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PubMed2003

Yes/no reversals as neurobehavioral sequela: a disorder of language, praxis, or inhibitory control?

This study identifies a linguistic phenomenon suggestive of damage to fronto-subcortical circuitry. Our objective was to determine the occurrence and neuroradiological/neurobehavioral correlates of yes/no reversals in corticobasal degeneration (CBD), and document occurrence of reversals in other neurological conditions. In a prospective study, we evaluated 34 CBD patients using a neuropsychologic battery and magnetic resonance imaging. Patients were subdivided into two groups: those with (n = 11) and without (n = 23) yes/no reversals. In a retrospective study conducted during the period of 1991-2001, we identified 33 patients for whom yes/no reversals occurred to compare correlates with prospective study findings. In the prospective study, 11 patients (32.3%) had yes/no reversals. Significant between-group differences were found in scores of lexical fluency (P = 0.02) and prehension (P = 0.03). Prehension scores correlated with facial praxis (P < 0.0001) and upper limb praxis scores (P < 0.0001) in the yes/no reversal group only. In the retrospective study, nine CBD patients and 24 non-CBD patients had yes/no reversals, with damage to fronto-subcortical areas present in all patients. Results suggest an association with deficits in mental flexibility and inhibitory control. High within-group correlations of lexical fluency and prehension with praxis scores suggest a relationship of yes/no reversals with multiple factors.

Aged↗
PubMed2004

[Reverse flow in fetal vessels and perinatal events].

UNLABELLED: BACKGROUND/PATIENTS: A reverse flow in the umbilical artery and/or fetal aorta is associated with a higher perinatal and neonatal mortality. 30 fetuses showed a reverse flow using pulsed wave Doppler sonography (group I). A matched-pair control group including 30 fetuses with the same gestational age as well as a normal Doppler flow pattern in the umbilical artery and/or fetal aorta was taken for comparison (group II). RESULTS: In the group with reverse flow the rates of pregnancies with pre-eclampsia (n = 19/30, p < 0.0001), intrauterine growth retardation (n = 25/30, p < 0.0001), oligohydramnios (n = 21/30, p < 0.0001) and nicotine abuse (n = 15/30, p < 0.01) were significantly higher compared to the control group. Postnatal data showed significantly lower pH values in group I (p < 0.01). 40 % of the fetuses with reverse flow died in utero whereas in 67 % the reverse flow was accompanied by an insufficiency of the placenta (IUGR, oligohydramnios, histopathological abnormalities of the placenta). None of the fetuses in the control group died in utero. The incidence of IUGR (< 5ht percentile) was 83 % in group I but only 3 % in group II. The perinatal and overall mortality (including neonatal mortality 7 - 28 days after birth) amounted to 27 % and 53 % in group I, respectively, compared to 3 % and 0 % in the control group (p < 0.001). In addition cerebral anomalies could be found by ultrasound in 50 % of the neonates who presented a reverse flow prenatally. In 28 % of the surviving newborns an intracerebral hemorrhage (ICH) could be detected. None of the newborns of group II developed an ICH. CONCLUSIONS: Pregnancies with a reverse flow in the umbilical artery and/or fetal aorta have to be considered as a high risk group with a poor prognosis. The reverse flow is mainly caused by chronic placental insufficiency with IUGR. With respect to the further neuromotor development the incidence and severity of cerebral lesions in affected fetuses should be considered when discussing the perinatal situation with the parents.

Adult↗
PubMed2002

Reversible maps in two-degrees of freedom Hamiltonian systems.

It has been shown that a sub-class of two-degrees of freedom Hamiltonian systems possesses a reversing symmetry discovered by Birkhoff in the restricted problem of three bodies. This mixed space-time reversing symmetry, which is different from the classical time reversal symmetry, can be shared by time-reversible as well as time-irreversible systems. Examples of time-irreversible systems which possess this reversing symmetry are the restricted problem of three bodies as shown by Birkhoff in 1915, and a special case of the motion of a rigid body with a fixed point discussed in this paper. If a Hamiltonian system possesses this Birkhoff reversing symmetry, then there exists a surface of section for which the corresponding Poincare map is Birkhoff-reversible. The Birkhoff-reversibility of this map may be used to study its global dynamics such as the locations and the distribution of the stable and unstable periodic points, the distribution of stable and chaotic regions, and the identification of the scattering regions. (c) 2002 American Institute of Physics.

