Showing papers in "Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology in 1995"

Colour preferences of flower-naive honeybees

Abstract: Flower-naive honeybees Apis mellifera L. flying in an enclosure were tested for their colour preferences. Bees were rewarded once on an achromatic (grey, aluminium or hardboard), or on a chromatic (ultraviolet) disk. Since naive bees never alighted on colour stimuli alone, a scent was given in combination with colour. Their landings on twelve colour stimuli were recorded. Results after one reward (“first test”) were analysed separately from those obtained after few rewards (“late tests”). 1) After pre-training to achromatic signals, bees preferred, in the first test, bee-uv-blue and bee-green colours. With increasing experience, the original preference pattern persisted but the choice of bee-blue and bee-green colours increased. 2) Neither colour distance of the test stimuli to the background or to the pre-training signal, nor their intensity, nor their green contrast, accounted for the colour choice of bees. Choices reflected innate preferences and were only associated with stimulus hue. 3) Bees learned very quickly the pre-trained chromatic stimulus, the original colour preferences being thus erased. 4) Colour preferences were strongly correlated with flower colour and its associated nectar reward, as measured in 154 flower species. 5) Colour preferences also resemble the wavelength dependence of colour learning demonstrated in experienced bees.

Innate colour preferences of flower visitors

Abstract: Freshly emerged flower visitors exhibit colour preferences prior to individual experience with flowers. The understanding of innate colour preferences in flower visitors requires a detailed analysis, as, on the one hand, colour is a multiple-signal stimulus, and, on the other hand, flower visits include a sequence of behavioural reactions each of which can be driven by a preferential behaviour. Behavioural reactions, such as the distant approach, the close-range orientation, the landing, and the extension of mouthparts can be triggered by colour stimuli. The physiological limitations of spectral sensitivity, the neuro-sensory filters, and the animals' different abilities to make use of visual information such as brightness perception, wavelength-specific behaviour and colour vision shape colour preferences. Besides these receiverbased factors, there are restrictions of flower colouration due to sender-based factors such as the absorption properties of floral pigments and the dual function of flower colours triggering both innate and learned behaviour. Recordings of the spectral reflection of coloured objects, which trigger innate colour preferences, provide an objective measure of the colour stimuli. Weighting the spectral reflection of coloured objects by the spectral composition of the ambient light and the spectral sensitivity of the flower visitors' photoreceptors allows the calculation of the effective stimuli. Perceptual dimensions are known for only a few taxa of flower visitors.

Chemical communication in heliothine moths. 5. Antennal lobe projection patterns of pheromone detecting olfactory receptor neurons in the male Heliothis virescens (Lepidoptera, Noctuidae)

Abstract: 1 Projection patterns of olfactory receptor neurons, specifically tuned to the two principal components of the female H virescens sex pheromone blend, and to a third pheromone-like compound of possible antagonistic significance, were examined using a combined electrophysiological and morphological technique 2 The macroglomerular complex consists of four major glomerular subdivisions 3 In the sensillum type containing a receptor neuron detecting the main pheromone component, Z11-16: AL, two cells were present When the sensillum was stimulated with Z11-16:AL, a single axon, stained by a method that selectively stains active neurons, was seen projecting into the large a glomerulus The b glomerulus was innervated by a second neuron in a few double stainings 4 In a second sensillum type, one receptor neuron tuned to the second major pheromone component, Z9-14:AL, was found In these sensilla, one or two receptor neurons of unknown specificity were also observed When the sensillum was stimulated with Z9-14: AL, a single neuron projecting into glomerulus a or two neurons projecting into glomerulus a were most often observed 5 In the third sensillum type, one neuron specifically tuned to Z11-16:AC projected to glomerulus c, and a second cell of unknown specificity projected to the same area 6 The axonal arborizations of different physiological receptor neuron types involved in the detection of the pheromone blend do not display a clearcut morphological separation into different glomeruli in the MGC A separation between neurons detecting attracting and repelling odours was, however, present

Electrophysiological responses of receptor neurons in mosquito maxillary palp sensilla to carbon dioxide

