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PubMed1982

Proximal and accommodative convergence and age.

The authors have estimated the phoria for distant and near fixation in two groups of subject (mean age 27. 5+/- 4.4 and 59.2 +/- 8.2 years). Different accommodative stimuli were induced by adding minus lenses for distant fixation and plus lenses for near fixation. Statistical analysis of the experimental data indicates that, for distant fixation, the value of phoria per unit of accommodative stimulus is significantly lower presbyopic than in nonpresbyopic subject. Also, during near fixation, the accommodative convergence (AC/A ratio) is more reliable in the presbyopic subjects when the accommodative stimulus is progressively reduced. This varying behavior indicates in presbyopic subjects that proximal convergence is of greater relative importance in the determination of the fusion-free position. In nonpresbyopic subjects, accommodative convergence is the more important component.

Accommodation, Ocular↗

PubMed2000

Convergent evolution of major histocompatibility complex molecules in humans and New World monkeys.

In both Old World and New World monkeys Mhc-DRB sequences have been found which resemble human DRB1*03 and DRB3 genes in their second exon. The resemblance is shared sequence motifs and clustering of the genes or the encoded proteins in phylogenetic trees. This similarity could be due to common ancestry, convergence at the molecular level, or chance. To test which of these three explanations applies, we sequenced segments of New World monkey and macaque genes which encompass the entire second exon and large parts of both flanking introns. The test strongly supports the monophyly of New World monkey DRB intron sequences. The phylogenies of introns 1 and 2 from DRB1*03-like and DRB3-like genes are congruent, but both are incongruent with the exon 2-based phylogeny. The matching of intron 1- and intron 2-based phylogenies with each other suggests that reciprocal recombination has not played a major role in exon 2 evolution. Statistical comparisons of exon 2 from different DRB1*03 and DRB3 lineages indicate that it was neither gene conversion (descent), nor chance, but molecular convergence that has shaped their characteristic motifs. The demonstration of convergence in anthropoid Mhc-DRB genes has implications for the classification, age, and mechanism of generation of DRB allelic lineages.

Amino Acid Sequence↗

PubMed1999

Transcriptional and structural study of a region of two convergent overlapping yeast genes.

The exceptionally close packing of many yeast genes and other chromosomal elements raises the question of how those elements are functionally insulated. All published work shows that natural insulators are very effective, but transcriptional interference (TI) occurs if they are mutated or if their natural context is altered. Mechanisms to avoid TI are poorly understood, but are thought to involve an interplay of cis sequences and trans factors in a chromatin context. We have studied the case of two convergent closely packed ORFs (56 bp of separation) in chromosome IX of Saccharomyces cerevisiae. mRNAs from POT1 and YIL161w overlap by up to 115 nt. Convergent transcription causes a small but noticeable negative effect on the level of POT1 mRNA and nucleosome displacement in the intergenic region. This suggests for the first time that some TI could occur in convergently transcribed yeast genes, even in a natural chromosomal context.

Fungal Proteins↗

PubMed2006

Convergence and contingency in production-precipitation relationships in North American and South African C4 grasslands.

Mesic grasslands in North America and South Africa share many structural attributes, but less is known of their functional similarities. We assessed the control of a key ecosystem process, aboveground net primary production (ANPP), by interannual variation in precipitation amount and pattern via analysis of data sets (15- and 24-year periods) from long-term research programs on each continent. Both sites were dominated by C(4) grasses and had similar growing season climates; thus, we expected convergence in precipitation-ANPP relationships. Lack of convergence, however, would support an alternative hypothesis-that differences in evolutionary history and purportedly greater climatic variability in South Africa fundamentally alter the functioning of southern versus northern hemisphere grasslands. Neither mean annual precipitation nor mean ANPP differed between the South African and North American sites (838 vs. 857 mm/year, 423.5 vs. 461.4 g/m(2) respectively) and growing season precipitation-ANPP relationships were similar. Despite overall convergence, there were differences between sites in how the seasonal timing of precipitation affected ANPP. In particular, interannual variability in precipitation that fell during the first half of the growing season strongly affected annual ANPP in South Africa (P < 0.01), but was not related to ANPP in North America (P = 0.098). Both sites were affected similarly by late season precipitation. Divergence in the seasonal course of available soil moisture (chronically low in the winter and early spring in the South African site vs. high in the North American site) is proposed as a key contingent factor explaining differential sensitivity in ANPP to early season precipitation in these two grasslands. These long-term data sets provided no support for greater rainfall, temperature or ANPP variability in the South African versus the North American site. However, greater sensitivity of ANPP to early season precipitation in the South African grassland suggests that future patterns of productivity may be more responsive to seasonal changes in climate compared with the North American site.

