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At least 811 records · Page 45Linked to original sources

PubMed2000

Responses of rat subicular neurons to convergent stimulation of lateral entorhinal cortex and CA1 in vivo.

There has been little electrophysiological examination of the afferent projection from lateral entorhinal cortex to dorsal subiculum. Here we provide evidence that synaptic inputs from lateral entorhinal cortex and CA1 converge onto single dorsal subicular neurons in vivo. Subicular responses to CA1 stimulation consisted of excitation and/or long-duration inhibition. Neurons excited by CA1 activation usually showed inhibition to entorhinal stimulation. The latter inhibition was usually of short duration, however, long duration inhibition was seen in a significant proportion of responses. Entorhinal stimulation produced excitatory responses in four bursting cells and it was these cells that also tended to show the longest inhibition. Only bursting cells could be driven antidromically by entorhinal stimulation. Biocytin-filled multipolar and pyramidal cells displayed excitation-inhibition sequences to CA1 and inhibition to entorhinal stimulation. These data strongly suggest that subicular inhibitory neurons receive excitatory input from CA1 and display mutual inhibition. The source of entorhinal-evoked inhibition is less clear. The relative sparseness of observed entorhinal-evoked responses suggests that the input to dorsal subiculum from any one part of lateral entorhinal cortex is spatially restricted. These data show that excitation-inhibition sequences can be seen in subicular pyramidal and multipolar cells and that single subicular neurons receive convergent inputs from CA1 and entorhinal cortex. We show for the first time that bursting cells can be driven both orthodromically and antidromically by direct entorhinal stimulation. These data support the existence of a reciprocal excitatory connection between lateral entorhinal cortex and dorsal subiculum and suggest further that this connection may involve only bursting subicular neurons.

Action Potentials↗

PubMed2001

Sciatic and vagal sensory inputs converge onto non-baroreceptive neurones of the rostral ventrolateral medulla.

Previous data suggested that somatic and vagal sensory afferent inputs may converge in the rostral ventrolateral medulla oblongata (RVLM). The aim of the present study was to establish the existence of convergence between inputs mediated via the cervical vagus and contralateral sciatic nerves using in vivo intracellular recordings. The majority of RVLM neurones that received input from the vagus or the sciatic nerves also responded to stimulation of the other nerve. In 72% of the neurones the response was excitation or inhibition to stimulation of both nerves, respectively. The most frequent response type was a short excitation in response to stimulation of both nerves. Only 8% of the neurones exhibited a visible response to stimulation of the aortic depressor nerve. The results provided experimental evidence that non-baroreceptive neurones of the RVLM are involved in coordination of somatic and visceral sensory inputs.

Animals↗

PubMed1997

Convergence of afferent inputs from the chorda tympani, lingual-tonsillar and pharyngeal branches of the glossopharyngeal nerve, and superior laryngeal nerve on the neurons in the insular cortex in rats.

The responses of single neurons in the insular cortex to electrical stimulation of the chorda tympani (CT), lingual-tonsillar branch of the glossopharyngeal (LT-IXth) nerve, pharyngeal branch of the glossopharyngeal (PH-IXth) nerve, and superior laryngeal (SL) nerve were recorded in anaesthetized and paralyzed rats. Ninety-four neurons responding to stimulation of at least one of the four nerves were identified from the insular cortex. Most of the neurons were located in the posterior portion of the insular cortex; the mean location was 0.8 mm anterior to the anterior edge of the joining of the anterior commissure (AC) and was 1.4 mm dorsal to the rhinal fissure (RF). Of the 94 neurons, 84 (89%) received convergent inputs from two or more nerves, and the remaining 10 (11%) received inputs from one nerve. The neurons responding to the CT stimulation were distributed more anteriorly than those responding to other three nerves in the anterior-posterior dimension. Our results indicate that the neurons recorded mainly from the posterior portion of the insular cortex receive convergent inputs from the oropharyngolaryngeal regions.

Animals↗

PubMed1998

Morphine microinjected into the nucleus raphe magnus does not block the activity of spinal trigeminal nucleus oralis convergent neurons in the rat.

