Association between continuity and access in primary care: a retrospective cohort study

BACKGROUND

Continuity of care is a tenet of primary care. Our objective was to explore the relation between a change in access to a primary care physician and continuity of care.

METHODS

We conducted a retrospective cohort study among physicians in a primary care network in southwest Alberta who measured access consistently between 2009 and 2016. We used time to the third next available appointment as a measure of access to physicians. We calculated the provider and clinic continuity, discontinuity and emergency department use based on the physicians' own panels. Physicians who improved, worsened or maintained their level of access within a given year were assessed in multilevel models to determine the association with continuity of care at the physician and clinic levels and the emergency department.

RESULTS

We analyzed data from 190 primary care physicians. Physicians with improved access increased provider continuity by 6.8% per year, reduced discontinuity by 2.1% per year, and decreased emergency department encounters by 78 visits per 1000 patients per year compared to physicians with stable access. Physicians with worsening access had a 6.2% decrease in provider continuity and an increased number of emergency department encounters (64 visits per 1000 panelled patients per year) compared to physicians with stable access.

INTERPRETATION

Changes in access to primary care can affect whether patients seek care from their own physician, from another clinic or at the emergency department. Improving access by reducing the delay in obtaining an appointment with one's primary care physician may be one mechanism to improve continuity of care.

Implementation of a Physician-Patient Attachment Initiative in Alberta

Attachment to a primary care physician (PCP) is a foundational component of the Patient's Medical Home. Yet how can attachment exist in a system that does not limit where patients seek care? This article describes a top-down approach with the ideologies of a bottom-up collaborative to address attachment within an Alberta primary care network. The steps taken to reduce the number of patients listed on multiple PCP panels from 27% to 4% will be described. Learnings from this initiative suggest that direct involvement with providers, coupled with engaged physician leadership, can create a local system of information delivery that supports the attachment of patients to their most responsible PCP.

The origin and evolution of mutations in acute myeloid leukemia

Most mutations in cancer genomes are thought to be acquired after the initiating event, which may cause genomic instability and drive clonal evolution. However, for acute myeloid leukemia (AML), normal karyotypes are common, and genomic instability is unusual. To better understand clonal evolution in AML, we sequenced the genomes of M3-AML samples with a known initiating event (PML-RARA) versus the genomes of normal karyotype M1-AML samples and the exomes of hematopoietic stem/progenitor cells (HSPCs) from healthy people. Collectively, the data suggest that most of the mutations found in AML genomes are actually random events that occurred in HSPCs before they acquired the initiating mutation; the mutational history of that cell is "captured" as the clone expands. In many cases, only one or two additional, cooperating mutations are needed to generate the malignant founding clone. Cells from the founding clone can acquire additional cooperating mutations, yielding subclones that can contribute to disease progression and/or relapse.

Background mutations in parental cells account for most of the genetic heterogeneity of induced pluripotent stem cells

To assess the genetic consequences of induced pluripotent stem cell (iPSC) reprogramming, we sequenced the genomes of ten murine iPSC clones derived from three independent reprogramming experiments, and compared them to their parental cell genomes. We detected hundreds of single nucleotide variants (SNVs) in every clone, with an average of 11 in coding regions. In two experiments, all SNVs were unique for each clone and did not cluster in pathways, but in the third, all four iPSC clones contained 157 shared genetic variants, which could also be detected in rare cells (<1 in 500) within the parental MEF pool. These data suggest that most of the genetic variation in iPSC clones is not caused by reprogramming per se, but is rather a consequence of cloning individual cells, which "captures" their mutational history. These findings have implications for the development and therapeutic use of cells that are reprogrammed by any method.

DNMT3A mutations in acute myeloid leukemia

BACKGROUND

The genetic alterations responsible for an adverse outcome in most patients with acute myeloid leukemia (AML) are unknown.

METHODS

Using massively parallel DNA sequencing, we identified a somatic mutation in DNMT3A, encoding a DNA methyltransferase, in the genome of cells from a patient with AML with a normal karyotype. We sequenced the exons of DNMT3A in 280 additional patients with de novo AML to define recurring mutations.

RESULTS

A total of 62 of 281 patients (22.1%) had mutations in DNMT3A that were predicted to affect translation. We identified 18 different missense mutations, the most common of which was predicted to affect amino acid R882 (in 37 patients). We also identified six frameshift, six nonsense, and three splice-site mutations and a 1.5-Mbp deletion encompassing DNMT3A. These mutations were highly enriched in the group of patients with an intermediate-risk cytogenetic profile (56 of 166 patients, or 33.7%) but were absent in all 79 patients with a favorable-risk cytogenetic profile (P<0.001 for both comparisons). The median overall survival among patients with DNMT3A mutations was significantly shorter than that among patients without such mutations (12.3 months vs. 41.1 months, P<0.001). DNMT3A mutations were associated with adverse outcomes among patients with an intermediate-risk cytogenetic profile or FLT3 mutations, regardless of age, and were independently associated with a poor outcome in Cox proportional-hazards analysis.

CONCLUSIONS

DNMT3A mutations are highly recurrent in patients with de novo AML with an intermediate-risk cytogenetic profile and are independently associated with a poor outcome. (Funded by the National Institutes of Health and others.).

