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PubMed1996

Synaptic interactions due to convergent input from gustatory afferent fibers in the rostral nucleus of the solitary tract.

1. Whole cell recordings from neurons in the rostral, gustatory nucleus of the solitary tract (rNST) were made using the "blind" patch-clamp technique in horizontal brain stem slices of rats. 2. Postsynaptic potentials (PSP) were elicited in 71 rNST neurons by electrical stimulation of the solitary tract (ST). To investigate PSPs evoked by convergent input from the chorda tympani and glossopharyngeal nerves, the ST was stimulated at levels where these two nerves terminate. These are referred to as rostral (rST) and intermediate (iST) ST, respectively. 3. When the rST was stimulated 72% of the PSPs were depolarizing, and 28% were hyperpolarizing (n = 64). Stimulation of the intermediate ST resulted in 75% depolarizing and 25% hyperpolarizing PSPs (n = 56). 4. Application of gamma-aminobuturic acid-A (GABAA) and glutamate receptor blockers revealed that all PSPs recorded in the present study were a composite of summed excitatory and inhibitory PSPs. Application of the GABAA receptor blocker bicuculline, by eliminating the hyperpolarizing component of a PSP, revealed the excitatory postsynaptic potential (EPSP) component of the potential. Bicuculline also increased the amplitude and prolonged the decay time of the depolarizing potentials once the hyperpolarizing potential component had been eliminated. These pure EPSP revealed by GABAA receptor blockade reversed at approximately 0 mV. 5. Application of glutamate ionotropic receptor blockers effectively eliminated the initiation of the synaptic responses evoked by ST stimulation. If the stimulus strength was increased, an inhibitory postsynaptic potential (IPSP) was elicited, presumably by direct activation of interneurons close to the stimulating electrode. These IPSPs had a mean reversal potential of -88 mV. 6. When synaptic responses were initiated by stimulation of the projection areas of both the chorda tympani and glossopharyngeal nerves, all neurons tested (n = 49) responded to stimulation of both sites on the ST. The resulting synaptic potential was a sum of the two individual synaptic potentials. 7. If stimulation of the rostral and intermediate sites both elicited depolarizing potentials, the potential resulting from stimulation of both sites was the arithmetical sum of the two individual PSPs. The EPSPs summed even if the time between stimulation of the rostral and intermediate sites was separated by < or = 100 ms. 8. Inhibitory PSPs evoked by simultaneous stimulation of the rostral and intermediate ST also summed. The summation was not linear and saturated at a mean level of -66 mV. 9. When the PSP at one stimulation site was excitatory but inhibitory at the other site, the PSP wave form resulting from dual stimulation was a complex mixture of the two individual potentials. The inhibitory potential was capable of blocking action potentials resulting from the excitatory PSP. 10. These results indicate that synaptic responses in rNST are complex mixtures of excitatory and inhibitory potentials. The synaptic potentials result from excitatory afferent input mediated by glutamate and inhibitory input derived from interneurons. Inhibitory transmission is mediated primarily at GABAA synapses. Stimulation of the rNST afferent input derived from the chorda tympani and glossopharyngeal nerves reveals complex convergent input. The complexity of these synaptic interactions indicates that considerable processing of gustatory information occurs at the first central synapse in the taste pathway.

Animals↗
PubMed1997

Converging inputs to the entorhinal cortex from the piriform cortex and medial septum: facilitation and current source density analysis.

