In vivo lymph node CEST-Dixon MRI in breast cancer patients with metastatic lymph node involvement

PURPOSE

Axillary lymph nodes (LNs) often present a reservoir for metastatic breast cancer, yet metastatic LN involvement cannot be discerned definitively using diagnostic imaging. This study investigated whether in vivo CEST may discriminate LNs with versus without metastatic involvement.

METHODS

3T MRI was performed in patients with breast cancer before clinically-indicated mastectomy or lumpectomy with LN removal, after which LN metastasic involvement was determined using histological evaluation. Non-contrast anatomical imaging, as well as B0 and B1 field maps, were acquired in sequence with three-point CEST-Dixon (3D turbo-gradient-echo; factor = 25; TR/TE1/ΔTE = 851/1.35/1.1 ms; spatial-resolution = 2.5 × 2.5 × 6 mm; slices = 10; four sinc-gauss pulses with duty-cycle = 0.5, total saturation duration = 701.7 ms; B1  = 1.5 μT; saturation offsets = -5.5 to +5.5 ppm; stepsize = 0.2 ppm; scan duration = 6 min 30 s). The mean z-spectrum from LNs with (n = 20) versus without (n = 22) metastatic involvement were analyzed and a Wilcoxon rank-sum test (significance: p < 0.05) was applied to evaluate differences in B0, B1 , and magnetization transfer ratio (MTR) in differing spectral regions of known proton exchange (nuclear Overhauser effect [NOE], amide, amine, and hydroxyl) between cohorts.

RESULTS

No difference in axillary B1 (p = 0.634) or B0 (p = 0.689) was observed between cohorts. Elevated MTR was observed for the NOE (-1.7 ppm; MTR = 0.285 ± 0.075 vs. 0.248 ± 0.039; p = 0.048), amine (+2.5 ppm; MTR = 0.284 ± 0.067 vs. 0.234 ± 0.31; p = 0.005), and hydroxyl (+1 ppm; MTR = 0.394 ± 0.075 vs. 0.329 ± 0.055; p = 0.002) protons in LNs from participants with versus without metastatic involvement.

CONCLUSIONS

Findings are consistent with a unique metastatic LN microenvironment detectable by CEST-Dixon and suggest that CEST MRI may have potential for mapping LN metastasis non-invasively in vivo.

Exploratory Multisite MR Spectroscopic Imaging Shows White Matter Neuroaxonal Loss Associated with Complications of Type 1 Diabetes in Children

BACKGROUND AND PURPOSE

Type 1 diabetes affects over 200,000 children in the United States and is associated with an increased risk of cognitive dysfunction. Prior single-site, single-voxel MRS case reports and studies have identified associations between reduced NAA/Cr, a marker of neuroaxonal loss, and type 1 diabetes. However, NAA/Cr differences among children with various disease complications or across different brain tissues remain unclear. To better understand this phenomenon and the role of MRS in characterizing it, we conducted a multisite pilot study.

MATERIALS AND METHODS

In 25 children, 6-14 years of age, with type 1 diabetes across 3 sites, we acquired T1WI and axial 2D MRSI along with phantom studies to calibrate scanner effects. We quantified tissue-weighted NAA/Cr in WM and deep GM and modeled them against study covariates.

RESULTS

We found that MRSI differentiated WM and deep GM by NAA/Cr on the individual level. On the population level, we found significant negative associations of WM NAA/Cr with chronic hyperglycemia quantified by hemoglobin A1c (P < .005) and a history of diabetic ketoacidosis at disease onset (P < .05). We found a statistical interaction (P < .05) between A1c and ketoacidosis, suggesting that neuroaxonal loss from ketoacidosis may outweigh that from poor glucose control. These associations were not present in deep GM.

CONCLUSIONS

Our pilot study suggests that MRSI differentiates GM and WM by NAA/Cr in this population, disease complications may lead to neuroaxonal loss in WM in children, and deeper investigation is warranted to further untangle how diabetic ketoacidosis and chronic hyperglycemia affect brain health and cognition in type 1 diabetes.

Silent infarction in sickle cell disease is associated with brain volume loss in excess of infarct volume

Introduction

Sickle cell disease (SCD) increases cerebral infarct risk, but reported effects on brain volume have varied. More detailed information using larger cohorts and contemporary methods could motivate the use of longitudinal brain volume assessment in SCD as an automated marker of disease stability or future progression. The purpose of this study was to rigorously evaluate whether children and young adults with SCD have reduced gray matter volume (GMV) and white matter volume (WMV) compared to healthy controls using high-resolution MRI. We tested the hypotheses that (i) elevated CBF, a marker of cerebral hemodynamic compensation in SCD, is associated with global and regional brain atrophy, and (ii) silent cerebral infarct burden is associated with brain atrophy in excess of infarct volume.

Methods

Healthy controls (n = 49) and SCD participants without overt stroke (n = 88) aged 7-32 years completed 3 T brain MRI; pseudocontinuous arterial spin labeling measured CBF. Multivariable linear regressions assessed associations of independent variables with GMV, WMV, and volumes of cortical/subcortical regions.

Results

Reduced hemoglobin was associated with reductions in both GMV (p = 0.032) and WMV (p = 0.005); reduced arterial oxygen content (CaO2) was also associated with reductions in GMV (p = 0.035) and WMV (p = 0.006). Elevated gray matter CBF was associated with reduced WMV (p = 0.018). Infarct burden was associated with reductions in WMV 30-fold greater than the infarct volume itself (p = 0.005). Increased GM CBF correlated with volumetric reductions of the insula and left and right caudate nuclei (p = 0.017, 0.017, 0.036, respectively). Infarct burden was associated with reduced left and right nucleus accumbens, right thalamus, and anterior corpus callosum volumes (p = 0.002, 0.002, 0.009, 0.002, respectively).

Discussion

We demonstrate that anemia and decreased CaO2 are associated with reductions in GMV and WMV in SCD. Increased CBF and infarct burden were also associated with reduced volume in subcortical structures. Global WMV deficits associated with infarct burden far exceed infarct volume itself. Hemodynamic compensation via increased cerebral blood flow in SCD seems inadequate to prevent brain volume loss. Our work highlights that silent cerebral infarcts are just a portion of the brain injury that occurs in SCD; brain volume is another potential biomarker of brain injury in SCD.

Peter Joseph Zanetti

Initially a small animal vet, he worked for the PDSA before becoming a meat inspector.

