Search tips
Search criteria 


Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Behav Brain Res. Author manuscript; available in PMC 2010 December 28.
Published in final edited form as:
PMCID: PMC2782724

Reversal of chlorpyrifos neurobehavioral teratogenicity in mice by nicotine administration and neural stem cell transplantation


Identifying the mechanisms underlying the adverse effects of developmental neurotoxicants enables the design of therapies that can potentially reverse neurobehavioral deficits in adulthood. We administered chlorpyrifos (CPF), a model organophosphate pesticide to pregnant mice and identified visuospatial deficits in adult offspring using performance in the Morris Maze. We then evaluated two strategies to reverse the effects, nicotine administration and transplantation of neural stem cells. Daily administration of nicotine prior to behavioral testing did not alter maze performance by itself, but completely reversed the deficits evoked by prenatal CPF exposure. Similarly, control animals grafted with neural stem cells in adolescence did not show any alterations in behavioral performance as adults, but the grafts completely reversed the effects of prenatal CPF treatment. This study thus provides a model for the development and application of both pharmacologic and cell-based therapies to offset the effects of neurobehavioral teratogens.

Keywords: Chlorpyrifos, Mice, Morris maze testing, Neural stem cell therapy, Neurobehavioral teratogenicity, Nicotine therapy, Prenatal exposure


Over recent decades, there has been an alarming rise in the incidence of neurodevelopmental disorders, coincident with increased exposures to neurotoxic chemicals in the environment, resulting in what has been termed a “silent pandemic” [10]. Although most toxicologic studies focus on the mechanisms underlying the effects of individual toxicants, it is obviously critical to design therapies that may be used to offset the consequences of such exposures, which are likely to remain problematic, given the thousands of new chemicals released each year, few of which are ever tested for developmental neurotoxicity. In earlier work, we showed how nicotine treatment in adulthood could offset the adverse effects of developmental neurotoxicants that target septohippocampal cholinergic projections, achieving restoration of synaptic and behavioral function through a pharmacologic intervention that offsets the deficiencies in cholinergic function [2]. In addition to its direct cholinergic actions, nicotine causes release of many other neurotransmitters, thus enabling it to reverse deficits involving other transmitters, such as norepinephrine [1, 31], dopamine [26], GABA [39] and glutamate [11]. Accordingly, nicotine therapy has been applied successfully in humans as well as in animal models for the reversal of cognitive dysfunction associated with surgical lesions or neurodegenerative disorders [23], and can be administered conveniently either by transdermal patches in humans [12] or by subcutaneously-implanted osmotic minipumps in animals [29, 30].

Nevertheless, there are clear liabilities of continuous pharmacologic replacement of deficient cholinergic synaptic function with nicotine, including loss of effect due to desensitization, cardiovascular complications, and addiction liability. Consequently, it would be valuable to design ameliorative therapies that might actually achieve permanent reversal of synaptic and neurobehavioral deficits. To that end, considerable attention is now being paid to neural stem cells, which have the potential to replace or rescue damaged neural circuits and/or induce trophic processes that foster endogenous repair mechanisms [6, 21]. We recently demonstrated the successful use of this strategy in reversing neurobehavioral deficits evoked by prenatal heroin exposure [5, 14]. Here, we provide a comparative proof-of-principle of the pharmacologic vs. stem-cell approach to amelioration of neurobehavioral teratogenicity of a defined environmental neurotoxicant, the organophosphate pesticide, chlorpyrifos (CPF). Organophosphates represent nearly 50% of all insecticide use worldwide [7] and are undergoing increased restriction specifically because of their propensity to elicit developmental neurotoxicity. Even low prenatal exposures to CPF compromise cognitive function in children [22]; in animal models, CPF disrupts synaptic development and function, involving not only hippocampal cholinergic systems but a wide variety of regions and circuits [28].

In the present study, we exposed mice to CPF prenatally at doses devoid of adverse effects on viability or morphogenesis, and evaluated cognitive deficits in adulthood. We then demonstrated equivalent reversal of the deficits by nicotine therapy in adulthood, and by administration of neural stem cells in adolescence.


