Specificity of prenatal cocaine on inhibition of locus coeruleus neurite outgrowth

Noradrenergic correlates of chronic cocaine craving: neuromelanin and functional brain imaging

Preclinical studies have implicated noradrenergic (NA) dysfunction in cocaine addiction. In particular, the NA system plays a central role in motivated behavior and may partake in the regulation of craving and drug use. Yet, human studies of the NA system are scarce, likely hampered by the difficulty in precisely localizing the locus coeruleus (LC). Here, we used neuromelanin imaging to localize the LC and quantified LC neuromelanin signal (NMS) intensity in 44 current cocaine users (CU; 37 men) and 59 nondrug users (NU; 44 men). We also employed fMRI to investigate cue-induced regional responses and LC functional connectivities, as quantified by generalized psychophysiological interaction (gPPI), in CU. Imaging data were processed by published routines and the findings were evaluated with a corrected threshold. We examined how these neural measures were associated with chronic cocaine craving, as assessed by the Cocaine Craving Questionnaire (CCQ). Compared to NU, CU demonstrated higher LC NMS for all probabilistic thresholds defined of 50-90% of the peak. In contrast, NMS of the ventral tegmental area/substantia nigra (VTA/SN) did not show significant group differences. Drug as compared to neutral cues elicited higher activations of many cortical and subcortical regions, none of which were significantly correlated with CCQ score. Drug vs. neutral cues also elicited "deactivation" of bilateral parahippocampal gyri (PHG) and PHG gPPI with a wide array of cortical and subcortical regions, including the ventral striatum and, with small volume correction, the LC. Less deactivation of the PHG (r = 0.40, p = 0.008) and higher PHG-LC gPPI (r = 0.44, p = 0.003) were positively correlated with the CCQ score. In contrast, PHG-VTA/SN connectivity did not correlate with the CCQ score. Together, chronic cocaine exposure may induce higher NMS intensity, suggesting neurotoxic effects on the LC. The correlation of cue-elicited PHG LC connectivity with CCQ score suggests a noradrenergic correlate of chronic cocaine craving. Potentially compensating for memory functions as in neurodegenerative conditions, cue-elicited PHG LC circuit connectivity plays an ill-adaptive role in supporting cocaine craving.

Prenatal and postnatal cocaine exposure enhances the induction and expression of locomotor sensitization to cocaine in rats

Prenatal and postnatal exposure to cocaine can affect the development and function of the central nervous system in offspring. It also produces changes in cocaine-induced dopamine release and increases cocaine self-administration and cocaine-induced conditioned place preference. Further, prenatal cocaine exposure involves greater risk for development of a substance use disorder in adolescents. Therefore, the objective of this study was to determine the effect of prenatal and postnatal cocaine exposure on locomotor sensitization in rats. A group of pregnant female Wistar rats were administered daily from day GD0 to GD21 with cocaine (cocaine pre-exposure group) and another group pregnant female rats were administered daily with saline (saline pre-exposure group). During lactation (PND0 to PND21) pregnant rats also received cocaine administration or saline, respectively. Of the litters resulting of the cocaine pre-exposed and saline pre-exposed pregnant female groups, only the male rats were used for the recording of the locomotor activity induced by different doses of cocaine (1, 5, 10, 20 and 40 mg/Kg/day) during the induction and expression of locomotor sensitization at different postnatal ages (30, 60, 90 and 120 days), representative of adolescence and adult ages. The study found that prenatal and postnatal cocaine exposure enhanced locomotor activity and locomotor sensitization, and such increase was dose- and age-dependent. This suggests that prenatal and postnatal cocaine exposure can result in increased vulnerability to cocaine abuse in young and adult humans.

Identification of biochemical and cytotoxic markers in cocaine treated PC12 cells

Cocaine is one of the powerful addictive drugs, widely abused in most Western countries. Because of high lipophilic nature, cocaine easily reaches various domains of the central nervous system (CNS) and triggers different levels of cellular toxicity. The aim of this investigation was to reproduce cocaine toxicity in differentiated PC12 cells through quantitative knowledge on biochemical and cytotoxicity markers. We differentiated the cells with 0.1 μg/ml nerve growth factor (NGF) for 5 days, followed by treatment with cocaine for 48 h at in vivo and in vitro concentrations. Results indicated that cocaine at in vivo concentrations neither killed the cells nor altered the morphology, but decreased the mitochondrial membrane potential that paralleled with increased lactate and glutathione (GSH) levels. On the other hand, cocaine at in vitro concentrations damaged the neurites and caused cell death, which corresponded with increased reactive oxygen species (ROS) generation, plasma membrane damage, and GSH depletion with no detectable nitric oxide (NO) level. While direct understanding of cocaine and cell interaction under in vivo animal models is impeded due to high complexity, our present in vitro results assisted in understanding the onset of some key events of neurodegenerative diseases in cocaine treated neuronal cells.

