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Biomedical subjects

J P Bennett

Publications and source records attributed to J P Bennett.

At least 55 records · Page 3Linked to original sources
PubMed1997

Loss of cell surface microvilli on rat basophilic leukaemia cells precedes secretion and can be mimicked using the calmodulin antagonist trifluoperazine.

OBJECTIVE: We studied changes in cell surface morphology following treatment with secretagogue or trifluoperazine in a mast cell model. MATERIALS AND METHODS: Rat basophilic leukaemia (RBL) cells were treated with antigen and or the calmodulin antagonist, 0-50 microM trifluoperazine (TFP). The release of a secretory granule enzyme, beta-hexosaminidase, into the external medium was used as a measure of secretion. Quantitation of cell surface microvilli was determined by using a computer with input from a digitising tablet from scanning electron micrographs. Cytoskeletal proteins present in microvilli were analysed by confocal immunofluorescence. RESULTS: When RBL cells are stimulated to secrete with an antigen, the cell surface is transformed from a microvillous morphology to a ruffled one. The cell surface rearrangement preceded beta-hexosaminidase secretion: the majority of microvilli disappeared rapidly after stimulation (t1/2 of 39 s) whereas secretion can only be measured after a lag of 47 s. The calmodulin antagonist, TFP did not inhibit antigen-induced secretion or loss of microvilli, however TFP alone caused a similar loss of microvilli but was unable to stimulate or potentiate secretion. The microvilli mostly disappeared within 30 s, and a half-maximal effect occurred at approximately 8 microM TFP. Using immunofluorescence, calmodulin was localized to punctate structures on the dorsal cell surface which presumably correspond to the microvilli, and which also stained for F-actin and myosin I. CONCLUSIONS: Loss of cell surface microvilli on RBL cells precedes secretion and could reflect a cytoskeletal rearrangement which facilitates fusion of secretory granules with the membrane. It can be mimicked using trifluoperazine and we suggest it may involve calmodulin-binding components of the microvillus cytoskeleton such as myosin I.

Animals↗
PubMed1997

Expression of serotonin transporter mRNA in rat brain: presence in neuronal and non-neuronal cells and effect of paroxetine.

The expression of serotonin transporter mRNA in rat brain was-examined by in situ hybridisation. Hybridisation was observed in cells of the known serotonergic nuclei and no other neuronal populations. It was also associated with ependymal cells of the aqueduct which may indicate a specialisation of this part of the ventricular system in anatomical and neurophysiological terms. The effect of the selective serotonin reuptake inhibitor paroxetine on neuronal expression of the serotonin transporter mRNA was examined. Quantitation at the cellular level in the dorsal and median raphe nuclei was carried out by analysis of the mean number of silver grains per cell in autoradiographed sections. No significant change (P > 0.1) in serotonin transporter mRNA expression was observed following 21 day administration of paroxetine (5 mg/kg per day).

Animals↗
PubMed1997

Evidence that spinal interneurons undergo programmed cell death postnatally in the rat.

Programmed cell death has been demonstrated in several specific neuronal populations as a mechanism for modulating the population size following differentiation, but its applicability to all neuronal types is unclear. Evidence for programmed cell death in some populations such as the numerous spinal interneurons has been lacking. We have studied the incidence of apoptosis in the rat spinal cord with three different methods and found a previously undocumented wave of apoptosis occurring in spinal grey matter shortly after birth. The apoptotic morphology was confirmed ultrastructurally. Dying cells were identified as neurons by immunocytochemical labelling for neuronal markers and had an anatomical distribution which indicated that most of the apoptotic cells were interneurons not motoneurons. This wave of apoptosis has the characteristics of a discrete developmental process and occurs later than that of either ventral horn motoneurons or dorsal root ganglion cells, to which most spinal interneurons are connected. These findings indicate that interneurons do undergo programmed cell death, and we suggest that this occurs in response to the earlier reduction in size of their main synaptic targets.

Aging↗
PubMed1997

Differential hydroxylation of salicylate in core and penumbra regions during focal reversible cerebral ischemia.

