Cocaine affects cerebral neocortical cytoarchitecture in primates only if administered during neocortical neuronogenesis

Reactive Oxygen Species Mediate Transcriptional Responses to Dopamine and Cocaine in Human Cerebral Organoids

Dopamine signaling in the adult ventral forebrain regulates behavior, stress response, and memory formation and in neurodevelopment regulates neural differentiation and cell migration. Excessive dopamine levels, including those due to cocaine use in utero and in adults, could lead to long-term adverse consequences. The mechanisms underlying both homeostatic and pathological changes remain unclear, in part due to the diverse cellular responses elicited by dopamine and the reliance on animal models that exhibit species-specific differences in dopamine signaling. In this study, we use the human-derived ventral forebrain organoid model of Xiang-Tanaka and characterize their response to cocaine or dopamine. We explore dosing regimens of dopamine or cocaine to simulate acute or chronic exposure. We then use calcium imaging, cAMP imaging, and bulk RNA-sequencing to measure responses to cocaine or dopamine exposure. We observe an upregulation of inflammatory pathways in addition to indicators of oxidative stress following exposure. Using inhibitors of reactive oxygen species (ROS), we then show ROS to be necessary for multiple transcriptional responses of cocaine exposure. These results highlight novel response pathways and validate the potential of cerebral organoids as in vitro human models for studying complex biological processes in the brain.

Reactive Oxygen Species Mediate Transcriptional Responses to Dopamine and Cocaine in Human Cerebral Organoids

Dopamine signaling in the adult ventral forebrain regulates behavior, stress response, and memory formation and in neurodevelopment regulates neural differentiation and cell migration. Excessive dopamine levels including due to cocaine use both in utero and in adults could lead to long-term adverse consequences. The mechanisms underlying both homeostatic and pathological changes remain unclear, partly due to the diverse cellular responses elicited by dopamine and the reliance on animal models that exhibit species-specific differences in dopamine signaling. To address these limitations, 3-D cerebral organoids have emerged as human-derived models, recapitulating salient features of human cell signaling and neurodevelopment. Organoids have demonstrated responsiveness to external stimuli, including substances of abuse, making them valuable investigative models. In this study we utilize the Xiang-Tanaka ventral forebrain organoid model and characterize their response to acute and chronic dopamine or cocaine exposure. The findings revealed a robust immune response, novel response pathways, and a potential critical role for reactive oxygen species (ROS) in the developing ventral forebrain. These results highlight the potential of cerebral organoids as in vitro human models for studying complex biological processes in the brain.

The Effects of Environmental Adversities on Human Neocortical Neurogenesis Modeled in Brain Organoids

Over the past decades, a growing body of evidence has demonstrated the impact of prenatal environmental adversity on the development of the human embryonic and fetal brain. Prenatal environmental adversity includes infectious agents, medication, and substances of use as well as inherently maternal factors, such as diabetes and stress. These adversities may cause long-lasting effects if occurring in sensitive time windows and, therefore, have high clinical relevance. However, our knowledge of their influence on specific cellular and molecular processes of in utero brain development remains scarce. This gap of knowledge can be partially explained by the restricted experimental access to the human embryonic and fetal brain and limited recapitulation of human-specific neurodevelopmental events in model organisms. In the past years, novel 3D human stem cell-based in vitro modeling systems, so-called brain organoids, have proven their applicability for modeling early events of human brain development in health and disease. Since their emergence, brain organoids have been successfully employed to study molecular mechanisms of Zika and Herpes simplex virus-associated microcephaly, as well as more subtle events happening upon maternal alcohol and nicotine consumption. These studies converge on pathological mechanisms targeting neural stem cells. In this review, we discuss how brain organoids have recently revealed commonalities and differences in the effects of environmental adversities on human neurogenesis. We highlight both the breakthroughs in understanding the molecular consequences of environmental exposures achieved using organoids as well as the on-going challenges in the field related to variability in protocols and a lack of benchmarking, which make cross-study comparisons difficult.

CYP3A5 Mediates Effects of Cocaine on Human Neocorticogenesis: Studies using an In Vitro 3D Self-Organized hPSC Model with a Single Cortex-Like Unit

Because of unavoidable confounding variables in the direct study of human subjects, it has been difficult to unravel the effects of prenatal cocaine exposure on the human fetal brain, as well as the cellular and biochemical mechanisms involved. Here, we propose a novel approach using a human pluripotent stem cell (hPSC)-based 3D neocortical organoid model. This model retains essential features of human neocortical development by encompassing a single self-organized neocortical structure, without including an animal-derived gelatinous matrix. We reported previously that prenatal cocaine exposure to rats during the most active period of neural progenitor proliferation induces cytoarchitectural changes in the embryonic neocortex. We also identified a role of CYP450 and consequent oxidative ER stress signaling in these effects. However, because of differences between humans and rodents in neocorticogenesis and brain CYP metabolism, translation of the research findings from the rodent model to human brain development is uncertain. Using hPSC 3D neocortical organoids, we demonstrate that the effects of cocaine are mediated through CYP3A5-induced generation of reactive oxygen species, inhibition of neocortical progenitor cell proliferation, induction of premature neuronal differentiation, and interruption of neural tissue development. Furthermore, knockdown of CYP3A5 reversed these cocaine-induced pathological phenotypes, suggesting CYP3A5 as a therapeutic target to mitigate the deleterious neurodevelopmental effects of prenatal cocaine exposure in humans. Moreover, 3D organoid methodology provides an innovative platform for identifying adverse effects of abused psychostimulants and pharmaceutical agents, and can be adapted for use in neurodevelopmental disorders with genetic etiologies.

