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PubMed1989

Convergence of serotonin-, enkephalin- and substance P-like immunoreactive afferent fibers onto cat medullary dorsal horn projection neurons: a triple immunocytochemical staining technique combined with the retrograde HRP-tracing method.

Convergence of serotonin (5-HT)-, enkephalin (ENK)-, and substance P (SP)-like immunoreactive (LI) afferent fibers onto cat medullary dorsal horn projection neurons was examined by retrogradely labeling trigeminothalamic neurons and immunocytochemically labeling 5-HT, ENK and SP fibers in the same tissue section using distinct chromogens. Convergence of 5-HT-, ENK- and SP-LI fibers upon single projection neurons was often observed in laminae I and V.

Animals↗

PubMed1992

Convergence and segregation of septal and median raphe inputs onto different subsets of hippocampal inhibitory interneurons.

The convergence and segregation of medial septal and median raphe afferents in the innervation of different subpopulations of GABAergic interneurons was investigated in the rat hippocampal formation. Following local injections of 5,7-dihydroxytryptamine into the median raphe nucleus destroying all serotonergic neurons, iontophoretic injections of Phaseolus vulgaris leucoagglutinin (PHAL) into the medial septum resulted in anterograde labelling of axons in the hippocampus. The labelled varicose fibres made multiple contacts with calbindin D28K-, parvalbumin-, and cholecystokinin-immunoreactive interneurons. These results disproved the possibility that PHAL-labelled afferents innervating hippocampal interneurons following septal PHAL injections would have been raphe axons passing through the injection site. In the second set of experiments a double anterograde tracing technique (PHAL from the septum and biotinylated-PHAL from the median raphe) and a triple or double immunostaining procedure was used to determine the types of interneurons (calbindin D28K-, parvalbumin-, or cholecystokinin-immunoreactive) innervated by one, or the other, or both pathways. The results showed that parvalbumin-containing neurons were innervated by septal afferents but avoided by raphe axons, whereas calbindin D28K-containing cells, and to a smaller extent cholecystokinin-containing cells served as targets for both pathways. In some cases the same individual calbindin D28K- or cholecystokinin-containing neurons received multiple contacts from afferents of both septal and raphe origin. Thus, our results indicate that different subcortical nuclei modulate largely different inhibitory circuits in the hippocampal formation. However, considering the occasional convergence of the two subcortical nuclei not only onto the same type, but even onto the same individual calbindin D28K-containing interneurons, we propose that a particular inhibitory function, most probably feed-forward inhibition in the distal dendritic region, is under the control of both pathways.

Afferent Pathways↗

PubMed1992

Convergence of oral and extraoral information in the superior secondary gustatory nucleus of the channel catfish.

Neurons within the superior secondary gustatory nucleus (nGS) of the channel catfish were examined electrophysiologically for responses to mechanical and chemical stimulation of neural peripheral receptive fields (RFs). Of the 28 single units sampled, 18 had mechanosensory RFs on the extraoral epithelium, two had RFs within the oropharyngeal cavity, and eight had RFs that included both oral and extraoral surfaces. RF sizes varied from approximately 2 cm2 on the ipsilateral lips and barbels to the whole body surface, bilaterally. No obvious correlation existed between RF pattern and recording location within the nGS. Eight of the mechanosensory nGS units also responded to amino acid taste stimuli with thresholds from micromolar to millimolar concentrations. The convergence of oral and extraoral information within the nGS determined electrophysiologically was corroborated anatomically by HRP labeling experiments. Restricted HRP injections into each of the primary gustatory nuclei of the medulla, the vagal (VL) and facial (FL) lobes, labeled fibers that appeared to terminate diffusely throughout the nGS, and injections into different portions of the nGS retrogradely labeled cells in both the FL and VL. The present electrophysiological and neuroanatomical data distinguish the convergent gustatory representation within the nGS of the catfish from the highly specific somatotopic and viscerotopic sensory maps previously identified in the FL and VL, respectively.

Afferent Pathways↗

PubMed1994

Polymodal sensory and motor convergence in substantia nigra neurons of the awake monkey.

