Cocaine-induced alterations in the density of monoaminergic receptors in the embryonic guinea pig cerebral wall

Chronic administration of a norepinephrine antagonist prevents and partially reverses escalation of cocaine self-administration

Anxiety is a critical component of the development and maintenance of drug addiction; however, anti-anxiety medications such as benzodiazepines and beta-blockers (β-adrenergic receptor antagonists) are not used for the treatment of substance use disorder, except for the management of acute withdrawal syndrome. Preclinical studies have shown that beta-blockers may reduce stress-induced relapse; however, the effect of beta blockers on the escalation and maintenance of drug intake has not been tested. To address this issue, we chronically administered the β-adrenergic receptor antagonist propranolol during the escalation or maintenance of cocaine intake in a model of extended access (6 h) to cocaine self-administration (0.5 mg/kg). The behavioural specificity of propranolol was tested using a non-drug reward (saccharin). Daily administration of propranolol (15 mg/kg) prevented the development of escalation of cocaine self-administration and partially reversed self-administration after the establishment of escalation of intake. Moreover, propranolol dose-dependently decreased the motivation for cocaine tested under a progressive ratio schedule of reinforcement during the development of escalation and after maintenance. Finally, propranolol administration had no effect on the escalation and maintenance of saccharin self-administration. These results demonstrate that chronic treatment with propranolol provides therapeutic efficacy in reducing cocaine self-administration during the development and after the establishment of escalation of cocaine self-administration in an animal model relevant to cocaine use disorder. These results suggest that beta blockers should be further investigated as a target for medication development for the treatment of cocaine use disorder.

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.

Dexmedetomidine as a Novel Countermeasure for Cocaine-Induced Central Sympathoexcitation in Cocaine-Addicted Humans

Cocaine-induced acute hypertension is mediated largely by increased central sympathetic nerve activity. We hypothesized that dexmedetomidine, a central sympatholytic, reverses cocaine-induced increases in sympathetic nerve activity, mean arterial pressure (MAP), and heart rate (HR) in cocaine-addicted subjects. First, we conducted a dose-finding study in 15 nontreatment-seeking cocaine-addicted subjects and 12 cocaine-naive healthy controls to find doses of intravenous dexmedetomidine that lower MAP and HR in the absence of acute-cocaine challenge. We then conducted a placebo-controlled treatment trial in 26 cocaine-addicted subjects to determine whether dexmedetomidine reverses MAP and HR increases after intranasal cocaine (3 mg/kg). Skin sympathetic nerve activity (measured in the second protocol) and skin vascular resistance (measured in both protocols) served as indices of cocaine-sensitive central sympathoexcitation. In doses up to 0.6 µg/kg IV, dexmedetomidine alone caused comparable dose-dependent decreases in blood pressure in cases and controls but a 1.0 µg/kg dose was required to lower HR. In cocaine-addicted subjects, low-dose dexmedetomidine (0.4 µg/kg; n=14) abolished cocaine-induced increases in skin sympathetic nerve activity (156±26 versus −15±22%, cocaine/placebo versus cocaine/dexmedetomidine; P <0.05), skin vascular resistance (+10±2 versus −2±3 U; P <0.05), and MAP (+6±1 versus −5±2 mm Hg; P <0.01) without affecting HR (+13±2 versus +9±2 bpm; P =ns). When dexmedetomidine was increased to 1 µg/kg (high dose; n=12) to reverse cocaine-induced increases in HR, MAP did not fall further and increased paradoxically in 4 of 12 subjects. Thus, in a low nonsedating dose, dexmedetomidine constitutes a putative new treatment for cocaine-induced acute hypertension but higher sedating doses can increase blood pressure unpredictably during acute-cocaine challenge and should be avoided.

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.

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.

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.

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 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.

