Melatonin reduces arousal and startle responsiveness without influencing startle habituation or affective startle modulation in young women

Melatonin has been suggested to affect human emotion, but conflicting evidence exists. Therefore, we tested the effect of a single dose of a 4 mg prolonged release formulation of melatonin on a biologically based model of emotional processing. Affective modulation of acoustic white noise startle (103 dB) by emotional slides selected from the International Affective Picture System (IAPS) was assessed in 16 healthy young women twice, in a double-blind, placebo-controlled, balanced cross-over design. Melatonin significantly reduced startle responsiveness, but did not impact affective startle modulation, nor startle habituation. Melatonin significantly reduced arousal ratings and induced a parasympathetically dominated heart rate variability pattern indicative of a non-aroused state. We conclude that melatonin reduces arousal and startle responsiveness. However, no evidence for a direct emotion-modulating effect of melatonin was found in this healthy cohort.     

Acoustic startle/escape reactions in tethered flying locusts: motor patterns and wing kinematics underlying intentional steering

We simultaneously recorded flight muscle activity and wing kinematics in tethered, flying locusts to determine the relationship between asymmetric depressor muscle activation and the kinematics of the stroke reversal at the onset of wing depression during attempted intentional steering manoeuvres. High-frequency, pulsed sounds produced bilateral asymmetries in forewing direct depressor muscles (M97, 98, 99) that were positively correlated with asymmetric forewing depression and asymmetries in stroke reversal timing. Bilateral asymmetries in hindwing depressor muscles (M127 and M128 but not M129) were positively correlated with asymmetric hindwing depression and asymmetries in the timing of the hindwing stroke reversal; M129 was negatively correlated with these shifts. Hindwing depressor asymmetries and wing kinematic changes were smaller and shifted in opposite direction than corresponding measurements of the forewings. These findings suggest that intentional steering manoeuvres employ bulk shifts in depressor muscle timing that affect the timing of the stroke reversals thereby establishing asymmetric wing depression. Finally, we found indications that locusts may actively control the timing of forewing rotation and speculate this may be a mechanism for generating steering torques. These effects would act in concert with forces generated by asymmetric wing depression and angle of attack to establish rapid changes in direction.Abbreviations ASR acoustic startle response - dB SPL decibel sound pressure level (re: 20 Pa RMS) - EMG electromyogram - FWA forewing asymmetry - HWA hindwing asymmetry     

Control of flight by means of lateral visual stimuli in gregarious desert locusts, Schistocerca gregaria

Abstract. Tethered flying locusts were stimulated either by a periodic grating or by a spotted 'swarm-simulating' pattern moving horizontally, parallel to their longitudinal body axis within their lateral visual fields. The direction of movement of the pattern was changed periodically from progressive to regressive and vice versa.
Both kinds of patterns induced a correlated modulation of yaw-torque and thrust. The two measured flight parameters were modulated independently of each other. Each parameter either increased with progressive and decreased with regressive pattern motion or vice versa. The characteristic curves of thrust and yaw-torque responses - i.e. response amplitude versus contrast frequency resp. angular velocity – measured upon stimulation with the periodic grating between 2 and 70 Hz were at a maximum at 10 Hz and decreased at higher and lower contrast frequencies. The shape of the curves was nearly identical. The characteristic curves measured upon stimulation with the 'swarm-simulating' pattern between 60 and 1500^o s^-1 could be simulated using the spatial wavelength content of the pattern and the characteristic curves for periodic gratings.
Therefore, we suggest that the speed and direction of locusts' flight result from the optomotor effectiveness of the pattern image formed by the neighbouring individuals under free flight. The measured responses would thus contribute to the common orientation of groups of locusts within a migrating swarm and thus to swarm cohesion.     

Adipokinetic hormone content of the corpora cardiaca in gregarious and solitary migratory locusts

Abstract. The adipokinetic hormone (AKH-I and AKH-II) content of the corpora cardiaca from adult males of crowded (gregarious) and isolated (solitary) Locusta migratoria migratorioides (Reiche & Fairmaire) was quantified by reverse-phase high-performance liquid chromatography.Significantly less total hormone was found in the corpora cardiaca of crowded locusts than in those glands of isolated locusts at the age of 12–19 days after fledging.The ratio of AKH-I/AKH-II was higher in crowded than in isolated locusts at this age.From the age of 12–19 days to that of 25–30 days, AKH content increased significantly in the corpora cardiaca of crowded locusts, but no such increase was found in the glands of isolated locusts, and at 25–30 days there were no significant differences in the AKH content of the glands from crowded and isolated locusts.     

