Prenatal intravenous cocaine and the heart rate-orienting response: a dose-response study

Neurochemical organization of the ventral striatum's olfactory tubercle

The ventral striatum is a collection of brain structures, including the nucleus accumbens, ventral pallidum and the olfactory tubercle (OT). While much attention has been devoted to the nucleus accumbens, a comprehensive understanding of the ventral striatum and its contributions to neurological diseases requires an appreciation for the complex neurochemical makeup of the ventral striatum's other components. This review summarizes the rich neurochemical composition of the OT, including the neurotransmitters, neuromodulators and hormones present. We also address the receptors and transporters involved in each system as well as their putative functional roles. Finally, we end with briefly reviewing select literature regarding neurochemical changes in the OT in the context of neurological disorders, specifically neurodegenerative disorders. By overviewing the vast literature on the neurochemical composition of the OT, this review will serve to aid future research into the neurobiology of the ventral striatum.

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.

Effects of prenatal cocaine exposure on pubertal development

The purpose of the current study was to examine the relationship between prenatal cocaine exposure (PCE) and pubertal development. Children (n=192; 41% with PCE) completed the Pubertal Development Scale (Petersen et al. 1988) and provided salivary dehydroepiandrosterone (DHEA) samples at 6month intervals from 11 to 13years. PCE was examined as a predictor of pubertal status, pubertal tempo, and DHEA levels in mixed models analyses controlling for age, sex, environmental risk, neonatal medical problems, other prenatal exposures, and BMI. PCE interacted with age such that PCE predicted slower pubertal tempo during early adolescence. PCE also interacted with age to predict slower increases in DHEA levels during early adolescence. These findings suggest that PCE may affect pubertal development and, if slower pubertal tempo continues, could lead to delayed pubertal status in mid-adolescence.

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.

Osmotically-induced genes are controlled by the transcription factor TonEBP in cultured cardiomyocytes

Changes in cardiac osmolarity occur in myocardial infarction. Osmoregulatory mechanisms may, therefore, play a crucial role in cardiomyocyte survival. Tonicity-responsive enhancer binding protein (TonEBP) is a key transcription factor participating in the adaptation of cells to increases in tonicity. However, it is unknown whether cardiac TonEBP is activated by tonicity. Hypertonicity activated transcriptional activity of TonEBP, increased the amounts of both TonEBP mRNA and protein, and induced both the mRNA and protein of TonEBP target genes (aldose reductase and heat shock protein-70). Hypotonicity decreased the amount of TonEBP protein indicating bidirectional osmoregulation of this transcription factor. Adenoviral expression of a dominant negative TonEBP suppressed the hypertonicity-dependent increase of aldose reductase protein. These results indicated that TonEBP controls osmoregulatory mechanisms in cardiomyocytes.

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.

The contribution of fetal drug exposure to temperament: potential teratogenic effects on neuropsychiatric risk

BACKGROUND

Preliminary evidence indicates that fetal drug exposure may be associated with alterations in temperament. However, studies often do not dissociate the potential effects of drug exposure from other perinatal or environmental factors that could influence temperament phenotypes.

METHODS

High risk children (n = 120) were followed from birth to 6 months of age to determine the effects of fetal drug exposure on temperament, after controlling for the child's gender, gestational age, medical morbidity, ethnicity, and maltreatment as well as the mother's stress, income adequacy, and quality of caregiving. Methods included medical chart review, questionnaires, and videotapes of mother-child interaction.

RESULTS

Preliminary analyses indicated that fetal drug exposure was associated with both distractibility and intensity of children's responses to the environment at 6 months of age. After adjusting for potentially confounding variables, drug exposure accounted for 12% of the variance in distractibility but was not a significant predictor in the regression model for intensity.

CONCLUSIONS

Findings suggest that drug-exposed children may experience difficulty sustaining their focus of attention and be more easily distracted by environmental stimuli than non-drug-exposed children. Results converge with previous research to implicate cortical hyperarousal, stemming from teratogenic effects on the dopaminergic system during fetal development.

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.

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.