Cocaine-induced neurodevelopmental deficits and underlying mechanisms

Exposure to drugs early in life has complex and long-lasting implications for brain structure and function. This review summarizes work to date on the immediate and long-term effects of prenatal exposure to cocaine. In utero cocaine exposure produces disruptions in brain monoamines, particularly dopamine, during sensitive periods of brain development, and leads to permanent changes in specific brain circuits, molecules, and behavior. Here, we integrate clinical studies and significance with mechanistic preclinical studies, to define our current knowledge base and identify gaps for future investigation. Birth Defects Research (Part C) 108:147-173, 2016. © 2016 Wiley Periodicals, Inc.

An in vitro model of human neocortical development using pluripotent stem cells: cocaine-induced cytoarchitectural alterations

Neocortical development involves ordered specification of forebrain cortical progenitors to various neuronal subtypes, ultimately forming the layered cortical structure. Modeling of this process using human pluripotent stem cells (hPSCs) would enable mechanistic studies of human neocortical development, while providing new avenues for exploration of developmental neocortical abnormalities. Here, we show that preserving hPSCs aggregates - allowing embryoid body formation - while adding basic fibroblast growth factor (bFGF) during neuroepithelial development generates neural rosettes showing dorsal forebrain identity, including Mash1(+) dorsal telencephalic GABAergic progenitors. Structures that mirrored the organization of the cerebral cortex formed after rosettes were seeded and cultured for 3 weeks in the presence of FGF18, BDNF and NT3. Neurons migrated along radial glia scaffolding, with deep-layer CTIP2(+) cortical neurons appearing after 1 week and upper-layer SATB2(+) cortical neurons forming during the second and third weeks. At the end of differentiation, these structures contained both glutamatergic and GABAergic neurons, with glutamatergic neurons being most abundant. Thus, this differentiation protocol generated an hPSC-based model that exhibits temporal patterning and a neuronal subtype ratio similar to that of the developing human neocortex. This model was used to examine the effects of cocaine during neocorticogenesis. Cocaine caused premature neuronal differentiation and enhanced neurogenesis of various cortical neuronal subtypes. These cocaine-induced changes were inhibited by the cytochrome P450 inhibitor cimetidine. This in vitro model enables mechanistic studies of neocorticogenesis, and can be used to examine the mechanisms through which cocaine alters the development of the human neocortex.

Modulation by cocaine of dopamine receptors through miRNA-133b in zebrafish embryos

The use of cocaine during pregnancy can affect the mother and indirectly might alter the development of the embryo/foetus. Accordingly, in the present work our aim was to study in vivo (in zebrafish embryos) the effects of cocaine on the expression of dopamine receptors and on miR-133b. These embryos were exposed to cocaine hydrochloride (HCl) at 5 hours post-fertilization (hpf) and were then collected at 8, 16, 24, 48 and 72 hpf to study the expression of dopamine receptors, drd1, drd2a, drd2b and drd3, by quantitative real time PCR (qPCR) and in situ hybridization (ISH, only at 24 hpf). Our results indicate that cocaine alters the expression of the genes studied, depending on the stage of the developing embryo and the type of dopamine receptor. We found that cocaine reduced the expression of miR-133b at 24 and 48 hpf in the central nervous system (CNS) and at the periphery by qPCR and also that the spatial distribution of miR-133b was mainly seen in somites, a finding that suggests the involvement of miR-133b in the development of the skeletal muscle. In contrast, at the level of the CNS miR-133b had a weak and moderate expression at 24 and 48 hpf. We also analysed the interaction of miR-133b with the Pitx3 and Pitx3 target genes drd2a and drd2b, tyrosine hydroxylase (th) and dopamine transporter (dat) by microinjection of the Pitx3-3'UTR sequence. Microinjection of Pitx3-3'UTR affected the expression of pitx3, drd2a, drd2b, th and dat. In conclusion, in the present work we describe a possible mechanism to account for cocaine activity by controlling miR-133b transcription in zebrafish. Via miR-133b cocaine would modulate the expression of pitx3 and subsequently of dopamine receptors, dat and th. These results indicate that miRNAs can play an important role during embryogenesis and in drug addiction.

