Biomedical subjects

G J Harry

Publications and source records attributed to G J Harry.

At least 37 records · Page 2Linked to original sources

PubMed1997

Trimethyltin induces gelatinase B and urokinase in rat brain.

The neurotoxicant trimethyltin (TMT) increases mRNA levels for cytokines, tumor necrosis factor-alpha, interleukin-1alpha, and interleukin-6. Cytokines induce matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA). MMPs and uPA disrupt extracellular matrix. Since matrix damage may play a role in the neuropathological changes seen with TMT toxicity, we determined the effect of TMT on proteolytic enzyme production. Adult rats were injected with 8.0 mg TMT/kg. At different times after TMT injection, tissue samples from frontal lobe and hippocampus were assayed for MMPs and uPA, using gelatin-substrate and casein/plasminogen-substrate zymography. Gelatinase B (92 kDa type IV collagenase) production increased significantly in frontal lobe tissue at 24, 48 and 96 h, and in hippocampus at 48 h compared to saline-injected controls. Gelatinase A (72 kDa type IV collagenase) was significantly decreased at 12 and 24 h in frontal lobe compared to controls. Urokinase-type PA was significantly increased in hippocampus at 12 and 96 h, and in frontal lobe at 96 h compared to controls. Gelatinase B and uPA are up-regulated by TMT in frontal lobe and hippocampus, suggesting that they may contribute to the neuropathology of TMT.

Animals↗

PubMed1997

Lead-induced developmental changes in AP-1 DNA binding in rat brain.

Exposure to lead during ontogeny is detrimental to the growth and development of the brain. Morphological abnormalities occur in the developing brain, which are manifested as mental retardation and other neurological disorders. Despite extensive research, the biochemical mechanism for neurological effects of lead has not been established but appears to be at the level of the genome since aberrant expression of developmentally-important genes has been reported. Basal levels of activator protein 1 (AP-1) transcription factor DNA binding are elevated in the rat brain during the early postnatal period. The AP-1 DNA binding complex is composed of a Jun:cAMP responsive element binding protein dimer, which appears to modulate expression of developmentally-important genes that contain AP-1 binding sites in their promoter. Brain regions from perinatally lead-exposed rats were examined on postnatal days 3, 9 and 15 for DNA binding activity to the AP-1 DNA sequence. AP-1 DNA binding activities were significantly increased on postnatal day 3 in hippocampus and cortex from lead-treated rats with no other area (frontal lobe or brainstem) or timepoint showing significant changes. Since no increases were detected in the level of Jun protein which is a component of the AP-1 binding complex, post-translational modification may be involved in enhancing DNA binding activity. By altering levels of AP-1 DNA binding to the promoter regions, lead exposure may be changing the levels of mRNA synthesis of developmentally important genes.

Animals↗

PubMed1997

Persisting learning deficits in rats after exposure to Pfiesteria piscicida.

Pfiesteria piscicida and other toxic Pfiesteria-like dinoflagellates have been implicated as a cause of fish kills in North Carolina estuaries and elsewhere. Accidental laboratory exposure of humans to P. piscicida has been reported to cause a complex syndrome including cognitive impairment. The current project was conducted to experimentally assess the possibility of cognitive effects of P. piscicida exposure in rats. Samples of water from aquaria in which P. piscicida zoospores were killing fish were frozen, a procedure that has been found to induce encystment. Thawed samples were injected into albino Sprague-Dawley rats. A significant learning impairment was documented in rats administered samples of P. piscicida that were recently frozen. Prolonged storage of Pfiesteria samples diminished the effect. No effect was seen in the recall of a previously learned task, but when the rats were called upon to learn a new task, the Pfiesteria-treated animals showed a significant learning deficit. This effect persisted up to at least 10 weeks after a single injection of Pfiesteria. The Pfiesteria-induced learning deficit did not seem to be associated with any obvious debilitation or health impairment of the exposed rats. Deficits in habituation of arousal and rearing behavior were detected using a functional observational battery. No Pfiesteria-induced effects on blood count and white cell differential or in a standard pathological screening of brain, liver, lung, kidney, and spleen tissue were seen at 2 months after exposure. These studies document a persistent learning impairment in rats after exposure to the dinoflagellate P.piscicida in otherwise physically well-appearing rats. This effect may partially model the symptoms of cognitive impairments that humans have shown after Pfiesteria exposure.