Activity of the forewing stretch receptor in immature and mature adult locusts

Maturation of the flight system of Locusta migratoria occurs during the first two weeks following imaginal ecdysis. One aspect of maturation is an increase in the wingbeat frequency from about 13 Hz to about 23 Hz. We investigated physiological and anatomical mechanisms that may contribute to this process. The difference between the frequencies of the central flight rhythms of immature and mature deafferented preparations was not as great as that between the wingbeat frequencies of immature and mature intact animals. Results from static and dynamic wing elevation showed that the intensity of the forewing stretch receptor response to a given stimulus increased during maturation. The diameter of the main stretch receptor axon was larger and the conduction velocity of signals conveyed along the forewing stretch receptor and the dorsal longitudinal motoneuron was faster in mature than in immature animals. We conclude that during maturation of the flight system the forewing stretch receptor responds to wing elevation with a higher frequency signal that reaches the central circuitry faster. These findings are discussed in the context of a model that describes the influence of stretch receptor input on wingbeat frequency along with other potential mechanisms involved in flight maturation.Abbreviations fDLMn forewing dorsal longitudinal motoneuron - fSR forewing stretch receptor - SR stretch receptor     

The role of proprioception for motor learning in locust flight

In a muscle-specific flight simulator (simulator driven by muscle action potentials) locusts (Locusta migratoria) show motor learning by which steering performance of the closed-loop muscles is improved. The role of proprioceptive feedback for this motor learning has been studied. Closed-loop muscles were cut in order to disable proprioceptive feedback of their contractions. Since there are no proprioceptors within the muscles, this is a muscle-specific deafferentation. Cut muscles are still activated during flight and their action potentials can be used for controlling the flight simulator. With cut muscles in closed-loop, steering is less reliable as can be seen from the frequent oscillations of the yaw angle. However, periods of stable flight indicate that deafferented muscles are still, in principle, functional for steering. Open-loop yaw stimuli reveal that steering reactions in cut muscles are weaker and have a longer delay than intact muscles. This is responsible for the oscillations observed in closed-loop flight. Intact muscles can take over from cut muscles in order to re-establish stable closed-loop flight. This shows that proprioceptive mechanisms for learning are muscle specific. A hypothetical scheme is presented to explain the role of proprioception for motor learning.     

Central nervous processing of behaviourally relevant odours in solitary and gregarious fifth instar locusts, Schistocerca gregaria

Physiological and morphological characteristics of antennal lobe neurons of solitary and gregarious fifth-instar nymphs of the desert locust, Schistocerca gregaria, were studied using intracellular recording and staining techniques. Physiological characteristics of antennal lobe neurons of both locust phases responding to stage-dependent aggregation pheromones, egg-laying attractants, a putative sex pheromone and plant-associated volatiles are described. Antennal lobe neurons showed excitatory, inhibitory, combined excitatory and inhibitory and delayed responses. In addition, one neuron␣showing an initial inhibition followed by an excitation and inhibition response was found. Pheromone-specific-, plant-specific- and pheromone-plant-generalist neurons were found in both locust phases. Antennal lobe neurons displayed stage- and phase-dependent differences in the processing of aggregation pheromone component input. Nymphal antennal lobe neurons showed stage-dependent response characteristics highly correlated with the preferential behavioural attraction to the nymphal aggregation pheromone. Phase-dependent differences were found in the response spectra and the sensitivity of the same neuron types. Neurons of solitary locusts responded significantly more frequently to some of the tested components than neurons of gregarious locusts. Furthermore, antennal lobe neurons of solitary locusts showed a higher sensitivity to most of the tested compounds. Accepted: 4 July 1998     

Visual control of steering in locust flight: the effects of head movement on responses to roll stimuli

The contribution of head movement to the control of roll responses in flying locusts (Locusta migratoria) has been examined (i) on a flight balance, recording the angles through which the locust turns when following an artificial horizon; (ii) by recording activity in a pair of flight muscles in restrained conditions; and (iii) by observations on free flying locusts. Responses were compared when the head was free to turn about the thorax, as normal, and when the head was waxed to the thorax, blocking any relative motion between the two (head-fixed). These experiments suggest that the major signal generating corrective roll manoeuvres is the visual error between the angle of the head and the horizon, rather than a signal that includes a measure of the head-thorax angle.

