Biomedical subjects

F J Seidler

Publications and source records attributed to F J Seidler.

At least 19 recordsLinked to original sources

PubMed2002

Adolescent nicotine administration alters serotonin receptors and cell signaling mediated through adenylyl cyclase.

Nicotine is a neuroteratogen that targets synaptic function during critical developmental stages and recent studies indicate that CNS vulnerability extends into adolescence, the age at which smoking typically commences. We administered nicotine to adolescent rats via continuous minipump infusions from PN30 to PN47.5, using 6 mg/kg/day, a dose rate that replicates the plasma nicotine levels found in smokers, and examined 5HT receptors and related cell signaling during nicotine administration (PN45) and in the post-treatment period (PN50, 60, 75). Adolescent nicotine decreased 5HT(2) receptor binding in brain regions containing 5HT projections (hippocampus and cerebral cortex), with selectivity for females in the cerebral cortex; regions containing 5HT cell bodies showed either an increase (midbrain in males) or no change (brainstem). In contrast, there were no significant changes in 5HT(1A) receptors; however, the ability of the receptors to signal through adenylyl cyclase (AC) showed a switch from stimulatory to inhibitory effects in females during the post-treatment period. There were also transient alterations in AC responses to beta-adrenergic receptor stimulation, as well as pronounced induction of the AC response to the non-receptor-mediated stimulant, forskolin. Our results indicate that adolescent nicotine exposure alters the concentrations and functions of postsynaptic 5HT receptors in a manner commensurate with impaired 5HT synaptic function. The direction of change, emergence of defects after the cessation of nicotine administration, and sex-preference for effects in females, all support a relationship of impaired 5HT function to the higher incidence of depression seen in adolescent smokers.

Adenylyl Cyclases↗

PubMed2002

Perinatal exposure to environmental tobacco smoke upregulates nicotinic cholinergic receptors in monkey brain.

In humans, perinatal exposure to environmental tobacco smoke (ETS) is associated with neurobehavioral deficits. In the current study, we exposed Rhesus monkeys to ETS in late gestation and in the early neonatal period, and examined changes in neurotransmitter receptors in the brainstem and caudal portion of the cerebral cortex. Nicotinic acetylcholine receptors were markedly upregulated and the effect was selective in that there were no changes in m(2)-muscarinic acetylcholine receptors or in beta-adrenergic receptors. Nicotinic receptor upregulation is indicative of chronic cell stimulation by nicotine, and is a hallmark of nicotine-induced neuroteratogenesis. These results indicate that perinatal ETS exposes the fetus and neonate to quantities of nicotine that are sufficient to alter brain development.

Animals↗

PubMed2002

Functional alterations in CNS catecholamine systems in adolescence and adulthood after neonatal chlorpyrifos exposure.

Chlorpyrifos (CPF), one of the most widely used pesticides, is a neurobehavioral teratogen in animals. We administered CPF to neonatal rats on postnatal days (PN) 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), regimens devoid of overt systemic toxicity. We then examined the impact on catecholaminergic systems in adolescence (PN30) and adulthood (PN60), assessing basal neurotransmitter content and transmitter utilization rates (turnover) in brain regions comprising the major noradrenergic and dopaminergic projections. Although CPF had only sporadic effects on basal norepinephrine and dopamine content, it profoundly suppressed norepinephrine turnover across multiple regions, indicative of net reductions in presynaptic activity. Dopamine turnover showed less consistent effects, with subnormal turnover in some regions and activation in others. We also evaluated whether CPF exposure altered the ability of catecholamine systems to respond to acute cholinergic stimulation, elicited by administration of a single challenge dose of nicotine. In the normal brain, nicotine increases the utilization of norepinephrine and dopamine. With only a few exceptions, animals receiving neonatal CPF exposure showed lasting desensitization of the nicotine response; not only was the activation by nicotine blunted in the CPF group, but in some regions the nicotine response was reversed, eliciting a reduction in transmitter turnover. These results indicate that neonatal CPF exposure produces widespread deficiencies in catecholaminergic synaptic function that persist into adulthood, and that are best revealed by dynamic measures of synaptic activity and responsiveness, as opposed to static markers like basal transmitter levels. The effects seen here are likely to contribute to alterations in behavioral performance that persist or emerge long after the termination of CPF exposure.

