Long-lasting CNS effects of a short-term chemical knockout of ornithine decarboxylase during development: nicotinic cholinergic receptor upregulation and subtle macromolecular changes in adulthood

Bacoside A: Role in Cigarette Smoking Induced Changes in Brain

Cigarette smoking (CS) is a major health hazard that exerts diverse physiologic and biochemical effects mediated by the components present and generated during smoking. Recent experimental studies have shown predisposition to several biological consequences from both active and passive cigarette smoke exposure. In particular, passive smoking is linked to a number of adverse health effects which are equally harmful as active smoking. A pragmatic approach should be considered for designing a pharmacological intervention to combat the adverse effects of passive smoking. This review describes the results from a controlled experimental condition, testing the effect of bacoside A (BA) on the causal role of passive/secondhand smoke exposure that caused pathological and neurological changes in rat brain. Chronic exposure to cigarette smoke induced significant changes in rat brain histologically and at the neurotransmitter level, lipid peroxidation states, mitochondrial functions, membrane alterations, and apoptotic damage in rat brain. Bacoside A is a neuroactive agent isolated from Bacopa monnieri. As a neuroactive agent, BA was effective in combating these changes. Future research should examine the effects of BA at molecular level and assess its functional effects on neurobiological and behavioral processes associated with passive smoke.

LPS-induced CCL2 expression and macrophage influx into the murine central nervous system is polyamine-dependent

Increased polyamine production is observed in a variety of chronic neuroinflammatory disorders, but in vitro and in vivo studies yield conflicting data on the immunomodulatory consequences of their production. Ornithine decarboxylase (ODC) is the rate-limiting enzyme in endogenous polyamine production. To identify the role of polyamine production in CNS-intrinsic inflammatory responses, we defined CNS sites of ODC expression and the consequences of inhibiting ODC in response to intracerebral injection of LPS±IFNγ. In situ hybridization analysis revealed that both neurons and non-neuronal cells rapidly respond to LPS±IFNγ by increasing ODC expression. Inhibiting ODC by co-injecting DFMO decreased LPS-induced CCL2 expression and macrophage influx into the CNS, without altering LPS-induced microglial or macrophage activation. Conversely, intracerebral injection of polyamines was sufficient to trigger macrophage influx into the CNS of wild-type but not CCL2KO mice, demonstrating the dependence of macrophage influx on CNS expression of CCL2. Consistent with these data, addition of putrescine and spermine to mixed glial cultures dramatically increased CCL2 expression and to a much lesser extent, TNF expression. Addition of all three polyamines to mixed glial cultures also decreased the numbers and percentages of oligodendrocytes present. However, in vivo, inhibiting the basal levels of polyamine production was sufficient to induce expression of apolipoprotein D, a marker of oxidative stress, within white matter tracts. Considered together, our data indicate that: (1) CNS-resident cells including neurons play active roles in recruiting pro-inflammatory TREM1-positive macrophages into the CNS via polyamine-dependent induction of CCL2 expression and (2) modulating polyamine production in vivo may be a difficult strategy to limit inflammation and promote repair due to the dual homeostatic and pro-inflammatory roles played by polyamines.

Brain noradrenaline changes in rats prenatally exposed to ozone

In the present study we considered the possible impairment of developmental noradrenergic maturity of the cerebellum, cerebral cortex and pons at 10-, 20- and 30-day-old rats arising from mothers subjected to 1ppm ozone concentration during pregnancy. The noradrenaline concentration was found to be significantly reduced in the cerebellum during the study, while in the cerebral cortex and the pons it was found to be reduced at days 10 and 30 respectively as compared to controls. We concluded that prenatal exposure of 1.0ppm ozone causes embryonic/fetal changes manifested in postnatal levels of noradrenaline concentrations in the brains of rats.

Zebrafish provide a sensitive model of persisting neurobehavioral effects of developmental chlorpyrifos exposure: comparison with nicotine and pilocarpine effects and relationship to dopamine deficits