This study investigated the effects of morphine microinjection into the nucleus raphe magnus (RMg) on electrically evoked C-fiber activities of convergent neurons in the spinal trigeminal nucleus oralis (Sp5O), in halothane-anesthetized rats. Although the neurons could be depressed by systemic morphine (6 mg/kg, i.v.) in a naloxone-reversible fashion, morphine microinjected into the RMg (2. 5 microgram or 5 microgram) neither depressed their C-fiber-evoked responses, nor the diffuse noxious inhibitory controls acting on them. It is concluded that the RMg is not involved in reinforcing descending inhibitory controls that are tonic or triggered by noxious stimuli acting on Sp5O convergent neurons.

Animals↗

PubMed1996

First synthesis of cellooctaose by a convergent synthetic method.

The first chemical synthesis of cellooctaose by a convergent synthetic method is described. A challenging glycosylation between cellotetraosyl donor 5 and acceptor 7 proceeded in a one-step reaction using a high-vacuum system for anhydrous glycosylation and minimizing imidate side reactions such as hydrolysis and glycosyl fluoride formation. Pivaloyl, allyl, and benzyl protecting groups of cellooctaose derivative 8 were completely removed with SeO2-AcOH, NaOMe-MeOH, and H2/Pd(OH)2-C, respectively. The acetylation after each deprotection step finally led to cellooctaose hexacosaacetate (20), which is useful for purification and structural identification. Finally, the acetyl derivative 20 was deacetylated with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in 20% MeOH-CH2Cl2 to give pure cellooctaose (21). The analogous synthetic route to the present convergent synthetic design of cellooctaose may be a most promising one that enables us to synthesize cellulose with a defined degree of polymerization (dp).

Acetylation↗

PubMed2003

Distinct functions of Rho and Rac are required for convergent extension during Xenopus gastrulation.

We have undertaken the first detailed analysis of Rho GTPase function during vertebrate development by analyzing how RhoA and Rac1 control convergent extension of axial mesoderm during Xenopus gastrulation. Monitoring of a number of parameters in time-lapse recordings of mesoderm explants revealed that Rac and Rho have both distinct and overlapping roles in regulating the motility of axial mesoderm cells. The cell behaviors revealed by activated or inhibitory versions of these GTPases in native tissue were clearly distinct from those previously documented in cultured fibroblasts. The dynamic properties and polarity of protrusive activity, along with lamellipodia formation, were controlled by the two GTPases operating in a partially redundant manner, while Rho and Rac contributed separately to cell shape and filopodia formation. We propose that Rho and Rac operate in distinct signaling pathways that are integrated to control cell motility during convergent extension.

Animals↗

PubMed1996

Effects of systemic morphine on the activity of convergent neurons of spinal trigeminal nucleus oralis in the rat.

The spinal trigeminal nucleus oralis has been shown to relay nociceptive inputs mainly from the oral and perioral regions. In this study, we examined the effects of intravenous administration of morphine on C-fiber-evoked activities of spinal trigeminal nucleus oralis convergent neurons in halothane-anesthetized rats. Morphine depressed the C-fiber-evoked responses of spinal trigeminal nucleus oralis convergent neurons in a dose-related (3-12 mg/kg range) and naloxone-reversible fashion. The ED50 was 6.1 mg/kg, a dose similar to that found in the spinal horn. The observed strong depressive action of morphine on noxious-evoked activities of spinal trigeminal nucleus oralis neurons is consistent with our previous statement, based on electrophysiological studies, that this region plays an important role in the transmission of trigeminal nociceptive information. The effect of morphine on the spinal trigeminal nucleus oralis neurons is discussed in relation to its possible site and mechanism of action.

Animals↗

PubMed1999

Cross-tolerance and convergent dependence between morphine and cannabimimetic agent WIN 55,212-2 in the guinea-pig ileum myenteric plexus.

