The Spatiotemporal Dynamics of Cerebral Autoregulation in Functional Magnetic Resonance Imaging

The thigh-cuff release (TCR) maneuver is a physiological challenge that is widely used to assess dynamic cerebral autoregulation (dCA). It is often applied in conjunction with Transcranial Doppler ultrasound (TCD), which provides temporal information of the global flow response in the brain. This established method can only yield very limited insights into the regional variability of dCA, whereas functional MRI (fMRI) has the ability to reveal the spatial distribution of flow responses in the brain with high spatial resolution. The aim of this study was to use whole-brain blood-oxygenation-level-dependent (BOLD) fMRI to characterize the spatiotemporal dynamics of the flow response to the TCR challenge, and thus pave the way toward mapping dCA in the brain. We used a data driven approach to derive a novel basis set that was then used to provide a voxel-wise estimate of the TCR associated haemodynamic response function (HRF TCR ). We found that the HRF TCR evolves with a specific spatiotemporal pattern, with gray and white matter showing an asynchronous response, which likely reflects the anatomical structure of cerebral blood supply. Thus, we propose that TCR challenge fMRI is a promising method for mapping spatial variability in dCA, which will likely prove to be clinically advantageous.

Measuring Arterial Pulsatility With Dynamic Inflow Magnitude Contrast

The pulsatility of blood flow through cerebral arteries is clinically important, as it is intrinsically associated with cerebrovascular health. In this study we outline a new MRI approach to measuring the real-time pulsatile flow in cerebral arteries, which is based on the inflow phenomenon associated with fast gradient-recalled-echo acquisitions. Unlike traditional phase-contrast techniques, this new method, which we dub dynamic inflow magnitude contrast (DIMAC), does not require velocity-encoding gradients as sensitivity to flow velocity is derived purely from the inflow effect. We achieved this using a highly accelerated single slice EPI acquisition with a very short TR (15 ms) and a 90° flip angle, thus maximizing inflow contrast. We simulate the spoiled GRE signal in the presence of large arteries and perform a sensitivity analysis. The sensitivity analysis demonstrates that in the regime of high inflow contrast, DIMAC shows much greater sensitivity to flow velocity over blood volume changes. We support this theoretical prediction with in-vivo data collected in two separate experiments designed to demonstrate the utility of the DIMAC signal contrast. We perform a hypercapnia challenge experiment in order to experimentally modulate arterial tone within subjects, and thus modulate the arterial pulsatile flow waveform. We also perform a thigh-cuff release challenge, designed to induce a transient drop in blood pressure, and demonstrate that the continuous DIMAC signal captures the complex transient change in the pulsatile and non-pulsatile components of flow. In summary, this study proposes a new role for a well-established source of MR image contrast and demonstrates its potential for measuring both steady-state and dynamic changes in arterial tone.

Neurofeedback Training versus Treatment-as-Usual for Alcohol Dependence: Results of an Early-Phase Randomized Controlled Trial and Neuroimaging Correlates

INTRODUCTION

Alcohol dependence is one of the most common substance use disorders, and novel treatment options are urgently needed. Neurofeedback training (NFT) based on real-time functional magnetic resonance imaging (rtf-MRI) has emerged as an attractive candidate for add-on treatments in psychiatry, but its use in alcohol dependence has not been formally investigated in a clinical trial. We investigated the use of rtfMRI-based NFT to prevent relapse in alcohol dependence.

METHODS

Fifty-two alcohol-dependent patients from the UK who had completed a detoxification program were randomly assigned to a treatment group (receiving rtfMRI NFT in addition to standard care) or the control group (receiving standard care only). At baseline, alcohol consumption was assessed as the primary outcome measure and a variety of psychological, behavioral, and neural parameters as secondary outcome measures to determine feasibility and secondary training effects. Participants in the treatment group underwent 6 NFT sessions over 4 months and were trained to downregulate their brain activation in the salience network in the presence of alcohol stimuli and to upregulate frontal activation in response to pictures related to positive goals. Four, 8, and 12 months after baseline assessment, both groups were followed up with a battery of clinical and psychometric tests.

RESULTS

Primary outcome measures showed very low relapse rates for both groups. Analysis of neural secondary outcome measures indicated that the majority of patients modulated the salience system in the desired directions, by decreasing activity in response to alcohol stimuli and increasing activation in response to positive goals. The intervention had a good safety and acceptability profile.

CONCLUSION

We demonstrated that rtfMRI-neurofeedback targeting hyperactivity of the salience network in response to alcohol cues is feasible in currently abstinent patients with alcohol dependence.

Vascular physiology drives functional brain networks

We present the first evidence for vascular regulation driving fMRI signals in specific functional brain networks. Using concurrent neuronal and vascular stimuli, we collected 30 BOLD fMRI datasets in 10 healthy individuals: a working memory task, flashing checkerboard stimulus, and CO2 inhalation challenge were delivered in concurrent but orthogonal paradigms. The resulting imaging data were averaged together and decomposed using independent component analysis, and three "neuronal networks" were identified as demonstrating maximum temporal correlation with the neuronal stimulus paradigms: Default Mode Network, Task Positive Network, and Visual Network. For each of these, we observed a second network component with high spatial overlap. Using dual regression in the original 30 datasets, we extracted the time-series associated with these network pairs and calculated the percent of variance explained by the neuronal or vascular stimuli using a normalized R2 parameter. In each pairing, one network was dominated by the appropriate neuronal stimulus, and the other was dominated by the vascular stimulus as represented by the end-tidal CO2 time-series recorded in each scan. We acquired a second dataset in 8 of the original participants, where no CO2 challenge was delivered and CO2 levels fluctuated naturally with breathing variations. Although splitting of functional networks was not robust in these data, performing dual regression with the network maps from the original analysis in this new dataset successfully replicated our observations. Thus, in addition to responding to localized metabolic changes, the brain's vasculature may be regulated in a coordinated manner that mimics (and potentially supports) specific functional brain networks. Multi-modal imaging and advances in fMRI acquisition and analysis could facilitate further study of the dual nature of functional brain networks. It will be critical to understand network-specific vascular function, and the behavior of a coupled vascular-neural network, in future studies of brain pathology.