BACKGROUND AND PURPOSE: Free radical-mediated damage during and/or after cerebral ischemia is thought to participate in the elaboration of stroke-related injury. To elucidate the role of this mechanism in cerebral damage, the study presented herein sought to clarify the spatial and temporal features of the free radical response to transient ischemia. With use of a reproducible model of in vivo focal ischemia/reperfusion, the time course of salicylate hydroxylation was measured in ischemic core and penumbra regions. METHODS: Transient focal cerebral ischemia was produced in Sprague-Dawley rats by occluding both carotid arteries and one middle cerebral artery for 3 hours, followed by reperfusion. Cerebral reperfusion was confirmed by visual inspection and iodo[14C]antipyrine autoradiography. A microdialysis probe was placed stereotactically in either the ischemic core or ischemic penumbra of the frontoparietal cortex; the probe was perfused with salicylate, and dialysate samples were analyzed by high-performance liquid chromatography for salicylate hydroxylation products. RESULTS: Salicylate hydroxylation was significantly increased during ischemia and was further increased during 6 hours of reperfusion in the penumbra compared with sham controls. In comparison, a delayed increase in hydroxylation was observed within the ischemic core region only after 3 hours of reperfusion. CONCLUSION: A differential generation of salicylate hydroxylation occurs in core and penumbra regions in association with focal ischemia/reperfusion of the rat neocortex. The early and progressive response in the penumbra suggests that free radical mechanisms may be continuously active in the aggravation of injury in the ischemic penumbra during ischemia and reperfusion. In contrast, the relatively delayed onset of hydroxylation in the core region indicates that this mechanism participates primarily in the late stages of ischemic injury in densely ischemic tissue. These findings are consistent with the concept that the role of free radicals in cerebral injury may differ qualitatively and/or quantitatively in areas of total and partial cerebral perfusion.

Animals↗
PubMed1997

Clinical correlates of sleep benefit in Parkinson's disease.

The phenomenon of sleep benefit, a period of lessened disability or feeling "on" upon awakening from sleep in the morning, has received scant attention in the literature on Parkinson's disease. We interviewed 162 consecutive patients regarding disease onset, medication history, and symptoms, evaluated them using the Unified Parkinson's Disease Rating Scale, and assessed them as to the presence or absence of sleep benefit. Thirty-three percent reported experiencing sleep benefit. Compared with patients not having sleep benefit, patients with sleep benefit tended to be younger at disease onset, have longer disease duration, take higher total daily doses of levodopa, have longer duration of levodopa treatment, and exhibit less cognitive and physical disability. The findings of this study suggest that sleep benefit is a common phenomenon that may be anticipated in a subgroup of patients with Parkinson's disease. The mechanisms underlying sleep benefit do not appear to be simple and may be multifactorial. Clinicians need to be aware of the authenticity of patients' reports of sleep benefit and consider the existence of this phenomenon when prescribing or adjusting patients' medication schedules.

Animals↗
PubMed1997

Efficacy of pramipexole, a novel dopamine agonist, as monotherapy in mild to moderate Parkinson's disease. The Pramipexole Study Group.

A total of 335 patients with early Parkinson's disease (PD) were enrolled in a multicenter, randomized, double-blind trial designed to assess the efficacy and safety of pramipexole. Entry was restricted to patients with idiopathic PD who were not receiving levodopa. Pramipexole was administered according to an ascending dose schedule up to 4.5 mg/d. During the 7-week dose-escalation phase, each subject was titrated to his or her maximally tolerated dose of study medication. This was followed by a 24-week period of maintenance therapy. The mean daily dose during the maintenance period was 3.8 mg. Pramipexole significantly reduced the severity of PD symptoms and signs compared with placebo, as measured by decreases in parts II (Activities of Daily Living) and III (Motor Examination) of the Unified Parkinson's Disease Rating Scale at week 24 compared with baseline (p < or = 0.0001). Differences between the active drug and placebo groups emerged at week 3 (1.5 mg/d) in the ascending-dose interval and persisted throughout the maintenance phase (p < or = 0.0001). The majority of patients completed the study (pramipexole 83%, placebo 80%). In the assessment of adverse events, nausea, insomnia, constipation, somnolence, and visual hallucinations occurred more frequently in the pramipexole treatment group compared with placebo patients. No clinically significant changes were noted in blood pressure or pulse rate. Overall, these results indicate that pramipexole is safe and effective in the treatment of early PD.