Abstract: Sensilla basiconica on the maxillary palps of female Aedes aegypti contain a receptor neuron which produces a phasic-tonic pattern of action potential response to low concentrations (150–300 ppm) of carbon dioxide (CO2), a stimulus known to be involved with host seeking behavior. These receptor neurons respond reliably to small increments in CO2 concentration (e.g., 50 ppm). We were particularly interested in evaluating the possibility that the sensitivity to step increases in CO2 concentration could be modulated by alterations in the background levels of CO2, over a range which might be encountered during host-seeking behavior. We report here that the response (impulses/s) to a single pulse of a given concentration of CO2 appears to be independent of the background level of CO2, unless that level is equal to or greater than the concentration of the stimulus pulse. Females of other mosquito species, including: Anopheles stephensi, Culex quinquefasciatus, Culiseta melanura, and Aedes taeniorhynchus, also possess sensilla with receptor neurons that respond with comparable sensitivity to CO2 stimulation. However, there is much interspecific variation in both the external morphology of the maxillary palp and the distribution of sensilla along the palp. Male Ae. aegypti have morphologically similar sensilla which also contain a receptor neuron that responds to CO2.

Migratory orientation of European Robins is affected by the wavelength of light as well as by a magnetic pulse

Abstract: The object of this study was to test the alternative hypotheses of magnetoreception by photopigments and magnetoreception based on magnetite. Migratory European Robins, Erithacus rubecula, were tested under light of different wavelengths; after these tests, they were subjected to a brief, strong magnetic pulse designed to alter the magnetization of single domain magnetite. In control tests under “white” light, the birds preferred the normal, seasonally appropriate migratory direction. Under 571 nm green light, they continued to be well oriented in the migratory direction, whereas under 633 nm red light, their behaviour was not different from random. The magnetic pulse had a significant effect on migratory orientation, but the response varied between individuals: some showed a persistent directional shift, while others exhibited a change in scatter; one bird was seemingly unaffected.

Desert ants Cataglyphis fortis use self-induced optic flow to measure distances travelled

Abstract: While foraging, desert ants of the genus Cataglyphis use a vector navigation (route integration) system for homing. Any vector navigation system requires that the animal is able to evaluate the angles steered and the distances travelled. Here we investigate whether the ants acquire the latter information by monitoring self-induced optic flow. To answer this question, the animals were trained and tested within perspex channels in which patterns were presented underneath a transparent walking platform. The patterns could be moved at different velocities (up to > 0.5 the ant's walking speed) in the same or in the opposite direction relative to the direction in which the animal walked. Experimental manipulations of the optic flow influenced the ant's homing distances (Figs. 2 and 4). Distance estimation depends on the speed of self-induced image motion rather than on the contrast frequency, indicating that the motion sensitive mechanism involved is different from mechanisms mediating the optomotor response. Experiments in which the ants walked on a featureless floor, or in which they wore eye covers (Fig. 6), show that they are able also to use additional (probably kinesthetic) cues for assessing their travel distance. Hence, even though optic flow cues are not the only ones used by the ants, the experiments show that ants are obviously able to exploit such cues for estimation of travel distance.

Pyramidal-cell plasticity in weakly electric fish: a mechanism for attenuating responses to reafferent electrosensory inputs.

Abstract: Recordings within the posterior eminentia granularis of the weakly electric fish, Apteronotus leptorhynchus, revealed multiple types of proprioceptive units responsive to changes in the position of the animal's trunk and tail. Intracellular labelling showed that the proprioceptor recordings were made from axons that ramify extensively within the EGp. The location of the somata giving rise to these axons is presently unknown. Electroreceptor afferent responses to electric organ discharge amplitude modulations caused by movement of the animal's tail were compared to responses caused by electronically generated AMs of similar amplitude and time course. These did not differ. Electrosensory lateral line lobe pyramidal cells responded significantly less to electric organ discharge amplitude modulations caused by changing the animal's posture as compared to electronically produced AMs, suggesting that central mechanisms attenuate pyramidal cell responses to reafferent electrosensory inputs. Experiments in which the pattern of reafferent input associated with changes in posture was altered revealed that the pyramidal cells learn, over a time course of several minutes, to reject new patterns of input. Both proprioceptive input and descending electrosensory input to the posterior eminentia granularis are involved in generating the observed plastic changes in pyramidal cell responsiveness.