Elevated magnetic resonance imaging measures of adipose tissue deposition in women with breast cancer treatment-related lymphedema

PURPOSE

Breast cancer treatment-related lymphedema (BCRL) is a common co-morbidity of breast cancer therapies, yet factors that contribute to BCRL progression remain incompletely characterized. We investigated whether magnetic resonance imaging (MRI) measures of subcutaneous adipose tissue were uniquely elevated in women with BCRL.

METHODS

MRI at 3.0 T of upper extremity and torso anatomy, fat and muscle tissue composition, and T₂ relaxometry were applied in left and right axillae of healthy control (n = 24) and symptomatic BCRL (n = 22) participants to test the primary hypothesis that fat-to-muscle volume fraction is elevated in symptomatic BCRL relative to healthy participants, and the secondary hypothesis that fat-to-muscle volume fraction is correlated with MR relaxometry of affected tissues and BCRL stage (significance criterion: two-sided p < 0.05).

RESULTS

Fat-to-muscle volume fraction in healthy participants was symmetric in the right and left sides (p = 0.51); in BCRL participants matched for age, sex, and BMI, fat-to-muscle volume fraction was elevated on the affected side (fraction = 0.732 ± 0.184) versus right and left side in controls (fraction = 0.545 ± 0.221, p < 0.001). Fat-to-muscle volume fraction directly correlated with muscle T₂ (p = 0.046) and increased with increasing level of BCRL stage (p = 0.041).

CONCLUSION

Adiposity quantified by MRI is elevated in the affected upper extremity of women with BCRL and may provide a surrogate marker of condition onset or severity.

CLINICAL TRIAL

NCT02611557.

A cross-sectional, case-control study of intracranial arterial wall thickness and complete blood count measures in sickle cell disease

In sickle cell disease (SCD), cerebral oxygen delivery is dependent on the cerebral vasculature's ability to increase blood flow and volume through relaxation of the smooth muscle that lines intracranial arteries. We hypothesised that anaemia extent and/or circulating markers of inflammation lead to concentric macrovascular arterial wall thickening, visible on intracranial vessel wall magnetic resonance imaging (VW-MRI). Adult and pediatric SCD (n = 69; age = 19.9 ± 8.6 years) participants and age- and sex-matched control participants (n = 38; age = 22.2 ± 8.9 years) underwent 3-Tesla VW-MRI; two raters measured basilar and bilateral supraclinoid internal carotid artery (ICA) wall thickness independently. Mean wall thickness was compared with demographic, cerebrovascular and haematological variables. Mean vessel wall thickness was elevated (P < 0·001) in SCD (1·07 ± 0·19 mm) compared to controls (0·97 ± 0·07 mm) after controlling for age and sex. Vessel wall thickness was higher in participants on chronic transfusions (P = 0·013). No significant relationship between vessel wall thickness and flow velocity, haematocrit, white blood cell count or platelet count was observed; however, trends (P < 0·10) for wall thickness increasing with decreasing haematocrit and increasing white blood cell count were noted. Findings are discussed in the context of how anaemia and circulating inflammatory markers may impact arterial wall morphology.

Monocarboxylate Transporters: Therapeutic Targets and Prognostic Factors in Disease

Solute carrier (SLC) transporters represent 52 families of membrane transport proteins that function in endogenous compound homeostasis and xenobiotic disposition, and have been exploited in drug delivery and therapeutic targeting strategies. In particular, the SLC16 family that encodes for the 14 isoforms of the monocarboxylate transporter (MCT) family plays a significant role in the absorption, tissue distribution, and clearance of both endogenous and exogenous compounds. MCTs are required for the transport of essential cell nutrients and for cellular metabolic and pH regulation. Recent publications have indicated their novel roles in disease, and thus their potential as biomarkers and new therapeutic targets in disease are under investigation. More research into MCT isoform function, specificity, expression, and regulation will allow researchers to exploit the potential utility of MCTs in the clinic as therapeutic targets and prognostic factors of disease.

N-Acetyl-l-cysteine effects on multi-species oral biofilm formation and bacterial ecology

Future therapies for the treatment of dental decay have to consider the importance of preserving bacterial ecology while reducing biofilm adherence to teeth. A multi-species plaque-derived (MSPD) biofilm model was used to assess how concentrations of N-acetyl-l-cysteine (NAC) (0, 0·1, 1, 10%) affected the growth of complex oral biofilms. Biofilms were grown (n = 96) for 24 h on hydroxyapatite discs in BMM media with 0·5% sucrose. Bacterial viability and biomass formation was examined on each disc using a microtitre plate reader. In addition, fluorescence microscopy and Scanning Electron Microscopy was used to qualitatively examine the effect of NAC on bacterial biofilm aggregation, extracellular components and bacterial morphology. The total biomass was significantly decreased after exposure of both 1% (from 0·48, with a 95% confidence interval of (0·44, 0·57) to 0·35, with confidence interval (0·31, 0·38)) and 10% NAC (0·14 with confidence interval (0·11, 0·17)). 16S rRNA amplicon sequencing analysis indicated that 1% NAC reduced biofilm adherence while preserving biofilm ecology.

SIGNIFICANCE AND IMPACT OF THE STUDY

As a compound with a wide safety margin, N-acetyl-l-cysteine (NAC) has the potential to be used as a long term anti-plaque bacteriostatic agent for managing chronic dental decay without substantially altering biofilm's bacterial ecology. The potential anti-caries benefit of NAC is directly related to reducing the biofilm coverage which reduces the degree of acid generation and the amount of time that the surface is exposed to a lower pH.

A reproducible oral microcosm biofilm model for testing dental materials

AIMS

Most studies of biofilm effects on dental materials use single-species biofilms, or consortia. Microcosm biofilms grown directly from saliva or plaque are much more diverse, but difficult to characterize. We used the Human Oral Microbial Identification Microarray (HOMIM) to validate a reproducible oral microcosm model.

METHODS AND RESULTS

Saliva and dental plaque were collected from adults and children. Hydroxyapatite and dental composite discs were inoculated with either saliva or plaque, and microcosm biofilms were grown in a CDC biofilm reactor. In later experiments, the reactor was pulsed with sucrose. DNA from inoculums and microcosms was analysed by HOMIM for 272 species. Microcosms included about 60% of species from the original inoculum. Biofilms grown on hydroxyapatite and composites were extremely similar. Sucrose pulsing decreased diversity and pH, but increased the abundance of Streptococcus and Veillonella. Biofilms from the same donor, grown at different times, clustered together.