Carbon↗

PubMed1981

The effect of systemic morphine upon diffuse noxious inhibitory controls (DNIC) in the rat: evidence for a lifting of certain descending inhibitory controls of dorsal horn convergent neurones.

The effects of exogenous opiates upon diffuse noxious inhibitory controls (DNIC) was investigated in intact anaesthetized rats. 58 convergent neurones, responding to both noxious and innocuous stimuli applied to their cutaneous receptive fields, were recorded at the lumbar level. These cells received A- and C-peripheral fibre inputs as shown by electrical stimulation of their receptive fields and were mainly located in the medial part of the dorsal horn. The immersion of the distal two-thirds of the tail in hot water (52 degrees C) induced strong inhibition of the responses to both A-(23%) and C-(69%) fibres. Post-effects of long duration were commonly observed after cessation of the conditioning stimulus. While systemic injection of morphine at a low dose-range (0.1-1 mg/kg) did not significantly affect the unconditioned responses, the DNIC-mediated inhibitions were profoundly altered. (a) DNIC of responses to C fibres were dose-dependently (P less than 0.01) lifted by morphine: (b) the post-effects observed after cessation of conditioning stimuli were dose-dependently (P less than 0.01) diminished; (c) DNIC of responses to A-fibre were similarly altered but this effect was less significant (P less than 0.05); (d) DNIC of responses to sustained moderate pressure were greatly diminished by morphine (P less than 0.01); and (e) these effects were specific since they were antagonized by the opiate antagonist, naloxone. In addition, they were shown to be stereospecific since while the dextrogyre stereoisomer, dextrorphan, was ineffective the levogyre derivative, levorphanol, induced a significant lifting of DNIC. It is concluded that morphine decreases the supraspinal inhibitory controls of dorsal horn convergent neurones, at least when these controls are triggered by noxious stimuli. Assuming that a basic somatosensory background activity (noise) is transmitted to higher centres by dorsal horn convergent neurones, and that the pain-signalling message is the contrast between the activity of the segmental pool of neurones induced by the noxious stimulus and the DNIC-mediated silence of the remaining neuronal population, it is proposed that, by a reduction in DNIC, low-dose morphine could restore the initial level of background activity, the final result being analgesia.

Animals↗

PubMed1983

Alterations in connections of the corpus callosum following convergent and divergent strabismus.

The connectivity of the corpus callosum in visual cortical areas 17 and 18 was studied in normal cats, in cats reared with unilateral convergent or divergent surgically-induced strabismus, and in a Siamese cat. The extents of the callosal cell and terminal zones were determined following multiple injections of horseradish peroxidase and tritiated amino-acids into one hemisphere. Following surgically-induced strabismus, abnormally wide callosal cell zones were seen in both the left and the right hemisphere irrespective of the direction of eye misalignment. Abnormally wide callosal terminal zones were seen in the hemisphere ipsilateral to the deviating eye in cats reared with unilateral convergent and divergent strabismus. Abnormally wide callosal zones were seen in cats which had strabismus induced as late as postnatal day 36. In a Siamese cat with a naturally-occurring convergent strabismus, callosal cells had a different distribution and were fewer in number compared to normal cats or cats with surgically induced strabismus. This implies that the abnormal callosal connectivity of Siamese cats is not a simple result of strabismus.

Animals↗

PubMed1984

Somato-visceral convergence in cat dorsal root ganglion neurones demonstrated by double-labelling with fluorescent tracers.