The cross-tolerance and convergent dependence between morphine and the cannabimimetic agent R(+)-[2,3-dihydro-5-methyl-3[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-+ ++benzoxazin-yl]-(1-naphthalenyl) methanone mesylate (WIN 55,212-2) were assessed in vitro on guinea-pig ileum. To induce tolerance and dependence the myenteric plexus-longitudinal muscle was incubated at 37 degrees C for 5 h with a fixed concentration representing the IC50 for each compound. Myenteric plexus-longitudinal muscle exposed to WIN 55,212-2 (5 x 10(-8) M) was less sensitive to its inhibitory effect on electrically evoked contractions than naive myenteric plexus-longitudinal muscle. The exposure to cannabinoid induced a parallel rightward shift in the lower part of the concentration-response curve of WIN 55,212-2 and a marked reduction in the maximal inhibitory effect of the drug. Myenteric plexus-longitudinal muscle tolerant to WIN 55,212-2 was subsensitive to the inhibitory effect of morphine on the twitch response. The cross-tolerance between WIN 55,212-2 and morphine was bidirectional. In fact, after 5 h the morphine (10(-7) M)-incubated myenteric plexus-longitudinal muscle was less sensitive to the inhibitory effect of WIN 55,212-2. The tissue tolerant to morphine or WIN 55,212-2 was tested for the presence of physical dependence. Naloxone (10(-5) M) produced a typical withdrawal contracture in morphine-tolerant myenteric plexus-longitudinal muscle which could be reduced by a 15-min pretreatment with WIN 55,212-2 (5 X 10(-8) M). In contrast, SR141716 (10(-6) M) [N-(piperidino)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyr azole-carboxamide], a concentration which fully antagonized the inhibitory effect of WIN 55,212-2 (10(-7) M) in control preparations, did not produce significant contracture in WIN 55,212-2-tolerant myenteric plexus-longitudinal muscle. The mechanisms underlying the cross-tolerance and convergent dependence remain to be ascertained.

Analgesics, Opioid↗

PubMed2000

Convergent evolution with combinatorial peptides.

Once the sequence of a genome is in hand, understanding the function of its encoded proteins becomes a task of paramount importance. Much like the biochemists who first outlined different biochemical pathways, many genomic scientists are engaged in determining which proteins interact with which proteins, thereby establishing a protein interaction network. While these interactions have evolved in regard to their specificity, affinity and cellular function over billions of years, it is possible in the laboratory to isolate peptides from combinatorial libraries that bind to the same proteins with similar specificity, affinity and primary structures, which resemble those of the natural interacting proteins. We have termed this phenomenon 'convergent evolution'. In this review, we highlight various examples of convergent evolution that have been uncovered in experiments dissecting protein-protein interactions with combinatorial peptides. Thus, a fruitful approach for mapping protein-protein interactions is to isolate peptide ligands to a target protein and identify candidate interacting proteins in a sequenced genome by computer analysis.

Amino Acid Sequence↗

PubMed2003

Converging flow chromatography in constant-pressure mode.

Dispersion in chromatographic processes can be reduced to a minimum using converging columns and a curved frit at the outlet. Working at constant pressure at the inlet the internal packing is increasingly compressed by the accelerated flow. Thus the packed bed is stabilized. Under these conditions the observed flux at the outlet and the power input of the pump are inversely related to the viscosity of the eluting solute. Comparing converging flow chromatography (CFC) with classical axial flow chromatography (AFC) and radial flow chromatography (RFC) the stationary phase is used more efficiently in CFC.

Chromatography↗

PubMed1997

Effect of convergence angle on retention of resin-bonded retainers cemented with resinous cements.

STATEMENT OF PROBLEM: Poor retention is a common cause of failure for resin-bonded restorations. PURPOSE: This study evaluated the effect of the convergence angle of tooth preparations on retention of resin-bonded restorations, luted with adhesive and conventional resinous cements. MATERIAL AND METHODS: A total of 80 posterior retainers with four different tooth preparation angles were cemented with two different resinous cements, and retentive strength was measured. RESULTS: The results indicated that (1) increased tapering of tooth preparations resulted in loss of retention and this variable was statistically significant for both cements used when convergence angles exceeded 10 degrees and (2) sandblasted nickel-chromium retainers, combined with adhesive resins, should provide sufficient retention for posterior resin-bonded fixed partial dentures.

Adhesives↗

PubMed1999

Gaze-shift dynamics in subjects with and without symptoms of convergence insufficiency: influence of monocular preference and the effect of training.

