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R K Murphey

Publications and source records attributed to R K Murphey.

At least 19 recordsLinked to original sources
PubMed1996

Mutations in the 8 kDa dynein light chain gene disrupt sensory axon projections in the Drosophila imaginal CNS.

Mutations in an 8 kDa (8x10(3) Mr) cytoplasmic dynein light chain disrupt sensory axon trajectories in the imaginal nervous system of Drosophila. Weak alleles are behaviorally mutant, female-sterile and exhibit bristle thinning and bristle loss. Null alleles are lethal in late pupal stages and alter neuronal anatomy within the imaginal CNS. We utilized P[Gal4] inserts to examine the axon projections of stretch receptor neurons and an engrailed-lacZ construct to characterize the anatomy of tactile neurons. In mutant animals both types of sensory neurons exhibited altered axon trajectories within the CNS, suggesting a defect in axon pathfinding. However, the alterations in axon trajectory did not prevent these axons from reaching their normal termination regions. In the alleles producing these neuronal phenotypes, expression of the cytoplasmic dynein 8 kDa light chain gene is completely absent. These results demonstrate a new function for the cytoplasmic dynein light chain in the regulation of axonogenesis and may provide a point of entry for studies of the role of cellular motors in growth cone guidance.

Amino Acid Sequence↗
PubMed1994

Retrograde signaling and the development of transmitter release properties in the invertebrate nervous system.

The dynamics of presynaptic transmitter release are often matched to the functional properties of the postsynaptic cell. In organisms ranging from cats to crickets, evidence suggests that retrograde signaling is essential for matching these presynaptic release properties to individual postsynaptic partners. Retrograde interactions appear to control the development of presynaptic, short-term facilitation and depression.

Animals↗
PubMed1994

The effect of neuronal growth on synaptic integration.

The way in which the dimensions of neurons change during postembryonic development has important effects on their electrotonic structures. Theoretically, only one mode of growth can conserve the electrotonic structures of growing neurons without employing changes in membrane electrical properties. If the dendritic diameters of a neuron increase as the square of the increase in dendritic lengths, then the neuron's electrotonic structure is conserved. We call this special mode of allometric growth "isoelectrotonic growth." In this study we compared the developmental changes in morphology of two identified invertebrate neurons with theoretical growth curves. We found that a cricket neuron, MGI, grows isoelectrotonically and thereby preserves its electrotonic properties. In contrast, the crayfish neuron, LG, grows in nearly isometric manner resulting in an increase in its electrotonic length.

Animals↗
PubMed1994

Long-term regulation of short-term transmitter release properties: retrograde signaling and synaptic development.

The dynamics of presynaptic transmitter release are often matched to the physiological properties and functions of the postsynaptic cell. In organisms ranging from cats to crickets, evidence suggests that retrograde signaling is essential for matching these presynaptic release properties to individual postsynaptic partners. Retrograde interactions appear to control the development of presynaptic, short-term facilitation and homosynaptic depression through local, retrograde signaling at the synapse.

Animals↗
PubMed1993

Transplantation of neurons reveals processing areas and rules for synaptic connectivity in the cricket nervous system.

In order to assess the nature of spatial cues in determining the characteristic projection sites of sensory neurons in the CNS, we have transplanted sensory neurons of the cricket Acheta domesticus to ectopic locations. Thoracic campaniform sensilla (CS) function as proprioceptors and project to an intermediate layer of neuropil in thoracic ganglia while cercal CS transduce tactile information and project into a ventral layer in the terminal abdominal ganglion (TAG). When transplanted to ectopic locations, these afferents retain their modality-specific projection in the host ganglion and terminate in the layer of neuropil homologous to that of their ganglion of origin. Thus, thoracic CS neurons project to intermediate neuropil when transplanted to the abdomen and cercal CS neurons project to a ventral layer of neuropil when transplanted to the thorax. We conclude that CS can be separated into two classes based on their characteristic axonal projections within each segmental ganglion. We also found that the sensory neurons innervating tactile hairs project to ventral neuropil in any ganglion they encounter after transplantation. Ectopic sensory neurons can form functional synaptic connections with identified interneurons located within the host ganglia. The new contacts formed by these ectopic sensory neurons can be with normal targets, which arborize within the same layer of neuropil in each segmental ganglion, or with novel targets, which lack dendrites in the normal ganglion and are thus normally unavailable for synaptogenesis. These observations suggest that a limited set of molecular markers are utilized for cell-cell recognition in each segmentally homologous ganglion. Regenerating sensory neurons can recognize novel postsynaptic neurons if they have dendrites in the appropriate layer of neuropil. We suggest that spatial constraints produced by the segmentation and the modality-specific layering of the nervous system have a pivotal role in determining synaptic specificity.