We have investigated the possibility of somato-visceral convergence in thoracic sensory dorsal root ganglia (DRG) of cats, using the technique of double-labelling with fluorescent tracers. Combinations of propidium iodide (PI) and Fast Blue (FB) or bisbenzimide (Bb) were found to be the most appropriate. FB or Bb were injected into the splanchnic nerve, and PI into the intercostal nerves. The 9th-11th thoracic cord segments and ganglia were removed after perfusal and frozen sections cut. Single- and double-labelled neurones were observed in the DRG and single-labelled neurones only in the ventral horn (PI) and lateral horn (FB, Bb) of the thoracic spinal cord. The double-labelled neurones accounted for approximately 1% of all labelled neurones, although this may be an underestimate due to the techniques used to prevent migration of the tracer from labelled cells. The double-labelled neurones provide evidence for somato-visceral convergence and indicate that the pre-spinal convergence hypothesis could explain the phenomenon of referred pain.

Animals↗

PubMed1985

The encoding of thermal stimuli applied to the tail of the rat by lowering the excitability of trigeminal convergent neurones.

Recordings were made from convergent neurones in the nucleus caudalis of the trigeminal complex. They could be excited by both innocuous and noxious stimuli applied to their excitatory receptive field located on the ipsilateral part of the muzzle. The responses to A- and C-fibre activation induced by supramaximal transcutaneous electrical stimulation of their receptive fields were conditioned by thermal stimuli applied to the tail, and the relationship between the conditioning temperatures and their ability to induce inhibitions of the evoked discharges of convergent neurones were investigated. During sequences of repetitive stimulation, the posterior two-thirds of the tail were immersed in a waterbath at various temperatures (36-52 degrees C) and the resultant inhibitions of responses were calculated. The threshold for obtaining an inhibitory effect ranged between 40 and 44 degrees C. Above this level, there was a highly significant correlation between the conditioning temperature and the degree of inhibition, which was very strong for the highest temperature (i.e. for 52 degrees C: 54.4 +/- 7.3 and 92.3 +/- 3.7% inhibitions being obtained for A- and C-fibre-evoked responses respectively); such a correlation concerned the inhibitions observed both during immersion of the tail and after the removal of the conditioning stimuli. In further experiments, identical conditioning stimuli were tested upon responses of trigeminal convergent neurones to microelectrophoretic applications of an excitatory amino acid, DL-homocysteate, and very similar results were obtained: a threshold for inhibition in the 40-44 degrees C range and a significant correlation between the conditioning temperature and the degree of inhibition in the 44-52 degrees C range (52 degrees C giving inhibitions of 98.8 +/- 0.4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1986

Lesions of dorsolateral funiculi (DLF) do not affect the depressive effects of systemic morphine upon dorsal horn convergent neuronal activities related to pain in the rat.

It has been shown that morphine could interact with supraspinal inhibitory controls which modulate the transmission of nociceptive messages at the spinal level. However, the way in which such interactions occur is still a subject of controversy. Based on behavioural experiments, it has been proposed that systemic morphine increases descending inhibitory controls travelling via the dorsolateral funiculus (DLF). To directly test this hypothesis from an electrophysiological standpoint, we have investigated the effects of morphine upon C-fibre responses of dorsal horn convergent neurones in rats with bilateral lesions of the DLF. Previous studies by our group have shown that 6 mg/kg morphine chlorhydrate was the intravenous mean effective dose for depressing by 50% (ED50) the C-fibre evoked responses of convergent neurones recorded at the lumbar level. In the present work, the effects of 6 mg/kg morphine were investigated under identical experimental conditions, except that a bilateral destruction of the dorsolateral funiculus (DLF) was performed previously. These lesions did not change the mean C-fibre evoked responses. Following morphine administration, the C-fibre evoked responses were depressed by 47.1 +/- 10.1% (n = 13) and reversal of these effects by naloxone was always observed. The A-fibre evoked responses, concurrently recorded, were not modified by the drug. As the depressive effects observed with this dose of morphine appear to be essentially of the same magnitude as those previously found in the intact or spinal preparations, we conclude that the DLF is not involved in the depressive effects of systemic morphine on dorsal horn convergent neurones.