Cocaine modulates the expression of opioid receptors and miR-let-7d in zebrafish embryos

Prenatal exposure to cocaine, in mammals, has been shown to interfere with the expression of opioid receptors, which can have repercussions in its activity. Likewise, microRNAs, such as let-7, have been shown to regulate the expression of opioid receptors and hence their functions in mammals and in vitro experiments. In light of this, using the zebrafish embryos as a model our aim here was to evaluate the actions of cocaine in the expression of opioid receptors and let-7d miRNA during embryogenesis. In order to determine the effects produced by cocaine on the opioid receptors (zfmor, zfdor1 and zfdor2) and let-7d miRNA (dre-let-7d) and its precursors (dre-let-7d-1 and dre-let-7d-2), embryos were exposed to 1.5 µM cocaine hydrochloride (HCl). Our results revealed that cocaine upregulated dre-let-7d and its precursors, and also increased the expression of zfmor, zfdor1 and zfdor2 during early developmental stages and decreased them in late embryonic stages. The changes observed in the expression of opioid receptors might occur through dre-let-7d, since DNA sequences and the morpholinos of opioid receptors microinjections altered the expression of dre-let-7d and its precursors. Likewise, opioid receptors and dre-let-7d showed similar distributions in the central nervous system (CNS) and at the periphery, pointing to a possible interrelationship between them.In conclusion, the silencing and overexpression of opioid receptors altered the expression of dre-let-7d, which points to the notion that cocaine via dre-let-7 can modulate the expression of opioid receptors. Our study provides new insights into the actions of cocaine during zebrafish embryogenesis, indicating a role of miRNAs, let-7d, in development and its relationship with gene expression of opioid receptors, related to pain and addiction process.

Gene expression profiling reveals distinct cocaine-responsive genes in human fetal CNS cell types

OBJECTIVES

Prenatal exposure to cocaine causes cytoarchitectural alterations in the developing neocortex. Previously, we reported that cocaine inhibits neural progenitor cell proliferation through oxidative endoplasmic reticulum stress and consequent down-regulation of cyclin A, whereas cyclin A expression was increased in astrocytes. In the present study, cell type-specific responses to cocaine were further explored.

METHODS

Gene expression profiles were examined in five types of cells obtained from the human fetal cerebral cortex at 20 weeks gestation. Cells were treated with 100 µM cocaine in vitro for 24 hr, followed by gene expression analysis using a human neural/stem cell/drug abuse-focused cDNA array, with verification by quantitative real-time RT-PCR.

RESULTS

Cocaine influenced transcription of distinct categories of genes in a cell type-specific manner. Cocaine down-regulated cytoskeleton-related genes including ezrin, γ2 actin, α3d tubulin and α8 tubulin in neural and/or A2B5+ progenitor cells. In contrast, cocaine modulated immune and cell death-related genes in microglia and astrocytes. In microglia, cocaine up-regulated the immunoregulatory and pro-apoptotic genes IL-1β and BAX. In astrocytes, cocaine down-regulated the immune response gene glucocorticoid receptor and up-regulated the anti-apoptotic genes 14-3-3 ε and HVEM. Therefore, cell types comprising the developing neocortex show differential responses to cocaine.

CONCLUSIONS

These data suggest that cocaine causes cytoskeletal abnormalities leading to disturbances in neural differentiation and migration in progenitor cells, while altering immune and apoptotic responses in glia. Understanding the mechanisms of cocaine's effects on human CNS cells may help in the development of therapeutic strategies to prevent or ameliorate cocaine-induced impairments in fetal brain development.

Cell-autonomous and cell-to-cell signalling events in normal and altered neuronal migration

The cerebral cortex is a complex six-layered structure that contains an important diversity of neurons, and has rich local and extrinsic connectivity. Among the mechanisms governing the cerebral cortex construction, neuronal migration is perhaps the most crucial as it ensures the timely formation of specific and selective neuronal circuits. Here, we review the main extrinsic and extrinsic factors involved in regulating neuronal migration in the cortex and describe some environmental factors interfering with their actions.

Prenatal cocaine exposure alters progenitor cell markers in the subventricular zone of the adult rat brain

Long-term consequences of early developmental exposure to drugs of abuse may have deleterious effects on the proliferative plasticity of the brain. The purpose of this study was to examine the long-term effects of prenatal exposure to cocaine, using the IV route of administration and doses that mimic the peak arterial levels of cocaine use in humans, on the proliferative cell types of the subventricular zones (SVZ) in the adult (180 days-old) rat brain. Employing immunocytochemistry, the expression of GFAP(+) (type B cells) and nestin(+)(GFAP(-)) (type C and A cells) staining was quantified in the subcallosal area of the SVZ. GFAP(+) expression was significantly different between the prenatal cocaine treated group and the vehicle (saline) control group. The prenatal cocaine treated group possessed significantly lower GFAP(+) expression relative to the vehicle control group, suggesting that prenatal cocaine exposure significantly reduced the expression of type B neural stem cells of the SVZ. In addition, there was a significant sex difference in nestin(+) expression with females showing approximately 8-13% higher nestin(+) expression compared to the males. More importantly, a significant prenatal treatment condition (prenatal cocaine, control) by sex interaction in nestin(+) expression was confirmed, indicating different effects of cocaine based on sex of the animal. Specifically, prenatal cocaine exposure eliminated the basal difference between the sexes. Collectively, the present findings suggest that prenatal exposure to cocaine, when delivered via a protocol designed to capture prominent features of recreational usage, can selectively alter the major proliferative cell types in the subcallosal area of the SVZ in an adult rat brain, and does so differently for males and females.