Journal Article↗
PubMed1993

Stereoscopic slant reversals: a new kind of 'induced' effect.

Data are presented from three experiments confirming an earlier finding that the stereoscopic slant perceived may be opposite to the geometrically predicted direction of slant (Gillam 1967). The stimulus for stereoscopic slant was created by imposing a disparity gradient on a frontal plane surface. Reversals are shown to occur readily for slants around a vertical axis but rarely for slant around a horizontal axis. Reversal frequency is greater for surfaces which have a regular pattern, providing good perspective information about slant. Cue conflict cannot explain reversals because adherence to perspective information predicts a perception of zero slant rather than reverse slant. A new explanation has been proposed attributing reversals to the ambiguity of horizontal disparity gradients and disambiguation of the disparity gradient by its relationship to the perspective gradient. It is shown that for any given disparity gradient there is a physical surface which would give rise to a slant reversed with respect to that normally predicted. Such a surface is eccentric in the field of view, with eccentricity given by the difference between the slants signalled by the disparity gradient and the perspective gradient. This explains why reversal responses to disparity gradients occur in the presence of perspective. It is proposed, on the basis of this analysis and the fact that reversals occur, that, like convergence and vertical disparity, perspective is a factor contributing to the correct scaling of disparity gradients in the horizontal meridian with respect to surface eccentricity.

Attention↗
PubMed1996

Cell density regulates cellular reversal frequency in Myxococcus xanthus.

Myxococcus xanthus is a Gram-negative bacterium that aggregates to form fruiting bodies when nutrients are limiting. Previous studies showed that the frz mutants that are defective in chemotaxis exhibited irregular and infrequent patterns of cellular reversal. In contrast, wild-type cells, when examined individually, reverse relatively frequently, about once every 6 min. It is not known how the change of reversal frequency effects cellular aggregation during fruiting body formation in M. xanthus. In this study, we stained cells with a tetrazolium dye so that we could track the reversal frequencies of single cells and cells in groups. We found that developmental cells in large groups reverse much less than cells in small groups or as single cells. This reduced cellular reversal frequency is related to the frz signal transduction system and correlated with the methylation of FrzCD (a methyl-accepting chemotaxis protein). Cells containing a mutation in the frz genes or in the genes required for social motility do not respond in this way. The reduction in cellular reversals as developmental cells accumulate in groups suggests a simple hypothesis for the aggregation of cells into discrete mounds during fruiting body formation. We also found that M. xanthus cells glide with equal frequency in the forward or reverse directions, indicating that cells do not contain a "head" or "tail."

Bacterial Proteins↗
PubMed2001

HIV-1 nucleocapsid protein and the secondary structure of the binary complex formed between tRNA(Lys.3) and viral RNA template play different roles during initiation of (-) strand DNA reverse transcription.