CPF administration

The study employed heterogeneous stock (HS/Ibg) mice, since this strain is especially fertile even under exposure to various insults [18]. Four females and one male were housed in each mating cage and maintained under standard conditions of 24° C and a 12-hr light - dark cycle. Females were checked daily at 08:00. Those that had mated, as evidenced by the existence of a vaginal plug, were then housed with other pregnant females (date was termed as gestational day 1, GD1). Chlorpyrifos administration paradigms were based on our previous work with other teratogens [36, 37]. In order to identify the maximum dose that allows normal pregnancy without fetal resorption or postnatal mortality, the pregnant mice were divided into several groups, each receiving either 1, 3, 5, 10 or 20 mg/kg/day CPF dissolved in DMSO vehicle, subcutaneously, on gestational days (GD) 9-18, the period in which most brain structures develop [25]. Controls received DMSO injections on the same schedule.

Beginning on GD18, each female was housed individually. Fostering of the offspring of CPF-exposed and control animals to controls was applied in approximately half of the litters, and took place within 24 h of birth. As there was no significant difference between fostered and non-fostered treated pups, the results from both groups were pooled for presentation. The pups were weaned at postnatal day (PN) 25, segregated by sex and housed in groups of five. Only a one male and one female pup from each litter were used in each experimental group in order to prevent bias resulting from litter effects. Approximately equal numbers of males and females were used and sex effects were taken into account in the analysis.

Monitoring general development of mothers and offspring

Maternal factors, as well as offspring development, were monitored. Of the daily pre-injection maternal body weights, GD9, 12, 15 and 18 are presented to show representative trends (Fig.1A) and on PN1, 7 and 14; maternal caretaking, measured by pup retrieval, was assessed on PN3 and 7. In the offspring, we monitored the sex ratio, litter size litter survival, and the development of body weight from birth to PN50. We also noted the ages of development of the righting and startle responses, appearance of fur, and eye and ear opening. To evaluate maternal caretaking, 6 pups were placed in their cage (17.5 × 28.0 cm) at the maximum possible distance from each other; we recorded the amount of time needed for the mother to retrieve the pups and return them to the nest. To evaluate the righting response, animals were placed on their backs and we measured the ability to to right themselves within 20 sec. To evaluate the startle response, we produced a sudden sound of approximately 100 dB immediately above the litter.

Fig 1
Effect of CPF treatment (1,3,5, 10 or 20 mg/kg/day) on maternal body weight.

Morris water maze evaluation

The Morris water maze was conducted in an adaptation of the apparatus originally developed for rats [19], with testing occurring on PN75. The test was performed in a round tank 87 cm in diameter, containing water (24°C) rendered opaque by adding powdered milk. A platform, 8 × 10 × 9 cm high, was placed 1 cm below the surface of the water. Mice were given two blocks of four trials on each day for four consecutive days [20]. On all trial days, each mouse was given 60 sec to swim, find the platform and climb onto it. The mouse was then left on the platform for 20 sec until placed in the water for another trial. Mice that failed to find the platform within 60 sec were removed from the water and placed on the platform for 20 sec until the next trial. A computerized video system was used to monitor and analyze the behavior in the maze. Performance was evaluated as the mean latency across the eight trials on a given day.

To control for possible non-hippocampal and/or activity-related factors, two control tests followed the Morris place test: a. Visible platform test (neural stem cells transplantation) – the mice were given four trials in which the platform was raised above water level; mice that required more than 40 sec to reach the visible platform on any trial were excluded from further analysis [33].b. Swimming speed (nicotine therapy) – the platform was removed and swimming speed over the missing platform and in the rest of the Morris maze was monitored in four 60 sec trials.

The Morris test established the 3 mg/kg/day dose of CPF as eliciting the greatest behavioral impairment, and the reversal studies therefore employed this dose.

Nicotine therapy

To assess the ability of nicotine to reverse the Morris Maze performance deficits, animals received an intraperitoneal injection of either 0.33 or 1 mg/kg of (-)-nicotine- hydrogen - (+) - tartrate (Sigma, Rehovot) or saline vehicle 20 min before each of the four daily Morris test sessions [40]. These doses are equivalent to 0.1 and 0.3 mg/kg of nicotine free base, respectively.

Neural stem cells therapy

To assess the therapeutic effect of neural stem cells, on PN35, animals received either transplantation of neural stem cells or DMEM control medium, and were tested for maze performance on PN75.