Peripheral ethanolamine plasmalogen deficiency: a logical causative factor in Alzheimer's disease and dementia

Although dementia of the Alzheimer's type (DAT) is the most common form of dementia, the severity of dementia is only weakly correlated with DAT pathology. In contrast, postmortem measurements of cholinergic function and membrane ethanolamine plasmalogen (PlsEtn) content in the cortex and hippocampus correlate with the severity of dementia in DAT. Currently, the largest risk factor for DAT is age. Because the synthesis of PlsEtn occurs via a single nonredundant peroxisomal pathway that has been shown to decrease with age and PlsEtn is decreased in the DAT brain, we investigated potential relationships between serum PlsEtn levels, dementia severity, and DAT pathology. In total, serum PlsEtn levels were measured in five independent population collections comprising >400 clinically demented and >350 nondemented subjects. Circulating PlsEtn levels were observed to be significantly decreased in serum from clinically and pathologically diagnosed DAT subjects at all stages of dementia, and the severity of this decrease correlated with the severity of dementia. Furthermore, a linear regression model predicted that serum PlsEtn levels decrease years before clinical symptoms. The putative roles that PlsEtn biochemistry play in the etiology of cholinergic degeneration, amyloid accumulation, and dementia are discussed.

Resolution-dependent estimates of multiple sclerosis lesion loads

BACKGROUND

Changes in brain lesion loads assessed with magnetic resonance imaging obtained at 1.5 Telsa (T) are used as a measure of disease evolution in natural history studies and treatment trials of multiple sclerosis.

METHODS

A comparison was made between the total lesion volume and individual lesions observed on 1.5 T images and on high-resolution 4 T images. Lesions were quantified using a computer-assisted segmentation tool.

RESULTS

There was a 46% increase in the total number of lesions detected with 4 T versus 1.5 T imaging (p < 0.005). The 4 T also showed a 60% increase in total lesion volume when compared with the 1.5 T (p < 0.005). In several instances, the 1.5 T scans showed individual lesions that coalesced into larger areas of abnormality in the 4 T scans. The relationship between individual lesion volumes was linear (slope 1.231) showing that the lesion volume observed at 4 T increased with the size of the lesion detected at 1.5 T. The 4 T voxels were less than one quarter the size of those used at 1.5 T and there were no consistent differences between their signal-to-noise ratios.

CONCLUSIONS

The increase in signal strength that accompanied the increase in field strength compensated for the loss in signal amplitude produced by the use of smaller voxels. This enabled the acquisition of images with improved resolution, resulting in increased lesion detection at 4 T and larger lesion volumes.

Generation and annotation of the DNA sequences of human chromosomes 2 and 4

Human chromosome 2 is unique to the human lineage in being the product of a head-to-head fusion of two intermediate-sized ancestral chromosomes. Chromosome 4 has received attention primarily related to the search for the Huntington's disease gene, but also for genes associated with Wolf-Hirschhorn syndrome, polycystic kidney disease and a form of muscular dystrophy. Here we present approximately 237 million base pairs of sequence for chromosome 2, and 186 million base pairs for chromosome 4, representing more than 99.6% of their euchromatic sequences. Our initial analyses have identified 1,346 protein-coding genes and 1,239 pseudogenes on chromosome 2, and 796 protein-coding genes and 778 pseudogenes on chromosome 4. Extensive analyses confirm the underlying construction of the sequence, and expand our understanding of the structure and evolution of mammalian chromosomes, including gene deserts, segmental duplications and highly variant regions.

Pathology-guided MR analysis of acute and chronic experimental allergic encephalomyelitis spinal cord lesions at 1.5T

PURPOSE

To directly correlate spinal cord pathology of guinea pigs with experimental allergic encephalomyelitis (EAE) to the MRI data obtained at 1.5T.

MATERIALS AND METHODS

Spinal cords from EAE animals were imaged in vivo with the following MRI sequences: T2-FSE, PD-FSE, fluid-attenuated inversion recovery (FLAIR)-FSE, T2-CSE, T1-CSE, T1-CSE + gadolinium-DTPA (Gd-DTPA), PD-CSE, and short-tau inversion recovery (STIR)-FSE. The spinal cords were removed and the lesions with specific pathological compositions were identified by histological analysis. Regions of interest (ROIs) were drawn on the corresponding MR images, and signal-to-noise ratios (SNRs) were measured for each MR sequence and compared with controls.

RESULTS

The receiver operating characteristic (ROC) analysis of STIR-FSE and PD-CSE was able to differentiate tissue that contained cellular infiltrates with a high degree of accuracy. The SNRs of T2-FSE, STIR-FSE, T2-CSE, PD-CSE, and T1-CSE + Gd-DTPA were elevated in lesions that contained cellular infiltrates alone, whereas the SNRs of PD-CSE and T1-CSE + Gd-DTPA were reduced in demyelinated lesions that also contained inflammation.

CONCLUSION

The SNR difference between the two lesion groups suggests that the combination of STIR-FSE, PD-CSE, and T1-CSE + Gd-DTPA sequences may be useful for differentiating inflammatory lesions containing demyelination from lesions with inflammation alone.

In vivo 4.0-T magnetic resonance investigation of spinal cord inflammation, demyelination, and axonal damage in chronic-progressive experimental allergic encephalomyelitis

PURPOSE

To image and dissect the lumbar spinal cord of guinea pigs with chronic-progressive experimental allergic encephalomyelitis (CP-EAE) and directly correlate the pathology to the magnetic resonance (MR) image data obtained at 4 T and determine if these MR contrasts can accurately differentiate a specific type of pathology from control tissue.

MATERIALS AND METHODS

The amount of inflammation, demyelination, and axonal pathology were quantified in the whole cord cross sections. The signal intensities (SIs) for 228 individual regions of interest (ROIs) (normal-appearing white matter (NAWM) and tissue containing inflammation with or without demyelination) were measured directly from the corresponding area on the MR images.

RESULTS

Conventional MR contrast SIs and magnetization transfer ratio (MTR) were related to the degree of demyelination and presence of inflammation. MTR and proton density-weighted (PDw) SIs were both moderately related to axonal density. The SIs for NAWM and in lesions containing both cellular infiltrates and demyelination in all conventional MR contrast images were also increased, whereas the MTR was decreased when compared to control tissue.

