were visible without staining, electrosensory activity indistinguishable from that of the primary electroreceptor afferents was recorded from the end bud surface (Figs. 3, 4).End buds were initially characterized as chemoreceptors (Johnston 1902) but were later correctly advanced as lateralis receptors based on the presence of presynaptic dense bodies in the receptor cells (Whitear and Lane 1981). Unlike all other low-frequency electroreceptors, end buds lack canals. The receptor cells contact the epidermal surface and possess apical microvilli rather than the kinocilium of most gnathostomes with homologous electrosensory systems of the primitive (non-teleost) type.Larval lampreys and newly transformed adults lack end buds although at least the latter are electroreceptive. End buds, therefore, may be the form taken by electroreceptors only in the final portion of a lamprey's life.     

Unusual discharge patterns of single fibers in the pigeon's auditory nerve

Summary Extracellular recording from single auditory nerve fibers in the pigeon,Columba livia, revealed some unusual discharge patterns of spontaneous and evoked activity.Time interval histograms (TIHs) of spontaneous activity showed a random interval distribution in 73% of the auditory fibers (Fig. 1a). The remaining 27% revealed periodicity in the TIHs (Fig. 1b–e), determined by the characteristic frequency (CF) of a given fiber. Normally, those fibers had a CF<2.2 kHz. In both cases spontaneous activity was irregular.The time pattern of quasiperiodic spontaneous firing in different auditory fibers is described by three main types of autocorrelation histograms (ACHs; decaying, nondecaying, and modulated), reflecting the spontaneous oscillations of the hair cell membrane potential (Fig. 1b–d).Single-tone suppression in auditory fibers with quasi-periodic spontaneous activity was found (Figs. 2, 10) and it could be observed if the eighth nerve was cut. There was no suppressive effect in fibres with random spontaneous firing.The frequency selectivity properties of auditory fibers were studied by means of an automatic method. Both simple (Fig. 4) and complex (Figs. 7, 8) response maps were found. Apart from the usual excitatory area, complex response maps were characterized by suppressive areas lying either above (Fig. 7), below (Fig. 8e), or on both sides of the CF (Fig. 8a–c). Generally, complex response maps were observed for fibers showing quasiperiodic spontaneous activity (Figs. 7, 8).Input-output functions at frequencies evoking single-tone suppression were nonmonotonic, while they were always monotonic at frequencies near the CF (Fig. 12).No difference in sharpness was observed between normal frequency threshold curves (FTCs) and exitatory areas of complex response maps (Fig. 9).On-off responses evoked by suppressive stimuli were found (Figs. 2, 3). They had a periodic pattern determined by the CF and did not depend on the stimulus frequency (Fig. 3).Low-CF fibers were observed which changed their time discharge structure to tone levels about 45 dB lower than their thresholds at the CF (Fig. 6).The observed features of the discharge patterns of the pigeon's auditory fibers reflect the distinctive nature of the fundamental mechanisms of auditory analysis in birds that are connected with electrical tuning of the hair cells and probably with the micromechanics of the bird's cochlea.Abbreviations ACH autocorrelation histogram - BP base period - CF characteristic frequency - FTC frequency threshold curve - IHC inner hair cell - OHC outer hair cell - PSTH peristimulus time histogram - TIH time interval histogram     

Mosquito circadian and circa-bi-dian flight rhythms: a two-oscillator model

Summary Circadian rhythmicity was found in the flight activity ofCuliseta incidens recorded in constant darkness for up to 14 weeks. The first nonhuman circa-bi-dian (about-two-day) rhythms were also found (Figs. 6–7). Circadian periods were either stable, remaining <24h (Fig. 1), or labile, with a change from <24h to >24 h (Fig. 2). Inactivity phenomena (day-skipping) were common in the latter group only (Fig. 5). The period at activity onset was much more labile than the period at offset (Fig. 4). The activity patterns of some period-lengthened animals suggested control by two oscillators which could temporarily or permanently uncouple (Figs. 8–9).A pacemaker model consisting of a labile evening (E) oscillator mutually coupled to a stable morning (M) oscillator is the most economical proposal which can account for these results. The view that E and M uncouple and run with different periods can account for many records in which the period was labile. Circa-bi-dian rhythms can be explained by the period of E lengthening to where it synchronizes with M in a 21 mode. Thus, E and M are proposed to behave similarly to the human activity and temperature oscillators. It is speculated that day-skipping might indicate that E oscillates between circadian and circa-bi-dian ranges without overt activity being expressed.Abbreviations LD1212 alternating 12h light, 12h dark - DD constant dark - LL constant light - period of rhythm - _on period at activity onset - _off period at activity offset - activity time - mean activity time     