Animals↗

PubMed1996

Developmental exposure to lead interferes with glial and neuronal differential gene expression in the rat cerebellum.

Exposure to lead (Pb) has been shown to disrupt developmental processes in the brain and to result in impaired brain function. In these studies, we examined the role of differential gene expression as a possible target site which may partially mediate Pb's neurotoxicity. Animals were lactationally exposed to 0.2% lead acetate from birth to weaning. On postnatal days (PND) 3, 6, 9, 12, 15, 20, 25, 30, 40, and 50, the cerebelli of control and Pb-exposed pups were examined, by Northern blot analysis for changes in the developmental profiles of neuronotypic and gliotypic markers: Growth-associated protein (GAP-43), myelin basic protein (MBP), and glial fibrillary acidic protein (GFAP), while actin was monitored as an indicator of generalized effects on developmental gene expression and exhibited no significant changes following Pb exposure. On PND 9, Pb exposure resulted in a significant stimulation in the expression of the neuronal GAP-43 mRNA. Although Pb induced an early onset of MBP gene expression, the mRNA levels for both MBP and GFAP were decreased between PND 20 and 50, in Pb-exposed animals. These studies suggest that exposure to Pb may selectively interfere with critical developmental gene expression.

Actins↗

PubMed1996

Lead-induced alterations of glial fibrillary acidic protein (GFAP) in the developing rat brain.

The developing nervous system is preferentially vulnerable to lead exposure with alterations in neuronal and glial cells of the brain. The present study examined early lead-induced alterations in the developing astrocyte population by examination of the developmentally regulated astrocyte specific protein, glial fibrillary acidic protein (GFAP). A developmental profile (Postnatal Day (PND) 6, 9, 12, 15, 20, and 25) for GFAP mRNA was generated for the cortex and hippocampus of developing Long-Evans hooded male rats under various lead exposure conditions: (1) prenatal (Gestational Day 13 to birth), (2) postnatal (Postnatal Day 1 to Postnatal Day 20), or (3) perinatal (Gestational Day 13 to Postnatal Day 20) exposure to lead acetate (0.2% in the drinking water of the dam). Control GFAP mRNA levels displayed a developmentally regulated profile of expression. In the cortex this was characterized by a transient elevation in peak level between PND 9 and PND 15 followed by a decline to within adult levels by PND 25. Under all lead acetate exposure conditions, the cortex showed an increase in the peak level of expression and extended the time of elevation of GFAP mRNA until PND 20. Levels of GFAP were elevated at PND 60 but not as early as PND 28. In the control hippocampus, levels of GFAP mRNA gradually increased until PND 20 followed by a sharp decline at PND 25. Postnatal and perinatal lead exposure followed a similar pattern; however, levels declined earlier at PND 20. Following prenatal lead exposure, levels of GFAP mRNA showed an earlier peak at PND 12 and a decrease as early as PND 15. By PND 60 protein level for GFAP was elevated in the postnatal lead exposure group only. As demonstrated by GFAP immunoreactivity, these lead-induced elevations were not associated with astrocyte hypertrophy. Following a physical injury in the cortex, astrocyte reactivity was similar between lead-exposed and control rats. These data suggest an alteration in the timing of astrocyte differentiation and maturation in the brain following developmental lead exposure.

Analysis of Variance↗

PubMed1996

GAP-43 mRNA expression in the developing rat brain: alterations following lead-acetate exposure.

The developmental neurotoxicity of environmental lead exposure manifests as alterations in neural functioning and perturbed axonal and dendritic development. To examine the hypothesis that such lead-induced alterations in the neural network are associated with an altered mRNA expression of a specific neural cell growth associated protein, mRNA levels of GAP-43 (growth associated protein 43) were measured in the cortex and hippocampus of developing Long-Evans hooded rats following various lead exposure paradigms. Postnatal developmental profiles (PND 6, 9, 12, 15, 20, and 25) of mRNA expression were generated following either prenatal (gestational day 13 to birth), postnatal (postnatal day 1 to postnatal day 20), or perinatal (gestational day 13 to postnatal day 20) exposure to lead acetate (0.2% in the drinking water of the dam). In control rats, GAP-43 mRNA levels displayed a distinct developmentally regulated profile of expression in both the cortex and hippocampus, characterized by an elevated level of expression within the first week of life. This peak level of expression was significantly depressed following either postnatal or perinatal exposure to lead acetate, while prenatal lead exposure produced an initial elevation of GAP-43 mRNA on postnatal day 6 followed by a sharp decline. These data suggest that lead exposure results in altered mRNA expression of a specific neural cell growth associated protein critical to the normal process of development. This perturbation in expression may play a role in the previously reported effects of lead acetate on axonal elongation during development of the nervous system and the subsequent alteration in nervous system functioning.