Resting-State Network Patterns Underlying Cognitive Function in Bipolar Disorder: A Graph Theoretical Analysis

Background: Synchronous and antisynchronous activity between neural elements at rest reflects the physiological processes underlying complex cognitive ability. Regional and pairwise connectivity investigations suggest that perturbations in these activity patterns may relate to widespread cognitive impairments seen in bipolar disorder (BD). Here we take a network-based perspective to more meaningfully capture interactions among distributed brain regions compared to focal measurements and examine network-cognition relationships across a range of commonly affected cognitive domains in BD in relation to healthy controls. Methods: Resting-state networks were constructed as matrices of correlation coefficients between regionally averaged resting-state time series from 86 cortical/subcortical brain regions (FreeSurferv5.3.0). Cognitive performance measured using the Wechsler Adult Intelligence Scale, Cambridge Automated Neuropsychological Test Battery (CANTAB), and Reading the Mind in the Eyes tests was examined in relation to whole-brain connectivity measures and patterns of connectivity using a permutation-based statistical approach. Results: Faster response times in controls (n = 49) related to synchronous activity between frontal, parietal, cingulate, temporal, and occipital regions, while a similar response times in BD (n = 35) related to antisynchronous activity between regions of this subnetwork. Across all subjects, antisynchronous activity between the frontal, parietal, temporal, occipital, cingulate, insula, and amygdala regions related to improved memory performance. No resting-state subnetworks related to intelligence, executive function, short-term memory, or social cognition performance in the overall sample or in a manner that would explain deficits in these facets in BD. Conclusions: Our results demonstrate alterations in the intrinsic connectivity patterns underlying response timing in BD that are not specific to performance or errors on the same tasks. Across all individuals, no strong effects of resting-state global topology on cognition are found, while distinct functional networks supporting episodic and spatial memory highlight intrinsic inhibitory influences present in the resting state that facilitate memory processing. Impact Statement Regional and pairwise-connectivity investigations suggest altered interactions between brain areas may contribute to impairments in cognition that are observed in bipolar disorder. However, the distributed nature of these interactions across the brain remains poorly understood. Using recent advances in network neuroscience, we examine functional connectivity patterns associated with multiple cognitive domains in individuals with and without bipolar disorder. We discover distinct patterns of connectivity underlying response-timing performance uniquely in bipolar disorder and, independent of diagnosis, inhibitory interactions that relate to memory performance.

Graded fMRI Neurofeedback Training of Motor Imagery in Middle Cerebral Artery Stroke Patients: A Preregistered Proof-of-Concept Study

Ischemic stroke of the middle cerebral artery (MCA), a major brain vessel that supplies the primary motor and premotor cortex, is one of the most common causes for severe upper limb impairment. Currently available motor rehabilitation training largely lacks satisfying efficacy with over 70% of stroke survivors showing residual upper limb dysfunction. Motor imagery-based functional magnetic resonance imaging neurofeedback (fMRI-NF) has been suggested as a potential therapeutic technique to improve motor impairment in stroke survivors. In this preregistered proof-of-concept study (https://osf.io/y69jc/), we translated graded fMRI-NF training, a new paradigm that we have previously studied in healthy participants, to first-time MCA stroke survivors with residual mild to severe impairment of upper limb motor function. Neurofeedback was provided from the supplementary motor area (SMA) targeting two different neurofeedback target levels (low and high). We hypothesized that MCA stroke survivors will show (1) sustained SMA-region of interest (ROI) activation and (2) a difference in SMA-ROI activation between low and high neurofeedback conditions during graded fMRI-NF training. At the group level, we found only anecdotal evidence for these preregistered hypotheses. At the individual level, we found anecdotal to moderate evidence for the absence of the hypothesized graded effect for most subjects. These null findings are relevant for future attempts to employ fMRI-NF training in stroke survivors. The study introduces a Bayesian sequential sampling plan, which incorporates prior knowledge, yielding higher sensitivity. The sampling plan was preregistered together with a priori hypotheses and all planned analysis before data collection to address potential publication/researcher biases. Unforeseen difficulties in the translation of our paradigm to a clinical setting required some deviations from the preregistered protocol. We explicitly detail these changes, discuss the accompanied additional challenges that can arise in clinical neurofeedback studies, and formulate recommendations for how these can be addressed. Taken together, this work provides new insights about the feasibility of motor imagery-based graded fMRI-NF training in MCA stroke survivors and serves as a first example for comprehensive study preregistration of an (fMRI) neurofeedback experiment.

Corrigendum: Cerebral Autoregulation Evidenced by Synchronized Low Frequency Oscillations in Blood Pressure and Resting-State fMRI

[This corrects the article DOI: 10.3389/fnins.2019.00433.].

Frontolimbic, Frontoparietal, and Default Mode Involvement in Functional Dysconnectivity in Psychotic Bipolar Disorder

BACKGROUND

Functional abnormalities, mostly involving functionally specialized subsystems, have been associated with disorders of emotion regulation such as bipolar disorder (BD). Understanding how independent functional subsystems integrate globally and how they relate with anatomical cortical and subcortical networks is key to understanding how the human brain's architecture constrains functional interactions and underpins abnormalities of mood and emotion, particularly in BD.

METHODS

Resting-state functional magnetic resonance time series were averaged to obtain individual functional connectivity matrices (using AFNI software); individual structural connectivity matrices were derived using deterministic non-tensor-based tractography (using ExploreDTI, version 4.8.6), weighted by streamline count and fractional anisotropy. Structural and functional nodes were defined using a subject-specific cortico-subcortical mapping (using Desikan-Killiany Atlas, FreeSurfer, version 5.3). Whole-brain connectivity alongside a permutation-based statistical approach and structure-function coupling were employed to investigate topological variance in individuals with predominantly euthymic BD relative to psychiatrically healthy control subjects.

RESULTS

Patients with BD (n = 41) exhibited decreased (synchronous) connectivity in a subnetwork encompassing frontolimbic and posterior-occipital functional connections (T > 3, p = .048), alongside increased (antisynchronous) connectivity within a frontotemporal subnetwork (T > 3, p = .014); all relative to control subjects (n = 56). Preserved whole-brain functional connectivity and comparable structure-function coupling among whole-brain and edge-class connections were observed in patients with BD relative to control subjects.

CONCLUSIONS

This study presents a functional map of BD dysconnectivity that differentially involves communication within nodes belonging to functionally specialized subsystems-default mode, frontoparietal, and frontolimbic systems; these changes do not extend to be detected globally and may be necessary to maintain a remitted clinical state of BD. Preserved structure-function coupling in BD despite evidence of regional anatomical and functional deficits suggests a dynamic interplay between structural and functional subnetworks.