In human immunodeficiency virus type 1 (HIV-1), the tRNA(Lys.3) primer and viral RNA template can form a specific complex that is characterized by extensive inter- and intramolecular interactions. Initiation of reverse transcription from this complex has been shown to be distinguished from subsequent elongation by early pausing events, such as at the +1 and +3 nucleotide positions. One major concern regarding the biological relevance of these results is that most kinetic studies of HIV-1 reverse transcription have been performed using tRNA(Lys.3)-viral (v) RNA complexes that were formed by heat annealing. In contrast, tRNA(Lys.3) in viruses is placed onto the primer binding site by nucleocapsid (NC) sequences of the Gag protein. In this study, we have further characterized the initiation features of reverse transcription in the presence of HIV-1 NC protein. In contrast to results obtained with a heat-annealed tRNA(Lys.3).vRNA complex, we found that polymerization reactions catalyzed by HIV-1 reverse transcriptase did not commonly pause at the +1 nucleotide position when a NC-annealed RNA complex was used, and that this was true regardless whether NC was actually still present during reverse transcription. This activity of NC required both zinc finger motifs, as demonstrated by experiments that employed zinc finger-mutated forms of NC protein (H23C NC and ddNC), supporting the involvement of the zinc fingers in the RNA chaperone activity of NC. However, NC was not able to help reverse transcriptase to escape the +3 pausing event. Mutagenesis of a stem structure within the tRNA(Lys.3). vRNA complex led to disappearance of the +3 pausing event as well as to significantly reduced rates of reverse transcription. Thus, this stem structure is essential for optimal reverse transcription, despite its role in promotion of the +3 pausing event.

Amino Acid Motifs↗
PubMed2002

Reverse optokinetic after-nystagmus generated by gaze fixation during optokinetic stimulation.

Gaze fixation during optokinetic stimulation generates an after-nystagmus with a slow component towards the reverse direction of the optokinetic stimulation. The duration and maximum slow component velocity (SCV) of this "reverse OKAN" were observed by changing the duration, velocity and direction of the optokinetic stimulation in nine normal volunteers. The duration of reverse OKAN increased with increasing stimulation time but was unaffected by changes in the stimulation velocity. The maximum SCV of reverse OKAN decreased with an increase in the stimulation velocity but was not significantly affected by changes in the optokinetic stimulation time. There was no directional difference among the horizontal, upwards and downwards reverse OKANs. The reverse OKAN was thought to be generated by a mechanism different from the velocity storage mechanism which produced optokinetic nystagmus and the first phase of OKAN. Retinal slip during the optokinetic stimulation was considered to be an input to the mechanism which generated the reverse OKAN. We hypothesize that the mechanism causing the reverse OKAN may be a generator of the second phase of OKAN, which was also intimately connected with self-motion sensation during the optokinetic stimulation.

Adult↗
PubMed1954

Reversal of the streptomycin injury of Escherichia coli.

The number of viable Escherichia coli in a young, actively growing culture is decreased approximately 99.9 per cent by a 30 second exposure to 25 phig. streptomycin/ml. The injury induced by the antibiotic is only potentially lethal, however, and may be reversed by subculture within 5 minutes into fresh culture medium, NH(4)NO(3), NH(4)Cl, (NH(4))(2)HPO(4), NH(4) citrate, and NH(4) tartrate. Subculturing into water, glucose, or MgSO(4) results in a more marked decrease in the number of viable organisms. In KNO(3), NaNO(3), K(2)HPO(4), and Na(2)SO(4) solutions reversal occurs first, followed by a rapid decrease in viability. True reversal of the streptomycin injury takes place, as demonstrated by the rapid rate of recovery to the viable count of the original culture. Development of resistance has been eliminated as the cause of regrowth since the streptomycin sensitivity of recovered cultures remained the same as that of the original culture. The use of water as diluent for viability determinations potentiates the lethal effect of streptomycin activity. Several compounds, at various dilutions, substituted for water as the diluent gave rise to four types of responses, group I, NH(4)NO(3), NH(4)Cl, KNO(3), NaNO(3), Ca(NO(3))(2), showed complete reversal of the streptomycin injury at all levels of the salts tested, from 0.01 to 0.5 M concentrations. Group II, NaCl and K(2)HPO(4) showed complete reversal at 0.03 and 0.1 M. Group III, glucose and urea allowed complete reversal at 0.5 M. Group IV, glycerol and glycerine showed no reversal at 0.5 M concentration. The reversal of the streptomycin injury to young actively growing bacteria is suggested as a tool for studying the pathology of the injury to the cells.

Anti-Bacterial Agents↗
PubMed2005

Reversal of diabetic peripheral neuropathy with phototherapy (MIRE) decreases falls and the fear of falling and improves activities of daily living in seniors.