CONCLUSION

The SIs from the conventional MR contrasts and MTR at 4 T were sensitive to the presence of disease within CP-EAE spinal cord, but were not specific to the underlying pathology.

The DNA sequence of human chromosome 7

Human chromosome 7 has historically received prominent attention in the human genetics community, primarily related to the search for the cystic fibrosis gene and the frequent cytogenetic changes associated with various forms of cancer. Here we present more than 153 million base pairs representing 99.4% of the euchromatic sequence of chromosome 7, the first metacentric chromosome completed so far. The sequence has excellent concordance with previously established physical and genetic maps, and it exhibits an unusual amount of segmentally duplicated sequence (8.2%), with marked differences between the two arms. Our initial analyses have identified 1,150 protein-coding genes, 605 of which have been confirmed by complementary DNA sequences, and an additional 941 pseudogenes. Of genes confirmed by transcript sequences, some are polymorphic for mutations that disrupt the reading frame.

Initial sequencing and comparative analysis of the mouse genome

The sequence of the mouse genome is a key informational tool for understanding the contents of the human genome and a key experimental tool for biomedical research. Here, we report the results of an international collaboration to produce a high-quality draft sequence of the mouse genome. We also present an initial comparative analysis of the mouse and human genomes, describing some of the insights that can be gleaned from the two sequences. We discuss topics including the analysis of the evolutionary forces shaping the size, structure and sequence of the genomes; the conservation of large-scale synteny across most of the genomes; the much lower extent of sequence orthology covering less than half of the genomes; the proportions of the genomes under selection; the number of protein-coding genes; the expansion of gene families related to reproduction and immunity; the evolution of proteins; and the identification of intraspecies polymorphism.

Comparison of four automated hematology analyzers

OBJECTIVE

To compare four automated hematology analyzers for efficiency and sensitivity.

DESIGN

Four automated hematology analyzers were compared in a side by side study: Bayer ADVIA 120 (Bayer Diagnostic Division, Tarrytown, NY), Beckman Coulter GEN S (Beckman Coulter, Brea, CA), Abbott CELL DYN 3500 and CELL DYN 4000 (Abbott Diagnostics, Santa Clara, CA). 164 specimens were analyzed for cell counts, indices, and the automated WBC differential (DLC). Tallies were kept of all interventions, defined as any parameter necessitating examination of a stained blood smear by a clinical laboratory scientist. A 400-cell manual differential was performed on each specimen and used as the reference to prepare truth tables for each type of WBC.

PATIENTS

Specimens comprised regular runs from this tertiary care teaching hospital. These included inpatients, outpatients, and oncology patients, including bone marrow transplant patients.

MAIN OUTCOME MEASURES

Results from the truth tables were used for calculating sensitivity and efficiency for each analyzer. Each DLC parameter was analyzed for variance using the one-way ANOVA test.

RESULTS

No intervention was required for 103 of 164 specimens for the CELL DYN 3500; the ADVIA gave 70 reportable DLCs without intervention, the GEN S provided 91 and the CELL DYN 4000 resulted in 117 of 164 DLCs without intervention. Agreement or efficiency was 65% for the CELL DYN 3500, 41% for the ADVLA, 58% for the GEN S, and 79% for the CELL DYN 4000. Sensitivity was 67% for the CELL DYN 3500, 86% for the ADVIA, 76% for the GEN S, and 71% for the CELL DYN 4000. Probability of significant variation was as follows for each parameter: % neutrophil 0.8747, % lymphocyte 0.8830, % monocyte 0.0296, % eosinophil 0.7903, and % basophil <.0001.

CONCLUSION

The analyzers tested were acceptable for routine laboratory work. Selection would depend on individual need with respect to sensitivity and efficiency. The clinical significance of disagreement between the DLC and the manual differential remains to be determined.

Agonistic behavior in groups of limbic epileptic male rats: pattern of brain damage and moderating effects from normal rats

Different ratios of normal male rats and male rats in which limbic seizures had been induced by a single systemic injection of lithium and pilocarpine were housed in groups of six. The group ratios ranged along the continuum from all normal rats to all experimental rats. The average numbers of episodes of boxing, biting and mounting--thrusting per rat per hour per group were recorded by direct observation (red light) for 1 h during the midscotophase. Groups that contained less than two normal rats exhibited significantly elevated amounts of agonistic (boxing, biting) behavior but not mounting behavior. Multiple regression analyses showed that combinations of neuronal loss within only two to three areas accommodated at least 50% of the variance in the numbers of these behaviors.

Normal spatial memory following postseizure treatment with ketamine: selective damage attenuates memory deficits in brain-damaged rodents

Within 30 min after the initiation of status epilepticus (SE) by lithium and pilocarpine, rats were injected with either acepromazine or ketamine. Compared to the rats that had received the acepromazine, the group that had received the ketamine displayed more accurate spatial memory. Their scores did not differ significantly from normal (non-seized) controls. Although the ketamine treatment did not significantly change the amount of neuronal loss within about 100 Paxinos and Watson structures, it was neuroprotective for several structures within the thalamus and portions of the temporal and parietal cortices. Ketamine-treated rats, however, displayed markedly more damage within the entorhinal cortices and amygdalohippocampal area.

Initial sequencing and analysis of the human genome

The human genome holds an extraordinary trove of information about human development, physiology, medicine and evolution. Here we report the results of an international collaboration to produce and make freely available a draft sequence of the human genome. We also present an initial analysis of the data, describing some of the insights that can be gleaned from the sequence.