Cerebral Autoregulation Evidenced by Synchronized Low Frequency Oscillations in Blood Pressure and Resting-State fMRI

Resting-state functional magnetic resonance imaging (rs-fMRI) is a widely used technique for mapping the brain’s functional architecture, so delineating the main sources of variance comprising the signal is crucial. Low frequency oscillations (LFO) that are not of neural origin, but which are driven by mechanisms related to cerebral autoregulation (CA), are present in the blood-oxygenation-level-dependent (BOLD) signal within the rs-fMRI frequency band. In this study we use a MR compatible device (Caretaker, Biopac) to obtain a non-invasive estimate of beat-to-beat mean arterial pressure (MAP) fluctuations concurrently with rs-fMRI at 3T. Healthy adult subjects (n = 9; 5 male) completed two 20-min rs-fMRI scans. MAP fluctuations were decomposed into different frequency scales using a discrete wavelet transform, and oscillations at approximately 0.1 Hz show a high degree of spatially structured correlations with matched frequency fMRI fluctuations. On average across subjects, MAP fluctuations at this scale of the wavelet decomposition explain ∼2.2% of matched frequency fMRI signal variance. Additionally, a simultaneous multi-slice multi-echo acquisition was used to collect 10-min rs-fMRI at three echo times at 7T in a separate group of healthy adults (n = 5; 5 male). Multiple echo times were used to estimate the R₂^∗ decay at every time point, and MAP was shown to strongly correlate with this signal, which suggests a purely BOLD (i.e., blood flow related) origin. This study demonstrates that there is a significant component of the BOLD signal that has a systemic physiological origin, and highlights the fact that not all localized BOLD signal changes necessarily reflect blood flow supporting local neural activity. Instead, these data show that a proportion of BOLD signal fluctuations in rs-fMRI are due to localized control of blood flow that is independent of local neural activity, most likely reflecting more general systemic autoregulatory processes. Thus, fMRI is a promising tool for studying flow changes associated with cerebral autoregulation with high spatial resolution.

The BOLD response in primary motor cortex and supplementary motor area during kinesthetic motor imagery based graded fMRI neurofeedback

There is increasing interest in exploring the use of functional MRI neurofeedback (fMRI-NF) as a therapeutic technique for a range of neurological conditions such as stroke and Parkinson's disease (PD). One main therapeutic potential of fMRI-NF is to enhance volitional control of damaged or dysfunctional neural nodes and networks via a closed-loop feedback model using mental imagery as the catalyst of self-regulation. The choice of target node/network and direction of regulation (increase or decrease activity) are central design considerations in fMRI-NF studies. Whilst it remains unclear whether the primary motor cortex (M1) can be activated during motor imagery, the supplementary motor area (SMA) has been robustly activated during motor imagery. Such differences in the regulation potential between primary and supplementary motor cortex are important because these areas can be differentially affected by a stroke or PD, and the choice of fMRI-NF target and grade of self-regulation of activity likely have substantial influence on the clinical effects and cost effectiveness of NF-based interventions. In this study we therefore investigated firstly whether healthy subjects would be able to achieve self-regulation of the hand-representation areas of M1 and the SMA using fMRI-NF training. There was a significant decrease in M1 neural activity during fMRI-NF, whereas SMA neural activity was increased, albeit not with the predicated graded effect. This study has important implications for fMRI-NF protocols that employ motor imagery to modulate activity in specific target regions of the brain and to determine how they may be tailored for neurorehabilitation.

The Functional Connectivity Between the Nucleus Accumbens and the Ventromedial Prefrontal Cortex as an Endophenotype for Bipolar Disorder

BACKGROUND

Alterations in functional connectivity between the nucleus accumbens (NAcc) and frontal cortices have been previously associated with the presence of psychiatric syndromes, including bipolar disorder (BD). Whether these alterations are a consequence or a risk factor for mental disorders remains unresolved.

METHODS

This study included 35 patients with BD, 30 nonaffected siblings of patients with BD, and 23 healthy control subjects to probe functional connectivity at rest between NAcc and the rest of the brain in a cross-sectional design. Blood oxygen level-dependent time series at rest from NAcc were used as seed region in a voxelwise correlational analysis. The strength of the correlations found was compared across groups after Fisher's Z transformation.

RESULTS

We found increased functional connectivity between the NAcc and the ventromedial prefrontal cortex-comprising mainly the subgenual anterior cingulate-in patients compared with healthy control subjects. Participants at increased genetic risk but yet resilient-nonaffected siblings-showed functional connectivity values midway between the former two groups.

CONCLUSIONS

Our results are indicative of the potential for the connectivity between NAcc and the ventromedial prefrontal cortex to represent an endophenotype for BD.

Cerebrovascular Function in the Large Arteries Is Maintained Following Moderate Intensity Exercise

Exercise has been shown to induce cerebrovascular adaptations. However, the underlying temporal dynamics are poorly understood, and regional variation in the vascular response to exercise has been observed in the large cerebral arteries. Here, we sought to measure the cerebrovascular effects of a single 20-min session of moderate-intensity exercise in the one hour period immediately following exercise cessation. We employed transcranial Doppler (TCD) ultrasonography to measure cerebral blood flow velocity (CBFV) in the middle cerebral artery (MCAv) and posterior cerebral artery (PCAv) before, during, and following exercise. Additionally, we simultaneously measured cerebral blood flow (CBF) in the internal carotid artery (ICA) and vertebral artery (VA) before and up to one hour following exercise cessation using Duplex ultrasound. A hypercapnia challenge was used before and after exercise to examine exercise-induced changes in cerebrovascular reactivity (CVR). We found that MCAv and PCAv were significantly elevated during exercise (p = 4.81 × 10^-5 and 2.40 × 10^-4, respectively). A general linear model revealed that these changes were largely explained by the partial pressure of end-tidal CO₂ and not a direct vascular effect of exercise. After exercise cessation, there was no effect of exercise on CBFV or CVR in the intracranial or extracranial arteries (all p > 0.05). Taken together, these data confirm that CBF is rapidly and uniformly regulated following exercise cessation in healthy young males.

Changes in arterial cerebral blood volume during lower body negative pressure measured with MRI

Cerebral Autoregulation (CA), defined as the ability of the cerebral vasculature to maintain stable levels of blood flow despite changes in systemic blood pressure, is a critical factor in neurophysiological health. Magnetic resonance imaging (MRI) is a powerful technique for investigating cerebrovascular function, offering high spatial resolution and wide fields of view (FOV), yet it is relatively underutilized as a tool for assessment of CA. The aim of this study was to demonstrate the potential of using MRI to measure changes in cerebrovascular resistance in response to lower body negative pressure (LBNP). A Pulsed Arterial Spin Labeling (PASL) approach with short inversion times (TI) was used to estimate cerebral arterial blood volume (CBV_a) in eight healthy subjects at baseline and −40 mmHg LBNP. We estimated group mean CBV_a values of 3.13 ± 1.00 and 2.70 ± 0.38 for baseline and lbnp respectively, which were the result of a differential change in CBV_a during −40 mmHg LBNP that was dependent on baseline CBV_a. These data suggest that the PASL CBV_a estimates are sensitive to the complex cerebrovascular response that occurs during the moderate orthostatic challenge delivered by LBNP, which we speculatively propose may involve differential changes in vascular tone within different segments of the arterial vasculature. These novel data provide invaluable insight into the mechanisms that regulate perfusion of the brain, and establishes the use of MRI as a tool for studying CA in more detail.