Chronic prenatal exposure to cocaine alters cerebrovascular responses in newborn pigs

Maternal cocaine abuse may increase the incidence of perinatal asphyxia. In nonexposed asphyxiated neonates, decreased cerebrospinal fluid (CSF) cAMP concentrations are associated with poor neurological outcome. On the other hand, cocaine increases central nervous system (CNS) cAMP. Therefore, we hypothesized that in utero cocaine exposure may increase brain cAMP and thereby preserve cerebrovascular responses to cAMP-dependent stimuli following asphyxia. Pregnant pigs received either cocaine (1 mg/kg, i.v.) twice weekly during the last trimester or normal saline vehicle (sham-control) and were allowed to deliver vaginally at term. Cranial windows were implanted in the newborn pigs within the first week of life and used to collect CSF for cAMP determinations and to assess changes in pial arteriolar diameters (PAD). In the first part of the study, pial arteriolar responses to different vasodilator and vasoconstrictor stimuli were evaluated in piglets prior to asphyxia (n = 20). In newborn pigs exposed to cocaine, cerebrovascular responses to hypercapnia and norepinephrine were significantly exaggerated compared to controls. Then, piglets were randomly selected for the second part of the study that involved prolonged asphyxia (n = 12). In cocaine-exposed but not sham-control piglets, CSF cAMP increased markedly during asphyxia. In the sham piglets, but not the cocaine-exposed piglets, CSF cAMP fell progressively below the baseline during recovery. Cerebrovascular reactivity to cAMP-dependent stimuli (hypercapnia and isoproterenol) was preserved during recovery from asphyxia in the cocaine-exposed piglets but significantly attenuated in the sham controls. We conclude that piglets with chronic prenatal exposure to cocaine show exaggerated cerebrovascular responses to vasogenic stimuli and preserved cAMP-dependent cerebral vasoreactivity following asphyxia.

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.

Ventilatory control in newborn mice prenatally exposed to cocaine

Infants born to mothers who used cocaine during pregnancy are at increased risk for neonatal death and respiratory impairments. Confounding factors such as multiple substance abuse make it difficult to isolate the effects of cocaine. We used a murine model to test the hypothesis that prenatal cocaine exposure may impair ventilatory responses to chemical stimuli in newborns. Seventy-two pregnant mice were randomly assigned to three groups: cocaine (COC), saline (SAL), and untreated (UNT). COC and SAL mice received subcutaneous injections of either 20 mg/kg of cocaine or a saline solution twice a day from gestational days 8-17. Ventilation (V'(E)) and tidal volume (V(T)), both divided by body weight, and breath duration (T(TOT)) were measured using whole-body plethysmography in freely moving COC (n = 47), SAL (n = 123), and UNT (n = 93) pups on postnatal day 2.The comparison between SAL and UNT pups showed significant differences in baseline breathing and in V'(E) responses to hypoxia, suggesting that maternal stress caused by injections affected the development of ventilatory control in pups. Baseline T(TOT) was significantly longer in COC than in SAL pups. V'(E) responses to hypoxia were significantly smaller in COC than in SAL pups (+27 +/- 35% vs. +38 +/- 25%), but V'(E) responses to hypercapnia were similar (29 +/- 15% vs. 25 +/- 23%).Thus, breathing control was impaired by prenatal cocaine exposure, possibly because of abnormal development of neurotransmitter systems, such as the dopamine and serotonin systems.

D1 dopamine receptor regulation of cell cycle in FGF- and EGF-supported primary cultures of embryonic cerebral cortical precursor cells

