Biomedical subjects

James P O'Callaghan

Publications and source records attributed to James P O'Callaghan.

At least 19 recordsLinked to original sources

PubMed2006

Recapitulation of cell signaling events associated with astrogliosis using the brain slice preparation.

Astroglial activation constitutes a dominant response to all types of injuries of the CNS. Despite the ubiquitous nature of this cellular reaction to neural injury, a little is known concerning the signaling mechanisms that initiate it. Recently, we demonstrated that astrocytic hypertrophy and enhanced expression of glial fibrillary acidic protein resulting from toxicant-induced neurodegeneration are linked to activation of the janus kinase (JAK)-signal transducer and activator of transcription-3 (STAT3) pathway. These observations implicate ligands at the gp130 receptor as potential upstream effectors of astrogliosis. Here we used the brain slice preparation to examine potential activators of the JAK-STAT3 pathway. Following incubation of freshly cut striatal slices in phosphate-free oxygenated buffer for up to 75 min, we found that slicing the striatum itself was a sufficient stimulus to initiate a rapid activation of the JAK-STAT3 pathway as assessed with immunoblots of pSTAT3((tyr705)) using phospho-state specific antibodies. The mRNA for the gp130 cytokines, leukemia inhibitory factor, interleukin-6 and oncostatin M or the beta-chemokine, monocyte chemoattractive protein (CCl2) also were up-regulated in the slice. Moreover, we could enhance the activation of STAT3((tyr705)) by adding exogenous cytokines to the slice and we could inhibit phosphorylation of STAT3((tyr705)) by addition of tyrosine kinase inhibitors (Lav A and AG490) or neutralizing antibodies directed against leukemia inhibitory factor or oncostatin M. These data suggest that STAT3 activation is an early event in slice-induced glial activation and establishes the brain slice preparation method as a reliable model to examine the signaling mechanisms that underlie glial activation.

Animals↗

PubMed2006

Identification and quantification of neuropeptides in brain tissue by capillary liquid chromatography coupled off-line to MALDI-TOF and MALDI-TOF/TOF-MS.

Capillary liquid chromatography (CLC) coupled off-line with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and TOF/TOF-MS were explored for identification and quantification of neuropeptides in microwave-fixed rat brain tissue. Sample was separated by gradient elution on 50-mum-inner diameter reversed-phase columns at 180 nL/min. Effluent was mixed with matrix solution and transferred to a MALDI target plate by pulsed electric field deposition, yielding sample spots with 200-300-mum diameter. Mass detection limits as low as 2 amol, corresponding to 1 pM concentration, were achieved for neuropeptides. CLC-MALDI-TOF-MS analysis of microwave-fixed rat striatum tissue yielded detection of over 400 distinctive peaks. CLC-MALDI-TOF/TOF-MS allowed identification of 10 peptides including 3 novel peptides. Quantification was evaluated using substance P as analyte and 15N3-labeled substance P as an internal standard. Quantification of substance P revealed approximately 6.8-fold higher levels than previously reported in the rat striatum. This increase is attributed to use of microwave fixation, which prevented degradation of the peptide, aggressive extraction procedures, and accounting for oxidation of substance P in the analysis. These results demonstrate that CLC-MALDI-TOF-MS is a versatile tool for neuropeptide analysis in brain tissue by allowing for detection, identification, and quantification.

Amino Acid Sequence↗

PubMed2006

Development of an animal model to study the potential neurotoxic effects associated with welding fume inhalation.

Serious questions have been raised regarding a possible causal association between neurological effects in welders and the presence of manganese in welding fume. An experimental model is needed that could examine the potential neurotoxic effect of manganese after pulmonary exposure to welding fume. The National Institute for Occupational Safety and Health (NIOSH) has recently finished construction of a completely automated, computer controlled welding fume generation and inhalation exposure system for laboratory animals. The system is comprised of a programmable six-axis robotic welding arm and a water-cooled arc welding torch. A flexible trunk has been attached to the robotic arm of the welder and is used to collect and transport fume from the vicinity of the arc to the animal exposure chamber. Preliminary fume characterization studies have indicated that particle morphology, size, and chemical composition were comparable to welding fume generated in the workplace. Animal inhalation studies are currently underway. With the development of this novel system, an animal model has been established using controlled welding exposures to investigate the possible mechanisms by which welding fume may affect the central nervous system.