Actins↗

PubMed1995

The reproductive and neural toxicities of acrylamide and three analogues in Swiss mice, evaluated using the continuous breeding protocol.

Acrylamide is a known genetic, reproductive, and neural toxicant, although it is not known if one effect is predominant. The toxicities of several structural analogues of acrylamide have been incompletely characterized, and the relative sensitivity of the second generation is not known. The present studies were designed to explore the relationship between neurotoxicity and reproductive toxicity, to further characterize the toxicities of three acrylamide analogues, and to evaluate the relative sensitivity of a second generation to these compounds. For the F0 generation, male and female Swiss CD-1 mice were provided drinking water containing acrylamide (ACR; 3, 10, 30 ppm), N,N'-methylenebisacrylamide (MBA; 10, 30, 60 ppm), N-(hydroxymethyl)acrylamide (HMA; 60, 180, 360 ppm), or methacrylamide (MACR; 24, 80, 240 ppm) during and after a 14-week cohabitation. The last litter was reared and dosed after weaning until mating at 74 +/- 10 days of age with the same level of compound given to the parents Neurotoxicity was assessed at several times in both generations by measuring forelimb and hindlimb grip strength. In the F0 generation, ACR caused an 11% decrease in pup number without measurable neurotoxicity; female fertility was not affected. Although both generations consumed the same amount of ACR, there were larger changes in the fertility-related endpoints in the F1 mice than in the F0's, with no concomitant change in organ weights or sperm parameters. In F0 mice, MBA reduced the number of live pups and their adjusted weight, with no neurotoxicity and no change in F0 female reproduction. MBA caused greater adverse effects in the second generation, concomitant with increased consumption. In the F0 generation, HMA caused the largest decrease in pup number during cohabitation (26%) together with a small effect on grip strength. Female reproduction was not affected. The second generation consumed more HMA and showed slightly greater toxic effects. In both generations, MACR was negative for both neurotoxicity and reproductive toxicity. Dominant-lethal studies showed that the fertility effects for ACR, MBA, and HMA could be explained by a male-mediated increase in postimplantation loss. These studies found that dominant lethality occurred without structural effects on the reproductive system in the presence of only minor effects on grip strength and without detectable neural histopathology. Female reproduction was not significantly affected by these compounds at the doses used. Thus, these data confirm the male as the affected gender and that the reproductive toxicity was greater than motoneuron toxicity when measured as grip strength.

Acrylamide↗

PubMed1995

Trimethyltin increases interleukin (IL)-1 alpha, IL-6 and tumor necrosis factor alpha mRNA levels in rat hippocampus.

Within the central nervous system (CNS), cytokines are though to have active roles in pathophysiological changes seen in various neurological diseases and trauma. The present study was undertaken to examine the early response of pro-inflammatory cytokines following exposure to a specific neurotoxicant (trimethyltin; TMT). mRNA levels for interleukin (IL)-1 alpha, IL-1 beta, IL-6 and tumor necrosis factor (TNF) alpha were measured in the hippocampus of adult male Long-Evans hooded rats following an acute injection of trimethyltin hydroxide (8 mg TMT/kg body weight). At various times following exposure (6 h to 8 days), hippocampal tissues were excised and relative changes in cytokine mRNA levels were assessed by reverse transcription and polymerase chain reaction. IL-1 alpha, IL-6 and TNF alpha mRNA levels in the hippocampus increased within 6 h and remained elevated for 8 days. Quantitative analysis of mRNA transcripts revealed a two-fold increase in both IL-6 and TNF alpha within 6 h and a continued elevation of TNF alpha to 9-fold by 12 h. Within 96 h, glial fibrillary acidic protein (GFAP) mRNA levels were elevated in the hippocampus. Histological examination showed sparse individual neuronal necrosis at this time in both the pyramidal and granule cell regions with no increase in astrocyte GFAP immunoreactivity. However, an early, 24 h, response of microglial cells was indicated by increased lectin binding. This morphological profile progressed over time to a profound neuronal loss in the CA3-4 granule cell layer and marked astrocyte hypertrophy. The onset of pro-inflammatory cytokine mRNA expression appears to be temporally associated with histological evidence of elevated microglia in the hippocampus. It is proposed that microglia and pro-inflammatory cytokines play a modulatory role in the early stages of TMT-induced neurotoxicity.