Animals↗

PubMed1993

Ascending and descending convergent inputs to neurons in the nucleus parabrachialis of the rat: an intracellular study.

Responses of the nucleus parabrachialis neurons (PBN) to electrical stimulation of the lateral hypothalamus (HL), central nucleus of the amygdala (Ac), dorsolateral funicullus in the spinal cord (SC), mediocaudal nucleus tractus solitarius (NTS), and substantia nigra (SN) were investigated in anesthetized rats by intracellular recording technique. Convergent excitatory postsynaptic potentials (EPSPs) were evoked on 8 of 36 neurons tested by both HL and NTS stimulation. The EPSPs evoked by HL stimulation were characterized as monosynaptic in 4 neurons. The EPSPs evoked by SC stimulation were characterized as monosynaptic in 2 of 36 neurons, moreover, these neurons were also antidromically activated by HL stimulation. Stimulation of Ac evoked EPSPs on 10 of 36 cells tested; 8 demonstrated to be monosynaptic. In addition, IPSP evoked by SN stimulation and EPSP evoked by NTS stimulation converged on three neurons. The results indicate that ascending and descending inputs converge on lateral PBN neurons.

Anesthesia↗

PubMed1990

Kappa opioid receptor-mediated depression of activity evoked in convergent dorsal horn cells by thermal and non-thermal noxious stimulation.

The response of convergent dorsal horn cells to tonic and phasic noxious heating and to noxious pinching was studied before and after topical application of a solution (30 nmol) of the kappa agonist U-50,488H to the dorsal surface of the spinal cord. U-50,488H depressed the discharge of convergent units evoked by thermal and mechanical nociceptive stimuli. The opiate antagonist WIN 44,441-3 reversed the effect of U-50,488H. It is concluded that kappa opioids are effective in preventing the depolarization of convergent dorsal horn neurons evoked by either thermal or non-thermal noxious stimuli.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1993

Reflection coefficients in pulsatile flow through converging junctions and the pressure distribution in a simple loop.

Analytical expressions for the reflection coefficients in pulsatile flow through converging junctions are derived by two independent methods and are used to study the effects of wave reflections on the pressure distribution in a simple vascular loop. A simulated physiological situation is used as an example in which the loop is formed by the combination of a bypass and a bypassed vessel, the relative diameter of the latter being varied in order to simulate a narrowing. The results demonstrate how, in the case of a converging junction, the effects of wave reflections on the pressure distribution in one vessel depend on conditions within the vessel itself as well as in the other. The new reflection coefficients take into account this interdependence of flow in the two vessels forming a converging junction, and are shown to be consistent with reflection coefficients commonly used in diverging junctions.

Aorta, Abdominal↗

PubMed1991

Converging eye movements evoked by microstimulation of the fastigial nucleus of macaque monkeys.

Stimulation of the dorsal part of the fastigial nucleus in macaques is known to evoke ipsilateral saccades, while those of the ventral part produce contralateral saccades. It was found that stimulation of the transitional zone moved the visual axis (eyes) to converge at an area (focus) in the oculomotor range, regardless of the initial eye position. These saccades were designated as 'converging saccades'. Converging saccades were directed to the focus, but the eyes did not attain the focus in one motion. Only the repetition of stimuli brought the eyes near the focus. When stimulation is applied to the transitional zone at progressively more ventral sites, the focus gradually shifted, starting from the ipsilateral hemifield to the contralateral hemifield by taking various routes.

Animals↗

PubMed1975

Binocular convergence in man during total sleep deprivation.

It was proposed that binocular convergence (lateral phoria) for near and far vision would reflect the states of visual functioning and that there would be a progressive reduction in phoria during sleep deprivation. Six young male subjects underwent two conditions of sleep deprivation on separate occasions. One condition incorporated a high visual load and the other a low load. Exercise and sound were balanced. Lateral phoria for near and far vision was carefully measured, regularly, before, during and after sleep deprivation. It was found that a reduction in convergence (exophoria) for both near and far vision became increasingly apparent with progressive sleep deprivation, especially with near vision and under high visual load. The near vision measure, which included accommodation convergence, appeared to be more sensitive to sleep deprivation generally, whereas far vision tended to produce a greater differentiation between the conditions. The implications of these findings for REM sleep and oculomotor innervation are discussed.