Aging↗

PubMed2002

Are developing beta-adrenoceptors able to desensitize? Acute and chronic effects of beta-agonists in neonatal heart and liver.

During fetal and neonatal development, beta-adrenergic receptors (beta-ARs) appear to be resistant to desensitization by beta-agonist drugs. To determine the mechanisms underlying the regulatory differences between adults and neonates, we administered isoproterenol, a mixed beta(1)/beta(2)-AR agonist, and terbutaline, a beta(2)-selective agonist. Effects were examined in the ensuing 4 h after a single injection, or after the last of four daily injections. We prepared cell membranes from heart (predominantly beta(1)-ARs) and liver (predominantly beta(2)-ARs) and assessed signal transduction in the adenylyl cyclase (AC) pathway. In the first few hours after a single administration of isoproterenol to adult rats, cardiac beta-ARs showed activation of G proteins (elevated AC response to forskolin) and desensitization of beta-AR-mediated responses; after the fourth injection, heterologous desensitization emerged, characterized by a loss of signaling mediated either through beta-ARs or glucagon receptors. Terbutaline evoked an increase in the forskolin response but no desensitization of receptor-mediated responses. When we gave the same treatments to neonatal rats, we observed cardiac G protein activation, but there was neither homologous nor heterologous desensitization of beta-ARs or glucagon receptors. In the adult liver, isoproterenol and terbutaline both failed to evoke desensitization, regardless of whether the drugs were given once or for 4 days. In neonates, however, acute or chronic treatment elicited homologous desensitization of beta-AR-mediated AC signaling, while sensitizing the response to glucagon. These results show that neonatal beta-ARs are inherently capable of desensitization in some, but not all, cell types; cellular responses can be maintained through heterologous sensitization of signaling proteins downstream from the receptor. Differences from adult patterns of response are highly tissue selective and are likely to depend on ontogenetic differences in subtypes of beta-ARs and AC.

Adenylyl Cyclases↗

PubMed2002

Beta-adrenoceptor control of G protein function in the neonate: determinant of desensitization or sensitization.

Neonatal beta-adrenoceptors (beta-ARs) are resistant to agonist-induced desensitization. We examined the functioning of G(i) and G(s) after repeated administration of beta-AR agonists to newborn rats. Isoproterenol (beta(1)/beta(2) agonist) obtunded G(i) function in the heart but not the liver; in contrast, terbutaline, a beta(2)-selective agonist, enhanced G(i) function. Isoproterenol, but not terbutaline, increased membrane-associated G((s)alpha), which would enhance receptor function. In addition, isoproterenol increased and terbutaline maintained the proportion of the short-splice (S) variant of G((s)alpha) in the membrane fraction; G((s)alpha)S is functionally more active than the long-splice variant. Either isoproterenol or terbutaline treatment increased G((s)alpha) in the cytosolic fraction, a characteristic usually associated with desensitization in the adult. Decreased G(i) activity, coupled with increased membrane-associated G((s)alpha) concentrations and maintenance or increases in membrane G((s)alpha)S, provide strong evidence that unique effects on G protein function underlie the ability of the immature organism to sustain beta-AR cell signaling in the face of excessive or prolonged stimulation; these mechanisms also contribute to tissue selectivity of the effects of beta-agonists with divergent potencies toward different beta-AR subtypes.

Adenylyl Cyclases↗

PubMed2002

beta-Adrenergic modulation of muscarinic cholinergic receptor expression and function in developing heart.