Neurofeedback training for alcohol dependence versus treatment as usual: study protocol for a randomized controlled trial

Background

Real-time functional magnetic resonance imaging (rtfMRI) is used for neurofeedback training (NFT). Preliminary results suggest that it can help patients to control their symptoms. This study uses rtfMRI NFT for relapse prevention in alcohol dependence.

Methods/design

Participants are alcohol-dependent patients who have completed a detoxification programme within the past 6 months and have remained abstinent. Potential participants are screened for eligibility, and those who are eligible are randomly assigned to the treatment group (receiving rtfMRI NFT in addition to treatment as usual) or the control group (receiving only treatment as usual). Participants in both groups are administered baseline assessments to measure their alcohol consumption and severity of dependence and a variety of psychological and behavioural characteristics that are hypothesised to predict success with rtfMRI NFT. During the following 4 months, experimental participants are given six NFT sessions, and before and after each session various alcohol-related measures are taken. Participants in the control group are given the same measures to coincide with their timing in the experimental group. Eight and 12 months after the baseline assessment, both groups are followed up with a battery of measures. The primary research questions are whether NFT can be used to teach participants to down-regulate their brain activation in the presence of alcohol stimuli or to up-regulate their brain activation in response to pictures related to healthy goal pursuits, and, if so, whether this translates into reductions in alcohol consumption. The primary outcome measures will be those derived from the functional brain imaging data. We are interested in improvements (i.e., reductions) in participants’ alcohol consumption from pretreatment levels, as indicated by three continuous variables, not simply whether or not the person has remained abstinent. The indices of interest are percentage of days abstinent, drinks per drinking day, and percentage of days of heavy drinking. General linear models will be used to compare the NFT group and the control group on these measures.

Discussion

Relapse in alcohol dependence is a recurring problem, and the present evaluation of the role of rtfMRI in its treatment holds promise for identifying a way to prevent relapse.

Trial registration

ClinicalTrials.gov Identifier: NCT02486900, registered on 26 June 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-016-1607-7) contains supplementary material, which is available to authorized users.

The absolute CBF response to activation is preserved during elevated perfusion: Implications for neurovascular coupling measures

Functional magnetic resonance imaging (fMRI) techniques in which the blood oxygenation level dependent (BOLD) and cerebral blood flow (CBF) response to a neural stimulus are measured, can be used to estimate the fractional increase in the cerebral metabolic rate of oxygen consumption (CMRO2) that accompanies evoked neural activity. A measure of neurovascular coupling is obtained from the ratio of fractional CBF and CMRO2 responses, defined as n, with the implicit assumption that relative rather than absolute changes in CBF and CMRO2 adequately characterise the flow-metabolism response to neural activity. The coupling parameter n is important in terms of its effect on the BOLD response, and as potential insight into the flow-metabolism relationship in both normal and pathological brain function. In 10 healthy human subjects, BOLD and CBF responses were measured to test the effect of baseline perfusion (modulated by a hypercapnia challenge) on the coupling parameter n during graded visual stimulation. A dual-echo pulsed arterial spin labelling (PASL) sequence provided absolute quantification of CBF in baseline and active states as well as relative BOLD signal changes, which were used to estimate CMRO2 responses to the graded visual stimulus. The absolute CBF response to the visual stimuli were constant across different baseline CBF levels, meaning the fractional CBF responses were reduced at the hyperperfused baseline state. For the graded visual stimuli, values of n were significantly reduced during hypercapnia induced hyperperfusion. Assuming the evoked neural responses to the visual stimuli are the same for both baseline CBF states, this result has implications for fMRI studies that aim to measure neurovascular coupling using relative changes in CBF. The coupling parameter n is sensitive to baseline CBF, which would confound its interpretation in fMRI studies where there may be significant differences in baseline perfusion between groups. The absolute change in CBF, as opposed to the change relative to baseline, may more closely match the underlying increase in neural activity in response to a stimulus.

Muscle development and lineage-specific expression of CiMDF, the MyoD-family gene of Ciona intestinalis

The expression pattern of CiMDF, the MyoD-family gene of Ciona intestinalis, was analyzed in unmanipulated and microsurgically derived partial embryos. CiMDF encodes two transcripts during development (coding for distinct proteins), the smaller of which, CiMDFa, was detected in maternal RNA. Zygotic activity of CiMDF initiated in cleaving embryos of 32-64 cells. Both CiMDFa and CiMDFb transcripts were detected at this time; however, CiMDFa accumulated more rapidly before declining in abundance such that, by the early tail-formation stage, CiMDFb was more prevalent. Microsurgical isolations of various lineage blastomeres from the eight-cell stage were used to analyze CiMDF expression in the two embryonic lineages that give rise to larval tail muscle-autonomously specified primary cells and conditionally specified secondary cells. CiMDFa and CiMDFb transcripts were detected in both lineages, suggesting that neither functioned in a lineage-specific manner. The data also demonstrated that CiMDF expression was autonomous in the primary lineage (i.e., cells derived from the B4.1 blastomeres) and correlated with histospecific differentiation of muscle. In the secondary lineage (i.e., cells derived from the A4.1 and b4.2 blastomeres), CiMDF expression was conditional and, as in the primary lineage, correlated with muscle differentiation. These experiments reveal similar patterns of CiMDF activity in the primary and secondary muscle lineages and imply a requirement for the expression of this gene in both lineages during larval tail muscle development.

Resistance mechanisms determining the in vitro sensitivity to paclitaxel of tumour cells cultured from patients with ovarian cancer

Paclitaxel, a drug which stabilises microtubules, demonstrates marked activity against ovarian cancer. We investigated the sensitivity to paclitaxel of tumour cells from disaggregated solid tumours or tumour-bearing ascites from 7 ovarian cancer patients, and 21 established tumour cell lines (ovarian, melanoma and lung). Response was quantitated by [3H]-thymidine incorporation in 96-well plates or by colony growth. Dose-response curves to paclitaxel were biphasic with a dose-dependent phase providing an IC50 value (50% reduction in incorporation) and dose-dependent "plateau" phase where the effect was independent of paclitaxel concentration. IC50 values ranged from 2.5 to 110 nM with evidence of multidrug resistance in the two most resistant cell lines. The "plateau" killing values varied from 0.1 log10 to > 3.4 log10 units reduction, and were found to be significantly correlated (r = 0.86; P < 0.0001) with logarithmic culture doubling times of the cell lines. Cellular glutathione levels were measured and found not to be significantly associated with response to paclitaxel. The results suggest that the ratio of paclitaxel exposure time to the culture doubling time is a major factor in paclitaxel cytotoxicity. The relationship between tumour cell cytokinetics and paclitaxel pharmacokinetics in vivo may therefore be crucial in determining clinical paclitaxel response.