CONCLUSIONS

This model produced reproducible microcosm biofilms that were representative of the oral microbiota. Sucrose induced changes associated with dental caries.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first use of HOMIM to validate an oral microcosm model that can be used to study the effects of complex biofilms on dental materials.

Quantifying dental biofilm growth using cross-polarization optical coherence tomography

AIMS

Quantifying the ex vivo growth of complex multispecies dental biofilms using cross-polarization 1310-nm optical coherence tomography (CP-OCT) system was investigated.

METHODS AND RESULTS

Bacterial microcosms, which were derived from plaque samples of paediatric subjects, were incubated in a biofilm reactor system containing discs of different dental materials for 72 h with daily sucrose pulsing (5×). CP-OCT analysis of biofilm mass was validated with crystal violet (CV) assays at various growth stages of these complex biofilms. CP-OCT was able to filter out the back-reflected signals of water layers in the hydrated biofilm and allowed for direct biofilm quantification. The overall depth-resolved scattering intensity of the biofilm showed very strong positive correlation with CV assay quantification (Spearman's ρ = 0.92) during the growth phase of the biofilm.

CONCLUSION

CP-OCT was able to quantify the mass of the biofilm by measuring the overall depth-resolved scattering of the biofilm.

SIGNIFICANCE AND IMPACT OF THE STUDY

CP-OCT has the ability to nondestructively monitor biofilm growth and elucidate the growth characteristics of these microcosms on different dental material compositions.

Reversal of profound rocuronium block monitored in three muscle groups with sugammadex in ponies

BACKGROUND

This clinical study evaluated the speed of reversal of profound rocuronium block in ponies using sugammadex and investigated the differences in onset and recovery from block in three different muscle groups.

METHODS

Anaesthesia was induced and maintained with isoflurane in oxygen 100% in eight ponies. Neuromuscular monitoring was performed at each site using acceleromyography: in the extensor muscles of the pelvic limb (peroneal nerve) and thoracic limb (radial nerve), and in the orbicularis oris muscle (OOM; facial nerve). Rocuronium 0.6 mg kg(-1) i.v. was administered, followed 5 min later by sugammadex 4 mg kg(-1) i.v. Onset time (onsetROC), maximum block, and time to recovery of the train-of-four ratio to 0.9 (TOFR=0.9) were recorded. The differences between monitored sites were compared using one-way anova followed by a post hoc Dunn's test.

RESULTS

Onset of ROC was significantly delayed in OOM compared with both limbs [pelvic limb, thoracic limb, and OOM: 43.1 (sd 16.9), 50.6 (15.9), and 204.4 (35.8) s, respectively; P<0.001]. Complete block was achieved in the pelvic and thoracic limbs, but in none of the eight ponies in the OOM [mean T1=15.3 (9.4)%; range: 7-36%]. No differences were observed between muscle sites in recovery to TOFR=0.9 [pelvic limb, thoracic limb, and OOM: 2.3 (0.9), 3.4 (1.7), and 2.8 (2.1) min, respectively]. No adverse effects of sugammadex were detected throughout the study period.

CONCLUSIONS

Sugammadex can be used to reverse profound rocuronium-induced block in ponies during isoflurane anaesthesia. Thoracic limb muscles represent a suitable alternative for monitoring neuromuscular block compared with pelvic limb muscles.

Is it time for the virtual chaperone in genitourinary medicine clinics?

The General Medical Council recommends that chaperones must be offered during intimate examinations. Implementation of these guidelines may serve to protect both patients and staff within the genitourinary (GU) medicine clinic, but is likely to have major ramifications from a practical, financial and staffing perspective. The Virtual Chaperone (VC) is an objective device making audio and visual recordings of patients' consultations and examinations. Information cannot be manipulated and is encrypted for security. It would not replace the human chaperone. This study investigated the attitudes of GU medicine staff and patients to the VC in an inner city sexual health clinic. Voluntary, anonymized questionnaires were distributed to all members of the multidisciplinary team and 200 patients. The patient response rate was 90% (n = 180). Only 40% of respondents felt the VC was acceptable in GU medicine clinics. Two-thirds felt unsure or were against the VC recording during consultations, and fewer wished the examination to be recorded. Most opted to switch off the video entirely. Almost 50% of respondents felt that the VC was designed to protect staff, whereas only 41% thought it would protect patients. The staff response rate was 69% (n = 35). Almost three-quarters of respondents were unsure or felt the device was unacceptable. Less than half would feel comfortable with the VC recording during consults. Overall, three-quarters of respondents were either unsure or did not support the introduction of the VC. There was a clear feeling (>80%) that the VC would protect staff and patients, 71% indicating that the trust would also benefit. Despite its success in other outpatient specialties, GU medicine staff and patients do not favour the introduction of the VC.

Remineralization of enamel caries can decrease optical reflectivity

The remineralization of enamel caries can lead to distinct optical changes within a lesion. We hypothesized that the restoration of mineral volume would result in a measurable decrease in the depth-resolved reflectivity of polarized light from the lesion. To test this hypothesis, we measured optical changes in artificial caries undergoing remineralization as a function of depth, using Polarization-sensitive Optical Coherence Tomography (PS-OCT). Lesions were imaged non-destructively before and after exposure to a remineralization regimen. After imaging, microradiographs of histological thin sections indicated that the significant reflectivity reduction measured by PS-OCT accurately represented the increase in mineral content within a larger repaired surface zone. Mineral volume changes arising from remineralization can be measured on the basis of the optical reflectivity of the lesion.

Two-stage revision of infected total knee replacements using articulating cement spacers and short-term antibiotic therapy

We present a series of 48 patients with infected total knee replacements managed by the use of articulating cement spacers and short-term parenteral antibiotic therapy in the postoperative period. All patients had microbiological and/or histological confirmation of infection at the first stage of their revision. They all underwent re-implantation and had a mean follow-up of 48.5 months (26 to 85).

Infection was successfully eradicated in 42 of the 48 patients (88%). Six had persistent infection which led to recurrence of symptoms and further surgery was successful in eliminating infection in four patients. These rates of success are similar to those of other comparable series. We conclude that protracted courses of intravenous antibiotic treatment may not be necessary in the management of the infected total knee replacement.

In addition, we analysed the microbiological, histological and serological results obtained at the time of re-implantation of the definitive prosthesis, but could not identify a single test which alone would accurately predict a successful outcome.