Imbalances of beta-adrenoceptor (beta-AR) and muscarinic ACh receptor (mAChR) input are thought to underlie perinatal cardiovascular abnormalities in conditions such as sudden infant death syndrome. Administration of isoproterenol, a beta(1)/beta(2)-AR agonist, to neonatal rats on postnatal days (PN) 2-5 caused downregulation of cardiac m(2)AChRs and a corresponding decrement in their control of adenylyl cyclase activity. Terbutaline, a beta(2)-selective agonist that crosses the placenta and the blood-brain barrier, was also effective when given either on PN 2-5 or during gestational days 17-20. Terbutaline failed to downregulate brain m(2)AChRs, even though it downregulated beta-ARs; beta-ARs and m(2)AChRs are located on different cell populations in the brain, but they are on the same cells in the heart. Destruction of catecholaminergic neurons with neonatal 6-hydroxydopamine upregulated cardiac but not brain m(2)AChRs. These results suggest that perinatal beta-AR stimulation shifts cardiac receptor production away from the generation of m(2)AChRs so that the development of sympathetic innervation acts as a negative modulator of cholinergic function. Accordingly, tocolytic therapy with beta-AR agonists may compromise the perinatal balance of adrenergic and cholinergic inputs.

Adenylyl Cyclases↗

PubMed2001

Heroin neuroteratogenicity: targeting adenylyl cyclase as an underlying biochemical mechanism.

Prenatal heroin exposure evokes neurochemical and behavioral deficits that in part, reflect disruption of septohippocampal cholinergic function. In earlier studies, we found that cholinergic synaptic defects involve changes in proteins, like protein kinase C, that are essential to receptor-mediated signaling. In the current study, we determined whether heroin targets another signaling protein, adenylyl cyclase (AC), which regulates the production of cAMP. Mice exposed to prenatal heroin showed subsequent postnatal elevations of AC activity that lasted into adulthood. The effect was most robust with stimulants that activate AC directly (forskolin, Mn(2+)), indicating increased expression of AC itself; we also identified shifts in catalytic properties suggestive of a change in the AC isoform. Superimposed on the overall induction of AC, there were transient deficits in the responses to stimulants working through G-proteins (NaF) or G-protein coupled receptors (isoproterenol, a beta-adrenoceptor agonist), indicating alterations at other steps in the signaling pathway. Effects on the regulation of AC activity were seen in brain regions with widely disparate maturational timetables and also occurred in regions, like the cerebellum, that are sparse in cholinergic input. These results suggest that the expression and/or function of signaling proteins distal to neurotransmitter receptors represent a major target for neurobehavioral teratogenesis by heroin; the fact that these targets are shared by otherwise unrelated neuroteratogens may account for a common set of neurochemical and behavioral anomalies in response to prenatal exposure to drugs or environmental chemicals.

Adenylyl Cyclases↗

PubMed2001

Beta-adrenoceptor signaling in the developing brain: sensitization or desensitization in response to terbutaline.

Beta(2)-adrenoceptor agonists are commonly used to arrest preterm labor but they also penetrate the placenta to stimulate fetal beta-adrenergic receptors (betaAR), and have been implicated in subsequent neurobehavioral deficits. We administered terbutaline to pregnant rats on gestational days (GD) 17-20 and during two postnatal (PN) periods, PN2-5 and PN11-14, that correspond to third trimester human neurological development. We then examined betaAR binding sites and adenylyl cyclase (AC) signaling in fetal brain or neonatal brain regions. Although fetal terbutaline administration evoked betaAR downregulation, the ability of isoproterenol to stimulate AC was enhanced instead of desensitized. Sensitization occurred at post-receptor signaling proteins, as augmented responses were also seen for stimulants that bypass the receptors to work on G-proteins (NaF) or that stimulate AC directly (forskolin and Mn(2+)). When terbutaline was given on PN2-5, betaAR downregulation was obtained in brainstem, forebrain and cerebellum, but desensitization of the AC response was seen only in the forebrain; the desensitization was heterologous, reflecting decrements in total AC activity rather than specific loss of the betaAR response. With treatment on PN11-14, only the cerebellum showed betaAR downregulation and induction at the level of post-receptor signaling proteins maintained the betaAR-mediated AC response. Our results indicate that, unlike the adult, betaAR signaling in the fetus and neonate is resistant to homologous desensitization by beta-agonists, and in fact, displays heterologous sensitization that sustains or enhances the overall response. The inability to desensitize betaAR responses may lead to disruption of neural cell development as a consequence of tocolytic therapy.