Serial repetition of cilia pairs along the tail surface of an ascidian larva

Regularly spaced cilia pairs were found in two rows immediately opposite to each other mid-dorsally and mid-ventrally along the larval tail surface of the ascidian protochordate Ciona intestinalis. There were approximately ten such equidistantly placed dorsal-ventral sets embedded in the matrix of the extracellular larval test which forms the flattened vertical tail fin. These immotile cilia originate from pairs of cell bodies in mid-dorsal and mid-ventral peripheral nerves running beneath the tail epidermis. The cilia and neural cell bodies were visualized by immunocytochemical staining with anti-tubulin antibodies; their nature was confirmed by ultrastructural examination. This pattern of cilia and neural cell body placement is conceivably related to the segmentation found in vertebrates.

Structure of the caudal neural tube in an ascidian larva: vestiges of its possible evolutionary origin from a ciliated band

Ultrastructural analysis and differential immunocytochemical staining with two antitubulin monoclonal antibodies were used to reexamine the organization and development of the neural tube in the larva of an ascidian, Ciona intestinalis, in appraisal of a theory that the dorsal tubular nervous system of the chordates evolved from two halves of a ciliated band in an auricularia-like larva of the kind found in echinoderms and hemichordates. One of the antibodies stained cilia in the nervous system and elsewhere; the other reacted primarily with neuronal axons. The caudal neural tube consists of four rows of large ciliated ependymal-glial cells enclosing an axial neural canal into which their single cilia extend. Two ventrolateral nerve tracts, containing axons, arise in the posterior brain region and extend along the length of the caudal tube, partially surrounded by the ependymal cells. The nonnervous, ciliated, ependymal neural tube of the ascidian larva with its two associated nerve tracts survives as a primitive early condition that could result from a ciliated band transformation. Tissues in the distal-most part of the ascidian larval tail have cell lineage origins that indicate an evolutionary history different from those in the proximal majority of the tail. The ependymal cells in this presumed later addition to the tail are not ciliated, although all of the others in the caudal ependymal tube appear to be.

Differentiation of tropomyosin-containing myofibrils in cleavage-arrested ascidian zygotes expressing acetylcholinesterase

Two muscle differentiation programs, acetylcholinesterase and tropomyosin-containing filaments and fibrils, occur together in the same cleavage-arrested zygotes (1-celled) of the ascidian Ciona intestinalis. Coexpression in such undivided but developing ‘embryos’ is consistent with the idea that separate elements of muscle differentiation are related at some regulatory level, perhaps through a single multi-gene regulatory factor. Fertilized Ciona eggs were exposed to cytochalasin B for 20 h and then briefly reacted histochemically for acetylcholinesterase activity. Strongly reacting specimens were selected and processed for transmission electron microscopy to reveal regions of muscle ultrastructure. Every acetylcholinesterase-reactive zygote tested contained muscle contractile elements; no example lacking acetylcholinesterase was found with myofilaments and myofibrils. As demonstrated by immunogold labelling, a polyclonal antibody to tropomyosin from Ciona adult body wall reacted differentially with the presumed ultrastructural muscle elements in cleavage-arrested zygotes. Site-specific reactions were also observed in larval tail muscle and the siphon muscles of postmetamorphic zooids.

Determination of Alkaline Phosphatase Expression in Endodermal Cell Lineages of an Ascidian Embryo

Ciona intestinalis embryos develop a strong histochemical localization of alkaline phosphatase activity in their known endodermal tissues. Such tissues arise solely from the four vegetal blastomeres at the 8-cell stage and six vegetal blastomeres at the 16-cell stage; these vegetal cells inherit an endodermal lineage cytoplasm. Pairs of blastomeres from the bilaterally symmetrical 8- and 16-cell stages were isolated and reared as partial embroys. Only those partial embryos derived from endoderm-containing lineages developed a histochemically localized alkaline phosphatase activity. From the results of such restricted developmental autonomy (self-differentiation), one can deduce that this enzymic expression of endodermal fate could be specified by events of cytoplasmic segregation that occur during the early cleavages. This conclusion offers additional support to the theory that specification of cell fate in ascidian embryos involves an early differential segregation of histodetermining egg cytoplasmic materials.

Two histospecific enzyme expressions in the same cleavage-arrested one-celled ascidian embryos

Fertilized eggs of the ascidian, Ciona intestinalis, were prevented from undergoing cytokinesis but not nuclear division by treatment with cytochalasin B. After appropriate times, such cleavage-arrested multinucleate zygotes developed acetylcholinesterase of larval tail muscle and an alkaline phosphatase ordinarily localized in the larval endoderm tissues. Separate histochemical reactions on one of a pair of samples taken from the eggs of single animals provided examples (6/34) in which the numbers of cytochalasin-treated embryos displaying the respective reaction product overlapped sufficiently (15-29%) to indicate that some of the zygotes had developed both enzymes in the same uncleaved single cell. With an actual dual-staining technique that can be applied to single cleavage-arrested zygotes, 62% of those developing a strong alkaline phosphatase reaction also had a strong acetylcholinesterase reaction. In other experiments, quantitative measurements of enzyme activity in homogenates of 114 single cleavage-arrested zygotes confirm directly that 18% of the zygotes produce both enzymes. There was no obligatory mutual exclusion of the potential for simultaneous expression of two tissue-specific characteristics that would ordinarily be segregated into different lineages during early cleavages. The cytoplasmic determinants believed responsible for these histotypic expressions can apparently function independently in the same cell.

Cytokeratin expression in cervical epithelium: an immunohistological study of normal, wart virus-infected and neoplastic tissue

In this study using a panel of anticytokeratin antibodies and an indirect immunoperoxidase method, we examined cervical squamous epithelia including mature stratified epithelium, immature squamous metaplasia, CIN 1, 2 and 3, wart virus infection and squamous carcinoma. Changes from the normal patterns of staining were inconsistently seen in CIN 1 and 2, but in CIN 3 the changes were more marked, and consisted of a loss of stratification of the staining pattern and a patchy reduction in staining. Invasive carcinomas showed a similar staining pattern to CIN 3 lesions.