Derivation of neural precursors and growth of neurospheres

We use standard procedures [3, 8] as described by in our previous publications [5, 14]. Neural stem cells were derived from newborn (PN1) HS/Ibg mice. Briefly, cerebral cortices were minced, dissociated by 30 min incubation with Trypsin and mechanical dissociation into single cells using a 5 ml pipette. The pellet was suspended in serum-free F12/DMEM medium, and then incubated at 37°C and 5% CO2 for up to 7 days. The cells were supplemented daily with growth factors; 10 ng/ml basic fibroblast growth factor-2 and 20 ng/ml epidermal growth factor (both from Peprotech Asia, Israel). The viability of the cells was monitored throughout the incubation using Trypan Blue. Under these conditions, most cells died and approximately 0.2% of cells proliferated into clusters of small round cells that grew into floating spheres. After three days of incubation, the cells were sedimented at 800 rpm for 8 min and were resuspended in half of the original volume and incubated for three more days. As already described, these spheres consisted mainly of PSA-NCAM+, nestin+, and NG2(−) cells that generated GFAP+ astrocytes, GalC+ oligodendrocytes and few neurofilament+ neurons upon differentiation [4, 8].

On transplantation day, 5-7 days old spheres were dissociated by trituration with 200 μl Accutase (Sigma), followed by 10 min incubation at 37°C in 5% CO2 to dissociate the spheres into single cells while minimizing cell death [34]. After being washed with 5 ml phosphate-buffered saline, cells were incubated with 1mM CM-Dil cell tracker (Invitrogen, Jerusalem, Israel), for 5 min at 37°C, and then for 15 min at 4°C [16]. The cells were triturated and washed with buffer and counted.

Sphere transplantation

Animals were anesthetized with an intraperitoneal injection of 80 mg/kg pentobarbital and placed in a stereotaxic apparatus. We then injected approximately 50,000 cells in a volume of 5μl using a 10μl Hamilton syringe, delivered into each hippocampus at the following coordinates: 1.8 mm posterior to bregma, ±1.5 mm lateral from the midline and 1.7 mm below calvarium [32, 38]. DMEM media was chosen as the control solution. Because Dil-labeled cells that die might transfer the cell tracker to neighboring host cells [15, 27], we ran two additional control groups: 1) animals that were transplanted with CM-Dil-labeled, adult frontal cortex-derived cells certain to die in the host brain and, 2) animals that were transplanted with CM-Dil-labeled adult subventricular zone-derived neural stem cells, destined to live.

Evaluation of the transplanted cells in the host brain

The fate of the transplanted cells was evaluated in sample groups of offspring. Twenty-four hours after behavioral testing, the mice were anesthetized with an overdose of pentobarbital and perfused transcardially with 4% paraformaldehyde (Gadot, Netanya, Israel). The brains were then removed and postfixed overnight at 4°C in 4% paraformaldehyde, cryoprotected in 30% sucrose for an additional 24 hours and finally deep frozen in liquid nitrogen and stored in -70°C. The entire hippocampal region was sliced into coronal 10μm frozen sections, using cryostat (Leica, Wetzlar, Germany). Every sixth section was mounted. Dil-positive cells were identified with fluorescent microscopy (Olympus, NY).

Statistical analysis

Data are presented as mean and standard errors, with differences between treatments established by multivariate ANOVAs incorporating all variables (prenatal treatment, postnatal treatment, sex, day of testing for the Maze performance), followed by Tukey test for post hoc analysis; where variance was heterogeneous, data were log-transformed for the statistical analyses. The global ANOVA did not identify any significant interaction of sex with treatment and accordingly, results from males and females are shown combined, although sex was retained as a factor for the statistical evaluations. Significance for all tests was assumed at the level p<0.05.


Dams given all but the highest dose of CPF showed normal body weight gain during pregnancy and nursing (Fig. 1); their maternal behavior as assessed by pup retrieval test was also normal (data not shown). At birth, CPF did not affect litter size or sex ratio (data not shown). Dams given 20 mg/kg/day, all died before delivery. CPF-exposed offspring did not show any significant changes in body weight development from newborn to young adult (Fig. 2A), nor were there significant differences in standard developmental landmarks (Fig. 2B).

Fig. 2Fig. 2
Effects of prenatal CPF exposure (1,3,5 or 10 mg/kg/day) on general parameters of pup development: body weight (A), and neurological and morphological developmental landmarks (B).

In adulthood (PN75) animals exposed to CPF prenatally showed significant deficits in Morris Maze performance, with a peak effect at 3 mg/kg CPF (Fig 3). For example, on the third testing day, the 3 mg/kg CPF offspring took 84% longer than control to reach the platform (p < 0.002). Consequently, the 3 mg/kg dose was employed in the subsequent reversal studies.