Prepulse inhibition of the startle reaction in the locust Locusta migratoria (Insecta: Orthoptera: Acridoidea)

A fast startle reaction of unrestrained sitting locusts (Locusta migratoria) can be elicited by sound pulses of steep rise time above 80 dB. The reaction consists of a fast jerky movement of legs and body with a mean latency of 35 ms and graded amplitude. The fast startle reaction did not result in any positional change; this was in contrast to acoustically induced escape reactions of flying Orthoptera. The startle reaction could be inhibited by pure tone stimuli of much lower intensity (60 dB) presented 160 ms before the startle-eliciting noise. This type of reflex modification is a striking convergence to the well-known prepulse inhibition of the mammalian startle response where it has been used to assess sensory thresholds. In the locust, prepulses between 3 and 20 kHz suppressed the startle reaction completely, with thresholds in the locust's hearing range as known from tympanal nerve recordings. No inhibition could be observed at prepulse frequencies of 40 kHz, although this frequency lies within the locust's hearing range. The presence of prepulse inhibition in an invertebrate preparation shows that it is not restricted to vertebrates.     

Neuronal co-processing of course deviations and head movements in locusts

Summary In Locusta migratoria, the major pathway from descending deviation detectors (DDNs; preceding paper, Hensler 1992) to wing motoneurons involves a population of thoracic interneurons (TINs). Nine TINs are characterized which receive input from cervical proprioreceptors. Responses to the combination of exteroreceptive input (signalling course deviation) and proprioreceptive input (monitoring movement and position of the head) are described and compared to those of DDNs to the same stimuli.Abbreviations AP action potential - DDN descending deviation detector neuron - TCG tritocerebral giant neuron - TIN thoracic interneuron     

Neuronal co-processing of course deviation and head movements in locusts

Summary Descending deviation detector neurons (DDNs) of Locusta migratoria are characterized physiologically by their responses to light on/off stimuli, simulated course deviation (rotation of an artificial horizon), passive rotation of the head, frontal wind, and flight activity. The investigation emphasises on the co-processing of exteroceptive input signalling course deviation (mainly movement of the retinal image, but also wind), and proprioceptive input signalling head movement and position. Stimuli were presented in combinations as expected during natural behavior. Eight DDNs are described for the first time, and 3 previously described DDNs are characterized further. Responses to horizon rotation and imposed head movements are assigned to one of 4 response types: (1) the horizon-only type codes retinal slip and/or the position of the horizon in the visual field but ignores cervical proprioception; (2) the head-only type ignores visually simulated course deviation but codes for movement or position of the head; (3) in the compensating type, head rolling causes visual input and cervical proprioceptive input of opposite signs, so that head movements themselves are ignored, whereas course deviations are recognized; (4) in the amplifying type, head rolling causes visual input and cervical proprioceptive input of the same sign, i.e. one input amplifies the other. This classification does not take the various responses to wind into account. In several DDNs, responses to phasic and tonic stimuli of the same modality, and/or responses to deviations about different axes could be assigned to different response types. Activity in DDNs has been shown previously to result in steering responses of wings, legs, abdomen and/or the head. It is proposed that different kinds of flight steering (e.g. corrective course control, intentional steering, orientation towards or away from a target) may be controlled by selective enhancement or suppression of responses or motor effects of DDN-subpopulations.Abbreviations AP action potential - DDN descending deviation detector neuron - DNI, DNC, DNM descending deviation detector neurons receiving major input from the ipsilateral, contralateral, and median ocellus respectively - PDDSMD protocerebral, descending direction-selective motion-detecting neuron - PI(2)5 descending deviation detector neuron with the cell body in the pars intercerebralis medialis - TCG tritocerebral commissure giant neuron     