Cell differentiation features in embryos resulting from interphylum nuclear transplantation: echinoderm nucleus to ascidian zygote cytoplasm

When an echinoderm nucleus was transplanted into an ascidian zygote cytoplast there was developmental cooperation at the cellular level between nucleus and cytoplasm of these normally nonhybridizable species. A blastula stage nucleus from the sand dollar Echinarachnius parma was injected into an activated but nonnucleate egg fragment of the ascidian Ciona intestinalis. During culture, some of the "hybrid" embryos displayed ultrastructural evidence of cellular differentiation. Two recognizable features were (1) extracellular matrix components, and (2) neural cell characteristics, including elaboration of associated cilia. Nonnucleate zygote fragments alone, and such fragments injected with seawater or punctured by glass needle, did not develop organized subcellular structures. Morphologic expressions resulting from nuclear transplantations between these two phyla (Echinodermata and Chordata) seemingly indicate functional interactions at a gene regulatory level. Creation of such nuclear-cytoplasmic hybrids suggests thereby a means of exploring the nature of the egg cytoplasmic agents in ascidian embryos that appear to determine gene expression related to histospecific differentiation products.

Determinative properties of muscle lineages in ascidian embryos

Blastomeres removed from early cleavage stage ascidian embryos and reared to ‘maturity’ as partial embryos often elaborate tissue-specific features typical of their constituent cell lineages. We used this property to study recent corrections of the ascidian larval muscle lineage and to compare the ways in which different lineages give rise to muscle. Our evaluation of muscle differentiation was based on histochemical localization and quantitative radiometric measurement of a muscle-specific acetylcholinesterase activity, and the development of myofilaments and myofibrils as observed by electron microscopy. Although the posterior-vegetal blastomeres (B4.1 pair) of the 8-cell embryo have long been believed to be the sole precursors of larval muscle, recent studies using horseradish peroxidase to mark cell lineages have shown that small numbers of muscle cells originate from the anterior-vegetal (A4.1) and posterior-animal (b4.2) blastomeres of this stage. Fully differentiated muscle expression in isolated partial embryos of A4.1-derived cells requires an association with cells from other lineages whereas muscle from B4.1 blastomeres develops autonomously. Clear differences also occurred in the time acetylcholinesterase activity was first detected in partial embryos from these two sources. Isolated b4.2 cells failed to show any muscle development even in combination with anterior-animal cells (a4.2) and are presumably even more dependent on normal cell interactions and associations. Others have noted an additional distinction between the different sources of muscle: muscle cells from non-B4.1 lineages occur exclusively in the distal part of the tail, while the B4.1 descendants contribute those cells in the proximal and middle regions. During the course of ascidian larval evolution tail muscle probably had two origins: the primary lineage (B4.1) whose fate was set rigidly at early cleavage stages and secondarily evolved lineages which arose later by recruitment of cells from other tissues resulting in increased tail length. In contrast to the B4.1 lineage, muscle development in the secondary lineages is controlled less rigidly by processes that depend on cell interactions.

Differentiation without cleavage: multiple cytospecific ultrastructural expressions in individual one-celled ascidian embryos

Multiple states of differentiation developed within the same undivided egg cytoplasm of ascidian zygotes cleavage-arrested with cytochalasin B. Complex ultrastructural traits of up to four quite diverse cell lineage components were observed in regions of the common cytoplasm in such multinucleate homokaryons of Ciona intestinalis: epidermal, muscle, notochordal, and neural. Almost all specimens among those selected as showing differentiation contained two such features, half of them had at least three, and a few expressed all four. The histospecific morphological characteristics noted were the extracellular test material of epidermal cell origin, muscle myofilaments and myofibrils, sheath components (leaflets and filaments) associated with notochordal cells, and the particular localized combinations of microtubules, filamentous structures, and cilia indicative of neural tissues. Cleavage-arrested one-celled embryos of Ascidia ceratodes served to demonstrate that those which were found cytochemically to contain muscle acetylcholinesterase always had myofibrils and myofilaments. Other arrested zygotes of Ascidia (unstained specimens) also had quite fully formed test material as well as myofilaments and myofibrils. The occurrence within the same cell of so many specific markers of diverse pathways of development is consistent with a theory about a primary level of regulation based on autonomous gene activation factors already present in the fertilized egg. If further investigation substantiates a real cytoplasmic continuity within these cleavage-arrested embryos, other theories that invoke cell interactions, temporal sequences of metabolically distinct microenvironments, and gradients of substances as causes of determinative change seem inadequate to account for the coexisting expressions of differentiation described here.

Lineage segregation and developmental autonomy in expression of functional muscle acetylcholinesterase mRNA in the ascidian embryo

Acetylcholinesterase is a histospecific marker of cell differentiation occurring only in the muscle and mesenchyme tissues of the ascidian embryo. The distribution of functional mRNA coding for this enzyme has been investigated and it is shown here that only cells of muscle and mesenchyme lineages possess such a template. Blastomeres of four cell lineage quadrants were separated microsurgically from eight-cell-stage embryos of Ciona intestinalis and raised in isolation until muscle development was well advanced. Measurement of enzyme activity in the resulting partial embryos revealed that acetylcholinesterase was limited to descendants of one blastomere pair, the B4.1 blastomeres containing muscle and mesenchyme lineages. To study the tissue distribution of acetylcholinesterase mRNA, RNA from partial embryos was translated in Xenopus laevis oocytes. When oocytes were injected with an appropriate template, they synthesized a biologically active acetylcholinesterase that could be selectively immunopurified with an antiserum to the ascidian enzyme. Under the conditions used the quantity of acetylcholinesterase mRNA was directly related to the enzyme activity in immunoprecipitates. Acetylcholinesterase mRNA was found only in B4.1 lineage partial embryos where it occurred in approximately the same amount as in whole embryos of the same age. Since there is a limited period from gastrulation until the middle tail-formation stage when functional acetylcholinesterase mRNA accumulates, the results of our mRNA distribution experiments strongly suggest that the gene for ascidian acetylcholinesterase is active only in muscle and mesenchyme tissues. The histospecific occurrence of this enzyme apparently does not involve selective, cell-specific control of translation.

Development of translationally active mRNA for larval muscle acetylcholinesterase during ascidian embryogenesis

Relative quantities of translationally active acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) mRNA present at various developmental stages were compared in embryos of the ascidian Ciona intestinalis. Purified RNA was tested for its translational capacity by microinjection into Xenopus laevis oocytes; the acetylcholinesterase produced was immunoprecipitated with antibody to Ciona acetylcholinesterase and enzyme activity was assayed radiometrically. With this protocol, enzyme synthesis was found to be directly related to the amount of RNA injected and to the oocyte incubation time. A functional template for acetylcholinesterase was first detected at 6 hr of development (late gastrula) and is probably present as early as 5 hr. The level of this template activity increased until the middle tail formation stage (11-12 hr after fertilization) and then remained constant until 16 hr of development (the final stage examined), 2 hr before hatching. These findings, and the results of previous actinomycin D inhibition experiments, indicate that mRNA for ascidian larval muscle acetylcholinesterase is first synthesized during gastrulation.

