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PubMed1977

Convergent and parallel evolution: a model illustrating selection, phylogeny and phenetic similarity.

A model is proposed which considers the structural relationships of body characteristics and their role in a concept wherein the phylogenetic relationship of the organisms under study is interpreted as constituting degrees of convergent or parallel evolution. The model also accounts for the relationships between selection pressures, phylogeny, and phenetic expression. The phenomena of convergent and parallel evolution are based upon the observations of similar characteristics, the geometric concept, magnitude and similarity of selection pressures, and the phylogenetic relationship of the groups in question.

Animals↗

PubMed1980

Multisensory convergence and interaction in the pulvinar-lateralis posterior complex of the cat's thalamus.

Responsiveness to visual, acoustic and somesthesic stimuli was studied in 260 units recorded within the associative thalamic nuclei of the cat (pulvinar-lateralis posterior complex and posterior group). Of the 123 units responding to one or more stimuli 41 (corresponding to 15% of the total) showed multisensory convergence. Bimodal, visual-somesthesic convergence was the most common finding, occurring in 33 units. Visual-somesthesic inhibitory interaction was observed only in the pulvinar nucleus, suggesting a peculiar synaptic organization of multisensory input to this nucleus.

Animals↗

PubMed1982

Convergent inputs from the dentate and the interpositus nuclei to pyramidal tract neurons in the motor cortex.

Effects of stimulation of the cerebellar nuclei were investigated by intracellular recordings from fast and slow pyramidal tract neurons and thalamocortical neurons in the cat. The present study demonstrated that: (1) the interpositus and the dentate nuclei excite PTNs in the motor cortex; (2) single pyramidal tract neurons receive convergent inputs from both nuclei, and (3) the convergence of the inputs from both nuclei occurs at the level of the ventrolateral nucleus of the thalamus.

Animals↗

PubMed1985

Convergence on the same neurons in the feline ventrobasal thalamus of terminals from the dorsal column and the lateral cervical nuclei: an ultrastructural study combining orthograde degeneration and anterograde axonal transport of lectin conjugated horseradish peroxidase.

After electrocoagulation of the dorsal column nuclei (DCN) and injections of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) into the lateral cervical nucleus (LCN), two kinds of changes in fibers and boutons were observed in the dorsolateral part of the thalamic ventroposterolateral nucleus (VPL). The axons and boutons from neurons in the DCN demonstrated dark degeneration, while the fibers and synaptic terminals from the LCN-neurons contained the characteristic needle-shaped peroxidase reaction products following incubation with tetramethylbenzidine (TMB). Occasionally dark degenerating boutons and boutons with TMB-positive reaction products showed synaptic contact with the same dendritic profiles. After consideration of the possibility of an axoaxonal transfer of the tracer it is concluded that the findings demonstrate convergence of synaptic input both from the DCN and from the LCN on the same postsynaptic VPL neurons. The present results are in accordance with earlier light microscopic and neurophysiological findings. It is also concluded that the ultrastructural technique employed in this study is well suited to reveal convergence of different afferent systems on the same postsynaptic neurons.

Afferent Pathways↗

PubMed1988

Convergence of noncholinergic afferent neurons in the inferior mesenteric ganglion of the guinea pig.

The pattern of noncholinergic innervation of principal ganglionic neurons from the lumbar colonic nerve (LCN) and lumbar splanchnic nerve (LSN) in the inferior mesenteric ganglion (IMG) of the guinea pig was studied with intracellular techniques. Simultaneous stimulation of the LCN and LSN at maximum frequency (20 Hz) and submaximal stimulus voltages (2-4 V) led to summation of slow excitatory postsynaptic potential (EPSPs) indicating convergence of neural input. Summation was observed with submaximal (but not maximal) stimulation parameters in cells with either large or small amplitude maximum slow EPSPs suggesting that each neuron has an individual maximum capacity to depolarize in response to non-cholinergic transmitter substances. The study indicates that neurons originating at both peripheral and central sites converge onto principal ganglionic neurons, thus these ganglionic neurons must perform a significant integrative function in the IMG.

Action Potentials↗

PubMed1990

Application of principal component analysis for characterizing convergence patterns of inputs in interneurones of the cat forelimb segments.

We attempted to quantitatively describe a variety of convergence patterns of inputs from peripheral nerves and descending tracts (13 sources) onto interneurones of the cat forelimb segments (C6-C8). To this end we applied principal component analysis using the latency of firing as the parameter of each input. The first 3 principal components thus obtained explained 65% of the total variance of convergence patterns and characterized the input pattern of each cell. The first principal component correlated mainly with inputs from pads and the median nerve, the second with the cortico- and rubro-spinal tracts and the third with the superficial radial nerve.

