Search PubMed⌕ Search

Biomedical subjects

R B Levine

Publications and source records attributed to R B Levine.

At least 55 records · Page 3Linked to original sources
PubMed1989

Development of the gin trap reflex in Manduca sexta: a comparison of larval and pupal motor responses.

1. Responses of motor neurons in larvae and pupae of Manduca sexta to stimulation of tactile sensory neurons were measured in both semi-intact, and isolated nerve cord preparations. These motor neurons innervate abdominal intersegmental muscles which are involved in the production of a general flexion reflex in the larva, and the closure reflex of the pupal gin traps. 2. Larval motor neurons respond to stimulation of sensory neurons innervating abdominal mechanosensory hairs with prolonged, tonic excitation ipsilaterally, and either weak excitation or inhibition contralaterally (Figs. 4A, 6). 3. Pupae respond to tactile stimulation of mechanosensory hairs within the gin traps with a rapid closure reflex. Motor neurons which innervate muscles ipsilateral to the stimulus exhibit a large depolarization, high frequency firing, and abrupt termination (Figs. 2, 4B). Generally, contralateral motor neurons fire antiphasically to the ipsilateral motor neurons, producing a characteristic triphasic firing pattern (Figs. 7, 8) which is not seen in the larva. 4. Pupal motor neurons can also respond to sensory stimulation with other types of patterns, including rotational responses (Fig. 3A), gin trap opening reflexes (Fig. 3B), and 'flip-flop' responses (Fig. 9). 5. Pupal motor neurons, like larval motor neurons, do not show oscillatory responses to tonic current injection, nor do motor neurons of either stage appear to interact synaptically with one another. Most pupal motor neurons also exhibit i-V properties similar to those of larval motor neurons (Table 1; Fig. 10). Some pupal motor neurons, however, show a marked non-linear response to depolarizing current injection (Fig. 11).

Action Potentials↗
PubMed1989

Expansion of the central arborizations of persistent sensory neurons during insect metamorphosis: the role of the steroid hormone, 20-hydroxyecdysone.

During insect metamorphosis many larval neurons persist but are modified to serve new behavioral roles at later stages of life. For example, certain larval mechanosensory neurons expand their central arborizations during pupal development and evoke a different behavioral response, the gin trap reflex. The role of the insect steroid hormone, 20-hydroxyecdysone (20-HE) in this developmental change was investigated by removing the normal source of the hormone, followed by topical application of 20-HE to the peripheral somata of the sensory neurons. In prepupal animals that were ligated between the abdomen and thorax to remove the source of ecdysteroids the sensory neurons retained a larval arborization pattern. Topical application of 20-HE to the peripheral sensory neuron somata caused the treated neurons to undergo terminal arbor expansion within the CNS. The treated sensory neurons were not able to evoke the normal pupal behavioral response, but instead caused a larval-like reflex response. In a previous study, sensory neurons that were treated peripherally with a juvenile hormone analog during the commitment peak of ecdysteroids were shown to retain a larval arborization pattern at pupation and to not evoke the gin trap reflex (Levine et al., 1986). Within 4 d of pupation, however, these neurons belatedly developed expanded terminal arbors and evoked the pupal reflex. In the present study, similarly treated animals were ligated at pupation to block the surge in ecdysteroids that normally occurs at this time. This treatment prevented both the delayed expansion and the reflex, whereas topical 20-HE application induced growth and allowed the treated sensory neurons to evoke the gin trap reflex. It is concluded that both 20-HE and juvenile hormone act directly on the cell bodies of the sensory neurons to regulate the growth of their central processes. This growth is necessary but not sufficient for the development of the gin trap reflex, suggesting that other steroid-dependent changes must also occur within the CNS. Thus, as in the vertebrates, steroid hormones direct important developmental events within the insect nervous system.

Animals↗
PubMed1988

Neural control of leg movements in a metamorphic insect: persistence of larval leg motor neurons to innervate the adult legs of Manduca sexta.