Cocaine Causes Apoptotic Death in Rat Mesencephalon and Striatum Primary Cultures

To study cocaine's toxic effects in vitro, we have used primary mesencephalic and striatal cultures from rat embryonic brain. Treatment with cocaine causes a dramatic increase in DNA fragmentation in both primary cultures. The toxicity induced by cocaine was paralleled with a concomitant decrease in the microtubule associated protein 2 (MAP2) and/or neuronal nucleus protein (NeuN) staining. We also observed in both cultures that the cell death caused by cocaine was induced by an apoptotic mechanism, confirmed by TUNEL assay. Therefore, the present paper shows that cocaine causes apoptotic cell death and inhibition of the neurite prolongation in striatal and mesencephalic cell culture. These data suggest that if similar neuronal damage could be produced in the developing human brain, it could account for the qualitative or quantitative defects in neuronal pathways that cause a major handicap in brain function following prenatal exposure to cocaine.

Prenatal cocaine exposure and gray matter volume in adolescent boys and girls: relationship to substance use initiation

BACKGROUND

Studies of prenatal cocaine exposure have primarily examined childhood populations. Studying adolescents is especially important because adolescence is a time of changing motivations and initiation of substance use.

METHODS

Using magnetic resonance imaging and whole-brain voxel-based morphometry, we assessed gray matter volume (GMV) differences in 42 prenatally cocaine exposed (PCE) and 21 noncocaine-exposed (NCE) adolescents, aged 14 to 17 years. Associations between GMV differences in significant clusters and the probability of substance use initiation were examined.

RESULTS

PCE relative to NCE adolescents demonstrated three clusters of lower GMV involving a limbic and paralimbic (p < .001, family-wise error [FWE] corrected), superior frontal gyrus (p = .001, FWE corrected), and precuneus (p = .019, FWE corrected) cluster. GMVs in the superior frontal and precuneus clusters were associated with initiation of substance use. Each 1-mL decrease in GMV increased the probability of initiating substance use by 69.6% (p = .01) in the superior frontal cluster and 83.6% (p = .02) in the precuneus cluster.

CONCLUSIONS

PCE is associated with structural differences in cortical and limbic regions. Lower GMVs in frontal cortical and posterior regions are associated with substance use initiation and may represent biological risk markers for substance use.

Effects of prenatal cocaine and heroin exposure on neuronal dendrite morphogenesis and spatial recognition memory in mice

Cocaine and heroin are psychoactive substances frequently used by woman abusers of childbearing age. In this study, we used in utero electroporation labeling technique and novelty recognition models to evaluate the effects of prenatal exposure of mice to cocaine or heroin on the morphological development of cortical neurons and postnatal cognitive functions. Our results showed that prenatal cocaine exposure increased dendrite outgrowth, and prenatal heroin exposure decreased dendrite length and branch number in pyramidal neurons in the somatosensory cortex. Furthermore, although no effects of prenatal cocaine or heroin exposure on novel object recognition were observed, offspring prenatally exposed to cocaine exhibited no exploration preference for objects placed in novel locations, and mice prenatally exposed to heroin showed a reduced tendency of exploration for objects in novel locations. These data demonstrate that maternal cocaine or heroin administration during pregnancy causes morphological alterations in pyramidal neurons in the somatosensory cortex and suggest that prenatal administration of addictive substances may impair short-term spatial memory in adult offspring.

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.

Prenatal IV Cocaine: Alterations in Auditory Information Processing

One clue regarding the basis of cocaine-induced deficits in attentional processing is provided by the clinical findings of changes in the infants' startle response; observations buttressed by neurophysiological evidence of alterations in brainstem transmission time. Using the IV route of administration and doses that mimic the peak arterial levels of cocaine use in humans, the present study examined the effects of prenatal cocaine on auditory information processing via tests of the auditory startle response (ASR), habituation, and prepulse inhibition (PPI) in the offspring. Nulliparous Long-Evans female rats, implanted with an IV access port prior to breeding, were administered saline, 0.5, 1.0, or 3.0 mg/kg/injection of cocaine HCL (COC) from gestation day (GD) 8-20 (1×/day-GD8-14, 2×/day-GD15-20). COC had no significant effects on maternal/litter parameters or growth of the offspring. At 18-20 days of age, one male and one female, randomly selected from each litter displayed an increased ASR (>30% for males at 1.0 mg/kg and >30% for females at 3.0 mg/kg). When reassessed in adulthood (D90-100), a linear dose-response increase was noted on response amplitude. At both test ages, within-session habituation was retarded by prenatal cocaine treatment. Testing the females in diestrus vs. estrus did not alter the results. Prenatal cocaine altered the PPI response function across interstimulus interval and induced significant sex-dependent changes in response latency. Idazoxan, an α(2)-adrenergic receptor antagonist, significantly enhanced the ASR, but less enhancement was noted with increasing doses of prenatal cocaine. Thus, in utero exposure to cocaine, when delivered via a protocol designed to capture prominent features of recreational usage, causes persistent, if not permanent, alterations in auditory information processing, and suggests dysfunction of the central noradrenergic circuitry modulating, if not mediating, these responses.