Animals↗
PubMed1993

Isolation of mutations affecting neural circuitry required for grooming behavior in Drosophila melanogaster.

We have developed a screen for the isolation of mutations that produce neural defects in adult Drosophila melanogaster. In this screen, we identify mutants as flies unable to remove a light coating of applied dust in a 2-hr period. We have recovered and characterized six mutations and have found that they produce coordination defects and some have reduced levels of reflex responsiveness to the stimulation of single tactile sensory bristles. The grooming defects produced by all six of the mutations are recessive, and each of the mutations has been genetically mapped. We have also used our assay to test the grooming ability of stocks containing mutations that produce known neural defects.

Animals↗
PubMed1993

A role for postsynaptic neurons in determining presynaptic release properties in the cricket CNS: evidence for retrograde control of facilitation.

Intracellular recording sin the cricket cercal system show that the synaptic terminals of a single sensory neuron can facilitate at one target, the medial giant interneuron (MGI), and simultaneously depress at another target, interneuron 10-3. A quantal analysis of transmission at these synapses demonstrates that facilitation and depression are properties of the presynaptic cell. For facilitating synapses contacting MGI, the mean quantal content (m), determined from the probability of the failures, increases for the second EPSP, while the quantal size (q) remains constant. Similarly, an analysis of depression for those synapses contacting 10-3 supports a presynaptic mechanism for depression. Since facilitation and depression are presynaptic and their expression at the synapses of a single, identified sensory neuron are correlated with the target interneuron, we conclude that these properties are regulated locally, at the synapse, possibly by an interaction with the postsynaptic cell.

Acoustic Stimulation↗
PubMed1992

Projections of leg proprioceptors within the CNS of the fly Phormia in relation to the generalized insect ganglion.

We previously reported a modality-specific layering of leg sensory axons in the CNS of the flies Phormia regina and Drosophila melanogaster with tactile and gustatory axons projecting into a ventral layer and the proprioceptive hair plate axons into an intermediate layer. Here the description is expanded to include the afferent projections of campaniform sensilla on the legs and wings of Phormia. The leg campaniform sensilla produce a number of patterns of projections within an intermediate layer of their ganglion, some of which project intersegmentally into the other thoracic ganglia. One of these patterns is shared by the hair plate sense organs. Selected wing campaniform sensilla were also stained and showed that there is little or no overlap between the projections of leg and wing campaniform sensilla. Similarities with the arrangement of campaniform sensilla and their central processes in Drosophila melanogaster are discussed. To apply the results of this study to a broader range of insects we provide an atlas of the fly CNS and compare it with the locust, which has been the model for much insect neuroanatomy and neurophysiology.

Animals↗
PubMed1991

Connectivity of identified central synapses in the cricket is normal following regeneration and blockade of presynaptic activity.