Animals↗

PubMed1992

Viscerosomatic convergence onto feline spinal neurons from esophagus, heart and somatic fields: effects of inflammation.

One objective of this study was to examine a mechanism for the inability of patients to distinguish esophageal pain from cardiac pain. Patients with esophageal disease and angina pectoris often perceive pain as originating from the same somatic fields. Another objective was to compare the effect of esophageal distension between animals with a non-inflamed or with an inflamed esophagus. For this study in anesthetized cats, we recorded extracellular action potentials from T2-T7 spinal neurons that responded to intraluminal distension of an untreated or a turpentine-inflamed distal esophagus. Threshold distension volumes were compared between these 2 groups of animals. Neurons also were examined for effects of intracardiac bradykinin injection and somatic stimuli. Results showed that spinal neurons responded to a smaller threshold distension volume when cells in animals with an inflamed distal esophagus were compared to cells in animals with a non-inflamed distal esophagus. Spinal neurons that received input from the distal esophagus also received convergent input from the heart and somatic fields. Our data supported the hypotheses that (1) referred pain from the distal esophagus resulted from activation of the same spinal neurons by visceral and somatic input, (2) pain originating from the distal esophagus and heart might be difficult to distinguish because of viscerosomatic and viscerovisceral convergence onto the same spinal neurons, and (3) an inflamed distal esophagus might be more sensitive to distension than a non-inflamed esophagus.

Afferent Pathways↗

PubMed1993

Modality-specific hypersensitivity of dorsal horn convergent neurones during reperfusion of their receptive fields on the rat's tail.

In rats anaesthetised with enflurane, we examined the responses of convergent neurones in the dorsal horn of the spinal cord to noxious thermal and mechanical stimulation and to innocuous brushing, during reperfusion of their receptive fields on the tail, following transient ischaemia. Neurones were included if they responded, before induction of ischaemia, to both pinching and brushing of receptive fields restricted to the tail. Ischaemia was induced by occluding the blood supply to the tail for 30 min using a tourniquet. Compared to their own responses before ischaemia, during reperfusion almost all the neurones (17 of 20) exhibited significantly increased activity to noxious pinching and innocuous brushing of their receptive fields, following 30 and 60 min of reperfusion. Receptive field size increased markedly in 16 of 20 of the neurones tested. Only 13 of 35 of the neurones responded to noxious thermal stimulation of the tail before induction of ischaemia, and of these only two exhibited enhanced sensitivity to thermal stimulation during reperfusion. Our results indicate that there is a population of convergent neurones that demonstrates hypersensitivity to mechanical stimulation of the rat's tail, but not to noxious thermal stimulation, during reperfusion of their receptive fields following transient ischaemia.

Animals↗

PubMed1995

Prostanoid synthesis in the spinal cord enhances excitability of dorsal horn convergent neurones during reperfusion of ischaemic receptive fields on the rat's tail.

In 40 rats anaesthetized with enflurane, we identified convergent dorsal horn neurones responding to both noxious (pinch) and innocuous (brush) mechanical stimulation of their receptive fields on the tail. We recorded extracellular activity before and during ischaemia of the receptive fields, as well as during subsequent reperfusion. Two NSAIDs, indomethacin and diclofenac sodium, or saline were applied locally to the spinal cord before the induction of ischaemia. During ischaemia, spontaneous activity of the neurones increased significantly, and the responses to both pinch and brush were reduced significantly; indomethacin and diclofenac sodium had no effect on either spontaneous activity or sensitivity to mechanical stimuli. The neurones became hypersensitive to both pinch and brush during reperfusion of their receptive field, and receptive field size increased. Application of indomethacin and diclofenac sodium to the spinal cord abolished both the hypersensitivity and the increase in receptive field size. Our results indicate that spinal cord prostanoid synthesis facilitates the enhanced excitability of dorsal horn convergent neurones to both noxious and innocuous mechanical stimuli during reperfusion of their receptive fields, but does not affect the neurones' responses to receptive field ischaemia, nor their responses to mechanical stimuli in the absence of a conditioning stimulus.

Animals↗

PubMed1987

The differential synaptic organization of the spinal and lemniscal projections to the ventrobasal complex of the rat thalamus. Evidence for convergence of the two systems upon single thalamic neurons.