Imaging Artificial Caries on the Occlusal Surfaces with Polarization-Sensitive Optical Coherence Tomography

Polarization-sensitive optical coherence tomography (PS-OCT) is a nondestructive imaging system that can utilize near-infrared (IR) light to produce depth-resolved images of dental enamel and has the potential to monitor early enamel occlusal caries. The objective of this study was to investigate the relationship between the magnitude of backscattered light and depolarization recorded by PS-OCT with changes in the enamel mineral volume in an artificial caries model. Artificial lesions were created on a selected region on the occlusal surfaces of sound posterior teeth (n=10) using a well-characterized 14-day pH cycling model. An all-fiber-based PS-OCT system operating at 1,310 nm was used to collect serial images at day 0 and day 14 prior to tooth sectioning. The quantitative mineral content profile and relative mineral loss, DeltaZ (%volxmicrom), of the carious enamel samples were obtained from transverse sections using high-resolution digital microradiography (DM). Line profiles of PS-OCT and DM images were used to evaluate the artificial caries severity and depth. The integrated reflectivity of the perpendicular-axis PS-OCT image, quantifying lesion severity, was correlated to the DeltaZ of the caries lesions. There was also a strong correlation between the lesion depth calculated from both imaging modalities. PS-OCT can image and quantify artificial occlusal caries by measuring the increase in backscattering and depolarization of near-IR light. This optical method has promising applications for in vivo detection and monitoring of early enamel occlusal caries.

Comparison of the analgesic effects of meloxicam and carprofen administered preoperatively to dogs undergoing orthopaedic surgery

Thirty-two dogs undergoing operations to repair a torn cranial cruciate ligament or a fractured long bone were randomly allocated to one of two treatment groups in a study on postoperative pain. Sixteen of the dogs were given 4 mg/kg carprofen and the other 16 were given 0.2 mg/kg meloxicam subcutaneously before the operation. The signs of pain shown by the animals were assessed for 24 hours on a visual analogue scale, a discontinuous scoring system, and a score based on five behavioural and physiological variables. The dogs' heart and respiratory rates and their mean arterial blood pressures were also measured non-invasively at each assessment. Blood samples were taken before the surgery and 24 hours after it, and the concentrations of urea and creatinine were measured in plasma. Both drugs were effective in relieving the signs of pain for up to 24 hours in all the dogs. There were no significant changes in the concentrations of urea and creatinine, and no adverse effects were reported during the postoperative period.

Isoflurane to prolong medetomidine/ ketamine anaesthesia in six adult female chimpanzees (Pan troglodytes)

Six adult female chimpanzees (Pan troglodytes) were anaesthetised for the placement of intrauterine contraceptive devices, microchips for identification, routine blood sampling, and physical measurements. Anaesthesia was induced with medetomidine in combination with ketamine administered by intramuscular injection with a projectile syringe. Induction was smooth and rapid, but five of the animals were insufficiently relaxed for orotracheal intubation. The plane of anaesthesia was deepened by administering isoflurane delivered in oxygen and nitrous oxide, and general anaesthesia was maintained for up to 74 minutes. The action of medetomidine was reversed at the end of each procedure with atipamezole, and the animals recovered smoothly and uneventfully.

Dendrotoxin sensitive potassium channels modulate GABA but not glutamate release in the rat entorhinal cortex in vitro

We have previously shown that the anticonvulsant drug, phenytoin, increases the frequency and amplitude of spontaneous inhibitory postsynaptic currents at GABA synapses on principal neurones in the rat entorhinal cortex. This effect is similar to that seen at other GABA synapses following blockade of voltage-gated potassium channels (Kv1.1, 1.2 and 1.6) with alpha-dendrotoxin. In the present study we examined whether dendrotoxins can alter GABA release at synapses in the entorhinal cortex. We recorded spontaneous inhibitory postsynaptic currents using whole cell voltage clamp techniques in slices of rat entorhinal cortex in vitro. alpha-Dendrotoxin evoked an increase in frequency and amplitude of spontaneous inhibitory postsynaptic currents, an effect that was blocked by prior perfusion with tetrodotoxin. The effect of the toxin did not occlude the increase in spontaneous inhibitory postsynaptic currents seen with phenytoin. Indeed, the effect of the two drugs together was, at least, additive on GABA release. Perfusion with the specific Kv1.1 blocker, dendrotoxin-K had no effect on GABA release. In addition, alpha-dendrotoxin had no effect on frequency or amplitude of spontaneous excitatory postsynaptic currents at glutamate synapses on entorhinal cortex neurones. We conclude that K-channels containing the Kv1.2 and/or 1.6 subunits modulate the release of GABA, but not glutamate in the entorhinal cortex. The modulation of GABA release by phenytoin is unlikely to be due to an effect on these channels.

Postanaesthetic cerebral necrosis in five horses

After being anaesthetised for between one hour 40 minutes and seven hours, five adult horses developed acute neurological signs and extensive cerebrocortical necrosis. Four of them had had abdominal surgery for colic and one had had repeated orthopaedic interventions. Between five hours and seven days after the surgery, all five horses suddenly developed severe signs of a predominantly prosencephalic disturbance: bilateral blindness with normal pupillary light responses, abnormal behaviour varying from propulsive pacing to head pressing profound lethargy and generalised seizures. They were euthanased between 24 hours and three weeks after the onset of these signs. In three of the cases a gross examination of the brain revealed patchy malacia of the cerebral grey matter and some discolouration of the adjacent white matter. Microscopical examination revealed lesions that varied from laminar neuronal necrosis in the grey matter of the cerebral cortex to more diffuse necrosis of the cortex and underlying white matter. Four of the five cases had had a period of hypercapnea while anaesthetised, and two of them (and possibly a third) had also had hypoxaemia.