In the mammalian fetus, proliferation of the majority of cells destined for the cerebral cortex takes place within the transient proliferative zones of the cerebral wall. Recent investigations have demonstrated that cell of these zones express high levels of D1 dopamine receptors (D1Rs). However, the specific roles of these receptors have not been investigated. The present study tests the hypothesis that D1Rs are capable of regulating the cell cycle of cerebral cortical precursor cells. For this purpose, primary cultures of cells of the proliferative zones from the cerebral wall of 14-day-old mouse fetuses were generated and maintained in the presence of either fibroblast growth factor-2 (FGF2) or epidermal growth factor (EGF). These growth factors were chosen as supporting two distinct populations of precursor cells in the fetal cortical proliferative matrix. The involvement of D1Rs in the regulation of proliferative activity was examined by the addition of a range of concentrations of the D1R-specific agonist, SKF82958, to the culture media. Bromodeoxyuridine incorporation assays demonstrated that exposure to this agonist led to a dose-dependent reduction of DNA synthesis in both FGF2- and EGF-supported cultures. Flow cytometric cell cycle assays further revealed that this was due to prevention of the transition of cells from the G1 phase to the S phase of the cell cycle. The D1R specificity of the effects of SKF82958 was supported in that they were blocked by the addition of the D1R antagonists, SCH23390 or NNC010756. We also found that D1R stimulation induced stronger suppression of proliferative activity in EGF-supported than in FGF2-supported cultures. Our observations suggest that D1Rs are capable of regulating the cell cycle during corticogenesis. Furthermore, they raise a possibility that these receptors may display different efficacies in affecting proliferative activity in FGF2-supported versus EGF-supported cerebral cortical precursor cells.

Consequences of maternal cocaine on cerebral microvascular functions in piglets

Maternal cocaine abuse is associated with fetal and neonatal neurological abnormalities. Prolonged exposure to cocaine can induce blood flow disorders, growth restriction, and hypoxia in the newborn. We investigated the impact of chronic fetal cocaine exposure on cerebral microvascular reactivity and autonomic function in the piglets. Pregnant pigs received cocaine (1 mg/kg i.v.; twice weekly) or saline throughout the last trimester. Prenatal exposure to cocaine did not have any significant effect on the birth weight of the piglets as compared to the control. Following delivery, effects of recurrent prenatal cocaine exposure on cerebral microvascular functions were examined in piglets (3-6 days old). Pial arteriolar responses to applications of 5-hydroxytryptamine (5-HT), endothelin-1 (ET-1), and clonidine were examined using closed cranial windows. Functional effects of prenatal cocaine exposure on changes in mean arterial pressure (MAP) and pial arteriolar diameter induced by intracisternal injection (i.c.) of clonidine (1 microg/kg) were also determined. Topical applications of 5-HT, ET-1, and clonidine dose-dependently decreased pial arteriolar diameter in the control and these constrictions were significantly enhanced in the in utero cocaine-exposed piglets. Prenatal cocaine exposure did not have any significant effects on the resting MAP and heart rate as there were no differences between the groups. IC clonidine caused sustained decrease in MAP in both groups but the decrease was more pronounced in the cocaine than the control group. IC clonidine causes cerebral microvascular dilation coincident with the development of hypotension. Such dilation was severely attenuated in the cocaine group, even though the hypotension was much more pronounced than in the control. In conclusion, prenatal cocaine exposure resulted in attenuated autoregulatory vasodilation and potentiated responses to vasoconstrictor agents. The mechanisms behind the effects of in utero cocaine exposure on alteration of newborn cerebral functions need further investigation. Such actions may be important in development of cerebral pathologies associated with recurrent prenatal cocaine exposure.

D1 dopamine receptor regulation of microtubule-associated protein-2 phosphorylation in developing cerebral cortical neurons

