ABSTRACT
Attention to urban agriculture (UA) has recently grown among practitioners, scientists, and the public, resulting in several initiatives worldwide. Despite the positive perception of modern UA and locally grown, fresh produce, the potential food safety risks connected to these practices may be underestimated, leading to regulatory gaps. Thus, there is a need for assessment tools to evaluate the food safety risks connected to specific UA initiatives, to assist practitioners in self-evaluation and control, and to provide policy makers and scholars a means to pursue and assess food safety in city regions, avoiding either a lack or an excess of regulation that could ultimately hinder the sector. To address this aim, this paper reviews the most recent and relevant literature on UA food safety assessments. Food safety indicators were identified first. Then, a food safety assessment framework for UA initiatives was developed. The framework uses business surveys and food analyses (if available) as a data source for calculating a food safety index for single UA businesses and the whole UA landscape of a given city region. The proposed framework was designed to allow its integration into the CRFS (City Region Food System) toolkit developed by FAO (Food and Agriculture Organization of the United Nations), RUAF foundation (Resource Centres on Urban Agriculture and Food Security) and Wilfrid Laurier University.
ABSTRACT
Sarcomas of the Ewing family of tumors are aggressive neoplasms occurring in bone and soft tissue of mostly children and young adults. Classical Ewing sarcomas are pathognomonically characterized by fusions between a gene of the RNA-binding TET family (EWSR1 or FUS) with a gene of the ETS-transcription family (FLI1, ERG, ETV1, ETV4 or FEV). Less frequent cases designated as Ewing-like sarcomas show different genetic rearrangements between EWSR1 and non-ETS genes (NFATC2, POU5F1, SMARCA5, PATZ, ZSG, SP3). Moreover, new molecular alterations biologically unrelated to Ewing sarcomas have recently been described in the category of undifferentiated round cell sarcomas including CIC-DUX4 fusions or BCOR alterations, each carrying unique gene expression signatures. In contrast to classical Ewing sarcomas, the morphologic spectrum of these tumor entities is much broader and includes round cell areas as well as spindled and myxoid components. The immunohistochemical profile with inconsistent CD99 positivity makes diagnosis more difficult and requires the use of a broad spectrum of antibodies and elaborate molecular work-up. Further studies for future therapeutic decision making in these newly described round cell sarcomas as well as for molecular subclassification of undifferentiated round cell sarcomas are ongoing.
Subject(s)
Sarcoma, Ewing , Sarcoma , Adenovirus E1A Proteins , Biomarkers, Tumor , Humans , Oncogene Proteins, Fusion , Proto-Oncogene ProteinsABSTRACT
This case report presents an osteosclerotic bone lesion in a 49-year-old man with MDM2 amplification. The final diagnosis shows metastasis to the bones from stomach cancer. In primary bone tumours, the MDM2 amplifications observed have been described for many other tumour entities as well, and therefore do not exclude bone metastasis from a carcinoma.
Subject(s)
Bone Neoplasms , Proto-Oncogene Proteins c-mdm2/genetics , Bone Neoplasms/genetics , Bone and Bones , Gene Amplification , Humans , Male , Middle AgedABSTRACT
BACKGROUND: Generalised anxiety disorder (GAD) is a frequent and severe disorder among older adults. For older adults with GAD the effect of the recommended treatment, cognitive behaviour therapy (CBT), is reduced. Physical exercise (PE) may enhance the effect of CBT by improving cognitive function and increasing levels of brain-derived neurotrophic factor (BDNF), a predictor of the effect of CBT in patients with anxiety. The aim of the study was to assess the feasibility of a randomized controlled trial (RCT) investigating treatment effect of the combination of CBT and PE for GAD in a sample of older adults, including procedures for assessment and treatment. METHODS: Four participants aged 62-70 years (M = 65.5, SD = 3.2) with a primary diagnosis of GAD were included. Participants received 15 weeks of PE in combination with 10 weeks of CBT. Participants completed self-report measures, and clinical, biological, physiological and neuropsychological tests at pre-, interim- and post-treatment. RESULTS: Procedures, protocols, and results are presented. One participant dropped out during treatment. For the three participants completing, the total adherence to PE and CBT was 80% and 100%, respectively. An independent assessor concluded that the completers no longer fulfilled the criteria for GAD after treatment. Changes in self-report measures suggest symptom reduction related to anxiety and worry. The sample is considered representative for the target population. CONCLUSIONS: The results indicate that combining CBT and PE for older adults with GAD is feasible, and that the procedures and tests are suitable and manageable for the current sample. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02690441. Registered on 24 February 2016, https://clinicaltrials.gov/ct2/show/NCT02690441 .