Converging inputs to the entorhinal cortex from the piriform cortex and medial septum: facilitation and current source density analysis. J. Neurophysiol. 78: 2602-2615, 1997. The entorhinal cortex receives sensory inputs from the piriform cortex and modulatory inputs from the medial septum. To examine short-term synaptic facilitation effects in these pathways, current source density (CSD) analysis was used first to localize the entorhinal cortex membrane currents, which generate field potentials evoked by stimulation of these afferents. Field potentials were recorded at 50-micron intervals through the medial entorhinal cortex in urethan-anesthetized rats and the one-dimensional CSD was calculated. Piriform cortex stimulation evoked a surface-negative, deep-positive field potential component in the entorhinal cortex with mean onset and peak latencies of 10.4 and 18.4 ms. The component followed brief 100-Hz stimulation, consistent with a monosynaptic response. CSD analysis linked the component to a current sink, which often began in layer I before peaking in layer II. A later, surface-positive field potential component peaked at latencies near 45 ms and was associated with a current source in layer II. Medial septal stimulation evoked positive and negative field potential components which peaked at latencies near 7 and 16 ms, respectively. A weaker and more prolonged surface-negative, deep-positive component peaked at latencies near 25 ms. The early components were generated by currents in the hippocampal formation, and the late surface-negative component was generated by currents in layers II to IV of the entorhinal cortex. Short-term facilitation effects in conscious animals were examined using electrodes chronically implanted near layer II of the entorhinal cortex. Paired-pulse stimulation of the piriform cortex at interpulse intervals of 30 and 40 ms caused the largest facilitation (248%) of responses evoked by the second pulse. Responses evoked by medial septal stimulation also were facilitated maximally (59%) by a piriform cortex conditioning pulse delivered 30-40 ms earlier. Paired pulse stimulation of the medial septum caused the largest facilitation (149%) at intervals of 70 ms, but piriform cortex evoked responses were facilitated maximally (46%) by a septal conditioning pulse 100-200 ms earlier. Frequency potentiation effects were maximal during 12- to 18-Hz stimulation of either the piriform cortex or medial septum. Occlusion tests suggested that piriform cortex and medial septal efferents activate the same neurons. The CSD analysis results show that evoked field potential methods can be used effectively in chronically prepared animals to examine synaptic responses in the converging inputs from the piriform cortex and medial septum to the entorhinal cortex. The short-term potentiation phenomena observed here suggest that low-frequency activity in these pathways during endogenous oscillatory states may enhance entorhinal cortex responsivity to olfactory inputs.

Animals↗
PubMed1998

Pattern of cardiorespiratory afferent convergence to solitary tract neurons driven by pulmonary vagal C-fiber stimulation in the mouse.

The central integration of signals from pulmonary vagal C-fibers (or type-J receptors) with those arising from cardiac, peripheral chemoreceptor, and baroreceptor afferents to neurons within the nucleus of the solitary tract (NTS) was studied in an arterially perfused working heart-brain stem preparation of adult mouse. Pulmonary vagal C-fibers were excited by right atrial injection of phenylbiguanide (PBG) while cardiac receptors were stimulated by left ventricular injection of veratridine (1-3 micrograms/kg) or mechanically by distension of the left ventricle (20-50 microl perfusate) using an indwelling cannula. Carotid body chemoreceptors were activated by aortic injection of Na cyanide, whereas baroreceptors were stimulated by increasing arterial perfusion pressure. Stimulation of pulmonary C-fibers and cardiac, chemo-, and baroreceptors all produced a reflex bradycardia (23-133 bpm). Central respiratory activity, as recorded from the phrenic nerve, was depressed by stimulating pulmonary C-fibers and cardiac and baroreceptors but enhanced in amplitude and frequency during chemoreceptor stimulation. Twenty-seven NTS neurons were excited and three were inhibited after pulmonary C-fiber stimulation displaying decrementing discharges with a peak firing frequency of up to 42 Hz (15 +/- 2.2 Hz, mean +/- SE) that lasted for 8.8 +/- 0.9 s. These responses occurred <1 s from the end of the PBG injection that was within the pulmonary circulation time. None of these cells responded to increases in right atrial pressure. All cells excited by PBG were also driven synaptically after electrical stimulation of the ipsilateral cervical vagus nerve at a latency of 32.9 +/- 3.2 ms (range 20-62 ms). None of these neurons had ongoing activity related to central respiratory activity. Convergence from cardiorespiratory afferents to 21 neurons driven by pulmonary C-fibers was tested. Twenty-five percent of cells were selectively excited by chemical stimulation of cardiac receptors alone, 19% were driven by peripheral chemoreceptors, and 38% responded to both cardiac and chemoreceptor activation. In contrast, only 13% of the cells activated by PBG injection responded to stimulation of baroreceptors and only 6% to cardiac mechanoreceptor stimulation. None of these neurons were activated by increasing right atrial pressure. The data indicate a high proportion of afferent convergence from pulmonary C-fibers, cardiac receptors, and peripheral chemoreceptors in the NTS. However, these neurons appear not to integrate inputs from cardiovascular mechanoreceptors. The significance of the data is discussed in relation to pathological disease states such as pulmonary congestion and cardiac failure.