Prenatal cocaine exposure alters alpha2 receptor expression in adolescent rats

BACKGROUND

Prenatal cocaine exposure produces attentional deficits which to persist through early childhood. Given the role of norepinephrine (NE) in attentional processes, we examined the forebrain NE systems from prenatal cocaine exposed rats. Cocaine was administered during pregnancy via the clinically relevant intravenous route of administration. Specifically, we measured alpha2-adrenergic receptor (alpha2-AR) density in adolescent (35-days-old) rats, using [3H]RX821002 (5 nM).

RESULTS

Sex-specific alterations of alpha2-AR were found in the hippocampus and amygdala of the cocaine-exposed animals, as well as an upregulation of alpha2-AR in parietal cortex.

CONCLUSION

These data suggest that prenatal cocaine exposure results in a persistent alteration in forebrain NE systems as indicated by alterations in receptor density. These neurochemical changes may underlie behavioral abnormalities observed in offspring attentional processes following prenatal exposure to cocaine.

Prenatal cocaine alters dopamine and sigma receptor binding in nucleus accumbens and striatum in dams and adolescent offspring

Maternal cocaine abuse is a societal problem with serious impact on both mother and child. Few studies exist that study the mother/offspring dyad of neurological effects of maternal cocaine abuse. The present study was designed to study alterations in D2, D3 and sigma receptor density in nucleus accumbens and striatum of dams and male and female offspring following gestational cocaine. Long-Evans female rats were implanted with an intravenous (i.v.) access port prior to breeding and were administered saline or 3.0 mg/kg of cocaine from gestational day (GD) GD8-20 (1 injection/day-GD8-14, 2 injections/day-GD15-20). Offspring were raised by maternal dams and allowed to mature until postnatal days 31-35, at which time dams and offspring were sacrificed for assay of radioligand binding. In dams, decreased D2 (24.6%) and D3 (36.9%) binding was observed in striatum. Female offspring displayed no differences in receptor binding in either region. Male offspring displayed decreased D2 receptor binding (27.1%) in nucleus accumbens and increased D3 (75.2% and 33.5%) and sigma receptor binding (73.4% and 53.1%) in accumbens and striatum, respectively. Collectively, these data clearly demonstrate that male offspring exhibit significant alterations in D2, D3 and sigma receptor binding. These results suggest that dams and offspring display long-lasting alterations (5 weeks) in dopamine receptor binding. These alterations in dopamine and sigma receptor binding in offspring following prenatal cocaine and rearing by maternal dams are sex specific and could have profound effects on the development of behavior.

Specificity of prenatal cocaine on inhibition of locus coeruleus neurite outgrowth

Prenatal cocaine exposure induces alterations in attentional function that presumably involve locus coeruleus noradrenergic neurons and their projections. Previous reports indicate that embryonic rat locus coeruleus neurons exposed to cocaine, both in vitro and in vivo, showed in decreased cell survival and inhibition of neurite outgrowth, and that the effects were most deleterious during early gestation. The present study performed in vitro addressed the specificity of the inhibitory effects of cocaine by comparing locus coeruleus neurite formation and extension to that of dopaminergic substantia nigra neurons following exposure to a physiologically-relevant dose of cocaine (500 ng/ml, two times a day, for four days) during peak neuritogenesis. Following cocaine treatment, immunocytochemistry (anti-norepinephrine antibody to locus coeruleus; anti-tyrosine hydroxylase antibody to substantia nigra) and image analysis were performed to measure a variety of neurite outgrowth parameters. For locus coeruleus neurons, cocaine treatment decreased the 1) number of cells initiating neurites [P<0.001], 2) mean number [P<0.05] and length of neurites [P<0.0001], 3) mean number [P<0.0016] and length of branched neurites [P<0.0006], and 4) mean length of the longest neurites [P<0.0001]. In comparison, substantia nigra neurons were not significantly affected by cocaine for any of the parameters examined. More importantly, a significant interaction between cocaine treatment and brain region was observed [P<0.0002] indicating greater vulnerability of locus coeruleus, relative to substantia nigra neurons, to cocaine exposure. These data support our hypothesis that cocaine targets the noradrenergic system by negatively regulating locus coeruleus neuronal outgrowth, which likely affects pathfinding, synaptic connectivity, and ultimately attentional behavior in cocaine-exposed offspring.

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.