OBJECTIVE: to determine whether restoration of sensation, impaired due to diabetic peripheral neuropathy (DPN), would reduce the number of falls and the fear of falling and improve activities of daily living (ADL) in a Medicare-aged population. DESIGN: retrospective cohort study of patients with documented, monochromatic near-infrared phototherapy (MIRE)-mediated, symptomatic reversal of DPN. SETTING: responses to a health status questionnaire following symptomatic reversal of DPN. PATIENTS: 252 patients (mean age 76 years) provided health information following symptomatic reversal of diabetic neuropathy (mean duration 8.6 months). MAIN RESULTS: incidence of falls and fear of falling decreased within 1 month after reversal of peripheral neuropathy and remained low after 1 year. Likewise, improved ADL were evident soon after reversal of peripheral neuropathy and showed further improvement after 1 year. Overall, reversal of peripheral neuropathy in a clinician's office and subsequent use of MIRE at home was associated with a 78% reduction in falls, a 79% decrease in balance-related fear of falling and a 72% increase in ADL (P < 0.0002 for all results). CONCLUSIONS: reversal of peripheral neuropathy is associated with an immediate reduction in the absolute number of falls, a reduced fear of falling and improved ADL. These results suggest that symptomatic reversal of diabetic neuropathy will have a substantial favourable, long-term socioeconomic impact on patients with DPN and the Medicare system, and improve the quality of life for elderly patients with diabetes and peripheral neuropathy.

Accidental Falls↗
PubMed1995

Transformation reversion induced in JB6 RT101 cells by AP-1 inhibitors.

The present study was directed to characterizing the reversion of neoplastic epidermal JB6 RT101 cells by AP-1 inhibiting drugs. Treatment of tumorigenic JB6 RT101 cells with retinoic acid (RA), fluocinolone acetonide (FA) or forskolin (FN) induced drug dependent (reversible) reversion of transformation. A synergistic effect on reversion was found with the three drugs in combination. Cells reverted by these three drugs also showed reduced levels of AP-1 transcription factor activity. After long term exposure of RT101 cells to FA, enrichment of flat revertants occurred in the population while a few unreverted cells formed foci. These unreverted cells appeared to be FA-resistant. Cloning of cells following RA treatment revealed stable reversion at least 2 months after drug withdrawal. Stable revertants showed lower basal AP-1 activity than RT101 cells (P < 0.01) and unstable revertants returned to transformed phenotype and elevated AP-1 activity within days following drug withdrawal. To our knowledge this is the first demonstration that drug induced reversion co-selects for reduced AP-1 activity. These data suggest that the JB6 RT101 cell line is a useful cell model for studying reversion of transformation and that inhibition of AP-1 activity may be one molecular mechanism of reversion. Considering the development of resistance with FA alone and the relative inefficiency of RA or FN alone, combinations of the three AP-1 activity inhibitors RA, FA and FN may be useful for further animal and clinical studies.

Animals↗
PubMed2005

Mechanisms and function of flower and inflorescence reversion.