We studied gaze-shift dynamics during several gaze-shift tasks and during reading, in five subjects with convergence insufficiency (C.I., a diminished ability to converge), and in ten subjects without C.I. Furthermore, we studied the effect of vergence training in order to verify previous claims that orthoptic exercises can improve vergence performance. We recorded binocular eye movements with the scleral coil technique. Subjects switched fixation between nearby and distant light emitting diodes (LEDs) arranged in isovergence arrays (distances 35 and 130 cm) in a dimly lit room. In both the C.I. and non-C.I. group, two classes of subjects occurred: vergence responders and saccadic responders. During pure vergence tasks, saccadic responders made saccades with no or little vergence; vergence responders made vergence movements with no or small saccadic components. In saccadic responders, fixation of nearby targets was monocular. Subjects with a preferred eye, according to our determination, used the preferred eye. The five C.I. subjects showed idiosyncratic responses with insufficient vergence during most trials. They all had a tendency to alternate fixation between the left and right eye. Vergence-version tasks always elicited larger vergence components than pure vergence tasks. During a reading task, vergence angles were more accurate than during gaze-shifts between LEDs. After the pre-training sessions, nine subjects (one of which had C.I.) practised a pure vergence task three times a day for at least 2 weeks. Vergence amplitudes of four of these subjects were larger after training. We conclude that vergence training can change oculomotor performance. Although C.I. is often associated with abnormal vergence dynamics, there are no typical C.I. vergence dynamics. Unstable monocular preferences may play a role in the aetiology of C.I.

Adult↗

PubMed1979

The effect of preoperative convergence exercises on the surgical outcome of primary exotropia.

In a retrospective study of 89 patients with exotropia, the authors investigated the influence of active convergence exercises in the postoperative angle of deviation and found that convergence exercises do not increase the incidence or the size of the esodeviation post-operatively.

Child↗

PubMed2003

Anatomical mechanisms and functional implications of multisensory convergence in early cortical processing.

Recent findings in both monkeys and humans indicate that multisensory convergence occurs in low-level cortical structures generally believed to be unisensory in function. In an in-depth treatment of this theme, this paper reviews anatomical and physiological findings relating to the convergence of visual, somatosensory and auditory signals at early stages of auditory cortical processing. We discuss the potential anatomical sources of the input, and the types of known projections, and attempt to integrate this information with the current hierarchical model of auditory processing. Finally, we consider the functional implications of multisensory integration in early sensory processing.

Animals↗

PubMed2003

Convergence of gastric vagal and cerebellar fastigial nuclear inputs on glycemia-sensitive neurons of lateral hypothalamic area in the rat.

Gastric vagal and cerebellar fastigial nuclear afferents have been implicated in the regulation of food intake by their communication with lateral hypothalamic area (LHA), which is generally referred to be the feeding center. This study was designed to examine the possible convergence of the inputs from the gastric vagal trunks and cerebellar fastigial nucleus (FN) on the LHA neurons. Among recorded 191 LHA neurons, 99 (51.8%) responded to the stimulation of the gastric vagal trunks, of which 55 (55.6%) also responded to the cerebellar FN stimulation. Of 62 LHA neurons that responded to the gastric vagal stimulation, 43 (69.4%) showed an inhibitory response to the intravenous glucose application indicating they were glycemia-sensitive neurons. When the gastric vagal trunks and cerebellar FN were stimulated simultaneously, a summation of the responses usually could be seen in the recorded LHA neurons (16/20, 80%). Moreover, of 45 LHA neurons that responded to both of the gastric vagal trunks and FN stimuli, 30 (66.7%) were identified to be glycemia-sensitive neurons. These results demonstrated that gastric vagal afferents could reach glycemia-sensitive neurons of the LHA, and that the inputs from cerebellar FN and gastric vagal trunks could converge onto glycemia-sensitive neurons in the LHA. According to the facts that gastric vagal inputs and blood glucose level may transmit meal-related visceral signals and FN may forward the somatic information to the LHA, we suggest that an integration of the somatic-visceral response related to the food intake may take place in the LHA following the gastric vagal and cerebellar FN afferent inputs and the integration may play an important role in the short-term regulation of feeding behavior.