Responses of substantia nigra (SN) pars compacta (SNc) and reticulata (SNr) neurons to sensory stimulation and movement were investigated in awake Macaca fascicularis. Concern was assigned to polysensory and sensory/motor convergence on the same cell, which were found in 12% and 9% of the neurons, respectively. Others were modality specific (35%) or unresponsive (44%). The convergence lends support to the notion that SN plays an important role in sensory-motor integration.

Acoustic Stimulation↗

PubMed1994

Diazepam attenuates hyperexcitability and mechanical hypersensitivity of dorsal horn convergent neurones during reperfusion of the rat's tail following ischaemia.

We have investigated the involvement of the GABAA-benzodiazepine receptor complex in nociceptive activity of convergent neurones in the spinal cord during ischaemia and reperfusion of their receptive fields on the rat's tail. In enflurane anaesthetized rats, extracellular recordings were made from convergent neurones located throughout the dorsal horn before, during and after 30 min of ischaemia. Following intrathecal saline pretreatment, there was a significant increase in spontaneous firing rate during ischaemia (219 +/- 21%, P < 0.02, n = 10) which persisted during reperfusion. After 10 min of reperfusion, the neurones exhibited a greater response than before ischaemia to both innocuous brush (54 +/- 11%, P < 0.05, n = 10) and noxious pinch (72 +/- 14%, P < 0.02, n = 10) and the enhanced sensitivity persisted over the 60-min reperfusion period. During reperfusion, receptive field size increased in most neurones tested. Intrathecal diazepam (100 and 500 micrograms) abolished the hyperexcitability and the hypersensitivity to both innocuous and noxious mechanical stimulation during reperfusion. The highest dose of diazepam (500 micrograms) also attenuated the increase in spontaneous firing rate during ischaemia. Diazepam, at the doses tested, had no effect on receptive field enlargements during reperfusion. The effect of 100 micrograms of diazepam was partially reversed by flumazenil (1 mg/kg i.p.) but not by naloxone (1 mg/kg i.p.). In the absence of ischaemia, diazepam had no effect on spontaneous firing rate nor on the responses to innocuous or noxious mechanical stimulation. Our results support an antinociceptive role for benzodiazepines in the dorsal horn elements responsible for reperfusion hyperalgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Neurons projecting from the entopeduncular nucleus to the thalamus receive convergent synaptic inputs from the subthalamic nucleus and the neostriatum in the rat.

The two major afferents of the entopeduncular nucleus are the subthalamic nucleus and the neostriatum, which have opposing physiological effects on entopeduncular neurons. Experiments were performed to test the hypothesis that individual entopeduncular neurons that project to the thalamus receive convergent synaptic input from both the subthalamic nucleus and the neostriatum in the rat. This was achieved using double anterograde tracing combined with retrograde tracing. In the electron microscope anterogradely labelled subthalamic (Subthalamic Type 1) and neostriatal terminals were observed to form asymmetrical and symmetrical synaptic contacts respectively, with all parts of entopeduncular neurons. Labelled subthalamic and neostriatal terminals were observed in convergent synaptic contact with entopeduncular neurons, some of which were retrogradely labelled from the thalamus. A second rarer type of terminal was labelled (Subthalamic Type 2) which formed symmetrical synaptic contacts with the proximal regions of unlabelled and retrogradely labelled entopeduncular neurons. These terminals are believed to be derived from the globus pallidus. It is concluded that the topographical and synaptic organization of the so-called direct (neostriatum to entopeduncular nucleus) and indirect pathways (involving the subthalamus and the globus pallidus) is capable of mediating the inhibition and excitation of output neurons in the entopeduncular nucleus that occur following neostriatal stimulation.

Animals↗

PubMed1988

Intracerebroventricular morphine restores the basic somesthetic activity of dorsal horn convergent neurones in the rat.

We have proposed that a painful focus will disturb the global activity of spinal and trigeminal convergent neurones in two complementary ways: by activation of the corresponding segmental pool of neurones and by an inhibition mediated by diffuse noxious inhibitory controls of the remaining neuronal population. Morphine (10 micrograms) administered within the third ventricle blocks diffuse noxious inhibitory controls acting on a basic somesthetic activity simulated by responses of convergent neurones to innocuous stimuli. It is proposed that analgesia induced by intracerebroventricular morphine could result, at least in part, from restoration of the basic somesthetic activity.