Adaptation, Physiological↗

PubMed2001

Neonatal chlorpyrifos administration elicits deficits in immune function in adulthood: a neural effect?

Neural input plays a key role in the establishment of immune function, and environmental agents or drugs that interfere with the development of the nervous system elicit corresponding immunologic deficits. In the current study, we gave neonatal rats the widely used organophosphate pesticide, chlorpyrifos (CPF), and determined the immediate and long-term effects on T-lymphocyte function. Exposure of neonatal rats to 1 mg/kg of CPF daily on postnatal days (PN) 1-4 had no immediate effect (PN5) on T-cell mitogenic responses to concanavalin A challenge. However, once the animals reached adulthood, T-cell responses were significantly impaired. There were no deficits in basal T-cell replication rates, implying that the adverse effect of CPF exposure was specific to mitogenic activation. Treatment during a later neonatal period (PN11-14) elicited similar deficits in adulthood. CPF administration leads to inhibition of cholinesterase, and a cholinergic connection is supported by the fact that the results seen here correspond to those seen with a direct cholinergic stimulant (nicotine) administered during gestation or adolescence. These results indicate that exposure to CPF during a developmental period in which this organophosphate pesticide is known to produce lasting changes in neural function, elicits corresponding, long-term deficits in immune competence.

Age Factors↗

PubMed2001

Adolescent nicotine: deficits in immune function.

Maternal cigarette smoking during pregnancy is known to alter immune function in the offspring and recent studies with animals indicate that prenatal nicotine exposure leads to lasting deficiencies in T-lymphocyte mitogenic responses, likely through excessive cholinergic stimulation during a critical stage of development. The current study was conducted to determine if the vulnerable period for nicotine-induced mis-programming of immune responses extends into adolescence, the stage at which most smokers begin tobacco use. Adolescent rats were given nicotine via osmotic minipump infusions on postnatal days (PN) 30-47.5, using a regimen that produces plasma levels (25 ng/ml) of nicotine similar to those in smokers or in users of transdermal nicotine patches. Toward the end of the infusion period (PN45) and 1 month after termination of nicotine exposure (PN80), we examined the mitogenic responses of splenocytes to Concanavalin A. Although no deficiencies were seen on PN45, there were robust decreases in mitogenic responses on PN80, with deficits apparent at both suboptimal and optimal concentrations of Concanavalin A. These results indicate that the adolescent immune system is vulnerable to nicotine-induced disruption of T-cell function.

Age Factors↗

PubMed2001

Fetal and adolescent nicotine administration: effects on CNS serotonergic systems.

Nicotine is a neuroteratogen that targets synaptic function during critical developmental stages and recent studies indicate that CNS vulnerability extends into adolescence, the time that smoking typically commences. We administered nicotine to pregnant or adolescent rats via continuous minipump infusions, using dose rates that replicate the plasma nicotine levels found in smokers. Fetal nicotine exposure (gestational days 4-21) decreased the cerebrocortical binding of paroxetine (PXT), a marker for the serotonin (5HT) transporter, likely indicative of a decrease in nerve terminals in that region; the effect lasted into adulthood. There was a corresponding increase in PXT binding in the midbrain/brainstem, the region containing the 5HT cell bodies that project to the cerebral cortex, a pattern typical of reactive sprouting in response to nerve terminal damage. After adolescent nicotine treatment (postnatal days 30-47), PXT binding was reduced in the hippocampus and striatum instead of the cerebral cortex, again accompanied by increased binding in the midbrain and brainstem; the patterns of effects within each region were gender-selective, although both males and females displayed abnormalities. Superimposed on this overall effect, there were transient increases in PXT binding, likely due to acute stimulant effects of nicotine. We also assessed 5HT presynaptic activity (5HIAA/5HT ratio). Withdrawal from adolescent nicotine treatment led to suppression of activity in the cerebral cortex and activation in the midbrain. These results indicate that both fetal and adolescent nicotine exposure elicit apparent damage to 5HT projections with reactive increases in regions containing 5HT cell bodies. Long-term changes in 5HT innervation and/or synaptic activity may play a role in the subsequent development of depression in the offspring of women who smoke during pregnancy or in adolescent smokers.