Cercal sensory neurons in the cricket innervate interneurons in the central nervous system (CNS) and provide a model system for studying the formation of central synapses. When axons of the sensory neurons were transected during larval development, the cell bodies and the soma-bearing portion of axons, which are located within the cercus, survived but lost their excitability for 9-10 days. During this period, the sensory neurons grew new axons and reinnervated the terminal abdominal ganglion. Physiological recordings showed that sensory neurons of known identity reestablished monosynaptic contacts with their normal postsynaptic interneuron. Moreover, each synapse exhibited a characteristic strength indistinguishable from the intact synapse in an unoperated cricket. Since this selective connectivity was apparent immediately after the excitability of the axotomized sensory neurons was restored, action potentials in the sensory neurons appear to be unnecessary for normal synaptic regeneration to occur. Consistent with this, the reinnervation process was unaffected even when action potentials in the sensory neurons were blocked by tetrodotoxin (TTX) immediately following axotomy until just before testing. During the normal course of development, the characteristic strength of individual synapses changes systematically, resulting in the developmental rearrangement of these synapses (Chiba et al., 1988). This synaptic rearrangement was also unaffected when action potentials in the sensory neurons were blocked by TTX for the last 30% of larval development. Therefore, in the cricket cercal sensory system, both regeneration of the central synapses following axotomy of the presynaptic sensory neurons and the normal rearrangement of connectivity during larval development appear not to require axonal action potentials.

Action Potentials↗
PubMed1990

Assembly of the cricket cercal sensory system: genetic and epigenetic control.

The cercal sensory system of the cricket is being examined using anatomical, physiological, and computer simulation techniques in order to better understand the assembly of sensory systems. This particular sensory system is of interest because it functions like numerically more complex vertebrate sensory systems but offers, to the neuroscientist, the technical advantages of a small number of large identified neurons. Two aspects of sensory processing are being examined in this system; the spatial aspects of a stimulus that tell an animal where a target is in its environment, and the qualities of a stimulus that help the animal to identify the stimulus. The spatial aspects of a stimulus are analyzed by a topographic mapping of the animal's sensory environment. The feature extraction machinery for other aspects of the stimulus lacks any obvious anatomical order and is embedded within the topographic map. We are attempting to tease apart the genetic and the epigenetic components of the assembly process for this sensory system. Here we review our progress with emphasis on the epigenetic aspects of its assembly. We describe previously published work on plasticity as well as new experiments focussed on the role of neuronal activity in the assembly of this neural circuit. Finally, we briefly describe simulation experiments that are helping us understand the role of various forms of synaptic plasticity in the determination of receptive fields.

Animals↗
PubMed1990

Rearing in darkness changes visually-guided choice behavior in Drosophila.

To test whether visual experience can affect development of visual behavior in the fruitfly, Drosophila, we measured the visually-guided choice behavior of groups of flies reared in complete darkness, compared with controls reared in a normal light/dark cycle. We used a simple visual preference test, i.e. choice among four different visual targets each consisting of vertical black lines of a particular width on a white background, using a blind testing procedure so that the individual rearing histories were not known by the tester. Both groups of flies were strongly attracted to the vertical lines; however, generally the dark-reared flies were more attracted to the wider stimulus lines than were the control flies. Control experiments in which normally reared adults were kept for several days in darkness showed that the effects of dark-rearing were not simply due to being in darkness, but depended upon the timing of the deprivation. The results indicate that the development of visual behavior can be affected by visual experience in Drosophila and thus open the possibility of using Drosophila for genetic dissection of mechanisms of visual plasticity.

Animals↗
PubMed1989

Modality-specific axonal projections in the CNS of the flies Phormia and Drosophila.

There is a rich history of behavioral and physiological studies on the leg sensory systems of flies. Here we examine the anatomy of the sensory axons of two species of fly and demonstrate that the location of the axonal projections in the CNS can be correlated with the modality they encode. We studied receptors associated with proprioceptive, tactile, and multimodal hairs. Proprioceptive hairs occur in clusters, called hair plates, and are situated near joints. The neuron innervating each proprioceptive hair has a large axon and coarse arborization in the intermediate neuropil. Tactile receptors have smaller arbors, which are located in a ventral region of the thoracic neuromere. Finally, the multimodal hairs are each innervated by one tactile and four chemosensory neurons. The single tactile neuron has a central arbor that is indistinguishable from those of the tactile hairs; the four chemosensory neurons project to yet a third region of neuropil near the ventral surface of each neuromere. Thus there is a clear modality-specific segregation of axonal arbors in the CNS. This organization is identical in Phormia and Drosophila and thus apparently highly conserved within the Diptera. We presume that, as in other insect sensory systems, this anatomical specificity is linked to synaptic specificity.