Chlorpyrifos (CPF) an organophosphate pesticide causes persisting behavioral dysfunction in rat models when exposure is during early development. In earlier work zebrafish were used as a complementary model to study mechanisms of CPF-induced neurotoxicity induced during early development. We found that developmental (first five days after fertilization) chlorpyrifos exposure significantly impaired learning in zebrafish. However, this testing was time and labor intensive. In the current study we tested the hypothesis that persisting effects of developmental chlorpyrifos could be detected with a brief automated assessment of startle response and that this behavioral index could be used to help determine the neurobehavioral mechanisms for persisting CPF effects. The swimming activity of adult zebrafish was assessed by a computerized video-tracking device after a sudden tap to the test arena. Ten consecutive trials (1/min) were run to determine startle response and its habituation. Additionally, habituation recovery trials were run at 8, 32 and 128 min after the end of the initial trial set. CPF-exposed fish showed a significantly (p<0.025) greater overall startle response during the 10-trial session compared to controls (group sizes: Control N=40, CPF N=24). During the initial recovery period (8 min) CPF-exposed fish showed a significantly (p<0.01) greater startle response compared to controls. To elucidate the contributions of nicotinic and muscarinic acetylcholine receptors to developmental CPF-mediated effects, the effects of developmental nicotine and pilocarpine exposure throughout the first five days after fertilization were determined. Developmental nicotine and pilocarpine exposure significantly increased startle response, though nicotine (group sizes: Control N=32, 15 mM N=12, 25 mM N=20) was much more potent than pilocarpine (group sizes: Control N=20, 100 microM N=16, 1000 microM N=12). Neither was as potent as CPF for developmental exposure increasing startle response in adulthood. Lastly, developmental CPF exposure decreased dopamine and serotonin levels and increased transmitter turnover in developing zebrafish larvae (N=4 batches of 50 embryos/treatment). Only the decline in dopamine concentrations persisted into adulthood (group sizes: Control N=14, CPF N=13). This study shows that a quick automated test of startle can detect persisting neurobehavioral impairments caused by developmental exposure to CPF. This may be helpful in screening for persisting neurobehavioral defects from a variety of toxicants.

Difluoromethylornithine (DFMO) reduces deficits in isolation-induced ultrasonic vocalizations and balance following neonatal ethanol exposure in rats

Neonatal ethanol (EtOH) exposure is associated with central nervous system dysfunction and neurotoxicity in rats. Increases in polyamine levels have been implicated as one underlying mechanism for some of EtOH's effects on the developing brain. In this study we addressed whether the inhibition of polyamine biosynthesis by alpha-difluoromethylornithine (DFMO) could reduce behavioral deficits induced by early EtOH exposure. Male and female rat pups received ethanol (6 g/kg/day EtOH i.g.), or isocaloric maltose (control) from postnatal days (PND) 1-8. On PND 8, animals were injected with either saline or DFMO (500 mg/kg, s.c.) immediately following the final neonatal treatment. Subjects were tested for isolation-induced ultrasonic vocalizations (USV) on PND 16; spontaneous activity in an open field apparatus on PND 20 and 21; and balance on PND 31. Animals exposed to EtOH neonatally displayed an increased latency to the first USV and reduced frequencies of USV, hyperactivity and preference for the center of the open field and poorer balance relative to controls. DFMO minimized these deficits in latency to the first USV and balance. These data provide further support that polyamines play a role in some of the functional deficits associated with EtOH exposure during early development and that reducing polyamine activity can improve outcome.

Age and gender differences in response to neonatal ethanol withdrawal and polyamine challenge in organotypic hippocampal cultures

BACKGROUND

Polyamines are synthesized and released in high concentrations during CNS development. These agents can potentiate N-methyl-D-aspartate receptor (NMDAR) function and appear to play an important role in CNS development. Previous work has shown that polyamine release is increased during ethanol withdrawal (EWD). This likely promotes NMDAR overactivity and contributes to neurotoxicity during EWD, however, little is known regarding such effects in early neonatal brain. The present study compared the effects of EWD and polyamine exposure on toxicity in hippocampal slice cultures derived from postnatal day 2 (PND 2) or postnatal day 8 (PND 8) day-old rats. Due to changes in NMDAR subtypes and response to polyamines, we predicted that slices taken from PND 2 pups would be more sensitive to EWD and polyamine challenge.

METHODS

Organotypic hippocampal slice cultures were obtained from neonatal rats either 2 or 8 days of age (PND 2 or PND 8). Five days after explantation, cultures were exposed to ETOH (50 mM- typically subthreshold for EWD induced cell death) for 10 days and then withdrawn from ETOH for 24-hour in the presence of 100 microM of the polyamine spermidine and/or 100 microM ifenprodil, an NMDAR antagonist that blocks the NMDAR that is the most sensitive to polyamine modulation. Cytotoxicity was measured after 24-hour by visualization of propidium iodide (PI) fluorescence.