Aging↗

PubMed2001

Alterations in serotonin transporter expression in brain regions of rats exposed neonatally to chlorpyrifos.

Chlorpyrifos (CPF), one of the most widely-used organophosphate pesticides, is a suspected neuroteratogen. We administered CPF to neonatal rats on postnatal days (PN) 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), treatments devoid of overt toxicity. At the end of the treatment period (PN5 and 15, respectively) and 5-7 days later, we then examined the effects on paroxetine (PXT) binding to the presynaptic 5HT high-affinity transporter, a marker for serotonin (5HT) projections. In males, we found a persistent decrease in PXT binding across the two different treatment regimens, with deficits apparent in a brain region containing 5HT terminal fields (forebrain) as well as in a region containing 5HT cell bodies (brainstem). In contrast, females given the early treatment regimen (PN1-4) showed deficits in the brainstem but transient elevations in the forebrain; the later treatment regimen (PN11-14) had no significant effect on PXT binding in females. These data are consistent with earlier work showing brainstem cell injury resulting from neonatal CPF exposure, and indicate specific damage to 5HT neurons, with a consequent loss of transporter expression in both terminal fields and perikarya. In females, the damage may be temporarily offset by initial trophic effects in the terminal region, consequent to the cholinergic stimulation evoked by cholinesterase inhibition via the active metabolite, CPF oxon. The gender-selective effects on 5HT systems are likely to contribute to similar gender dimorphism in behavioral performance. Because the CPF effects involve 5HT, a neurotransmitter intimately involved in the control of mood, we suggest the need to evaluate behaviors that typify animal models of depression.

Animals↗

PubMed2001

Persistent behavioral consequences of neonatal chlorpyrifos exposure in rats.

Chlorpyrifos (CPF) is a widely used insecticides which has been shown to alter brain cell development. The current project was conducted to determine whether there are persistent behavioral effects of early [1 mg/kg/day postnatal days (PNDs) 1-4] or late (5 mg/kg/day PNDs 11-14) postnatal CPF exposure in rats. We tested spontaneous alternation in a T-maze, locomotor activity in the Figure-8 apparatus and learning in the 16-arm radial maze, throughout adolescence and into adulthood. Exposure during either neonatal period elicited significant long-term effects on cognitive behavior. In the radial-arm maze, as has been seen previously, control male performed more accurately than control females. Early postnatal CPF exposure reversed this effect. With exposure on PNDs 1-4, females in the CPF group showed a reduction in working and reference memory errors in the radial maze, reducing their error rate to that seen in control males; in contrast, CPF-exposed males exhibited an increase in errors during the initial stages of training. When animals were exposed on PNDs 11-14 and then tested in adolescence and adulthood, males showed a significant slowing of response latency in the T-maze and the rate of habituation in the Figure-8 apparatus was slowed in both sexes. When females were challenged acutely with the muscarinic antagonist, scopolamine, they did not show reference memory impairment, whereas controls did; these results suggest that adaptations occur after CPF exposure that lead to loss of muscarinic cholinergic control of reference memory. No such changes were seen with a nicotinic cholinergic antagonist (mecamylamine). These results indicate that early neonatal exposure to CPF induces long-term changes in cognitive performance that, in keeping with the neurochemical changes seen previously, are distinctly gender-selective. Additional defects may be revealed by similar strategies that subject the animals to acute challenges, thus uncovering the adaptive mechanisms that maintain basal performance.