This study addresses the hypothesis that the previously described capacity of D1 dopamine receptors (D1Rs) to regulate dendritic growth in developing cortical neurons may involve alterations in the phosphorylation state of microtubule-associated protein-2 (MAP2). The changes in phosphorylation of this protein are known to affect its ability to stabilize the dendritic cytoskeleton. The study involved two systems: primary cultures of mouse cortical neurons grown in the presence of the D1R agonists, SKF82958 or A77636, and the cortex of neonatal transgenic mice overexpressing the D1A subtype of D1R. In both models, a decrease in dendritic extension corresponded with an elevation in MAP2 phosphorylation. This phosphorylation occurred on all three amino acid residues examined in this study: serine, threonine, and tyrosine. In cultured cortical neurons, D1R stimulation-induced increase in MAP2 phosphorylation was blocked by the protein kinase A (PKA) inhibitor, H-89, and mimicked by the PKA activator, S(p)-cAMPS. This indicates that D1Rs modulate MAP2 phosphorylation through PKA-associated intracellular signaling pathways. We also observed that the elevations in MAP2 phosphorylation in neuronal cultures in the presence of D1R agonists (or S(p)-cAMPS) were maintained for a prolonged time (up to at least 96 hr). Moreover, MAP2 phosphorylation underwent a substantial increase between 24 and 72 hr of exposure to these drugs. Our findings are consistent with the idea that D1Rs can modulate growth and maintenance of dendrites in developing cortical cells by regulating the phosphorylation of MAP2. In addition, our observations suggest that MAP2 phosphorylation by long-term activation of D1Rs (and PKA) can be divided into two phases: the initial approximately 24-hr-long phase of a relatively weak elevation in phosphorylation and the delayed phase of a much more robust phosphorylation increase taking place during the next approximately 48 hr.

Primates exposed to cocaine in utero display reduced density and number of cerebral cortical neurons

This study examined the effects of cocaine use during the second trimester of pregnancy on cerebral neocortical volume and density, and total number of neocortical neurons and glia in offspring. We also evaluated the extent of postnatal recovery of cytoarchitectural abnormalities previously observed in the neocortex of two-month-old primates born from cocaine-treated mothers (Lidow [1995] Synapse 21:332-334). Pregnant monkeys received cocaine orally (20 mg/kg/day) from the 40th to 102nd days of pregnancy (embryonic day [E]40-E102). On E64 and E65, the animals were injected with [(3)H]thymidine. Cerebral hemispheres of the offspring were examined at three years of age. We found a reduction in the neocortical volume and density and total number of neocortical neurons. The observed reduction in neuronal number within the neocortex was not accounted for by the increase in the number of neurons in the white matter of cocaine-exposed animals, because the number of these "extra" neurons was equal to only half that of missing neurons. We detected no significant changes in the number of neocortical glia. The cytoarchitectural abnormalities in the neocortex of prenatally cocaine-exposed three-year-old monkeys closely resembled previously described neocortical abnormalities in similarly exposed two-month-old animals: the neocortex lacked a discernible lamination; the majority of the cells labeled by [(3)H]thymidine injected during neocortical neurogenesis did not reach their proper position within the cortical plate. Therefore, postnatal maturation is not associated with significant improvement in neocortical organization in primates prenatally exposed to cocaine. There was, however, a postnatal recovery of low glial fibrillary acidic protein (GFAP) immunoreactivity previously observed in 2-month-old cocaine-exposed animals.

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

Previously, we demonstrated that chronic exposure of fetal monkeys to cocaine could result in development of the neocortex with significant cytoarchitectonic abnormalities [Synapse, 21 (1995) 435-444]. In the present study, we examined the developmental time-frame within which neocortical cytoarchitecture is susceptible to modifications by prenatal cocaine exposure. For this purpose, we assessed the integrity of cortical lamination and the position, density, and total number of occipital cortical neurons in 2-month-old monkeys which were prenatally exposed to chronic cocaine treatment either prior to the period of neocortical neuronogenesis, during the period of neocortical neuronogenesis, or after the period of neocortical neuronogenesis. We found that cocaine can interfere with the neocortical laminar organization and induce a reduction in the density and number of neocortical neurons only if it is administered at the time of neocortical neuronogenesis. During this window of vulnerability, an abnormal neocortex is generated as long as cocaine exposure is maintained, with corticogenesis becoming normal as soon as the administration of this drug is discontinued.