Differential effects of low frequency, low intensity (<6 mG) nocturnal magnetic fields upon infiltration of mononuclear cells and numbers of mast cells in Lewis rat brains

Immediately after inoculation to induce experimental allergic encephalomyelitis, 64 female Lewis rats were exposed to either a reference condition (<10 nT) or to one of two frequencies (7 Hz, 40 Hz) of magnetic fields whose two intensities (either 50 nT or 500 nT) were amplitude-modulated for 6 min once per hour between midnight and 8 h for 15 nights. Rats that had been exposed to the 7 Hz, low intensity fields displayed fewer numbers of foci of infiltrations of mononuclear cells compared to all other groups that did not differ significantly from each other. Rats exposed to the 5 mG (500 nT), 40 Hz magnetic fields displayed more foci in the right thalamus while those exposed to the 5 mG, 7 Hz fields displayed more foci in the left thalamus. Numbers of mast cells within the thalamus were also affected by the treatments. These results suggest that weak magnetic fields can affect the infiltration of immunologically responsive cells and the presence of mast cells in brain parenchyma. Implications for the potential etiology of 'electromagnetic sensitivity' symptoms are discussed.

Suppression of experimental allergic encephalomyelitis is specific to the frequency and intensity of nocturnally applied, intermittent magnetic fields in rats

Female Lewis rats (n=72) were inoculated with an emulsion of spinal cord and complete Freund's adjuvant. They were then exposed for approximately 6 min every hour between midnight and 08:00 h for 2 weeks to either 7 or 40 Hz amplitude-modulated magnetic fields whose temporal pattern was designed to simulate a (geomagnetic) storm sudden commencement. The peak strengths of the fields averaged between either 30-50 nT (low intensity) or 500 nT (high intensity). Rats exposed to the 7 Hz, low intensity magnetic fields displayed significantly less severe overt signs of experimental allergic encephalomyelitis than rats exposed to either of the two intensities of the 40 Hz fields, the high intensity 7 Hz field, or the reference (<10 nT) condition. The latter groups did not differ significantly from each other. Predicted severity based upon the numbers of foci of infiltrations of lymphocytes within the brains of the rats also demonstrated the ameliorating effects of the low intensity, 7 Hz exposures. These results suggest very specific characteristics of complex, weak magnetic fields within the sleeping environment could affect the symptoms of autoimmunity.

Ventricular enlargement and the lithium/pilocarpine seizure model: possible explanation for agonistic behaviour

Rats treated with the NMDA-blocker, ketamine hydrochloride 30 minutes after the induction of seizures by lithium pilocarpine exhibited statistically smaller lateral ventricles in the left hemisphere compared to rats that had received acepromazine after the induction of these seizures. In addition, the ketamine-treated rats had more neurons and glial cells surrounding the ventricles. These results suggest a neuroprotective effect of ketamine, such that there is less atrophy surrounding the ventricles and therefore, a smaller degree of dilatation. The possibility that insidious neuronal atrophy and death associated with the ventricular enlargement encourages the marked aggression in the epileptic rats not treated by ketamine is discussed.

Suppression of experimental allergic encephalomyelitis in rats exposed nocturnally to magnetic fields

After inoculation with spinal cord and complete Freund's adjuvant, female Lewis rats were exposed to weak, 7 Hz complex magnetic fields or to the control condition. The computer-generated magnetic field, whose amplitude varied from 15 nT to 60 nT every 6 to 12 sec, was presented for 6 min every hour between midnight and 0800 of the scotophase. In two replicates of the experiment, the rats exposed to the field displayed statistically significant suppression relative to sham-field controls (effect size = 55%) of the overt symptoms of experimental allergic encephalomyelitis which included hindleg paralyses.

Infiltration of lymphocytes in the limbic brain following stimulation of subclinical cellular immunity and low dosages of lithium and a cholinergic agent

This experiment was designed to investigate the hypothesis that single small dosages of lithium (1.5 mEq/kg), the muscarinic agent pilocarpine (15 mg/kg) and spinal cord emulsion encourage perivascular infiltration of lymphocytes into the brain even when overt symptoms of experimental allergic encephalomyelitis are not apparent. The brains of rats that had received this small dosage of lithium and pilocarpine exhibited discernable infiltrations of lymphocytes within limbic tracts but no discernable neuronal loss. Although the brains of the rats that displayed overt seizures following larger dosages of lithium (3 mEq/kg) and pilocarpine (30 mg/kg) exhibited the usual pattern of neuronal loss within multiple thalamic and limbic structures and conspicuous foci of lymphocytic infiltration (particularly within the hippocampal formation) the correlation between the numbers of foci and the proportions of neuronal damage in these structures was not significant statistically. These results indicate that infiltrations of lymphocytes into brain parenchyma are not simple artifacts of the amount of neuronal damage and may be sensitive toxicological markers for subclinical interactions between drugs and immune responses.

Fulminant CNS perivascular lymphocytic proliferation: association with sargramostim, a hematopoietic growth factor

Sargramostim (GM-CSF) therapy was instituted in a 49-year-old woman with hepatitis C on chronic interferon alpha-2b therapy. Within two weeks, she developed progressive confusion, lethargy, and gait disturbance. At autopsy 4 months later, diffuse perivascular nonmonoclonal lymphoid infiltrates were demonstrated throughout the central nervous system (CNS). As the use of hematopoietic growth factors in clinical practice increases, potential adverse effects, such as the fulminant CNS lymphocytic proliferation in this patient, are more likely to be encountered.

"Subclinical" dosages of lithium and pilocarpine that do not evoke overt seizures affect long-term spatial memory but not learning in rats

After training is an automated radial maze, 11 male rats were injected with either "subclinical" dosages of lithium and pilocarpine or saline and then tested 5 days or 4 months later. When employed as their own controls or when compared with a saline-injected reference group, the rats that had received the lithium and pilocarpine displayed memory deficits but not learning learning deficits after the longest of the two delays (effect size was 41%). These results suggest that subtle disruption in memory but not learning to criterion could be associated with "subclinical electrical seizures" or the micromorphological changes associated with this activity.