ABSTRACT
A 49-year-old woman consulted her general practitioner (GP) regarding epigastric pain that she had experienced for 2 months. Physical examination and laboratory results were unremarkable. An abdominal ultrasound indicated a solid pancreatic tumor, which was confirmed on subsequent CT and MRI. Endoscopic ultrasound (EUS) showed a well-defined heterogeneous, predominantly hypoechoic mass in the pancreatic body, so a neuroendocrine tumor (NET) was suspected. However, EUS-guided fine-needle aspiration (EUS-FNA) was performed and based on (immuno-)histochemical findings, the extremely rare diagnosis of a perivascular epithelioid cell tumor (PEComa) of the pancreas was made. Due to the malignant potential of pancreatic PEComas, laparoscopic left-sided pancreatectomy was performed. We present a case diagnosed by preoperative EUS-FNA highlighting the clinical and endosonographic features which help to distinguish it from its most important differential diagnosis, neuroendocrine tumors (NETs) of the pancreas.
ABSTRACT
BACKGROUND: The sporadic adult onset ataxias of unknown etiology (SAOA) denote the non-hereditary degenerative adult onset ataxias that are distinct from multiple system atrophy (MSA). OBJECTIVE: To define and characterize the clinical phenotype of sporadic adult onset ataxia of unknown etiology (SAOA). DESIGN: A survey of clinical features, nerve conduction and evoked potentials, autonomic tests, and magnetic resonance imaging (MRI)-based brain morphometry was conducted in patients with SAOA. PATIENTS: Study subjects were a consecutive sample of 27 patients (11 male, 16 female) who met the diagnostic criteria for SAOA (age 55 +/- 13 years; age at disease onset 47 +/- 14 years; disease duration 8 +/- 7 years). RESULTS: All patients presented with a cerebellar syndrome. The most frequent extracerebellar symptoms were decreased vibration sense in 70% and decreased or absent ankle reflexes in 33% of the patients. Nerve conduction studies revealed a polyneuropathy in 26% of the patients. Somatosensory evoked potentials were abnormal in 44%, and central motor conduction time in 17% of patients. Autonomic testing revealed an affected autonomic nervous system in 58% of patients. Voxel-based brain morphometry showed a predominant reduction of gray matter in the cerebellum which was significantly correlated with disease stages. A loss of white matter was found in both middle cerebellar peduncles and the outer edge of the pons. CONCLUSIONS: The data show that SAOA is a predominantly, but not exclusively cerebellar disorder. Clinical, electrophysiological, and imaging findings showed some similarities with multiple system atrophy which raises the question of an overlap of these two disorders.
Subject(s)
Ataxia/physiopathology , Electrophysiology/methods , Magnetic Resonance Imaging/methods , Adult , Age of Onset , Ataxia/pathology , Brain/pathology , Brain/physiopathology , Brain Mapping , Evoked Potentials, Motor/physiology , Evoked Potentials, Somatosensory/physiology , Female , Heart Rate/physiology , Humans , Male , Middle Aged , Neural Conduction/physiology , Reaction Time/physiology , Statistics, NonparametricABSTRACT
On account of the considerable variability of the clinical situation, treatment of soft tissue sarcoma requires an individually oriented multimodal approach. In the case of patients with superficial low-grade tumors measuring less than 5 cm in diameter, resection alone is usually adequate. In the event of medium-grade lesions, resection with negative margins, resection in combination with radiotherapy achieves excellent local control rates associated with an overall survival rate of almost 80%. In patients with high-grade sarcomas measuring more than 5 cm in diameter, local control can be achieved with resection and radiotherapy, although every second such patient develops metastases. For patients with local recurrence, further resection should be considered/performed. Radiotherapy is all the more effective, the smaller the postoperative tumor cell burden.