Polycomblike PHD fingers mediate conserved interaction with enhancer of zeste protein

The products of Polycomb group (PcG) genes are required for the epigenetic repression of a number of important developmental regulatory genes, including homeotic genes. Enhancer of zeste (E(Z)) is a Drosophila PcG protein that previously has been shown to bind directly to another PcG protein, Extra Sex Combs (ESC), and is present along with ESC in a 600-kDa complex in Drosophila embryos. Using yeast two-hybrid and in vitro binding assays, we show that E(Z) binds directly to another PcG protein, Polycomblike (PCL). PCL.E(Z) interaction is shown to be mediated by the plant homeodomain (PHD) fingers domain of PCL, providing evidence that this motif can act as an independent protein interaction domain. An association was also observed between PHF1 and EZH2, human homologs of PCL and E(Z), respectively, demonstrating the evolutionary conservation of this interaction. E(Z) was found to not interact with the PHD domains of three Drosophila trithorax group (trxG) proteins, which function to maintain the transcriptional activity of homeotic genes, providing evidence for the specificity of the interaction of E(Z) with the PCL PHD domain. Coimmunoprecipitation and gel filtration experiments demonstrate in vivo association of PCL with E(Z) and ESC in Drosophila embryos. We discuss the implications of PCL association with ESC.E(Z) complexes and the possibility that PCL may either be a subunit of a subset of ESC.E(Z) complexes or a subunit of a separate complex that interacts with ESC.E(Z) complexes.

The Trithorax-mimic allele of Enhancer of zeste renders active domains of target genes accessible to polycomb-group-dependent silencing in Drosophila melanogaster

Two antagonistic groups of genes, the trithorax- and the Polycomb-group, are proposed to maintain the appropriate active or inactive state of homeotic genes set up earlier by transiently expressed segmentation genes. Although some details about the mechanism of maintenance are available, it is still unclear how the initially active or inactive chromatin domains are recognized by either the trithorax-group or the Polycomb-group proteins. We describe an unusual dominant allele of a Polycomb-group gene, Enhancer of zeste, which mimics the phenotype of loss-of-function mutations in trithorax-group genes. This mutation, named E(z)(Trithorax mimic) [E(z)(Trm)], contains a single-amino-acid substitution in the conserved SET domain. The strong dominant trithorax-like phenotypes elicited by this E(z) allele suggest that the mutated arginine-741 plays a critical role in distinguishing between active and inactive chromatin domains of the homeotic gene complexes. We have examined the modification of E(z)(Trm) phenotypes by mutant alleles of PcG and trxG genes and other mutations that alter the phosphorylation of nuclear proteins, covalent modifications of histones, or histone dosage. These data implicate some trxG genes in transcriptional repression as well as activation and provide genetic evidence for involvement of histone modifications in PcG/trxG-dependent transcriptional regulation.

NR2B-containing NMDA autoreceptors at synapses on entorhinal cortical neurons

We have previously shown that presynaptic N-methyl-D-aspartate receptors (NMDARs) can facilitate glutamate release onto principal neurons in the entorhinal cortex (EC). In the present study, we have investigated the subunit composition of these presynaptic NMDARs. We recorded miniature alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (mEPSCs), from visually identified neurons in layers II and V of the EC in vitro. In both layers, bath application of the NR2A/B subunit-selective agonist, homoquinolinic acid (HQA), resulted in a marked facilitation of mEPSC frequency. Blockade of presynaptic Ca(2+) entry through either NMDARs or voltage-gated Ca(2+) channels with Co(2+) prevented the effects of HQA, confirming that Ca(2+) entry to the terminal was required for facilitation. When the NR2B-selective antagonist, ifenprodil, was applied prior to HQA, the increase in mEPSC frequency was greatly reduced. In addition, we found that an NMDAR antagonist blocked frequency-dependent facilitation of evoked release and reduced mEPSC frequency in layer V. Thus we have demonstrated that NMDA autoreceptors in layer V of the EC bear the NR2B subunit, and that NMDARs are also present at terminals onto superficial neurons.

Activation of presynaptic group III metabotropic glutamate receptors depresses spontaneous inhibition in layer V of the rat entorhinal cortex

Whole cell voltage clamp recording was used to investigate neurotransmitter release onto neurones in deep and superficial layers of rat entorhinal cortex in vitro. Activation of metabotropic glutamate receptors with the agonist (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid depressed spontaneous release of the inhibitory neurotransmitter GABA in layer V, but not in layer II. Depression of transmitter release did not persist in the presence of the sodium channel blocker tetrodotoxin. It seems likely that activation of presynaptic glutamate heteroreceptors inhibits action potential dependent release of neurotransmitter via a direct action at the presynaptic terminal. We confirmed that depression of inhibitory neurotransmission in layer V was mediated by group III metabotropic glutamate receptors using a specific group III antagonist, (RS)-cyclopropyl-4-phosphonophenylglycine. Application of the antagonist alone did not alter the frequency of spontaneous neurotransmitter release, suggesting that the metabotropic glutamate receptor is not tonically active. In layer V of the entorhinal cortex, activation of presynaptic metabotropic glutamate receptors enhances spontaneous glutamate release, and inhibits spontaneous release of GABA. These effects may combine to increase random action potential firing in this layer, thereby reducing its capacity for synchrony generation. Our results are consistent with an anticonvulsant action for group III metabotropic glutamate receptors in the entorhinal cortex.

Effects of medetomidine and buprenorphine administered for sedation in dogs

Medetomidine at doses of 10, 20 or 30 microg/kg was administered along with 10 microg/kg buprenorphine intramuscularly to 48 dogs requiring sedation for various diagnostic or therapeutic procedures. The heart rate, respiratory rate and degree of sedation were recorded before and 30 minutes after administration of the drugs. Heart rate fell by a mean of 55 per cent and respiratory rate by a mean of 62 per cent. Mean sedation scores were increased in all groups. Administration of atipamezole at the end of the period of sedation produced rapid recoveries, with a mean time to standing of 12 minutes. Animals that were anaesthetised required much less thiopentone than the 10 mg/kg recommended after premedication with acepromazine maleate.

Debunking the pathological model--the functions of an Internet discussion group

In recent years there has been a profusion of resources about Down syndrome available on the World Wide Web and for increasing numbers of people the internet is the resource first contacted when new information is required on a topic. The present paper examined the function of a discussion group which is used primarily by parents of people with Down syndrome. Qualitative research methodology (content analysis) was used to analyse the daily discussions over a 5 month period in 1998 (February to July) and over a 2-week follow up period six months later (January 1999). The analysis revealed themes of celebration, seeing the child before seeing the handicap, hope and optimism, a sense of purpose in life and of being like a family within this group.

Autobiographical memory and parasuicide in borderline personality disorder

BACKGROUND

Several studies have found that parasuicidal patients are poor at recalling specific autobiographical memories when tested with the word-cueing paradigm and two studies have reported some evidence that over-general recall is a risk factor for repetition of parasuicide. The aim of the present study was to test whether this association could be replicated with a sample of patients suffering from borderline personality disorder (BPD).