Emergent properties following brain injury: the claustrum as a major component of a pathway that influences nociceptive thresholds to foot shock in rats

Flinch (pain) thresholds for electric current delivered to the feet were correlated with the amount of necrosis within the diencephalon and telencephalon for rats in which seizures had been induced by lithium and pilocarpine about two months before the testing. The shared variance of the quantitative damage within the claustrum, the anterior part of the paraventricular nucleus of thalamus, (central) mediodorsal thalamus, and lateral amygdala (ventromedial part) explained 81% of the variance in the nociceptive (flinch) thresholds. A primary role of the claustrum within the neuropathways that mediate the response to the interoceptive and "painful" characteristics of stimuli is indicated. The concept of primary pathways versus "emergent" pathways subsequent to excitotoxic damage within the neuromatrix is discussed.

Long-term consequences of subtle stimuli during the first twenty-four hours of seizure-induced brain injury

Chronically epileptic (induced by a single systemic injection of lithium and pilocarpine about 30 days before the experiment began) male rats were trained within a radial maze while they were administered either GABA-pentin (Neurontin), or prednisolone or given no treatment. There was no significant improvement in learning or memory between the groups. Numbers of trials per day were positively correlated with the time required to display the overt stereotyped forelimb clonus after the single pilocarpine injection. The numbers of correct trials completed during the first few days of acquisition were significantly greater for the rats that had receive weak (1 microT) complex, pulsed magnetic fields over the right hemisphere during the first 24 hr. after seizure induction than for those who received the same field over the left hemisphere or that had been exposed to reference conditions. Implications of the enhanced sensitivity of limbic neurons to subtle electromagnetic interaction during electrical lability are discussed.

Demands during maze. learning in limbic epileptic rats: selective damage in the thalamus?

A qualitatively evident enhancement of chromolytic neurons within the lateral posterior thalamus of rats in which limbic seizures had been induced by lithium and pilocarpine and who were later trained for spatial memory was assessed quantitatively. The significant increase in the numbers of chromolytic neurons and the decrease in the numbers of normal neurons for these rats compared to the reference brains suggested these morphological changes were recent. The hypothesis that excessive stimulation of the lateral posterior nucleus by daily training in a radial maze may have facilitated the necrosis was supported by the inverse relationship between a linear combination of the numbers of normal neurons and oligodendroglia and the rate of learning during the earlier but not the later sessions. An implication for iatrogenic effects from rehabilitation of humans following brain injury was suggested.

Interhemispheric modulation of dopamine receptor interactions in unilateral 6-OHDA rodent model

A critical assumption in the unilateral 6-hydroxydopamine (6-OHDA) model is that interactions between the intact and denervated hemispheres do not influence the response to insult. The present study examined this issue by assessing the effects of unilateral substantia nigra 6-OHDA lesions in rats that previously had received corpus callosum transections, a treatment designed to minimize interhemispheric influences. Quantitative autoradiography in the caudate-putamen ipsilateral to the lesion revealed that corpus callosum transection did not alter the increase in D2-like receptors ([125I]-epidepride-labeled sites) that is induced by unilateral 6-OHDA lesion. There were no effects of either 6-OHDA lesion or transection on D1 receptor density ([125I]-SCH23982 autoradiography). As a functional endpoint, dopamine-stimulated cAMP efflux was measured in superfused striatal slices. In this paradigm, the net effect of dopamine (DA) represents a combination of D1 receptor-mediated stimulation and D2 receptor-mediated inhibition. 6-OHDA lesion increased cAMP efflux induced by exposure to 100 microM DA alone; corpus callosum transection did not alter this effect. An interaction between 6-OHDA lesion and transection status was revealed, however, by comparison of results obtained with DA alone vs. DA plus the D2 antagonist sulpiride (to block the D2 inhibitory effects of 100 microM DA). This comparison revealed two important effects of 6-OHDA lesion in rats with an intact corpus callosum: 1) a moderate decrease in dopamine D1 receptor-mediated stimulation; and 2) a dramatic decrease in the ability of D2 receptors to inhibit this stimulation. Corpus callosum transection prevented these effects of 6-OHDA. These results provide a biochemical demonstration of D1:D2 receptor uncoupling in unilateral 6-OHDA lesioned rats, and suggest that interhemispheric influences (e.g., contralateral cortico-striatal glutamatergic projections) may contribute to lesion-induced alterations in D1:D2 receptor interactions.

Dihydrexidine, a novel full efficacy D1 dopamine receptor agonist

The present work provides a detailed pharmacological characterization of dihydrexidine (DHX) (trans-10,11-dihydroxy- 5,6,6a,7,8,12b-hexahydrobenzo[a]phenanthridine), the first high-potency, full efficacy, bioavailable D1 dopamine receptor agonist. DHX represents a new conformationally rigid structural class of dopamine receptor ligands. It competes stereoselectively and potently for D1 binding sites in rat striatal membranes labeled with [3H]SCH23390 with an IC50 of about 10 nM compared to about 30 nM for the prototypical D1 agonist SKF38393. Like other dopamine agonists, DHX has a shallow competition curve (nH = ca. 0.7) that can be fitted by a two-site model consisting of high-affinity (63%; KD = 3 nM) and low-affinity (37%; KD = 75 nM) sites. DHX was screened for activity against 40 other binding sites, and was inactive (IC50 greater than 10 microM) against all except D2 dopamine receptors (IC50 = 130 nM) and alpha 2 adrenoreceptors (IC50 = ca. 230 nM). Functionally, DHX is a full efficacy dopamine D1 agonist. In homogenates of rat striatum, DHX or dopamine doubles the rate of cyclic AMP synthesis, whereas SKF38393 only causes a maximal increase of about 50%. These effects of DHX are blocked by the selective D1 antagonist SCH23390, but are not affected by D2, 5-hydroxytryptamine2, muscarinic, or alpha or beta adrenergic antagonists. Because DHX is known to cause D2-like behavioral effects at high doses, the nature of its D2 activity was characterized using prolactin release as an end-point. DHX and the prototypical D2 agonist quinpirole both caused a significant inhibition of the prolactin release induced by 5-hydroxytryptophan. These effects of DHX are not due to "indirect" alterations at the presynaptic terminal, because DHX is essentially inactive at inhibiting the dopamine uptake system, and does not cause the release of dopamine. These data demonstrate the utility of DHX for probing the biochemistry and function of D1 dopamine receptors.