Activities of Daily Living↗
PubMed1997

Cybrids in Alzheimer's disease: a cellular model of the disease?

The mitochondrial electron transport chain enzyme cytochrome c oxidase (COX) is defective in patients with sporadic Alzheimer's disease (AD). This defect arises from the mutation of mitochondrial DNA (mtDNA). To develop a tissue culture system that would express this genetically derived bioenergetic lesion and permit characterization of its functional consequences, we depleted Ntera2/D1 (NT2) teratocarcinoma cells of endogenous mtDNA and repopulated them with platelet mtDNA from AD patients. Cytochrome c oxidase activity was depressed in the resulting AD cytoplasmic hybrids (cybrids) compared with cybrids prepared with mtDNA from non-AD controls. Reactive oxygen species (ROS) production and free radical scavenging enzyme activities were significantly elevated in AD cybrids. A COX defect in NT2 AD cybrid lines indicates that AD patients possess mtDNA COX gene mutations that are sufficient for determining this biochemical lesion. Expression of unique functional characteristics (increased ROS production and free radical scavenging enzyme activities) relevant to neurodegeneration demonstrates the utility of these cells in defining AD pathophysiology at a cellular level. This in vitro tissue culture model of AD may prove useful in drug screening.

Alzheimer Disease↗
PubMed1997

Circular ruffle formation in rat basophilic leukemia cells in response to antigen stimulation.

Rat basophilic leukemia cells have previously been described to undergo striking cell surface changes after IgE-mediated stimulation of histamine secretion, whereby the dorsal surface loses its microvilli and acquires characteristic wavy ruffles. We have found using scanning electron microscopy, phase contrast and immunofluorescence, that a proportion of these cells also exhibit the formation of circular membrane ruffles on their dorsal surface after exposure to an IgE-directed secretagogue; some cells also develop circular membrane ruffles following stimulation by phorbol myristate acetate or by calcium ionophore A23187. A flattened morphology appears to be linked to circular membrane ruffle formation in that these ruffles were found in areas of presumed cell spreading which are largely devoid of intermediate filaments and displaced to one side of the cell's nucleus, and they were not observed on rounded cells. This is in contrast to the wavy ruffles which are found on the entire cell surface including the region overlying the nucleus, and which are observed in rounded cells as well as spread cells. Circular ruffle formation and secretion are triggered by similar concentrations of antigen, but the circular ruffles are formed more slowly and only become abundant at times after most of the histamine has been released. The circular membrane ruffles showed no obvious association with endocytosis, as detected using fluorescein isothiocyanate-dextran as a fluid phase marker. The position of accumulation of endocytotic vesicles occurring subsequent to secretion was not found to be related to the circular membrane ruffles, but was observed around the nucleus. Circular membrane ruffles contain F-actin, and their formation is prevented by cytochalasin D. At least three types of myosin, types I, II and V are present and presumably play a role in circular ruffle formation.

Actin Cytoskeleton↗
PubMed1996

Development of striatal dopaminergic function. I. Pre- and postnatal development of mRNAs and binding sites for striatal D1 (D1a) and D2 (D2a) receptors.