The visual control of behaviour in fiddler crabs

Abstract: The distribution of resolution around the eye of the fiddler crab Uca pugilator was measured using the pseudopupil, and the results were compared with various behavioural thresholds. As noted previously (Zeil et al. 1986) the eye has a band of greatly increased vertical resolution around the middle with inter-ommatidial angles as small as 1° (Figs. 1–3). In life this band images the horizon. The horizontal resolution is nearly constant throughout the eye. Males notice females when they subtend 2 to 3 inter-ommatidial angles, and distinguish males from females when they subtend 6 to 7 ommatidia (Fig. 6). Potential predators are detected when they subtend only one inter-ommatidial angle, and move through a similar angle. Using models, it was found that males respond to moving objects of the right size as though they were conspecifics, although they do not resemble crabs in shape. It is concluded that only one feature distinguishes other crabs from predators: whether they appear below or above the crab's horizon.

Spectral regions in which aquatic insects see reflected polarized light

Abstract: For diverse water insects (species of Hydrophilidae, Hadraenidae, Dytiscidae, Haliplidae and aquatic Heteroptera), the attractiveness of an artificial water surface was found to vary when the polarization of the reflected light, the property by which these insects identify water, was abolished in different regions of the spectrum. The sensitivity maxima of their reflection-polarization visual systems (λmax(POL)) thus determined were in various spectral regions, between λ < 360 nm (UV) and λ ca. 550 nm (yellow-green). Species with λmax(POL) at the short-wavelength end of the spectrum would be able to identify bodies of water by polarization regardless of whether the subsurface reflection was bright or dark; nevertheless, this group includes forms that avoid water with a bright subsurface because of the intensity of the reflected light. Species with λmax(POL) in the long-wavelength region fail to use certain bodies of water with a bright subsurface as habitats because the light they reflect at the longer wavelengths is insufficiently polarized. That the POL system of a species has a large λmax could affect habitat choice; on the other hand, it could also be that systems operating in the long-wavelength region were produced in the course of adaptation to the light conditions in or above the habitat.

Androgen increases olfactory receptor response to a vertebrate sex pheromone

Abstract: Although it is well known that responses to ethologically-relevant odors are influenced by endocrine factors, it has not been clear whether these hormonal effects might be mediated at the level of the peripheral sensory neurons. During an investigation of hormonal pheromones in South-East Asian Cyprinids, we observed that in adult male Puntius schwanenfeldi, an androgen-dependent sex character was correlated with electro-olfactogram response to a putative sex pheromone (15-keto-prostaglandin-F2α). As secondary sex characteristics are androgen-dependent in male teleosts, this observation suggested a functional relationship between androgen and peripheral olfactory receptor response. We therefore investigated this possibility using androgen implants.

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

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

The modulatory effects of serotonin and octopamine in the visual system of the honey bee ( Apis mellifera L.)

Abstract: 1. Honeybees respond to a stripe pattern moving up- and downward with direction specific antennal responses. The reflex can be evoked for one antenna by stimulating the ipsilateral compound eye. The direction specific antennal response (DAR) was measured with an optoelectronic device. The effects of local injection of serotonin and octopamine into different neuropils of the visual system were determined by observing changes in the direction-specific antennal response. 2. Serotonin application (approximately 500 pl at a concentration of 10−5M) into the ipsilateral lobula leads to an immediate and long lasting (at least 30 min) decrease of the DAR when the ipsilateral compound eye is stimulated. The response to stimulation of the contralateral eye is also reduced. 3. Octopamine application (approximately 500 pl at a concentration of 10−6M) into the ipsilateral lobula leads to a small enhancement of the DAR. The effect is similar when the ipsi- or contralateral eye is stimulated. 4. The modulation of the direction-specific antennal response is dose-dependent for serotonin. The two amines act in a functionally antagonistic way. 5. Serotonin injection (approximately 500 pl, 10−5M) into the medulla or lamina leads to lasting reductions of the ipsilateral DAR whereas octopamine has no effect. 6. The experiments suggest that octopamine and serotonin are functionally antagonistic in their modulation of motion-sensitive neurons in the lobula and that serotonin can modulate visual neurons also in other optic neuropils.