Serotonergic modulation of the acoustic startle response in rats during preweaning development

The involvement of serotonin (5-HT) in modulating the acoustic startle response (ASR) is well established in adult rats, but 5-HT involvement during the preweaning period, when 5-HT neurons undergo extensive development, has not previously been described. Three 5-HT receptor subtypes are reported to modulate the ASR in adult rats: 5-HT1A and 5-HT2 receptor agonists facilitate the ASR, whereas 5-HT1B agonists decrease the response. In the present study, the effects of 5-HT agonists and generalized 5-HT depletion on the ASR were studied in preweanling animals, using independent groups of Long-Evans rats tested on postnatal day (PND) 13, 17 and 21. 8-Hydroxy-2-(di-n-propylamino) tetralin (8OHDPAT, 62-1000 micrograms/kg), a 5-HT1A receptor agonist, and 5-methoxy-N,N-dimethyl tryptamine (MeODMT, 2-4 mg/kg), a nonselective 5-HT agonist, had no effect on PND 13 and then increased the ASR on PND 17 and 21. The 5-HT2 receptor antagonists cyproheptadine (5 mg/kg) and ketanserin (5 mg/kg) blocked the effect of MeODMT at both ages, providing some evidence that MeODMT increased the ASR through 5-HT2 receptors. 1-(m-Chlorophenyl) piperazine (mCPP, 1-5 mg/kg), a 5-HT1B agonist, had no effect on ASR amplitude on PND 13 or 17 and then produced a dose-related decrease in the response on PND 21. Generalized depletion of 5-HT by 80-90% in whole-brain and spinal cord, using p-chlorophenylalanine (PCPA, 300 mg/kg 24 hr prior to testing), did not alter ASR amplitude at any age.(ABSTRACT TRUNCATED AT 250 WORDS)

A critical evaluation of cysteamine as a tool to deplete somatostatin in the rat central nervous system

The wide central nervous system (CNS) distribution of somatostatin (SRIF) as well as the well documented reduction in SRIF concentration in the cerebral cortex in patients with Alzheimer's disease have served as an impetus for studies of this peptide's neurobiological role in the brain. These studies were designed to evaluate the efficacy of centrally administered cysteamine (CYS) as a tool to deplete SRIF in the hypothalamus (HYP) and extrahypothalamic brain areas. Somatostatin was measured by RIA in the frontal cortex (COR), hippocampus (HIP), and HYP in rats after seven daily infusions of CYS into unilateral cannulae stereotaxically positioned into either the lateral ventricle (LV; 300 micrograms/2 microliters) or the dorsal HIP (100 micrograms/2 microliters), and after single (300 mg/kg) or daily (100 mg/kg) sc injections; rats were killed 4 or 24 h after the last injection. After LV infusions, the SRIF concentration was significantly reduced only in the HYP (35% at 4 h and 27% at 24 h). After HIP infusions, the SRIF concentration was significantly reduced only in the HYP at 4 h (23%); no reductions were observed at 24 h. Both a single and repeated sc administrations of CYS reduced SRIF in the HYP only 24 h after treatment (54% and 50%, respectively). Acute sc CYS reduced SRIF in the COR (23%) and the HYP (29%) 4 h after treatment; repeated sc CYS reduced SRIF in the COR (25%) and the HYP (63%). Although the reduction of SRIF in the HYP was increased by repeated sc dosing, the reduction of extrahypothalamic SRIF by sc CYS was relatively small in magnitude and was not enhanced by repeated dosing. These results suggest that CYS is not an ideal tool for depletion of extrahypothalamic SRIF after sc or CNS administration and, moreover, raise serious questions about studies in which behavioral or endocrine alterations after CYS treatment were attributed to specific actions on SRIF-containing neurons.

Protection of phosphoglycerate kinase against in vitro aging by selective cysteine methylation

Recent studies have demonstrated that the aging effects in phosphoglycerate kinase (PGK) may be simulated in vitro by prolonged incubation of the enzyme under nonreducing conditions followed by reduction with excess 2-mercaptoethanol. The simulated-old enzyme thus produced appears to be identical to native old PGK and, like the latter enzyme, may be successfully rejuvenated by an unfolding-refolding procedure. A model for PGK aging was proposed in which initial and reversible oxidation of the enzyme is followed by conformational modifications that persist after the enzyme is re-reduced. The role of specific cysteine oxidation in the initial step of PGK aging was tested in the present study by selectively methylating the fast-reacting cysteine residues in this enzyme, thus blocking the putative oxidation sites, and producing in vitro a young form of PGK that is immune to aging. The methylation was performed by treating the enzyme with excess iodomethane and monitoring the reaction by determining the concentration of unreacted cysteines in the enzyme as a function of time. Unmethylated controls were incubated similarly but in the absence of iodomethane. The methylated as well as control samples of PGK were subsequently incubated under conditions which caused native young PGK to develop the age-related effects and become identical to native old PGK. In contrast, the methylated enzyme remained identical to young PGK. These findings strongly support the hypothesis that cysteine oxidation is an essential step in the aging of rat muscle phosphoglycerate kinase.