During metamorphosis of the hawkmoth Manduca sexta, the larval thoracic legs along with their associated sensory organs and muscles degenerate and new adult legs develop. The larval legs are small and relatively simple structures capable of lateral extension and medial flexion allowing them to grasp the substrate as the caterpillar crawls along. By contrast, the adult legs are used for walking with an alternating gait. They are much larger than the larval legs and articulate such that they are capable of movement in several directions. This change in form and function is accompanied by a reorganization of the neural circuits controlling leg movements. In a previous report (Kent and Levine: J. Comp. Neurol. 271:559-576, '88) we described motor neurons innervating the larval prothoracic legs, and here we describe motor neurons innervating the prothoracic legs of the adult. Using a combination of cobalt staining methods and the persistent fluorescent dye Fluoro-Gold, we have found that some, if not all, larval leg motor neurons are retained and innervate the new adult leg muscles. Moreover, we have been able to discover the fate of individual larval leg motor neurons by marking a single larval neuron with Fluoro-Gold and using a second fluorescent dye to double label the same neuron in the adult. Our results suggest that specific larval leg motor neurons innervate corresponding muscles in the adult stage, although their apparent function is significantly different. In addition, the motor neurons undergo significant remodeling of their dendritic branching patterns during metamorphosis, alterations which doubtless contribute to their new roles in adult behavior.

Animals↗
PubMed1988

Neural control of leg movements in a metamorphic insect: sensory and motor elements of the larval thoracic legs in Manduca sexta.

During the metamorphosis of the hawkmoth Manduca sexta the larval thoracic legs degenerate to be replaced in the adult by legs of very different form and function. This change must be accompanied by a reorganization of the neural circuits controlling leg movements. As an initial step in the study of this reorganization we describe here the sensory and motor elements of this circuitry in the larval stage of life. Sensory neurons innervating mechanoreceptive hairs on the thoracic surface were stained individually with cobalt. Those innervating hairs on the general thoracic surface project topographically into two ventral regions of the segmental ganglia. Sensory neurons innervating leg sensilla also map topographically to the more ventral of these regions but in addition have arborizations in a midlateral region. The density of branching within this lateral "leg neuropil" is greatest for sensory neurons form sensilla on the more distal leg segments. Leg motor neurons were identified with intracellular recording and cobalt injection techniques. Those innervating muscles controlling distal leg segments have dense dendritic arbors in the lateral "leg neuropil," while motor neurons controlling more proximal segments and muscles of the ventral body wall have extensive arborizations in a dorsomedial region of the ganglion. In general, flexor motor neurons are excited by medial and inhibited by lateral leg sensilla, while the opposite is true of extensors. Distal segment motor neurons respond most strongly to sensory neurons from distal segments, thus suggesting some interaction within the lateral "leg neuropil." Thus, in the larval nervous system a highly ordered array of of sensory and motor elements underlies the specific behavioral responses of the legs to tactile stimulation.

Action Potentials↗
PubMed1986

Paget disease: unusual radiographic manifestations.

Paget disease (osteitis deformans) is not a difficult diagnosis when presented with typical radiographic features. However, an atypical appearance or an unusual location can be a diagnostic challenge, so we have emphasized the less common presentations, with their diagnostic clues. We have also considered such complications as malignant degeneration, fracture, and coexistent systemic disease, which can obscure the underlying Paget disease. The etiology, pathogenesis, and effects on bone structure and function attributed to Paget disease are updated.

Adult↗
PubMed1986

Endocrine regulation of the form and function of axonal arbors during insect metamorphosis.

By discrete manipulation of the endocrine cues that control insect metamorphosis, it has been possible to examine the mechanisms governing the growth of neural processes during development. During the transition from larva to pupa in the hawkmoth, Manduca sexta, identified sensory neurons reorganize their central projections to evoke a new behavior--the gintrap reflex. Topical application of a juvenile hormone analog to the peripheral cell bodies of these sensory neurons during a critical period of development caused them to retain their larval commitment rather than undergo pupal development with the rest of the animal. The sensory neurons retained the larval arborization pattern within the pupal CNS and were unable to evoke the gin-trap reflex. Thus, the hormonal environment of the cell body is critical for controlling growth and synapse formation by distant axonal processes.

Animals↗
PubMed1985

Driller wrist (vibratory arthropathy).

Driller wrist is an occupational disease with pathophysiologic changes resulting from recurrent use of vibratory tools. The entity includes the clinical finding of Raynaud phenomena with or without associated bone changes in the wrist. Osseous involvement is usually mild and is associated with cystic changes of the carpals and occasionally other structures. Two cases are reported, one with typical cystic abnormalities and the other with more severe disease which progressed to joint instability.