Quantitative receptor autoradiography with iodinated ligands, quantitative in situ hybridization histochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to describe the prenatal and early postnatal ontogeny (embryonic day 14 to postnatal day 7, or E14 to P7) of striatal D1 and D2 dopamine receptor binding sites and mRNA levels, respectively, in relation to the development of dopaminergic nigrostriatal innervation D1 dopamine receptor, measured by [125I]SCH23982 binding, and dopamine transporter binding sites, measured by [125I]RTI-55 binding, were present in low amounts beginning on E14 (2-3% and 0.3-0.6% of adult values, respectively) and increased slowly during the prenatal period. D2 receptor binding sites, measured with [125I]spiperone, were also detected on E14 but in higher relative quantities (17% of adult values) than D1 receptor and dopamine transporter binding sites at the same age. Other than abrupt declines in the late prenatal period for D1 and D2 receptor binding sites, all three binding sites increased throughout development and increased maximally between P7 and adulthood. On P5, both D1 and D2 receptors were functionally coupled to their respective G proteins, based on GTP-induced decreases in affinity of dopamine for [125I]SCH23982 and [125I]spiperone binding. D1 receptor mRNA was present in E14 striatal anlage, increased prenatally, declined on P0, then increased to a peak on P5, after which it declined to its lowest levels (20% of peak values) in the adult. In contrast, D2 receptor mRNA levels were presented also on E14, increased to a peak on P0, declined until P5, and increased thereafter to adulthood. Anatomically, nigrostriatal innervation and D1 and D2 receptor mRNA levels increased from the medial to lateral striatal quadrants. In contrast, D1 and D2 receptor binding site ontogency exhibited fairly homogenous distributions from E18 to P7. D1 and D2 receptor mRNAs appear to be expressed early in prenatal development before there is any significant dopaminergic innervation. In contrast, the majority of D1 and D2 receptor binding activity, representing expressed receptor proteins, develops in the postnatal period and correlates well with the increase in dopaminergic innervation. Intrinsic genetic programming is more likely to be responsible for D1 and D2 receptor gene transcription in striatal neuroblasts and newly born neurons, while factors derived from ingrowing dopaminergic afferents may direct post-transcriptional dopamine receptor development. The dissociation between the ontogeny of dopamine receptor binding sites and mRNAs suggests that the developmental regulation of D1 and D2 receptor synthesis is independent of D1 and D2 receptor gene transcription.

Animals↗
PubMed1996

Development of striatal dopaminergic function. II: Dopaminergic regulation of transcription of the immediate early gene zif268 and of D1 (D1a) and D2 (D2a) receptors during pre- and postnatal development.

We investigated cocaine- and apomorphine-mediated induction of the zinc finger immediate early gene (IEG), zif268, during striatal ontogeny. Acute cocaine or apomorphine treatment increased striatal zif268 mRNA on embryonic day 20 (E20), postnatal day 5 (P5), and in adults, but not on E15, with developmentally distinct anatomical profiles. SCH23390 pretreatment completely attenuated zif268 gene expression at all ages, but eticlopride treatment of E20 and P5 rats prior to cocaine enhanced zif268 expression beyond that observed with cocaine alone. In adults, eticlopride pretreatment partially attenuated the cocaine-mediated increase in zif268 expression. E20 and P5 D2 receptors appear to be negatively coupled to zif268 expression; whereas the adult D2 receptor, like the D1 receptor, appears to stimulate zif268 expression. Acute cocaine increased D1 but not D2 receptor mRNA levels within 24 h but had no effect on D1 or D2 receptor binding. By late embryonic development, some striatal neurons possess DA receptors coupled to IEG (zif268) activation. Postnatally, D1 receptor activation consistently increases zif268 transcription, but the coupling of D2 receptors to zif268 changes from decidedly negative at an early postnatal age to slightly positive in adults. These results are consistent with a role for DA in regulating striatal neuronal differentiation and development.

Animals↗
PubMed1996

Development of striatal dopaminergic function. III: Pre- and postnatal development of striatal and cortical mRNAs for the neurotrophin receptors trkBTK+ and trkC and their regulation by synaptic dopamine.

Known neurotrophins in the nigrostriatal system include brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) which exert biological effects after high affinity binding to their respective tyrosine kinase receptors, trkB and trkC. We measured striatal trkBTK+ and trkC mRNAs in rat brain sections with in situ hybridization histochemistry. Both trkBTK+ and trkC transcripts were present in the striatal anlage at embryonic day (E) 14 or 16. Striatal trkBTK+ mRNA levels increased to a peak in the late prenatal period and gradually declined in the postnatal period. In contrast, striatal trkC mRNA levels peaked on E16, then declined to fairly constant levels. Striatal trkBTK+ gene expression increased from the medial to lateral quadrants throughout development, whereas trkC mRNA increased from the lateral to medial quadrants prenatally but increased from the dorsal to ventral quadrants on postnatal days (P) 1 and 3. The distinct spatiotemporal developmental profiles of trkBTK+ and trkC mRNA suggest that their respective ligands BDNF and NT-4/5, and NT-3, may have specialized functions in striatal neuronal development. Because neurotransmitters may regulate neurotrophin function in developing neural systems, we treated rats of various ages with the indirect dopamine agonist cocaine and measured the effects of cocaine treatment on transcription of the trk genes. Acute 1 h cocaine treatment increased trkBTK+ and trkC mRNA levels in the P5 striatum but not in the E15, E20, or adult striatum. The trkBTK+ effect was blocked by pretreatment with the D1 receptor antagonist, SCH23390, and was not affected by pretreatment with the D2 receptor antagonist, eticlopride. In contrast, trkC regulation may be mediated by independent stimulation of D1 and D2 receptors. We hypothesize that the endogenous nigrostriatal neurotransmitter dopamine can modulate striatal neurotrophin responsiveness and thereby influence striatal neuronal development during a defined developmental period.