Animals↗

PubMed1995

Exposure to lead-acetate modulates the developmental expression of myelin genes in the rat frontal lobe.

Postnatal exposure to high levels (4%) of lead (Pb) have been shown to disrupt myelin formation and result in abnormal conduction of nerve impulses, components necessary for information processing in the CNS. To investigate whether the pathological changes in myelin, due to Pb exposure, might be partially mediated by modulations of the expression of genes involved in CNS myelin, we have examined the developmental profiles of the proteolipid protein (PLP) and myelin basic protein (MBP), two major structural constituents of CNS myelin and 2',3'-cyclic nucleotide 3' phosphodiesterase (CNP), a non-structural enzyme associated with myelin formation. Rat pups were postnatally exposed, from birth to weaning, to moderate amounts of Pb (0.2%), in the drinking water of the dam, and their frontal cortices were assayed for changes in the expression profile of the above genes by Northern Analysis. On PND 20, Pb resulted in a dramatic stimulation of the mRNA levels of PLP and a small increase in MBP mRNA levels, but had no effect on the CNP message. These data suggest that moderate levels of Pb selectively interfere with the gene expression of structural proteins of CNS myelin and may thus influence the composition of myelin in this way.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗

PubMed1994

Differential effects of polychlorinated biphenyl congeners on phosphoinositide hydrolysis and protein kinase C translocation in rat cerebellar granule cells.

Previous reports from our laboratory have suggested that the neuroactivity of some polychlorinated biphenyl (PCB) congeners is associated with perturbations in cellular Ca(2+)-homeostasis. We have characterized further the neurochemical effects of PCBs on signal transduction in primary cultures of cerebellar granule cells. The present experiments found that neither 2,2'-dichlorobiphenyl (DCBP), an ortho-substituted congener, nor 3,3',4,4',5-pentachlorobiphenyl (PCBP), a non-ortho-substituted congener, affected basal phosphoinositide (PI) hydrolysis in cerebellar granule cells. However, at concentrations up to 50 microM, DCBP potentiated carbachol-stimulated PI hydrolysis, while decreasing it at 100 microM. PCBP, on the other hand, had no effect on carbachol-stimulated PI hydrolysis in concentrations up to 100 microM. [3H]Phorbol ester ([3H]PDBu) binding was used to determine protein kinase C (PKC) translocation. DCBP increased [3H]PDBu binding in a concentration-dependent manner and a twofold increase was observed at 100 microM in cerebellar granule cells. PCBP had no effect on [3H]PDBu binding at concentrations up to 100 microM. The effect of DCBP on [3H]PDBu binding was time-dependent and was also dependent on the presence of external Ca2+ in the medium. To test the hypothesis that DCBP increases [3H]PDBu binding by acting on receptor-activated calcium channels, the effects of DCBP were compared to those of L-glutamate. The effects of DCBP (50 microM) and glutamate (20 microM) were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Effect of lead acetate on nitrite production by murine brain endothelial cell cultures.

One of the mechanisms by which lead may cause a perturbation in the nervous system is the alteration of endothelial cell function. This study investigated the effect of lead acetate on constitutive and cytokine-induced production of nitrite, a marker of nitric oxide, in brain microvascular endothelial cells. Nitric oxide synthase may be a target for lead and changes in its function can result in a cascade of physiological effects seen in vivo. Concentrations of 10, 100, and 1000 nM lead acetate, in the presence or absence of 100 ng lipopolysaccharide/ml, 400 U interferon-gamma/ml and 100 U tumor necrosis factor-alpha/ml, were added to confluent cultures of brain microvascular endothelial cells. Concentrations of lead acetate as low as 10 nM decreased constitutive levels of nitrite by 50% without inhibiting the inducible levels. Addition of 1 microM lead acetate had no effect on [3H]L-leucine incorporation, lactate dehydrogenase release, or cellular morphology, indicating that the effect was selective. Increasing the concentration of extracellular calcium to 2 mM abolished the inhibitory effect of lead acetate on the constitutive production of nitrite. These studies suggest that low concentrations of lead are capable of inhibiting nitrite produced by the calcium-dependent constitutive form of nitric oxide synthase while the calcium-independent, inducible form of nitric oxide synthase is not affected. These data provide another testable hypothesis for the as yet undetermined mechanisms of lead neurotoxicity.