The dorsal eye of the dragonfly Sympetrum: specializations for prey detection against the blue sky

Abstract: Dragonflies of the genus Sympetrum have compound eyes conspicuously divided into dorsal and ventral regions. Using anatomical, optical, electrophysiological, in-vivo photochemical and microspectrophotometrical methods, we have investigated the design and physiology of the dorsal part which is characterized by a pale yellow-orange screening pigment and extremely large facets. The upper part of the yellow dorsal region is a pronounced fovea with interommatidial angles approaching 0.3°, contrasting to the much larger values of 1.5°–2° in the rest of the eye. The dorsal eye part is exclusively sensitive to short wavelengths (below 520 nm). It contains predominantly blue-receptors with a sensitivity maximum at 420 nm, and a smaller amount of UV-receptors. The metarhodopsin of the blue-receptors absorbs maximally at 535 nm. The yellow screening pigment transmits longwavelength light (cut-on 580 nm), which increases the conversion rate from metarhodopsin to rhodopsin (see Fig. 11a). We demonstrate that because of the yellow pigment screen nearly all of the photopigment is in the rhodopsin state under natural conditions, thus maximizing sensitivity. Theoretical considerations show that the extremely long rhabdoms (1.1 mm) in the dorsal fovea are motivated for absorption reasons alone. A surprising consequence of the long rhabdoms is that the sensitivity gain, caused by pumping photopigment into the rhodopsin state, is small. To explain this puzzling fact we present arguments for a mechanism producing a gradient of rhodopsin concentration along the rhabdom, which would minimize saturation of transduction units, and hence improve the signal-to-noise ratio at high intensities. The latter is of special importance for the short integration time and high contrast sensitivity these animals need for spotting small prey at long distances.

Visual pigments and spectral sensitivity of the diurnal gecko Gonatodes albogularis

Abstract: The visual pigments and oil droplets in the retina of the diurnal gecko Gonatodes albogularis were examined microspectrophotometrically, and the spectral sensitivity under various adapting conditions was recorded using electrophysiological responses. Three classes of visual pigments were identified, with λmax at about 542, 475, and 362 nm. Spectral sensitivity functions revealed a broad range of sensitivity, with a peak at approximately 530–540 nm. The cornea and oil droplets were found to be transparent across a range from 350–700 nm, but the lens absorbed short wavelength light below 450 nm. Despite the filtering effect of the lens, a secondary peak in spectral sensitivity to ultraviolet wavelengths was found. These results suggest that G. albogularis does possess the visual mechanisms for discrimination of the color pattern of conspecifics based on either hue or brightness. These findings are discussed in terms of the variation in coloration and social behavior of Gonatodes.

Specificity and sensitivity of the olfactory organ of the zebrafish, Danio rerio

Abstract: 1. The specificity and sensitivity of the olfactory organ of adult zebrafish, Danio rerio, to selected amino acid, bile acid, and steroid odorants were characterized using the electro-olfactogram recording technique. The olfactory organ was responsive to 28 of the 29 odorants tested. 2. All of the 100 microM amino acid and bile acid stimulants elicited a negative-going response that was significantly greater than the response to the artificial fresh-water control. The general pattern of relative stimulatory effectiveness established for the amino acid stimuli was neutral amino acids > basic amino acids > acidic amino acids > imino acids. The general pattern of relative stimulatory effectiveness of 100 microM bile acid stimuli was taurine-conjugated bile acids > glycine-conjugated bile acids approximately non-conjugated bile acids. The responses to the most stimulatory bile acid odorants were up to 40% larger than the responses to the most stimulatory amino acid odorants. 3. The response threshold for cysteine and taurocholic acid, the most stimulatory of the amino acid and bile acid stimuli tested, was approximately 10(-8) M. Females are significantly more sensitive to these odorants than males.

The fast mandible strike in the trap-jaw ant Odontomachus I. Temporal properties and morphological characteristics

Abstract: Ants of the ponerine genus Odontomachus employ a trap-jaw mechanism that allows them to instantaneously close their long, sturdy mandibles to catch prey or to defend themselves. Photoelectric scanning has revealed that these trap-jaws can be closed in less than 0.5 ms and that they decelerate before they collide with each other. The mandible strike is released in a reflexlike action when particular trigger hairs are touched. This reflex takes 4 to 10 ms and is probably the fastest reflex yet described for any animal. This speed is based on a catch mechanism in the mandible joint that keeps the extended mandibles open during contraction of the powerful closer muscle and allows the potential energy it produces to be stored within cuticular elements, apodemes, and the closer muscle itself. During a strike a relatively small specialized trigger muscle unlocks the catch, instantaneously releasing the stored energy to accelerate the mandible.

Motor patterns during kicking movements in the locust

Abstract: Locusts (Schistocerca gregaria) use a distinctive motor pattern to extend the tibia of a hind leg rapidly in a kick. The necessary force is generated by an almost isometric contraction of the extensor tibiae muscle restrained by the co-contraction of the flexor tibiae (co-contraction phase) and aided by the mechanics of the femoro-tibial joint. The stored energy is delivered suddenly when the flexor muscle is inhibited. This paper analyses the activity of motor neurons to the major hind leg muscles during kicking, and relates it to tibial movements and the resultant forces.