Afferent Pathways↗
PubMed2000

Convergence of multimodal sensory input onto higher-level neurons of the crayfish olfactory pathway.

Intracellular electrophysiological studies of lateral protocerebral interneurons (LPIs) in the crayfish Procambarus clarkii have revealed convergence of multimodal sensory information onto these higher-level cells of the crustacean central olfactory pathway. Antennular stimulation by odors or electrical shocks generates excitatory-inhibitory sequences in some LPIs as does electrical or hydrodynamic stimulation of the antennae. Photic stimulation of the ipsilateral compound eye generates excitatory responses in LPIs, usually in the form of trains of impulse bursts that are timed to the peaks of the spontaneous oscillatory activity that characterizes these neurons. Focal electrical stimulation of the olfactory lobe, the termination point of antennular afferent input, or the accessory lobe, where higher-level visual and tactile inputs converge, also generates brief excitation and a delayed, prolonged inhibition in LPIs. Both phases of this activity are thought to be transmitted to the lateral protocerebrum via deutocerebral projection neurons, which have extensive dendritic arborizations in the olfactory lobe and the accessory lobe. The excitatory pathway is thought to synapse directly with target LPIs, whereas the inhibitory pathway is probably indirect and mediated through GABAergic interneurons within the lateral protocerebrum. There is evidence that both presynaptic and postsynaptic inhibition suppress activity in LPIs. Preliminary observations suggest that a small cluster of neurons adjacent to the hemi-ellipsoid body are inhibitory to LPI activity. Multimodal inhibitory and excitatory modulation of LPI activity may play a part in the contextual identification of odors in the crayfish olfactory system.

Action Potentials↗
PubMed1992

Chromatophore systems in teleosts and cephalopods: a levels oriented analysis of convergent systems.

The neural control of chromatophore display in cephalopod mollusks and teleost fishes is reviewed in the context of convergence of functional-anatomical pathways and mechanisms at several levels of organization. The effector elements or chromatophores are different in origin and design in the two groups of animals. Major functional differences appear to be in the speed of response (greatest in cephalopods) and the magnitude of non-neural control mechanisms (greatest in teleosts). Despite the differences, the elements demonstrate striking overall functional similarity. Elements of different types form highly organized array patterns of similar general complexity. Innervation patterns in cephalopods and teleosts seem comparable, with control being unidirectional (albeit in opposite directions); some elements demonstrate polyaxonal innervation. Motor units in both groups are generally composed of many chromatophores. Packard's concept of 'cronological units' of similar age-classes of chromatophores being innervated by similar age-classes of motor neurons greatly simplifies the understanding of relationships between the static arrays and the physiological units that utilize them to produce chromatic displays. The lower motor control areas for both groups have been grossly identified. Chromatomotor neurons in cephalopods are mostly located in the chromatophore lobes of the subesophageal brain while comparable systems in teleosts are situated in sympathetic chain ganglia (preganglionics) and the rostral spinal cord (postganglionics). Chromatic components are the simplest visually detectable units of color display, e.g. vertical bands and fin spots. They combine to form more complex chromatic patterns, which, in turn, are integrated with components of skin texture, posture and movement to produce display behaviors. Complexity of such systems seems to be of the same order of magnitude in both cephalopods and teleosts. Areas of the CNS related to each of the categorical levels have not been clearly defined. Crude patterning may take place in the basal and, perhaps, peduncle lobes in cephalopods and in the lower and intermediate medulla in teleosts. In both groups, higher level control relates to areas involved in sensorimotor integration and mediation of agonistic, sexual, and, perhaps, other types of behavior: the peduncle and optic lobes in cephalopods and the hypothalamus, tegmentum, otic tectum, torus semicircularis, thalamus and telencephalon in fishes. The systems appear to parallel each other in being organized hierarchically, with similar levels of complexity. Some of the regions may be especially important for regulating color patterns in response to visual input. Overall, chromatomotor control systems in cephalopods and teleosts demonstrate many apparent convergent features. Possible factors responsible for the similarities are discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Resting discharge and sensitivity of ampullary electroreceptors in Clarias gariepinus related to convergence ratio during ontogeny.