Characterisation of columnar neurons and visual signal processing in the medulla of the locust optic lobe by system identification techniques

We describe visual responses of seventeen physiological classes of columnar neuron from the retina, lamina and medulla of the locust (Locusta migratoria) optic lobe. Many of these neurons were anatomically identified by neurobiotin injection. Characterisation of neuronal responses was made by moving and flash stimuli, and by two system identification techniques: 1. The first-order spatiotemporal kernel was estimated from response to a spatiotemporal white-noise stimulus; 2. A set of kernels to second order was derived by the maximal-length shift register (M-sequence) technique, describing the system response to a two-channel centre-surround stimulus. Most cells have small receptive fields, usually with a centre diameter of about 1.5°, which is similar to that of a single receptor in the compound eye. Linear response components show varying spatial and temporal tuning, although lateral inhibition is generally fairly weak. Second-order nonlinearities often have a simple form consistent with a static nonlinear transformation of the input from the large monopolar cells of the lamina followed by further linear filtering.Abbreviations LMC large monopolar cell - LVF long visual fibre - RF receptive field - SMC small monopolar cell - SVF short visual fibre     

The neuroethology of escape in crabs: from sensory ecology to neurons and back

A major challenge in neurobiology is to understand how brains function in animals behaving in the complexity of their natural environment. Progress will depend on our ability to correctly interpret results from laboratory experiments in the light of information processing demands identified by studying the organization of behaviour and the flow of information in naturally behaving animals. Predator avoidance responses of semi-terrestrial crabs offer an excellent opportunity for such an approach. We review here findings from two distinct lines of research: (1) Field studies which have characterized the structure and context of escape behaviour to real and dummy predators, and (2) Laboratory studies which have used computer-simulated images and in vivo intracellular recordings to identify and characterize individual neurons implicated in the control of escape. The results of both approaches highlight the influence of behavioural and environmental context in structuring escape. In order to understand how context and the complex flow of signals are processed and translated into behaviour in natural environments it is imperative that future studies take electrophysiology outdoors.     

The role of octopamine in locusts and other arthropods

The biogenic amine octopamine and its biological precursor tyramine are thought to be the invertebrate functional homologues of the vertebrate adrenergic transmitters. Octopamine functions as a neuromodulator, neurotransmitter and neurohormone in insect nervous systems and prompts the whole organism to “dynamic action”. A growing number of studies suggest a prominent role for octopamine in modulating multiple physiological and behavioural processes in invertebrates, as for example the phase transition in Schistocerca gregaria. Both octopamine and tyramine exert their effects by binding to specific receptor proteins that belong to the superfamily of G protein-coupled receptors. Since these receptors do not appear to be present in vertebrates, they may present very suitable and specific insecticide and acaricide targets.     

The role of Slit-Robo signaling in the generation, migration and morphological differentiation of cortical interneurons

Cortical interneurons in rodents are generated in the ventral telencephalon and migrate tangentially into the cortex. This process requires the coordinated action of many intrinsic and extrinsic factors. Here we show that Robo1 and Robo2 receptor proteins are dynamically expressed throughout the period of corticogenesis and colocalize with interneuronal markers, suggesting that they play a role in the migration of these cells. Analysis of Robo mutants showed a marked increase in the number of interneurons in the cortices of Robo1^−/−, but not Robo2^−/−, animals throughout the period of corticogenesis and in adulthood; this excess number of interneurons was observed in all layers of the developing cortex. Using BrdU incorporation in dissociated cell cultures and phosphohistone-3 labeling in vivo, we demonstrated that the increased number of interneurons in Robo1^−/− mice is, at least in part, due to increased proliferation. Interestingly, a similar increase in proliferation was observed in Slit1^−/−/Slit2^−/− mutant mice, suggesting that cell division is influenced by Slit-Robo signaling mechanisms. Morphometric analysis of migrating interneurons in Robo1^−/−, Robo2^−/− and Slit1^−/−/Slit2^−/−, but not in Slit1^−/− mice, showed a differential increase in neuronal process length and branching suggesting that Slit-Robo signaling also plays an important role in the morphological differentiation of these neurons.     