Flower and inflorescence reversion involve a switch from floral development back to vegetative development, thus rendering flowering a phase in an ongoing growth pattern rather than a terminal act of the meristem. Although it can be considered an unusual event, reversion raises questions about the nature and function of flowering. It is linked to environmental conditions and is most often a response to conditions opposite to those that induce flowering. Research on molecular genetic mechanisms underlying plant development over the last 15 years has pinpointed some of the key genes involved in the transition to flowering and flower development. Such investigations have also uncovered mutations which reduce floral maintenance or alter the balance between vegetative and floral features of the plant. How this information contributes to an understanding of floral reversion is assessed here. One issue that arises is whether floral commitment (defined as the ability to continue flowering when inductive conditions no longer exist) is a developmental switch affecting the whole plant or is a mechanism which assigns autonomy to individual meristems. A related question is whether floral or vegetative development is the underlying default pathway of the plant. This review begins by considering how studies of flowering in Arabidopsis thaliana have aided understanding of mechanisms of floral maintenance. Arabidopsis has not been found to revert to leaf production in any of the conditions or genetic backgrounds analysed to date. A clear-cut reversion to leaf production has, however, been described in Impatiens balsamina. It is proposed that a single gene controls whether Impatiens reverts or can maintain flowering when inductive conditions are removed, and it is inferred that this gene functions to control the synthesis or transport of a leaf-generated signal. But it is also argued that the susceptibility of Impatiens to reversion is a consequence of the meristem-based mechanisms controlling development of the flower in this species. Thus, in Impatiens, a leaf-derived signal is critical for completion of flowering and can be considered to be the basis of a plant-wide floral commitment that is achieved without accompanying meristem autonomy. The evidence, derived from in vitro and other studies, that similar mechanisms operate in other species is assessed. It is concluded that most species (including Arabidopsis) are less prone to reversion because signals from the leaf are less ephemeral, and the pathways driving flower development have a high level of redundancy that generates meristem autonomy even when leaf-derived signals are weak. This gives stability to the flowering process, even where its initiation is dependent on environmental cues. On this interpretation, Impatiens reversion appears as an anomaly resulting from an unusual combination of leaf signalling and meristem regulation. Nevertheless, it is shown that the ability to revert can serve a function in the life history strategy (perenniality) or reproductive habit (pseudovivipary) of many plants. In these instances reversion has been assimilated into regular plant development and plays a crucial role there.

Environment↗
PubMed2005

Functional interaction of reverse gyrase with single-strand binding protein of the archaeon Sulfolobus.

Reverse gyrase is a unique hyperthermophile-specific DNA topoisomerase that induces positive supercoiling. It is a modular enzyme composed of a topoisomerase IA and a helicase domain, which cooperate in the ATP-dependent positive supercoiling reaction. Although its physiological function has not been determined, it can be hypothesized that, like the topoisomerase-helicase complexes found in every organism, reverse gyrase might participate in different DNA transactions mediated by multiprotein complexes. Here, we show that reverse gyrase activity is stimulated by the single-strand binding protein (SSB) from the archaeon Sulfolobus solfataricus. Using a combination of in vitro assays we analysed each step of the complex reverse gyrase reaction. SSB stimulates all the steps of the reaction: binding to DNA, DNA cleavage, strand passage and ligation. By co-immunoprecipitation of cell extracts we show that reverse gyrase and SSB assemble a complex in the presence of DNA, but do not make stable protein-protein interactions. In addition, SSB stimulates reverse gyrase positive supercoiling activity on DNA templates associated with the chromatin protein Sul7d. Furthermore, SSB enhances binding and cleavage of UV-irradiated substrates by reverse gyrase. The results shown here suggest that these functional interactions may have biological relevance and that the interplay of different DNA binding proteins might modulate reverse gyrase activity in DNA metabolic pathways.

Archaeal Proteins↗
PubMed2000

A prospective comparison of the standard and reverse robinson cervical grafting techniques: radiographic and clinical analyses.

The authors performed a prospective study of 63 patients with cervical radiculopathy treated with Robinson anterior cervical discectomy and fusion and compared the traditional or standard and reverse graft techniques. Modifications of the standard Robinson grafting techniques have been proposed. The reverse graft technique has theoretical advantages, including limiting the deleterious effects of graft extrusion and maintaining rigid middle column support. A radiographic evaluation and an assessment of clinical outcome based on the criteria of Odom were performed prospectively for as long as 1 year after surgery. Thirty-one patients were treated with the standard grafting technique and 32 with the reverse graft orientation. The radiographic evaluation showed no significant differences between the two techniques with regard to sagittal alignment and disk heights. The overall fusion grade was higher in the reverse graft technique (p < 0.05). There were 93% and 96% good to excellent results in the standard graft and reverse graft groups, respectively. The authors report no significant differences associated with the standard or reverse anterior cervical grafting techniques in terms of radiographic alignment or disk height loss over time or at early clinical outcome. However, improved fusion grade was noted with the reverse graft technique, which may be related to end plate and intervertebral space preparation. The reverse grafting technique is an acceptable alternative to the standard graft orientation.