Air Pollutants, Occupational↗

PubMed2006

Corticosterone regulates expression of CCL2 in the intact and chemically injured hippocampus.

Expression of the chemokine (C-C motif) ligand 2 (CCL2), also known as, monocyte chemoattractant protein (MCP)-1, increases in response to disease-, trauma-, or toxicant-induced damage to the central nervous system (CNS). In the periphery, endogenous and exogenous glucocorticoids are known to suppress CCL2 expression associated with inflammatory conditions. However, such actions of glucocorticoids on CCL2 expression in the CNS remain unknown. Here, we explored the effects of the glucocorticoid, corticosterone (CORT), on the expression of CCL2 and its receptors, CCR2 and CCR5, in the hippocampal formation using intact, adrenalectomized (ADX) and trimethyltin (TMT)-treated rats. An immunosuppressive regimen of CORT did not alter the mRNA expression of CCL2 or its receptors in the hippocampus. ADX, however, markedly increased the expression of CCL2 and CCR2 mRNAs in the hippocampus, while CORT replacement reversed the effects of ADX on CCL2 gene expression. Hippocampal damage resulting from systemic administration of the organometallic neurotoxicant, TMT, was associated with microglial activation, as evidenced by enhanced expression of microglial markers integrin alphaM (CD11b) and F4/80, as well as, microglia-associated factors, CCL2 and IL-1alpha. An immunosuppressive dose of CORT, suppressed TMT-induced expression of CCL2. Given the association of CCL2 with microglial activation, it appears that CORT may play a role in regulating microglial activation. However, CORT treatment did not alter TMT-mediated neuronal damage and astrogliosis. Such observations suggest that injury-related expression of microglia-associated chemokines and cytokines may subserve a role unrelated to neuronal damage. In summary, our data indicate that in the CNS, CCL2 gene expression is under negative regulation by glucocorticoids.

Adrenalectomy↗

PubMed2006

Minocycline attenuates microglial activation but fails to mitigate striatal dopaminergic neurotoxicity: role of tumor necrosis factor-alpha.

Activated microglia are implicated in the pathogenesis of disease-, trauma- and toxicant-induced damage to the CNS, and strategies to modulate microglial activation are gaining impetus. A novel action of the tetracycline derivative minocycline is the ability to inhibit inflammation and free radical formation, factors that influence microglial activation. Minocycline is therefore being tested as a neuroprotective agent to alleviate CNS damage, although findings so far have yielded mixed results. Here, we showed that administration of a single low dose of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (METH), a paradigm that causes selective degeneration of striatal dopaminergic nerve terminals without affecting the cell body in substantia nigra, increased the expression of mRNAs encoding microglia-associated factors F4/80, interleukin (IL)-1alpha, IL-6, monocyte chemoattractant protein-1 (MCP-1, CCL2) and tumor necrosis factor (TNF)-alpha. Minocycline treatment attenuated MPTP- or METH-mediated microglial activation, but failed to afford neuroprotection. Lack of neuroprotection was shown to be due to the inability of minocycline to abolish the induction of TNF-alpha and its receptors, thereby failing to modulate TNF signaling. Thus, TNF-alpha appeared to be an obligatory component of dopaminergic neurotoxicity. To address this possibility, we examined the effects of MPTP or METH in mice lacking genes encoding IL-6, CCL2 or TNF receptor (TNFR)1/2. Deficiency of either IL-6 or CCL2 did not alter MPTP neurotoxicity. However, deficiency of both TNFRs protected against the dopaminergic neurotoxicity of MPTP. Taken together, our findings suggest that attenuation of microglial activation is insufficient to modulate neurotoxicity as transient activation of microglia may suffice to initiate neurodegeneration. These findings support the hypothesis that TNF-alpha may play a role in the selective vulnerability of the nigrostriatal pathway associated with dopaminergic neurotoxicity and perhaps Parkinson's disease.