Subject(s)
Sarcoma , Combined Modality Therapy , Diagnosis, Differential , Histiocytoma, Malignant Fibrous/diagnosis , Humans , Incidence , Liposarcoma/diagnosis , Neoplasm Metastasis , Neoplasm Recurrence, Local , Prognosis , Sarcoma/diagnosis , Sarcoma/epidemiology , Sarcoma/mortality , Sarcoma/radiotherapy , Sarcoma/therapy , Sarcoma, Synovial/diagnosisABSTRACT
The plasma membrane has been implicated as one of the critical targets of photodynamic action. We observed that plasma membrane depolarization is an early event in the photodynamic action of zinc phthalocyanine disulfonate in mouse myeloma cells, showing both photosensitizer concentration and light dose dependence. The depolarization was observed immediately upon exposure to light, while membrane integrity was retained and showed a strong correlation with cell killing. In this study the use of channel blockers and alteration of ion concentration was employed to determine the factors involved in the membrane depolarization process. A general rise in cation permeability is associated with the depolarization. Loss of intracellular potassium was detected and an increase in intracellular free calcium was also observed. Sodium was found to strongly influence the photosensitized depolarization.
Subject(s)
Calcium/metabolism , Indoles/pharmacology , Light , Membrane Potentials/radiation effects , Organometallic Compounds/pharmacology , Animals , Calcium Channel Blockers/pharmacology , Cell Membrane/physiology , Cell Membrane/radiation effects , Cell Survival/drug effects , Indicators and Reagents , Membrane Potentials/drug effects , Mice , Potassium Channels/drug effects , Tumor Cells, CulturedABSTRACT
BACKGROUND/AIM: TGDc-01 is a new, portable, transpalpebral tonometry device. The aim of this study was to evaluate the reproducibility of this method, including intraobserver and interobserver deviations, and to compare the results with those of Goldmann applanation tonometry and palpation of intraocular pressure (IOP). METHODS: A total of 40 eyes of 20 healthy volunteers were included. Two independent parallel observers (1 and 2) performed three replicate measurements per eye, respectively, both using TGDc01 tonometry, one observer (3) performed three replicate measurements using Goldmann applanation tonometry, and one observer (4) measured the IOP via palpation. Intraindividual deviations within and between both observers using TGDc-01 tonometry and between all three methods were investigated about clinically relevance by comparison of medians and quartiles, statistically significance by pairwise sign tests. Comparisons between observers and methods were based on averaged IOP values of the three individual measurements for each observer and each patient. Intraobserver deviations were analysed by means of Friedman tests. RESULTS: Observers 1 and 2 showed a statistically significant intraobserver deviation when using TGCc-01 (Friedman p = 0.007 for observer 1 and p = 0.002 for observer 2). There was no statistically significant interobserver deviation between observers 1 and 2 (sign test p = 0.200); however, in 45% of the eyes interobserver deviations were larger than plus or minus 3 mm Hg. The median intraindividual deviation between TGDc-01 and Goldmann (TGDc-01 minus Goldmann) was 0 mm Hg (interquartile range -1; 2 mm Hg; sign test p = 0.522); but deviations were larger than plus or minus 3 mm Hg for 38% of the 40 eyes. Median intraindividual deviation between TGDc-01 and palpation (TGDc-01 minus palpation) was -2 mm Hg (interquartile range -4; 1 mm Hg; sign test p = 0.018), but deviations were larger than plus or minus 3 mmHg for 43% of eyes. Median intraindividual deviation between Goldmann and palpation (palpation minus Goldmann) was 2 mm Hg (interquartile range -2; 4 mm Hg; p = 0.429), but deviations were larger than plus or minus 3 mm Hg in 48% of the eyes. CONCLUSION: Interobserver deviations using TGDc-01 tonometry and intraindividual deviations between TGDc-01 tonometry, Goldmann applanation tonometry, and palpation of IOP were found to be clinically relevant. Thus, according to our results TGDc-01 could not be established as a substitute or diagnostic alternative method for Goldmann applanation tonometry. But as deviations between TGDc01 and Goldmann turned out smaller than between palpation of IOP and Goldmann, TGDc-01 seems to provide a better choice for tonometry in patients, in whom Goldmann applanation tonometry is not possible.
Subject(s)
Intraocular Pressure , Tonometry, Ocular/methods , Adult , Equipment Design , Female , Humans , Male , Observer Variation , Palpation , Reproducibility of Results , Tonometry, Ocular/instrumentationABSTRACT
Laser-assisted microdissection is a powerful tool for the analysis of morphologically defined cell populations. We report here that the combination of microdissection and real-time RT-PCR technologies together with an optimized RNA microscale extraction procedure allows the reproducible determination of gene expression levels in archival formalin-fixed, paraffin-embedded tissue samples.