Animals↗

PubMed2001

Persistent cholinergic presynaptic deficits after neonatal chlorpyrifos exposure.

The commonly-used organophosphate insecticide, chlorpyrifos (CPF), impairs brain cell development, axonogenesis and synaptogenesis. In the current study, we administered CPF to neonatal rats on postnatal (PN) days 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), treatments that were devoid of overt toxicity. We then examined two cholinergic synaptic markers, choline acetyltransferase activity (ChAT) and [3H]hemicholinium-3 binding (HC-3) in the hippocampus, midbrain, striatum, brainstem and cerebral cortex in the juvenile (PN30) and young adult (PN60). Across all brain regions, CPF exposure evoked significant reductions in both markers, with larger effects on HC-3 binding, which is responsive to neuronal impulse activity, than on ChAT, a constitutive marker. Superimposed on the deficits, there were gender-selective effects and distinct regional disparities in the critical exposure period for vulnerability. In the hippocampus, either the early or late treatment regimen evoked decreases in ChAT but the early regimen elicited a much larger decrease in HC-3; effects persisted into adulthood. In the midbrain, CPF administration on PN1-4 elicited deficits similar to those seen in the hippocampus; however, exposure on PN11-14 elicited changes preferentially in females. Gender selectivity was also apparent in the striatum, in this case reflecting deficits in females after CPF treatment on PN1-4. In contrast, the effects of CPF on the brainstem were relatively more robust in males; effects in the cerebral cortex were less notable than in other regions. These results indicate that neonatal CPF exposure produces widespread deficiencies in cholinergic synaptic function that persist into adulthood. The effects are likely to contribute to gender-selective alterations in behavioral performance that persist or emerge long after the termination of exposure and well after the restoration of cholinesterase activity.

Acetylcholine↗

PubMed2001

Perinatal exposure to environmental tobacco smoke induces adenylyl cyclase and alters receptor-mediated cell signaling in brain and heart of neonatal rats.

Perinatal exposure to environmental tobacco smoke (ETS) has adverse effects on neurobehavioral development. In the current study, rats were exposed to ETS during gestation, during the early neonatal period, or both. Brains and hearts were examined for alterations in adenylyl cyclase (AC) activity and for changes in beta-adrenergic and m2-muscarinic cholinergic receptors and their linkage to AC. ETS exposure elicited induction of total AC activity as monitored with the direct enzymatic stimulant, forskolin. In the brain, the specific coupling of beta-adrenergic receptors to AC was inhibited in the ETS groups, despite a normal complement of beta-receptor binding sites. In the heart, ETS evoked a decrease in m2-receptor expression. In both tissues, the effects of postnatal ETS, mimicking passive smoking, were equivalent to (AC) or greater than (m2-receptors) those seen with prenatal ETS mimicking active smoking; the effects of combined prenatal and postnatal exposure were equivalent to those seen with postnatal exposure alone. These data indicate that ETS exposure evokes changes in cell signaling that recapitulate those caused by developmental nicotine treatment. Since alterations in AC signaling are known to affect cardiorespiratory function, the present results provide a mechanistic link reinforcing the participation of ETS exposure, including postnatal ETS, in disturbances culminating in events like Sudden Infant Death Syndrome.

Adenylyl Cyclases↗

PubMed2001

Adolescent nicotine exposure produces immediate and long-term changes in CNS noradrenergic and dopaminergic function.