Quantitative regulation of acetylcholinesterase development in the muscle lineage cells of cleavage-arrested ascidian embryos

Some embryos of Ciona intestinalis which were permanently cleavage-arrested with cytochalasin B at the 1-cell, 4-cell, or 8-cell stages produced, after 12 or 16 h of development time (18 degrees C), a level of muscle acetylcholinesterase activity equal to that found in normal early and later larval stage embryos of the same age. Enzyme activity was measured quantitatively in single whole embryos by a colorimetric procedure using microdensitometry. Quantitative regulation of a differentiation end product indicated that the usual transcriptional and translational control mechanisms for that histospecific protein continued to operate normally in the cleavage-arrested embryos. Acetylcholinesterase expression was apparently regulated independently of the usual cell cytoplasmic volume in the muscle lineage cells and possibly also independently of the normal nuclear number in the lineage. There is an egg cytoplasmic determinant that is segregated into the muscle lineage cells during cleavage and which appears to specify the pathway of larval muscle development. Quantitative control of muscle acetylcholinesterase is possibly one of the consequences of how the agent releases genetic expression in the presumptive muscle cells. Quantitative regulation was not, however, a general functional activity of cleavage-arrested embryos. Mitochondrial cytochrome oxidase, an enzyme whose development is believed to be unaffected by cytoplasmic determinants, was not regulated quantitatively in cleavage-arrested embryos. Cytochrome oxidase activity of cleavage-arrested embryos, measured in single whole embryos by a colorimetric microdensitometry assay, increased only slightly during 16 h of development time whereas the activity in normal control embryos doubled during that time.

Developmental autonomy of muscle fine structure in muscle lineage cells of ascidian embryos

We have observed ultrastructural features of muscle differentiation in the muscle lineage cells of cleavage-arrested whole embryos and partial embryos of ascidians. Whole embryos of Ciona intestinalis and Ascidia ceratodes were cleavage-arrested with cytochalasin B at the 8-cell stage and reared to an age equivalent to several hours after hatching; these embryos formed extensive myofilaments which were often further organized into myofibrils of different sizes and densities in the peripheral cytoplasm of the two muscle lineage blastomeres (B4.1 pair). Developing myofibrils in cleavage-arrested embryos resembled the muscle elements observed in normal hatched larvae, but were less uniformly organized. A similar development of myofilaments and myofibrils occurred in the muscle lineage cells of multicellular partial embryos reared to "hatching" age. These partial embryos resulted from the isolated muscle lineage pair (B4.1) of blastomeres of the 8-cell stage (Ciona and Ascidia), and from a muscle lineage blastomere pair (B5.2) isolated at the 16-cell stage (Ascidia). Muscle lineage cells in the partial embryos were readily identified by the dense aggregates of mitochondria in their cytoplasm. Taken together, these results from the two kinds of partial embryo effectively eliminate inductive interactions with embryonic tissues other than mesodermal as a necessary factor in the onset of self-differentiation in muscle lineage cells. The relative complexity of muscle phenotype expressed in cleavage-arrested and partial embryos attests to an unusually strong developmental autonomy in the ascidian muscle lineages. This autonomy lends further support to the theory that a localized and segregated egg cytoplasmic determinant is responsible for larval muscle development in ascidian embryos.

Quantitative measurement by microdensitometry of tyrosinase (dopa oxidase) development in whole small ascidian embryos

Embryos of the ascidian, Ciona intestinalis, were fixed in either cold (5 degree C) 70% ethanol or cold absolute methanol during their tyrosinase development phase and incubated in buffered (pH 7.2) solutions of the enzyme substrate L-dihydroxyphenylalanine. Optical density of the reaction product (melanin) was measured in the whole small embryos at 450 nm with a Vickers M85 scanning and integrating microdensitometer. The frequency distribution of the reaction density in embryos of a population was Gaussian, and the mean optical density in embryos samples (N = 25) increased linearly with incubation time when a saturation level of substrate was used. Absolute optical density units of dopa oxidase activity in embryos increased linearly in proportion to the development time preceding melanin granulogenesis thereby suggesting that the enzyme activity measured by this procedure is proportional to the amount of tyrosinase present. Since this developmental increase in activity was blocked by treatment of the embryos with puromycin, an inhibitor of protein synthesis, the change is apparently caused by new enzyme synthesis. The microdensitometry assay also confirmed results obtained previously with a radiometric assay: embryos cleavage-inhibited at 7 h development time with cytochalasin B to produce giant melanocytes developed only the same amount of enzyme activity as control embryos.

Acetylcholinesterase development in extra cells caused by changing the distribution of myoplasm in ascidian embryos

This research shows that myoplasmic crescent material of the ascidian egg has both functional autonomy and functional specificity in establishing the differentiation pathway of muscle lineage cells. The cytoplasmic segregation pattern in eggs of Styela plicata was altered by compression of the embryos during third cleavage. This caused a meridional division instead of the normal equatorial third cleavage; first and second cleavages are meridional. Since eggs of S. plicata have a pronounced yellow myoplasmic crescent, one observes directly that third cleavage under compression resulted in a flat 8-cell stage with four cells containing yellow myoplasm instead of the two myoplasm-containing cells that would be formed by normal equatorial division at third cleavage. If such altered 8-cell-stage embryos were released from compression and kept from undergoing further divisions by continuous treatment with cytochalasin B, some embryos eventually developed histospecific acetylcholinesterase in three and four cells instead of in just the two muscle lineage cells found in cleavage-arrested normal 8-cell stages. The wider myoplasmic distribution effected by altering the division plane at third cleavage apparently caused a change in developmental fate of the extra cells receiving myoplasm. This meridional third cleavage also resulted in a changed nuclear lineage pattern. Two nuclei that would ordinarily be in ectodermal lineage cells after third cleavage were now associated with yellow myoplasm. Acetylcholinesterase development in these cells demonstrates that nuclear lineages are not responsible for muscle acetylcholinesterase development in the ascidian embryo.

Development of acetylchilinesterase during embryogenesis of the ascidian Ciona intestinalis

We have characterized the embryonic muscle cell cholinesterase of the solitary ascidian, Ciona intestinalis (L.). The effects of selective enzyme inhibitors and the inhibition of enzyme activity at high concentrations of substrate suggest that the muscle cell enzyme is an acetylcholinesterase (E.C. 3.1.1.7). After gastrulation and before hatching, acetylcholinesterase activity increased 35- to 40-fold; after hatching (18 hours postfertilization) this activity continued to increase, leveling off at about 36 hours of development. Histochemical observations showed that before hatching acetylcholinesterase was located principally in the muscle cells of the tail and, after hatching, it began to develop in cells of the adult musculature and brain. Inhibition of protein syntnesis by puromycin and of RNA synthesis by actinomycin D, suggest that both protein and RNA synthesis were required for the increase in acetylcholinesterase activity observed in unhatched embryos. Although the continued increase in enzyme activity duirng embryonic development was sensitive to puromycin at all times tested, the actinomycin D sensitivity of this increase was restricted to a discrete time that was completed by about 11 hours of development.