Accommodation, Ocular↗

PubMed1983

Convergence of cardiac and cutaneous afferents onto neurons in the dorsal horn of the spinal cord in the cat.

Convergence of cardiac and cutaneous afferents onto neurons in the dorsal horn of the spinal cord was demonstrated in the cat. Responses of neurons to cutaneous stimulation revealed that they were either nociceptive specific (NS) or wide dynamic range (WDR) neurons. NS neurons were located in lamina I and outer zone of lamina II (IIo). WDR neurons were located in laminae I and IIo as well as laminae IV-VI. Since all the neurons responsive to electrical stimulation of the inferior cardiac nerve responded to cutaneous nociceptive input, it was inferred that the sensation evoked by excitation of dorsal horn neurons by cardiac afferents is pain. The observed convergence is suggested as a mechanism for referred pain, and convergence onto WDR neurons provides an explanation for the phenomenon of allodynia in a stage between anginal attacks.

Afferent Pathways↗

PubMed1984

Pigeon's eyes converge during feeding: evidence for frontal binocular fixation in a lateral-eyed bird.

Pigeons' head-in-space and eye-in-head positions were simultaneously recorded (EOG) in video during feeding. A linear correlation was found between the experimentally measured eye convergence (sum of both EOGs ) and grain parallax (calculated from interocular and eye-to-grain distances). This graded convergence of the eyes on approaching a target is considered evidence of frontal binocular fixation. Since such convergence prevails when the animal is forced to rely on frontal monocular or on lateral vision, a central mechanism controlling frontal fixation in the pigeon must be presupposed .

Animals↗

PubMed1992

Pre-spinal convergence between thoracic and visceral nerves of the rat.

Dichotomizing sensory axons have been demonstrated in a number of species and are of significance in understanding the possible mechanisms underlying referred pain. The present study reviews work employing fluorescent dyes as tracers to demonstrate afferent dichotomization in the peripheral nervous system. Dichotomization between the intercostal and splanchnic nerves of the rat was demonstrated by means of intraneural transport of Diamidino yellow or Fast blue. Frequency of pre-spinal somato-visceral convergence averaged 2% (range 0.1-21%). Average frequency of convergence was 8.3% (range 2-23.1%) between internal and external intercostal nerves. Control experiments in which axoplasmic transport was inhibited by vinblastine ruled out the possibility of errors from non-axoplasmic transport of the markers. Thoraco-visceral pre-spinal convergence occurs in the rat and is variable in extent.

Afferent Pathways↗

PubMed1983

Do convergent neurones in the spinal dorsal horn discriminate nociceptive from non-nociceptive information?

Thirty convergent neurones responding to both noxious and non-noxious cutaneous stimuli were recorded at the lumbar level in either anaesthetized 'intact' rats or unanaesthetized 'spinal' rats. Their responses to radiant heat application and to repetitive innocuous mechanical stimulation of the centre of their receptive fields were analysed, both in terms of the maximal and the mean firing rates. These neurones increased their discharge rates in relation to the temperature applied to their receptive fields with the highest levels being produced by noxious intensities. This finding confirms earlier reports suggesting the capacity of these neurones to encode nociceptive information of thermal origin. However, a very high level of firing could also be evoked by repetitively applied innocuous mechanical stimuli. This was a consistent finding, observed both in intact and spinal animals, which was true for the two subgroups into which we divided the convergent neurones (warming/noxious heat units and noxious heat units). These results are discussed in terms of the role of convergent neurones in nociception. It is suggested that a single channelled signal emanating from these neurones could not be the basis of a clear nociceptive message to the brain; two alternative hypotheses involving multichannelled organizations of impulses are proposed for discussion.

Animals↗