Fig 3
Dose response (1,3,5 or 10 mg/kg/day) for the effect of prenatal CPF exposure on Morris-Maze performance, determined as the latency to reach and climb on the platform. ANOVA indicates significant deficits caused by CPF (p < 0.003 overall, individually ...

By themselves, nicotine injections (DMSO+nicotine) had no effect on Morris Maze performance but nicotine at either the low or high dose reversed the deficits evoked by prenatal CPF exposure (Fig. 4A). The differences in latency did not reflect alterations in swimming ability (Fig. 4B).

Fig. 4Fig. 4
A. Effects of prenatal CPF exposure (3 mg/kg/day) and subsequent nicotine therapy on Morris Maze performance: (A) latency to reach and climb on the platform; (B) Swimming speed.

In the immunocytochemical studies designed to evaluate the fate of the transplanted cells (Fig 5), Dil-labeled neural precursors were identified in the brain of the grafted animals, mainly in the regions near the lateral ventricles and the cerebral cortex. Fig. 5A shows Dil-labeled transplanted cells near the lateral ventricle. No Dil-labeled cells could be identified in any of the groups that were not grafted with these labeled cells. In the study designed to address the concern of non-specific Dil staining, no Dil-labeled cells were found in the control group transplanted with Dil-labeled adult cortical cells (Fig. 5B) suggesting that the dead adult cells did not “spill” Dil to be uptaken by neighboring cells. On the other hand, Dil-labeled neural stem cells derived from the adult subventricular zone migrated extensively and could be seen in great numbers throughout the brain, shown here along the corpus callosum (Fig. 5C) suggesting that Dil labels both young and adult cells, specifically, directly and that concern about inadvertent labeling due to spillage and subsequent uptake, is not relevant in the present investigation.

Fig 5Fig 5Fig 5
A. Dil labeled cells in the area near the lateral ventricles (red). B. Control for Dil specificity: Brain tissue of a mouse transplanted with adult cortical cells, pre-labeled with Dil. No Dil marked cells can be visualized. C. Control for Dil specificity: ...

In the behavioral studies, mice exposed prenatally to CPF and receiving the sham transplantation procedure (CPF+sham) again displayed impaired Morris water maze performance (Fig. 6). By itself, transplantation of neural stem cells (DMSO+NSC) had no effect, but transplantation reversed the deficits evoked by prenatal CPF exposure (CPF+NSC vs. CPF+sham, p < 0.0001). The visible platform test showed no difference between groups (data not shown), thus excluding the contribution of motor, visual and other non-hippocampal factors to the prenatal CPF-induced deficits or their reversal by transplantation.

Fig. 6
Effects of prenatal CPF exposure (3 mg/kg/day) and subsequent transplantation of neural stem cells on Morris Maze performance. Mice exposed prenatally to CPF (CPF+sham) required more time than controls (Control+sham) to reach the platform (p < ...


Our results indicate that neural stem cells given in adolescence can completely reverse neurobehavioral deficits evoked by prenatal CPF exposure, equivalent to the ameliorating effects of nicotine administration delivered in adulthood. The demonstrable effect of the stem cell therapy on behavioral performance, weeks after delivery of cells, strongly suggest that a permanent reversal of CPF-induced deficits. These findings thus provide a proof-of-principle of the ability of this therapy to achieve a lasting amelioration of neurodevelopmental damage.

Although the majority of studies of CPF-induced developmental neurotoxicity have been conducted in rats, establishing a parallel model in mice has clear importance not only for the ability to isolate and use neural stem cells and related tools, but also for the design of future work on gene-environment interactions. The effects of neonatal CPF treatment on behavioral endpoints in mice were reported recently [24] and the present study extends the mouse model to include prenatal exposure regimens. In particular, we were able to identify the threshold for maternal toxicity and to show that neurobehavioral deficits are evoked at much lower doses that do not compromise maternal, fetal or neonatal viability, and that are not dysmorphogenic. Parallel to the earlier findings in the rat, we found a nonmonotonic dose-effect curve on behavior [17]; this is likely due to the positive trophic effects of cholinergic hyperstimulation, resulting from cholinesterase inhibition at higher doses, as discussed earlier [17]. Similarly, although neonatal CPF exposure in rats and mice produce sex-selective neurobehavioral deficits [24, 28], exposures begun in midgestation target both sexes equivalently, as found here in mice and previously in rats [13].