Cocaine alters BDNF expression and neuronal migration in the embryonic mouse forebrain

Prenatal cocaine exposure impairs brain development and produces lasting alterations in cognitive function. In a prenatal cocaine exposure mouse model, we found that tangential migration of GABA neurons from the basal to the dorsal forebrain and radial neuron migration within the dorsal forebrain were significantly decreased during the embryonic period. The decrease in the tangential migration occurred early in gestation and normalized by late gestation, despite ongoing cocaine exposure. The decrease in radial migration was associated with altered laminar positioning of neurons in the medial prefrontal cortex. The cocaine exposure led to transient decreases in the expression of Tbr2 and Tbr1, transcription factors associated with intermediate progenitor cells and newborn neurons of the dorsal forebrain, respectively, although neurogenesis was not significantly altered. Since cocaine can modulate brain derived neurotrophic factor (BDNF) expression in the mature brain, we examined whether cocaine can alter BDNF expression in the embryonic brain. We found a transient decrease in BDNF protein expression in the cocaine-exposed embryonic forebrain early in gestation. By late gestation, the BDNF expression recovered to control levels, despite ongoing cocaine exposure. In basal forebrain explants from cocaine-exposed embryos, cell migration was significantly decreased, corroborating the in vivo data on tangential GABA neuron migration. Since BDNF can influence tangential neuronal migration, we added BDNF to the culture medium and observed increased cell migration. Our data suggest that cocaine can alter tangential and radial neuronal migration as well as BDNF expression in the embryonic brain and that decreased BDNF may mediate cocaine's effects on neuronal migration.

Annual Research Review: New frontiers in developmental neuropharmacology: can long-term therapeutic effects of drugs be optimized through carefully timed early intervention?

Our aim is to present a working model that may serve as a valuable heuristic to predict enduring effects of drugs when administered during development. Our primary tenet is that a greater understanding of neurodevelopment can lead to improved treatment that intervenes early in the progression of a given disorder and prevents symptoms from manifesting. The immature brain undergoes significant changes during the transitions between childhood, adolescence, and adulthood. Such changes in innervation, neurotransmitter levels, and their respective signaling mechanisms have profound and observable changes on typical behavior, but also increase vulnerability to psychiatric disorders when the maturational process goes awry. Given the remarkable plasticity of the immature brain to adapt to its external milieu, preventive interventions may be possible. We intend for this review to initiate a discussion of how currently used psychotropic agents can influence brain development. Drug exposure during sensitive periods may have beneficial long-term effects, but harmful delayed consequences may be possible as well. Regardless of the outcome, this information needs to be used to improve or develop alternative approaches for the treatment of childhood disorders. With this framework in mind, we present what is known about the effects of stimulants, antidepressants, and antipsychotics on brain maturation (including animal studies that use more clinically-relevant dosing paradigms or relevant animal models). We endeavor to provocatively set the stage for altering treatment approaches for improving mental health in non-adult populations.

Cocaine causes deficits in radial migration and alters the distribution of glutamate and GABA neurons in the developing rat cerebral cortex

Prenatal cocaine exposure induces cytoarchitectural changes in the embryonic neocortex; however, the biological mechanisms and type of cortical neurons involved in these changes are not known. Previously, we found that neural progenitor proliferation in the neocortical ventricular zone (VZ) is inhibited by cocaine; here, we examine the changes in cortical neurogenesis and migration of glutamate and GABA neurons induced by prenatal cocaine exposure. Pregnant rats received 20 mg/kg of cocaine intraperitoneally twice at an interval of 12 h during three periods of neocortical neurogenesis. Neocortical area and distribution of developing neurons were examined by counting Tuj1+, glutamate+, or GABA+ cells in different areas of the cerebral cortex. Cocaine decreased neocortical area by reducing the size of the Tuj1+ layer, but only when administered during early periods of neocortical neurogenesis. The number of glutamatergic neurons was increased in the VZ but was decreased in the outer cortical laminae. Although the number of GABA+ neurons in the VZ of both the neocortex and ganglionic eminences was unchanged, GABA+ cells decreased in all other neocortical laminae. Tangential migration of GABA+ cells was also disrupted by cocaine. These findings suggest that in utero cocaine exposure disturbs radial migration of neocortical neurons, possibly because of decreased radial glia guiding support through enhanced differentiation of neocortical VZ progenitors. Cocaine interrupts radial migration of both glutamatergic and GABAergic neurons within the neocortex, in addition to the tangential migration of GABAergic neurons from the subcortical telecephalon. This may result in abnormal neocortical cytoarchitecture and concomitant adverse functional effects.

Superoxide production after acute and chronic treatment with methylphenidate in young and adult rats

The prescription of methylphenidate (MPH) has dramatically increased in this decade for attention deficit hyperactivity disorder (ADHD) treatment. The action mechanism of MPH is not completely understood and studies have been demonstrated that MPH can lead to neurochemical adaptations. Superoxide radical anion is not very reactive per se. However, severe species derived from superoxide radical anion mediate most of its toxicity. In this study, the superoxide level in submitochondrial particles was evaluated in response to treatment with MPH in the age-dependent manner in rats. MPH was administrated acutely or chronically at doses of 1, 2 or 10 mg/kg i.p. The results showed that the acute administration of MPH in all doses in young rats increased the production of superoxide in the cerebellum and only in the high dose (10mg/kg) in the hippocampus, while chronic treatment had no effect. However, acute treatment in adult rats had no effect on production of superoxide, but chronic treatment decreased the production of superoxide in the cerebellum at the lower doses. Our data suggest that the MPH treatment can influence on production of superoxide in some brain areas, but this effect depends on age of animals and treatment regime with MPH.