The halteres of the blowfly Calliphora

We quantitatively analysed compensatory head reactions of flies to imposed body rotations in yaw, pitch and roll and characterized the haltere as a sense organ for maintaining equilibrium. During constant velocity rotation, the head first moves to compensate retinal slip and then attains a plateau excursion (Fig. 3). Below 500°/s, initial head velocity as well as final excursion depend linearily on stimulus velocities for all three axes. Head saccades occur rarely and are synchronous to wing beat saccades (Fig. 5). They are interpreted as spontaneous actions superposed to the compensatory reaction and are thus not resetting movements like the fast phase of vestibulo-ocular nystagmus in vertebrates. In addition to subjecting the flies to actual body rotations we developed a method to mimick rotational stimuli by subjecting the body of a flying fly to vibrations (1 to 200 m, 130 to 150 Hz), which were coupled on line to the fly's haltere beat. The reactions to simulated Coriolis forces, mimicking a rotation with constant velocity, are qualitatively and to a large extent also quantitatively identical to the reactions to real rotations (Figs. 3, 7–9). Responses to roll- and pitch stimuli are co-axial. During yaw stimulation (halteres and visual) the head performs both a yaw and a roll reaction (Fig. 3e,f), thus reacting not co-axial. This is not due to mechanical constraints of the neck articulation, but rather it is interpreted as an advance compensation of a banked body position during free flight yaw turns (Fig. 10).     

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).     

Perception of size and lightness of human observers: two criteria for holistic and analytic processing show no correlation in individuals

Results of a triad-classification task and a multidimensional-scaling (MDS) experiment are compared for individual observers. Both paradigms are designed to reveal whether stimuli are perceived in aholistic oranalytic manner (Garner 1974). Subjects differed substantially and consistently in their triad classification pattern (Figs. 3, 5): The majority of subjects selected stimuli according todimensional criteria; this classification type is thought to indicate an analytic stimulus processing. Approximately one third of subjects, however, used a classification according to overall similarity (indicating holistic processing). Except for the very first session (Fig. 3a), virtually no intermediate classifications occurred (Fig. 3b, c). This clear separation into two classification types suggests that there actually existtwo strongly preferred processing modes.Intraindividual variability between sessions in general was small (Fig. 5). In one case, however, a spontaneous switching from a purely dimensional classification to a purely similarity classification occurred (Fig. 5d). This indicates that the observers have different processing options at their disposal, and are not forced to use a particular processing mode by the stimulus type — as has been supposed in the original concept of integrality/separability of stimuli (Garner 1974). In the MDS experiment also substantial interindividual differences in the best-fitting Minkowski metric were found, indicating different processing types. However, for individuals participating in both experiments, there wasno correlation between the results of the two experimental paradigms. This is interpreted as a result of the subject's ability to choose between a few perceptual-processing options.     

Acoustic orientation in adult, female crickets (Gryllus bimaculatus de Geer) after unilateral foreleg amputation in the larva