Based on the known targeting of hippocampal cholinergic pathways by developmental exposure to CPF [28] and the role of these projections in Morris Maze performance, the ability of nicotine to reverse the deficits was not unexpected; indeed, we showed earlier that the effects of prenatal phenobarbital exposure, which target these same projections, are likewise reversed by nicotine therapy in adulthood [2]. By implication, the lasting repair wrought by the neural stem cells is likely to involve the same circuits. However, stem cell effects are not limited to cholinergic projections, nor to the hippocampus. Indeed, the development of procedures for the production of neural stem cells in various laboratories, including ours [5, 14], has led to therapeutic application in animal models of a wide spectrum of brain defects, including Parkinson’s disease [6, 35] and cognitive disorders [5, 14, 21]. The rationale behind the use of neural stem cells for the reversal of neurobehavioral birth defects, is that the cells will differentiate in a region-specific manner [9], dictated in part by the specific sites at which deficits are present [4]. More recently, stem cell therapies were shown to induce the formation of endogenous neural precursors in the host brain [5]. These findings suggest that stem cell therapies will be able to reverse multiple types of neurodevelopmental deficits; this is particularly important for toxicants like CPF, that target a wide variety of neurotransmitter systems and neural circuits. Future work should thus concentrate on whether the stem cell approach can reverse, for example, CPF-induced serotonergic deficits that contribute to impaired emotional and appetitive behaviors [28].

In conclusion, we were able to reverse CPF neurobehavioral teratogenicity through two different strategies, one involving nicotine therapy in adulthood, and the other, neural stem cell treatment delivered in adolescence. Although nicotine therapy is more facile for clinical application, it requires lifelong treatment with an agent known to be involved in cardiovascular complications, carcinogenesis and addiction; further, its actions are directed primarily toward cholinergic function and only secondarily to the actions of other neurotransmitters, thus limiting its potential applicability. Neural stem cell therapy, on the other hand, represents a one-time treatment that produces potentially permanent reversal of neurobehavioral deficits, but has substantial procedural limitations that place it much further from immediate clinical application. Recent developments, including adult-derived stem cells, techniques to minimize immune rejection, and delivery via peripheral injection, are all likely to contribute to further advances for this approach.


Supported by grants from The United States-Israel Binational Science Foundation BSF2005003 and NIH ES014258.


analysis of variance
dimethyl sulfoxide
gestational day
glial fibrillary acidic protein
heterogeneous stock
proteoglycan NG2
neural stem cells
poly-sialated neural cell adhesion molecule
protein kinase C
postnatal day


Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.