Animal studies have only recently begun to address whether nicotine evokes unique or persistent effects on brain structure or function during adolescence, the period in which smokers typically begin their habit. In the current study, we examined the impact of adolescent nicotine treatment on catecholaminergic synaptic function in rats infused with nicotine on postnatal days 30-47.5, using a paradigm that reproduces the plasma levels of nicotine found in smokers. We assessed norepinephrine and dopamine content, turnover (an index of neural activity), and the response to an acute challenge dose of nicotine. In the midbrain, the region most closely associated with addiction, both norepinephrine and dopamine turnover were activated during the infusion period, an effect not seen in any other region for norepinephrine, and only in the striatum for dopamine. In the immediate post-infusion period (PN50-60), there was a decrement in midbrain catecholamine turnover restricted to males, whereas there was a later-emerging (PN80) activation of these pathways. Again, this pattern was not observed in any other region: the cerebral cortex showed post-treatment increases in turnover without gender selectivity, the striatum showed late-emerging deficits in dopamine turnover and the hippocampus displayed a profound deficit in noradrenergic activity that was limited to females. We also assessed the catecholaminergic response to an acute challenge with nicotine (0.3 mg/kg s.c.). The midbrain once more displayed unique properties; there was initial suppression of responses followed by post-treatment rebound elevations that were more prominent in males and eventual deficits that, in the case of dopamine, were selective for males. With the exception of the cerebellum, other regions showed the initial loss of response during the infusion period but no persistent changes in responsiveness. The current results indicate that adolescent nicotine produces immediate and long-term changes in CNS catecholaminergic systems, with regional targeting and gender selectivity corresponding to the changes seen previously in nicotinic receptor upregulation or indices of cell damage. These effects may underlie long-term behavioral changes associated with adolescent nicotine exposure.

Animals↗

PubMed2001

Does the developmental neurotoxicity of chlorpyrifos involve glial targets? Macromolecule synthesis, adenylyl cyclase signaling, nuclear transcription factors, and formation of reactive oxygen in C6 glioma cells.

The widespread use of chlorpyrifos (CPF) has raised major concerns about its potential to cause fetal or neonatal neurobehavioral damage, even at doses that do not evoke acute toxicity. CPF has been shown to inhibit replication of brain cells, to elicit alterations in neurotrophic signaling governing cell differentiation and apoptosis, and to evoke oxidative stress. However, the specific cell types targeted by CPF have not been clarified, an issue of vital importance in establishing the boundaries of the critical period in which the developing brain is vulnerable. In the current study, we evaluated the effects of CPF on C6 glioma cells, a well-established glial model. In undifferentiated C6 cells, CPF inhibited DNA synthesis in a concentration-dependent manner, with greater potency than had been seen previously with neuronal cell lines. Just as found after in vivo CPF treatment or with neuronal cell lines, the effects on cell replication were independent of cholinergic stimulation, as cholinergic antagonists did not block CPF-induced inhibition. CPF interfered with cell signaling mediated through adenylyl cyclase at the level of G-protein function; the effects again were greater in undifferentiated C6 cells but were still detectable in differentiating cells. In contrast, differentiation enhanced the ability of CPF to elicit the formation of reactive oxygen species and to evoke deficits in Sp1, a nuclear transcription factor essential for differentiation. These results indicate that glial-type cells are targeted by CPF through the same multiple mechanisms that have been demonstrated for the effects of CPF on brain development in vivo. Because glial development continues long after the conclusion of neurogenesis, and given that CPF targets events in both glial cell replication and the later stages of differentiation, the vulnerable period for developmental neurotoxicity of CPF is likely to extend well into childhood.

Adenylyl Cyclases↗

PubMed2001

Generation of reactive oxygen species by xanthine derivatives in MDA-MB-231 human breast cancer cells.

Theophylline reduces cell number in MDA-MB-231 cells through mechanisms over and above phosphodiesterase inhibition. In the current study, we used an intracellular fluorescent dye to show that theophylline and, to a much greater extent, 3-isobutyl-1-methylxanthine, evoke the generation of reactive oxygen species and also sensitize the cells to insult by other oxidants. Xanthine derivatives may therefore offer novel strategies for antitumor therapeutics.

1-Methyl-3-isobutylxanthine↗