Summary InGryllus bimaculatus females one foreleg was amputated at the coxa-trochanter joint in the 2nd, 4th or 8th/9th larval instar. A leg of up to normal length is regenerated (Fig. 1) but it lacks a functional ear. In spite of the, usually shorter, regenerated foreleg, the adult one-eared crickets show no impairments in walking when tested on a locomotion compensator. Without sound they walk erratically and most of them weakly circle towards the intact side (Fig. 2).With calling song presentation three response types can be distinguished:tracking (Fig. 3A), hanging on (Fig. 3B) or continuouscircling towards the intact side (Fig. 3C, D). Turning tendencies in monaurals increase with song intensity and exceed those of intact and bilaterally operated animals (Fig. 4). Course deviations towards the intact side also slightly increase with intensity (Fig. 5). Course stability is reduced compared to that of intact animals but exceeds that of bilaterally operated crickets (Figs. 5, 6). It is best at 60 dB and deteriorates at higher sound intensities (Fig. 6). The percentage of monaurals tracking or hanging on decreases with increasing intensity (Fig. 7B). Tracking is established in most animals but it is limited to a narrow intensity range (Fig. 7A, C). Apart from an increased percentage of tracking after early operations (Fig. 7D), there are no prominent changes in orientational parameters with the date of foreleg amputation.Reamputation of the regenerated leg in the adult monaurals does not significantly impair acoustic orientation (Figs. 8, 9), but occlusion of the ipsilateral prothoracic spiracle does (Figs. 10, 11).An attempt is made to correlate the behavioral performance with the activity of auditory interneurons which have undergone morphological and physiological changes (Fig. 12).     

Observations on the leg receptors ofCiniflo (Araneida: Dictynidae)

Summary The curved, blunt-tipped hairs on the legs ofCiniflo have a structure characteristic of contact chemoreceptors. Using a hair tip recording technique, it has been possible to confirm that these sensilla do respond to contact stimulation by certain chemical substances (Figs. 1 and 3). A few experiments were also performed onTegenaria (Fig. 2). So far, positive responses to some monavalent salts (Figs. 1 and 2) and hydrochloric acid (Fig. 3) have been established, involving perhaps 5 to 6 chemoreceptor units in all. However, each sensillum is known to have 19 chemoreceptor cells and thus most of the reaction spectrum of the sensillum remains unknown. The suggestion that, in contrast to insect contact chemoreceptors (which usually have only 4–7 sensory units), some of the dendrites may be very specific receptor units and are perhaps involved in the detection of contact pheromones or other equally specific substances, is discussed.One of the authors (DJH) would like to thank the Science Research Council for a research studentship, during which this work was carried out. Thanks are also due to Mr. J. Scott, Mr. C. Gilbert and Mr. R. Stevenson for their excellent technical help.     

Centrophobism inDrosophila melanogaster

Summary The term centrophobism is introduced to describe a newly discovered modification of search behavior in the walking fruitfly,Drosophila melanogaster: the avoidance of the center of an arena after diethylether narcosis. Evidence for the effect is obtained by comparison of the tracks of etherized and non-etherized flies under the influence of olfactory attractant around the center of the arena (Fig. 3). The tracks can be distinguished by their mean radial distance from the central district of the arena. Centrophobia denotes the relative difference of the distances of etherized flies and non-etherized controls (Fig. 4).Etherized flies avoid the center of the arena in spite of the attraction of olfactory, thermal or visual cues. The avoidance is significant even in the absence of conspicuous sensory cues for the discrimination of center and surround. The centrophobia obtained in the arena can be used to estimate the efficacy of attractants in the non-etherized control flies (Figs. 6, 7).The lowest possible dose of ether sufficient to elicit narcosis is sufficient to induce centrophobia. None of the other prevalent insect anaesthetics, CO₂, N₂ and cold, substitutes ether in the present experiments (Figs. 8, 9).Centrophobia arises immediately after ether narcosis. Once induced the effect lasts apparently undiminished for the life time of the flies (Fig. 9).Centrophobia has been found in either sex of the 9 strains tested so far (Fig. 5). Four strains including mutants deficient in wing formation (vestigial) or learning (dunce) show either temporal decline or partial suppression of centrophobia. The anomalous properties are actually due to enhanced spontaneous centrophobism in the non-etherized control groups of these strains (Fig. 10).     