The ampullary electroreceptor organs of the teleost fish Clarias gariepinus converge to single afferent neurons. During the first 4 months of ontogeny the convergence ratio (CR) increases from 1 to 3. Extracellular single-unit recordings show that a 3-fold increase in CR results on average in a 3.6-fold increase in sensitivity measured at stimulus frequencies of 2, 8 and 20 Hz, and in a small but significant 1.1-fold increase in resting discharge. Adaptation of the primary afferents could account for the differences between changes in sensitivity and resting discharge.

Afferent Pathways↗
PubMed1995

Chromosomal painting shows that "marked chromosomes" in lesser apes and Old World monkeys are not homologous and evolved by convergence.

Cytogeneticists have long held that the single pair of metacentric, NOR-bearing "marked chromosomes" in lesser apes (Hylobatidae) and Old World monkeys (Cercopithecidae) are homologous. Hylobatids have sometimes been excluded from Hominoidea (great apes and humans) and phylogenetically allied with the lower primates, primarily on the basis of this shared "trait." However, in situ hybridization of human chromosome-specific DNA probes to chromosomes of Hylobates lar, H. syndactylus, H. concolor, Cercopithecus aethiops, Macaca fuscata, Colobus guereza, and Presbytis cristata showed that the so-called "marked chromosomes" in Hylobatidae and Cercopithecidae evolved by convergence. Therefore, "marked chromosomes" cannot be used to exclude gibbons from Hominoidea or to link Hylobatidae with monkeys. Chromosomal painting is a powerful tool to resolve problems of chromosomal homology and helps eliminate phylogenetic errors due to confusing convergence with homology. Chromosomal painting improves the confidence in using cytogenetic data for evolutionary studies, especially in phylogeny and taxonomy.

Animals↗
PubMed1980

[Convergence nystagmus: an oculographic analysis].

Convergence nystagmus and nystagmus retractorius represent important ocular motor disorders in cases of periaqueductal involvement and serve as valuable topographical clue in the Sylvian aqueduct syndrome. The oculographic tracings of a 34-year-old male suffering from a pinealoma are presented. It is outlined, under which circumstances convergence nystagmus is elicited, and the typical features of this disconjunctive nystagmus are discussed.

Adult↗
PubMed1980

[Sensory binocular relationships in divergent strabismus and convergent strabismus].

The adaptive processes mentioned here (which include inhibitory phenomena and modifications in spatial localization) were observed, using a stereoprojector which polarized light. Comparing the adaptive processes in convergent and divergent strabismus has led to the following observations: (1) there are differences between the two types of strabismus; these differences appear not only at the level of the binocular sensory parameter but also at the level of motor and accommodative parameters; adaptive processes are less deep and less serious in divergent and strabismus; these differences are also manifest in therapy: divergent strabismus is curable whatever the age, treatment is much shorter. These observations were the starting point for using prismatic overcorrection to induce a state of 'sensory divergence' as treatment in cases of convergent strabismus with anomalous retinal correspondence. The excellent results obtained using this method of treatment are not only due to the action on sensory binocular relations, but also to the fact that prismatic overcorrection also modifies abnormal motor patterns. Treating strabismus must involve the entire disturbed optico-sensorimotor complex.

Accommodation, Ocular↗
PubMed1993

Quantification of left-to-right atrial shunting and defect size after balloon mitral commissurotomy using biplane transesophageal echocardiography, color flow Doppler mapping, and the principle of proximal flow convergence.