1. Anderson DJ, Puttfarcken PS, Jacobs I, Faltynek C. Assessment of nicotinic acetylcholine receptor-mediated release of [(3)H]-norepinephrine from rat brain slices using a new 96-well format assay. Neuropharmacology. 2000;39:2663–2672. [PubMed]
2. Beer A, Slotkin TA, Seidler FJ, Yanai J. Nicotine therapy in adulthood reverses the synaptic and behavioral deficits elicited by prenatal exposure to phenobarbital. Neuropsychopharmacology. 2005;30:156–165. [PubMed]
3. Ben-Hur T, Ben-Menachem O, Furer V, Einstein O, Mizrachi-Kol R, Grigoriadis N. Effects of proinflammatory cytokines on the growth, fate, and motility of multipotential neural precursor cells. Mol Cell Neurosci. 2003;24:623–631. [PubMed]
4. Ben-Hur T, Einstein O, Mizrachi-Kol R, Ben-Menachem O, Reinhartz E, Karussis D, Abramsky O. Transplanted multipotential neural precursor cells migrate into the inflamed white matter in response to experimental autoimmune encephalomyelitis. Glia. 2003;41:73–80. [PubMed]
5. Ben-Shaanan TL, Ben-Hur T, Yanai J. Transplantation of neural progenitors enhances production of endogenous cells in the impaired brain. Molecular Psychiatry. 2008;13:222–231. [PubMed]
6. Bjorklund LM, Sanchez-Pernaute R, Chung S, Andersson T, Chen IY, McNaught KS, Brownell AL, Jenkins BG, Wahlestedt C, Kim KS, Isacson O. Embryonic stem cells develop into functional dopaminergic neurons after transplantation in a Parkinson rat model. Proc Natl Acad Sci U S A. 2002;99:2344–2349. [PubMed]
7. Casida JE, Quistad GB. Organophosphate toxicology: safety aspects of nonacetylcholinesterase secondary targets. Chem Res Toxicol. 2004;17:983–998. [PubMed]
8. Einstein O, Karussis D, Grigoriadis N, Mizrachi-Kol R, Reinhartz E, Abramsky O, Ben-Hur T. Intraventricular transplantation of neural precursor cell spheres attenuates acute experimental allergic encephalomyelitis. Mol Cell Neurosci. 2003;24:1074–1082. [PubMed]
9. Eriksson C, Bjorklund A, Wictorin K. Neuronal differentiation following transplantation of expanded mouse neurosphere cultures derived from different embryonic forebrain regions. Exp Neurol. 2003;184:615–635. [PubMed]
10. Grandjean P, Landrigan PJ. Developmental neurotoxicity of industrial chemicals. Lancet. 2006;368:2167–2178. [PubMed]
11. Gray R, Rajan AS, Radcliffe KA, Yakehiro M, Dani JA. Hippocampal synaptic transmission enhanced by low concentrations of nicotine. Nature. 1996;383:713–716. [PubMed]
12. Hanson K, Allen S, Jensen S, Hatsukami D. Treatment of adolescent smokers with the nicotine patch. Nicotine Tob Res. 2003;5:515–526. [PubMed]
13. Icenogle LM, Christopher NC, Blackwelder WP, Caldwell DP, Qiao D, Seidler FJ, Slotkin TA, Levin ED. Behavioral alterations in adolescent and adult rats caused by a brief subtoxic exposure to chlorpyrifos during neurulation. Neurotoxicol Teratol. 2004;26:95–101. [PubMed]
14. Katz S, Ben-Hur T, Ben-Shaanan TL, Yanai J. Reversal of heroin neurobehavioral teratogenicity by grafting of neural progenitors. Journal of Neurochemistry. 2008;104:38–49. [PubMed]
15. Kruyt MC, De Bruijn J, Veenhof M, Oner FC, Van Blitterswijk CA, Verbout AJ, Dhert WJ. Application and limitations of chloromethyl-benzamidodialkylcarbocyanine for tracing cells used in bone Tissue engineering. Tissue Eng. 2003;9:105–115. [PubMed]
16. Lee G, Kim H, Elkabetz Y, Al Shamy G, Panagiotakos G, Barberi T, Tabar V, Studer L. Isolation and directed differentiation of neural crest stem cells derived from human embryonic stem cells. Nat Biotechnol. 2007;25:1468–1475. [PubMed]
17. Levin ED, Addy N, Baruah A, Elias A, Christopher NC, Seidler FJ, Slotkin TA. Prenatal chlorpyrifos exposure in rats causes persistent behavioral alterations. Neurotoxicol Teratol. 2002;24:733–741. [PubMed]
18. McClearn GE, Wilson JR, Meredith W. The use of isogenic and heterogenic mouse stock in behavioral research. In: Lindzey G, Thiessen DD, editors. Contributions to behavior-genetic analysis; the mouse as a prototype. Appleton-Century-Crofts; New York: 1970. pp. 3–22.
19. Morris R. Developments of a water-maze procedure for studying spatial learning in the rat. J Neurosci Methods. 1984;11:47–60. [PubMed]