Oriented responses of the triatomine bugs Rhodnius prolixus and Triatoma infestans to vertebrate odours on a servosphere

Abstract: Oriented responses of both R. prolixus and T. infestans adults were recorded on a servosphere to mouse-odour, one of its components (CO2), and to rabbit urine-odour. The volatiles were delivered in an air-stream under controlled conditions which excluded other sensory modalities. In stimulus-free air the triatomines walked preferentially downwind in straight bouts interrupted by stops or periods at relatively low speeds, all of variable duration. In odour-laden air, bugs maintained their typical walking habit but switched from negative to positive anemotaxis. The characteristic response to odour onset was to stop, sample the air with the antennae, turn upwind in situ, and then walk off in the direction of the source for at least a few seconds, i.e., odour mediated anemotaxis. Mouse-odour caused T. infestans to increase its speed to 5.3 cms-1. Both species continued with the upwind response for some time after odour delivery ceased, but the crosswind component of the tracks was more prominent during this period — an effort, we presume, by the bugs to re-contact an odour plume. This investigation provides unequivocal evidence for host finding in triatomines by olfactory cues alone.

Making learning easy: the acquisition of visual information during the orientation flights of social wasps

Abstract: The flights of individual wasps (Vespula) were recorded as they approached a small feeder on the ground that was marked by a black cylinder ca 15 cm away. Two navigational strategies are used in these approaches. Initially, the wasp aims at the cylinder, treating it as a beacon and fixating it with frontal retina. In the last stage of the flight, the wasp assumes a preferred orientation so that the cylinder takes up a constant, more peripheral retinal position as the wasp nears the feeder. Path guidance by image-matching is likely to be limited to this final segment of the return. Wasps could gain the information needed for these distinct navigational strategies during the learning flights that they perform on their initial departures from the feeder. They fly away from the feeder in a series of arcs while turning at a mean angular velocity of 226°/s. The cylinder tends to be viewed with frontal retina during the arcs suggesting that the information required for aiming at the cylinder is acquired then. For image matching, the appearance of the cylinder needs to be learnt when the wasp is in the orientation that it adopts close to the feeder on its return flight. Wasps tend to assume this orientation during learning flights while they face the feeder. Such inspections of the feeder occur at the ends of arcs when a wasp's turning velocity is low.

Acoustic pattern recognition and orientation in orthopteran insects: parallel or serial processing?

Abstract: In grasshoppers the acoustic information for pattern recognition and directional analysis is processed via parallel channels and not serially This can be concluded from the following results established by behavioural experiments:

The whole-body shortening reflex of the medicinal leech: motor pattern, sensory basis, and interneuronal pathways.

Abstract: The leech whole-body shortening reflex consist of a rapid contraction of the body elicited by a mechanical stimulus to the anterior of the animal. We used a variety of reduced preparations - semi-intact, body wall, and isolated nerve cord - to begin to elucidate the neural basis of this reflex in the medicinal leech Hirudo medicinalis. The motor pattern of the reflex involved an activation of excitatory motor neurons innervating dorsal and ventral longitudinal muscles (dorsal excitors and ventral excitors respectively), as well as the L cell, a motor neuron innervating both dorsal and ventral longitudinal muscles. The sensory input for the reflex was provided primarily by the T (touch) and P (pressure) types of identified mechanosensory neuron. The S cell network, a set of electrically-coupled interneurons which makes up a 'fast conducting pathway' in the leech nerve cord, was active during shortening and accounted for the shortest-latency excitation of the L cells. Other, parallel, interneuronal pathways contributed to shortening as well. The whole-body shortening reflex was shown to be distinct from the previously described local shortening behavior of the leech in its sensory threshold, motor pattern, and (at least partially) in its interneuronal basis.