Morphological and physiological properties of pheromone-triggered flipflopping descending interneurons of the male silkworm moth,Bombyx mori

1. The morphology of descending interneurons (DNs) which have arborizations in the lateral accessory lobe (LAL) of the protocerebrum, the higher order olfactory center, and have an axon in the ventral nerve cord (VNC), were characterized in the male silkworm moth, Bombyx mori.
2. Two clusters (group I, group II) of DNs which have arborizations mainly in the LALs were morphologically characterized. The axons of these DNs are restricted to the dorsal part of the each connective (Figs. 1–5).
3. Pheromonal responses of the group I and group II DNs were characterized. Flipflopping activity patterns, which have two distinct firing frequencies (high and low) in response to sequential pheromonal stimulation, were usually recorded (Figs.6–10).
4. Two types of flipflopping activity patterns were classified into those that had an antiphasic relationship (called the ‘FF’ type) between the left and right connectives and those with a synchronized relationship (‘ff’ type) (Figs. 8–12). We propose that some group II DNs show ‘FF’ flipflopping activity patterns (Fig. 10).
5. A state transition was usually elicited by less than 10 ng bombykol, the principal pheromone component. Extra impulses were elicited during constant light stimulation (Fig. 9).
6. Our results suggest that the LAL olfactory pathways might be important for producing flipflopping activity patterns (Fig. 11).

     

Characterization of vibrational and visual signals which elicit spawning behavior in the male himé salmon (landlocked red salmon,Oncorhynchus nerka)

Himé salmon (landlocked red salmon, Oncorhynchus nerka) have an elaborate communication system, which ensures synchronous spawning by both sexes and successful fertilization. Both the vibrational and visual signals have been suggested to be involved in this communication system. To characterize these signals, vibrating or stationary three-dimensional models of various types were presented to the male, and male behavior elicited was examined. The results showed that the vibrating model mimicking certain aspects of the female behavior (prespawning act) elicits the spawning in the male (Figs. 2, 3, 5). Furthermore, it was found that (1) the presence of both the vibrational and visual cues (Figs. 6, 7), and (2) spatial coincidence of these two cues (Fig. 8) are necessary for eliciting this behavior. Based on these results it was supposed that the vibrational and visual informations converge at the central nervous system where they are integrated to elicit the spawning.     

Splitting of the circadian rhythm of activity in hamsters: Effects of exposure to constant darkness and subsequent re-exposure to constant light

Summary The circadian rhythm of wheel running behavior was observed to dissociate into two distinct components (i.e. split) within 30 to 110 days in 56% of male hamsters exposed to constant light (Figs. 1–2). Splitting was abolished in all 16 animals that were transferred from constant light (LL) to constant darkness (DD) within 1–4 days of DD, and the components of the re-fused activity rhythm assumed a phase relationship that is characteristic of hamsters maintained in DD (Figs. 3–5). Re-fusion of the split activity rhythm was accompanied by a change in period (); in 14 animals increased while in the other 2 animals decreased after transfer to DD.After 10–30 days in DD, the hamsters were transferred back into LL at various time points throughout the circadian cycle. A few of these animals went through two or three LL to DD to LL transitions. The effect of re-exposure to LL was dependent on the phase relationship between the transition into LL and the activity rhythm. A rapid (i.e. 1–4 days) induction of splitting was observed in 7 of 9 cases when hamsters were transferred into LL 4–5 h after the onset of activity (Fig. 5). In the other 2 animals, the activity pattern was ultradian or aperiodic for 20 to 50 days before eventually coalescing into a split activity pattern. In contrast, transfer of animals (n = 13) from DD to LL at other circadian times did not result in the rapid induction of splitting and the activity rhythm continued to free-run with a single bout of activity (Fig. 5). Importantly, a transfer from DD to LL 4–5 h after the onset of activity did not induce splitting if the hamsters had not shown a split activity rhythm during a previous exposure to LL (n=10; Fig. 6).These studies indicate that transfer of split hamsters from LL to DD results in the rapid re-establishment of the normal phase relationship between the two circadian oscillators which underlie the two components of activity during splitting. In addition, there appears to be a history-dependent effect of splitting which renders the circadian system susceptible to becoming split again. The rapid re-initiation of the split condition upon transfer from DD to LL at only a specific circadian time is discussed in terms of the phase response curve for this species.Abbreviation PRC phase response curve This investigation was supported by NIH grants HD-09885 and HD-12622 from the National Institute of Child Health and Human Development and by a grant from the Whitehall FoundationRecipient of Research Career Development Award K04 HD-00249 from the National Institute of Child Health and Human Development     

CO2 sensitive receptors on labial palps ofRhodogastria moths (Lepidoptera: Arctiidae): physiology,fine structure and central projection