METHOD

Twenty-three patients with BPD completed a version of the Autobiographical Memory Test (AMT) and self-report measures of depression, anxiety and trait anger. In a structured interview, they also reported the number of times they had engaged in parasuicidal acts during the previous 4 months.

RESULTS

The number of general memories produced on the AMT made a significant contribution to the prediction of the frequency of parasuicidal acts in a multiple regression analysis but the partial correlation in the final equation was negative. That is, those who showed greatest over-general recall reported fewest parasuicidal acts. Anxiety and depression, but not trait anger, also made significant independent contributions to the prediction of parasuicide.

CONCLUSION

Over-general autobiographical recall may help to protect borderline individuals from parasuicidal acts by helping them to avoid distressing memories.

A pilot study of chronomodulated infusional 5-fluorouracil chemoradiation for pancreatic cancer

BACKGROUND

Dose limiting acute toxicity from chemoradiation for pancreatic cancer occurs in 15% -20% of patients treated with post-operative adjuvant therapy. Reported here is a pilot study using chronomodulated infusional 5-fluorouracil (5-FU) chemoradiation (CIC) for pancreatic cancer, a treatment designed to reduce normal tissue toxicity and maintain efficacy, with specific evaluation of acute and late morbidity, patterns of disease progression, and survival.

PATIENTS AND METHODS

Twenty-three patients with adenocarcinoma of the pancreas were treated with 5-FU CIC between January 1997 and September 1999. The median age was 64, and there were 9 males and 14 females. Six patients were considered unresectable and seventeen others were treated post-operatively. The median external beam irradiation dose was 50.4 Gy. 5-FU infusion was given five days per week (300 mg/m2/d) and the median total dose was 8.4 g/m2. The chronomodulated 5-FU infusion consists of a low basal infusion rate for 16 hours followed by an eight-hour escalating-deescalating infusion peaking at 10 p.m. All patients were followed from the time of initial diagnosis until last follow-up or death; the median follow-up was 16 months.

RESULTS

No RTOG grade 3 or 4 hematologic toxicity occurred. Twelve of seventeen patients treated postoperatively have been controlled locally, and seven patients have no evidence of disease. The median survival is 28 months and one-year actuarial survival is 88% in the group of resected patients. The 6 patients treated for unresectable disease have a median survival of 13 months.

CONCLUSIONS

Acute toxicity of 5-FU CIC appears to be less frequent and less severe than that reported with flat infusional or bolus 5-FU based chemoradiation used for adjuvant post-operative therapy for pancreatic cancer. This method may warrant further examination, as it may be attractive for the elderly or those who cannot tolerate the toxicity associated with standard post-operative treatment protocols.

Outpatient laparoscopic cholecystectomy: patient outcomes after implementation of a clinical pathway

OBJECTIVE

To determine the success of a clinical pathway for outpatient laparoscopic cholecystectomy (LC) in an academic health center, and to assess the impact of pathway implementation on same-day discharge rates, safety, patient satisfaction, and resource utilization.

SUMMARY BACKGROUND DATA

Laparoscopic cholecystectomy is reported to be safe for patients and acceptable as an outpatient procedure. Whether this experience can be translated to an academic health center or larger hospital is uncertain. Clinical pathways guide the care of specific patient populations with the goal of enhancing patient care while optimizing resource utilization. The effectiveness of these pathways in achieving their goals is not well studied.

METHODS

During a 12-month period beginning April 1, 1999, all patients eligible for an elective LC (n = 177) participated in a clinical pathway developed to transition LC to an outpatient procedure. These were compared with all patients undergoing elective LC (n = 208) in the 15 months immediately before pathway implementation. Successful same-day discharges, reasons for postoperative admission, readmission rates, complications, deaths, and patient satisfaction were compared. Average length of stay and total hospital costs were calculated and compared.

RESULTS

After pathway implementation, the proportion of same-day discharges increased significantly, from 21% to 72%. Unplanned postoperative admissions decreased as experience with the pathway increased. Patient characteristics, need for readmission, complications, and deaths were not different between the groups. Patients surveyed were highly satisfied with their care. Resource utilization declined, resulting in more available inpatient beds and substantial cost savings.

CONCLUSIONS

Implementation of a clinical pathway for outpatient LC was successful, safe, and satisfying for patients. Converting LC to an outpatient procedure resulted in a significant reduction in medical resource use, including a decreased length of stay and total cost of care.

Epidural analgesia in the dog and cat

SUMMARY

A brief outline of the history of epidural analgesia is followed by a review of the anatomy of the epidural space with particular reference to epidural block. The technique of epidural injection in the dog is described as are the indications for the technique. These include the provision of anaesthesia for such procedures as orthopaedic surgery of the hind limb and caesarian section. The cardiovascular effects of epidural block are discussed and suggestions are made for the prevention of hypotension. The various drugs and their combinations which may be used for epidural administration are outlined. The commonest used local anaesthetic agents are bupivacaine and lidocaine. Epidural administration of opioid drugs is a relatively new technique which is used to provide intra- and post-operative analgesia. Morphine is the drug of choice for this indication. The use of other classes of drugs, such as the alpha 2 agonists and ketamine, are also considered. A variety of side-effects, contra-indications and complications are described together with methods for reducing their incidence and effects.

Laminar differences in recurrent excitatory transmission in the rat entorhinal cortex in vitro

Paired intracellular recordings were used to investigate recurrent excitatory transmission in layers II, III and V of the rat entorhinal cortex in vitro. There was a relatively high probability of finding a recurrent connection between pairs of pyramidal neurons in both layer V (around 12%) and layer III (around 9%). In complete contrast, we have failed to find any recurrent synaptic connections between principal neurons in layer II, and this may be an important factor in the relative resistance of this layer in generating synchronized epileptiform activity. In general, recurrent excitatory postsynaptic potentials in layers III and V of the entorhinal cortex had similar properties to those recorded in other cortical areas, although the probabilities of connection are among the highest reported. Recurrent excitatory postsynaptic potentials recorded in layer V were smaller with faster rise times than those recorded in layer III. In both layers, the recurrent potentials were mediated by glutamate primarily acting at alpha-amino-3-hydroxy-5-methyl-4-isoxazole receptors, although there appeared to be a slow component mediated by N-methyl-D-aspartate receptors. In layer III, recurrent transmission failed on about 30% of presynaptic action potentials evoked at 0.2Hz. This failure rate increased markedly with increasing (2, 3Hz) frequency of activation. In layer V the failure rate at low frequency was less (19%), and although it increased at higher frequencies this effect was less pronounced than in layer III. Finally, in layer III, there was evidence for a relatively high probability of electrical coupling between pyramidal neurons. We have previously suggested that layers IV/V of the entorhinal cortex readily generate synchronized epileptiform discharges, whereas layer II is relatively resistant to seizure generation. The present demonstration that recurrent excitatory connections are widespread in layer V but not layer II could support this proposal. The relatively high degree of recurrent connections and electrical coupling between layer III cells may be a factor in it's susceptibility to neurodegeneration during chronic epileptic conditions.

