Biomedical subjects

N J Strausfeld

Publications and source records attributed to N J Strausfeld.

13 recordsLinked to original sources

PubMed1992

Small-field neurons associated with oculomotor control in muscoid flies: cellular organization in the lobula plate.

In muscoid flies, the lobula plate is the last station in the optic lobes for processing spectrally independent information from retinotopic afferents. Until recently, it was thought that most lobula plate neurons were color-insensitive wide-field tangential neurons that respond to direction-specific motion. It has been suggested that certain of these supply inputs to premotor descending neurons involved in the control of flight and head movements. The present account describes a Golgi and cobalt-silver analysis that reports evidence for additional lobula plate outputs, which are numerically complex and structurally elaborate. Beneath a retina with approximately 4,000 ommatidia, each of at least 15 populations of morphologically distinct small-field neurons comprises approximately 110-440 elements that contribute to an isomorphic neural assembly subtending the whole retina. Morphologically small-field efferents form three classes according to the origin of their axons and their arborization in the lobula plate and lobula. Neurons arising from the lobula plate, or shared by it and the lobula, visit dorsal descending neurons supplying the neck and flight motor in contrast to output neurons from the lobula, which project to ventral descending neurons supplying leg motor neuropils. The possible functional significance of small-field lobula plate outputs onto descending neurons in the dorsal deutocerebrum is discussed.

Animals↗

PubMed1992

Small-field neurons associated with oculomotor and optomotor control in muscoid flies: functional organization.

In fleshflies, Sarcophaga bullata, intracellular recording and Lucifer yellow dye-filling have revealed small-field elements of sexually isomorphic retinotopic arrays in the lobula and lobula plate, the axons of which project to premotor channels in the deutocerebrum that supply head-turning and flight-steering motor neurons. The dendrites of the small-field elements visit very restricted oval areas of the retinotopic mosaic, comprising fields that are typically 6-8 input columns wide and 12-20 high. Their physiologically determined receptive fields are also small, typically 20 degrees or less in diameter. The neurons are hyperpolarized in stationary illumination and are transiently depolarized by light OFF and to a lesser degree by light ON. Motion of a striped grating elicits a periodic excitation at the fundamental or second harmonic of the stimulus temporal contrast frequency. The arrangement of these elements in retinotopic arrays with their small receptive fields and flicker-sensitive dynamic properties make these neurons well suited for the position-dependent, direction-insensitive detection of small objects in the fly's visual field, which is known to drive fixation and tracking.

Animals↗

PubMed1992

Premotor descending neurons responding selectively to local visual stimuli in flies.

The responses of dorsal descending neurons suggest great versatility of the visual system in detecting features of the visual world. Although wide-field motion-sensitive neurons respond to symmetric visual flow fields presented to both eyes, other neurons are known to respond selectively to asymmetric movement of the visual surround. The present account distinguishes yet a third class of descending neurons (DNs) that is selectively activated by local presentation of moving gratings or small contrasting objects. Excitation of these DNs in response to local motion contrasts with their inhibitory responses to wide-field motion. The described DNs invade dorsal neuropil of the pro- and mesothoracic ganglia where they converge with other morphologically and physiologically characterized descending elements. Axon collaterals of DNs visit thoracic neuropil containing the dendrites of motor neurons supplying indirect neck and flight muscles. The present results are discussed with respect to the organization of small-field retinotopic outputs from the lobula, and with respect to the parallel projection of many information channels from the brain to the neck and flight motors.

Animals↗

PubMed1991

Structural organization of male-specific visual neurons in calliphorid optic lobes.

The superiority of male flies over female flies in locating and intercepting small rapidly moving targets has been ascribed to differences in their visual systems. In males, this sexual dimorphism is externally expressed by an area of high visual acuity called the acute zone. Selective cobalt uptake reveals 12 types of male-specific visual interneurons in the male lobula, the axons of which terminate in neuropil supplying premotor descending neurons to neck and flight motor circuits. The dendritic fields of the individual male-specific neurons can be extrapolated out into visual space to demonstrate that each is assigned a discrete area of the visual panorama. The dendritic fields of 10 of the 12 male-specific neurons subtend areas of the retina associated with the male acute zone. The functional significance of male-specific neurons is discussed with respect to their putative receptive field and a model circuit for target location by male flies.

Animals↗

PubMed1991

The functional organization of male-specific visual neurons in flies.