The synaptic organization of terminals originating either from the spinal cord (spinothalamic) or from the dorsal column nuclei (lemniscal) was investigated in the ventrobasal complex of the rat thalamus. Wheatgerm agglutinin conjugated to horseradish peroxidase was used as an anterogradely transported axonal tracer, using benzidine dihydrochloride as a chromogen for the identification by electron microscopy of spinal and lemniscal projections to the ventrobasal thalamus. A double anterograde tract tracing strategy, based labeling by wheatgerm agglutinin conjugated to horseradish peroxidase of spinal terminals and simultaneous visualization of lemniscal terminals identified by Wallerian degeneration induced by lesion of the neurons of origin in the dorsal column nuclei, was used to compare the postsynaptic elements contacted by the two pathways and to look for a possible convergence of the two pathways onto single thalamic neurons. Spinal and lemniscal terminals are large (2-2.5 microns mean average diameter) terminals containing several mitochondria and numerous rounded vesicles. A quantitative analysis of the mean average diameters of the terminals revealed that one could not differentiate between synapses formed by the two pathways on a morphological basis. Terminals of the two pathways make asymmetrical contacts (Gray type I) with dendrites of varying diameter, dendritic protrusions, and cell somata. A quantitative analysis of the least diameter of the postsynaptic elements demonstrates projections of the two systems to different, partially overlapping regions of thalamic neurons. Lemniscal terminals originating from the dorsal column nuclei frequently contact cell somata; axosomatic spinothalamic contacts are uncommon. In addition, lemniscal projections tend to contact more proximal dendrites than do spinal projections, and this differential synaptic organization is statistically significant. From a functional point of view, this differential synaptic organization might indicate that lemniscal inputs have greater influence than spinal inputs in affecting the activity of thalamic neurons. Labeled spinothalamic terminals contact the same dendritic profile as do degenerating lemniscal terminals in about 10% of single sections. Because the present study did not include a complete reconstruction of ventrobasal complex neurons of the thalamus or even regions of dendritic arbors, the degree of convergence is likely to be significantly underestimated. These findings indicate that the anatomical basis exists for an interaction between nociceptive and non-nociceptive somesthetic systems at the level of single ventrobasal neurons of the thalamus of the rat.

Animals↗

PubMed1990

Acupuncture and diffuse noxious inhibitory controls: naloxone-reversible depression of activities of trigeminal convergent neurons.

Recordings were made from convergent neurons in trigeminal nucleus caudalis of the rat. These neurons could be activated by both innocuous and noxious mechanical stimuli applied to their excitatory receptive fields on the ipsilateral part of the muzzle. Percutaneous application of suprathreshold, 2 ms square-wave electrical stimuli to the centre of the excitatory field resulted in responses to A- and C-fibres being observed. The effects on these responses of manual acupuncture performed by a traditional Chinese acupuncturist at the "Zusanli" point on the right hindlimb were compared with the effects induced by acupuncture applied at a non-acupoint, next to "Zusanli". In addition, the effects of acupuncture were compared with the inhibitory effects evoked by noxious thermal stimulation of the left hindlimb on the responses of the same neurons. This last type of inhibition has been described previously by our group and termed diffuse noxious inhibitory controls. Acupuncture, either applied at "Zusanli" or at a non-acupoint and noxious thermal stimulation induced similar strong inhibitory effects on the C-fibre-evoked responses of trigeminal convergent neurons (77.9 +/- 4.4%; 72.5 +/- 4.6% and 78.5 +/- 3.6% inhibition, respectively) and these inhibitions were followed by long-lasting aftereffects. In addition, both the acupuncture- and noxious thermal stimulation-evoked inhibitions were significantly reduced by systemic naloxone (0.4 mg/kg, i.v.). Since the antinociceptive effects elicited by acupuncture (i) had a similar magnitude and time-course to those evoked by noxious thermal stimulation, (ii) exhibited a lack of topographical specificity and (iii) involved an opioidergic link, we would suggest that, at least in our experimental conditions, acupuncture manoeuvres trigger the neuronal mechanisms involved in diffuse noxious inhibitory controls.

Acupuncture Points↗

PubMed1981

Chorda tympani and vagus nerve convergence onto caudal brain stem neurons in the rat.