Animals↗

PubMed1984

Viscerosomatic convergence onto T2-T4 spinoreticular, spinoreticular-spinothalamic, and spinothalamic tract neurons in the cat.

Neurons of T2 to T4 spinal segments were antidromically activated from the medullary reticular formation and the contralateral region in or near the ventral posterior lateral nucleus of the thalamus. Sixty-seven percent of the spinoreticular neurons projected to the ipsilateral, contralateral, or both ipsilateral and contralateral medullary reticular formation. In addition, 21% of the cells projected to the reticular formation and thalamus and 12% projected only to the thalamus. These cells received both visceral and somatic inputs. Electrical stimulation of cardiopulmonary sympathetic afferent fibers elicited an early peak of cell activity in 30 cells, an early and late peak in 38 cells, and only a late peak in 1 cell. Seventy-one percent of the cells had simple somatic receptive fields; these fields were localized to the left forelimb and left upper thorax. The remaining 29% of the cells had complex receptive fields that often extended to the hind limb as well as bilaterally. Classification of all cells according to threshold for activation of the somatic receptive field showed that 86% of the cells were high-threshold, 10% were wide dynamic range, and 4% were high-threshold but, in addition, were inhibited during hair movement. Viscerosomatic convergence onto these cells support Ruch's convergence projection theory for referred pain. These projecting neurons may be involved with referred pain associated with angina pectoris. In addition, they may also be involved with cardiovascular adjustments.

Animals↗

PubMed1988

Distribution of the flux control in convergent metabolic pathways: theory and application to experimental and simulated systems.

1. Metabolic systems involving branched convergent pathways are analyzed under Flux Control Theory, obtaining a relationship between the contribution of every convergent pathway to the total flux and its Flux Control Coefficient. 2. An experimental model system is carried out to demonstrate the physical application of some conclusions of theoretical treatment. 3. Two different types of branched pathways are simulated by computer. 4. In both cases results are in agreement with the theoretical conclusions, showing in addition some new aspects on metabolic control.

Computers↗

PubMed1991

Convergence of the axial walls of full veneer crown preparations in a dental school environment.

This research report used a simple and accurate method of measuring the convergence of full veneer crown preparations. A random sample of 909 dies was selected from all dies of full veneer crown preparations done at the University of Colorado, School of Dentistry student clinic over a 6-year period. All preparations were accomplished by third- and fourth-year dental students under either normal clinic conditions or under special (proficiency) testing conditions. The mean convergence angles were 19 degrees (S.D. +/- 9.8 degrees) for nonexamination conditions and 15.7 degrees (S.D. +/- 5.5 degrees) for examination procedures. These angles are far in excess of those normally recommended in the fixed prosthodontic textbooks. The values obtained in this investigation agree with the findings of most of the current published studies on the subject.

Bicuspid↗

PubMed1982

The effect of convergence on the vestibulo-ocular reflex and implications for perceived movement.

The apparent motion of a fixated stimulus during head translation in the dark was found to depend on the magnitude of the vestibulo-ocular reflex (VOR). Absolute convergence level determines VOR magnitude and thereby influences apparent motion during head movement by determining the magnitude and direction of the pursuit effort required to maintain gaze stability. The results are discussed in terms of the biological utility of the coupling between convergence and the VOR in maintaining image stability, and the role of the pursuit eye movement system in illusory movement.

Fixation, Ocular↗

PubMed1987

Verbal expression of right cerebrovascular accident patients: convergent and divergent language.

This investigation examined the role of the right hemisphere in language expression. Three groups of 12 subjects each--right CVAs, left CVAs, and controls--performed convergent and divergent language tasks of naming, function, and connected speech. For all convergent tasks and for number of words, number of message units, and fluency in divergent connected speech, controls surpassed both brain-damaged groups, who performed similarly. For the other divergent tasks, controls were superior to the brain-damaged groups, but the right CVAs outperformed the left CVAs. In general, verbal expression problems of right-hemisphere-damaged patients were almost as severe as those of left-hemisphere-damaged patients.