Summary The tips of the labial palps ofRhodogastria possess a pit housing uniform sensilla (Fig. 1), histologically characterized by wall-pores and receptor cells with lamellated outer dendrites (Fig. 2). The receptor cell axons project to glomeruli in the deutocerebrum (cf. Fig. 3) which are not innervated by antennal receptors. From their histology as well as from their central projection these sense organs are identical with palpal pit organs of other Lepidoptera (Lee et al. 1985; Kent et al. 1986; Lee and Altner 1986).Physiologically, the palp-pit receptors respond uniformly; they are most excitable by stimulation with carbon dioxide (Fig. 6) while they exhibit relatively moderate responses to various odorants (Fig. 4). The responses to CO₂ (Fig. 7) show a steep dose-response characteristic. In ambient atmosphere (i.e., ca. 0.03% CO₂) the cells are in an excited condition already; the seeming spontaneous activity exhibited in air is decreased if the preparation is kept under N₂ or O₂ or CO₂-free air (Figs. 7, 10). There is hardly any adaptation of the responses to continuous or repeated stimulation (Fig. 8). Perhaps CO₂ sensitivity is correlated with sensilla characterized by both wall-pores and lamellated dendrites. Pilot tests indicate that CO₂ perception might be widespread in the Lepidoptera (cf. Fig. 12), but the biological significance remains obscure.     

On the nature of the uncoupling effect of fatty acids

The effect of palmitic acid on the electrical potential difference across the inner mitochondrial membrane appears to depend on the medium in which mitochondria are incubated. In medium A (cf. Luvisettoet al. (1987),Biochemistry,26, 7332–7338) decreases much more than in medium B (cf. Rottenberg and Hashimoto (1986),Biochemistry,25, 1747–1755) at concentrations of fatty acid which equally stimulate the rate of respiration in state 4. Valinomycin and NaCl were both present in medium B and absent in medium A. However, in both media the pattern of the P/O ratio as a function of antimycin in the presence of a constant amount of palmitic acid or of FCCP shows similar behaviour. We conclude that in both media palmitic acid increases the membrane conductance to protons, but for unclear reasons the assay fails to measure the decline of in medium B. However, the increase in membrane conductance induced by palmitic acid does not quantitatively account for the stimulation of the rate of respiration.     

Die Wirkung von „Störlicht” auf die Blütenbildung von Sinapis alba L.

Summary The induction of flowering in mustard (Sinapis alba L.) was studied by means of night-breaks (Störlicht). The plants were cultivated under fully controlled conditions: 8000 Lux white light (mixed fluorescent and incandescent) 18°C, 80% relative humidity. Raised under our conditions in short days (8 hours of white light) mustard behaved as a quantitative long-day plant (Fig. 2). Flowering can be promoted by long-day treatment (Fig. 3). The long day (16 hours of white light) can be replaced by a short day plus a night-break. The highest effectiveness of the night-break is found near the middle of the dark period (Figs. 4, 5). —The spectral dependence of flower induction was studied with blue, green, yellow, red (Fig. 1) and far-red light using a 2-hour break near the middle of the dark period. The dose response curves (Fig. 6) and the action spectrum (Fig. 7) indicate a very strong effectiveness in the blue part of the spectrum, a small response in red and yellow light and no response at all in green and far-red light. The participation of phytochrome is indicated (Table 1), but no far-red reversibility could be detected (Table 2). Simultaneous irradiation with red and far-red light yielded significant enhancement effects (Fig. 8). In view of the strong shadowing in the leaves (Figs. 9, 10) these data are interpretable on the basis of phytochrome.     

Optical properties of the ocelli of Calliphora erythrocephala and their role in the dorsal light response

The 3 ocelli of the blowfly Calliphora erythrocephala, grouped close together on the top of the head (Fig. 1), have large, extensively overlapping visual fields. Together they view the entire upper hemisphere of the surroundings plus part of the lower hemisphere (Figs. 5, 7). It is shown for the lateral ocelli that despite the underfocussing of the ocellar lens large patterns are imaged on the receptor mosaic. Because of the astigmatism of the lens, patterns in longitudinal orientations are more accurately represented than in others (Fig. 3). Nevertheless, an artifical horizon rotated around the long axis of the animal does not elicit head roll. Likewise, changes of overall brightness in the visual field of the median and one lateral ocellus elicit only weak phasic-tonic dorsal light responses of the animal which supplement the tonic dorsal light responses mediated by the compound eyes (Figs. 9, 10). Our results show that, in Calliphora, the ocelli have little influence on head orientation during flight, and must be assumed to serve other functions.Abbreviations body pitch angle - head-tilt angle - DNOVS descending neuron of the ocellar and vertical cell systems - HR head roll - spatial wavelength - R roll angle - SD standard deviation     