Melanoprotein: absence of a direct melanin-protein relationship in chick embryo melanocytes

Short-term synthesis of radioactivity labeled melanin (using DL-[2-14C]tyrosine or 2-[2-14C]thiouracil) by chick retinal pigment tissues in vitro was not influenced by inhibitors of protein synthesis, puromycin and cycloheximide. Co-ordinate synthesis of protein is, therefore, unnecessary for melanin synthesis, and melanoproteins must represent secondary interactions between melanin and protein. Melanin was isolated from chick embryo feather germs by extracting the proteins with hot dodecyl sulfate/mercaptoethanol. Melanin isolated from tissues incubated previously in L-[U-14C]valine medium had no associated radioactivity compared to the radioactivity of melanin prepared from tissues incubated in DL-[2-14C]tyrosine or 2-[2-14C]thiouracil. If melanoproteins exist at all, they are non-covalently bonded associations of melanin and melanosomal proteins.

Theophylline incorporation into the nucleic acids of theophylline-stimulated melanoma cells

Theophyllin, an inhibitor of cAMP-degrading phosphodiesterase, stimulates melanin biosynthesis in cultures of RPMI 3460 hamster melanoma cells. Although theophylline does produce an initial transient elevation of intracellular cAMP levels, long-term treatment with theophylline produces a significant decrease in cAMP content. There is an inhibition of the theophylline stimulation by dibutyryl-cAMP; this is apparently caused by interference of dibutyryl-cAMP with the uptake and incorporation of theophylline, as shown by experiments with 3H-theophylline. An alternative theory is that theophylline, being a methylxanthine compound, is metabolized by the cell and possibly causes melanotic stimulation by becoming incorporated into cellular nucleic acids or by altering the normal nucleic acid metabolism. The following observations are consistent with this theory: (u) 3H-theophylline was incorporated into both trichloroacetic acid (TCA)-soluble and TCA-insoluble cell fractions; most of the insoluble label became soluble after digestion with ribonuclease and deoxyribonuclease. (2) These nuclease digests of the 3H-theophylline-labeled TCA-insoluble cell fractions contained 3H-labeled material that chromatographed differently from normal nucleotides on ion exchange thin layer sheets. (3) The acid-soluble pool of 3H label disappeared rapidly while both the insoluble label and the induction of melanogenesis remained stable for 50 hr after the removal of exogenous 3H-theophylline.

Segregation during cleavage of a factor determining endodermal alkaline phosphatase development in ascidian embryos

Localized alkaline phosphatase activity (EC 3.1.3.1) develops progressively in endodermal tissues of the presumptive digestive system in Ciona intestinalis embryos. It was first detected histochemically at late gastrulation, and a puromycin sensitivity period coincident with this time suggests that new alkaline phosphatase is synthesized. Embryos in which cell division was blocked with cytochalasin B at early cleavage stages up to the 64-cell stage, eventually differentiated strong alkaline phosphatase activity in certain cells at each cleavage-arrested stage. The maximum cell numbers and their positions were identical to those of the previously known endodermal cell lineage. Actinomycin D did not prevent development of endodermal alkaline phosphatase when administered from fertilization onwards, nor did other inhibitors of RNA synthesis (chromomycin A3, cordycepin, and daunomycin). There is probably a preformed maternal mRNA for endodermal alkaline phosphatase present in the unfertilizec Ciona egg. Either this RNA itself, or some related translation factor, is localized in the egg cytoplasm and segregated during early cleavages into the endodermal cell lineage of the embryo.

Mammalian melanocytes do not use phenylalanine for melanin synthesis

Hamster melanoma cells (RPMI 3460) were examined for their ability to utilize phenylalanine for melanin biosynthesis. There was a small but significant incorporation of L-[1-1414C] phenylalanine into hot acid-insoluble cellular material in the presence of cycloheximide. However, this radioactivity was removable from the acid-insoluble fraction by pronase digestion. A similar percentage of L-[U-14C] leucine incorporation was likewise resistant to cycloheximide inhibition. Residual protein synthesis is apparently responsible for the incorporation of both amino acids. Cycloheximide did not inhibit melanin synthesis. These results suggest that mammalian melanocytes do not use phenylalanine for melanin synthesis. Phenylalanine is not incorporated directly into melanin, nor do the cells appear to convert it to tyrosine via a phenylalanine hydroxylase.

Stimulation of melanotic expression in a melanoma cell line by theophylline

Theophylline, a phosphodiesterase inhibitor, was found to be a potent stimulator of melanogenesis in the RPMI 3460 hamster melanoma cell line. This stimulation was greater than that caused by either dibutyryl cyclic AMP (db-cAMP) or another phosphodiesterase inhibitor, papaverine. Theophylline and db-cAMP treatments also produced strikingly different morphologies in the monolayered cells. The theophylline effect on melanogenesis was diminished by db-cAMP, whereas simultaneous treatment of cells with db-cAMP and papaverine produced greater stimulation of melanotic activity than either agent acting alone. Theophylline, therefore, may have phenotypic effects that are at least partially independent of phosphodiesterase inhibition. Theophylline stimulated melanin biosynthesis, as measured by rates of 2-[2-14C] thiouracil incorporation, and also caused an increase in the level of tyrosinase (EC 1.10.3.1) activity. This melanotic stimulation was prevented by the presence of cordycepin or cycloheximide. Theophylline inhibited DNA synthesis and mitosis in the melanoma cell cultures but stimulated protein synthesis. However, inhibition of proliferation and the first appearance of induced melanotic activity did not bear an immediate direct relationship to one another.

Effects of formalin on bladder urothelium

Formalin instillation into canine bladders was followed by serial radiographic and histologic evaluation. A generalized slough of epithelial tissue was seen with the deposition of an amorphous substance. Telangiectasia resulted in moderate bleeding. No ureterovesical junction obstruction was seen and reflux occurring in 60 per cent of the animals reverted to normal. Correlation with clinical experience is made.

Retroperitoneal fibrosis associated with retroperitoneal abscess

A case of retroperitoneal fibrosis associated with retroperitoneal abscess is reported. The causation and treatment of idiopathic and nonidiopathic retroperitoneal fibrosis are discussed.