Adult↗

PubMed1985

Convergence of vagal and gustatory afferent input within the parabrachial nucleus of the rat.

Our previous anatomical and electrophysiological studies demonstrated that first-order hepatic and gustatory afferents project to separate regions of the solitary nucleus (NST) and no intra-NST interaction of these two sensory systems could be demonstrated. However, iontophoretic injections of horseradish peroxidase into physiologically identified zones of the NST revealed that both of these regions send overlapping projections to the immediately subjacent parvocellular reticular formation as well as the postero-medial parabrachial nucleus (PBN). The present electrophysiological studies demonstrate that an interstitial zone of neurons in the caudal, medial PBN, indeed, receive convergent input from second-order gustatory and vagal afferents. Co-activation of these PBN units by the simultaneous arrival of both input sources frequently resulted in an additive interaction of evoked activity. PBN units lateral and caudal to this zone responded to vagal stimulation only, while units in the anterior and extreme medial portion of the PBN only responded to gustatory stimulation. By virtue of the efferent projections of the PBN, one might speculate that the convergence of information at this locus may, eventually, play a role in directing long term feeding behavior patterns such as learned taste aversion as well as the more transient changes in taste preference with visceral loading.

Animals↗

PubMedDate not supplied

Electrophysiological analysis of the convergence of peripheral inputs onto neurons of the coeliac ganglion in the guinea pig.

The convergence of intestinofugal axons from different intestinal regions onto individual neurons in the coeliac ganglion of the guinea pig was investigated using intracellular recording methods in vitro. Peripheral nerve trunks from the distal ileum, the most proximal colon and the colon near the colonic flexure were electrically stimulated along with preganglionic fibres running in the splanchnic nerve. Fast cholinergic excitatory synaptic potentials (EPSPs) were seen in ganglion cells in response to stimulation of each nerve trunk. Roughly half of 78 neurons impaled received inputs from stimulation of peripheral nerves, and almost all of these received input from the proximal colon. Most cells responded to stimulation of more than one peripheral nerve indicating that coeliac neurons receive converging inputs from intestinofugal neurons located in more than one intestinal region. In a second series of experiments, segments of intestine were left attached to the ganglion and distended with saline to stimulate peripheral mechanosensory input to the coeliac ganglion. In each experiment, two segments were stimulated. A subgroup of ganglion cells exhibited spontaneous fast EPSPs and the frequency of these potentials was increased by distension of one or other of the attached intestinal segments. However, few neurons responded to distension of both of the attached intestinal segments suggesting that some of the intestinofugal inputs to the coeliac ganglion identified by electrical stimulation may be sensitive to sensory modalities other than distension. Hexamethonium (0.5 mM) applied to the intestine, and not to the coeliac ganglion, reduced the frequency of the spontaneous synaptic potentials seen in coeliac ganglion cells, but did not abolish the response to distension of the colon (n = 8). When the Ca2+ concentration of the solution bathing the proximal colon was reduced to block all synaptic transmission in the enteric plexuses the background synaptic input was further depressed, but again the response to distension was little changed (n = 4). This suggests that at least some of the neurons projecting from the colon to the coeliac ganglion are first order mechanosensory neurons.

Animals↗

PubMed1995

'Aortic baroreceptor' neurons in the nucleus tractus solitarius in rats: convergence of cardiovascular inputs as revealed by heartbeat-locked activity.

Rat aortic depressor nerve (ADN) contains only baroreceptor afferents. We identified 'aortic baroreceptor' neurons in the nucleus tractus solitarius (NTS) as those responding to electrical stimulation of the ADN and attempted to demonstrate convergence of cardiovascular mechanoreceptor inputs in these 'baroreceptor' neurons. In chloralose-urethane-anesthetized rats, ADN stimulation evoked either short or long latency responses (SLR, LLR) in 193 neurons of the NTS. 28 (SLR, 15; LLR, 13) demonstrated ongoing activities with cardiac rhythm despite the fact that the ADN had been cut peripherally. In 12 (SLR, 5; LLR, 7) of the 28 neurons, heartbeat-locked activity was abolished by carotid occlusion (CO), and augmented by methoxamine-induced blood pressure elevation, indicating that the heartbeat-locked activity originated from carotid sinus baroreceptors (CSB). In 11 neurons (SLR, 6; LLR, 5), the heartbeat-locked activity was not affected by CO but was abolished by topical application of lidocain on the ipsilateral cervical vagus, suggesting that the heartbeat-locked activity originated mostly from cardiac mechanoreceptors. The origin of the heartbeat-locked activity of the remaining 5 neurons could not be determined. The onsets, as well as peaks of the heartbeat-locked activity of vagal origin appeared significantly earlier than those of CSB origin. In conclusion, NTS neurons receive converging projection not only from the two major arterial baroreceptors but also from the arterial baroreceptors and cardiac mechanoreceptors, thereby integrating sensory information of vascular and cardiac origins.