Neurons responsive to chorda tympani (CT) and cervical vagus (CV) nerve stimulation were identified electrophysiologically in the caudal brain stem of the anesthetized rat. All identified dually responsive (CT/CV) neurons included in this study were orthodromically activated by both CT and CV stimulation (n = 80). These cells were located mainly in the lateral nucleus tractus solitarius (nts) or more ventrally in the region of nucleus ambiguus (amb). No CT/CV cells were found to lie clearly within the dorsal motor nucleus of the vagus nerve. Among CT/CV neurons in nts, there was no correlation of response latency to Ct stimulation versus response latency to CV stimulation, while CT/CV neurons found in the region of amb demonstrated a good correlation between the two stimuli and suggested that sensory convergence occurred prior to the level of amb. Conditioning pulses applied to CV were able to alter the neural response of characteristics to CT test pulses in a majority of the units tested. It is concluded that oropharyngeal afferents converge on brain stem neurons that are also responsive to vagal afferent input. These dually responsive CT/CV neurons are implicated in the integration of sensory information relevant for cephalic phase reflexes.

Animals↗

PubMed1984

Anatomical evidence for convergence of olfactory, gustatory, and visceral afferent pathways in mouse cerebral cortex.

Flavor perception requires the neural integration of olfactory, gustatory and, possibly, visceral afferent information. Presently, it is not known where, or how this integration takes place in the brain. Neuroanatomical data presented here suggest that pathways subserving these sensory modalities converge in mouse insular cortex after surprisingly few synaptic relays. Orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to label main olfactory bulb (MOB) efferents. A projection into layer I of insular cortex was present in every case. Bulb transections were made to provoke anterograde degeneration and EM analysis confirmed that the olfactory projection to insular cortex was a terminal pathway. WGA-HRP injections in the MOB-recipient zone of insular cortex resulted in ortho and retrograde labeling of ascending and descending gustatory-visceral afferent pathways. It is concluded that in the mouse, there is a remarkably direct convergence of olfactory and gustatory-visceral sensory pathways in insular cortex. Together with the descending connections from insular cortex to the amygdala and to brainstem autonomic structures, it is possible that the cortical integration of olfactory and gustatory-visceral information could modulate mechanisms involved in food selection and autonomic reactions relating to the chemical senses. Basic mechanisms subserving flavor perception might be usefully modelled in mouse insular cortex.

Afferent Pathways↗

PubMed1991

Convergence from the preoptic area and arcuate nucleus to the median eminence in acupuncture and nonacupuncture point stimulation analgesia.

Lesion of the preoptic area (POA) or medial arcuate nucleus (M-HARN) abolished acupuncture analgesia (AA). Potentials in the median eminence (ME) evoked by stimulation of the acupuncture point (AP) were not affected by lesion of either the POA or M-HARN alone, but were abolished by concurrent lesion of both. No analgesia was produced by stimulation of the POA. Analgesia produced by stimulation of the M-HARN was abolished by lesion of the POA, and the abolished analgesia was restored by concurrent stimulation of the POA and M-HARN, hence POA and M-HARN outputs might converge in the ME to produce AA. Similar convergence from the anterior arcuate nucleus (A-HARN) and POA to the ME was observed in analgesia (NAA) produced by stimulation of a nonacupuncture point (NAP). Two pathways diverged from the lateral hypothalamus in the AA afferent pathway and two from the lateral periaqueductal central gray (L-PAG) in the NAA afferent pathway. POA potentials evoked by stimulation of the AP were reversed by naloxone, and those evoked by stimulation of the AP were reversed by dexamethasone. ACTH sensitive sites were found in both the L-PAG and the anterior hypothalamus.

Acupuncture Analgesia↗

PubMed1995

Convergence of afferents from the SLN and GPN in cat medullary swallowing neurons.

We demonstrated the convergence of information from the pharyngeal and laryngeal mucosa, transmitted by the glossopharyngeal nerve (GPN) and superior laryngeal nerve (SLN), in the nucleus of the tractus solitarius (NTS). First, the distribution of terminals of the GPN and SLN in the NTS was examined by an HPR tracing technique in cats, and the synapse formation of these neurons with NTS neurons was demonstrated by electron microscopy. The HRP-labeled SLN and GPN terminals were localized in a small area of the interstitial subnucleus of the NTS, slightly rostral to the obex, forming synapses with NTS neurons. Next, using extracellular recording in anesthetized cats, we determined whether or not swallowing-related neurons in the medulla oblongata receive peripheral inputs. Convergence of peripheral sensory inputs from the SLN and GPN was observed in more than 80% of the NTS cells. These results suggest that the NTS is not only a sensory-relay nucleus but also integrates information necessary for eliciting protective reflexes of the upper airway, such as swallowing.

Afferent Pathways↗

PubMed1995

Convergence of laryngeal afferents with different natures upon cat NTS neurons.