Subject(s)
Dissection/methods , Gene Expression , Reverse Transcriptase Polymerase Chain Reaction , Histological Techniques , Humans , Lasers , Neoplasms/metabolism , RNA/metabolism , Receptor, ErbB-2/metabolismABSTRACT
Alertness, the most basic intensity aspect of attention, probably is a prerequisite for the more complex and capacity demanding domains of attention selectivity. Behaviorally, intrinsic alertness represents the internal (cognitive) control of wakefulness and arousal; typical tasks to assess optimal levels of intrinsic alertness are simple reaction time measurements without preceding warning stimuli. Up until now only parts of the cerebral network subserving alertness have been revealed in animal, lesion, and functional imaging studies. Here, in a 15O-butanol PET activation study in 15 right-handed young healthy male volunteers for this basic attention function we found an extended right hemisphere network including frontal (anterior cingulate-dorsolateral cortical)-inferior parietal-thalamic (pulvinar and possibly the reticular nucleus) and brainstem (ponto-mesencephalic tegmentum, possibly involving the locus coeruleus) structures, when subjects waited for and rapidly responded to a centrally presented white dot by pressing a response key with the right-hand thumb.
Subject(s)
Attention/physiology , Brain/anatomy & histology , Brain/physiology , Signal Detection, Psychological , Adult , Analysis of Variance , Brain Stem/anatomy & histology , Brain Stem/physiology , Frontal Lobe/anatomy & histology , Frontal Lobe/physiology , Humans , Male , Nerve Net/anatomy & histology , Nerve Net/physiology , Parietal Lobe/anatomy & histology , Parietal Lobe/physiology , Reaction Time , Reference Values , Thalamus/anatomy & histology , Thalamus/physiology , Tomography, Emission-Computed , VolunteersABSTRACT
In order to study neural systems which are involved in motor timing we used whole-brain functional resonance imaging while subjects performed a paced finger-tapping task (PFT) with their right index finger. During one condition, subjects were imaged while tapping in synchrony with tones separated by a constant interval (auditory synchronisation, AS), followed by tapping without the pacing stimulus (auditory continuation, AC). In another condition, subjects were imaged while tapping in synchrony with a visual stimulus presented at the same frequency as the tones (visual synchronisation, VS) followed by a tapping sequence without visual pacing (visual continuation, VC). The following main results were obtained: (1) tapping in the context of visual pacing was generally more variable than tapping in the context of auditory stimuli; (2) during all conditions, a fronto-parietal network was active including the dorsal lateral premotor cortex (dPMC), M1, S1, inferior parietal lobule (LPi), supplementary motor cortex (SMA), the right cerebellar hemisphere, and the paravermial region; (3) stronger activation in the bilateral ventral premotor cortex (vPMC), the left LPi, the SMA, the right inferior cerebellum, and the left thalamus during both auditory conditions (AS and AC) compared to the visual conditions (VS and VC); (4) stronger activation in the right superior cerebellum, the vermis, and the right LPi during the visual conditions (VS and VC); (5) similar activations for the AS and AC conditions; but (6) marked differences between the VS and VC conditions especially in the dorsal premotor cortex (dPMC) and LPi areas; and (7) finally, there were no activations in the auditory and visual cortices when the pacing stimuli were absent. These findings were taken as evidence for a general difference between the motor control modes operative during the auditory and visual conditions. Paced finger tapping in the context of auditory pacing stimuli relies more on brain structures subserving internal motor control while paced finger-tapping in the context of visual pacing stimuli relies on brain structures relying on the subserving processing or imagination of visual pacing stimuli.
Subject(s)
Acoustic Stimulation , Cerebral Cortex/physiology , Fingers/physiology , Movement/physiology , Photic Stimulation , Adult , Brain Mapping , Cues , Humans , Magnetic Resonance Imaging , MaleABSTRACT
This study examined the neural areas involved in the recognition of both emotional prosody and phonemic components of words expressed in spoken language using echo-planar, functional magnetic resonance imaging (fMRI). Ten right-handed males were asked to discriminate words based on either expressed emotional tone (angry, happy, sad, or neutral) or phonemic characteristics, specifically, initial consonant sound (bower, dower, power, or tower). Significant bilateral activity was observed in the detection of both emotional and verbal aspects of language when compared to baseline activity. We found that the detection of emotion compared with verbal detection resulted in significant activity in the right inferior frontal lobe. Conversely, the detection of verbal stimuli compared with the detection of emotion activated left inferior frontal lobe regions most significantly. Specific analysis of the anterior auditory cortex revealed increased right hemisphere activity during the detection of emotion compared to activity during verbal detection. These findings illustrate bilateral involvement in the detection of emotion in language while concomitantly showing significantly lateralized activity in both emotional and verbal detection, in both the temporal and frontal lobes.