Developmental chlorpyrifos and methyl parathion exposure alters radial-arm maze performance in juvenile and adult rats

Although the use of organophosphate (OP) insecticides has been restricted, sufficient exposure can occur to induce detrimental neurobehavioral effects. In this study, we measured physical and reflex development and spatial learning and memory in rats repeatedly exposed to incremental doses of chlorpyrifos (CPS) and methyl parathion (MPS) from postnatal day (PND) 1 to PND21. Other than decreased body weight in the higher dosage groups, no effects on physical or reflex development were observed. Significant hippocampal cholinesterase inhibition was induced in all treatment groups for up to 19 days following exposure. Beginning on PND36, working and reference memory was tested using a 12-arm radial maze, with subject animals trained and tested 4 days a week for 4 weeks. In males, working memory was decreased with the medium and high dosage of MPS but only the high dosage of CPS; while in females, no deficits were observed. For reference memory, errors were significantly increased in males exposed to the high dosage of CPS and all dosages of MPS. In females, enhanced performance was observed within the medium and high dosages of CPS but not with MPS. These data show that repeated developmental exposure to OP insecticides can induce sex-selective alterations and long-lasting changes in spatial learning and memory formation when measured using a radial arm maze and that MPS and CPS induce different neurobehavioral outcomes.

Modes and mishaps of neuronal migration in the mammalian brain

The ability of neurons to migrate to their appropriate positions in the developing brain is critical to brain architecture and function. Recent research has elucidated different modes of neuronal migration and the involvement of a host of signaling factors in orchestrating the migration, as well as vulnerabilities of this process to environmental and genetic factors. Here we discuss the role of cytoskeleton, motor proteins, and mechanisms of nuclear translocation in radial and tangential migration of neurons. We will also discuss how these and other events essential for normal migration of neurons can be disrupted by genetic and environmental factors that contribute to neurological disease in humans.

Dopamine, cocaine and the development of cerebral cortical cytoarchitecture: a review of current concepts

Exposure of the developing fetus to cocaine produces lasting adverse effects on brain structure and function. Animal models show that cocaine exerts its effects by interfering with monoamine neurotransmitter function and that dopamine is cocaine's principal monoamine target in the fetal brain. This review will examine the role of dopamine receptor signaling in the regulation of normal development of the cerebral cortex, the seat of higher cognitive functions, and discuss whether dopamine receptor signaling mechanisms are the principal mediators of cocaine's deleterious effects on the ontogeny of cerebral cortical cytoarchitecture.

A mechanism for the inhibition of neural progenitor cell proliferation by cocaine

BACKGROUND

Prenatal exposure of the developing brain to cocaine causes morphological and behavioral abnormalities. Recent studies indicate that cocaine-induced proliferation inhibition and/or apoptosis in neural progenitor cells may play a pivotal role in causing these abnormalities. To understand the molecular mechanism through which cocaine inhibits cell proliferation in neural progenitors, we sought to identify the molecules that are responsible for mediating the effect of cocaine on cell cycle regulation.

METHODS AND FINDINGS

Microarray analysis followed by quantitative real-time reverse transcription PCR was used to screen cocaine-responsive and cell cycle-related genes in a neural progenitor cell line where cocaine exposure caused a robust anti-proliferative effect by interfering with the G1-to-S transition. Cyclin A2, among genes related to the G1-to-S cell cycle transition, was most strongly down-regulated by cocaine. Down-regulation of cyclin A was also found in cocaine-treated human primary neural and A2B5+ progenitor cells, as well as in rat fetal brains exposed to cocaine in utero. Reversing cyclin A down-regulation by gene transfer counteracted the proliferation inhibition caused by cocaine. Further, we found that cocaine-induced accumulation of reactive oxygen species, which involves N-oxidation of cocaine via cytochrome P450, promotes cyclin A down-regulation by causing an endoplasmic reticulum (ER) stress response, as indicated by increased phosphorylation of eIF2alpha and expression of ATF4. In the developing rat brain, the P450 inhibitor cimetidine counteracted cocaine-induced inhibition of neural progenitor cell proliferation as well as down-regulation of cyclin A.

CONCLUSIONS

Our results demonstrate that down-regulation of cyclin A underlies cocaine-induced proliferation inhibition in neural progenitors. The down-regulation of cyclin A is initiated by N-oxidative metabolism of cocaine and consequent ER stress. Inhibition of cocaine N-oxidative metabolism by P450 inhibitors may provide a preventive strategy for counteracting the adverse effects of cocaine on fetal brain development.

Microanatomy in 21 day rat brains exposed prenatally to cocaine

We examined cell minicolumns, apical dendrite bundles, and inhibitory interneurons, in prefrontal and somatosensory cortex of 21-day-old rat brains exposed to cocaine during fetal development. Cell columns and apical dendrite bundles were found to be narrower, or closer together, in all three areas following in utero cocaine exposure. The inter-rater reliability among different observers was R(2)=0.89. The number of cells stained for glutamic acid decarboxylase (GAD) was not significantly different in the prenatal cocaine exposed group compared to saline controls. The present data suggests that recreational doses of cocaine administered intravenously in early pregnancy, have the capacity to modify the maturation of the ontogenetic cell column.