Animals↗

PubMed2002

Convergent-flow tracer tests in heterogeneous media: combined experimental-numerical analysis for determination of equivalent transport parameters.

In modeling transport within naturally heterogeneous aquifers, it is usually assumed that the transport equations valid at local scales can also be applied at larger scales. At larger scales, the heterogeneous domain is represented by an equivalent homogeneous medium. Convergent-flow tracer tests constitute one of the most frequently used field tests to estimate effective input parameters of equivalent homogeneous aquifers. Traditionally, statistical approaches applied to groundwater flow and solute transport have provided tools to estimate these equivalent parameters. These approaches are based on a number of simplifications including the assumption that the point transmissivity values follow a multilog-normal random function. Several investigators have found that this assumption may not be valid in many field cases. In order to study the applicability of the equivalent homogeneous formulation in a nontraditional stochastic field, a number of experimental and numerical studies were conducted. The results are used to determine the apparent values of porosity and dispersivity that would be obtained if convergent-flow tracer tests were conducted in a deterministically generated heterogeneous transmissivity field displaying anisotropy in the correlation structure. It is shown that in this particular heterogeneous media, apparent porosity strongly depends on connectivity rather than on transmissivity. This dependence on connectivity questions the theoretical results obtained in continuum equivalent fields to estimate effective porosity.

Models, Theoretical↗

PubMed2001

The convergence of vulnerable characteristics and health insurance in the US.

This study defines vulnerability as a multi-dimensional construct, reflected in the convergence of predisposing, enabling, and need attributes of risk. Using race, income, and self-perceived health status as indicators and based on eight rounds of the US 1996 panel of the Medical Expenditure Panel Survey, the study examined how the interactions of these vulnerable characteristics affect insurance coverage, a critical measure of health care access. The results of the study demonstrate insurance coverage does vary with the extent of vulnerability. While race and income significantly influence insurance coverage, respectively, there was relatively little disparity in insurance due to health status. Between race and income, income was a more significant predictor of lack of insurance coverage since low-income people regardless of race and health were significantly more likely to be uninsured or partially insured. However, it is important to note that minorities were disproportionately over-represented in the low-income or bad health groups so that any adverse association between income, bad health, and insurance status would affect minorities significantly more than whites. Among those with insurance, the most vulnerable group, the minority-low-income-bad health group or those with all the three vulnerability indicators, were most likely to be publicly insured. A policy implication is to target limited resources on insurance coverage for the more vulnerable groups, those with a convergence or cluster of predisposing, enabling, and need attributes of risk.

Health Services Research↗

PubMed2002

Serotonin alters multi-segmental convergence patterns in spinal cord deep dorsal horn and intermediate laminae neurons in an in vitro young rat preparation.

Each spinal neuron has a receptive field that corresponds to stimulation of a specific area of skin or subcutaneous tissue. Receptive fields are plastic and can be altered during development and injury but the actions of neuromodulators, such as serotonin (5-hydroxytryptamine, 5-HT) on receptive field properties are not well known. We used stimulation of multiple adjacent dorsal root spinal segments as a measure of "receptive field size" to determine the effects of 5-HT on multi-segmental convergent input onto neurons in laminae IV-VII. Whole-cell patch-clamp recordings were undertaken in the in vitro hemisected thoracolumbar spinal cord of rats aged 8-10 days old. Based on synaptic responses, neurons could be divided into two predominant groups and 5-HT exerted different effects on these groups. The first group received excitatory post-synaptic potentials (EPSPs) from the homonymous dorsal root but inhibitory post-synaptic potentials (IPSPs) with increasing amplitude from more distant dorsal roots. In this group, 5-HT preferentially depressed the IPSPs from adjacent nerve roots while leaving the EPSP intact. The second group received short-latency EPSPs from all segments stimulated and 5-HT potently depressed all synaptic input. In both populations the depressant actions of 5-HT increased with dose (0.1-10.0 microM). Bicuculline and strychnine did not affect the 5-HT induced short-latency synaptic depression. These results suggest that descending serotonergic systems depress spinal sensory convergence in a graded and differentiated manner. The findings are discussed in relation to the modulation of nociceptive signaling.

Animals↗