Amino Acid Oxidoreductases↗

PubMed1994

Developmental profiles of ornithine decarboxylase activity in the hippocampus, neocortex and cerebellum: modulation following lead exposure.

Ornithine decarboxylase (ODC) is a growth-associated enzyme which is critical for cell growth and transformation. ODC activity follows a specific ontogenetic pattern of activity in distinct brain regions according to their developmental stage. Perturbations in the pattern of ODC activity have been associated with brain damage including arrested cerebral growth. Modulations in the pattern of ODC activity were examined in the hippocampus, neocortex and cerebellum of neonatal rats (PND 3, 6, 9, 15) exposed via the dam to 0.2% lead-acetate (Pb2+ prenatally (gestational day 13 to birth), postnatally (PND 1-15) or perinatally (gestational day 13 to PND 15). Prenatal exposure to Pb2+ perturbed the profile of ODC activity in all three brain regions examined, while postnatal exposure to Pb2+ resulted in prolonged stimulations of ODC activity in the cerebellum. Following prenatal exposure, these effects were manifested as a stimulation of ODC activity in the hippocampus, a repression of activity in the neocortex and a combination of these effects in the cerebellum. Perinatal exposure to Pb2+ transiently modulated the pattern of ODC activity similarly in all three brain regions, in a characteristic manner irrespective of their developmental stage. These Pb(2+)-induced modulations of ODC activity suggest that polyamine-dependent processes may play a significant role in the manifestation of Pb(2+)-induced neurotoxicity dependent upon developmental factors at specific exposure periods.

Aging↗

PubMed1994

Modulation of developmental cerebellar ornithine decarboxylase activity by lead-acetate.

The developing brain is particularly susceptible to the neurotoxic effects of lead exposure. The ontological profile of ornithine decarboxylase (ODC) activity in the cerebellum was examined following lactational exposure of rats to 0.2% lead acetate (Pb). Relative to controls, Pb-exposure induced ODC activity levels in a transient manner with a 50% increase at postnatal day (PND) 6, a 20% increase at PND 9, returning to control basal levels by PND 15. These effects were seen at exposure levels of Pb that did not alter the normal growth and body weight of either the lactating dam or the developing pups. Basal cerebellar ODC activity in homogenates was increased with addition of low concentrations of Pb acetate (0.01 microM and 0.1 microM), while concentrations of 1 microM or greater were inhibitory. The effects of Pb acetate on tissue ODC activity in vitro were not mimicked by the addition of calcium chloride. Unlike tissue ODC activity, incubation of these metals with a pure ODC protein preparation exhibited fluctuations in ODC activity possibly due to the ionic interactions of Pb or calcium chloride. Calcium homeostatic mechanisms appeared to be unchanged with Pb exposure, at this dose, in that neither 45Ca-uptake (both mitochondrial and microsomal) nor synaptosomal Ca(2+)-ATPase activity was altered. These data suggest that alterations in ODC activity may be indicative of subtle toxicant induced perturbations during early development. Although the precise mechanism by which Pb may induce ODC activity in developing tissue is unknown, our results suggest that Pb may specifically alter ODC activity via cytosolic interactions.

Age Factors↗

PubMed1993

Correlations between developmental ornithine decarboxylase gene expression and enzyme activity in the rat brain.

The rise and decline in cerebral ODC activity during specific stages of development has been attributed to cytoplasmic intermediates which regulate ornithine decarboxylase activity. Here we examine whether transcriptional regulation contributes to the production of the developmental profiles of ODC activity. Postnatal cerebellar and neocortical tissue were obtained from Long-Evans hooded rats at postnatal days (PND) 5, 10, 15, 20, 25, 30, 90 and probed for ODC and actin gene expression, by Northern analysis. Our results indicate that ODC gene expression in the cerebellum was elevated at PND 5 and 10 followed by a gradual drop to the adult low levels by PND 20. By contrast, high levels of ODC gene expression in the neocortex were seen at PND 5 with an abrupt decrease at day 10 to low adult levels. The expression of the ODC gene in the neocortex follows closely the pattern for the ODC enzyme activity; however, it tends to remain elevated longer in the cerebellum. The levels of actin gene expression exhibited a distinct developmental profile in the postnatally developing cerebellum. However, actin mRNA levels remained unchanged in the neocortex, consistent with the prenatal development of this region. Our findings suggest that ODC gene expression may play an important role in the production of the ontogenetic patterns of ODC activity.