Animals↗
PubMed1996

Dose-related effects of continuous levodopa infusion in rats with unilateral lesions of the substantia nigra.

Preclinical studies in rats have demonstrated markedly different effects of intermittent and continuous levodopa administration on many biochemical and functional parameters yet the dose regimens employed have not been fully evaluated. In this study, rats with unilateral 6-hydroxydopamine nigral lesions were administered levodopa (0-1200 mg/kg/day) and benserazide (25 mg/kg/day) subcutaneously via osmotic minipump and studied 20-22 h later for rotational behavior, striatal dopamine concentration, and regional cerebral glucose utilization (RCGU). Levodopa infusion at 100 mg/kg/day resulted in minimal rotation and minimal striatal dopamine replacement but did increase RCGU in the subthalamic nucleus and decrease RCGU in the lateral habenula, consistent with a selective inhibition of the striatopallidal GABAergic (indirect striatal output) pathway. Levodopa infusion at 100 mg/kg/day did not significantly increase RCGU in the entopeduncular nucleus (EP) and substantia nigra pars reticulata (SNr), as does the acute injection of levodopa (25-50 mg/kg), indicating that this levodopa dose elicits only part of the spectrum of metabolic effects elicited by acute levodopa injection. Higher doses of levodopa (400-1200 mg/kg/day) resulted in moderate rates of rotation, dose-dependent increases in striatal dopamine, and increased RCGU in the EP and SNr, consistent with activation of the striatonigral GABAergic (direct striatal output) pathway. In the EP and SNr, the two major output nuclei of the basal ganglia, levodopa infusion at 800 and 1200 mg/kg/day reproduced the metabolic effects elicited by acute injection of levodopa. These results demonstrate, for the first time, dose-dependent effects of levodopa on distinct populations of striatal output neurons which may be relevant to the pathogenesis of levodopa-induced dyskinesias in Parkinson's disease. The minimal dopamine replacement and partial functional effects elicited by levodopa infusion at 100 mg/kg/day indicate the need for caution in the interpretation of prior studies of continuous levodopa infusion which employed this dose.

Animals↗
PubMed1996

Origin and functional consequences of the complex I defect in Parkinson's disease.

The mitochondrial electron transport enzyme NADH:ubiquinone oxidoreductase (complex I), which is encoded by both mitochondrial DNA and nuclear DNA, is defective in multiple tissues in persons with Parkinson's disease (PD). The origin of this lesion and its role in the neurodegeneration of PD are unknown. To address these questions, we created an in vitro system in which the potential contributions of environmental toxins, complex I nuclear DNA mutations, and mitochondrial DNA mutations could be systematically analyzed. A clonal line of human neuroblastoma cells containing no mitochondrial DNA was repopulated with mitochondria derived from the platelets of PD or control subjects. After 5 to 6 weeks in culture, these cytoplasmic hybrid (cybrid) cell lines were assayed for electron transport chain activities, production of reactive oxygen species, and sensitivity to induction of apoptotic cell death by 1-methyl-4-phenyl pyridinium (MPP+). In PD cybrids we found a stable 20% decrement in complex I activity, increased oxygen radical production, and increased susceptibility to 1-methyl-4-phenyl pyridinium-induced programmed cell death. The complex I defect in PD appears to be genetic, arising from mitochondrial DNA, and may play an important role in the neurodegeneration of PD by fostering reactive oxygen species production and conferring increased neuronal susceptibility to mitochondrial toxins.

1-Methyl-4-phenylpyridinium↗
PubMed1996

Dopamine neurons from transgenic mice with a knockout of the p53 gene resist MPTP neurotoxicity.