Intracellular recording and Lucifer yellow dye filling of male fleshflies, Sarcophaga bullata, have revealed male-specific neurons in the lobula, the axons of which project to the origin of premotor channels supplying flight motor neurons. Dendrites of male-specific neurons visit areas of the retinotopic mosaic supplied by the retina's acute zone, which is used by males to keep the image of a conspecific female centered during aerial pursuit. Only males engage in high-speed aerobatic chases, and male-specific neurons are suspected to underlie this behavior. Physiological determination of receptive fields of male-specific neurons substantiates the fields predicted from anatomical studies and demonstrates that they subtend the acute zone. Male-specific neurons respond in a manner predicted on theoretical grounds from observations of tracking behavior. Such properties include directional selectivity to visual motion and higher sensitivity to motion of small images than to wide-field motion. The present account substantiates and extends neuroanatomical evidence that predicts that male-specific lobula neurons comprise a distinct circuit mediating conspecific tracking.

Animals↗

PubMed1991

Descending pathways connecting the male-specific visual system of flies to the neck and flight motor.

During sexual pursuit, male flies Sarcophaga bullata, stabilize the image of a pursued target on the dorso-frontal acute zone of their compound eyes. By retinotopic projection, this region is represented in the upper frontal part of the lobula where it is sampled by ensembles of male-specific motion- and flicker-sensitive interneurons. Intracellular recordings of descending neurons, followed by biocytin injection, demonstrate that male-specific neurons are dye-coupled to specific descending neurons and that the response characteristics of these descending neurons closely resemble those of male-specific lobula neurons. Such descending neurons are biocytin-coupled in the thoracic ganglia, revealing their connections with ipsilateral frontal nerve motor neurons supplying muscles that move the head and with contralateral basalar muscle motor neurons that control wing beat amplitude. Recordings from neck muscle motor neurons demonstrate that although they respond to movement of panoramic motion, they also selectively respond to movement of small targets presented to the male-specific acute zone. The present results are discussed with respect to anatomical and physiological studies of sex-specific interneurons and with respect to sex-specific visual behavior. The present study, and those of the two preceding papers, provide a revision of Land and Collett's hypothetical circuit underlying target localization and motor control in males pursuing females.

Animals↗

PubMed1990

Descending neurons supplying the neck and flight motor of Diptera: organization and neuroanatomical relationships with visual pathways.

In dipterous insects, a volume of behavioral and electrophysiological studies promote the contention that three wide-field motion-sensitive tangential neurons provide a necessary and sufficient input to specific channels that drive the torque motor during flight. The present studies describe the results of neuroanatomical investigations of the relationships between motion-sensitive neuropil in the fly optic lobes and descending neurons that arise from a restricted area of the brain and supply segmental neck and flight motor neuropil. The present observations resolve at least 50 pairs of descending neurons supplying flight motor centers in the thoracic ganglia. The majority of descending neurons receive a distributed output from horizontal motion-sensitive neurons. However, the same descending neurons are also visited by numerous small-field retinotopic neurons from the lobula plate as well as hitherto undescribed small tangential neurons. Neuroanatomical studies, using cobalt, Golgi, and Texas red histology, demonstrate that these smaller inputs onto descending neurons have dendrites that are organized at specific strata in retinotopic neuropil and that these correspond to horizontal and vertical motion sensitivity layers. Conclusions that only a restricted number of wide-field neurons are necessary and sufficient for visually stabilized flight may be premature. Rather, neuroanatomical evidence suggests that descending neurons to the flight motor may each be selectively tuned to specific combinations of wide- and small-field visual cues, so providing a cooperative descending network controlling the rich repertoire of visually evoked flight behavior.

Animals↗

PubMed1990

Descending neurons supplying the neck and flight motor of Diptera: physiological and anatomical characteristics.

In Diptera, dorsal neuropils of the pro-, meso-, and metathoracic ganglia supply motor neurons to neck and flight muscles. Motor circuits are supplied by more than 50 pairs of descending neurons (DNs) whose dendritic trees in the brain are restricted to dorsal neuropils of the deutocerebrum where they are grouped together into discrete clusters. Each cluster is visited by wide-field motion-sensitive neurons and by morphologically small-field retinotopic elements. This organization suggests that flight descending neurons should respond to complex stimuli reflecting panoramic movement and small-field motion. Intracellular recordings, combined with dye filling, confirm this. Certain descending neurons responding to visual flow fields terminate bilaterally in superficial pterothoracic neuropils, at the level of indirect (power) flight muscle motor neurons. Other DNs terminate laterally, and provide segmental collaterals to areas containing neck and direct (steering) flight muscle motor neurons. Such DNs are activated by wide-field directional stimuli corresponding to pitch, roll, or yaw, and to small-field stimuli. Appropriate directional mechanosensory stimuli also activate dorsal descending neurons. The significance of dorsal descending neurons for the control of flight is discussed and compared with studies on course deviation neurons in other insects. It is suggested that, in Diptera, dorsal descending neurons may separately be involved in the control of velocity, stabilization, and steering manoeuvres.