Humans↗
PubMed1985

The Maquet principle. Anterior displacement of the tibial tubercle in the treatment of patellofemoral disorders: radiologic appearance.

Anterior displacement of the tibial tubercle is a well-accepted orthopedic procedure in the treatment of certain patellofemoral disorders. The radiologic appearance of surgical procedures utilizing the Maquet principle has not been described in the radiologic literature. Familiarity with the physiologic and biochemical basis for the procedure and its postoperative appearance is necessary for appropriate roentgenographic evaluation and the radiographic recognition of complications.

Adult↗
PubMed1985

Rheumatoid arthritis: skeletal manifestations observed on portable chest roentgenograms.

This report describes the thoracic skeletal radiographic findings of rheumatoid arthritis, observed on portable chest examinations of 21 patients. Their pathophysiology is reviewed and additional examples of a recently described finding are illustrated: erosion of the medial surface of the proximal humerus with subsequent pathologic fracture, associated with superior and medial migration of the humeral head. It has been proposed that erosion of the medial aspect of the proximal humerus is due to impingement wear, and that pathologic fracture results from the fulcrum effect of the inferior lip of the glenoid on the humerus. Rheumatoid arthritis is often diagnosed by the clinician rather than the radiologist. However, in acutely ill patients receiving portable chest radiographs, complete history and laboratory findings are often unavailable. Attention to the thoracic skeleton may clarify pleural and/or parenchymal lung disease in these patients.

Adult↗
PubMed1985

Dendritic reorganization of abdominal motoneurons during metamorphosis of the moth, Manduca sexta.

During metamorphosis in the hawkmoth Manduca sexta, muscles of the abdominal body wall undergo a reorganization. Many die at the end of larval life and are replaced in the adult by newly generated muscles. We have identified several of the motoneurons innervating these muscles and followed them through metamorphosis. The morphology of larval motoneurons is correlated with their target location. Those with medial targets have bilateral dendritic fields, whereas those with lateral targets have dendrites restricted to one side of the segmental ganglion. Some motoneurons innervate the same muscle in all stages of life, but the majority lose their larval targets following entry into the pupal stage. Although some of the latter group also die at this time, most survive to innervate a new adult target. These "respecified" motoneurons undergo a period of dramatic dendritic growth during metamorphosis. The results demonstrate that these identified neurons are capable, under the appropriate conditions of existing in more than one stable morphology.

Abdominal Muscles↗
PubMed1985

Submucosal colonic edema--urticaria of the colon.

Radiographically, colonic urticaria presents a non-specific pattern of submucosal edema. Previously unreported diverticulitis with colonic distention resulting in the flat, polygonal, mosaic pattern typical of this entity is described.

Colonic Diseases↗
PubMed1984

Changes in neuronal circuits during insect metamorphosis.

During metamorphosis insects undergo dramatic changes in both form and behaviour. Cell birth and death, as well as neurone respecification all contribute to the overall reorganization of the nervous system. Within the visual and chemosensory processing areas of the insect brain large numbers of newly-generated adult neurones are incorporated into the larval nervous system. In the abdominal ganglia, however, identified larval neurones are retained to assume a new adult role. This respecification of motor neurone function involves not only the acquisition of a new target muscle, but also the reorganization of dendritic morphology, and alterations in the interconnections between neurones. For example, an identified abdominal motor neurone in the hawkmoth, Manduca sexta, grows new dendritic processes and changes its synaptic relationship with an abdominal stretch receptor such that an interaction that was inhibitory during larval life, becomes excitatory in the adult. In another example, identified sensory neurones that evoke a larval flexion behaviour, later participate in the defense gin trap reflex that is characteristic of the pupa. In both instances the formation of new pathways is a two-step process in that the new circuits do not become behaviourally relevant as they are formed, but instead are activated abruptly at the appropriate time. For the gin trap reflex an identified peptide hormone is responsible for activating the circuit.

Abdomen↗
PubMed1983

Peptide activation of a simple neural circuit.

Pupae of the tobacco hornworm moth display a characteristic reflex response to tactile stimulation of sensory hairs located in the gin-trap. The reflex is not functional in the prepupa, but is activated abruptly as the animal enters the pupal stage by the direct action of an identified peptide hormone. The neuronal pathway between the sensory and motor neurons involved in the reflex is not direct, and the site of hormone action was localized to the connection between an interganglionic interneuron, and the motorneurons.