The life cycle of Gregarina ronderosi n. sp. (Apicomplexa: Gregarinidae) in the Argentine grasshopper Dichroplus elongatus (Orthoptera: Acrididae)

Gregarina ronderosi n. sp. is described based on life cycle observations conducted on nymphs and adults of its natural host, the grasshopper Dichroplus elongatus. Following ingestion of oocysts by the host, parasite development occurs between the epithelium and the food mass in the midgut and gastric caeca. Gametocysts are liberated in the faeces. Natural prevalence in the type locality, Girondo, northwestern Buenos Aires Province, was 39.7% (n=131). The earliest trophozoites seen were small (< or = 10 microm), somewhat ovoid, unsegmented bodies. Fully developed trophozoites (the body is divided into epimerite, protomerite, and deutomerite) were slender, with conical or globular epimerites in attached or unattached forms, respectively. Trophozoites varied greatly in size [total length: 10.4-275.1 microm; mean (+/-S.E.): 126.3+/-78.9]. Gamonts, which were the most common stages observed and filled the midgut and gastric caeca in grasshoppers kept in rearing rooms, had a stocky appearance and also varied greatly in size (total length: 80-348 microm; 205+/-13). Association of gamonts was precocious, biassociative, and caudofrontal. Gametocysts were spherical and highly variable in size (96-376 microm in diameter; 202.8+/-52.5), and normally have 14 sporoduct basal discs. Everted sporoducts were up to 60 microm long. Oocysts were uniformly doliform in shape, measured (5+/-0.08 by 3.2+/-0.06 microm) and contained eight sporozoites. Wall reinforcements (carinae) were present. No infection resulted in experimentally inoculated Locusta migratoria, which is a host of Gregarina acridiorum. G. ronderosi is strikingly similar to G. acridiorum, but has larger oocysts.     

Neurophysiology of the vibration sense in locusts and bushcrickets: The responses of ventral-cord neurones

In the locustid Locusta migratoria and the tettigoniids Decticus verrucivorus and Tettigonia cantans, comparative aspects of physiological properties of vibratory/auditory ventral-cord neurones were studied by single cell recordings.These neurones all receive inputs from both vibratory and auditory receptors. Nevertheless, they can be classified into “V neurones” responding preferentially to vibration stimuli, “VS neurones” responding to vibration and airborne sound, and “S neurones” responding preferentially to airborne sound. In every group, there are several types with different physiological properties, normally represented by one neurone on each body side.In Locusta and in the tettigoniid species, the same physiological types of vibratory/auditory neurones were found, although there are differences in the synaptic connectivity of the vibration receptors of the different legs. In Locusta, the middle leg receptors have the strongest influence on the generation of suprathreshold responses of the central neurones, whereas in the tettigoniids the receptors of the ipsilateral fore leg are the most influential.Two of the V neurones receive inputs mainly from campaniform sensilla and other low-frequency vibration receptors, the other V and VS neurones are mainly influenced by the subgenual receptors. Central information processing results in preferential responses to different frequency/intensity ranges in different neurones.Most VS neurone types show the same response characteristics (e.g. time pattern of response, habituation) either to vibration or to airborne-sound stimuli. Simultaneous presentation of both stimuli leads to qualitative changes in the response characteristics. Therefore, the co-processing of auditory and vibratory signals seems to be very important in the acoustic behaviour of grasshoppers.     

Ontogeny of routine swimming speed and startle responses in red drum, with a comparison of responses to acoustic and visual stimuli

Routine swimming speed of larval red drum Sciaenops ocellatus increased throughout development but most rapidly for larvae >10 mm L _T. Red drum of all sizes swam faster than predicted by published summary equations based on other species, possibly due to more advanced development at a given length. Frequency and magnitude of startle responses increased over the larval period for both types of stimuli with most of the improvement taking place before larvae reached 8 mm L _T. Time to response for an acoustic and visual stimulus decreased early in the larval period but levelled off after 10 mm L _T. Response distance and response speed for both stimuli generally increased throughout the larval period, but response duration remained constant. Visually stimulated responses were generally longer in duration and distance covered than acoustically stimulated responses, while mean response speeds were similar.