Animals↗

PubMed1990

Cluster organization and response characteristics of the giant fiber pathway of the blowfly Calliphora erythrocephala.

Intersegmental descending neurons (DNs) link the insect brain to the thoracic ganglia. Iontophoresis of cobalt or fluorescent dyes reveals DNs as uniquely identifiable elements, the dendrites of which are situated within a characteristic region of the lateral deutocerebrum. Here we demonstrate that DNs occur as discrete groups of elements termed DN clusters (DNCs). A DNC is a characteristic combination of neurons that arises from a multiglomerular complex in which the main components of each glomerulus are a characteristic ensemble of sensory afferents. Other neurons involved in the complex are local interneurons, heterolateral interneurons that connect DNCs on both sides of the brain, and neurons originating in higher centers of the brain. We describe the structure, relationships, and projections of eight DNs that contribute to a descending neuron cluster located ventrally in the lateral deutocerebrum, an area interposed between the ventral antennal lobes and the laterally disposed optic lobes. We have named this cluster the GDNC because its most prominent member is the giant descending neuron (GDN), which plays a cardinal role in the midleg "jump" response and which is implicated in the initiation of flight. The GDN and its companion neurons receive primary mechanosensory afferents from the antennae, terminals of wide- and small-field retinotopic neurons originating in the lobula, and endings derived from sensory interneurons that originate in leg neuropil of the thoracic ganglia. We demonstrate that DNs of this cluster share morphological and functional properties. They have similar axon trajectories into the thoracic ganglia, where they invade functionally related neuropils. Neurons of the GDNC respond to identical stimulus paradigms and share similar electrophysiological characteristics. Neither the GDN nor other members of its cluster show spontaneous activity. These neurons are reluctant to respond to unimodal stimuli, but respond to specific combinations of visual and mechanosensory stimulation. These results suggest that in flies groups of morphologically similar DNs responding to context-specific environmental cues may cooperate in motor control.

Action Potentials↗

PubMed1990

Structure, distribution and number of surface sensilla and their receptor cells on the olfactory appendage of the male moth Manduca sexta.

Distribution and neuronal organization of sensilla on the surface of the annulate flagellar segment of the antenna of the male Manduca sexta were studied by scanning and transmission electron microscopy. Nine types of sensilla were identified and their bipolar neurons ascribed to specific sensory modalities on the basis of their cuticular and dendritic morphology. Cuticle morphology identifies two types of sensilla trichodea, two types of sensilla basiconica and one type of sensillum coeloconicum. Certain of these olfactory sensilla are further subdivided on the basis of their dendritic structures. One type of sensillum chaeticum was interpreted as a contact chemoreceptor. A second type of sensillum coeloconicum and a styliform sensilla complex were interpreted as bimodal hygro- and thermosensilla. A second species of sensillum chaeticum serves mechanosensation. Counts from annuli situated about midway along the flagellum revealed a total of about 2200 sensilla supplied by approximately 5160 sensory neurons. A conservative estimate suggests that a male antenna with 85-90 annuli provides the flagellar nerve with at least 3.6 x 10(5) receptor axons, a number that exceeds previous estimates by almost 50% Each species of receptor has a characteristic location on the annulus. Of the 2100 or so sensilla situated on the dorsal, ventral and the leading edge surfaces, about 800 consist of male-specific type-I trichoids containing pheromone-sensitive receptors. Arciform arrays of these sensilla on the upper and lower surfaces of each annulus presumably optimize the capture and absorption of odour molecules. The trailing edge of the flagellum, which is thickly covered by scales and was assumed until now to lack receptors, contains both mechanosensitive and contact chemoreceptors. The modality of non-olfactory receptors is considered with respect to similar elements that have been functionally identified in other species. The coexistence of non-olfactory sensilla with olfactory elements is discussed with respect to current knowledge of the organization of olfactory centres in the brain.