RESULTS

There were clear age and gender-dependent differences in response to EWD and to polyamines. EWD produced significant increases in PI uptake in all subregions (CA1, CA3 and DG) of cultures derived from PND 2 pups, but not PND 8 pups. Exposure of cultures to spermidine for 24-hour also produced significant increases in cytotoxicity in all 3 regions of PND 2 cultures with no gender differences. In contrast, there were both gender and region-specific differences in response to spermidine in cultures from PND 8. While the CA1 region of both sexes displayed increased cytotoxicity following spermidine exposure, only females showed increased cytotoxicity in the CA3 region while the DG appeared relatively insensitive to spermidine. Exposure to spermidine during EWD produced enhanced toxicity in all 3 hippocampal subregions in tissue from both PND 2 and PND 8 rats and this was reduced or prevented by co-exposure to ifenprodil. Of interest, the PND 2 hippocampus was significantly more sensitive than the PND 8 hippocampus to the toxic effects of EWD and to spermidine during EWD in the DG and CA3 regions.

CONCLUSIONS

Hippocampal slice cultures derived from PND 2 rats were more sensitive to the toxic effects of both EWD and EWD + spermidine exposure than were those derived from PND 8 rats. These findings are similar to recent behavioral data collected from our lab showing greater sensitivity to ETOH's behavioral teratogenic effects when ETOH exposure in vivo occurred during the first postnatal week relative to the second postnatal week. Ifenprodil's ability to block the toxic effects of spermidine during EWD suggests that excess activity of NR2B subunits of the NMDAR contributed to the excitatory and cytotoxic effects of EWD plus spermidine. While no sex differences in toxicity were observed in cultures taken from pups during the first postnatal week, these data do suggest that later in neonatal life (i.e., the second postnatal week), the female hippocampus may be more sensitive to polyamine-induced neurotoxicity than males.

Neurogenesis of the cholinergic medial septum in female and male C57BL/6J mice

Sex differences exist in the structure and function of the cholinergic septo-hippocampal system throughout the lifespan of mammals. How and when these sex differences originate is unclear. Because estrogen modulates sexual differentiation of several brain regions during development and influences neurogenesis in adult mammals, we hypothesized that sexual dimorphism of the cholinergic septo-hippocampal system would extend to its neurogenesis. A birthdating agent 5'-bromo-2'-deoxyuridine (BrdU) was injected into pregnant dams on one of eight gestational days, ranging from embryonic day (E)10 to E17. The offspring were euthanized at 2 months of age, and brains were processed for BrdU and choline acetyltransferase (ChAT) immunoreactivity to label cholinergic neurons that became postmitotic on a given embryonic day and survived to adulthood. Unbiased stereology was used to compare the number of double-labeled neurons in the medial septum (MS) of female and male offspring. Cholinergic neurons in the MS were generated primarily between E11 and E14, similar to other published reports. We found sex differences in the pattern of peak neurogenesis but not in the length of neurogenesis, or in total number of neurons generated in the MS. Additionally, in adult female and male mice, we estimated the total number of cholinergic neurons using unbiased stereology and found no sex differences in the number of cholinergic neurons or in the volume of the MS in adulthood. These results suggest that sex differences noted in the function of the postnatal cholinergic septo-hippocampal system may originate from its neurogenesis.

Alpha7 nicotinic acetylcholine receptors targeted by cholinergic developmental neurotoxicants: nicotine and chlorpyrifos

Alpha7 nicotinic acetylcholine receptors (nAChRs) play a role in axonogenesis, synaptogenesis and synaptic plasticity, and are therefore potential targets for developmental neurotoxicants. We administered nicotine to neonatal rats during discrete periods spanning the onset and peak of axonogenesis/synaptogenesis, focusing on three brain regions with disparate distributions of cell bodies and neural projections: brainstem, forebrain and cerebellum. Nicotine treatment on postnatal days (PN) 1-4 had little or no effect on alpha7 nAChRs but treatment during the second (PN11-14) or third (PN21-24) weeks elicited significant decrements in receptor expression in brainstem and cerebellum, regions containing cell bodies that project to the forebrain. Exposure to chlorpyrifos, a neurotoxicant pesticide that acts partially through cholinergic mechanisms, also elicited deficits in alpha7 nAChRs during the second postnatal week but not the first week. For both nicotine and chlorpyrifos, the effects on alpha7 nAChRs were distinct from those on the alpha4beta2 subtype. Continuous prenatal nicotine exposure, which elicits subsequent, postnatal deficits in axonogenesis and synaptogenesis, also produced delayed-onset changes in alpha7 nAChRs, characterized by reductions in the forebrain and upregulation in the brainstem and cerebellum, a pattern consistent with impaired axonogenesis/synaptogenesis and reactive sprouting. Males were more sensitive to the persistent effects of prenatal nicotine exposure on alpha7 nAChRs, a pattern that mimics neurobehavioral deficits resulting from this treatment. The present findings reinforce the mechanistic involvement of alpha7 nAChRs in the actions of developmental neurotoxicants, and its biomarker potential for neuroteratogens that target neuritic outgrowth.