Cocaine Exposure Results in Formation of Dendritic Varicosity in Rat Primary Hippocampal Neurons

While it has been well documented that drugs of abuse such as cocaine can cause enhanced progression of HIV-Associated Neuropathological Disorders (HAND), the underlying mechanisms mediating these effects remain poorly understood. In the present study, we explored the impact of cocaine exposure (I μM and 10 μM) on the dendritic beading in rat primary hippocampal neurons. Using the approach of transfection with green fluorescent protein, we observed significant dendritic swelling in hippocampal neurons exposed to 10 μM but not 1 μM of cocaine when compared with the saline treated group. Cocaine exposure also resulted in decreased expression of the synaptic plasticity gene, Arc as evidenced by Western blotting. Intriguingly, cocaine exposure of primary neurons in the presence of the neurotoxin-HIV envelope protein gp 120, resulted in increased enhancement of neuronal beading as compared with exposure of neurons to either agent alone. Taken together these findings imply that cocaine in co-operation with HIV protein exacerbates neuronal damage in the brains of HIV-infected cocaine abusers.

Neurotoxic profiles of HIV, psychostimulant drugs of abuse, and their concerted effect on the brain: current status of dopamine system vulnerability in NeuroAIDS

There are roughly 30-40 million HIV-infected individuals in the world as of December 2007, and drug abuse directly contributes to one-third of all HIV infections in the United States. Antiretroviral therapy has increased the lifespan of HIV-seropositives, but CNS function often remains diminished, effectively decreasing quality of life. A modest proportion may develop HIV-associated dementia, the severity and progression of which is increased with drug abuse. HIV and drugs of abuse in the CNS target subcortical brain structures and DA systems in particular. This toxicity is mediated by a number of neurotoxic mechanisms, including but not limited to, aberrant immune response and oxidative stress. Therefore, novel therapeutic strategies must be developed that can address a wide variety of disparate neurotoxic mechanisms and apoptotic cascades. This paper reviews the research pertaining to the where, what, and how of HIV and cocaine/methamphetamine toxicity in the CNS. Specifically, where these toxins most affect the brain, what aspects of the virus are neurotoxic, and how these toxins mediate neurotoxicity.

Developmental neurotoxicity testing in vitro: models for assessing chemical effects on neurite outgrowth

In vitro models may be useful for the rapid toxicological screening of large numbers of chemicals for their potential to produce toxicity. Such screening could facilitate prioritization of resources needed for in vivo toxicity testing towards those chemicals most likely to result in adverse health effects. Cell cultures derived from nervous system tissue have proven to be powerful tools for elucidating cellular and molecular mechanisms of nervous system development and function, and have been used to understand the mechanism of action of neurotoxic chemicals. Recently, it has been suggested that in vitro models could be used to screen for chemical effects on critical cellular events of neurodevelopment, including differentiation and neurite growth. This review examines the use of neuronal cell cultures as an in vitro model of neurite outgrowth. Examples of the cell culture systems that are commonly used to examine the effects of chemicals on neurite outgrowth are provided, along with a description of the methods used to quantify this neurodevelopmental process in vitro. Issues relating to the relevance of the methods and models currently used to assess neurite outgrowth are discussed in the context of hazard identification and chemical screening. To demonstrate the utility of in vitro models of neurite outgrowth for the evaluation of large numbers of chemicals, efforts should be made to: (1) develop a set of reference chemicals that can be used as positive and negative controls for comparing neurite outgrowth between model systems, (2) focus on cell cultures of human origin, with emphasis on the emerging area of neural progenitor cells, and (3) use high-throughput methods to quantify endpoints of neurite outgrowth.