Wind-evoked evasive responses in flying cockroaches

1. A standing cockroach (Periplaneta americana) responds to the air displacement made by an approaching predator, by turning away and running. The wind receptors on the cerci, two posterior sensory appendages, excite a group of ventral giant interneurons that mediate this response. While flying, these interneurons remain silent, owing to strong inhibition; however, the dorsal giant interneurons respond strongly to wind. Using behavioral and electromyographic analysis, we sought to determine whether flying cockroaches also turn away from air displacement like that produced by an approaching flying predator; and if so, whether the cerci and dorsal giant interneurons mediate this response.
2. When presented with a wind puff from the side, a flying cockroach carries out a variety of maneuvers that would cause a rapid turn away and perhaps a dive. These are not evoked if the cerci are ablated (Figs. 4, 5, 6).
3. This evasive response appears to be mediated by a circuit separate from that mediating escape when the cockroach is standing (Fig. 7).
4. The dorsal giant interneurons respond during flight in a directional manner that is suited to mediate this behavior (Fig. 8).
5. Recordings of the wind produced by a moving model predator (Fig. 9), together with measurements of the behavioral latency of tethered cockroaches, suggest that the evasive response would begin just milliseconds before a predator actually arrives. However, as explained in the Discussion section, under natural conditions, the evasive response may well begin earlier, and could indeed be useful in escaping from predators.
6. If cockroaches had a wind-mediated yaw-correcting behavior, as locusts have, this could conflict with the wind-evoked escape. In fact, cockroaches show the opposite, yaw-enhancing response, mediated by the cerci, that does not present a conflict with escape (Figs. 10–14).

     

Properties of elementary movement detectors in the flyCalliphora erythrocephala

Summary Experiments, involving sequential micro-stimulation of two (or more) adjacent neuroommatidia in the compound eye of the blowfly,Calliphora erythrocephala (Mg.), are presented. These experiments, using brief flashes of 3 ms duration with low intensities in the order of 8·10^–3 Cd/m², are performed to isolate individual response contributions of single Elementary Movement Detectors in the input micro-circuitry of the motion-sensitive directionally-selective H1-neuron (Figs. 4 through 6). A two-dimensional mapping of single EMD contributions to the overall response will be presented for the dark adapted eye (Fig. 7). It is concluded that under such low illumination levels (when compared to normal daylight situations, where illumination typically varies between 1 and 200 Cd/m²), contributions from EMD's with sampling bases up to 8 _h, oriented along the horizontal sensitivity axis of the neuron, contribute to the total response of the neuron. In addition, results will be presented for similar experiments, in which various backgrounds with different sizes and intensities are superimposed on the sequence of stimulus flashes (Fig. 8). The dependence of the relative contributions for the smallest four sampling bases (i.e. 2, ..., 8 times _h) on background size, background intensity and distance of the background field to the projections of the flashes, will be discussed. Supplementary experiments (Figs. 9 through 12) will be presented, which indicate that when in addition to an ongoing sequence in (for instance) the null direction, thus inhibiting the activity of the neuron, a second sequence is presented somewhere in the receptive field of the H1-neuron, the total response is a non-linear combination of both individual responses. Interpretation in terms of a pooling correlation scheme, which, over a limited target region, sums the activities of the EMD's in a highly non-linear fashion, provides a qualitative explanation.Abbreviations EMD elementary movement detecors - H1-neuron horizontally-selective motion sensitive neuron in the lobula plate - PSTH post stimulus time histogram - inter-ommatidial angle - FFRP far field radiation pattern - F1 wild-type - R _1–6 classes of retinula cells in each fly ommatidium - C _x,y nomenclature for the EMD's