Possible brainstem involvement in the modification of thermoregulatory processes by chlordecone in rats

The involvement of the central nervous system in the hypothermia induced by chlordecone was studied by evaluating the effects of infusions of chlordecone injected into the lateral and third ventricles and the cisterna magna on colonic temperature (Tcol). Compared to rats given vehicle, infusions of 40, 320 or 800 micrograms of chlordecone into the lateral ventricle or 320 or 800 micrograms of chlordecone into the third ventricle, through chronic indwelling cannulae, did not change significantly Tcol. However, intracisternal infusions of 80, 160, 320 or 800 micrograms of chlordecone produced significant hypothermia (maximally 2.2 degrees C) which persisted for as long as 6 hr. Intracisternal infusions of chlordecone also produced a rapid increase in the temperature of the tail skin (Tsk) which persisted throughout the period of hypothermia. This suggests that the hypothermia produced by central administration of chlordecone is related to peripheral vasodilation. Since chlordecone has been reported to induce release of NE in the brainstem, and NE is known to modulate tonic vasomotor control in the medulla, the effects of NE infused intracisternally were studied. Intracisternal infusions of NE (16 micrograms) significantly decreased Tcol and increased Tsk, supporting the hypothesis that hypothermia induced by chlordecone is associated with vasodilatory effects, mediated by an adrenergic mechanism in the brainstem.

Pharmacological evaluation of central adrenergic involvement in chlordecone-induced hypothermia

Adrenergic involvement in the hypothermia produced by systemically administered chlordecone (CLD) was evaluated in the rat using intracisternal pretreatment with 6-hydroxydopamine (6-OHDA), alpha-adrenergic receptor antagonists (phenoxybenzamine and phentolamine) and beta-adrenergic antagonists (propranolol and atenolol). The effect of intraperitoneal administration of 75 mg/kg of chlordecone on colonic temperature (Tcol) in male Fischer-344 rats was measured 7 days after administration of 6-OHDA and 30 min following pretreatment with the receptor antagonists. Prior depletion of catecholamines in brain with 250 micrograms of 6-OHDA administered intracerebrally attenuated hypothermia induced by chlordecone, without affecting basal Tcol. Phenoxybenzamine (10 or 20 micrograms) and phentolamine (5 or 10 micrograms) also reduced the hypothermic response to chlordecone. The beta-adrenergic receptor antagonists propranolol (50 or 100 micrograms) and atenolol (10 or 20 micrograms) did not attenuate chlordecone-induced hypothermia. These data suggest that the hypothermia induced by chlordecone is a result of alterations in central alpha-adrenergic functions, possibly involved with the sympathetic control of vasomotor tone.

Convulsant properties of cyclotrimethylenetrinitramine (RDX): spontaneous audiogenic, and amygdaloid kindled seizure activity

Dose-effect and time course relationships were determined for the effects of the explosive cyclotrimethylenetrinitramine (RDX) on seizure susceptibility. Male Long Evans rats treated with 0-60 mg/kg RDX po were monitored for spontaneous seizures during an 8-hr interval between dosing and audiogenic (AG) seizure testing. Blood samples for analyzing plasma RDX concentrations were obtained immediately thereafter. Spontaneous and AG seizures were observed at dosages as low as 10-12.5 mg/kg, with significant seizure incidence induced by dosages of 25.0 mg/kg (5.34 micrograms RDX/ml plasma) and 50.0 mg/kg (8.28 micrograms RDX/ml plasma), respectively. Spontaneous seizure incidence peaked at 2 hr for all RDX treatment groups, then decreased (12.5 and 25.0 mg/kg) or remained elevated (50.0 mg/kg) for the remaining 6 hr. In contrast, AG seizures (37.5 mg/kg) could be elicited only at 8 and 16 hr, despite significant elevation of plasma RDX concentrations at 2 and 4 hr. Because limbic system involvement was suggested by spontaneous seizure characteristics, the rate of amygdaloid kindling was measured following daily treatment with 6.0 mg/kg. This dosage significantly accelerated kindling development without inducing spontaneous seizures or producing an accumulation of RDX in plasma. These data provide preliminary evidence that limbic structures may participate in RDX-induced seizure susceptibility.

Chlordecone-induced effects on thermoregulatory processes in the rat

To investigate the mechanism(s) involved in chlordecone (CLD)-induced hypothermia, we examined colonic (Tcol) and tail skin (Tsk) temperatures, preferred ambient temperature (Ta), evaporative water loss, and metabolic rate following CLD exposure in the rat. Single ip dosages (0, 50, and 75 mg/kg) in corn oil were administered to Fischer-344 rats. At a Ta of 22.5 degrees C, Tcol was reduced by 50 and 75 mg/kg as early as 0.5 hr, and this effect persisted for 4 hr after dosing. Tcol was increased 24 hr after both CLD dosages. Tsk was elevated 2, 3, 4, and 6 hr after 75 mg/kg and 2 hr after 50 mg/kg. At Ta of 30.5 degrees C, Tcol was decreased at early exposure times after both dosages and was increased 3, 4, and 6 hr after 75 mg/kg. At 10.0 degrees C, an enhanced hypothermia was observed 1-6 hr following 50 and 75 mg/kg CLD. The preferred Ta was significantly decreased by approximately equal to 2.8 degrees C following CLD exposure while activity within the temperature gradient was unchanged. At 25.0 degrees C, evaporative water loss was decreased while metabolic rate was not affected by CLD administration. To study the enhanced hypothermia at 10.0 degrees C, metabolic rate was measured continuously for 2 hr following 75 mg/kg CLD and found to be significantly different from controls. The intensified hypothermia in the cold may be due to the inability of the CLD-treated rat to stimulate metabolic thermogenesis in response to cold in addition to the loss of body heat following cutaneous vasodilation. These data suggest that CLD-induced hypothermia at a neutral Ta is associated with cutaneous vasodilation and not with a decreased metabolic rate or increased evaporative water loss.