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

PubMed2006

The pharmacology of wakefulness.

Being awake, alert, and able to function in our 24-7 world is a challenge in the face of the fatigue and sleepiness engendered by long work hours, unusual work schedules, sickness, and other factors. Development of effective treatments to combat fatigue and sleepiness requires an understanding of the neurobiology of wakefulness. In this brief review, we examine the neuroanatomical, neurochemical, and molecular basis of the wakeful state to provide a framework for understanding current and future pharmacologic approaches to modification of wakefulness. The spontaneously awake state can be defined as a natural state of vigilance or arousal differing from natural sleep in both behavior and neural activity. These differences have long intrigued researchers and largely have been characterized in the brain areas and neurochemical systems affecting the sleep and wake states. Many of the strategies for promoting the awake condition involve manipulation or modulation of specific neurochemical systems with the ultimate goal of enhancing wakefulness, diminishing sleepiness, or both. Wakefulness is an important cortical function that depends on the coordinated effort of multiple brain areas including the thalamus, hypothalamus, and basal forebrain to integrate and relay information from the brainstem to the cortex. Norepinephrine and serotonin-long considered arousal-enhancing transmitters as well as glutamate, acetylcholine, histamine, and the neuromodulators hypocretin-orexins and adenosine, are known to affect the signal transduction in these brain areas and initiate, promote, or enhance wakefulness. Use of molecular tools to evaluate the awake, asleep, and sleep-deprived state has revealed novel insights concerning the gene expression events associated with wakefulness. Understanding wakefulness at this level undoubtedly will contribute to the development of pharmacologic approaches to promote or enhance the wakeful state. We caution, however, that sleep may have a necessary, restorative function for the brain; therefore, prolonging wakefulness for long periods through artificial means could have unexpected and perhaps detrimental consequences on brain health.

Brain↗

PubMed2006

Deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP-induced neurotoxicity: role of TNF-alpha.

Enhanced expression of tumor necrosis factor (TNF) -alpha, is associated with the neuropathological effects underlying disease-, trauma- and chemically induced neurodegeneration. Previously, we have shown that deficiency of TNF receptors protects against MPTP-induced striatal dopaminergic neurotoxicity, findings suggestive of a role for TNF-alpha in neurodegeneration. Here, we demonstrate that deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP. MPTP-induced expression of microglia-derived factors, TNF-alpha, MCP-1, and IL-1alpha, preceded the degeneration of striatal dopaminergic nerve terminals and astrogliosis, as assessed by loss of striatal dopamine and TH, and an increase in striatal GFAP. Pharmacological neuroprotection with the dopamine reuptake inhibitor, nomifensine, abolished striatal dopaminergic neurotoxicity and associated microglial activation. Similarly, in mice lacking TNF receptors, microglial activation was suppressed, findings consistent with a role for TNF-alpha in striatal MPTP neurotoxicity. In the hippocampus, however, TNF receptor-deficient mice showed exacerbated neuronal damage after MPTP, as evidenced by Fluoro Jade-B staining (to identify degenerating neurons) and decreased microtubule-associated protein-2 (MAP-2) immunoreactivity. These effects were not accompanied by microglial activation, but were associated with increased oxidative stress (nitrosylation of tyrosine residues). These findings suggest that TNF-alpha exerts a neurotrophic/neuroprotective effect in hippocampus. The marked differences we observed in the regional density, distribution and/or activity of microglia and microglia-derived factors may influence the region-specific role for this cell type. Taken together, our results are indicative of a region-specific and dual role for TNF-alpha in the brain: a promoter of neurodegeneration in striatum and a protector against neurodegeneration in hippocampus.

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

PubMed2005

Sample-dependent effects on the neuropeptidome detected in rat brain tissue preparations by capillary liquid chromatography with tandem mass spectrometry.