Subject(s)
Auditory Cortex/physiology , Dominance, Cerebral/physiology , Emotions/physiology , Magnetic Resonance Imaging , Verbal Learning/physiology , Adult , Brain Mapping , Humans , Language , MaleABSTRACT
The relationship between activity within the human auditory cortices and the duration of heard tones was investigated by measuring the hemodynamic response with functional magnetic resonance imaging. We demonstrate that there is no significant influence of stimulus duration as used here on the intensity and spatial extent of the hemodynamic response in the auditory cortices. We found however, that the time course of the hemodynamic response to the repeated stimulus presentation exhibited a characteristic decline after the first stimulus exposure during the activation period. The possible reasons for this time course are currently unknown, however, several factors may be involved, including top-down mechanisms and/or the interplay of tissue perfusion and oxygen consumption.
Subject(s)
Auditory Cortex/metabolism , Brain Mapping/methods , Evoked Potentials, Auditory/physiology , Oxygen/blood , Acoustic Stimulation , Adult , Humans , Male , Time FactorsABSTRACT
Whole-head functional MR images were acquired while 10 subjects were asked to tap with their right index finger in synchrony with a visual stimulus appearing regularly with a frequency of 1.5 Hz, or irregularly with a mean frequency of 1.5 Hz. Performance data show that during regular tapping most taps were close to stimulus onset. However, when the subjects paced their tapping according to the irregular stimuli, most taps appeared about 300 ms after the onset of the pacing stimuli. Comparing the brain activations resulting from regular tapping with those from irregular tapping, we found increased activation in left precuneus only. Comparing irregular versus regular tapping shows increased activity in right cerebellar nuclei and vermis, left ventrolateral thalamus, left sensorimotor cortex, left and right pre-SMA and left SMA proper. These results show that during irregular pacing the motor areas are more strongly activated than during regular pacing. In addition, further neural systems are involved in the motor control during irregular pacing: cerebellar vermis and a cerebello-thalamo-cortical system. The latter is supposedly involved in error correction in the context of visually guided movements.
Subject(s)
Brain Mapping/methods , Magnetic Resonance Imaging , Motor Cortex/physiology , Movement/physiology , Photic Stimulation/methods , Somatosensory Cortex/physiology , Adult , Auditory Cortex/blood supply , Auditory Cortex/physiology , Behavior/physiology , Cerebellum/physiology , Female , Fingers/physiology , Functional Laterality/physiology , Hemodynamics/physiology , Humans , Male , Parietal Lobe/physiology , Periodicity , Reaction Time/physiology , Reference Values , Temporal Lobe/blood supply , Temporal Lobe/physiology , Ventral Thalamic Nuclei/physiologyABSTRACT
We studied the effects of different movement speeds of unimanual right hand movements on functional magnetic resonance signal changes in the sensorimotor cortex using echo planar imaging (EPI). Six healthy right-handed subjects were scanned at rest and while executing a finger tapping task with their right index finger. Movement frequency was visually paced at rates ranging from 0.5 to 5 Hz, separated by 0.5 Hz steps. The blood oxygen level dependent (BOLD) response within the left sensorimotor cortex was linearly and positively related to movement frequency. However, this relation holds (r2 = 0.91) only for movement frequencies faster than 1 Hz (1.5-5 Hz). For the slower frequencies there was an initial sharp increase of the BOLD response from 0.5 to 1 Hz followed by an activity drop for 1.5 Hz. These results are compatible with the idea that two different motor control modes are operative during slow or fast movements. During slow movements a computational demanding on-line feedback control mode is operative resulting in strong BOLD signals indicating extensive neural activity. During faster movements on the other hand a program-like motor control mode is operative resulting in less demanding neural computations. The amount of neural computation for the latter control mode increases with increasing movement speed.