Animals↗

PubMed1989

Physiology and morphology of projection neurons in the antennal lobe of the male moth Manduca sexta.

1. We have used intracellular recording and staining, followed by reconstruction from serial sections, to characterize the responses and structure of projection neurons (PNs) that link the antennal lobe (AL) to other regions of the brain of the male sphinx moth Manduca sexta. 2. Dendritic arborizations of the AL PNs were usually restricted either to ordinary glomeruli or to the male-specific macroglomerular complex (MGC) within the AL neuropil. Dendritic fields in the MGC appeared to belong to distinct partitions within the MGC. PNs innervating the ordinary glomeruli had arborizations in a single glomerulus (uniglomerular) or in more than one ordinary glomerulus of one AL (multiglomerular) or in one case, in single glomeruli in both ALs (bilateral-uniglomerular). One PN innervated the MGC and many or all ordinary glomeruli of the AL. 3. PNs with dendritic arborizations in the ordinary glomeruli and PNs associated with the MGC typically projected both to the calyces of the ipsilateral mushroom body and to the lateral protocerebrum, but some differences in the patterns of termination in those regions have been noted for the two classes of PNs. One PN conspicuously lacked branches in the calyces but did project to the lateral protocerebrum. The PN innervating the MGC and many ordinary glomeruli projected to the calyces of the ipsilateral mushroom body and the superior protocerebrum. 4. Crude sex-pheromone extracts excited all neurons with arborizations in the MGC, although some were inhibited by other odors. One P(MGC) was excited by crude sex-pheromone extract and by a mimic of one component of the pheromone blend but was inhibited by another component of the blend. 5. PNs with dendritic arborizations in ordinary glomeruli were excited or inhibited by certain non-pheromonal odors. Some of these PNs also responded to mechanosensory stimulation of the antennae. 6. The PN with dendritic arborizations in the MGC and many ordinary glomeruli was excited by crude sex-pheromone extracts and non-pheromonal odors and also responded to mechanosensory stimulation of the antenna.

Action Potentials↗

PubMed1977

Vision in insects: pathways possibly underlying neural adaptation and lateral inhibition.

Like horizontal cells in vertebrate retinas, horizontal amacrine cells beneath the insect eye intervene between receptors and interneurons at the first level of synapses. Synaptic arrangements between amacrines and interneurons that give rise to regular networks of axon collaterals may explain recent electrophysiological observations of lateral inhibition beneath the insect retina. Neural adaptation mechanisms acting on single retinotopic channels or assemblies of channels can also be referred to reciprocal relationships between receptors and first-order interneurons as well as to centrifugal cells from levels of so-called photopic receptor endings.

Adaptation, Physiological↗

PubMedDate not supplied

Neuronal basis for parallel visual processing in the fly.

Behavioral and electrophysiological studies of insects demonstrate both spectrally independent and chromatically dependent behaviors and interneurons. This account describes the neuroanatomical identification of two parallel retinotropic subsystems, one supplying descending channels to spectrally independent neck and flight motor circuits, the other supplying polychromatic channels to neuropils associated with leg motor circuits in the thoracic ganglia. In the compound eye, two classes of photoreceptors contribute to each of several thousand sampling units. High-sensitivity, chromatically uniform short-axon photoreceptors (R1-R6) supply the lamina's external plexiform layer and are presynaptic to L1, L2 efferents. These project in parallel with a second system of trichromatic long-axon receptors and the L3 efferent. Both pathways supply columns of the medulla, equal in number to ommatidia. Golgi and cobalt-silver impregnation demonstrates that neurons from the medulla diverge to two deeper regions, the lobula plate and lobula, the former a thin tectum of neuropil dorsal to the more substantial lobula. Layer relationships between medulla neurons and their afferent supply suggest that the lobula plate and lobula are each supplied by one or the other, but not both, of the two parallel subsystems. Independence of the two parallel pathways is suggested by ablation of the photoreceptor layer leading to selective degeneration of the motion-sensitive lobula plate neuropil. In addition, octets of small-field neurons associated with the R1-R6/L1, L2 pathway give rise to synaptic complexes with motion-sensitive neurons of the lobula plate. A variety of behavioral and electrophysiological studies provide supporting evidence that certain insects possess parallel visual pathways comparable to the magnocellular and parvocellular subsystems of primates.

Animals↗