Stimulants and the developing brain

For almost 70 years, children have received stimulants for the treatment of attention deficit hyperactivity disorder [ADHD (initially called hyperkinetic syndrome)], with little understanding of the long-term effects of these drugs on brain development. The maturation and refinement of the brain during childhood and adolescence, including the overproduction and selective elimination of synapses, is based on genetic programming and experience. The effects of stimulant drugs during different stages of this process have unique short-term, acute effects that also influence their long-term effects. Chronic, pre-pubertal exposure alters the expected developmental trajectory of brain structure and function and results in a different topography in adulthood. The timing of exposure (childhood versus adolescence), the age of examination after drug exposure (immediately or delayed into adulthood) and sex influence the observable effects. Preclinical studies of the effects of stimulant exposure provide increased understanding about the impact of stimulant drugs on brain development and provide insight into new treatment options for ADHD and other disorders of childhood.

Neuropathology of the cerebral cortex observed in a range of animal models of prenatal cocaine exposure may reflect alterations in genes involved in the Wnt and cadherin systems

Several recent reports show that the cerebral cortex in humans and animals with altered expressions of Wnt/cadherin network-associate molecules display cytoarchitectural abnormalities reminiscent of cortical dysplasias seen in some (mouse-, rat-, and monkey-based) animal models of prenatal cocaine exposure. Therefore, we employed oligo microarrays followed by real-time RT-PCR to compare expressions of genes involved in Wnt and cadherin systems in the cerebral wall of 18-day-old (E18) fetuses from cocaine-treated (20 mg/kg cocaine, s.c., b.i.d., E8-18) and drug-naive (saline, s.c.) mice. The pregnant mice chronically treated with cocaine in the above-described manner represent one of the animal models producing offspring with widespread cortical dysplasias. Out of more than 150 relevant genes in the arrays, 32 were upregulated and 9 were downregulated in cocaine-exposed fetuses. The majority of these genes (30 out of 41) were similarly affected in the frontal and occipital regions of the cerebral wall. We also used Western immunoblotting to examine the ability of cocaine to regulate the protein levels of beta-catenin, the key functional component of both Wnt and cadherin systems. While the total cell levels of beta-catenin were increased throughout the cerebral wall of cocaine-exposed fetuses, its nuclear (gene-transcription driving) levels remained unaltered. This suggests a transcription-unrelated role for cocaine-induced upregulation of this protein. Overall, our findings point to an intriguing possibility that that cerebral cortical dysplasias observed in several animal models of prenatal cocaine exposure may be at least in part related to alterations in the Wnt/cadherin molecular network.

Cocaine-induced changes in the expression of apoptosis-related genes in the fetal mouse cerebral wall

It has been demonstrated that exposure to cocaine increases cell death in the fetal CNS. To examine the molecular mechanisms of this effect, we employed mouse oligo microarrays followed by real-time reverse transcriptase-polymerase chain reaction (real-time RT-PCR) to compare expressions of apoptosis-related genes in the cerebral wall of 18-day-old (E18) fetuses from cocaine-treated (20 mg/kg cocaine, s.c., b.i.d., E8th-E18th) and drug-naive (saline, s.c.) mice. Out of approximately 400 relevant genes in the arrays, 53 showed alterations in expression in cocaine-exposed fetuses. Upregulation was observed in 35 proapoptotic and 8 antiapoptotic genes; 4 proapoptotic and 6 antiapoptotic genes were down-regulated. The affected genes encode a wide range of apoptosis-related proteins, including death receptors (NTF-R1, NTF-R2, DR3, DR5, LTbeta-R, GITR, P57 TR-1) and their adaptor and regulatory proteins (MASGE-D1, TRAF-2, SIVA, MET, FLIP, FAIM, IAP1, ATFA), members of transcription regulatory pathways (JNK, NF-kappaB, P53), members of BCL-2 family of proteins (BID, BAD, BAX, BIK, NIP21, NIP3, NIX, BCL-2), DNA damage sensor (PARP-1), caspases and their substrates and regulatory proteins (caspases 8, 4, 9, and 3, ACINUS, CIDE-A, CIDE-B, GAS2), mitochondrially released factors (cytochrome c, AIF, PRG3), specific endoplasmic reticulum- and oxidative stress-associated factors (BACH2, ABL1, ALG2, CHOP), members of cell survival AKT and HSP70 pathways (PIK3GA, PTEN, HSP70, BAG1, BAG2), and others. This suggests that cocaine affects survival of developing cerebral cells via multiple apoptosis-regulating mechanisms.