Afferent Pathways↗
PubMed1989

The refinement of invertebrate synapses during development.

Evidence is provided that during invertebrate development synapses undergo a period of refinement during which there are changes in synaptic connectivity and specific synaptic properties. It appears that extrinsic cues such as competition and neural activity are involved in guiding these synaptic changes in invertebrates. Comparisons are made with findings in the vertebrate literature.

Animals↗
PubMed1989

Genetic control of sexually dimorphic axon morphology in Drosophila sensory neurons.

The mechanism by which orderly axonal projections are formed during development remains an important and largely unsolved problem in neurobiology. It may be possible to examine the control of axon growth in Drosophila and take advantage of genetic tools to better understand the phenomenon. We show here that some gustatory axons in Drosophila are sexually dimorphic and that genes involved in sex determination control the anatomy of these axons. Both males and females possess gustatory receptors on their legs but males possess more of these receptors than females. More significantly, the axons of the male receptors usually cross the midline and they never do so in females, indicating a central zone of bilateral input in the male but not in the female nervous system. In chromosomal females, expressing a tra or Sxl mutation, the gustatory system is transformed toward the male phenotype. Mutant XX adults resemble normal males externally, because they have more gustatory receptors, and internally, because their axons cross the midline. Gynandromorphs show that the sex of the sensory neuron, and apparently not the central nervous system, controls the growth of the axons. We conclude that the anatomical site of control for this dimorphism is the gustatory neurons.

Animals↗
PubMed1989

Compartments and the topography of leg afferent projections in Drosophila.

The legs of Drosophila are covered with mechanosensory bristles, innervated by sensory neurons that project to the CNS in a very orderly manner. We examined this afferent projection by staining the sensory neurons associated with identified bristles in wild-type, engrailed and scute flies. We observe that anterior neurons project to an anterior region of the ventral neuropil, while posterior neurons project to a more posterior region. We rule out that this difference depends on the compartment of origin of the receptors. Our results also argue against explanations based on other factors that might correlate to anterior/posterior position: peripheral organization of the leg nerve, competitive interactions, or differences in times of birth. We suggest that position itself is the primary determinant of this projection.

Afferent Pathways↗
PubMed1988

Synaptic rearrangement during postembryonic development in the cricket.

Synaptic rearrangement during development is a characteristic of the vertebrate nervous system and was thought to distinguish vertebrates from the invertebrates. However, examination of the wind-sensitive cercal sensory system of the cricket demonstrates that some identified synaptic connections systematically decrease in strength as an animal matures, while others increase in strength over the same period. Moreover, a single sensory neuron could increase the strength of its synaptic connection with one interneuron while decreasing the strength of its connection with another interneuron. Thus, rather than being a hallmark of the vertebrate nervous system, synaptic rearrangement is probably characteristic of the development of many if not all nervous systems.

Action Potentials↗
PubMed1987

Segmental origins of the cricket giant interneuron system.

The segmental origins of the cricket giant interneuron system have been studied by staining these neurons with cobalt during the last half of embryonic development. The results demonstrate that the interneurons are derived from three distinct clusters of embryonic neurons that form a serially repeating pattern in each abdominal ganglion. Some of the neurons previously described in adults (Mendenhall and Murphey, '74; Murphey, '85) have been identified in embryos and are described here with respect to this pattern. These neurons include both giant interneurons and several non-giant mechanosensory interneurons that mediate several different sensory modalities. The anatomical organization of this system is compared to similar mechanosensory systems in other insects and crustacea.

Abdomen↗