Administration of nicotine to adolescent rats evokes regionally selective upregulation of CNS alpha 7 nicotinic acetylcholine receptors

Alpha 7 Nicotinic acetylcholine receptors (nAChRs) play a role in axonogenesis, synaptogenesis and synaptic plasticity, and are therefore targets for developmental neurotoxicants. We administered nicotine to adolescent rats and evaluated the effects on alpha 7 nAChRs in the striatum, brainstem and cerebellum. During the period of nicotine administration (30-47.5 days of age), nicotine elicited alpha 7 nAChR upregulation with a regional hierarchy of striatum>brainstem>cerebellum. Values returned to normal or became slightly subnormal almost immediately after the cessation of treatment (50 days of age) with no further changes through 75 days of age. The temporal and regional patterns of the effects on alpha 7 nAChRs were distinct from those reported earlier for the alpha 4 beta 2 subtype, and neither adult nor fetal/neonatal administration upregulates the alpha 7 subtype in the striatum. Targeting of the striatum is thus unique to nicotine exposure during adolescence and parallels earlier work showing regionally selective effects of this treatment on synaptic signaling. We obtained preliminary evidence for nicotine-induced oxidative stress as a potential contributory mechanism. The present findings reinforce the concept of biologically distinct effects of nicotine in the adolescent brain and provide evidence for a mechanistic involvement of alpha 7 nAChRs in its unique effects during this developmental period.

Effects of prenatal nicotine exposure on primate brain development and attempted amelioration with supplemental choline or vitamin C: neurotransmitter receptors, cell signaling and cell development biomarkers in fetal brain regions of rhesus monkeys

Studies in developing rodents indicate that nicotine is a neuroteratogen that disrupts brain development by stimulating nicotinic acetylcholine receptors (nAChRs) that control neural cell replication and differentiation. We administered nicotine to pregnant Rhesus monkeys from gestational day 30 through 160 by continuous infusion, achieving maternal plasma levels comparable to those in smokers (30 ng/ml). Fetal brain regions and peripheral tissues were examined for nAChR subtypes, other neurotransmitter receptors, and indices of cell signaling and cell damage. Nicotine evoked nAChR upregulation, but with distinct regional disparities indicative of selective stimulatory responses. Similarly, indices of cell loss (reduced DNA), cell size and neuritic outgrowth (protein/DNA and membrane/total protein ratios) were distinct for each region and did not necessarily follow the rank order of nAChR upregulation, suggesting the involvement of additional mechanisms such as oxidative stress. We then attempted to offset the adverse effects of nicotine with standard dietary supplements known to interact with nicotine. By itself, choline elicited nicotine-like actions commensurate with its promotion of cholinergic neurotransmission. When given in combination with nicotine, choline protected some regions from damage but worsened nicotine's effects in other regions. Similarly, Vitamin C supplementation had mixed effects, increasing nAChR responses while providing protection from cell damage in the caudate, the brain region most susceptible to oxidative stress. Our results indicate that nicotine elicits neurodevelopmental damage that is highly selective for different brain regions, and that dietary supplements ordinarily thought to be neuroprotectant may actually worsen some of the adverse effects of nicotine on the fetal brain.

Determination of the effectiveness of components of the herbal medicine Toki-Shakuyaku-San and fractions of Angelica acutiloba in improving the scopolamine-induced impairment of rat's spatial cognition in eight-armed radial maze test

The improving effects of various components of Toki-Shakuyaku-San (TSS) and fractions isolated from Angelica acutiloba Radix (Toki) on scopolamine-induced spatial memory impairment were investigated in eight-armed radial maze. The scopolamine-induced memory impairment was characterized by prominent increase of error choices in addition to decreased correct choices. Toki, Cnidium officinale Rhizoma (Senkyu), Poria cocos Hoelen (Bukuryo), Alisma orientale Rhizoma (Takusha), and Atractylodes lancea Rhizoma (Sojutsu) increased the correct choices, while only the Toki, Sojutsu, and Takusha decreased the error choices. No effect was produced by Paeonia lactiflora Radix (Shakuyaku). Investigation of effects of fractions isolated from Toki revealed that its activity mainly resided in the butanol layer and its contents of N-methyl-beta-carboline-3-carboxamide and amines. Moreover, the alkaloid, internal and external solutions (containing poly-, di-, and monosaccharides) obtained by dialysis with Visking cellophane tubing also improved the memory. However, no improving properties were detected for methanol and hexanol layers, L-(-)-tryptophan, L-arginine, L-(-)-lysine, and choline chloride. The results showed that the TSS components could improve the reference and working memory impaired by scopolamine. The improving effect of TSS is produced greatly by the Toki component, the activity of which was greatly produced by the fraction extracted by butanol.