The effect of sample extraction and preparation on neuropeptidomic analysis of brain tissue by capillary liquid chromatography with tandem mass spectrometry was investigated. In agreement with previous reports, analysis of peptide extracts of brain tissue from animals sacrificed by microwave irradiation, which fixes tissue, allows identification of neuronally derived peptides whereas similar analysis of tissue from animals sacrificed without fixation does not. A comparison of a physical method for cell lysis (sonication) to physical combined with chemical cell lysis (sonication with detergent treatment) revealed that the latter method increased the number of neuronally derived peptides positively identified by approximately 3-fold, from 16 to 44, for analysis of microwave-fixed rat striatum. Use of synaptosome preparations also allowed detection of neuronally derived peptides (23 positively identified) without a requirement of microwave fixation, suggesting that this method may be a useful alternative for sample preparation. Although numerous peptides were identified in these experiments, several known neuropeptides were not detected including neuropeptide Y and neurotensin. Chemical properties such as hydrophobicity and atypical gas-phase fragmentation were found to account for the inability to detect these peptides. These results suggest that further improvement in sample preparation and automated spectral interpretation are needed to provide better coverage of neuropeptides in mammalian tissues. A total of 39 novel neuronally derived peptides, including some originating from proenkephalin and phosphatidylethanolamine binding protein, were identified in striatum and synaptosome.

Amino Acid Sequence↗

PubMed2005

Calcium/calmodulin-dependent protein kinase II activity and expression are altered in the hippocampus of Pb2+-exposed rats.

In the present study, we examined whether calcium/calmodulin-dependent protein kinase II (CaMKII) is affected by chronic developmental Pb2+ exposure. The effects of Pb2+ exposure on rat hippocampal CaMKII were assessed by measuring CaMKII activity, phosphorylation of CaMKII at threonine-286, and CaMKII alpha and beta protein levels. In the hippocampus of Pb2+-exposed 50-day-old rats known to exhibit deficits in hippocampal long-term potentiation (LTP) and spatial learning, there was a marked reduction (41%) in the apparent maximal velocity (Vmax) of CaMKII and a significant increase (22%) in apparent affinity of the enzyme. These Pb2+-induced changes in CaMKII activity could not be explained by changes in enzyme phosphorylation at threonine-286 or sensitivity to calmodulin. In vitro incubation of hippocampal homogenates from control rats, but not from Pb2+-exposed rats, with Pb2+ prior to assay recapitulated the increase in the affinity of the enzyme observed with in vivo exposure to Pb2+. Western blots of cytosolic and membrane fractions from hippocampus showed a significant decrease in the levels of CaMKII-beta but not alpha protein in the cytosolic fraction of Pb2+-exposed rats. These findings indicate effects of developmental Pb2+ exposure on CaMKII, a component of calcium signaling associated with synaptic plasticity, learning, and memory.

Animals↗

PubMed2005

Microscale sample deposition onto hydrophobic target plates for trace level detection of neuropeptides in brain tissue by MALDI-MS.

A sample preparation method that combines a modified target plate with a nanoscale reversed-phase column (nanocolumn) was developed for detection of neuropeptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A gold-coated MALDI plate was modified with an octadecanethiol (ODT) self-assembled monolayer to create a hydrophobic surface that could concentrate peptide samples into a approximately 200-500-microm diameter spot. The spot sizes generated were comparable to those obtained for a substrate patterned with 200-microm hydrophilic spots on a hydrophobic substrate. The sample spots on the ODT-coated plate were 100-fold smaller than those formed on an unmodified gold plate with a 1-microl sample and generated 10 to 50 times higher mass sensitivity for peptide standards by MALDI-TOF MS. When the sample was deposited on an ODT-modified plate from a nanocolumn, the detection limit for peptides was as low as 20 pM for 5-microl samples corresponding to 80 amol deposited. This technique was used to analyze extracts of microwave-fixed tissue from rat brain striatum. Ninety-eight putative peptides were detected including several that had masses matching neuropeptides expected in this brain region such as substance P, rimorphin, and neurotensin. Twenty-three peptides had masses that matched peaks detected by capillary liquid chromatography with electrospray ionization MS.

Amino Acid Sequence↗

PubMed2005

Depression, cytokines, and glial function.