Subject(s)
Motor Cortex/physiology , Somatosensory Cortex/physiology , Adult , Fingers/physiology , Humans , Linear Models , Magnetic Resonance Imaging , Male , Movement/physiology , Oxygen/bloodABSTRACT
This study investigates the importance of DNA damage in viral inactivation by phenothiazines and light. Phenothiazines, including methylene blue (MB), toluidine blue and azure B are of particular interest because of their ability to bind to nucleic acids in vitro. Initial studies employing phages T7, MS2 and PM2 indicated that both DNA and RNA phages as well as enveloped and nonenveloped phages can be inactivated by phenothiazine photosensitization. PM2, which contains a lipid-protein bilayer and supercoiled DNA, was used for the mechanistic studies to model blood-borne viruses. Viral DNA damage was assessed following treatment of phage to known levels of viral inactivation by extracting the DNA and analyzing for both direct and piperidine-catalyzed strand cleavage by gel electrophoresis. DNA strand cleavage was found to be both sensitizer concentration and light dose dependent. Both viral inactivation and DNA damage were found to be oxygen-dependent events. In parallel experiments, strand cleavage of isolated PM2 DNA treated with MB and light was also found to be oxygen dependent, in contrast to some previous reports. Transfection studies, which measure the infectivity of the extracted viral DNA, indicated that DNA from MB-treated phage was just as capable of generating progeny virus as the untreated controls. It was therefore concluded that the observed DNA damage is not correlated with loss of phage infectivity.
Subject(s)
Bacteriophages/radiation effects , DNA Damage , Bacteriophage T7/drug effects , Bacteriophage T7/radiation effects , Bacteriophages/drug effects , Blood/microbiology , DNA, Viral/drug effects , DNA, Viral/radiation effects , Humans , In Vitro Techniques , Levivirus/drug effects , Levivirus/radiation effects , Methylene Blue/pharmacology , Photosensitizing Agents/pharmacologyABSTRACT
The effect of photodynamic action on plasma membranes was examined using a fluorescent potentiometric indicator [di-SBA-C2(3)] to measure alterations in the plasma membrane potential of mouse myeloma cells treated with zinc phthalocyanine sulfonate and light. Plasma membrane depolarization was observed to be an early event in photodynamic action, showing both photosensitizer concentration and light dose dependence. Depolarization occurred while membrane integrity was retained and appears to be an early event preceding cell death.
Subject(s)
Cell Membrane/physiology , Indoles/pharmacology , Organometallic Compounds/pharmacology , Tumor Cells, Cultured/physiology , Zinc/pharmacology , Animals , Cell Line , Cell Membrane/drug effects , Cell Membrane/radiation effects , Light , Membrane Potentials/drug effects , Membrane Potentials/radiation effects , Mice , Multiple Myeloma , Potentiometry , Tumor Cells, Cultured/drug effects , Tumor Cells, Cultured/radiation effectsABSTRACT
Singlet oxygen activates the mutagenicity of several benzo[a]pyrene (BP) derivatives in the absence of mammalian metabolic action. This has been demonstrated using a separated-surface-sensitizer system for generating chemically pure singlet oxygen, eliminating most of the complications that arise with singlet oxygen generation by conventional photosensitization. Salmonella typhimurium bacteria were exposed to singlet oxygen in the presence of certain BP derivatives and the mutation frequency determined with an azaguanine forward mutation assay. The mutation frequency was increased by exposure to singlet oxygen compared to light-only controls for those BP derivatives that were saturated at either the 7,8 or 9,10 positions but not both. The increase in mutation frequency depends on both the concentration of BP derivative and on the dose of singlet oxygen. Mutation frequency was also significantly increased when bacteria were treated with a solution of trans-7,8-dihydrodiol-BP that had been separately exposed to singlet oxygen, unequivocally demonstrating that the mutagenicity is due to the formation of a product of BP derivative oxidation by singlet oxygen and that this product has a lifetime at least on the order of minutes in acetonitrile. The requirement for singlet oxygen rather than some other form of reactive oxygen was confirmed by determination of the gas phase lifetime of the intermediate responsible for activating mutagenicity. This was performed by measuring the dependence of the mutation frequency on the distance separating the sensitizer from the target. This gives a value of 88 +/- 35 ms, which is in excellent agreement with the mean value of 89 ms calculated from previous independent determinations of the gas phase lifetime of singlet oxygen reported in the literature.