We have examined MPTP toxicity to dopamine neurons of mice homozygous for a transgenic knockout of the p53 growth control gene (p53-/-). MPTP at a total dose of 96 mg/kg administered in four doses over two days produced a non-homogeneous loss of striatal dopamine transport sites and quantitatively reduced 3H-mazindol binding to similar degrees in p53-/- and wild type controls 2 and 3 weeks after starting MPTP. Nigral DA neurons stained immunohistochemically for tyrosine hydroxylase were counted using both manual and automated methods and found to be reduced 29-34% in wild type controls but were not reduced in p53-/-. Mean DA neuronal surface areas were reduced 63-68% by MPTP in controls and 35-50% in p53-/-. We conclude that p53 protein appears necessary for complete expression of MPTP neurotoxicity to dopamine neurons. Our findings suggest that the p53 gene and other growth control genes may regulate dopamine neuronal death in PD.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1996

Floristic summary of plant species in the air pollution literature.

A floristic summary and analysis was performed on a list of the plant species that have been studied for the effects of gaseous and chemical air pollutants on vegetation in order to compare the species with the flora of North America north of Mexico. The scientific names of 2081 vascular plant species were extracted from almost 4000 journal articles stored in two large literature databases on the effects of air pollutants on plants. Three quarters of the plant species studied occur in North America, but this was only 7% of the total North American flora. Sixteen percent and 56% of all North American genera and families have been studied. The most studied genus is Pinus with 70% of the North American species studied, and the most studied family is the grass family, with 12% of the species studied. Although Pinus is ranked 86th in the North American flora, the grass family is ranked third, indicating that representation at the family level is better than at the genus level. All of the top ten families in North America are represented in the top 20 families in the air pollution effects literature, but only one genus (Lupinus) in the top ten genera in North America is represented in the top thirteen genera in the air pollution literature.

Journal Article↗
PubMed1996

Chicken myosin IB mRNA is highly expressed in lymphoid tissues.

Little is known about the functions of members of the myosin I family in vertebrates. Chicken myosin IB is a member of the amoeba-type subclass of myosin I molecules and tissue localisation studies may provide possible clues to the functions of these myosin I molecules. The expression of the mRNA of this unconventional myosin IB was analysed by in situ hybridization and compared with that of the well characterised brush border myosin I on frozen sections of tissues from the adult domestic chicken. High levels of myosin IB mRNA were found in the intestine and spleen, but were not found in other tissues examined such as brain, heart, lung, liver and kidney. In the intestine, myosin IB mRNA was much more abundant in the lamina propria than in the enterocytes, whereas brush border myosin I mRNA was restricted to the enterocytes. In the spleen, myosin IB mRNA expression was abundant in regions of white pulp, namely germinal centres, periellipsoid lymphocyte sheaths and periarteriolar lymphocyte sheaths. Lymphocytes are the major cell type in both the lamina propria and the white pulp of the spleen, which suggests that chicken myosin IB is highly expressed in lymphocytes. Lymphocyte recirculation depends on their migration through the endothelial layer and it is possible that myosin IB may have a role to play in this type of cell motility.

Animals↗
PubMed1995

BIOLEFF: three databases on air pollution effects on vegetation.

Three databases on air pollution effects on vegetation were developed by storing bibliographic and abstract data for technical literature on the subject in a free-form database program, 'askSam'. Approximately 4 000 journal articles have been computerized in three separate database files: BIOLEFF, LICHENS and METALS. BIOLEFF includes over 2 800 articles on the effects of approximately 25 gaseous and particulate pollutants on over 2 000 species of vascular plants. LICHENS includes almost 400 papers on the effects of gaseous and heavy metal pollutants on over 735 species of lichens and mosses. METALS includes over 465 papers on the effects of heavy metals on over 830 species of vascular plants. The combined databases include articles from about 375 different journals spanning 1905 to the present. Picea abies and Phaseolus vulgaris are the most studied vascular plants in BIOLEFF, while Hypogymnia physodes is the most studied lichen species in LICHENS. Ozone and sulfur dioxide are the most studied gaseous pollutants with about two thirds of the records in BIOLEFF. The combined size of the databases is now about 5.5 megabytes.

Journal Article↗