Differential actions of PKA and PKC in the regulation of glutamate release by group III mGluRs in the entorhinal cortex

In a previous study we showed that activation of a presynaptically located metabotropic glutamate receptor (mGluR) with pharmacological properties of mGluR4a causes a facilitation of glutamate release in layer V of the rat entorhinal cortex (EC) in vitro. In the present study we have begun to investigate the intracellular coupling linking the receptor to transmitter release. We recorded spontaneous alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated excitatory postsynaptic currents (EPSCs) in the whole cell configuration of the patch-clamp technique, from visually identified neurons in layer V. Bath application of the protein kinase A (PKA) activator, forskolin, resulted in a marked facilitation of EPSC frequency, similar to that seen with the mGluR4a specific agonist, ACPT-1. Preincubation of slices with the PKA inhibitor H-89 abolished the effect of ACPT-1, as did preincubation with the adenylate cyclase inhibitor, SQ22536. Activation of protein kinase C (PKC) using phorbol 12 myristate 13-acetate (PMA) did not affect sEPSC frequency; however, it did abolish the facilitatory effect of ACPT-1 on glutamate release. A robust enhancement of EPSC frequency was seen in response to bath application of the specific PKC inhibitor, GF 109203X. Both H-89 and the group III mGluR antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG) abolished the effects of GF 109203X. These data suggest that in layer V of the EC, presynaptic group III mGluRs facilitate release via a positive coupling to adenylate cyclase and subsequent activation of PKA. We have also demonstrated that the PKC system tonically depresses transmitter release onto layer V cells of the EC and that an interaction between mGluR4a, PKA, and PKC may exist at these synapses.

The anticonvulsant, lamotrigine decreases spontaneous glutamate release but increases spontaneous GABA release in the rat entorhinal cortex in vitro

It has been suggested that the anticonvulsant effect of lamotrigine resides with it's ability to block voltage gated Na-channels at presynaptic sites, thus stabilizing the presynapse, and, consequently, reducing the release of synaptic transmitters. Neurochemical studies have shown that it can inhibit the veratrine-stimulated release of the excitatory transmitter, glutamate from cortical tissue, but that at slightly higher concentrations it also reduces the release of the inhibitory transmitter, GABA. In the present study we examined the effect of the drug on the release of these transmitters at synapses in the rat entorhinal cortex, using the whole-cell patch clamp technique to record spontaneous excitatory (EPSCs) and inhibitory postsynaptic currents (IPSCs). Lamotrigine reduced the frequency, but not the amplitude of spontaneous EPSCs. This clearly indicated a presynaptic effect to reduce the release of glutamate. However, the same effect was observed when we tested the drug on miniature EPSCs, recorded in the presence of TTX and Cd, showing that blockade of Na-channels or Ca-channels was not a prerequisite for inhibition of glutamate release. In contrast to it's effects on EPSCs, lamotrigine increased both the frequency and amplitude of spontaneous IPSCs, suggesting that the drug was acting presynaptically to enhance GABA release. Again, similar effects were seen with miniature IPSCs recorded in TTX. These opposite effects of lamotrigine on glutamate and GABA release are similar to those we have reported previously with phenytoin, and suggest that reciprocal modulation of the background release of the major excitatory and inhibitory transmitters may be a significant factor in dampening excitability in pathologically hyperexcitable cortical networks.

Cardiac output measured by lithium dilution, thermodilution, and transesophageal Doppler echocardiography in anesthetized horses

OBJECTIVE

To assess the suitability of lithium dilution as a method for measuring cardiac output in anesthetized horses, compared with thermodilution and transesophageal Doppler echocardiography.

ANIMALS

6 horses (3 Thoroughbreds, 3 crossbreeds).

PROCEDURE

Cardiac output was measured in 6 anesthetized horses as lithium dilution cardiac output (LiDCO), thermodilution cardiac output (TDCO), and transesophageal Doppler echocardiographic cardiac output (DopplerCO). For the LiDCO measurements, lithium chloride was administered i.v., and cardiac output was derived from the arterial lithium dilution curve. Sodium nitroprusside, phenylephrine hydrochloride, and dobutamine hydrochloride were used to alter cardiac output. Experiments were divided into 4 periods. During each period, 3 LiDCO measurements, 3 DopplerCO measurements, and 3 sets of 3 TDCO measurements were obtained.

RESULTS

70 comparisons were made between LiDCO, DopplerCO, and triplicate TDCO measurements over a range of 10 to 43 L/min. The mean (+/- SD) of the differences of LiDCO - TDCO was -0.86 +/- 2.80 L/min; LiDCO = -1.90 + 1.05 TDCO (r = 0.94). The mean of the differences of DopplerCO - TDCO was 1.82 +/- 2.67 L/min; DopplerCO = 2.36 + 0.98 TDCO (r = 0.94). The mean of the differences of LiDCO - DopplerCO was -2.68 +/- 3.01 L/min; LiDCO = -2.53 + 0.99 DopplerCO (r = 0.93).

CONCLUSIONS AND CLINICAL RELEVANCE

These results indicate that lithium dilution is a suitable method for measuring cardiac output in horses. As well as being accurate, it avoids the need for pulmonary artery catheterization and is quick and safe to use. Monitoring cardiac output during anesthesia in horses may help reduce the high anesthetic mortality in this species.

On-line quantitative analysis of surface electromyography of the pelvic floor in patients with faecal incontinence

BACKGROUND

Needle electromyography (EMG) remains the 'gold standard' for the assessment of external anal sphincter innervation. It is, however, an invasive and poorly tolerated technique. In this study a quantitative form of surface electromyography was compared with needle EMG of the external anal sphincter.