BACKGROUND: The flow convergence region (FCR), a zone of progressive laminar velocity acceleration, can be imaged by color Doppler proximal to stenotic and regurgitant orifices. Theoretically, FCR proximal to a discrete circular and planar orifice consists of concentric hemispheric shells of equal and accelerating velocities centered at the orifice. According to the continuity principle, flow rate across any of these isovelocity surfaces equals flow rate through the orifice. The aim of this study was to investigate whether these principles could be applied to quantify left-to-right shunting and the size of atrial septal defects after balloon mitral commissurotomy. METHODS AND RESULTS: Biplane transesophageal echocardiography (TEE) with color flow imaging was performed on 36 consecutive patients (mean age, 57 +/- 16 years; range, 14-78 years) immediately before and within 24 hours of balloon (Inoue, n = 33; Mansfield, n = 3) mitral commissurotomy. Left-to-right atrial shunting was detected by TEE in 33 patients (92%) and by oximetry in 11 patients (31%). The radius r of FCR was measured from the first aliasing limit, at a Nyquist velocity reduced to 11 cm/sec by zero-shifting, to the orifice in the atrial septum. FCR was assumed to be hemispherical. Hence, flow rate (Q) was calculated as 2 pi r2 Vr, where Vr is the velocity at a radial distance r. The velocity profile of transatrial flow was assessed by means of high pulse repetition frequency, from which the maximum flow velocity (Vp) and the velocity-time integral (VTI) were obtained. The flow area of the atrial septal defect was calculated as Qm, the maximal flow rate, divided by Vp. Hence, shunt flow was calculated as flow area x VTI x heart rate. FCR was analyzed in two orthogonal planes. Mean Qm (38.1 +/- 26.5 versus 5.3 +/- 2.7 mL/sec), flow area (22.1 +/- 11.2 versus 4.4 +/- 2.0 mm2), and shunt flow (1,590 +/- 1,070 versus 200 +/- 130 mL/min) on transverse plane imaging were all significantly higher in patients with shunts detected by oximetry than in those without. Similar results were obtained from longitudinal plane imaging. Qm correlated well with oximetric shunt flow (r = 0.89-0.94, p < 0.001) and shunt ratio (r = 0.91-0.94, p < 0.001). Flow area correlated closely (r = 0.93-0.94, p < 0.001) with area determined by direct measurement from two-dimensional echocardiography. Shunt flow determined by FCR also correlated closely (r = 0.94-0.98, p < 0.001) with that determined by oximetry and that derived from two-dimensional echocardiography and pulsed Doppler (r = 0.96, p < 0.001). CONCLUSIONS: The flow convergence region imaged by TEE color flow mapping provides new and accurate quantitative information on atrial shunt flow and defect size after balloon mitral valvotomy. It is a quick, reliable, and fairly simple method that can be readily incorporated into routine clinical practice.

Adolescent↗
PubMed1996

Effective regurgitant orifice area by the color Doppler flow convergence method for evaluating the severity of chronic aortic regurgitation. An animal study.