Adult↗
PubMed2002

Effect of forward and reverse selection for ethanol-induced locomotor response on other measures of ethanol sensitivity.

BACKGROUND: Ethanol sensitivity may be a predictor of genetic predisposition to ethanol abuse. To examine ethanol sensitivity in rodents, two lines of mice were bred in replicate for high (FAST-1 and -2) and low (SLOW-1 and -2) locomotor stimulant responses to ethanol. After large differences between the lines developed and further response to selection seemed to have arrested, reverse selection was initiated by breeding the slowest FAST mice with each other and the fastest SLOW mice with each other. The reverse-selected lines, named r-FAST and r-SLOW, were virtually equally sensitive to the stimulant effects of the selection dose of ethanol after 16 generations of reverse selection. METHODS: These experiments used this unique genetic model to examine two responses, putatively genetically correlated with sensitivity to ethanol stimulation: handling-induced convulsions during chronic ethanol withdrawal, and ethanol-induced hypothermia. Ethanol clearance, for which a small difference was previously found between the FAST and SLOW lines, was also examined. RESULTS: Handling-induced convulsions during chronic ethanol withdrawal were significantly greater in both FAST lines compared with both SLOW lines. Reverse selection eliminated the difference between the replicate 1 lines but did not alter the difference between the replicate 2 lines. Ethanol-induced hypothermia was greater in both SLOW lines compared with the FAST lines. This difference was significantly reduced by reverse selection in r-SLOW mice only. Ethanol clearance rates were similar among all lines and replicates. CONCLUSIONS: These data demonstrate the usefulness of reverse-selected lines for examining putatively genetically correlated traits. Changes in the correlated traits demonstrated the existence of persistent trait-relevant genetic heterogeneity and some genetic overlap between the correlated traits and the selection trait. Absence of a change after reverse selection suggests that trait-relevant genetic heterogeneity was eliminated by forward selection or, alternatively, that the trait was not influenced by genes associated with successful reverse selection.

Animals↗
PubMed2004

Reversal of disc cupping after intraocular pressure reduction in topographic image series.

PURPOSE: To identify and characterize 'reversal' of optic nerve cupping following intraocular pressure (IOP) lowering in scanning laser tomography (SLT) longitudinal image series. METHODS: Modification was made to a previously described analytical approach to longitudinally study putatively increased rim area following IOP lowering. Sustained IOP reduction of 25% was by topical medication. Forty SLT image series with equivalent follow up were assessed: 10 with ocular hypertension (OHT), 10 with primary open angle glaucoma (POAG), and as controls, 20 normal. Reproducible rim area reversal was identified by sector and its time-course over 1 year examined. RESULTS: By a 2-of-3 reproducibility criterion, reversal following IOP lowering was confirmed in about a third of treated eyes (POAG and OHT) but not in any controls. Rim sectors showing reversal were mostly nasal, with a few occurring superotemporally. Reversal in a fifth of treated eyes persisted for at least 1 year; all these were in the nasal half of the disc. The number of sectors with persisting reversal affected less than 6% of all treated eyes' rim sectors. CONCLUSION: Rim area is not uncommonly increased after IOP lowering and this 'reversal' may persist for at least a year. Within topically treated eyes having IOP lowering of at least 25%, the proportion of rim sectors with persistent reversal appears small. Nevertheless, the effects of IOP reduction on topography, especially in the short term, should be considered when longitudinally assessing progressive rim loss in SLT images.

Aged↗
PubMed2006

Partial cricotracheal resection for successful reversal of laryngotracheal separation in patients with chronic aspiration.