It has been known for some time that cytokines made and released during systemic illness can result in a constellation of symptoms strikingly similar to those observed in depression. The overlap of the symptoms of depression and systemic illness raises the intriguing possibility that cytokines may be involved in the development and maintenance of mood disorders. Cytokines are small ubiquitous pleiotropic molecules that are made and released in response to a variety of stimuli. They have a multitude of actions throughout the body, including actions on the central and peripheral nervous systems. Alterations in the levels of circulating cytokines, especially the key proinflammatory cytokines, interleukin 6 and tumor necrosis factor alpha , have been linked to a variety of disease states including those involving central nervous system depression. In this brief review, epidemiological and clinical data on depression, as well as findings from relevant animal models, are examined for links between cytokine expression and depression. We suggest that glial cells, both as a source and target of cytokines, represent the overlooked targets involved in the etiology of depression.

Animals↗

PubMed2005

Glial fibrillary acidic protein and related glial proteins as biomarkers of neurotoxicity.

A variety of '-omic' technologies are being increasingly applied in preclinical safety assessments. Such approaches, however, have not been implemented in neurotoxicity safety evaluations. Current regulatory guidelines for assessing neurotoxicity emphasise reliance on traditional histopathological stains and behavioural testing batteries. Although these methods may be sufficient to detect some neurotoxic effects, they lack both the sensitivity and specificity required for broad-scale neurotoxicity screening. The glial reaction to nervous system damage, often termed gliosis, represents a hallmark of all types of nervous system injury. As such, the development and implementation of gliosis biomarkers represents a broadly applicable approach for neurotoxicity safety assessment. Using a panel of known neurotoxic agents, the authors have shown that the astroglial protein, glial fibrillary acidic protein (GFAP), can serve as one such biomarker of neurotoxicity. Qualitative and quantitative analysis of GFAP has shown this biomarker to be a sensitive and specific indicator of the neurotoxic condition. The implementation of GFAP and related glial biomarkers in neurotoxicity screens may serve as the basis for further development of molecular signatures predictive of adverse effects on the nervous system.

Biomarkers↗

PubMed2004

Focused microwave irradiation of the brain preserves in vivo protein phosphorylation: comparison with other methods of sacrifice and analysis of multiple phosphoproteins.

At any point in time, net protein phosphorylation represents the contribution of protein kinase and protein phosphatase activities affecting a specific site on a given substrate. Preservation of phosphorylated proteins in neural tissues has traditionally included flash-freezing or fresh tissue processing following tissue isolation. Rapid heat inactivation of protein kinases and phosphatases by focused microwave irradiation sacrifice represents another method to preserve, in vivo, brain protein phosphorylation state. In this study, we compared preservation of the phosphorylation state of a variety of phosphoproteins in the brain following sacrifice of mice by decapitation, decapitation into liquid nitrogen and focused microwave irradiation. We found that microwave irradiation generally provided the highest and most consistent levels of protein phosphorylation, regardless of the substrates examined in striatum and hippocampus. In general, flash-freezing resulted in the least preservation of phospho-state with ERK1/2 and CREB showing almost complete dephosphorylation. When regions of freshly decapitated brains were homogenized and incubated on ice for 30 min, ERK1/2 phosphorylation was completely lost, whereas it was well preserved in microwaved samples left at room temperature for 2 h. Loss of ERK1/2 phosphorylation in the fresh samples could not be attributed to substrate proteolysis. Our results indicate that focused microwave irradiation sacrifice may be required to achieve biologically relevant data for the in vivo protein phosphorylation state of many phosphoproteins.

Animals↗

PubMed2004

Induction of gp130-related cytokines and activation of JAK2/STAT3 pathway in astrocytes precedes up-regulation of glial fibrillary acidic protein in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of neurodegeneration: key signaling pathway for astrogliosis in vivo?