Actins↗

PubMed1993

Effects of selected neuroactive chemicals on calcium transporting systems in rat cerebellum and on survival of cerebellar granule cells.

This investigation examined the relationship between alteration of Ca(2+)-transport systems and cytotoxicity in vitro for a number of neuroactive chemicals including environmental pollutants. 45Ca2+ uptake as a measure of Ca2+ sequestration was determined in mitochondria and microsomes isolated from cerebella of adult male Long-Evans hooded rats by differential centrifugation. Ca2+ extrusion, measured as Ca(2+)-ATPase activity, was determined in synaptosomes prepared by sucrose density gradient. Cytotoxicity (lactate dehydrogenase leakage) was assessed in primary cultures of cerebellar granule cells from 6- to 8-day-old Long-Evans rats. N-Methyl-D-aspartic acid (NMDA) did not alter synaptosomal Ca(2+)-ATPase activity or 45Ca2+ uptake in mitochondria and microsomes. However, chlorpromazine (CPZ), aluminum (Al), permethrin (PER), and deltamethrin (DEL) inhibited Ca2+ sequestration by mitochondria and microsomes. The IC50 values (microM) for CPZ, Al, PER, and DEL were 67.8, 671, 4.2, and 91.2 for mitochondrial 45Ca2+ uptake, and 129.9, 1384, > 50, and > 200 for microsomal 45Ca2+ uptake, respectively. CPZ, PER, and DEL also inhibited synaptosomal Ca(2+)-ATPase activity in a concentration-dependent manner with IC50 values of 62.5, > 400, and 246.9 microM, indicating an effect on the Ca(2+)-extrusion process. Al increased Ca(2+)-ATPase activity (EC50 = 833 microM). Although NMDA did not inhibit Ca(2+)-transport systems, it was cytotoxic at 250 microM and higher concentrations after 2 hr of exposure. Similarly, CPZ was cytotoxic at concentrations of 25 and 10 microM after 4 hr exposure. However, PER, DEL, and Al were not cytotoxic at any concentration up to 500 microM. Of all the chemicals tested, CPZ was the most potent in inhibiting Ca(2+)-transporting systems and was also cytotoxic.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗

PubMed1993

Trimethyltin-induced c-fos expression: adolescent vs neonatal rat hippocampus.

In the adult animal, the immediate early genes such as c-fos and c-jun, and other activity-dependent genes such as ornithine decarboxylase (ODC) are induced within minutes to hours in response to perturbations to the cellular environment. We have examined the induction of these genes following acute exposure to trimethyltin (TMT) using Northern blot analysis. The induction of these genes within the hippocampus and the cerebellum was examined half an hour following acute exposure to TMT (4 mg/kg, sc). In the neonatal (PND 4) rat hippocampus, the basal expression of c-fos, c-jun, and ODC appeared to be unaltered following TMT exposure. However, in the adolescent (PND 35) rat, TMT exposure produced a dramatic induction of c-fos mRNA in the hippocampus within half an hour, while beta-actin expression remained constant. No TMT-induced changes in the expression of c-fos were seen in the cerebellum of adolescent animals. Furthermore, expression of c-jun mRNA was not altered in either the mature hippocampus or the cerebellum half an hour following TMT exposure. These results suggest that c-fos may be involved in the response of the brain to TMT in an age-dependent and region-specific manner.

Aging↗

PubMed1993

Comparative effects of two polychlorinated biphenyl congeners on calcium homeostasis in rat cerebellar granule cells.