OBJECTIVE: To present our experience with successful reversal of laryngotracheal separation in patients with chronic aspiration, to discuss our surgical technique, and to review the literature. STUDY DESIGN: Retrospective case review. METHODS: The medical records of two patients who underwent a successful reversal of laryngotracheal reversal after separation were reviewed. The two patients were evaluated clinically with videostroboscopy and videofluoroscopy. RESULTS: Both patients presented with intractable aspiration despite protective tracheostomy because of impairment of lower cranial nerve function. After laryngotracheal separation, swallowing rehabilitation was safely possible, and neurologic improvement allowed reversal of the separation procedure. For reversal, we present the use of a partial cricotracheal resection with tracheocricothyropexia similar to the technique used for subglottic stenosis. Both patients were successfully reversed. Satisfactory voice and swallowing function 7 and 10 years after reversal, respectively, could be assessed through our evaluation. Review of the literature revealed a total of 13 cases of successful reversal after laryngotracheal separation. Technical details of surgery and functional results are rarely reported.

Adult↗
PubMed1981

Recovery from monocular deprivation in the monkey. III. Reversal of anatomical effects in the visual cortex.

Transneuronal autoradiography was used to study the effects of visual deprivation on the ocular dominance stripes in layer IVc of the striated cortex of Erythrocebus patas (Old World) monkeys. The animals were studied after: (a) 21-28 days of monocular deprivation starting at, or within, a few days of birth; (b) the same treatment followed by a further 3, 6, 15 or 126 days of monocular vision through both eyes (reopening). One other monkey was monocularly deprived from birth to 1890 days. In most cases the behaviour of the ocular dominance stripes formed by the initially closed eye was studied. After 24 days of monocular deprivation from birth, the input from the normal eye was distributed uniformly within layer IVc, with no periodicity evident. After 21 days of deprivation, the deprived eye's input formed narrow stripes occupying about 38% of layer IVc in the operculum. Seven months of monocular deprivation reduced this to about 29%. Opening the closed eye after the deprivation produced no change in the area innervated: when periods of 15 or 96 days of binocular vision followed the deprivation, the areas innervated by the initially deprived eye were 26 and 30% respectively. However, in both cases the deprived eye's input formed blobs and spots, rather than uniformly narrow stripes. In contrast to reopening, reverse suturing increased the fraction of layer IVc occupied by input form the initially deprived eye. In the operculum, the effects of reverse suturing appeared to be fully developed after only 6 days of reversal: the initially deprived eye's stripes having expanded to occupy about 50% of layer IVc. A further 9 days' reversal produced little change in this. In the visual cortex in the calcarine fissure, the effect of the initial deprivation ws more severe, and the expansion induced by reverse suturing more pronounced. The initial deprivation caused the stripes to shrink to occupy 24% of layer IVc; after 6 days of reverse sulture the proportion increased to 52%, while after 15 days of reverse suture about 88% of IVc was occupied. These results show that reverse suturing can cause fresh growth of afferent axons in regions of layer IVc from which they had been at least partially removed, either by the normal process of segregation, or as a consequence of monocular deprivation. Taken in conjuction with the findings of the accompanying two papers (Blackemore et al...

Animals↗
PubMed1968

In vitro phytochrome dark reversion process.

Thermal reversion of the far-red absorbing form of phytochrome to the red absorbing form in darkness has been investigated in crude and partially purified isolates from a number of etiolated and light grown higher plants. The influence of temperature, aging and urea on the rate of reversion was also determined.Phytochrome isolated from all higher plants underwent reversion. The reversion proceeded in at least 2 distinct stages; a short rapid initial phase being followed a slow phase which continued for many hours. Reversion rate was highest in phytochrome isolated from green leaves of parsnip (Pastinacea sativa) and lowest in that isolated from etiolated oats (Avena sativa). Although the rate of reversion could be changed by modifying the tertiary structure of the protein component, the large differences in rate appeared to be characteristic of the plant source. Observed in vitro rates of reversion are slower than those occurring in vivo. Removal of other buffer solubilized material during purification had little effect on the rate of reversion of phytochrome isolated from etiolated material.

Journal Article↗