The fast mandible strike in the trap-jaw ant Odontomachus - II. Motor control

Abstract: Ants of the ponerine genus Odontomachus employ a trap jaw mechanism for prey catching or defense. The mandible strike is released within less than 10 ms upon stimulation of particular mechanosensory trigger hairs. It is based on the storage of mechanical energy produced by the large but slow mandible closer muscle which cocks the mandible several seconds in advance of the strike.The strike is released from the catch by a small trigger muscle composed of tubular fibers. It features fast potentials and highly synchronized activation of all its muscle fibers only a few milliseconds in advance of the strike. The trigger muscle is supplied by two unusually large motor neurons that are enclosed in a glial sheath. The trap jaw action is thus controlled by a system composed of 2 giant sensory and 2 giant motor neurons on either side. The giant neurons are most likely monosynaptically coupled. The large axon diameter and the synaptic coupling result in high conduction velocity which underlies the very fast mandible reflex. The reflex activity is modulated by antennal and other sensory input probably converging onto the large dendritic trees of the trigger motor neurons.

Modulation rate transfer functions to low-frequency carriers in three species of cetaceans

Abstract: A temporal modulation rate transfer function (MRTF) is a quantitative description of the ability of a system to follow the temporal envelope of a stimulating waveform. In this study MRTFs were obtained from three cetacean species: the false killer whale Pseudorca crassidens; the beluga whale Delphinapterus leucas; and the bottlenosed dolphin Tursiops truncatus, using auditory-evoked potentials. Steady-state electrophysiological responses were recorded noninvasively from behaving, alert animals using suction cup electrodes placed on the scalp surface. Responses were elicited using continuous two-tone (TT) and sinusoidally amplitude-modulated (SAM) stimuli. MRTFs were obtained for modulation frequencies ranging from 18–4019 Hz using carrier and primary frequencies of 500, 1000, 4000, and 10000 Hz. Scalp potentials followed the low-frequency temporal envelope of the stimulating waveform; this envelope following response (EFR) was the dependent variable in all experiments. MRTFs were generally low-pass in shape with corner frequencies between approximately 1–2 kHz.

Ink secretion by the marine snail Aplysia californica enhances its ability to escape from a natural predator

Abstract: 1. Aplysia californica incorporates toxins and pigments from its red seaweed diet into its body and ink, purportedly as a defense against predation. We tested ink's potential defensive function by assessing the survival of green seaweed-fed (red algal toxin deprived) snails in encounters with a natural predator, the sea anemone Anthopleura xanthogrammica. 2. Red seaweed-fed Aplysia secreted copious amounts of ink when ensnared in anemone tentacles. A similar amount of ink applied to “inkless” (green-fed) snails as they were engulfed by an anemone enhanced their survival [71% survived (ink) vs 7% (seawater control)]. Ink caused anemones to reject whitefish (a familiar food) [50% rejected (ink) vs 10% (seawater control)], triggering gastrovascular eversions, which ejected ink as well as prey from their digestive cavities. Snails with only a passive chemical defense (algal toxins, no ink) escaped less often than snails with only an active chemical defense (ink, no red algal toxins) (20% survived vs 71%) and about as often as “red algal toxin deprived” snails (20% vs 12%). Snails avoided ink by chemical orientation, thus avoiding potential sites of ongoing predation. 3. The survival value of ink and the snail's aversion to it supports ink's proposed anti-predator function.

Two regions in the isolated brainstem of the frog that modulate respiratory-related activity.

Abstract: Using microinjection techniques, we have explored the isolated, complete midline sectioned brainstem of the frog (Rana catesbeiana) to identify regions that influence the endogenous respiratory-related motor activity. Ten-nanoliter injections of lidocaine (1%), GABA (100 mM) and glutamate (10 and 100 mM) into discrete regions of the rostral and the caudal brainstem produced different effects on the phasic neural discharge. In the rostral site lidocaine, GABA and glutamate injections altered neural burst frequency with little or no effect on burst amplitude. In the caudal site, responses to lidocaine and GABA injections consisted primarily of decreases in neural burst amplitude, often, but not always associated with minor decreases in burst frequency. In this same region, the response to glutamate was characterized by a temporary interruption of the rhythmic neural burst activity. The largest responses to substance injection in both regions were obtained at sites ranging between 200 and 500 μm from the ventral surface, in the ventral medullary reticular formation. The results reveal the existence of two areas in the frog brainstem that influence respiratory motor output, one related to the respiratory burst frequency and the other related to the amplitude of the motor output.