METHODS

Invasive needle EMG to assess mean fibre density and neuromuscular jitter was compared directly with quantitative surface EMG in 37 patients with faecal incontinence and 12 age-matched controls.

RESULTS

There was a significant positive correlation between mean fibre density on needle EMG and maximum turns rate on surface EMG (rs = 0.48 (95 per cent confidence interval 0.28-0.76), P = 0.003). Furthermore, surface EMG was able to discriminate between patients with normal neuromuscular jitter and those with increased jitter, a measure of progressive denervation and reinnervation, on the basis of reduced rectified mean surface signal (P = 0.02, Fisher's exact test).

CONCLUSION

Quantitative surface EMG may potentially replace invasive needle EMG as the investigation of choice in the assessment of anal sphincter electrophysiology.

Activation of presynaptic group III metabotropic receptors enhances glutamate release in rat entorhinal cortex

The role of group III metabotropic glutamate receptors (mGluRs) in modulating excitatory synaptic transmission was investigated in the rat entorhinal cortex (EC) in vitro. AMPA receptor-mediated excitatory postsynaptic currents (EPSCs) were recorded in the whole cell configuration of the patch-clamp technique from visually identified neurons in layers V and II. In layer V, bath application of the specific group III mGluR agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4, 500 microM) resulted in a marked facilitation of both spontaneous and activity-independent "miniature" (s/mEPSC) event frequency. The facilitatory effect of L-AP4 (100 microM) on sEPSC frequency prevailed in the presence of DL-2-amino-5-phosphonopentanoic acid (100 microM) but was abolished by the group III antagonist (RS)-cyclopropyl-4-phosphonophenylglycine (20 microM). These data confirmed that group III mGluRs, and not N-methyl-D-aspartate (NMDA) receptors were involved in the response to L-AP4. Bath application of the specific mGluR4a agonist (1S,3R,4S)-1-aminocyclopentane-1,2, 4-tricarboxylic acid (20 microM) also had a facilitatory effect on sEPSC frequency, suggesting involvement of mGluR4a. In layer II neurons, L-AP4 caused a reduction in sEPSC frequency but did not affect mEPSCs recorded in the presence of tetrodotoxin. These findings suggest that a group III mGluR with mGluR4a-like pharmacology is involved in modulating synaptic transmission in layer V cells of the EC. The effect on mEPSCs suggests that this receptor is located presynaptically and that its activation results in a direct facilitation of glutamate release. This novel facilitatory effect is specific to layer V and, to our knowledge, is the first report of a direct facilitatory action of group III mGluRs on synaptic transmission. In layer II, L-AP4 had an inhibitory effect on glutamate release similar to that reported in other brain regions.

Reciprocal modulation of glutamate and GABA release may underlie the anticonvulsant effect of phenytoin

Although conventional wisdom suggests that the effectiveness of phenytoin as an anticonvulsant is due to blockade of Na+-channels this is unlikely to be it's sole mechanism of action. In the present paper we examined the effects of phenytoin on evoked and spontaneous transmission at excitatory (glutamate) and inhibitory (GABA) synapses, in the rat entorhinal cortex in vitro. Evoked excitatory postsynaptic potentials at glutamate synapses exhibited frequency-dependent enhancement, and phenytoin reduced this enhancement without altering responses evoked at low frequency. In whole-cell patch-clamp recordings the frequency of excitatory postsynaptic currents resulting from the spontaneous release of glutamate was reduced by phenytoin, with no change in amplitude, rise time or decay time. Similar effects were seen on miniature excitatory postsynaptic currents, recorded in the presence of tetrodotoxin. Evoked inhibitory postsynaptic potentials at GABA synapses displayed a frequency-dependent decrease in amplitude. Phenytoin caused a reduction in this decrement without affecting the responses evoked at low frequency. The frequency of spontaneous GABA-mediated inhibitory postsynaptic currents, recorded in whole-cell patch mode, was increased by phenytoin, and this was accompanied by the appearance of much larger amplitude events. The effect of phenytoin on the frequency of inhibitory postsynaptic currents persisted in the presence of tetrodotoxin, but the change in amplitude distribution largely disappeared. These results demonstrate for the first time that phenytoin can cause a simultaneous reduction in synaptic excitation and an increase in inhibition in cortical networks. The shift in balance in favour of inhibition could be a major factor in the anticonvulsant action of phenytoin.

Autobiographical memory and dissociation in borderline personality disorder

BACKGROUND

This study investigated whether individuals with borderline personality disorder (BPD) tend to be overgeneral in their autobiographical recall and whether the extent of their overgeneral recall covaries with their susceptibilities to dissociative experiences, as expected on theoretical grounds.

METHODS

Twenty-three patients with BPD and 23 matched controls completed the Autobiographical Memory Test (AMT) and self-report measures of depression, anxiety, trait anger and dissociative experiences.

RESULTS

Participants with BPD scored significantly higher than the control group on the measures of depression, anxiety, trait anger, and dissociative experiences and also retrieved significantly more general memories on the AMT. The number of general memories retrieved by the BPD group correlated significantly with their dissociation scores but not with their scores on mood measures.

CONCLUSIONS

Patients with BPD have difficulties in recalling specific autobiographical memories. These difficulties are related to their tendency to dissociate and may help them to avoid episodic information that would evoke acutely negative affect.

Molecular genetic analysis of the Drosophila trithorax-related gene which encodes a novel SET domain protein

The products of the trithorax and Polycomb groups genes maintain the activity and silence, respectively, of many developmental genes including genes of the homeotic complexes. This transcriptional regulation is likely to involve modification of chromatin structure. Here, we report the cloning and characterization of a new gene, trithorax-related (trr), which shares sequence similarities with members of both the trithorax and Polycomb groups. The trr transcript is 9.6 kb in length and is present throughout development. The TRR protein, as predicted from the nucleotide sequence of the open reading frame, is 2431 amino acids in length and contains a PHD finger-like domain and a SET domain, two highly conserved protein motifs found in several trithorax and Polycomb group proteins, and in modifiers of position effect variegation. TRR is most similar in sequence to the human ALR protein, suggesting that trr is a Drosophila homologue of the ALR. TRR is also highly homologous to Drosophila TRITHORAX protein and to its human homologue, ALL-1/HRX. However, preliminary genetic analysis of a trr null allele suggests that TRR protein may not be involved in regulation of homeotic genes (i.e. not a member of the trithorax or Polycomb groups) or in position effect variegation.