20. Nilsson OG, Shapiro ML, Gage FH, Olton DS, Bjorklund A. Spatial learning and memory following fimbria-fornix transection and grafting of fetal septal neurons to the hippocampus. Exp Brain Res. 1987;67:195–215. [PubMed]
21. Qu T, Brannen CL, Kim HM, Sugaya K. Human neural stem cells improve cognitive function of aged brain. Neuroreport. 2001;12:1127–1132. [PubMed]
22. Rauh VA, Garfinkel R, Perera FP, Andrews HF, Hoepner L, Barr DB, Whitehead R, Tang D, Whyatt RW. Impact of prenatal chlorpyrifos exposure on neurodevelopment in the first 3 years of life among inner-city children. Pediatrics. 2006;118:e1845–1859. [PMC free article] [PubMed]
23. Rezvani AH, Levin ED. Cognitive effects of nicotine. Biol Psychiatry. 2001;49:258–267. [PubMed]
24. Ricceri L, Venerosi A, Capone F, Cometa MF, Lorenzini P, Fortuna S, Calamandrei G. Developmental neurotoxicity of organophosphorous pesticides: fetal and neonatal exposure to chlorpyrifos alters sex-specific behaviors at adulthood in mice. Toxicol Sci. 2006;93:105–113. [PubMed]
25. Rodier PM. Critical periods for behavioral anomalies in mice. Environ Health Perspect. 1976;18:79–83. [PMC free article] [PubMed]
26. Rowell PP, Larson BT. Ergocryptine and other ergot alkaloids stimulate the release of [3H]dopamine from rat striatal synaptosomes. J Anim Sci. 1999;77:1800–1806. [PubMed]
27. Schormann W, Hammersen FJ, Brulport M, Hermes M, Bauer A, Rudolph C, Schug M, Lehmann T, Nussler A, Ungefroren H, Hutchinson J, Fandrich F, Petersen J, Wursthorn K, Burda MR, Brustle O, Krishnamurthi K, von Mach M, Hengstler JG. Tracking of human cells in mice. Histochem Cell Biol. 2008;130:329–338. [PubMed]
28. Slotkin TA. Developmental neurotoxicity of organophosphates: a case study of chlorpyrifos. In: Gupta RC, editor. Toxicity of Organophosphate and Carbamate Pesticides. San Diego, San Diego: 2005. pp. 293–314.
29. Slotkin TA. Fetal nicotine or cocaine exposure: which one is worse? J Pharmacol Exp Ther. 1998;285:931–945. [PubMed]
30. Slotkin TA. Nicotine and the adolescent brain: insights from an animal model. Neurotoxicol Teratol. 2002;24:369–384. [PubMed]
31. Sorenson EM, Shiroyama T, Kitai ST. Postsynaptic nicotinic receptors on dopaminergic neurons in the substantia nigra pars compacta of the rat. Neuroscience. 1998;87:659–673. [PubMed]
32. Steingart RA, Silverman WF, Barron S, Slotkin TA, Awad Y, Yanai J. Neural grafting reverses prenatal drug-induced alterations in hippocampal PKC and related behavioral deficits. Brain Res Dev Brain Res. 2000;125:9–19. [PubMed]
33. Tombaugh GC, Rowe WB, Rose GM. The slow afterhyperpolarization in hippocampal CA1 neurons covaries with spatial learning ability in aged Fisher 344 rats. J Neurosci. 2005;25:2609–2616. [PubMed]
34. Wachs FP, Couillard-Despres S, Engelhardt M, Wilhelm D, Ploetz S, Vroemen M, Kaesbauer J, Uyanik G, Klucken J, Karl C, Tebbing J, Svendsen C, Weidner N, Kuhn HG, Winkler J, Aigner L. High efficacy of clonal growth and expansion of adult neural stem cells. Lab Invest. 2003;83:949–962. [PubMed]
35. Wang X, Lu Y, Zhang H, Wang K, He Q, Wang Y, Liu X, Li L. Distinct efficacy of pre-differentiated versus intact fetal mesencephalon-derived human neural progenitor cells in alleviating rat model of Parkinson’s disease. Int J Dev Neurosci. 2004;22:175–183. [PubMed]
36. Yanai J, Abu-Roumi M, Silverman WF, Steingart RA. Neural grafting as a tool for the study and reversal of neurobehavioral birth defects. Pharmacol Biochem Behav. 1996;55:673–681. [PubMed]
37. Yanai J, Avraham Y, Levy S, Maslaton J, Pick CG, Rogel-Fuchs Y, Zahalka EA. Alterations in septohippocampal cholinergic innervations and related behaviors after early exposure to heroin and phencyclidine. Brain Res Dev Brain Res. 1992;69:207–214. [PubMed]
38. Yanai J, Pick CG. Neuron transplantation reverses phenobarbital-induced behavioral birth defects in mice. Int J Dev Neurosci. 1988;6:409–416. [PubMed]
39. Yang X, Criswell HE, Breese GR. Nicotine-induced inhibition in medial septum involves activation of presynaptic nicotinic cholinergic receptors on gamma-aminobutyric acid-containing neurons. J Pharmacol Exp Ther. 1996;276:482–489. [PubMed]
40. Zhou M, Suszkiw JB. Nicotine attenuates spatial learning deficits induced in the rat by perinatal lead exposure. Brain Res. 2004;999:142–147. [PubMed]