Steering by echolocation: a paradigm of ecological acoustics

Abstract: 1. Flights of three big brown bats (Eptesicus fuscus) landing on a hand and catching a suspended mealworm were video analysed. 2. Results were consistent with the bats using the same basic control procedure in the quite different approach tasks — namely keeping τ(r) = krand τ(a)τ(r) = kαr. Here r is the current distance to the destination; α is the angle between the current direction of the destination and the goal direction of final approach (βmin); τ(r) = r/r, \(\tau (\alpha ) = \alpha /\dot \alpha \); and kr, kαr are constants. 3. The bats were each quite consistent on a particular task (hand or mealworm) in the values they used for the control parameters kr, kαrand βmin. However, different values were used in the two tasks, which reflected the different behaviour required at the destination. Flights to hand required twisting and landing upside down and approach angle βmin was closer to vertical and krwas smaller and corresponded to decelerating nearly to a stop. In contrast, the mealworms were caught in mid flight and approach angle βmin was shallower and speed of approach was about constant. 4. τ(r) might be registered acoustically by τ(echo-delay) or by τ(echo-intensity). τ(α) might be registered by the bat's directional hearing and gravity sense. 5. The bats learned the tasks easily, suggesting that the control procedure they used in the experiments was part and parcel of the natural skills they had developed in the wild.

Photoperiodic activation of fos-like immunoreactive protein in neurones within the tuberal hypothalamus of Japanese quail.

Abstract: Photoperiodic stimulation of quail (Coturnix coturnix japonica) resulted in the appearance of a nuclear fos-like protein within neurones of the basal tuberal hypothalamus. On transfer to long days the number of neurones containing this fos-like immunoreactivity increased from about 150 to 700, the neurones being scattered throughout the length of the tubero-infundibular complex. This activation had occurred by early in the second long day and was maintained for at least three long days. Over this period circulating levels of LH increased seven-fold, indicating that photoperiodic induction had taken place in the birds. A similar time-course of fos-like induction occurred in castrated quail exposed to a single long day and then returned to short days. Activation mirrored the long-term changes in LH secretion found in this paradigm and fos-like immunoreactivity showed the same “carry-over” characteristics of photoperiodic induction, being maximal two days after the quail had been exposed to the single long day (and were again on short days) and when LH secretion was at its maximum. Activation of fos-like immunoreactive cells did not take place when long-day quail were transferred to short photoperiods. The evidence supports the view that the neurones being activated are involved in a specific fashion in the avian photoperiodic response.

Membrane and firing properties of avian medial vestibular nucleus neurons in vitro

Abstract: The intrinsic membrane and firing properties of medial vestibular nucleus (MVN) neurons were investigated in slices of the chick brainstem using intracellular recording and current injection. Avian MVN neurons fired spontaneous action potentials with very regular interspike intervals. The rapid repolarization of all action potentials was followed by an after-hyperpolarization. Intracellular injection of steps of hyperpolarizing current revealed both an inward rectification of the membrane potential during the step and a rebound depolarization following the offset of the step. In some neurons, the rebound depolarization resulted in bursts of action potentials. Steps of depolarizing current applied to spontaneously active neurons evoked increases in firing rate that were higher at the onset of the step than during the steady-state response. The relationship between current and firing rate was linear. The membrane and firing properties of avian MVN neurons were distributed continuously across the population of recorded neurons. These properties appear identical to those of rodent MVN neurons, suggesting that the composition and distribution of ion channels in the MVN neuronal membrane has been highly conserved across vertebrate species.

Stimulus-response properties of cricket cereal filiform receptors

Abstract: The dynamic ranges and stimulus-response properties of a large sample of cereal filiform receptors in Acheta domesticus were investigated electrophysiologically. The relation between receptor response and stimulus velocity was a sigmoid function, the log-linear portion of which spanned 1–1.5 log units of peak air-current velocity. Different receptors responded over different but overlapping velocity ranges, such that the system velocity sensitivity range spanned at least 2.5 log units. Plots of receptor response amplitude vs. stimulus direction were sinusoidal, with a period of 360°. Long-hair receptors responded in phase with air-current velocity, and intermediate-hair receptors responded in phase with air-current acceleration. These results extend those of Shimozawa and Kanou (1984a) and Kamper and Kleindienst (1990), in which the dynamics of receptor responses were shown to depend on hair length. When individual hairs were directly mechanically deflected, their receptors responded in phase with the first derivative of hair deflection. The signal transform between the air-current stimulus and the receptor response is comprised of two processes, one biomechanical/aerodynamic and one membrane biophysical. The results of this study suggest that the parametric sensitivities of receptors are primarily determined by hair biomechanical/aerodynamic properties.