Animals↗

PubMed1989

A proposed relationship between increases in the number of olfactory receptor neurons, convergence ratio and sensitivity in the developing rat.

In the rat neonate, as in other altricial young, olfaction, in contrast to vision and hearing, is functional at birth, being critically important in feeding, growth and other aspects of infant-mother interaction. Yet, olfactory sensitivity, i.e., the ability to detect odors at low levels, is poor in the newborn, improving dramatically in the first few postnatal weeks. To find a neural explanation for this phenomenon at the level of peripheral olfactory system, we present quantitative light microscopic data which reveal that during the suckling period of postnatal development the surface area of the olfactory receptor sheet and the total number of olfactory receptor neurons increase by about 8- and 12-fold respectively, being about 15 mm2 and 1.0 million on each nasal half of the newborn. Since the number of mitral cells, the principal relay neurons of the olfactory bulb, is already established at birth, at about 40,000 per olfactory bulb, it may be estimated that the convergence ratio of the olfactory neurons to mitral cells increases by more than 10-fold in the suckling period. We propose that the increased number of primary sensory afferent units and the higher convergence upon the central relay cells enhances the physiological capacities of the olfactory afferent pathway, increasing the opportunity for spatial summation and facilitation. The latter changes may lead to reduced olfactory thresholds and improved sensitivity with development. The relative contribution of these peripheral changes in enhancement of olfactory sensitivity during growth is discussed in the light of our knowledge on the developing olfactory system.

Animals↗

PubMed1995

Layer I of primary sensory neocortex: where top-down converges upon bottom-up.

A fundamental paradigm shift is underway in the behavioural neurosciences which promotes renewed discussion of neural correlates of conscious sensation. A growing body of evidence that the primary sensory areas are central to conscious processing is inconsistent with conventional bottom-up models of passive sensory transformation. The new paradigm emphasizes the interaction of top-down corticocortical influences with bottom-up sensory feedback. This review develops the new interactive paradigm with respect to the behaviourally relevant N1 component of the somatosensory evoked response in primary somatosensory neocortex which is only observed during conscious states and predicts touch discrimination behaviour. N1 is generated by layer I excitation apparently in response to backward projections from higher order cortical areas. The backward corticocortical projections mediating top-down influences are anatomically concentrated in layer I where they strongly excite the subpopulation of pyramidal neurons with extensive distal apical dendrites. This subpopulation includes the forward-projecting pyramids subserving corticocortical reentrance as well as the corticobulbar projections mediating cortical control over fine sensory-oriented movements. This interactive paradigm views conscious sensation as an active behaviour with the optimal spatial resolution of primary areas serving as the sensory-motor interface at the major convergence point between reentrant bottom-up and top-down pathways. A device is proposed for the reconstruction of cortical sensory processing based upon the central importance of the primary area as the focus of convergent top-down cortical projections.

Animals↗

PubMed1987

Medical sociology and epidemiology: convergences, divergences and legitimate boundaries.

For the purpose of exploring the existence of problem areas that may give rise to the question whether there is a tendency to (illegitimately) trespass across boundaries between medical sociology and epidemiology, important convergences and divergences between both disciplines are described. To assemble arguments for the legitimacy of fields of study we trace comparatively the history of both disciplines, definitions of their fields under study and aims of study, as well as characteristic concepts and constructs. Current research themes are taken from international journals; divergent interests are briefly described and potential 'trespassing' of boundaries is discussed, referring to themes showing convergences of interest.

Authorship↗