Accuracy of frozen section diagnosis of the salivary gland

Three hundred and one salivary gland lesions (162 benign, 72 malignant, and 67 benign non-neoplastic) of 677 cases were evaluated by use of intraoperative frozen sections by 66 pathologists. In seven patients, the diagnosis was deferred for permanent sections. In four cases (1.3%), the diagnosis at permanent section changed from one category of benign tumor to another, and in five cases (1.7%), from one category of malignant tumor to another. In four tumors, a frozen section diagnosis of benign was changed to malignant on permanent sectioning; all four involved acinic cell carcinomas. Only two tumors were incorrectly diagnosed as malignant. We conclude that diagnoses of most salivary gland lesions based on frozen section examination are reliable and accurate. However, the literature does indicate that caution should be exercised when malignant tumors are dealt with.

Tin distribution in adult rat tissues after exposure to trimethyltin and triethyltin

The time course of distribution of tin in the adult rat was determined in brain, liver, kidneys, heart, and blood following single ip administrations of trimethyltin hydroxide (TMT) and triethyltin bromide (TET). Adult Long-Evans rats were killed 1, 4, 12, and 24 hr, and at 5, 10, or 22 days following injection of TMT and TET (N = 6/time), and tissues were analyzed for total tin by atomic absorbance spectroscopy. TET exposure resulted in higher tin concentrations in brain, liver, and kidney tissues, while the two trialkyltins resulted in approximately equal tin concentrations in the heart and blood. Rates of elimination of tin (expressed as elimination rate constants, Kel) were greater in all tissues following TET exposure than following TMT exposure. The concentration of tin in the brain 12 hr after TMT exposure was 4.4, 8.5, and 12.7 ng tin/mg protein for dosages of 3.0, 6.0, and 9.0 mg/kg, respectively. Tin was evenly distributed across the cerebellum, medulla-pons, hypothalamus, hippocampus, and striatum following TMT exposure. These results describe major differences in the disposition and rates of elimination of tin from body tissues after TMT and TET exposure, and demonstrate that the regional disposition of tin is not related to the region-specific pathology reported following TMT exposure.

Distribution of tin in brain subcellular fractions following the administration of trimethyl tin and triethyl tin to the rat

The time course of tin distribution in homogenates and subcellular fractions of rat brain was determined following the acute administration of trimethyl tin (TMT) and triethyl tin (TET) to the rat. Exposure to TMT resulted in lower concentrations but greater persistence of tin in subcellular fractions compared to exposure to TET. A delayed accumulation of tin in the mitochondrial fraction was observed following the administration of TMT but not TET. Analysis of total protein and mitochondrial markers did not reveal differences between the compositions of mitochondrial fractions prepared from control and TMT-treated subjects.

Tin distribution in adult and neonatal rat brain following exposure to triethyltin

The uptake, distribution, and elimination of tin were determined in adult and neonatal (Postnatal Day 5) rat brain following ip administration of triethyltin bromide (TET). Groups of five adult CD rats were killed at 10 min, 1 hr, 4 hr, 24 hr, 5 days, or 10 days following acute exposure to 6.0 mg/kg TET; an additional group of adult animals was killed at 24 hr following exposure to either 3.0, 6.0, or 9.0 mg/kg (N = 5/dosage). The time course for tin distribution in 5-day-old rat pups was determined by killing pups 10 min, 30 min, 1 hr, 4 hr, 8 hr, 12 hr, 24 hr, 5 days, 10 days, or 22 days following exposure to either 3.0 or 6.0 mg/kg TET (N = 4/dosage/time). Tin analyses were performed by flameless atomic absorption spectrophotometry. The t1/2 for total tin in the adult rat brain following 6.0 mg/kg TET was determined to be 8.0 days. The maximum concentration in the adult was reached at 24 hr and corresponded to 4.6, 9.6, and 16.6 ng tin/mg protein for dosages of 3.0, 6.0, and 9.0 mg/kg, respectively. Tin was evenly distributed across all brain areas studied. For animals exposed to 6.0 mg/kg TET on Postnatal Day 5, the t1/2 for total tin in the brain was 7.3 days. A maximum concentration of 9.9 ng tin/mg protein was reached at 8 hr postexposure. The rate of elimination of tin from the brain (as measured by the elimination rate constant kel) did not differ significantly between adults and neonates. However, due to a dilution effect by the rapid brain growth of the neonate, the concentration of tin in the neonatal brain following TET administration decreased significantly faster than that in the adult.

Acute behavioral toxicity of carbaryl and propoxur in adult rats

Motor activity and neuromotor function were examined in adult CD rats exposed to either carbaryl or propoxur, and behavioral effects were compared with the time course of cholinesterase inhibition. Rats received an IP injection of either 0, 2, 4, 6 or 8 mg/kg propoxur or 0, 4, 8, 16 or 28 mg/kg carbaryl in corn oil 20 min before testing. All doses of propoxur reduced 2 hr activity in a figure-eight maze, and crossovers and rears in an open field. For carbaryl, dosages of 8, 16 and 28 mg/kg decreased maze activity whereas 16 and 28 mg/kg reduced open field activity. In order to determine the time course of effects, rats received a single IP injection of either corn oil, 2 mg/kg propoxur or 16 mg/kg carbaryl, and were tested for 5 min in a figure-eight maze either 15, 30, 60, 120 or 240 min post-injection. Immediately after testing, animals were sacrificed and total cholinesterase was measured. Maximum effects of propoxur and carbaryl on blood and brain cholinesterase and motor activity were seen within 15 min. Maze activity had returned to control levels within 30 and 60 min whereas cholinesterase levels remained depressed for 120 and 240 min for propoxur and carbaryl, respectively. These results indicate that both carbamates decrease motor activity, but behavioral recovery occurs prior to that of cholinesterase following acute exposure.