Some polychlorinated biphenyls (PCBs) have been reported to alter locomotor activity and decrease brain dopamine function in laboratory animals. PCBs with ortho- and/or parachlorine substitutions and varying number of chlorinations are known to decrease cell dopamine content in vitro and have been detected in brains of animals exposed to PCBs, suggesting that the neurotoxicity could be mediated by ortho-substituted congeners. Dopamine or other neurotransmitter uptake and release phenomena are dependent on the maintenance of intracellular Ca2+ homeostasis, and perturbations in Ca2+ homeostasis could lead to altered cell function and/or death. We compared the effects of two PCB congeners on Ca2+ homeostasis in cerebellar granule cells: 2,2'-dichlorobiphenyl (DCBP), a putative neurotoxic congener, and 3,3',4,4',5-pentachlorobiphenyl (PCBP), a presumed nonneurotoxic congener. In cerebellar granule cells (6-8 days in vitro), DCBP was cytotoxic as indicated by a significant increase in LDH leakage at 200 microM after 2 hr of exposure and at 100 microM after 4 hr exposure. PCBP, on the other hand, did not affect LDH leakage even at 200 microM for up to 4 hr. Although both congeners increased cerebellar granule cell [Ca2+]i, DCPB was more effective in increasing [Ca2+]i to a greater extent than PCBP. The increase in [Ca2+]i produced by both congeners was not transient, but a steady rise was observed with time. To understand cellular Ca(2+)-buffering capacity, Ca2+ sequestration and Ca2+ extrusion were studied in mitochondria, microsomes, and synaptosomes, isolated from adult rat cerebellum. DCBP was a potent inhibitor of 45Ca2+ uptake by mitochondria (IC50 = 6.17 +/- 0.53 microM) and microsomes (IC50 = 7.61 +/- 0.35 microM). PCBP inhibited Ca2+ sequestration by mitochondria (68% of control) and microsomes (72% of control), but the effects were much less than those produced by equivalent concentrations of DCBP. Synaptosomal Ca(2+)-ATPase was inhibited by DCBP, but not by PCBP. These results indicate that at concentrations where cytotoxicity in cerebellar granule cells was not observed, DCBP increased intracellular [Ca2+]i, and at the same concentrations, Ca2+ sequestration by intracellular organelles and Ca(2+)-ATPase in synaptic plasma membrane were inhibited. Although PCBP increased [Ca2+]i in cerebellar granule cells to some extent, it was not potent in affecting Ca2+ sequestration or Ca2+ extrusion in adult cerebellar components. Hence, PCBP-induced slight increase of [Ca2+]i levels in the cells might have been associated with effective Ca2+ sequestration by intracellular organelles, as seen in cerebellar preparations. The results of this study support the hypothesis that the position of chlorine substitution on the biphenyl ring and/or number of chlorine substitutions may have significant implications for predicting potential effects of PCB congeners in the nervous system, and perturbations in Ca2+ homeostasis might play a significant role in the neuroactivity of PCBs.

Animals↗

PubMed1993

Developmental changes in carbachol-stimulated inositolphosphate release in pigmented rat retina.

Carbachol-stimulated release of inositolphosphates (IP) was studied in the whole retina from Long-Evans rats of different ages (day 5, 10, 15, 20, adult) following in vitro incorporation of [3H]myo-inositol. Unlike the albino rat retina, the pigmented retina was highly light-sensitive, making it necessary to dark adapt the animals and perform retinal dissections under low illumination to prevent light-induced IP release. Retinae from postnatal day 10 rats showed the highest amount of carbachol-stimulated IP released. This response to carbachol decreased with age until postnatal day 20 when it reached adult levels. The pigmented rat retina showed a sharp fall in the degree of carbachol (1 mM)-stimulated IP released at the time of eye-opening (450% above basal in retinae from 10 day old animals, as compared to 230% above basal in 15 day old retinae). Basal release of IP was not altered in the retina during development. Muscarinic cholinergic receptor density was, however, found to increase 5 fold with age, reaching adult levels by PND 20. Retinal weight and protein per retina also increased (four fold) from day 5 to adult; however, the in vitro incorporation of [3H]myo-inositol into phosphoinositides (calculated as per mg protein) did not change during development. Thus, in animals prior to eye opening, a much higher proportion of phosphoinositides appears to be hydrolyzed upon muscarinic receptor stimulation. During retinal development a change in sensitivity to the agonist-sensitive pool(s) of phosphoinositides may occur and/or there may be alterations in the efficacy of receptor coupling to the second messenger system resulting in the disassociation observed between the drastic increase in receptor number and the apparent decrease in receptor-stimulated release of IP.

Aging↗