Reactive gliosis is a hallmark of disease-, trauma-, and chemical-induced damage to the central nervous system. The signaling pathways associated with this response to neural injury remain to be elucidated, but recent evidence implicates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway. Here, we used the known dopaminergic neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to selectively damage striatal dopaminergic nerve terminals and elicit a glial response. We then analyzed changes in gene expression and protein phosphorylation, in vivo, to identify ligands and mediators of the JAK-STAT pathway that accompany glial activation. Administration of MPTP caused rapid tyrosine (Tyr-705) phosphorylation and nuclear translocation of STAT3 in striatal astrocytes, prior to the induction of glial fibrillary acidic protein mRNA and protein. Pharmacological protection of dopaminergic nerve terminals with nomifensine abolished MPTP-mediated phosphorylation and translocation of STAT3 and prevented induction of astrogliosis. Among the Janus kinase family of tyrosine kinases, only JAK2 was associated with the phosphorylation of STAT3 after MPTP and, inhibition of JAK2 by AG490, in vivo, attenuated both the phosphorylation of STAT3 and induction of GFAP. The p44/42 mitogen-activated protein kinase (MAPK; ERK1/2) also was activated by MPTP, but was not associated with activation of STAT3, because serine (Ser-727) was not phosphorylated. The mRNA for ligands of the gp130-JAK/STAT3 signaling pathway, interleukin-6, leukemia inhibitory factor, and oncostatin M were elevated prior to activation of STAT3 and induction of astrogliosis; neuroprotection with nomifensine blocked these effects of MPTP. Taken together, our results suggest that the gp130-mediated activation of JAK2/STAT3 signaling pathway may play a key role in the induction of astrogliosis.

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

PubMed2004

Brain concentrations of d-MDMA are increased after stress.

RATIONALE: In the mouse but not the rat, d-3,4-methylenedioxymethamphetamine (d-MDMA) is a dopaminergic neurotoxicant. Various stressors and hypothermia protect against d-MDMA-induced neurotoxicity through unknown mechanisms, one of which could be a reduction in the distribution of d-MDMA to the brain. OBJECTIVES: We determined striatal levels of d-MDMA in relation to body temperature in mice exposed to a neurotoxic regimen of d-MDMA in the presence or absence of various stressors. METHODS: Female C57BL6/J mice received a neurotoxic regimen of d-MDMA (15.0 mg/kg s.c. as the base every 2 hx4) alone or in combination with manipulations with a known neuroprotective status. d-MDMA levels were determined by HPLC with fluorometric detection while rectal temperature provided core temperature status. Levels of dopamine, tyrosine hydroxylase and GFAP were used to assess neurotoxicity. RESULTS: Restraint, ethanol co-treatment and cold stress were neuroprotective, caused hypothermia and increased striatal d-MDMA levels by 4- to 7-fold. Corticosterone treatment, as a stress mimic, did not alter striatal d-MDMA or temperature and was not protective. The protective glutamate receptor antagonist, MK-801, doubled striatal d-MDMA levels and caused hypothermia. CONCLUSIONS: Although stress and other protective manipulations can alter the striatal concentration of d-MDMA their hypothermia-inducing properties appear a more likely determinant of their neuroprotection against the striatal dopaminergic neurotoxicity of d-MDMA.

Animals↗

PubMed2004

Selective changes in gene expression in cortical regions sensitive to amphetamine during the neurodegenerative process.

Gene expression profiles in several brain regions of adult male rats were evaluated following a d-amphetamine (AMPH) exposure paradigm previously established to produce AMPH neurotoxicity. Escalating doses of AMPH (5-30 mg/kg) were given over the course of 16 h per day in an 18 degrees C environment for 2 days. This paradigm produces neurotoxicity but eliminates or minimizes the hyperthermia and seizure activity that might influence gene expression in a manner unrelated to the neurotoxic effects of AMPH. The expression of 1185 genes was monitored in the striatum, parietal cortex, piriform cortex and posteriolateral cortical amygdaloid nucleus (PLCo) using cDNA array technology, and potentially significant changes were verified by RT-PCR. Gene expression was determined at time points after AMPH when neurodegeneration was beginning to appear (16 h) or maximal (64 h). Expression was also determined 14 days after AMPH to find long-term changes in gene expression that might be biomarkers of a neurotoxic event. In the parietal cortex there was a two-fold increase in neuropeptide Y precursor protein mRNA whereas nerve growth factor-induced receptor protein I-A and I-B mRNA decreased 50% at 16 h after the end of AMPH exposure. Although these changes in expression were not observed in the PLCo, insulin-like growth factor binding protein 1 mRNA was increased two-fold in the PLCo at 16 and 64 h after AMPH. Changes in gene expression in the cortical regions were all between 1.2- and 1.5-fold 14 days after AMPH but some of these changes, such as annexin V increases, may be relevant to neurotoxicity. Gene expression was not affected by more than 1.5-fold at the time points in the striatum, although 65% dopamine depletions occurred, but the plasma membrane-associated dopamine transporter and dopamine D2 receptor were decreased about 40% in the substantia nigra at 64 h and 14 days post-AMPH. Thus, the 2-day AMPH treatment produced a few changes in gene expression in the two-fold range at time points 16 h or more after exposure but the majority of expression changes were less than 1.5-fold of control. Nonetheless, some of these lesser fold-changes appeared to be relevant to the neurotoxic process.