To clarify the convergence of laryngeal afferents within the nucleus tractus solitarius (NTS) in the cat, we examined in the medulla the response characteristics of superior laryngeal nerve (SLN) fibers and NTS neurons to mechanical and chemical stimulation applied to laryngeal mucosa by extracellular recordings. The response was recorded in 75 SLN primary afferent fibers (PAFs) and 92 NTS neurons. PAFs of the SLN consisted of numerous monomodal mechanosensitive fibers and a small number of chemosensitive and polymodal fibers. On the other hand, the majority of NTS neurons had a polymodal nature. Thus, laryngeal information is considered to be integrated in modality into NTS neurons. All mechanosensitive fibers received information from a small restricted field in the larynx. On the contrary, each NTS neuron responded to mechanical stimulation over a wide laryngeal field, indicating that information from different sites spatially converge on NTS neurons. Our results suggest that caudal NTS neurons play a cardinal role in integrating laryngeal afferents, which are thought to elicit laryngeal reflexes.

Afferent Pathways↗

PubMed1996

Evaluation of aortic regurgitation with digitally determined color Doppler-imaged flow convergence acceleration: a quantitative study in sheep.

OBJECTIVES: The aim of the present study was to validate a digital color Doppler-based centerline velocity/distance acceleration profile method for evaluating the severity of aortic regurgitation. BACKGROUND: Clinical and in vivo experimental applications of the flow convergence axial centerline velocity/distance profile method have recently been used to estimate regurgitant flow rates and regurgitant volumes in the presence of mitral regurgitation. METHODS: In six sheep, a total of 19 hemodynamic states were obtained pharmacologically 14 weeks after the original operation in which a portion of the aortic noncoronary (n = 3) or right coronary (n = 3) leaflet was excised to produce aortic regurgitation. Echocardiographic studies were performed to obtain complete proximal axial flow acceleration velocity/distance profiles during the time of peak regurgitant flow (usually early in diastole) for each hemodynamic state. For each steady state, the severity of aortic regurgitation was assessed by measurement of the magnitude of the regurgitant flow volume/beat, regurgitant fraction and instantaneous regurgitant flow rates determined by using both aortic and pulmonary artery electromagnetic flow probes. RESULTS: Grade I regurgitation (regurgitant volume/beat < 15 ml, six conditions), grade II regurgitation (regurgitant volume/beat between 16 ml and 30 ml, five conditions) and grade III-IV regurgitation (regurgitant volume/beat > 30 ml, eight conditions) were clearly separated by using the color Doppler centerline velocity/distance profile domain technique. Additionally, an equation for correlating "a" (the coefficient from the multiplicative curve fit for the velocity/distance relation) with the peak regurgitant flow rates (Q [liters/min]) was derived showing a high correlation between calculated peak flow rates by the color Doppler method and the actual peak flow rates (Q = 13a + 1.0, r = 0.95, p < 0.0001, SEE = 0.76 liters/min). CONCLUSIONS: This study, using quantified aortic regurgitation, demonstrates that the flow convergence axial centerline velocity/distance acceleration profile method can be used to evaluate the severity of aortic regurgitation.

Animals↗

PubMed1996

Current status of flow convergence for clinical applications: is it a leaning tower of "PISA"?

Spatial appreciation of flow velocities using Doppler color flow mapping has led to quantitative evaluation of the zone of flow convergence proximal to a regurgitant orifice. Based on the theory of conservation of mass, geometric analysis, assuming a series of hemispheric shells of increasing velocity as flow converges on the orifice--the so-called proximal isovelocity surface area (PISA) effect--has yielded methods promising noninvasive measurement of regurgitant flow rate. When combined with conventional Doppler ultrasound to measure orifice velocity, regurgitant orifice area, the major predictor of regurgitation severity, can also be estimated. The high temporal resolution of color M-mode can be used to evaluate dynamic changes in orifice area, as seen in many pathologic conditions, which enhances our appreciation of the pathophysiology of regurgitation. The PISA methodology is potentially applicable to any restrictive orifice and has gained some credibility in the quantitative evaluation of other valve pathology, particularly mitral and tricuspid regurgitation, and in congenital heart disease. Although the current limitations of PISA estimates of regurgitation have tempered its introduction as a valuable clinical tool, considerable efforts in in vitro and clinical research have improved our understanding of the problems and limitations of the PISA methodology and provided a firm platform for continuing research into the accurate quantitative assessment of valve regurgitation and the expanding clinical role of quantitative Doppler color flow mapping.

Blood Flow Velocity↗