BACKGROUND: The aim of the present study was to evaluate dynamic changes in aortic regurgitant (AR) orifice area with the use of calibrated electromagnetic (EM) flowmeters and to validate a color Doppler flow convergence (FC) method for evaluating effective AR orifice area and regurgitant volume. METHODS AND RESULTS: In 6 sheep, 8 to 20 weeks after surgically induced AR, 22 hemodynamically different states were studied. Instantaneous regurgitant flow rates were obtained by aortic and pulmonary EM flowmeters balanced against each other. Instantaneous AR orifice areas were determined by dividing these actual AR flow rates by the corresponding continuous wave velocities (over 25 to 40 points during each diastole) matched for each steady state. Echo studies were performed to obtain maximal aliasing distances of the FC in a low range (0.20 to 0.32 m/s) and a high range (0.70 to 0.89 m/s) of aliasing velocities; the corresponding maximal AR flow rates were calculated using the hemispheric flow convergence assumption for the FC isovelocity surface. AR orifice areas were derived by dividing the maximal flow rates by the maximal continuous wave Doppler velocities. AR orifice sizes obtained with the use of EM flowmeters showed little change during diastole. Maximal and time-averaged AR orifice areas during diastole obtained by EM flowmeters ranged from 0.06 to 0.44 cm2 (mean, 0.24 +/- 0.11 cm2) and from 0.05 to 0.43 cm2 (mean, 0.21 +/- 0.06 cm2), respectively. Maximal AR orifice areas by FC using low aliasing velocities overestimated reference EM orifice areas; however, at high AV, FC predicted the reference areas more reliably (0.25 +/- 0.16 cm2, r = .82, difference = 0.04 +/- 0.07 cm2). The product of the maximal orifice area obtained by the FC method using high AV and the velocity time integral of the regurgitant orifice velocity showed good agreement with regurgitant volumes per beat (r = .81, difference = 0.9 +/- 7.9 mL/beat). CONCLUSIONS: This study, using strictly quantified AR volume, demonstrated little change in AR orifice size during diastole. When high aliasing velocities are chosen, the FC method can be useful for determining effective AR orifice size and regurgitant volume.

Animals↗
PubMed1990

Insignificant bilateral convergence of preganglionic vagal fibers on postganglionic neurons to the canine heart.

We determined the extent of convergence of preganglionic fibers from the right and left vagus nerves on postganglionic neurons that supply the sinoatrial node in chloralose-anesthetized dogs. We administered hemicholinium-3 and stimulated the right vagus nerve at a high frequency to deplete acetylcholine from the postganglionic parasympathetic neurons supplied by that nerve. We compared the effects of this "depletion regimen" with the responses in two control groups: a stimulation control group, which was subjected to high-frequency right vagus stimulation only, and a drug control group, which received a hemicholinium-3 infusion only. The effects of right vagus stimulation did not differ from those of left vagus stimulation in either of the control groups. In the animals subjected to the depletion regimen, the responses to right vagus stimulation were almost abolished. However, the left vagus nerve retained its ability to prolong cardiac cycle length in these animals. Thus, our experiments indicate that left vagus preganglionic fibers do not converge with right vagus preganglionic fibers on a substantial pool of postganglionic neurons that innervate the canine sinoatrial node.

Acetylcholine↗
PubMed2001

Convergent decomposition techniques for training RBF neural networks.

In this article we define globally convergent decomposition algorithms for supervised training of generalized radial basis function neural networks. First, we consider training algorithms based on the two-block decomposition of the network parameters into the vector of weights and the vector of centers. Then we define a decomposition algorithm in which the selection of the center locations is split into sequential minimizations with respect to each center, and we give a suitable criterion for choosing the centers that must be updated at each step. We prove the global convergence of the proposed algorithms and report the computational results obtained for a set of test problems.

Algorithms↗
PubMed1998

Weight-value convergence of the SOM algorithm for discrete input.

Some insights on the convergence of the weight values of the self-organizing map (SOM) to a stationary state in the case of discrete input are provided. The convergence result is obtained by applying the Robbins-Monro algorithm and is applicable to input-output maps of any dimension.

Algorithms↗
PubMed2002

Combining convergence and diversity in evolutionary multiobjective optimization.

Over the past few years, the research on evolutionary algorithms has demonstrated their niche in solving multiobjective optimization problems, where the goal is to find a number of Pareto-optimal solutions in a single simulation run. Many studies have depicted different ways evolutionary algorithms can progress towards the Pareto-optimal set with a widely spread distribution of solutions. However, none of the multiobjective evolutionary algorithms (MOEAs) has a proof of convergence to the true Pareto-optimal solutions with a wide diversity among the solutions. In this paper, we discuss why a number of earlier MOEAs do not have such properties. Based on the concept of epsilon-dominance, new archiving strategies are proposed that overcome this fundamental problem and provably lead to MOEAs that have both the desired convergence and distribution properties. A number of modifications to the baseline algorithm are also suggested. The concept of epsilon-dominance introduced in this paper is practical and should make the proposed algorithms useful to researchers and practitioners alike.

Algorithms↗