Animals↗
PubMed1982

The action of peptides and cyclic nucleotides on the nervous system of an insect.

Eclosion hormone (EH) is a moderate-sized peptide that acts on the insect nervous system to release the stereotyped behaviors involved in shedding the old skin (eclosion) as well as to activate new reflex pathways. The action of the peptide has been studied by using two preparations. The first preparation involves the preeclosion and eclosion motor programs that can be released from the isolated abdominal central nervous system (CNS) in response to EH. The target sites associated with the release of these programs are scattered throughout the CNS, each apparently being associated with a segmental component of one of the programs. A fully coordinated behavioral response requires that all these segmental elements be exposed to the peptide. The second preparation has allowed the cellular analysis of a simple multisegmental reflex that is turned on by EH. The data indicate that the reflex pathway is activated by the peptide through the selective action on a key synaptic junction. In the case of both of these preparations, the action of EH appears to involve an increase in cyclic GMP levels in the CNS. The manner by which these increases result in altered neuronal activity remains unknown.

Action Potentials↗
PubMed1980

Mechanisms responsible for changes observed in response properties of partially deafferented insect interneurons.

1. Two pairs of large sensory interneurons, the medial and lateral giant interneurons (MGI and LGI), in the abdominal nervous system of crickets were examined after being partially deafferented throughout postembryonic development. Each of these interneurons receives a synaptic input from sensory neurons in a pair of appendages called cerci. The experiment consisted of removing one of these appendages at hatching and examining the morphological and physiological consequences for the MGI and LGI. 2. The morphological consequences of deafferentation were examined by injecting neurons with cobalt acetate and intensifying the profiles either in section or whole mount with a modified Timm's method. We confirmed previous reports that the main dendritic branches were shorter than controls when deafferented. In addition, we demonstrated that the many spinelike processes projecting from the main dendrites were shorter than in controls. The density of spines per unit length of main dendrite was approximately the same on control and treated dendrites. Neither the MGI nor the LGI sprouted new dendrites into normally afferented areas as a result of partial deafferentation. Short periods of deafferentation late in development had similar though less drastic effects on the structure of MGI. 3. The MGI was found to receive stronger than normal excitatory input from the remaining cercus when one cercus was absent throughout postembryonic development. An examination of remaining inhibitory inputs to both the MGI and the LGI demonstrated that these pathways were weaker than normal. The results suggest that the increase in excitability observed in MGI when partially deafferented for long periods is due to removal of inhibition rather than direct changes in the strength of excitatory inputs.

Animals↗
PubMed1980

Loss of inhibitory synaptic input to cricket sensory interneurons as a consequence of partial deafferentation.

1. In a companion paper (5) we suggested that the enhanced ability of excitatory pathways to drive deafferented interneurons in crickets could be attributed to a reduction in the effectiveness of remaining inhibitory pathways impinging on these neurons. 2. In order to test this idea more directly, we examined a sensory interneuron in the cricket known as sensory interneuron 10-3 (SI 10-3). We first demonstrated that SI 10-3 was more sensitive to remaining excitatory inputs after partial deafferentation. 3. We then tested the ability of inhibitory inputs to suppress a train of current-evoked action potentials. Brief (100 ms) depolarizing current pulses were injected into the soma of SI 10-3 and the number of action potentials counted. Next, an identical depolarizing pulse was injected into the interneuron coincident with activation of the inhibitory pathway by a tone (75 dB at 450 Hz). Activation of the inhibition decreased the number of current-evoked action potentials. In order to quantify this effect, current-tone pairs were presented at four current intensities. Over the range of current intensities used, the relationship between current intensity and number of action potentials (AP/I curve), elicited with or without tones, was linear (Fig. 7A). 4. In control preparations, tones always lowered the calculated slope of the observed curve and its y intercept. In treated specimens inhibiting tones decreased the slope of the AP/I curve less than in control specimens. Based on this evidence, we concluded that the inhibitory pathway had been disrupted by partial deafferentation. This releases the giant neuron from inhibition, allowing it to respond more strongly to remaining excitatory inputs.

Animals↗