Altering the course of neurodevelopment: a framework for understanding the enduring effects of psychotropic drugs

Childhood is a time filled with wondrous changes, as brain plasticity permits experiences to shape the immature brain to meet the demands of the environment. Change occurs at various levels--from neuroanatomy, including within a given region and its connectivity to other regions, to the function of neurotransmitter systems and their reactivity to pharmacological agents in the short- and long-term. The nature and degree to which drug exposure influences the final adult topography is influenced greatly by the maturational phase of these critical factors. Moreover, evidence is slowly emerging that suggests that the long-term effects of drug exposure are delayed and expressed once the vulnerable system reaches maturation (i.e., typically during adulthood). This phenomenon is known as neuronal imprinting and occurs when the effects of drug exposure outlast the drug itself. Thus, understanding the persistent effects critically depends on the window of observation. Embracing this concept should influence how we conduct preclinical assessments of developmental drug exposure, and ultimately how we conduct clinical assessments of drug efficacy, effectiveness, and safety for the treatment of childhood psychiatric disorders. In this article, we present a model to provide a heuristic framework for making predictions about imprinted effects of childhood drug exposure. We then review epidemiological data on attention deficit hyperactivity disorder (ADHD) and childhood depression, prescription practices, and what is known regarding the long-term consequences of drug exposure in these populations. We conclude with a discussion of the current status of preclinical studies on juvenile stimulant exposure.

Neuropathological consequences of prenatal cocaine exposure in the mouse

We have developed an animal model in Swiss Webster mice to identify mechanisms by which prenatal exposure to cocaine results in persistent alterations in brain structure and function. Clinical data suggests that children who demonstrate the largest impairments in prenatal brain growth, which are positively correlated with the highest level of prenatal cocaine exposure, are more likely to demonstrate selective impairment in postnatal brain growth, as well as postnatal impairments in motor function, attention and language skills. We conducted neuroanatomic studies to identify the postnatal evolution of structural changes in the primary somatosensory (SI) cortex of the developing mouse brain following prenatal exposure to cocaine. Our previous work, and that of others, provides evidence that many of the processes underlying corticogenesis are disrupted by gestational exposure of the developing mouse brain to cocaine, and that from the earliest phases of corticogenesis that there is an imprecision in the development of cortical lamination. We performed morphometric comparisons between the brains of animals prenatally exposed to varying amounts of cocaine with vehicle and malnutrition controls on postnatal (P) days P9 and P50. We found that on P50, but not P9, the relative number of cortical neurons in S1 is significantly less in cocaine exposed animals as compared with controls. The significant decrease in the number of cells in cocaine exposed animals on P50 is evident as a decreased density of cells restricted to the infragranular compartment (layers V and VI). Those changes are not seen in malnourished animals. Taken together our findings support the conclusion that cocaine-induced alterations in SI cortical cytoarchitectonics are in part a consequence of altered postnatal survival of infragranular cortical neurons, which are lost during the interval between P9 and P50. Determining whether a similar process is evident in a subset of humans following in utero cocaine exposure is a high priority for future clinical brain imaging studies, because analogous structural changes could impact the brain function and behavioral repertoire of infants and children following significant prenatal exposures.

Cocaine-induced inhibition of process outgrowth in locus coeruleus neurons: role of gestational exposure period and offspring sex

Cocaine use during pregnancy is associated with neurobehavioral problems in school-aged children that implicate alterations in attentional processes, potentially due to impairments in the noradrenergic system. We analyzed locus coeruleus (LC) neurite outgrowth characteristics following the administration of a physiologically relevant dose of cocaine (3.0 mg/kg) issued during critical phases of gestation (gestational day (GD)8-14, GD15-21, GD8-21). Results showed that cocaine inhibits LC neurite outgrowth and development, as evidenced by a decrease in total neurite length, a decrease in neurite length per cell, and a decrease in the percentage of cells with neurites. Morphological differences between cultures treated with and without cocaine were also evident. Further, the specific gestational exposure period effects were also dependent upon sex of the fetus. Finally, a discriminant function analysis suggested that the pattern and magnitude of alterations that defined the GD8-14 exposure were significantly different from that of the GD15-21 or GD8-21 exposures. Collectively, these data demonstrate a direct, disruptive effect of cocaine on noradrenergic neurons and may provide a neurobiological basis for changes in attentional function seen in offspring exposed to cocaine in utero.

Cocaine exposure decreases GABA neuron migration from the ganglionic eminence to the cerebral cortex in embryonic mice

Recurrent exposure of the developing fetus to cocaine produces persistent alterations in structure and function of the cerebral cortex. Neurons of the cerebral cortex are derived from two sources: projection neurons from the neuroepithelium of the dorsal pallium and interneurons from the ganglionic eminence of the basal telencephalon. The interneurons are GABAergic and reach the cerebral cortex via a tangential migratory pathway. We found that recurrent, transplacental exposure of mouse embryos to cocaine from embryonic day 8 to 15 decreases tangential neuronal migration and results in deficits in GABAergic neuronal populations in the embryonic cerebral wall. GABAergic neurons of the olfactory bulb, which are derived from the ganglionic eminence via the rostral migratory pathway, are not affected by the cocaine exposure suggesting a degree of specificity in the effects of cocaine on neuronal migration. Thus, one mechanism by which prenatal cocaine exposure exerts deleterious effects on cerebral cortical development may be by decreasing GABAergic neuronal migration from the ganglionic eminence to the cerebral wall. The decreased GABA neuron migration may contribute to persistent structural and functional deficits observed in the exposed offspring.