Amphetamine↗

PubMed2004

Associations of cortical astrogliosis with cognitive performance and dementia status.

We examined 204 decedents of the autopsy component of the Honolulu-Asia Aging Study, a longitudinal cohort study, who had been clinically assessed for dementia. A sensitive ELISA technique was used to quantify glial fibrillary acidic protein (GFAP), a marker for astrogliosis, in four specific cortical brain regions and assess associations between GFAP and 1) a measure of cognitive function, 2) several clinical dementia conditions, and 3) neuritic plaque (NP) and neurofibrillary tangle (NFT) formation. Cognitive function was inversely associated with GFAP in the occipital, parietal and temporal lobes, but not in the frontal lobe. This relationship remained significant when the contribution of NP and NFT counts was removed. Further, compared to brain samples from non-demented individuals, significantly greater GFAP levels were found in samples from individuals diagnosed with Alzheimer's disease, mixed dementia, and vascular mediated dementia. Because elevated levels of GFAP reflect astroglial responses to even subtle forms of neural damage, our data indicate that increments in GFAP may provide independent, supporting evidence for the damage underlying dementia, even in the absence of other evidence of neuropathology such as the presence of NPs or NFTs. Our findings underscore the need to look beyond standard neuropathological measures putatively linked to specific neuropathological conditions in efforts to identify common cellular and molecular processes that contribute to dementia.

Aged↗

PubMed2003

Neuronal and astroglial responses to the serotonin and norepinephrine neurotoxin: 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine.

1-Methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP) causes long-term loss of forebrain serotonin (5-HT) and norepinephrine (NE) and consequently, is unlike 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its other 2'-analogs that primarily deplete striatal dopamine (DA). In the present investigation into the acute effects of 2'-NH2-MPTP in mice, profound decreases in cortical and hippocampal 5-HT and NE to 10 to 40% of control were observed as early as 30 min post-treatment and lasted throughout the ensuing 21 days. Striatal DA was decreased to 60 to 80% of control during the first 48 h but returned to normal by 72 h. Reactive gliosis, which occurs in response to neurodegeneration was not evident by immunocytochemistry but was detected by enzyme-linked immunosorbent assay, where glial fibrillary acidic protein (GFAP) was increased to 130% of control in cortex, hippocampus, and brain stem 48 to 72 h post-treatment. To explore the possibility that 5-HT modulates the astrocytic response to injury, 2'-NH2-MPTP was used to damage 5-HT axons 2 weeks before administration of the potent DA neurotoxin 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'-CH3-MPTP). Despite a 90% decrement in striatal DA in 2'-NH2-MPTP/2'-CH3-MPTP-treated mice, increases in GFAP were attenuated compared to mice treated with 2'-CH3-MPTP alone. Thus, 2'-NH2-MPTP causes severe and immediate decrements in 5-HT and NE in frontal cortex and hippocampus, yet induces a modest GFAP response compared with other MPTP analogs that have their primary effect on DA. These results demonstrate the importance of obtaining quantitative assessments of GFAP to detect astroglial responses associated with selective damage to neurotransmitter systems with low-density innervation and suggest that serotonin may facilitate the astrocytic response to striatal injury.

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