Sex mediates dopamine and adrenergic receptor expression in adult rats exposed prenatally to cocaine

The extent of catecholaminergic receptor and respective behavioral alterations associated with prenatal cocaine exposure varies according to exogenous factors such as the amount, frequency, and route of maternal exposure, as well as endogenous factors such as specific brain regions under consideration and sex of the species. The goal of the current study was to use autoradiography to delineate possible moderators of dopaminergic and adrenergic receptor expression in adult rat offspring exposed to cocaine in utero. The current study demonstrated sex-dependent D1 receptor, alpha2, and noradrenergic transporter binding alterations in prelimbic, hippocampus, and anterior cingulate regions of adult rat brains exposed to cocaine during gestational days 8-21. Of further interest was the lack of alterations in the nucleus accumbens for nearly all receptors/transporters investigated, as well as the lack of alterations in D3 receptor binding in nearly all of the regions investigated (nucleus accumbens, prelimbic region, hippocampus, and cingulate gyrus). Thus, the current investigation demonstrated persistent receptor and transporter alterations that extend well into adulthood as a result of cocaine exposure in utero. Furthermore, the demonstration that sex played a mediating role in prenatal cocaine-induced, aberrant receptor/transporter expression is of primary importance for future studies that seek to control for sex in either design or analysis.

Cocaine exposure in vitro induces apoptosis in fetal locus coeruleus neurons through TNF-alpha-mediated induction of Bax and phosphorylated c-Jun NH(2)-terminal kinase

Cocaine exposure results in aberrant outgrowth and decreased survival for locus coeruleus (LC), a noradrenergic population of neurons that putatively regulates attentional function; however, the underlying mechanisms for these events are not known. We previously showed that cocaine exposure in vitro activates pro-apoptotic Bax, caspase-9, and caspase-3 in LC neurons dissected from embryonic day 14 rats, implicating that apoptosis may be orchestrated via signal transduction events. In the current study in vitro, we examined upstream events to determine the role of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNF-alpha), on LC signal transduction, because cocaine exposure to LC neurons triggered TNF-alpha expression at 30 min as measured by ELISA. Exposure of LC neurons to recombinant-TNF-alpha resulted in decreased metabolic activity, an indicator of reduced neuron viability [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay], and increased apoptosis (terminal deoxynucleotidyl transferase-mediated DNA nick end labeling assay). Pro-apoptotic caspase-3 was induced by cocaine starting at 30 min. Recombinant-TNF-alpha induced caspase-3 activity earlier than cocaine (15 and 20 min). The caspase-3 levels were significantly reduced when cocaine and TNF-alpha were combined with neutralizing-TNF-alpha (nTNF-alpha), respectively. Further, cocaine alone elevated phospho-p38-mitogen-activated protein kinases that persisted when combined with nTNF-alpha. However, both cocaine and TNF-alpha independently increased phospho-c-Jun NH(2)-terminal kinase and Bax levels at concurrent time periods (30 min and 1 h), and this elevation was attenuated in the presence of nTNF-alpha. These simultaneous molecular events triggered by cocaine and TNF-alpha implicate a potential apoptotic signal transduction pathway via induction of phospho-c-Jun NH(2)-terminal kinase and Bax that may lead to caspase-3 activation and apoptosis in cocaine-exposed fetal LC neurons.

Cocaine exposure in vitro induces apoptosis in fetal locus coeruleus neurons by altering the Bax/Bcl-2 ratio and through caspase-3 apoptotic signaling

Cocaine inhibits survival and growth of rat locus coeruleus (LC) neurons, which may mediate alterations in attention, following in utero exposure to cocaine. These effects are most severe in early gestation during peak neuritogenesis. Prenatal cocaine exposure may specifically decrease LC survival through an apoptotic pathway involving caspases. Dissociated fetal LC neurons or substantia nigra (SN) neurons (control) were exposed in vitro to a pharmacologically active dose of cocaine hydrochloride (500 ng/ml) and assayed for apoptosis using terminal deoxynucleotidyl transferase mediated DNA nick end labeling and Hoechst methodologies. Cocaine exposure decreased survival and induced apoptosis in LC neurons, with no changes in survival of SN neurons. Activation of apoptotic signal transduction proteins was determined using enzyme assays and immunoblotting at 30 min, 1 h, 4 h and 24 h. In LC neurons, Bax levels were induced at 30 min and 1 h, following cocaine treatment, and Bcl-2 levels remained unchanged at all time points, altering the Bax/Bcl-2 ratio. The ratio was reversed for SN neurons (elevated Bcl-2 levels and transient reduction of Bax levels). Further, cocaine exposure significantly increased caspase-9 and caspase-3 activities at all time points, without changes in caspase-8 activity in LC neurons. In addition, cleavage of caspase-3 target proteins, alpha-fodrin and poly (ADP-ribose) polymerase (PARP) were observed following cocaine treatment. In contrast, SN neurons showed either significant reductions, or no significant changes, in caspase-3, -8 or -9 activities or caspase-3 target proteins, alpha-fodrin and PARP. Thus, cocaine exposure in vitro may preferentially induce apoptosis in fetal LC neurons putatively regulated by Bax, via activation of caspases and their downstream target proteins.