Cocaine effects on the developing brain: current status

The present paper reports on the results obtained in a rabbit model of prenatal cocaine exposure that mimics the pharmacokinetics of crack cocaine in humans, and relates these findings to studies in other species including humans. A general finding is that prenatal exposure to cocaine during neurogenesis produces dysfunctions in signal transduction via the dopamine D(1) receptor and alterations in cortical neuronal development leading to permanent morphological abnormalities in frontocingulate cortex and other brain structures. Differences in the precise effects obtained appear to be due to the dose, route and time of cocaine administration. Related to these effects of in utero cocaine exposure, animals demonstrate permanent deficits in cognitive processes related to attentional focus that have been correlated with impairment of stimulus processing in the anterior cingulate cortex. The long-term cognitive deficits observed in various species are in agreement with recent reports indicating that persistent attentional and other cognitive deficits are evident in cocaine-exposed children as they grow older and are challenged to master more complex cognitive tasks.

Consequences of prenatal cocaine exposure in nonhuman primates

The extent to which cocaine abuse by pregnant women can affect development of their offspring remains a matter of significant debate. In large part, this is due to difficulties in accurate determination of the type, dose, and pattern of cocaine administration by drug abusing women as well as to difficulties in controlling for a wide range of potentially confounding variables, such as other drugs used, race, socioeconomic status, and level of prenatal care. On this background, examination of the effects of prenatal cocaine exposure in highly controlled nonhuman primate models represents an important complement to the human research. The present review summarizes the data obtained in several different rhesus monkey models of cocaine exposure in utero. These data demonstrate the potential of prenatal cocaine exposure to interfere with structural and biochemical development of the brain leading to behavioral deficits at birth and/or during adulthood. However, the differences in the outcomes between individual models also suggest that the specific types and severity of cocaine effects are likely dependent on the route, dose, gestational period, and daily pattern of administration.

The effects of prenatal cocaine exposure on reversal learning using a simple visual discrimination task in rhesus monkeys

The purpose of this research was to determine if adult animals that were exposed to cocaine prenatally would be able to adapt to changes in the rules of reinforcement for a simple discrimination task. Treatment groups included 0.0, 1.0, and 3.0 mg cocaine/kg/day and an escalating-dose group that began treatment at 3.0 mg cocaine/kg/day, after which the dose was increased by 0.5 mg cocaine/kg/day every 2 weeks throughout the pregnancy. All animals performed a color and position discrimination task for food reinforcers for approximately 6 years before the present study. For this task, subjects were presented with colored stimuli that determined the correctness of subsequent position choices: left for red or yellow and right for blue or green. At 7 years of age, the rules for obtaining reinforcement were reversed. Animals exposed to all doses of cocaine showed impaired reversal performance. Further, animals exposed to the escalating doses of cocaine continued to show this impairment for over 285 sessions (about 21/2 years). The number of sessions required by subjects to master these contingency changes indicated that, using a task with which they have an extensive history, cocaine-exposed animals have greater difficulty in adapting to important changes in their environment.

Dopamine modulates cell cycle in the lateral ganglionic eminence

Dopamine is a neuromodulator the functions of which in the regulation of complex behaviors such as mood, motivation, and attention are well known. Dopamine appears in the brain early in the embryonic period when none of those behaviors is robust, raising the possibility that dopamine may influence brain development. The effects of dopamine on specific developmental processes such as neurogenesis are not fully characterized. The neostriatum is a dopamine-rich region of the developing and mature brain. If dopamine influenced neurogenesis, the effects would likely be pronounced in the neostriatum. Therefore, we examined whether dopamine influenced neostriatal neurogenesis by influencing the cell cycle of progenitor cells in the lateral ganglionic eminence (LGE), the neuroepithelial precursor of the neostriatum. We show that dopamine arrives in the LGE via the nigrostriatal pathway early in the embryonic period and that neostriatal neurogenesis progresses in a dopamine-rich milieu. Dopamine D1-like receptor activation reduces entry of progenitor cells from the G(1)- to S-phase of the cell cycle, whereas D2-like receptor activation produces the opposite effects by promoting G(1)- to S-phase entry. D1-like effects are prominent in the ventricular zone, and D2-like effects are prominent in the subventricular zone. The overall effects of dopamine on the cell cycle are D1-like effects, most likely because of the preponderance of D1-like binding sites in the embryonic neostriatum. These data reveal a novel developmental role for dopamine and underscore the relevance of dopaminergic signaling in brain development.

The intersection of stress, drug abuse and development

Use or abuse of licit and illicit substances is often associated with environmental stress. Current clinical evidence clearly demonstrates neurobehavioral, somatic growth and developmental deficits in children born to drug-using mothers. However, the effects of environmental stress and its interaction with prenatal drug exposure on a child's development is unknown. Studies in pregnant animals under controlled conditions show drug-induced long-term alterations in brain structures and functions of the offspring. These cytoarchitecture alterations in the brain are often associated with perturbations in neurotransmitter systems that are intimately involved in the regulation of the stress responses. Similar abnormalities have been observed in the brains of animals exposed to other adverse exogenous (e.g., environmental stress) and/or endogenous (e.g., glucocorticoids) experiences during early life. The goal of this article is to: (1) provide evidence and a perspective that common neural systems are influenced during development both by perinatal drug exposure and early stress exposure; and (2) identify gaps and encourage new research examining the effects of early stress and perinatal drug exposure, in animal models, that would elucidate how stress- and drug-induced perturbations in neural systems influence later vulnerability to abused drugs in adult offspring.